patai's chemistry of functional groups || synthesis and uses of organogold compounds

Synthesis and uses of organogoldcompounds

HUBERT SCHMIDBAUR, ANDREAS GROHMANN, M. ELENA OLMOSand ANNETTE SCHIER

Lehrstuhl fur Anorganische und Analytische Chemie, Technische UniversitatMunchen, D-85747 Garching, GermanyFax: 49-89-289-13125. E-mail: [email protected]

I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1II. SYNTHESIS OF �-BONDED ORGANOGOLD COMPLEXES . . . . . . . 2

A. Complexes of the Type [RAuL] . . . . . . . . . . . . . . . . . . . . . . . . . . 2B. Gold(I) Complexes Containing the Structural Building Block C(AuL)n,

n � 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16C. Gold(I) Complexes with Two Gold–Carbon Bonds . . . . . . . . . . . . . 21D. Complexes of Gold(I), Gold(II) and Gold(III) with Ylide Ligands . . . 25

1. Mononuclear ylide complexes . . . . . . . . . . . . . . . . . . . . . . . . . 252. Di- and polynuclear ylide complexes . . . . . . . . . . . . . . . . . . . . 30

E. Gold(III) Complexes with One Gold–Carbon Bond . . . . . . . . . . . . . 46F. Gold(III) Complexes with Two Gold–Carbon Bonds . . . . . . . . . . . . 50

1. Diorganylgold(III) halides and pseudohalides . . . . . . . . . . . . . . . 502. Diorganylgold(III) complexes with group 16 donor ligands . . . . . . 513. Diorganylgold(III) complexes with group 15 donor ligands . . . . . . 54

G. Gold(III) Complexes with Three Gold–Carbon Bonds . . . . . . . . . . . 60H. Gold(III) Complexes with Four Gold–Carbon Bonds . . . . . . . . . . . . 65

III. HOMO- AND HETEROMETALLIC GOLD CLUSTERS CONTAININGGOLD–CARBON BONDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

IV. SYNTHESIS AND PROPERTIES OF ALKENE, ALKYNE, CARBENEAND RELATED COMPLEXES OF GOLD . . . . . . . . . . . . . . . . . . . . 67

V. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

I. INTRODUCTION

Organogold chemistry is one of the oldest sub-disciplines of organometallic chemistryand the first successful syntheses date back to the first decade1,2 of this century and to the

1

PATAI's Chemistry of Functional Groups, Online © 2009 John Wiley & Sons, Ltd.This article is © 2009 John Wiley & Sons, Ltd.This article was published in PATAI's Chemistry of Functional Groups in 2009 by John Wiley & Sons, Ltd.DOI: 10.1002/9780470682531.pat0213

Hubert Schmidbaur, Andreas Grohmann, M. Elena Olmos and Annette Schier

late 1950s3. It has developed only slowly, but has matured considerably after the 1970s.This evolution is reflected also by this summary of the syntheses and uses of organogoldcompounds.

The presentation of the material in this chapter largely follows an order of increasingoxidation states, except where a classification of ligand type (as in the case of the ylidecomplexes) facilitates a generalizing treatment. Reviews published during the last fifteenyears include general surveys of organogold chemistry4,5 as well as more specializedaccounts on topics such as coordination chemistry6–10 and arylgold chemistry 11,12. Forfurther information, the reader is also referred to the classical book on Gold Chemistry13

and to the Dictionary of Organometallic Compounds as another highly useful compila-tion of data concerning the organic chemistry of gold14. This article concentrates on theprogress in the syntheses of organogold compounds since 198015, i.e. it complements theOrganogold Gmelin volume which is comprehensive up to 1980. As in previous treatises,cyanide and isocyanide complexes of gold are excluded.

II. SYNTHESIS OF s-BONDED ORGANOGOLD COMPLEXES

A. Complexes of the Type [RAuL]

Complexes of this type may contain a variety of organic residues R, such as alkyl,vinyl, alkynyl or aryl. The neutral donor group L is most commonly a tertiary phosphineor an isocyanide ligand, and polynuclear complexes with bridging polyfunctional donorligands are also known4,13,15. From a practical point of view, the series of organogold(I)and isocyanide complexes is of particular interest since some of its members hold promiseas precursors for the chemical vapour deposition of gold films. A selection of these andother compounds of the type [RAuL] is presented in Tables 1–3.

Alkylgold(I) phosphine complexes are usually synthesized by reaction of an alkyl-lithium or a Grignard reagent with a complex gold(I) halide, and the correspondingisocyanide complexes are accessible by analogous routes. Typical examples for the prepa-ration of this type of complexes are given in equations 1 and 216,13c. In a modifiedsynthesis of alkylgold(I) phosphine complexes, tris(phosphinegold(I))oxonium tetraflu-oroborates are used instead of (phosphine)gold(I) halides and considerably shorterreaction times and generally higher yields of organogold compounds have been reported(equations 3 and 4, R D e.g. C6H5CH2). In addition, the separation of starting materialsand final products is facilitated by the low solubility of the oxonium salt in com-mon solvents such as ether or tetrahydrofuran31,32. Photophysical and luminescenceproperties33,34, photoelectron spectra35 and the electronic structure36,37 of alkylgold(I)complexes have been investigated.

P

P Au

Au

Cl

ClPh2

+ 2 LiCH3

P

P Au

Au

CH3

CH3

Ph2

−2 LiCl

Ph2

Ph2

(1)

[AuCl(SMe2)CMeMgClC CNMe�MgCl2, �SMe2��! [AuMe(CNMe)] �2�

[(Ph3PAu)3O][BF4]1. RLi��!2. H2O

[AuR(PPh3)] �3�

[(Ph3PAu)3O][BF4]1. RMgCl��!

2. H2O[AuR(PPh3)] �4�

2


Synthesis and uses of organogold compounds

TABLE 1. Gold(I) complexes of the type [RAuL]

Complex M.p.(° C) Reference

R D alkyl

[fAuMeg2f(Ph2P)2CCH2CH2g] 203(d) 16

[AuMe(TPA)]a 143(d) 17

[AuMef(Ph2PCH2PPh2)Fe(CO)2(�4-MeC5H5)g] 141– 142 18

[AuMe(AsPh3)] — 19

[AuMe(CNMe)] 95(d) 13c

[AuMe(CNPr-i)] <40(d) 13c

[AuMe(CNC6H11-c)] 88(d) 13c

[AuMe(CNPh)] 102(d) 13c

R D functionalized alkyl and related ligands

[Au(CCl3)(PPh3)] >200(d) 20

[Au(CF3)(PMe3)] 191 – 193(d) 21, 22

[Au(CH2CN)(PPh3)] 141 – 142 23

[Au(CCl2CN)(PPh3)] 172 – 173 23

[AufCH(CN)(COOEt)g(PPh3)] 147 – 149 24, 25

[AufC(DN(C6H3Me2-2,6))(CH2COPh)g] 160(d) 26

[Au(CDNC(Me)DCHS)] — 27

[Au(CDNC6H4S-o)(PPh3)] 155 – 156 27

[Au(CDCHCHDNS)(PPh3)] 157 – 158 28

[Au2f(CH2)3PPh2g2] — 29

[Au2f2-C(SiMe3)2(C5H4N)g2] 122(d) 30

[Auf2-(1-Ph-closo-1,2-C2B10H10)g(PPh3)] — 19

[Auf2-(1-Ph-closo-1,2-C2B10H10)g(AsPh3)] — 19

R D vinyl

[Au(HCDCH2)(CNMe)] — 13c

[Au(HCDCH2)(CNBu-t)] — 13c

aTPA: 1,3,5-triaza-7-phosphaadamantane.

Haloalkylgold(I) complexes can be prepared by photochemical insertion of fluoro-alkenes into the gold–carbon bond of methylgold(I) complexes and this and relatedprocesses involving other metals have been reviewed38. In addition, several new routesto haloalkylgold(I) complexes have been established39,40. These include the directauration of halocarbons such as chloroform with tris(triphenylphosphinegold(I))oxoniumtetrafluoroborate (see also above) to give the halomethylgold(I) derivatives(equation 5)20,23 and the reaction of bis(trifluoromethyl)cadmium with (phosphine)gold(I)halides (equation 6)21,22. The auration product of chloroform is unstable with respectto decomposition into (triphenylphosphine)gold(I) chloride and dichlorocarbene, ashas been ascertained by scavenging experiments with olefins20. An unusual reactionis reported for the chloromethyl complex [Au(CH2Cl)(PPh3)]: Interaction with[PtMe2(2,20-bipy)] �2, 20-bipy D 2, 20-bipyridine� results in oxidative addition to give

3



[PtClMe2(CH2AuPPh3)(2,20-bipy)], a rare example of a heteronuclear �-methylenecomplex that does not contain either a metal–metal bond or an additional bridgingligand41.

CHCl3[(Ph3PAu)3O][BF4]��!

NaH[Au(CCl3)(PPh3)] �5�

2 [AuCl(PEt3)] + (CF3)2Cd Ð DME ��! 2[AuCF3(PEt3)] + CdCl2(DME D CH3OCH2CH2OCH3)

�6�

Alkylgold(I) complexes in which the alkyl group carries a donor functionality rep-resent a special class of compounds in that they often form di- or oligonuclear arrays.Pertinent examples include the complex [Ph2P(CH2)3Au]2, which is prepared accordingto equation 7 and for which a dimeric structure is proposed29. The cyclic structure of thecompound [f2-C(SiMe3)2(C5H4N)gAu]2 has been established by X-ray crystallography30.By contrast, the complex Pt[C6H4f2-CH(AuPPh3)PPh2g]2 represents a heterobimetallicspecies in which gold(I) is not part of a cyclic arrangement42.

[Ph2P(CH2)3]2Zn + 2 [AuCl(CO)]−ZnCl2, −2 CO

P

Au P

Au

Ph2

Ph2

(7)

Several alkyl ligands derived from organic molecules in which the functional groupsinduce ˛-hydrogen acidity have been used to prepare the respective gold(I) complexes.Particularly interesting are thiazolyl and isothiazolyl compounds, which are precursorsfor the synthesis of gold(I) carbene complexes27,28. Recently reported examples includevarious ketone and sulphonic acids derivatives, and C-coordination is observed in allcases43. The syntheses have been carried out by one of the following four methods:

(1) The original ‘alkyllithium route’ (cf equation 1)27,28,31,43,44.(2) The modified alkyllithium route (cf equation 3)46.(3) Deprotonation and subsequent auration with stable gold(I) alkoxides (equation 8)47.

[AufOCH�CF3�2g�PPh3�]C CH2(CN)COOEt ��! [AufCH(CN)COOEtg�PPh3�]

C�CF3�2CHOH �8�

(4) Reaction of silyl enol ethers with complex (phosphine)gold(I) halides in the presenceof caesium fluoride (equation 9)26, or of enol ethers with [(Ph3PAu)3O][BF4]25.

OSiMe3

+ [AuCl(PPh3)]CsF

−CsCl, −Me3SiF

O

AuPPh3 (9)

4



Silylcyclopropyl ethers have been used for the preparation of (phosphine)gold(I) homoeno-late complexes (equation 10)48.

+ [AuCl(PPh3)]CsF

−CsCl, −Me3SiF[Au(CH2CH2COPh)(PPh3)]

Ph

OSiMe3

(10)

Less general reactions include the C-auration of pyrazolone derivatives with(phosphine)gold(I) halide in the presence of an aqueous base49, and the auration of apalladium(II) phosphinoenolate complex with [AuCl(PPh3)] in the presence of AgBF4,resulting in the metallation of the C˛ carbon atom of the former enolate moiety(equation 11)50 (Table 2)

+ [AuCl(PPh3)]

AgBF4−AgCl

N

P

O

Pd

Ph2

Ph

H

[BF4]

N

P

O

Pd

Ph2

Ph

H

AuPPh3

(11)

Finally, there are numerous complexes in which one or both protons in the methy-lene bridge of geminal diphosphine disulphides such as bis(diphenylphosphino)methanedisulphide have been substituted with a (phosphine)gold(I) unit, as illustrated by thereaction products of equation 1251. Deprotonation and subsequent auration can be accom-plished by using gold(I) complexes containing basic ligands, such as [Au(acac)(PPh3)]51

TABLE 2. Alkylgold(I) complexes with carbonyl or sulphonylfunctional groups

Complex Reference

[AufCH(Ph)SO2Bu-tg(PPh3)] 44

[Auf(CCH2CH2)CO(CHCH2CH2)g(PPh3)] 45

[AufCH2COC5H4Mn(CO)3g(PPh3)] 46

[AufCH(CN)2g(PPh3)] 47

[Au(CH2COCH2CH2CHDCH2)(PPh3)] 48

5



or [(Ph3PAu)3O][BF4]52, which are displaced as the conjugate acid in the process. Evena tetranuclear gold(I) complex, [Au2(PPh2CHfAu(acac)gPh2P)2], with two basic ligands,can be used as a base for the deprotonation and this allows the synthesis of hexanucleargold derivatives, such as the one represented in equation 1353. Since the diphosphine lig-ands offer the possibility of further gold coordination at the phosphorus centres, they areversatile building blocks for the preparation of homo- and heteropolynuclear complexesand a large variety of structural types have been prepared54–57.

Ph2(S=)P

Ph2(S=)P H

H[Au(acac)(PPh3)]

−acacH

Ph2(S=)P

Ph2(S=)P AuPPh3

H+

Ph2(S=)P

Ph2(S=)P AuPPh3

AuPPh3

(12)

PAu

Au P

C

P

P

C(acac)Au

H

H

Au(acac)

Ph2

Ph2

Ph2

Ph2

+ 2 [Au(C6F5)3(Ph2PCH2PPh2)]

PAu

Au P

C

P

P

CAu

H

H

Au

Ph2

Ph2

Ph2

Ph2

−2 acacH

PC

P Au(C6F5)3Ph2Ph2

H

PC

P

H

(C6F5)3AuPh2 Ph2

(13)

There has been considerable activity concerning the synthesis and exploration of pos-sible applications58 of alkynylgold(I) compounds in recent years and a number of X-raystructural (see below) as well as Mossbauer59 studies have appeared. Previous routesto such complexes generally start with HAuCl4, which is reduced by SO2 in the pres-ence of acetate, followed by addition of the terminal acetylene. In this way polymericgold(I) acetylides [Au(C�CR)]n are obtained. The oligomeric compound of general for-mula [Au(C�CBu-t)]n has also recently been prepared by treatment of [Au(NH3)2]C witht-BuC�CH60,61.

Compounds of the type [Au(C�CR)]n have been used for the introduction of theacetylide ligand into heterobimetallic complexes of the late transition metals62– 64. Theyreact with electron-rich metal complexes by incorporation of the [Au(C�CR)] unit toform neutral gold–metal clusters65,66, and they can be transformed into alkynylgold(I)complexes of the type [Au(C�CR)(L)] simply by addition of suitable donor ligands,such as amines, tertiary phosphines or isocyanides14,67. The reaction of [Au(C�CPh)]nwith bis(diphenylphosphino)methane affords the photoluminescent trinuclear complex[Au3(C�CPh)2(�-dppm)2][Au(C�CPh)2] �dppm D Ph2PCH2PPh2� (Figure 1). Not onlyneutral ligands, but also halide ions have recently been added to [Au(C�CR)]n, givinganionic species of the general type [Au(C�CR)(X)]� 68�70.

6



Ph2P

Au

C

C

C

Au

C PPh2

Au

PPh2

C Ph2PPh C

HH

Ph

C[PhC Au C CPh]−

+HH

FIGURE 1. Structure of [Au3(C�CPh)2(�-Ph2PCH2PPh2)2][Au(C�CPh)2]

However, the preparation of complexes of the type [Au(C�CR)(L)] as outlined aboveoften fails, since the initially formed [Au(C�CR)]n compounds may readily decompose,depending on the nature of the acetylide ligand. Several novel synthetic routes to alkynyl-gold(I) compounds that circumvent this problem have been established. Complex gold(I)chlorides containing a variety of tertiary phosphines have been found to react with awide range of terminal acetylenes, either in diethylamine in the presence of copper(I)halides71, or in alcoholic solution in the presence of sodium alkoxide71–74, to affordthe corresponding alkynylgold(I) complexes in good yield. These transformations areequally applicable to unsubstituted acetylene, which gives dinuclear gold(I) acetylides[Au2(C�C)(PR3)2]72– 74. Examples are shown in equations 14 and 15.

[AuCl�PPh3�]C HC�CC6F5

Et2NH/Cu(I)Cl��!�[Et2NH2]Cl

[Au�C�CC6F5��PPh3�] �14�

[AuClfP�C6H4Me-4�3g]C HC�CMeEtOH/NaOEt��!�HCl

[Au�C�CMe�fP�C6H4Me-4�3g] �15�

An alternative high-yield method for preparing gold(I) phenylacetylides involves theelectrochemical oxidation of gold metal in an acetonitrile solution of the acetylene75, withthe target compounds precipitating during electrolysis. The measured current efficiencyof about 1 mol Faraday�1 implies the following simple electrode processes:

Cathode: e� C �PhC�CH�! �PhC�C�� C 1/2H2(g)

Anode: Au! AuC C e�

Overall reaction: AuC �PhC�CH�! �PhC�C�AuC 12 H2

Other routes that have led to alkynylgold(I) complexes have employed acetylaceto-natogold(I) derivatives76, alkylgold(I) complexes26 and N-substituted (phosphine)gold(I)imidazoles77, respectively. The anionic ligands in these reagents are sufficiently basicto deprotonate the acetylene moiety, thus forming acetylide complexes such as thoseshown in Figure 277. Also NH3 can act as a deprotonating base, as demonstrated in

7



HO C C AuPPh3

MeO

OH

C C AuPPh3

FIGURE 2. Alknylgold(I) complexes77

the reaction of [Au(NH3)2]C with phenylacetylene to give [Au(C�CPh)(NH3)] in excel-lent yield60. Finally, compounds of the type [Au(C�CH)(PR3)] (R D Ph, C6H4OMe-4)have been obtained by treating the bis(acetylide)aurate(I) with bis(phosphine)gold(I)derivatives76. A collection of other alkynylgold complexes is listed in Table 3. Thealkynylgold(I) complexes of the type [Au(C�CBu-t)(R2PCH2PR2)] contain monodentatediphosphine ligands and can undergo ligand exchange reactions78. Thermolysis of thedinuclear [Au2(C�CBu-t)2(Ph2PCH2PPh2)] in refluxing toluene leads to intermolecularelimination of t-BuC�CH and formation of the stable tetragold(I) complex representedin equation 1679.

Ct-BuC Au P

Au P

CH2

Ct-BuC

2

Ph2

Ph2

toluene, reflux

CH−t-BuC

Ct-BuC Au P

Au P

C

Ct-BuC

Ph2

Ph2

H

AuPPh2

CH2

Ph2

PAuCt-BuC (16)

Alkynylgold(I) halide anion complexes have been prepared from suitable gold(I)acetylide precursors by addition of halide ion, as illustrated in equation 1770, or reactinga bis(acetylide)aurate(I) with a dihalogenoaurate(I) (equation 18)76.

1/n[Au�C�CPh�]n C [NEt4]Cl ��! [NEt4][Au�C�CPh�Cl �17�

[N�PPh3�2][Au�C�CH�2]C [N�PPh3�2][AuCl2] ��! 2[N�PPh3�2][Au�C�CH�Cl]�18�

Bifunctional acetylene ligands such as R2PC�CH or p-C�N-C6H4�C�CH have beenemployed in the synthesis of novel classes of metal-containing polymers. The polymerbackbone contains both unsaturated organic fragments and inorganic elements, such asgold or a combination of gold and phosphorus. These materials are therefore expectedto show electrical conductivity or optical non-linearity81,83–85. Modes of preparation ofsuch compounds have been summarized in equation 19 and Scheme 1.

[AuCl�Ph2PC�CH�]NaOMe��! [fAu�Ph2PC�C�gx] �19�

Polymers have also been prepared from diphosphines and diacetylides, both of whichact as bridging ligands and alternate along the polymeric chain (Figure 3). The synthesis

8



TABLE 3. Alkynylgold(I) complexes


[Au(C�CPh)]n 180(d) 75[Au(C�CH)(PPh3)] 168 72, 76[Au(C�CH)(PPh2Np)]a — 74

[Au(C�CH)(PPh2Bp)]b — 74[Au(C�CH)(NH3)] — 60[Au(C�CMe)(PMe3)] 123(d) 13c, 71[Au(C�CMe)(PPh3)] 173 – 175 71[Au(C�CCF3)(PPh3)] 155 72[Au(C�CEt)(PPh3)] 154 – 155 72[Au(C�CPr-n)(PPh3)] 256 – 259 71[Au(C�CBu-n)(PPh3)] 279 – 281 71[Au(C�CBu-t)(PMe3)] 183 – 186 71[Au(C�CBu-t)(PPh3)] 181 – 182 71[Au(C�CCH2OH)(PPh3)] 234 – 235 71[Au(C�CCH2OMe)fP(C6H4Me-4)3g] — 80[Au(C�CCH2CH2OH)(PPh3)] 248 – 250 71[Au(C�CCO2Me)(PPh3)] 239 – 240 71[Au(C�CPh)(PMe3)] 196 – 198 71[Au(C�CPh)fPPh(OMe)2g] 212– 215 71[Au(C�CPh)(PPhFc2)]c — 74[Au(C�CPh)(PPh3)] 163 – 165 72, 75[Au(C�CPh)fP(C6H4Me-4)3g] 146– 148 72

[Au(C�CPh)(phen)]d 95–97 75[Au(C�CC6F5)(PPh3)] 235 – 236 71[Au(C�CBu-t)(Me2PCH2PMe2)] 165(d) 78[Au(C�CBu-t)(Ph2PCH2PPh2)] 99(d) 78[Au(C�CPPh2)]x — 81[Au2(C�C)(PPh3)2] — 72[Au2(C�C)fP(C6H4Me-4)3g2] 110– 115 72, 82[Au2(C�C)fP(C6H4OMe-4)3g2] 125 72, 82[Au2fp-C�C�(C6H4)n�C�Cg(PMe3)2], n D 1, 2 — 83[Au2(C�CBu-t)2(Ph2PCH2PPh2)] — 79[Au2(C�CPh)2(Ph2PC6H4PPh2-p)] — 83[Au2(C�CPh)2(Ph2PCH2CH2PPh2)] — 58[Au(C�CMe)(CNMe)] 140(d) 13c[Au(C�CBu-t)(CNMe)] 180– 181(d) 13c[Au(C�CH)Cl]� 192 76[Au(C�CH)Br]� 186 76[Au(C�CPh)Cl]� — 70[Au(C�CPh)Br]� — 70[Au(C�CPh)I]� — 70

aNp, 1-naphthyl.bBp, 4-biphenylyl.cFc, ferrocenyl.dphen, 1,10-phenanthroline.

9


Schmidbaur, Andreas Grohmann, M. Elena Olmos and Annette Schier

CBu−t)6]6[(AuC + NC C C H

NC C C H

80°C/C6H6

CH−t-BuC

AuCCt-Bu

NC C C HAuCCt-Bu

x

SCHEME 1. Synthesis of (isocyano)gold(I) acetylide polymers

starts from digold(I) acetylides [(AuC�CArC�CAu)x] (Ar D e.g. 1,4-C6H4), prepared byreaction of the diacetylene with [AuCl(SMe2)] in the presence of sodium acetate as base.Reaction of the starting material with diphosphine, PP, gives polymers of the generalformula [(C�CArC�C�Au�PP�Au�)x].

C C Au PR2

PR2

Au C CAu P

C

C

Au

PR2

C C Au P

C

C

Au

R2

R2 n

FIGURE 3. Suggested structures of [fAu(R2P�C�C)g]n and [(Ar�C�C�Au�C�C)n]

10



M

OC

C C

M

Ph AuPR3

CO

CO

OC

MCO

C

CM

Ph

AuPPh2CH2Ph2PAuCO

CO

CO

MCO

C

CM

CO

CO

M = Mo, W

R = Ph, Me

M = Mo, W

Ph

OC

FIGURE 4. Heteropolynuclear complexes with bridging alkynylphosphinegold(I) units

Some heteropolynuclear gold-containing acetylides are also known, such as the din-uclear [Fef(C�C)Au(PPh3)g(�5-C5H5)(Ph2PCH2PPh2)] and [Ruf(C�C)Au(PPh3)g(�5-C9H7)L2] (L2 D (PPh3)2; (PPh3)(PMe3); (PPh2)2(CH2)n, n D 1, 2), obtained from thecorresponding ethynyl complexes of iron or ruthenium and (triphenylphosphine)gold(I)chloride in the presence of Tl(acac)86, or the tri- or hexanuclear gold(I) and group 6 metalcomplexes represented in Figure 487–90.

The chemistry of arylgold(I) complexes [ArAuL] has developed rapidly in recentyears and two reviews have appeared11,12. The available synthetic methods allowthe preparation of complexes with a diverse range of ligands L, including tertiaryphosphines, amines, isocyanides, tetrahydrothiophene, and tertiary arsines. Difunctionalphosphines such as bis(diphenylphosphino)amine give the corresponding dinucleararylgold(I) complexes91,92, and a dimeric orthometallated phenylphosphine complexof formula [Au2fC6H4(PPh2)g2] has also been prepared93. Both types of complexesundergo two-centre oxidative addition reactions reminiscent of those described for thestructurally related gold(I) ylide complexes (see below). Also trinuclear arylgold(I)phosphine derivatives have been described33,94,95, and some of these are luminescentmaterials33.

In analogy to the synthesis of the alkyl derivatives, arylgold compounds [ArAuL](L being a neutral donor ligand) can be prepared from complex gold(I) halides via theorganolithium or the Grignard route96,97. [ArAuL] complexes can also be synthesized withligands L that are only weakly coordinating (such as tetrahydrothiophene, SC4H8)92–100

(equation 20); derivatives may then be obtained through displacement of this ligand by avariety of other, more strongly coordinating donors (equation 21)101. These may includeunusual species such as alkylidyne complexes [W(�CR)(CO)2(Me2PCH2CH2PMe2)Cl],which react to give heteronuclear complexes with bridging carbyne ligands betweentungsten and gold102. Several tricoordinate arylgold(I) diphosphine complexes haverecently been prepared by displacement of tetrahydrothiophene with the metallodiphos-phine 1,10-bis(diphenylphosphino)octamethylferrocene or with bis(diphenylphosphino)-o-carborane103.

[Au�SC4H8�2]ClO4 C [NBu4][Au�C6H2F3-2,4,6�2] ��!2[Au�C6H2F3-2,4,6��SC4H8�]C [NBu4]ClO4 �20�

[Au�C6F5��SC4H8�]C H2NCH2CH2NH2 ��! [Au�C6F5��H2NCH2CH2NH2�] �21�

11



Treatment of (phosphine)gold(I) halides or tris(phosphinegold(I))oxonium salts withsodium tetraphenylborate affords arylgold(I) phosphine species through an unusual phenyltransfer reaction. Examples of this novel synthetic route are given in equations 22104

and 23105.

[Au(TPA)3]ClC Na[BPh4] ��! [AuPh(TPA)]C NaClC 2TPAC BPh3 �22�

TPA D 1,3,5-triaza-7-phosphaadamantane

[�t-Bu3PAu�3O][BF4]C Na[BPh4] ��! 3[AuPh�PBu-t3�]C Na[BF4]C PhBO �23�

TABLE 4. Arylgold(I) complexes of the type [ArAuL]


[AuPh(CNMe)] — 13c[Au2Ph2fC6H4(CH2PPh2)2-1,4g] 135(d) 105

[AufC6H5(�6-Cr(CO)3)g(PPh3)] — 109[AufC6H4NO2-2g(AsPh3)] — 108[AufC6H4NO2-2g(SbPh3)] 120(d) 108[AufC6H4NO2-2g(phen)]a 100(d) 108[AufC6H2(NO2)3-2,4,6g(dmphen)]a — 110[Au2fC6H4PPh2-2g2] — 93[Au2fC6H4AsPh2-2g2] — 111[Au(C6H2F3-2,4,6)(SC4H8)] 73(d) 93[Au(C6F5)fN(DCPh2)NDCPh2g] — 112[Au2(C6F5)2f(Ph2P)2CH2g] — 113[Au2(C6F5)2fPh2As)2CH2g] 189(d) 107[Au2(C6F5)2f(Ph2PC5H4)2Feg] 245(d) 114[Au2(C6F5)2fPh2PC(Ph2PAuPPh2)2CPPh2g] 170 94[Au2(C6F5)2fAu(Ph2PCHPPh2Me)2g]C — 115[Au2(C6F5)2f(Ph2P)2Mn(CO)4g]� — 116[Au2(C6F5)2f(Ph2P)2NHg] 205 92[Au2(C6Cl5)2f(Ph2P)2NHg] 144(d) 92[Au2(C6F5)2(S2CPEt3)] 144 117[Au2(C6F5)2f(Ph2PS)2CH2g] 185 118

[Au2(C6F5)2(L)]b 195 119

[Au2(C6F5)2(L0)]b 143 119[Au3(C6F5)3f(Ph2P)3CHg] 220(d) 94[Au(C6F5)f[W](CC6H4Me-4)g]c — 102

[(AuC3N2Me)3]d 272–275(d) 120[Au(C6F5)Cl]� — 121[Au(C6F5)fPh2PC(PPh2)2gMo(CO)4]� 108 99[Au(C6H2F3-2,4,6)Br]� — 122[Au(C6H2F3-2,4,6)(SCN)]� — 122[AufC6H2(NO2)3-2,4,6gCl]� — 110

aphen, 1,10-phenanthroline; dmphen, 2,9-dimethyl-1,10-phenanthroline.bHL, C3H5NS2(1,3-thiazolidine-2-thione); HL0, C5H5NS(pyridine-2-thione).c[W], [W(CO)2(Me2PCH2CH2PMe2)Cl].dC3N2, C2-imidazolyl.

12



A selection of arylgold(I) complexes that have recently been prepared is presentedin Table 4. Complexes of the type [ArAuL] readily undergo oxidative addition ofhalogen, acyl halides or similar reagents to give gold(III) complexes of the type[ArAu(X)2L]106–108. Mesityl(triphenylphosphine)gold(I) (mesityl D C6H2Me3-2,4,6)reacts with [Ag(OSO2CF3)L] (L D PPh3, SC4H8), giving rise to polynuclear derivativesin which the mesityl group acts as a bridge between a gold and a silver centre98.

Anionic complexes [ArAuX]�, in which X is a halide or pseudohalide donor lig-and, have so far only been isolated if the aryl group is strongly electron-withdrawing,as in nitrophenyl or pentafluorophenyl derivatives11,12,121. Two methods of preparationhave been reported: One relies on the displacement of weakly coordinating ligands,such as tetrahydrothiophene, SC4H8

122 or triphenylarsine97 by halide or pseudohalideions, while the other involves the arylation of dihalogenoaurate ions with dialkylmercurycompounds110. Examples of both types of reactions are presented in equations 24 and 25,respectively.

[Au�C6H2F3-2,4,6��SC4H8�]C [N�PPh3�2]SCN ��![N�PPh3�2][Au�C6H2F3-2,4,6�(SCN)]C SC4H8 �24�

[PPh3�CH2Ph�][AuCl2]C [HgfC6H2�NO2�3-2,4,6g2] ��![PPh3�CH2Ph�][AufC6H2�NO2�3-2,4,6gCl]C [HgfC6H2�NO2�3-2,4,6gCl] �25�

(Phosphine)gold(I) complexes containing a cyclopentadienyl or related ligand have beenthe subject of a number of studies, the major question being the degree of fluxionality insuch molecules. Several cyclopentadienyl complexes have been prepared (Table 5) eitherby the organolithium method123 or by direct auration of the parent cyclopentadiene withtris(triphenylphosphinegold(I))oxonium tetrafluoroborate124,125 (equations 26 and 27). Aunique reaction is that of pentakis(methoxycarbonyl)cyclopentadiene (1)126, which is astrong acid and will displace weaker organic acids upon interaction with their metal salts(equation 28)127.

[AuCl�PPr-i3�]C LiC5H5 ��! [Au�C5H5��PPr-i3�]C LiCl �26�

[�Ph3PAu�3O][BF4]C 3C5Ph4H2 ��! 3[Au�C5Ph4H��PPh3�]C [H3O][BF4] �27�

[Au�CO2Me��PPh3�]C C5�CO2Me�5H ��! [AufC5�CO2Me�5g�PPh3�]CMeCO2H �28�

MeO

OMe O

O OMe

OMe

O H

O

(1)

O

MeO

13



Cyclopentadienyl- and pentamethylcyclopentadienylgold(I) complexes react withterminal acetylenes such as HC�CH, HC�CPh and HC�CCO2Me to give thecorresponding alkynylgold(I) compounds123. A most unusual reactivity towards auratingagents such as (triphenylphosphine)gold(I) tetrafluoroborate is observed with thetetraphenylcyclopentadienylgold(I) phosphine complex, which can add one or even two(triphenylphosphine)gold(I) units to form dinuclear compounds containing 3-centre–2-electron bonds124–130.

Gold(I) complexes of Cp-related ligands have also been prepared. 9-Fluorenyl (tri-phenylphosphine)gold(I) (2)131 can be obtained via the oxonium salt route, but the reducedC�H acidity of fluorene requires the use of an additional base, such as sodium hydride,to deprotonate the hydrocarbon.

H AuPPh3

(2)

Ferrocenylgold compounds have been prepared by the organolithium method andauration of one or both of the cyclopentadienyl rings could be achieved24. Similar totetraphenylcyclopentadienylgold(I) phosphine complexes, these compounds can incorpo-rate additional (phosphine)gold(I) units upon interaction with (triphenylphosphine)gold(I)tetrafluoroborate to give electron-deficient species as described below.

Reaction of C-imidazolyllithium derivatives with (triphenylphosphine)gold(I) chlorideresults in the formation of C-aurated imidazolylgold(I) compounds106,120,132. In these,the imidazole ring can act as a donor ligand towards other imidazolylgold(I) units anddisplacement of phosphine leads to the formation of cyclic trimers like 3. These kindsof species undergo oxidative addition reactions to give trinuclear gold(III) derivatives orgold(I) carbene complexes.

N

NCH3

Au Au

N

N

N

N

Au

CH3(3)

3CH

14



Several metallocene complexes of cobalt and rhodium have been studied in whichone cyclopentadienyl ring is replaced by a diborole moiety133. Under suitable conditions,auration of the C-2 carbon atom occurs (equation 29). Cyclopentadienyl and related gold(I)complexes are given in Table 5.

Rh

BB

Me

Me H

−

Rh

BB

Me

Me H[AuCl(PPh3)]

−Cl−

AuPPh3

Me Me Me Me (29)

Iminoalkyl complexes of gold(I) can be prepared by the simultaneous treatment ofa (phosphine)gold halide [AuX(PR3)] with isocyanides and alcohols in the presence ofalkali (equation 30)134. In some cases, an intermolecular reaction similar to that observedfor imidazolylgold(I) compounds results in the displacement of the phosphine ligands bythe iminoalkyl moiety to form cyclic oligomers135.

[AuCl�PBu-t3�]C CNCH2TsCMeOHC KOH ��![AufC(OMe)�NCH2Tsg�PBu-t3�]C KClC H2O �30�

A related compound is obtained upon auration of an unusual tungsten carbene thioketeneadduct, as shown in equation 31136.

TABLE 5. Cyclopentadienyl and related gold(I) complexes


[Au(C5H5)(PMe3)] 87(d) 123

[Au(C5H5)(PPr-i3)] 105(d) 123

[Au(C5Me5)(PPr-i3)] 92(d) 123

[Au(C5Me5)(PPh3)] 83(d) 123

[Au(C5HPh4)(PPh3)] 159 – 160(d) 125

[AufC5(CH2Ph)5g(PPh3)] — 128

[AufC5Me(CO2Me)4g(PPh3)] 157 – 159 129

[AufC5(CO2Me)5g(PPh3)] 145 127

[Au(C13H9)(PPh3)]a 135–137(d) 131

[Au2(C5H4FeC5H4)(PPh3)2] 105–106(d) 24

[AufC(NMe)CHCHNg]3 — 120

[Auf(C3B2HMe4)Co(C5H5)g(PPh3)]b 190(d) 133

aC13H9, 9-fluorenyl.bC3B2HMe4, 2,3,4,5-tetramethyl-2,3-dihydro-1H-1,3-diborol-2-yl.

15



C(OC)5WLi + [AuCl(PPh3)]

S(OC)5W

C

Ph

C

OEtPh

S

C

C

AuPPh3

C

Ph

Ph OEt

−LiCl (31)

B. Gold(I) Complexes Containing the Structural Building Block C(AuL)n ,n �� 2

The first compounds to be characterized in which a single carbon atom acts asa bridging ligand between two gold(I) units are the tolyl and ferrocenyl derivatives[4-MeC6H4(AuPPh3)2][BF4] and [f(C5H5)Fe(C5H4)g(AuPPh3)2][BF4], respectively,prepared as shown in equation 32137.

2[4-MeC6H4�AuPPh3�]C H[BF4] ��! [4-MeC6H4�AuPPh3�2][BF4]C C6H5Me �32�

Protonation of the aryl moiety in the starting material liberates the electrophilic species[Au(PPh3)]C, which subsequently attacks a second molecule of the arylgold(I) complex.

Similar complexes have subsequently been prepared. One example is the tolyl complex[4-MeC6H4fAu2(Ph2PCH2CH2)2g][BF4], in which the two independent PPh3 groups havebeen replaced by the bidentate chelating ligand 1,4-bis(diphenylphosphino)butane138.The reaction leading to such species is obviously not affected by the accumulation ofpositive charges within the same molecule, as indicated by the facile preparation of stable[fC5H4(AuPPh3)2gFefC5H4(AuPPh3)2g][BF4]2 (equation 33)24. The syntheses of unusualtrinuclear complexes [Ph4C5(AuPPh3)3][BF4]124,130 and [(CN)2C(AuPPh3)3][BF4]25

along a similar route provide other cases in point.

Fe

AuPPh3

Ph3PAu

+ 2 [Au(PPh3)][BF4]

FeAuPPh3

AuPPh3

Ph3PAu

Ph3PAu

[BF4]2

(33)

16



There has also been a report of dinuclear gold(I) alkynyl complexes,[RC�C(AuPPh3)2][BF4] (R D Ph, i-Pr), which are prepared in the same way139–141.

A related group of compounds has aryl groups bridging gold atoms or gold and asecond metal, thus giving cyclic oligomers like [Au(C6H2F3-2,4,6)]4 (prepared by theinteraction of the diarylaurate with H[PF6]) or [Au(C6H2Me3-2,4,6)]5 (equation 34 andFigure 5)142– 144. [Au(C6H2Me3-2,4,6)]5 will react with mono- and bidentate phosphineligands to give the respective mesitylgold(I) phosphine complexes145.

5 [AuCl�CO�]C 5 [MgBr�C6H2Me3-2,4,6�] ��! [Au�C6H2Me3-2,4,6�]5 C5 COC 5 MgBrCl �34�

Complexes in which an aliphatic carbon atom acts as a bridging ligand between twogold(I) units are well represented146. Several of these can be considered to be derivedfrom the simplest hydrocarbon, methane, by formal substitution of two hydrogen atomswith isolobal (phosphine)gold(I) units. A few examples of these diaurio(I)methanes andrelated complexes are shown in Figure 6, and Table 6 offers a more comprehensive

Au Au

Au

Au

Au

FIGURE 5. Structure of [Au(C6H2Me3-2,4,6)]5

CNC

NC AuPPh3

AuPPh3 C

O

Me

OO

Me AuPPh3

AuPPh3

CMe3P

Me3P AuMe

AuMeC

EtOOC

Ph3P AuPPh3

AuPPh3+

FIGURE 6. Structures of some diaurio(I)methanes and related complexes

17



TABLE 6. Compounds containing the structural building block C(AuL)2

Complex Reference

[(Ph3PAu)2f�C(CN)2g] 25

[(Ph3PAu)2(�C.CO.NMe.CO.NMe.CO)] 147

[(Ph3PAu)2(�C.CMe.N.NPh.CO)] 49, 153a

[(Ph3PAu)2(�CHPPh3)]C 153c

[(MeAu)2f�C(PMe3)2g] 149

[(Ph3PAu)2f�C(PMePh2)2g]2C 154

[(Ph3PAu)2f�C(PPh3)(CONMe2)g] 151

[(Ph3PAu)2f�C.B(NPr-i2).C(SiMe3)2.B(NPr-i2)g] 155

[(Ph3PAu)2f�C.PPh2(Fe(CNPh)3Cl)PPh2)g]C 156

[(Ph3PAu)2(�CfPPh2AuPh2Pg2C�)(AuPPh3)2]2C 53, 55

[f(PhMe2PAu)2(�CPPh3)2gCDO] 157

[(Ph3PAu)2f�C(COOEt)PPh2CH(COOEt)(AuPPh3)g]C 158

listing. [(NC)2C(AuPPh3)2] can be prepared by auration of C�H acidic maleodinitrilewith tris(triphenylphosphinegold(I))oxonium tetrafluoroborate, [(Ph3PAu)3O][BF4]25. Ina similar way, the methylene group of N-alkylated barbituric acid can be doubly auratedby reaction with sodium methoxide/methanol in the presence of [AuCl(PPh3)]147,148. Ahexanuclear gold(I) complex featuring two C(AuPPh3)2 units can be obtained throughtwo alternative synthetic methods, one of them involving an intramolecular deprotonationof the starting material when treated with [Au(PPh3)2]ClO4, as shown in equation 3553.The bis(ylide) derivative [(Me3P)2C(AuMe)2] has been prepared by reaction of hexam-ethylcarbodiphosphorane with methyl(trimethylphosphine)gold(I)149.

Ph2 Ph2

+ 2 [Au(PPh3)2]ClO4

−2 acacH

(ClO4)2

P Au

C

P Au

P

P

CPh3PAu

Ph3PAu

AuPPh3

AuPPh3

Ph2 Ph2

Ph2 Ph2P Au

C

P Au

P

P

C(acac)Au

H

H

Au(acac)

Ph2 Ph2

(35)

A number of other diaurated ylide derivatives have been obtained from the interactionof functionalized phosphonium salts such as [Ph3PCH2(C5H4N-2)]ClO4 with two equiv-alents of (triphenylphosphine)gold(I) acetylacetonate, which induce double deprotonationand subsequent auration of the methylene group (Scheme 2)150– 152.

18



NPPh3

ClO4 + 2 [Au(acac)(PPh3)]

N ClO4AuPPh3

AuPPh3Ph3P

N

AuPPh3

AuPPh3

Ph3P

AgONO2

OClO3

AgNO3

−2 acacH

SCHEME 2. Synthesis and adduct formation of diaurated ylide derivatives

Triple auration is achieved in the reaction of the silylated ylide Me3PDCHSiMe3 with[AuCl(PPh3)] in the presence of caesium fluoride, as shown in equation 36154. For othercompounds with triply aurated elements, see elsewhere159–161.

PMe3

CH SiMe3

2+ 4 [AuCl(PPh3)] + 3 CsF

−2 Me3SiF, −3 CsCl−[(Me3PCH2AuPPh3)Cl]

Cl

PMe3

C

Au

AuPPh3Ph3PAu

PPh3

(36)

Bis(trimethylsilyl)methyl (triphenylphosphine)gold(I) reacts with the oxonium salt[(Ph3PAu)3O][BF4] to give a mixture of two products (equation 37)162. One has beenidentified as a disilyl diauriomethane, while the major product is found to be the stabletrinuclear complex [(Ph3PAu)3f�-C(SiMe3�2g][BF4]. Clearly, this compound forms fromthe diauriomethane precursor by incorporation of yet another [Au(PPh3)]C unit, eventhough the result is a positively charged species with a hypercoordinate carbon atom.

[�Me3Si�2CH�AuPPh3�]C [�Ph3PAu�3O][BF4] ��! [�Me3Si�2C�AuPPh3�2] C[��-Me3Si�2C�AuPPh3�3][BF4] �37�

A different triauriomethane derivative is an important intermediate in an unusual trans-formation which provides access to gold–carbon compounds of even higher nuclearity,containing the structural fragment [RC(AuL)4]C. The overall reaction is depicted inScheme 3163.

19



NO

Me

Me

Me

3 n-BuLi + 3 Me3SiCl

−3 n-BuH, −3 LiClO

N

Me3Si

MeMe

C

C

SiMe3Me3Si

[AuCl(PPh3)] + CsF

ON

C

MeMe

PPh3Au

PPh3PAuPh3PAu

Au

Au N

C

O

MeMe

AuPPh3

AuPPh3

AuPPh3

+

+

2 [Me3SiF2]−

SCHEME 3. Synthesis of a polynuclear organogold(I) cluster featuring tetraaurated, pentacoordinatecarbon atoms

The synthesis starts from 2,4,4-trimethyl-4,5-dihydrooxazole, a compound with markedC�H acidity in the exocyclic methyl group. Triple lithiation followed by derivatiza-tion with chlorotrimethylsilane affords a triply silylated, open-chain ketenimine which isreacted with [AuCl(PPh3)] in the presence of caesium fluoride to give a dimeric, octanu-clear gold(I) cluster. The reaction proceeds beyond the stage of a triauriomethyl oxazolinylderivative which, in fact, can only be observed as a side product.

The simplest tetra-aurated carbon-centred complex is the cation in [HC(AuPPh3)4][BF4],which is formed in the reaction of (trimethylsilyl)diazomethane with tris(triphenylphos-phinegold(I))oxonium tetrafluoroborate together with two by-products (equation 38)153c.Formally, it represents the product of the protonation of the neutral tetra-auriomethanemolecule. This indicates that the species [C(AuPPh3)4] is a strong Lewis base153d.

[�Ph3PAu�3O][BF4]CMe3SiCHN2�N2��! [HC�AuPPh3�4][BF4]C . . . �38�

Hypercoordinate, tetra-aurated carbon centres in which all gold(I) atoms carry aphosphine ligand have also been realized in the ethane-derived complexes of the type[H3C�C(AuPR3)4][BF4]164. The common starting material for this series of compoundsis 1,1,1-tris(dimethoxyboryl)ethane, which is reacted with (phosphine)gold(I) halides inthe presence of caesium fluoride to give the pentacoordinate organogold(I) clusters asair-stable substances (equation 39). Complexes containing four monodentate phosphineligands PR3 (R D Ph, c-C6H11) or two intramolecularly bridging bidentate diphosphine

20



ligands 1,2-(Ph2PCH2CH2)2C6H4 have been prepared.

H3C-C[B(OMe)2]3 + 4 [AuCl{P(c-C6H11)3}] + 4 CsF

CH3

C(c-C6H11)3PAu AuP(C6H11-c)3

AuP(C6H11-c)3(c-C6H11)3PAu

[BF4] + 4 CsCl + 2 B(OMe)3

(39)

In the many attempts to synthesize homoleptic polyauriomethanes C(AuPR3)4, thepreparation has only been successful if phosphine ligands of sufficient steric bulk wereemployed. Tetrakis[(tricyclohexylphosphine)gold(I)]methane is obtained from a mixtureof C[B(OMe)2]4, [AuClfP(c-C6H11)3g] and CsF as a colourless crystalline solid with theexpected tetrahedral array of gold atoms around the central carbon atom165.

In the presence of sterically less demanding phosphine ligands L [such as PPh3 orP(C6H4Me-4)3] the reactions (equation 40)166 proceed beyond the stage of tetra-aurationat carbon and homoleptic penta-aurated cations [C(AuPR3)5]C are produced in high yield.

H2CfB(OMe)2g2 C [AuCl�PPh3�]/CsFC [P(O)�NMe2�3] ��! [C�AuPPh3�5][BF4]

�40�

Dications [C(AuPR3)6]2C with a large variety of phosphine ligands have beencharacterized (R D Et, i-Pr, Ph, C6H4X-4 with X D Cl, Br, NMe2, OMe, Me) andthe isolation of species containing tailor-made chelating phosphine ligands is equallystraightforward167–170. The salts are stable, colourless, crystalline substances. Theyare accessible in high yields and have been found to be diamagnetic in all cases. Atypical reaction is given in equation 41. For further information on this general class ofcompounds the reader is referred elsewhere171– 181.

CfB(OMe)2g4 C 6 [AuCl�PPh3�]C 6 CsF ��! [C�AuPPh3�6][MeOBF3]2 C6 CsClC 2 B(OMe)3 �41�

C. Gold(I) Complexes with Two Gold–Carbon Bonds

Simple dialkylaurates(I) are best prepared by the interaction of an alkylgold(I)phosphine adduct with an organolithium reagent13a. This method has also beenused for the preparation of complexes containing functionalized alkyl groups, asshown in equation 4231, although these can alternatively be obtained by treatmentof (tetrahydrothiophene)gold(I) chloride with two equivalents of alkyllithium, as inthe case of thiazolyl27 or isothiazolyl28 complexes (equation 43). Treatment of theproduct of reaction 42 with potassium carbonate affords the analogous potassiumbis(diethylcarbamoylcyclopropyl)aurate, which possesses a dimeric structure in the

21



solid state31.

O

Et2NAuPPh3

O

Et2NLi+

−PPh3

Au

Et2N

O

NEt2

O

Li

(42)

[AuCl(SC4H8)] + 2

−LiCl−SC4H8

Li

NS

Li

NS

Au NS

(43)

The stabilization of dialkylaurate(I) by means of functionalized alkyl groupsappears to be a general phenomenon. An example is provided by the complex[Ph3PDNDPPh3][Au(acac)2] which is a versatile precursor for other dialkylauratederivatives and related compounds76,182. Some relevant reactions are summarized inScheme 4. Similar products have also been obtained from complex gold(I) halides byreaction with carbanionic ligands such as bis(diphenylphosphino)methanide115.

Related dialkynylaurates(I) are accessible from dialkylaurates by treatmentwith terminal acetylenes (Scheme 4). Alternatively, the bis(phenylacetylide) com-plex [PPN][Au(C�CPh)2] may be prepared by metathesis of the organocuprate[PPN][Cu(C�CPh)2] with various gold(I) complexes such as [Au(C�CPh)(PPh3)],[AuCl(PPh3)], [AuCl(C�CPh)]� or [Au(C�CPh)]n183. A less straightforward synthesisof dialkynylaurates(I) starts from gold(I) iodide and potassium acetylide, requiring liquidammonia as the reaction medium184. Metal–metal contacts are the dominating feature inthe solid state structures of a series of related (in most cases heterometallic) organogoldcompounds, prepared from the alkynylgold(I) complexes [PPN][Au(C�CPh)2] or[Au(C�CPh)(PPh3)] by reaction with the coinage metal acetylides [Cu(C�CR)]n,

22



N

CH

R3P

Au CH

ClO4

R = C6H4Me-4

R′CH

RAu CH

R′

R[PPN]

R = R′ = CN

R = R′ = CO2Me

R = CN, R′ = CO2Me

[PPN][Au(C CH)2]

[PPN][Au(C CSiMe3)2]

i

ii

iii iv

v

[Au{CH(PPh2)2}]n

[PPN][Au(acac)2]

−2 TlCl+2 Tl(acac)

[PPN][AuCl2]

PR3

N

SCHEME 4. Preparation and reactions of homoleptic dialkylaurates with functionalized ligands.Conditions: i, 2HC�CSiMe3, �2 acacH; ii, 2 HC�CH, �2 acacH; iii, 2 CH2RR0, �2 acacH; iv,2 [R3PfCH2(2-C5H4N)g]ClO4, �2 acacH, - [PPN]ClO4; v, CH2(PPh2)2, - acacH, -[PPN]acac

[Ag(C�CR)]n or [Au(C�CR)]n (R D Ph or C6H4Me-4)185–191. The structure of a het-erometallic pentanuclear cluster is given in Figure 7.

The reaction of polymeric long-chain gold(I) acetylides with isocyanides results in theformation of alkynylgold(I) isocyanide complexes, as represented in equation 44, someof them displaying liquid-crystalline properties (m D 6, 8, 10, 12; X D H, OCnH2nC1;n D 4, 6, 8, 10).

Ph

C

C

Au

C

C

Ph

Ph

C

C

Au

C

C

Ph

Ph

C

C

Au

C

C

Ph

Cu

Cu

FIGURE 7. Structure of the pentanuclear cluster [Au3Cu2(C�CPh)6]�

23



C CmH2m+1

n

N X

X N C Au C C CmH2m+1

AuC + C

(44)

Diarylaurate(I) complexes have been prepared by a variety of methods, depending onthe nature of the aromatic ligands11,12,192,193. While diarylaurates as such are generallymore stable than their unfunctionalized dialkyl analogues, this stability is particularlyenhanced with aryl groups bearing a number of strongly electron-withdrawing ligands.Polyhalophenylaurates(I) have been much studied recently and their preparation and prop-erties have been the subject of two reviews11,12. The most versatile method for thepreparation of such compounds is the arylation of a complex gold(I) halide with two equiv-alents of aryllithium (equation 45). These compounds show a propensity for metal–metalaggregation when treated with reagents such as AgClO4 (equation 46)194,195.

[AuCl�SC4H8�]C 2Li�C6H2F3-2,4,6�C NBu4Cl ��! NBu4[Au�C6H2F3-2,4,6�2] C2LiCl C SC4H8 �45�

NBu4[AuR2]C AgClO4 C L ��! 1/n[AuR2AgL]n C NBu4ClO4 �46�

R D C6H5,C6Cl5,C6H2F3-2,4,6;L D N,P,O,S donors, olefin, acetylene, arene

There are a number of compounds in which an arylgold(I) moiety is bonded to abis(diphenylphosphino)methanide group, which in turn acts as a bridging ligand in apolynuclear gold or gold/silver complex11,12,196. An example is shown in Scheme 5197,198.

2 [AuCl(CH2PPh3)] + 2 CH2(PPh2)2−2 [PPh3Me]Cl

P

C

P

PAu

Au P

C

Ph2 Ph2

Ph2 Ph2

H H

2 [Au(C6F5)(SC4H8)]−2 SC4H8

P

C

P

PAu

Au P

C

Ph2 Ph2

Ph2 Ph2

(F5C6)Au

H

H

Au(C6F5)

SCHEME 5. Synthesis of a polynuclear gold complex containing bis(diphenylphosphino)methanideligands

24



AuAu

Au

P

C HC

PPh3

PH

P Au P

Ph2

Ph2

Ph2 Ph2

2+

F5C6

C6F5Ph3P

FIGURE 8. Structure of the tetranuclear [Au4(C6F5)2f(Ph2P)2CHg2(PPh3)2] (ClO4)2

The product thus obtained undergoes oxidative addition of halogens, leading to unusualtetranuclear species, which give cationic complexes by substitution of the halogen atomsby a neutral ligand (Figure 8)199– 202.

D. Complexes of Gold(I), Gold(II) and Gold(III) with Ylide Ligands

There now exists a large number of methods for the synthesis of organogold complexeswith various ylide ligands. In an extensive reaction chemistry, successive oxidation of thegold centres [Au(I)! Au(II)! Au(III)] can often be accomplished. Ylide complexesof gold have therefore been summarized in the following sections regardless of theiroxidation state.

1. Mononuclear ylide complexes

Mononuclear ylide complexes of gold(I) and gold(III) have been obtained in a varietyof ways203,204, as detailed below. The largest number of complexes of both gold(I) andgold(III) has been prepared with phosphorus ylides, but species containing arsenic orsulphoxonium ylides have also been reported. Some prototypes are summarized in Table 7.

The reaction of alkylgold(I) phosphine complexes with ylides leads to alkylgoldmonoylide species with concomitant liberation of phosphine, as illustrated in equation 4715.

[AuR�PR0003 �]C R003PDCR02 ��! [AuR�CR02PR003�]C PR0003 �47�

R D alkylR0 D H, alkyl, arylR00,R000 D alkyl, aryl

Haloarylgold(I) ylide complexes have been generated from suitable precursors via anindirect route: The interaction of phosphonium halides with [Au(C6F5)(SC4H8)] leadsto phosphonium organo(halo)aurates which can subsequently be reacted with base togive the respective ylide derivatives (Scheme 6). Gold(III) ylide complexes of the type[Au(C6F5)3(ylide)] have been prepared analogously from [Au(C6F5)3(SC4H8)]210.

[Au(C6F5)(SC4H8)] + [H3CPPh3]Cl

−SC4H8

[H3CPPh3][AuCl(C6F5)] NaH−H2, −NaCl

[Au(C6F5)(CH2PPh3)]

SCHEME 6. Synthesis of haloarylgold(I) ylide complexes

25



TABLE 7. Mononuclear ylide complexes of gold(I) and gold(III)

Complex M.p. (° C) Reference

Gold(I)

[AuCl(CH2PPh2Me)] 148(d) 205[AuClfCH(PPh3)C(DO)CH3g] 154 206[AuClfCH(PPh3)CO2Meg] 180 207[AuCl(Ph3PDCDPPh3)] 250(d) 208[AuBr(CH2PPh3)] 164(d) 205[Au(CN)(CH2PPh3)] 185 – 188 209[Au(C6F5)(CH2PPh3)] 157 210[Au(C6F5)(CH2AsPh3)] 144 210[Au(C�CPh)(CH2PPh3)] — 211[AufCo(CO)4g(CH2PPh3)] — 211[Au(CH2PPh3)(SC4H8)]ClO4 — 211[Au(CH2PPh3)(SbPh3)]ClO4 — 211[Au(CH2PPh3)(phen)ClO4

a — 211[Au(CH2AsPh3)(SC4H8)]ClO4 — 211[AufCH(PPh3)C(DO)CH3g(PPh3)]ClO4 125 206[AufCH(PPh3)CO2CH3g(PPh3)]ClO4 97 207[Au(CH2PMe3)2]BF4 214(d) 205

[Au(CH2PMe3)2][AuIII(1,2-Me2C2B9H9)2] — 212[AufCH(PPh3)C(DO)CH3g2]ClO4 128 206[AufCH(PPh3)CO2CH3g2]ClO4 125 207[AufCH2S(DO)Me2g2]Cl — 213[Ph3PDNDPPh3][AufCH2P(S)Ph2g2] — 214

Gold(III)

[AuCl3fCH(PPh3)C(DO)CH3g] 120 206[AuCl3fCH(PPh3)CO2CH3g] 161 207[AuCl2fCH(PPh3)C(DO)CH3g2]ClO4 130 206[AuCl2fCH(PPh3)CO2CH3g2]ClO4 150 207[AuBrfCH2P(S)Ph2g2] — 215[Au(S2CNEt2)2fCH2P(S)Ph2g] 156 215[AuI3(CH2PPh3)] 133(d) 216trans-[AuI2(CN)(CH2PPh3)] 165 – 170 209[Au(SCN)3(CH2PPh3)] 140(d) 216[AuMe3(CH2PPh3)] — 217[AuMe3fCH2S(DO)Me2g] — 217

[AuMe2(�2-CH2PMe2BH2PMe2CH2)] — 218[Au(C6F5)3(CH2PPh3)] 252 210[Au(C6F5)3(CH2PPh2Me)] — 219[Au(C6F5)3(CH2AsPh3)] 231 210cis-[Au(C6F5)2Cl(CH2PPh3)] 214(d) 220trans-[Au(C6F5)Cl2(CH2PPh3)] 135(d) 216

aphen, 1,10-phenanthroline.

26



[AuCl(PR′′′3)] [Au(CR′2PR′′3)(PR′′′3)]Cl −PR′′′3[Au(CR′2PR′′3)2]Cl

R′′3P C R′2R′′3P C R′2

R′ = H, alkyl, arylR′′, R′′′ = alkyl, aryl

SCHEME 7. Synthesis of bis(ylide)gold(I) complexes

Ph2P PPh2

Au+ −

Cl

FIGURE 9. A chelated bis(ylide)gold(I) complex

The reaction of (phosphine)gold(I) halides with ylides of the type R02CDPR003proceeds in two steps: Initial displacement of halide gives an isolable monoylidespecies, which can be transformed into a bis(ylide)gold(I) complex if an excessof ylide is employed (Scheme 7)15. In some instances, however, the reactionproduces the bis(ylide) species directly, regardless of the relative ratios ofgold(I) halide and ylide employed, as in the case of the bis(cyclopropylide)complex [AufC(c-CH2)2PPh3g2]Cl221. Obviously, bis(ylide) complexes form particularlyeasily with a chelating bis(ylide) ligand, an example being the compound1,3-propanediylbis[(9-fluorenylidene)diphenylphosphorane]gold(I) chloride (Figure 9)222.Facile double substitution also occurs with amino-substituted phosphorus ylides andsulphoxonium ylides to give complexes such as [AufCH2P(NMe2)3g2]Cl222– 224 and[AufCH2S(DO)(CH3)2g2]Cl213.

Carbonyl-stabilized phosphorus ylides are less nucleophilic and hence do not react with(phosphine)gold(I) halides, but their gold(I) complexes can be generated from precursorssuch as [Au(acac)(PPh3)] or [AuCl(SC4H8)] by reaction with phosphonium salts andylides, respectively, and again both mono- and bis(ylide) complexes have been obtained(equation 48 and Scheme 8)206,207. The ylide carbon atoms in these complexes are centresof chirality, but no stereospecificity was observed in the coordination process and racemicmixtures are formed throughout.

CR

O

ClO4 + [Au(acac)(PPh3)] ClO4

R = Me, Ph, OMe, OEt

C

Ph3P H

H CR

O

C

Ph3P AuPPh3

H−acacH

(48)

27



[AuCl(SC4H8)] + Ph3PCHC( O)R

R = Me, Ph, OMe, OEt

−SC4H8

R C

O

C

Ph3PAuCl

HPh3PCHC( O)R + NaClO4

−NaCl

R C

O

C

Ph3PAu

H

C

C

PPh3

HR

O

ClO4

SCHEME 8. Synthesis of gold(I) complexes containing carbonyl-stabilized phosphorus ylides

An alternative strategy for the preparation of mononuclear ylide complexes is tostart from gold(I) precursors which already contain an ylide ligand. Displacement insuch complexes of tetrahydrothiophene, SC4H8, by neutral or anionic ligands (includingpolyfunctional phosphines, acetylides, carbonyl metalates and methanide complexes)leads to a variety of mono-, di- and tetranuclear compounds of remarkable stability(Scheme 9)55,114,211.

[Au(CH2PPh3)(SC4H8)]ClO4

[Au(CH2PPh3)(SbPh3)]ClO4 [{Au(CH2PPh3)}2(dppm)](ClO4)2

[Au{Co(CO)4}(CH2PPh3)][Au(C CPh)(CH2PPh3)]

[{(Ph3PCH2)Au}HC(Ph2PAuPPh2)2CH{Au(CH2PPh3)}](ClO4)2

i

iiiii

v

iv

vivii

[Au(CH2PPh3)(phen)]ClO4

[AuCl(CH2PPh3)]

SCHEME 9. Preparation of phosphorus ylide gold(I) complexes by displacement of tetrahydrothiophene(SC4H8). Conditions; i, [Ag(ClO4)(SC4H8)]; ii, SbPh3; iii, phen (1,10-phenantroline); iv, dppm(bis(diphenylphosphino)methane); v, [N(PPh3)2][Co(CO)4]; vi, [HC(Ph2PAuPPh2)2CH]; vii, PhC�CH,KOH

Interaction of gold(I) ylide dimers such as [Au(CH2)2PPh2]2225,226 or gold(I) ylide

monomers such as [Au(C6F5)(CH2PPh3)]205 with HCl, HBr or acetyl bromide givesgold(I) mono(ylide) complexes in which a halide is the second ligand. Acids with weaklycoordinating anions X�(BF4

�, ClO4�) convert the haloarylgold(I) ylide complexes into

bis(ylide) species of the type [Au(ylide)2]X205.Conversely, certain mono(ylide) complexes are accessible from the respective bis(ylide)

compounds. Reaction between complexes of the type [Au(ylide)2]ClO4 and aurates(I) suchas NR4[AuX2] (X D Cl, Br, C6F5, C6Cl5) affords neutral halogold(I) and (haloaryl)gold(I)

28



ylide species, respectively (equation 49). Related gold(III) complexes have been preparedin a similar manner220.

[Au�CH2PPh3�2]ClO4 C NBu4[Au�C6F5�2] ��! 2[Au�C6F5��CH2PPh3�] CNBu4ClO4 �49�

A few mono(ylide) complexes of gold(I) have been obtained from the interaction ofphosphorus ylides with [Au(CO)Cl] and AuCN. The complex [AuCl(Ph3PDCDPPh3)]forms readily when carbonylgold(I) chloride is reacted with hexaphenylcarbodiphospho-rane. It is stable to oxygen and water and also thermally stable up to 250° C208. Similarly,the reaction of gold(I) cyanide with triphenylphosphonium methylide yields the complex[Au(CN)(CH2PPh3)]. The complex undergoes oxidative addition reactions with halogensX2 to give the gold(III) complexes trans-[AuX2(CN)(CH2PPh3)] (X D Cl, Br, I)209.

A number of mononuclear gold(III) ylide complexes may be similarly preparedby oxidative addition of halogens to suitable gold(I) ylide precursors. Thisapproach is exemplified by complexes of the general types [AuX3(ylide)]216, trans-[Au(C6F5)X2(ylide)]216 and trans-[AuX2(ylide)2]ClO4 (X D Cl, Br)206,207, some ofwhich may be further converted into the related iodo or thiocyanato complexesby reaction with potassium iodide or potassium thiocyanate216. Additionally, a fewmethods for the direct synthesis of gold(III) ylide complexes have been described.Thus, interaction of trimethylgold(III) phosphine complexes with phosphonium orsulphoxonium ylides results in the displacement of phosphine to yield complexes suchas [AuMe3(CH2PPh3)] and [AuMe3fCH2S(DO)Me2g], respectively, which are again ofremarkable stability217. A gold(III) complex containing a chelating bis(ylide) ligandis represented by the species [AuMe2(�2-CH2PMe2BH2PMe2CH2)], obtained from thereaction of dimethylgold(III) chloride with lithium boranato-bis(dimethylphosphoniummethylide), as shown in equation 50218.

Me2P

Li

PMe2

H2B

+ 1/2 Au Au

Me

Me

Me

Me

−LiClMe2P

Au

PMe2

H2B

Me Me

Cl

Cl (50)

The reaction chemistry of both mono- and bis(ylide) complexes of gold(I) has beenexplored for several cases. In carbonyl-stabilized ylide ligands, the acidic proton of the˛-methylene group can be replaced by yet another gold(I) unit leading to polynuclearspecies (equations 51 and 52)206,207.

Ph3P

C

MeOOC

AuPPh3

HClO4

[Au(acac)(PPh3)]

−acacH

Ph3P

C

MeOOC

AuPPh3

AuPPh3

ClO4

(51)

The haloarylgold(I) ylide complexes were also investigated regarding their reactiv-ity towards chlorobis(pentafluorophenyl)thallium(III). Partial oxidation of gold(I) to givechloro-substituted haloarylgold(III) ylide complexes was observed, together with formation

29



of bis(ylide) complexes of monovalent gold (equation 53)227.

Ph3P

C

EtOOC

Au

H

ClO4 + 2 [Au(acac)(PPh3)]C

H COOEt

PPh3

Ph3P

C

EtOOC

Au

AuPPh3

ClO4 + 2 acacHC

Ph3PAu COOEt

PPh3

(52)

[Tl�C6F5�2Cl]C [Au�C6F5��CH2PPh3�] ��! trans-[Au�C6F5�2Cl�CH2PPh3�] C[Au�CH2PPh3�2][Au�C6F5�4]C Tl�C6F5�3 C TlCl �53�

Bimetallic gold–silver complexes may be prepared from gold(I) bis(ylide) speciessuch as [Au(CH2PPh3)2]ClO4 and AgClO4 (leading to neutral clusters, equation 54) or[Ag(ClO4)(PPh3)] (leading to dicationic species)228.

2[Au�CH2PPh3�2]ClO4 C 2AgClO4 ��![�Ph3PCH2�2Auf�-Ag�OClO3�2g2Au�CH2PPh3�2] �54�

2. Di- and polynuclear ylide complexes

In addition to the mononuclear gold(I) ylide complexes described above, a large numberof dinuclear compounds have been prepared in which the ylide moiety functions as abridging ligand. Complexes with two bridging ylide groups and two gold atoms in ametallacyclic array are by far the most numerous, but variants containing one ylide andone diphosphine or thiolate bridge as well as open-chain compounds with one bridgingylide ligand between two gold centres have also been reported. A selection of complexesof this type is shown in Table 8.

Five general methods for the preparation of such complexes have been established,their applicability depending on the nature of the ylide ligand: Complexes suchas [Au2f(CH2)2PR2g2] or [Au2fCH2P(S)Ph2g2] are accessible by transylidation ofthe corresponding mononuclear bis(ylide) compounds (equation 55)203,204,230,231, whilespecies of the type [Au2f(CHPPh3)2COg2]2C and [Au2f(CH2PMe2)2BH2g2] havebeen prepared from complex gold chlorides by reaction with the lithium salt ofthe appropriate ligand157,158,218. The third method employs symmetric diphosphineprecursors, from which the asymmetric complexes [Au2f(CH2)2PR2gfPPh2CHPPh2g]and [Au2f(CH2)2S(O)NMe2gfPPh2CH2PPh2g]C can be made by reaction with oneequivalent of ylide ligand146,232. Most of the asymmetric complexes as well as open-chain di- and trinuclear derivatives have been obtained treating the bis(ylide) complex[Au2f(CH2)2PPh2g2] with a gold(I) precursor containing the second ligand throughylide transfer reactions (equation 56)233–237. Some other asymmetric derivatives withone or two bridging ligands can be synthesized from open-chain [Au2X2(ylide)]�

30



TABLE 8. Dinuclear Au(I) complexes with bridging ylideligands

Complex Reference

[Au2f(CH2)2PEt2g2] 203, 204[Au2f(CH2)2P(CH2)4g2] 203, 204[Au2f(CH2)2PPh2g2] 203, 204[Au2f(CH2)2PMePhg2] 229[Au2f(CH2)2PMePhg2(SO2)2] 229[Au2fCH2P(S)Ph2g2] 230[Au2fCH(PPh2Me)P(S)Ph2g2]2C 231[Au2f(CHPPh3)2COg2]2C 157[Au2f(CH(CO2R))2PPh2g2] 158[Au2f(CH2PMe2)2BH2g2] 218[Au2f(CH2)2PBu-t2gfPPh2CHPPh2g] 232[Au2f(CH2)2S(O)NMe2gfPPh2CH2PPh2g]C 246[Au2f(CH2)2PPh2gfPPh2NHPPh2g]C 233[Au2f(CH2)2PPh2gfPPh2(C5H4N-2)g] 233[Au2f(CH2)2PPh2gfS2CNEt2g] 233[Au2f(CH2)2PPh2gfS2COPr-ig] 234[Au2f(CH2)2PPh2gfS2CP(c-C6H11)3g]C 235[Au2f(CH2)2PPh2gfSC5H4N-2g] 236[Au2Cl2f(CHPPh3)2COg] 157[Au2Cl2f(CH2)2PPh2g]� 237[Au2f(CH2)2PPh2g(PPh3)2]C 237[Au2f(CH2)2PPh2g(SC4H8)2]C 237[Au3f(CH2)2PPh2g2(PPh2Me)2]C 237

complexes by precipitation of silver halide233,237 or displacement of a highly stablegold species (such as [Au(C6F5)(PPh3)]233) when reacted with the appropriate silversalt, which contains the second ligand. A less general route has been used for thepreparation of [Au2Cl2f(CHPPh3)2COg], starting from the appropriate diphosphoniumsalt and [AuCl(ylide)]157. Other data are given elsewhere238–242.

2 [Au(CH2PMeR2)2]X

R2P

AuPR2

Au + 2 [PMe2R2]X

+

+−

−(55)

[Au2f�CH2�2PPh2g2]C 2/n[Au�S2COR�]n ��! 2[Au2f(CH2)2PPh2gfS2CORg]R D Me, Et, i-Pr

�56�

Dinuclear bis(ylide) complexes are characterized by a rich reaction chemistry whichinvolves the [Au. . .Au] structural unit and, to a lesser extent, the bridging ylide ligands.The attractive Au. . .Au interactions facilitate oxidative addition to the metal centres which,depending on the type of substrate, may lead to bicyclic Au(II) compounds containing adiscrete transannular Au�Au bond, conventional Au(III) complexes as well as Au(III) ‘A-frame’ species containing bridging methylene groups, and mixed-valence Au(I)/Au(III)complexes243. In some cases, further derivatization of the resulting compounds by ligandexchange is also possible. An overview of these reactions in given in Schemes 10–14 forthe example of [Au2f(CH2)2PPh2g2] and derivatives, and Tables 9–11 contain examples

31


Ph2P

Au

Au

PPh 2

NO

2

NO

2

Ph2P

Au

Au

PPh 2

X X

X =

Cl,

Br

Ph2P

Au

Au

PPh 2

X

XX

X

Ph2P

Au

Au

PPh 2

OC

OPh

OC

OPh

CH

3NO

2

(

25 °C

)

o

r N

2O4

Ph2P

Au

Au

PPh 2

CH

NO

2OC

OPh

OC

OPh

CH

3NO

2

(0

°C)

Ph2P

Au

Au

PPh 2

X2

[X =

Cl,

Br,

I]

(PhC

OO

) 2

X2

SOC

l 2[X

= C

l]

Ph2P

Au

Au

PPh 2

C6F

5

C6F

5

[T1(

C6F

5)2C

l]

Ph2P

Au

Au

PPh 2

CN

CN

Hg(

CN

) 2

Ph2P

Au

Au

PPh 2

SeC

6H5

Cl

(C6H

5Se)

2, C

l−

SCH

EM

E10

.Pr

epar

atio

nof

dinu

clea

rA

u(I)

and

Au(

III)

com

plex

esfr

om[A

u 2f(C

H2) 2

PPh 2

)g 2]

byox

idat

ive

addi

tion

32


Ph2P

Au

Au

PPh 2

S S

S S

PPh 2

Au

Au

Ph2P

S S

S S

PPh 2

Au

Au

Ph2P

CF 3

CF 3

PPh 2

Au

Au

Ph2P

X′

L

ClO

4

PPh 2

Au

Au

Ph2P

XX

Cd(

CF 3

) 2[X

= B

r]

PPh 2

Au

Au

Ph2P

X′

X′

2 A

gX′

[X =

Cl]

X′ =

C6F

5; L

= P

Ph3,

SC

4H8,

P(C

6H4M

e-4)

3,

AsP

h 3, C

5H5N

X′ =

C6H

2F3-

2,4,

6; L

= P

Ph3,

SC

4H8

[Au(

PPh 3

)L]C

lO4

[L

= P

Ph3,

SC

4H8]

[X′ =

C6F

5, C

6H2F

3-2,

4,6]

H2S

[X =

PhC

OO

]

[X′ =

C6F

5, C

6H2F

3-2,

4,6]

PPh 2

Au

Au

Ph2P

X′

X′ =

C6F

5, C

6H2F

3-2,

4,6

Cl[A

g(C

lO4 )

L]

2 [A

gX′(L

)][X

= C

l]

PPh 2

Au

Au

Ph2P

LL

PPh 2

Au

Au

Ph2P

S 2C

NR

2

S 2C

NR

2

R =

Me,

Et

2 N

aS2C

NR

2

[L =

SC

4H8]

PPh 2

Au

Au

Ph2P

L′

L′

(ClO

4)2

X′ =

ClO

4, L

= S

C4H

8, P

Ph3

X′ =

NO

3, L

= P

Me 3

L′ =

C5H

5N, A

sPh 3

, CH

2PPh

3,

S(M

eS)C

HN

R (

R =

C6H

4Me-

4, C

6H4M

e-2,

C6H

4OM

e-4,

C6H

3Me 2

-3,5

)

PPh 2

Au

Au

Ph2P

SSC

(NPh

)(N

HPh

)

SSC

(NPh

)(N

HPh

)

X′ =

Br,

SC

N, N

O3,

MeC

O2,

C6H

2F3-

2,4,

6,

C6F

5, S

2CN

(CH

2Ph)

2

2 SC

(NH

Ph) 2

,O

2, O

H−

[X =

Cl]

PPh 2

Au

Au

Ph2P

X′

X

AgX

[Au(

NO

3)(P

Ph3)

]

[

X′ =

C6F

5]

X′ =

C6F

5; X

= N

O3,

MeC

OO

, ClO

4

X′ =

C6H

2F3-

2,4,

6; X

= C

lO4

(X′) 2

[Au 2

Cl 2

{(C

H2)

2PPh

2}2]

2 L

′[L

= S

C4H

8] SCH

EM

E11

.D

eriv

atiz

atio

nof

dinu

clea

rA

u(II

)co

mpl

exes

bylig

and

subs

titut

ion

33


P

Au

P

Au

H8C

4S

Ph2

SC4H

8

P

Au

P

Au

Ph3P

PPh 3

Ph2

P

Au

P

Au

LL

Ph2

P

Au

P

Au

Ph3P

Ph2

PPh 3

Ph2

P

Au

P

Au

R3P

SC4H

8

Ph2

Ph2

P

Au

P

Au

Ph3P

L

Ph2

Ph2

[Au(

PR3)

(SC

4H8)

]+

or [

Au(

C6F

5)(S

C4H

8)]

L

[R =

Ph]

2+ 2+

2+2+

2+2+

[Ag(

ClO

4)(P

R3)

]

[Ag(

ClO

4)(P

Ph3)

]M

X

PR3

= PP

h 3, P

Ph2M

e, P

(C6H

4OM

e-4)

3L

= C

5H5N

, AsP

h 3, P

Ph2M

e

S(M

eS)C

HN

R′

[

R =

Ph]

+

Ph2

Ph2

Ph2

34


P

Au

P

Au

R3P

Ph2

OC

lO3

Ph2

P

Au

P

Au

R3P

X

Ph2

Ph2

P

Au

P

Au

Ph3P

S

Ph2

+ +

AgC

lO4

PR3 =

PPh

3, P

Ph2M

ePR

3 =

PPh 3

, X =

Cl,

S 2C

N(C

H2P

h)2

PR3

= PP

h 2M

e, X

= C

l

R′ =

C6H

4Me-

2, C

6H4O

Me-

4,

C6H

3Me 2

-3,5

CH

MeS

NH

R′

2+

P

Au

P

Au

MeP

h 2P

Ph2

OH

2

P

Au

P

Au

R3P

PR3

Ph2

Ph2

P

Au

P

Au

XX

Ph2

Ph2

2+2+

OH

2

[PR

3 =

PPh

2Me]

+

Ph2

Ph2

SCH

EM

E12

.Pr

epar

atio

nof

asym

met

ric

catio

nic

Au(

II)

com

plex

esby

ligan

dsu

bstit

utio

n

35


P

Au

P

Au

Br

BrCl

CH

Cl 2

Ph2

Ph2

P

Au

P

Au

Ph2

Ph2

Cl

CC

l 3C

Cl 4

/ T

HF

P

Au

P

Au

Cl

ClCl

CC

l 3

Ph2

Ph2

P

Au

P

Au

Ph2

Ph2

Br

Br

R =

CH

3, C

H2P

h

P

Au

P

Au

Ph2

Ph2

Br

CH

Br 2

P

Au

P

Au

Ph2

Ph2

CH

Br 3

CH

Cl 2

Br

CC

l 4

RB

r

RI

P

Au

P

Au

Ph2

Ph2

IR

P

Au

P

Au

Br

BrBr

CH

2CF 3

Ph2

Ph2

Br 2

[R =

CH

2CF 3

]

P

Au

P

Au

H3C

CH

3

Ph2

Ph2

LiC

H3

[ R

= C

H3]

R =

CH

3, C

H2C

H3,

CH

2CF 3

, CH

2SiM

e 3

P

Au

P

Au

Ph2

Ph2

XX

CH2

P

Au

P

Au

Ph2

Ph2

X′

X

CH2

P

Au

P

Au

Ph2

Ph2

X′

CH

2X[X

= C

l

X′ =

Br,

I]

CH

2XX

′

[X

= C

l, X

′ = B

r, I

or

X =

CN

, X′ =

Br

or X

= C

(O)P

h, X

′ = B

r]

P

Au

P

Au

Ph2

Ph2

NC

CN

CH2

CH

2ClB

rA

gCN

CH

2X2

or

1. X

2; 2

. CH

2N2

[X

= C

l, B

r, I

]

SCH

EM

E13

.Pr

epar

atio

nof

Au(

II)

and

Au(

III)

com

plex

esfr

om[A

u 2f(C

H2) 2

PPh 2g 2

byox

idat

ive

addi

tion

ofal

kyl

halid

es

36


P

Au

Au

PCH

3

H3C

Ph2

Ph2

P

Au

Au

PPh2

Ph2

CH2

Br

P

Au

Au

PPh2

Ph2

CH2

H3C

P

Au

Au

PPh2

Ph2

CH2

F 5C

6C

6F5

P

Au

Au

PPh2

Ph2

X

H2

C

P

Au

Au

PPh2

Ph2

CH2

IL

[X=

I]

P

Au

Au

PPh2

Ph2

CH2

LL

2 A

g(O

ClO

3), 2

L

P

Au

Au

PPh2

Ph2

CH2

Br

CH

2PM

e 3

Me 3

PC

H2

Br

P

Au

Au

PPh2

Ph2

CH2

Me 3

PH2C

CH

2PM

e 3

Br 2

L=

SC4H

8, P

Ph3

(ClO

4)2

P

Au

Au

PPh2

Ph2

CH2

L′

L′

L′=

AsP

h 3, C

5H5N

, phe

n

(ClO

4)2

P

Au

Au

PPh2

Ph2

X

H2

C

2 L

′

MX

X=

SCN

, S 2

CN

Me 2

L=

SC4H

8, P

Ph3

Me 3

P=C

H2

[X=

Br]

P

Au

Au

PPh2

Ph2

CH2

IL

′

L′=

AsP

h 3, C

5H5N

, phe

n

ClO

4C

lO4

L′

2 A

gC6F

5

[X=

I][X

=I]

Ag(

OC

lO3)

L

[X=

Br]

2 C

H3L

i

CH

3

CH

3

X

X

SCH

EM

E14

.D

eriv

atiz

atio

nof

Au(

III)

‘A-f

ram

e’co

mpl

exes

bylig

and

subs

titut

ion

37



TABLE 9. Dinuclear Au(II) complexes with bridging ylide ligands

[Au2X2f(CH2)2PR2g2] R X Reference

Me Cl 247Me Br 247Ph Cl 153b, 248aPh Br 249Ph SCN 249Ph NO2 250Ph NO3 249Ph MeCO2 249, 251Ph PhCO2 252Ph S2CNMe2 253Ph S2CNEt2 253Ph S2CN(CH2)4-c 253Ph S2CN(CH2Ph)2 249Ph S4 254Ph SSC(NPh)(NHPh) 255Ph CF3 256Ph C6H2F3-2,4,6 249Ph C6F5 249, 256Ph CN 257

[Au2X2f(CH2)P(S)Ph2g2] X

Cl 258I 230

[Au2X2f(CH2)2PPh2gfL�Lg] L�L X

S2COMe Br 234S2COEt Cl 234

S2COPr-i I 234S2CNMe2 Cl 259S2CNEt2 I 259

S2CN(CH2Ph)2 Br 259SC5H4N-2 Br 266SC5H4N-2 SCN 266

[Au2XX0f(CH2)2PPh2g2] X X0

C6H5Se Cl 260C6H2F3-2,4,6 Cl 261C6H2F3-2,4,6 ClO4 201

C6F5 Cl 261C6F5 NO3 261C6F5 SCN 261C6F5 MeCOO 261C6F5 ClO4 201

S4 S5 254

[Au2R0Xf(CH2)2PR2g2] R R0 X

Me CH2Ph Br 262Me Me I 262, 263Me CH2SiMe3 I 262

38



TABLE 9. (continued )

Ph Me ClO4 201Ph Me Br 262Ph CH2Ph Br 262Ph Me I 262Ph CH2CH3 I 264Ph CH2SiMe3 I 262Ph CH2CF3 I 264Ph CH2Cl Br 265, 266Ph CH2CN Br 267Ph CH2C(O)Ph Br 267Ph CH2Cl I 268Ph CHBr2 Br 269Ph CCl3 Cl 153b, 248a

[Au2X2f(CH2)2PPh2gfL�Lg](ClO4) L�L X

S2CP(c-C6H11)3 Cl 235S2CP(c-C6H11)3 C6F5 235Ph2PCH2PPh2 Br 259Ph2PNHPPh2 I 259

[Au2XLf(CH2)2PPh2g2][X0] X L X0

I CH2PMe3 I 270Cl PPh2Me ClO4 271

ClO4 PPh2Me ClO4 271C6H2F3-2,4,6 SC4H8 ClO4 261

C6F5 C5H5N ClO4 261C6F5 PPh3 ClO4 261C6F5 AsPh3 ClO4 261

[Au2L2f(CH2)2PPh2g2][X’]2 L X0

CH2PMe3 I 270CH2PPh3 ClO4 261

S(MeS)CHN(C6H4Me-4) ClO4 253S(MeS)CHN(C6H3Me2-3,5) ClO4 253

SC4H8 ClO4 249C5H5N ClO4 249PPh3 ClO4 249

AsPh3 ClO4 249SbPh3 ClO4 249PMe3 NO3 249

[Au2LL0f(CH2)2PPh2g2] (ClO4)2 L L0

PPh3 SC4H8 271PPh3 C5H5N 271PPh3 PPh2Me 271PPh3 AsPh3 271

PPh2Me SC4H8 271PPh2Me OH2 271

P(C6H4OMe-4)3 SC4H8 271

(continued overleaf )

39



TABLE 10. Dinuclear Au(III) complexes with bridging ylide ligands

[Au2(X2)2f(CH2)2PR2g2] R X2 Reference

Me Cl2 247(cis/trans) Ph Cl2 244(trans/trans) Ph Cl2 272(cis/cis) Ph Br2 273(trans/trans) Ph Br2 244, 274(cis/cis) Ph C6H4S2 275

[Au2X2(RY)f(CH2)2PPh2g2] X2 R Y

(trans/trans) Cl2 CCl3 Cl 153b, 248(cis/trans) Br2 CH2CF3 Br 276(trans/trans) Br2 CHCl2 Cl 276

[Au2(�-CH2)X2f(CH2)2PR2g] R X

Me Cl 277Me Br 277Me I 277t-Bu Cl 247Ph Br 265, 266Ph I 278Ph CN 257, 268Ph PhCOO 268Ph SCN 268, 278Ph S2CNMe2 278Ph CH3 279Ph C6F5 278

[Au2(�-CHY)X2f(CH2)2PPh2g2] Y X

NO2 PhCOO 250, 280

[Au2(�-CH2)XX0f(CH2)2PR2g2] R X X0

Ph Cl Br 268Ph Cl I 268Ph Br CH3 279

[Au2(�-CH2)LXf(CH2)2PPh2g2][X0] L X X0

CH2PMe3 Br Br 281PPh3 I ClO4 278

AsPh3 I ClO4 278C5H5N I ClO4 278SC4H8 I ClO4 278phen I ClO4 278

[Au2(�-CH2)L2f(CH2)2PPh2g2][X]2 L X

CH2PMe3 Br 281PPh3 ClO4 278

AsPh3 ClO4 278C5H5N ClO4 278SC4H8 ClO4 278phen ClO4 278

40



TABLE 11. Dinuclear mixed-valence Au(I)/Au(III) complexeswith bridging ylide ligands

Complex Reference

[AufAuBr2gf(CH2)2PPh2g2] 282

[AufAuMe2gf(CH2)2PPh2g2] 279

[AufAuCl2gfCH2P(S)Ph2g2] 215

[AufAuI2gfCH2P(S)Ph2g2] 230, 283

[Au2Cl2f(CH2)2PPh2gf�-(CH2)2PPh2g] 283

[Au2(C6F5)2f(CH2)2PPh2gfS2CNMe2g] 259

[Au2f(CH2)2PPh2gfS2CNMe2g(PPh3)2]2C 259

[Au2f(CH2)2PPh2gfS2CN(CH2Ph)2g(PPh3)2]2C 259

of the various types of products thus obtained. Conversions involving the bridging ylideligands include isomerizations229,244, acid-induced cleavage reactions to give mononu-clear species245, oxidative cleavage to give ring-opened dimeric complexes246 and replace-ment of acidic protons with further gold(I) units to give polynuclear complexes reminiscentof the polyauriomethanes146,157,158.

Some substrates (e.g. halogens) react with dinuclear gold(I) ylide complexes by two-centre two-electron oxidative addition to give the corresponding gold(II) complexes asisolable species (Scheme 10). Further oxidative addition of halogens to the dihalide com-plexes cleaves the metal–metal bond, leading to dimeric gold(III) ylide complexes asgeometrical isomers with ligands in a trans/trans273,274, cis/trans244 or cis/cis275 geom-etry, which have all been structurally characterized (Figure 10). Interestingly, some ofthese species interconvert in solution upon prolonged standing244.

With benzoyl peroxide, the dimer [Au2f(CH2)2PPh2g2] gives a dinuclear gold(II) ylidecomplex containing oxygen-bound carboxylate ligands250. This compound shows interest-ing reactivity in the presence of nitromethane as co-solvent. If kept at 0° C, a dibenzoatecomplex (with A-frame geometry) can be isolated wherein a CHNO2 group bridges twoAu(III) centres280, while at ambient temperature and upon prolonged standing the reac-tion gives a nitritogold(II) complex, as illustrated in Scheme 10. The latter compoundmay also be prepared directly by reacting [Au2f(CH2)2PPh2g2] with N2O4

250.As can be seen in Scheme 11, various procedures have been established for the further

derivatization of dinuclear gold(II) ylide complexes by ligand substitution. Halide lig-ands can be substituted by neutral donor ligands such as tetrahydrothiophene or pyridine(giving the corresponding cationic complexes)249, or with other anionic ligands (such as

P

P

Au

Au

X

X

X

X

P

XAu

Au

X

X

X

P

X

XAu

Au

X

X

P

P

trans/trans cis/trans cis/cis

FIGURE 10. The possible geometrical isomers of Au(III) ylide dimers: trans/trans, cis/trans, cis/cis

41



pseudohalides, carboxylates or dithiocarbamates)249,253. The digold(II) dibenzoate com-plex reacts with hydrogen sulphide in tetrahydrofuran to give macrocyclic complexes inwhich two [Au2f(CH2)2PPh2g2] units are bridged by two polysulphide chains254. Theintroduction of carbanionic groups is also straightforward, leading to organogold(II) com-plexes with exocyclic trifluoromethyl256, pentafluorophenyl249,256, or phosphorus ylideligands261,270. While substitution usually occurs at both gold(II) centres simultaneously,some asymmetric derivatives have been prepared from pentafluorophenyl complexes261.

A number of asymmetric cationic Au(II) complexes with a phosphine ligand havebeen synthesized starting from the symmetric triphenylphosphine or tetrahydrothiophenederivatives (Scheme 12)253,271. In solution, some of these products are in equilibriumwith an equimolecular mixture of the corresponding symmetric derivatives.

Considerable effort has been expended to elucidate the course of oxidative additionreactions of haloalkanes to dinuclear gold(I) bis(ylide) complexes39, experimentalevidence supporting the notion that the order of reactivity of such substratesis inversely proportional to the carbon–halogen bond dissociation energies269. Asshown in Scheme 13, [Au2f(CH2)2PPh2g2] reacts with alkyl halides RX (X D Br, I)to give asymmetrically substituted bicyclic digold(II) complexes262–264,284,285. Thereaction is reversible if R bears no electron-withdrawing substituents264. Further,[Au2f(CH2)2PPh2g2] catalyzes SN2 halogen exchange between CH3Br and CD3I in aprocess which is thought to involve an SN2 reaction between the free alkyl halide and thepostulated intermediate [Au2f(CH2)2PPh2g2fC(H or D)3g]X262,285. There is no indicationthat alkyl halides RX add to [Au2f(CH2)2PPh2g2] by two-electron oxidation of a singlegold centre, although asymmetric gold(I)/gold(III) complexes do form when complexessuch as [Au2(CH3)(I)f(CH2)2PPh2g2] are reacted with LiCH3 (Scheme 13)263. As maybe expected, digold(II) haloalkyl halide complexes are susceptible to further oxidativeaddition when treated with halogen. The reaction, which can be used to prepare digold(III)haloalkyl trihalide complexes (Scheme 13)276, apparently proceeds via an intermediatecationic �-halogeno A-frame species, as suggested by the isolation of small quantities of[Au2(�-Br)f(CH2)2PPh2g2][IBr2] from the mixture of [Au2(CH2CF3)(I)f(CH2)2PPh2g2]and Br2

273. Several geometrical isomers of the digold(III) haloalkyl trihalide complexeshave been studied by X-ray techniques276.

With methylene dihalides CH2X2 (X D Cl, Br, I), dimeric gold(I) ylide complexesundergo a two-centre four-electron oxidative addition reaction to give gold(III) ‘A-frame’complexes in which a methylene group bridges two gold centres (Scheme 14)247,277.Alternatively, such complexes have been prepared by the reaction of [Au2f(CH2)2PPh2g2]first with a halogen and then with diazomethane268. While no dinuclear gold(II)haloalkyl halide complexes are isolated from the reactions of symmetrical methylenedihalides, the intermediacy of such species is documented for asymmetric substrates,as exemplified by the reactions of [Au2f(CH2)2PPh2g2] with CH2ClBr265, CH2ClI268,CH2Br(CN)267, or CH2BrfC(DO)Phg267 (Scheme 13). There is structural evidence forthe formation of a carbene intermediate preceding the formation of an ‘A-frame’ complexcontaining a bridging methylene group265,266. The formulation of the final productas the mixed halogenated �-methylene ‘A-frame’ species is tentative (Scheme 13); atleast in the case of CH2ClBr, further halide exchange with solvent molecules leads tothe formation of the symmetrically substituted �-methylene dibromo complex [Au2(�-CH2)Br2f(CH2)2PPh2g2], which has been structurally characterized265,266. A relatedreaction is the treatment of [Au2f(CH2)2PPh2g2] first with CH2ClBr and then withsilver salts such as AgCN, AgSCN or AgOOCPh to give the symmetrically disubstituted�-methylene complexes257,268. Derivatization of digold(III) �-methylene dihalide

42



complexes with other reagents to introduce carbanionic ligands278,279, pseudohalides278,phosphorus ylides281 or neutral donor ligands278 has also been reported (Scheme 14). Thetreatment with organolithium compounds gives several well-defined products, includinga partially alkylated intermediate and a mixed-valence Au(I)/Au(III) species. The doublymethylated complex [Au2(CH3)2f(CH2)2PPh2g2] undergoes thermally induced reductiveelimination of alkane, the dinuclear gold(I) bis(ylide) complex being regenerated in theprocess279.

The reaction of [Au2f(CH2)2PPh2g2] with trihalomethanes can afford two products(Scheme 13): Initially, a digold(II) halomethyl halide species is formed, as exemplified bythe isolation of [Au2(CHBr2)(Br)f(CH2)2PPh2g2] from a mixture of [Au2f(CH2)2PPh2g2]and CHBr3

269. In a second step, renewed oxidative addition leads to theformation of digold(III) halomethyl trihalide complexes, as shown in Scheme 13for the substrate CHCl2Br276. Tetrahalomethanes react in an analogous way, theinteraction of [Au2f(CH2)2PPh2g2] with CCl4 having been studied in some detail248:Oxidative addition of one equivalent of the reagent leads to the isolable digold(II)halomethyl halide species [Au2(CCl3)(Cl)f(CH2)2PPh2g2] which, in the presence oftetrahydrofuran, reacts a second time with CCl4 to give the digold(III) trichloromethyltrichloride complex [Au2(CCl3)Cl3f(CH2)2PPh2g2]. By contrast, prolonged interaction of[Au2f(CH2)2PPh2g2] and CCl4 in the absence of tetrahydrofuran generates the digold(II)dichloride complex [Au2Cl2f(CH2)2PPh2g2] and it has been noted that the two productsdo not interconvert in the presence of CCl4. Reactions in the CCl4/tetrahydrofuran solventmixture are accompanied by the formation of chloroform, suggesting a radical pathwaywith tetrahydrofuran as a hydrogen source for CCl3 radicals.

Two-electron oxidative addition of reagents to dinuclear gold(I) ylide complexesusually involves both gold centres to yield Au(II)/Au(II) complexes. Remarkably,both Au(I)/Au(III) and Au(II)/Au(II) complexes have been obtained from the reactionof dimeric Au(I) methylenethiophosphinate complexes with iodine. As illustrated inScheme 15, the isovalent isomer contains both bridging ligands in a geometry whichis trans to S, while the mixed-valence isomer exhibits a linear S�Au(I)�S and a square-planar trans-[AuIIII2C2] unit230. A related mixed-valence dichloride is also known215.

S

Ph2P

Au S

PPh2

Au

S

Ph2P

Au S

PPh2

Au

I

I

S

Ph2P

Au

PPh2

SAu

I

I

I2/CH2I2/1,2-C2H4Cl2

I2/1,2-C2H4Cl2

SCHEME 15. Synthesis of isovalent and mixed-valent isomers of [Au2I2fCH2P(S)Ph2g2]

43



Methylenethiophosphinate ligands have also been used to synthesize dinucleargold/mercury complexes which show a similar isomerism: Depending on the syntheticprocedure, species containing S�Au�C/S�Hg�C or S�Au�S/C�Hg�C structural unitsare obtained286. The latter isomer undergoes an interesting ring expansion reaction upontreatment with diazomethane, in the course of which one methylene group inserts intoeach gold–sulphur bond to give a ten-membered heterobimetallic ring287. Oxidativeaddition of chlorine gives the symmetrical complex containing a metal–metal bonded[Cl�Au�Pt�Au�Cl] unit, rather than a mixed-valence species214.

A number of other procedures have led to mixed-valence Au(I)/Au(III) ylide complexes,but these do not involve oxidative addition in the key step. Thus, reaction of digold(II)bis(ylide) dihalide complexes such as [Au2I2f(CH2)2PPh2g2] with various phosphorusylides in a 1 : 2 molar ratio leads to the formation of dicationic complexes with aAu(I)/Au(III) constitution270, as shown by Mossbauer spectroscopy288. This result is inagreement with the finding that oxidative addition of CH3I to [Au2f(CH2)2PPh2g2] yieldsthe asymmetrically substituted digold(II) complex, whereas attempts to carry out furtheralkylation with LiCH3 afford only a mixed-valence isomer (Scheme 13). Apparently, thestrong trans influence of two alkyl groups at the Au�Au bond results in the destabilizationof this structural unit and induces disproportionation (Scheme 16).

Ph2P

Au

PPh2

Au

X

X

Ph2P

Au

PPh2

Au

X

CH2PR3

X

P

Au

P

Au X

P

Au

PPh2

P

Au

P

Au 2 I

PR3

PR3

R3PCH2

[X = Br, R = Ph; X = I, R = Me, Ph]

2 R3PCH2

X = I; R3 = Me3,

MePh2, Ph3]

MePh2PCH2

MePh2PCH2

[R3 = MePh2]

Ph2

Ph2

Ph2

Ph2Ph2

SCHEME 16. Preparation of mixed-valent gold ylide complexes from a digold(II) precursor

Treatment of the digold(III) complex [Au2Br4f(CH2)2PPh2g2] with AgCN under suit-able conditions has been reported to produce in a single-centre reduction process themixed-valence complex [Au(AuBr2)f(CH2)2PPh2g2], which was characterized by X-ray

44



crystallography and photoelectron spectroscopy282. Neutral or dicationic open-chain di-nuclear Au(I)/Au(III) complexes with one ylide bridging the gold atoms and anotherylide or dithiocarbamate ligand in a chelating mode can be obtained by disproportiona-tion of [Au2Cl2f(CH2)2PPh2g2] in polar solvents such as nitromethane (equation 57)283 orby treating [Au2I2f�CH2)2PPh2gfS2CNMe2g] with [Ag(C6F5)] or [Ag(OClO3)(PPh3)]259.For the dithiocarbamate complexes it is not clear which one of the difunctional ligands isacting as a chelate and which one acts as a bridge.

Ph2P

Au

PPh2

Au

Cl

Cl

Ph2P

ClAu

PPh2

Au

Cl

CH3NO2(57)

Complexes containing direct bonds between gold(I) and gold(III) or gold(II) which areunsupported by other ligands could be prepared in straightforward reactions, as illustratedin equations 58289, 59200 and 60201.

P

Au

P

Au + [Au(C6F5)3(OEt2)] −Et2O

Ph2

Ph2P

Au

P

Au

Ph2

Ph2

Au(C6F5)3 (58)

P

Au

P

Au

Ph2

Ph2

2 F5C6 C6F5 + 2 [Au(C6F5)3(OEt2)]

−C12F10, −2 Et2O

P

Au

P

Au

Ph2

Ph2

F5C6 Au

C6F5

C6F5

P

Au

P

Au

Ph2

Ph2

C6F5 [Au(C6F5)4]

(59)

45



P

Au

P

AuF5C6 SC4H8

Ph2

Ph2

2 ClO4 +

P

Au

P

Au

Ph2

Ph2

P

Au

P

Au

Ph2

Ph2P

P

Au

Ph2

Ph2

F5C6

P

Au

P

Au

Ph2

Ph2

Au C6F5 (ClO4)2

(60)

E. Gold(III) Complexes with One Gold–Carbon Bond

Alkylgold(III) complexes containing one gold–carbon bond are still rare13a,290, andonly a few trifluoromethyl compounds of the type [Au(CF3)X2(PR3)] (X D Br, I; R DMe, Et, Ph) have been reported, which are formed by oxidative addition of halogen tothe respective trifluoromethyl(phosphine)gold(I) complex21. By contrast, various methodsnow exist for the synthesis of monoarylgold(III) species. One of the earliest establishedprocedures involves the electrophilic substitution by gold(III) at the aromatic ring ofbenzene derivatives (‘auration’)13. Recently, systems such as the trichloro(phenyl)aurateanion have been investigated with respect to their ligand substitution kinetics and thetrans influence of the aryl ligand has been assessed291.

Another synthesis of monoarylgold(III) compounds starts from pentahaloaryl or mesityl-gold(I) complexes, which are sufficiently stable to undergo oxidative addition of halogenwithout cleavage of the gold–carbon bond, as illustrated in equation 6111,12,97. In theseproducts, the thiophene ligand may then be substituted by other neutral or anionic lig-ands (e.g. phosphine, isocyanide, 1,10-phenanthroline, halide) and a wide variety ofderivatives has thus been obtained, examples of which are given in Table 1296. Thistype of compound may be further derivatized by treatment with AgClO4, giving four-coordinate cationic complexes of the types [Au(C6F5)X(phen)]ClO4 (X D Cl, Br) and[Au(C6F5)(PPh3)(phen)](ClO4)2

292.

[Au�C6F5��SC4H8�]C Cl2 ��! [Au�C6F5�Cl2�SC4H8�] �61�

Some pentafluorophenyl dithiolate complexes have recently been synthesized from[Au(C6F5)Cl2L] (L D PR3, AsPh3, SC4H8) using tin or zinc derivatives as dithiolate

46



TABLE 12. Some monoarylgold(III) complexes


[Au(C6F5)Cl2(SC4H8)] — 11

[Au(C6Cl5)Cl2(SC4H8)] — 11

[Au(C6F5)Br2(CNC6H4Me-4)] 148(d) 11

[Au(C6F5)Cl2(phen)]a 149(d) 292

[Au(C6F5)Cl2(pdma)]b 100 292

[Au(C6F5)(3,4-S2C6H3Me)]3 — 293

[Au(C6F5)(1,2-S2C6H4)(1,2-SC6H4SPPh3)] — 293

[Au(C6F5)(1,2-S2C6H4)(PPh3)] 222 294

[Au(C6F5)(dmit)(AsPh3)]c 190(d) 294

[Au(C6F5)Br2Cl]� — 11

[Au(C6F5)(dmit)(SCN)]�c — 293

[Au(C6F5)Cl(phen)]Ca 195(d) 292

[Au(C6F5)(PPh3)(phen)]2Ca 147(d) 292

[AufC6H4(NDNPh)-2gCl2] 218(d) 295

[AufC6H4(NDNPh)-2g(CH3COO)2] 140(d) 296

[AufC6H4(NDNPh)-2g(OOC�COO)] 129(d) 296

[AufC6H4(NDNPh)-2gCl2(PPh3)] 181(d) 295

[fAufC6H4(NDNPh)-2gCl2g2(Ph2PCH2CH2PPh2)] 169 295

[AufC6H4(NDNPh)-2gCl3]� 83 295

[AufC6H4(NDNPh)-2gCl(PPh3)2]C 136(d) 295

[AufC6H4(NDNPh)-2g(C5H5N)2]2C 210(d) 296

[fAufC6H4(NDNPh)-2g(PPh3)2g2]4C 185(d) 297

[AufC6H4(CH2NMe2)-2gCl2] 185(d) 298

[AufC6H4(CH2NMe2)-2gI2] 105(d) 298

[AufC6H4(CH2NMe2)-2gCl(PPh3)]C 174 298

[AufC6H4(CH2NMe2)-2g(phen)]2Ca — 11

[AufC6H4(CH2NMe2)-2g(CN)(phen)]Ca 125(d) 299

[AufC6H4(CH2NMe2)-2g(phen)(PPh3)]2Ca 145 299

[AufC6H4(2-C5H4N)-2gCl2] — 300

[Au(C6H4f2-(CMe2)C5H4Ng-2)Cl2] 283– 284 301

[Au(C6H4f2-(CHMe)C5H4Ng-2)Cl(dppe)]Cd 100– 102 301

[Au(C6H4f2-(CH2)C5H4Ng-2)(dppe)]2Cd 175(d) 301

[Auf4-MeOC6H4-(Phbipy)gCl]Ce — 302

[Au(C6H3fNDNC6H4(C4H9-40)-2g,C4H9-5)Cl2] 137 303

[Au(C6H3fNDNC6H4(C10H21-40)-2g,C10H21-5)Cl3]� 118 303

[Au(C6H2Me3-2,4,6)gCl3]� — 97

[Au(C6H2Me3-2,4,6)gBr3]� — 97

aphen, 1,10-phenanthroline.bpdma, phenylene-1,2-bis(dimethylarsine).cdmit, 1,3-dithiol-2-thione-4,5-dithiolate.ddppe, 1,2-bis(diphenylphosphino)ethane.e4-MeOPh-(Phbipy), 40-(4-methoxyphenyl)-60-phenyl-2,20-bipyridine.

47



transfer agents293,294. Tetrahydrothiophene as the neutral ligand is also displaced and atrinuclear complex is isolated (equation 62)293. Further reaction of these trinuclear com-pounds with neutral or anionic ligands breaks the Au3S3 ring, leading to mononuclearcomplexes293.

3[Me2Sn�S2C6H4�]C 3 trans-[C6F5Au�SC4H8�Cl2] ��! [C6F5Au�S2C6H4�]3C3 Me2SnCl2 �62�

Arylgold(III) complexes [Au(Ar)X2L] may also be obtained by arylation of[AuCl3(SC4H8)] or [AuCl4]� with arylmercury(II) compounds. Two examples ofthis conversion are presented in equations 63 and 64295,298. With 4,40-disubstitutedazobenzenes as aryl groups, the reaction with [AuCl4]� follows the samepathway, but when chloroarylmercurials are treated with [AuCl3(SC4H8)], anionicaryltrichloroaurates(III) are obtained303. The derivatization of [Au(Ar)X2L] (bysubstitution of the chloride ligands or displacement of the N-donor) is straightforwardand examples of products obtained from reactions with neutral or anionic ligandsare listed in Table 12. These may again be transformed in subsequent conversions.Specifically, [Au(C6H4fCH2NMe2g-2)(phen)](ClO4)2 reacts with triphenylphosphine togive the pentacoordinated complex [Au(C6H4fCH2NMe2g-2)(phen)(PPh3)](ClO4)2

299.

Ph

2 + [NMe4]2[Hg2Cl6] + 2 SC4H8

2 NMe4Cl

N N

Au

Cl

Cl

2 [AuCl3(SC4H8)] + 2 [Hg{C6H4(N NPh)-2} Cl]

(63)

4

4 [AuCl4]− + 2 [Hg{C6H4(CH2NMe2)-2}2]

+ [Hg2Cl6]2− + 2 Cl−

N

Au

MeMe

Cl

Cl

(64)

Several closely related arylgold(III) complexes have also been formed in the courseof cyclometalation processes. The reaction of substituted pyridine ligands such as 2-phenylpyridine or 2-benzylpyridines (denoted HL) with [AuCl4]� at ambient temperature

48



yields non-metallated gold(III) complexes which, upon heating, are transformed into themetallated compounds [Au(L)Cl2]300,301. The process with 2-phenylpyridine is illustratedin equation 65. This product has also been prepared by transmetallation of the appro-priate arylmercury(II) chloride with [AuCl4]�, a reaction resembling that depicted inequation 63. With 2-benzylpyridine, other metallated and non-metallated species can beprepared by substitution of the chlorine atoms301. The ligand 6-(2-thienyl)-2,20-bipyridinegives analogous reactions with Na[AuCl4]304– 306. The structure of the product is givenin Figure 11.

N

+ Na[AuCl4] −NaCl N

Au ClCl

Cl

N

AuCl

Δ−HCl

Cl

(65)

Several metallated cationic compounds with bipyridine and phenanthroline derivativesas aryl groups have been described in recent years. The ligand (HL) is treated with

N

N

S

Au

NCl

Cl

N

S

AuCl

Cl

FIGURE 11. Structure of the dimeric complex [fAu(thbipy)Cl2g2] [thbipy D 6-(2-thienyl)-2,20-bipyridine]

49



[AuCl4]� and a silver salt in acetonitrile at reflux temperature as shown in equation 66307.

N

N

Ph

2 + K[AuCl4] + 2 AgX

−2 AgCl, −KClCH3CN, reflux

N

N

Ph

Au

C

ClN

N

Ph

H

X + X

X = C7H7SO3

(66)

F. Gold(III) Complexes with Two Gold–Carbon Bonds

1. Diorganylgold(III) halides and pseudohalides

Compounds of the type [AuR2X]2 have been known for a long time, the organicligands being unsubstituted alkyl groups in the majority of cases13. One of the simplestrepresentatives is the dimethylchlorogold(III) [Au2(�-Cl)2Me4], whose traditional synthe-sis with Grignard reagents or methyllithium gives very low yields. An improved syntheticmethod using SnMe4 as alkylating agent, which affords higher yields under better reactionconditions, has recently been published (equation 67)308,309.

2 HAuCl4 + 4 SnMe4−2 HCl

Cl

Au

Cl

AuMe

Me

Me

Me+ 4 SnMe3Cl (67)

Trifluoromethylated complexes are potentially useful precursors for chemical vapourdeposition studies as they are expected to show enhanced volatility310. This is indeed

50



observed for the dimeric complexes [Au2(�-Br)2(CF3)4] and [Au2(�-I)2(CF3)4], whichare accessible by cocondensation of gold with CF3Br and CF3I, respectively, and maybe sublimed at room temperature (10�2 Torr)311. cis-[Au(CF3)2I(PMe3)] is formed inquantitative yield by oxidative addition of trifluoromethyl iodide to [Au(CF3)(PMe3)],the reaction being assumed to proceed via a radical intermediate21,22.

Diarylaurate(III) complexes of the type [AuR2X2]� (R D C6F5, C6F3H2-2,4,6; X DCl, Br, I) were first prepared by oxidative addition of halogen to the correspondingorganogold(I) complexes [AuR2]� 11– 13. Reaction of these compounds with AgClO4results in the abstraction of halide anion to give the dimeric diarylgold(III) halides [Au2(�-X)2(C6F5)4] (X D Cl, Br) which, in turn, can react with sodium azide or potassiumthiocyanate to give the corresponding dinuclear pseudohalide derivatives. Treatmentof the dimeric chloride complex with Tl(acac) results in the formation of monomeric[Au(C6F5)2(acac)], while the cleavage of the chloro bridges with neutral ligands yieldscomplexes of the types [Au(C6F5)2(L-L)][Au(C6F5)2Cl2] (L-L D 1, 10-phenanthrolineand related ligands) or [Au(C6F5)2Cl(L)] (L D pyridine)312.

The preparation of diarylaurate(III) complexes of the type [AuR2X2]� by oxidativeaddition of halogens as described above is not generally applicable, as less stableorganogold(I) derivatives usually react with cleavage of the gold–carbon bonds under thegiven conditions. An alternative synthesis of diarylgold(III) halides uses organomercurialsas arylating reagents and compounds of the type [NMe4][cis-AuR2Cl2] can be preparedwhere R D C6H4NO2-2 or C6H3Me-2, NO2-6 (equation 68)313. The complexes maythen be derivatized by substitution of one or both halide ligands with various reagents.Thus, reaction with KCN results in substitution of both halide ligands by cyanide, whiletreatment with neutral mono- or bidentate ligands leads to neutral or cationic complexes,as illustrated in equations 69–71313.

2[Hg�C6H4NO2-2�2]C [AuCl4]� ��! [Au�C6H4NO2-2�2Cl2]�C2[Hg�C6H4NO2-2�Cl] �68�

[NMe4][Au�C6H4NO2-2�2Cl2]C 2 KCN ��! [NMe4][Au�C6H4NO2-2�2�CN�2]C2 KCl �69�

[NMe4][Au�C6H4NO2-2�2Cl2]C PPh3 ��! [Au�C6H4NO2-2�2Cl�PPh3�]C[NMe4]Cl �70�

[NMe4][Au�C6H4NO2-2�2Cl2]C Ph2PCH2CH2PPh2 C NaClO4 ��![Au�C6H4NO2-2�2��

2-Ph2PCH2CH2PPh2�]ClO4 C [NMe4]ClC NaCl �71�

Gold is incorporated in a carbocyclic ring in the auracyclopentadiene derivative [Au2(�-Cl)2(C4Ph4)2]. The reaction with various anionic and neutral ligands leads to cleavage ofthe chloride bridges and some of the resulting products are illustrated in Scheme 17314.

2. Diorganylgold(III) complexes with group 16 donor ligands

Dimethyl(acetylacetonato)gold(III), [AuMe2(acac)] (4), is of great interest as aprecursor for the chemical vapour deposition of gold315.

The complex [Au(C4Ph4)(acac)] can be prepared from the auracyclopentadiene species[AuCl(C4Ph4)(SC4H8)] or [Au2(�-Cl)2(C4Ph4)2] by reaction with Tl(acac) and has been

51



Au

Ph

Ph

Ph

Ph

NC5H5

Cl

Au

Ph

Ph

Ph

Ph

Cl

Cl

−

2

Au

Ph

Ph

Ph

Ph

Au

Ph

Ph

Ph

Ph

Cl

Cl

− 2 C5H5N

+ 2 C5H5N+ 2 Cl−

− 2 Cl−

Au

Ph

Ph

Ph

Ph

L

L

Au

Ph

Ph

Ph

Ph

Cl

Cl

Au

Ph

Ph

Ph

Ph

L-L

Cl

2

phenphen=phenanthroline

phen=phenanthroline 2 phen

2

SCHEME 17. Reactions of [Au2(�-Cl)2(C4Ph4)2] with mono- and bidentate ligands

O C

CH

CO

CH3

CH3

Au

(4)

H3C

H3C

used as the starting material in the synthesis of several other complexes with oxygendonor ligands, as illustrated in Scheme 18316.

Sulphur donor ligands have also been employed in the synthesis of severaltypes of dialkyl- and diarylgold(III) complexes. A dimeric dimethylgold(III) thiolatemay be prepared from [Au2(�-I)2Me4] by reaction of either sodium thiolate orsodium thioxanthate, the latter reaction proceeding through an intermediate whichdecomposes with liberation of carbon disulphide (Scheme 19)317. With other chelating

52



Au

Ph

Ph

Ph

Ph

O

O

Au

Ph

Ph

Ph

Ph

O

O

Au

Ph

Ph

Ph

Ph

O C

CH

CO

Me

Me

Au

Ph

Ph

Ph

Ph

NH3

CH3

O

O

Au

Ph

Ph

Ph

Ph

N

O

1/2 (COOH)2

[NH4][CH3COO] 2-HOC6H4NH2

1/2

H2

SCHEME 18. Preparation of auracyclopentadiene derivatives with O donor ligands

Me

Au

I

I

Me

Au

Me

Me

Me

Au

S

S

Me

Au

Me

Me

Et

Et

2 NaSEt

−2 NaI

NaS

C

S

SEt2

2

Me

Au

S

S

Me

C SEt

−2 CS2

−2 NaI

SCHEME 19. Synthesis of [Au2(�-SEt)2Me4]

53



S,S donor ligands, [Au2(�-I)2Me4] gives a variety of stable mononuclear, neutraldimethylgold(III) complexes, examples being the compounds [Au(CH3)2fS2P(CH3)2g]and [Au(CH3)2f(CH3)2P(S)NP(S)(CH3)2g]317. An analogous reaction is that of[Au2(�-Cl)2(C6F5)4] with dialkyldithiocarbamates, which leads to complexes such as[Au(C6F5)2(S2CNMe2)]318. Diorganogold(III) dialkyldithiocarbamates have also beenobtained together with other products from the oxidative addition of tetraalkylthiuramdisulphides to organogold(I) complexes [AuR(PPh3)] (R D alkyl, phenyl, ferrocenyl), asillustrated in equation 72319.

[Au�Fc��PPh3�]CMe2NC�DS�S�SC�DS�NMe2 ��! [Au�Fc�fSC�DS�NMe2g2]C[Au�Fc�2fSC�DS�NMe2g]C . . . �72�

Several other compounds with chelating sulphur-containing ligands are known320.Treatment of cis-[Au(C6F5)2Cl(�1-Ph2PCH2PPh2)] with elemental sulphur leads to oxi-dation of the non-coordinated phosphorus centre to give the phosphine sulphide, whichadopts a chelating bonding mode upon further reaction of the complex with AgClO4.The resulting compound can be deprotonated with sodium hydride to give the methanidederivative. The reactions of these products with a variety of gold and silver compoundsreadily give polynuclear complexes containing carbon–metal bonds (Scheme 20)321.

1/8 S8

−H2

−NaClO4NaH

ClAgClO4

−AgCl

[Au(C6F5)3(OEt2)]

−Et2O

+

ClO4

Ph2Ph2

Au(C6F5)3

H

F5C6

Au

Cl

F5C6 PPh2CH2PPh2

F5C6

Au

PF5C6

SPPh2

Ph2

F5C6

Au

Cl

F5C6 PPh2CH2P(S)Ph2

F5C6

Au

PF5C6

SPPh2

Ph2

F5C6

Au

PF5C6

S

C

PPh2

H

F5C6

Au

PF5C6

S

C

PPh2

SCHEME 20. Diarylgold(III) complexes with a chelating P, S donor ligand

3. Diorganylgold(III) complexes with group 15 donor ligands

Complexes with amide ligands may be prepared by reaction of [Au2(�-I)2Me4] withmetal amides. Depending on the reaction conditions, Au�N heterocycles of varying ringsize are obtained (Scheme 21)322–324.

54



[Au2(μ-I)2Me4]

KNH2NH3 (1)

LiNHMeC6H12/Et2O

LiNMe2

Et2O

[Au2(μ-NHMe)2Me4]

[Au2(μ-NMe2)2Me4]

[Au4(μ-NH2)4Me8] +[Au3(μ-NH2)3Me6]

SCHEME 21. The synthesis of dimethylgold(III)amides

Dimethylgold(III) nitrate forms mononuclear complexes with a wide rangeof polynuclear nitrogen-donor ligands (L) containing imidazole (cf 5)325,326,pyridine325–327, pyrazole (cf 6)325,327,328 and other functionalities329. A complex (7) withan ambidentate N,P-donor ligand derived from 1,3,5-triaza-7-phosphoniaadamantane saltshas been obtained by reaction of dimethylchlorogold(III) with an equimolecular quantityof the ligand330. By contrast, simple pyrazole ligands (pzH) react with dimethylgold(III)nitrate in water to give dimeric complexes of the type [AuMe2(pz)]2 (8)331.

N

N

Au

N

N

H3C

H3C

CH3

OH

NCH3

(5)

+

N N

N

Au

N

H3C

H3C

(6)

B

N

N

N

N

N N

N

Au

N

H3C

H3C

(8)

Au

CH3

CH3

H3C

Au

H3C

P

N N

N

H3C

+

H3C

Au

H3C

Cl

Cl

−

(7)

H3C

Structurally related complexes can also be prepared by the reaction of gold(III) dihalideprecursors with Grignard reagents (equation 73)332 and by treatment of the auracyclopen-tadiene derivative [Au(C4Ph4)(acac)] with protonated nitrogen ligands, similar to thereactions depicted in Scheme 18316. The complexes prepared according to equation 73

55



show interesting luminescence properties332.

N

N

Au

Cl

Cl

ClO4 + 2

Me

MgBr

Me

Me

−2 MgBrCl

N

N

AuMeMe

Me

Me

Me

Me

ClO4

(73)

Several types of diarylgold(III) complexes with chelating C,N-donor ligands are knownwhich can be prepared by arylation of suitable gold(III) precursors with organomercury(II)reagents11,12. An example is shown in Scheme 22333. The analogous complexes withAr D �2-fC6H4(CH2NMe2)-2g have also been prepared334. Sequential arylation allowsthe synthesis of complexes with two different aryl ligands, as illustrated in Scheme 23335.The doubly C,N-chelated cationic complexes can be derivatized further by reactions withanionic (halide, cyanide, acetate) or neutral ligands (pyridine).

Sequential arylation has also been used to prepare diarylgold(III) complexes in whichthe second aryl ligand does not carry a potential donor group, and complexes such as 9 and10 have been obtained from reactions analogous to the first step in Scheme 23336–339.The chlorine ligand in these complexes is readily substituted and bromide, iodide andacetate derivatives as well as a cationic pyridine adduct have been synthesized, togetherwith other related species.

Upon treatment with phosphine or chloride, some of the C,N-chelated diarylgold(III)chloride complexes undergo reductive elimination of the aryl ligands to give biaryls. Thehigh-yield reaction proceeds at room temperature and can be used for the synthesis of

56



N

Au

N ClN

Ph

N

Ph

AgClO4

− AgCl

N

Au

N NN

Ph Ph

ClO4

− 1/2 [NMe4]2[Hg2Cl6]

[NMe4][AuCl4] + [Hg{C6H4(N NPh)-2}2]

SCHEME 22. Synthesis of diarylgold(III) complexes using organomercury(II) reagents

N

Au

N Cl N

Ph

AgClO4

− AgCl

N

Au

N N

Ph

ClO4

Cl

Au

N Cl

NPh)-2}2]+ [Hg{C6H4(N

Me Me Me Me

Me Me

− [Hg{C6H4(N NPh)−2}Cl]

SCHEME 23. Synthesis of diarylgold(III) complexes using organomercury(II) reagents

57



NF

Cl

Au

F

FF

F

(10)

NN

NO2Cl

Au

(9)

Ph MeMe

both symmetrical and asymmetrical products. An example is given in equation 74340.

N

Au

Cl

NMe2

PPh3

−[AuCl(PPh3)]

Me Me

(74)

Gold(III) complexes with one aryl and one acetonyl ligand form as products of anunusual auration of acetone341. Thus [Auf�2-C6H4(NDNPh)-2gCl2], when treated inacetone with various reagents such as Tl(acac), KCN, AgClO4, 1,10-phenanthrolineor diarylmercury(II) compounds (e.g. [Hg(C6F5)2]), gives [Auf�2-C6H4(NDNPh)-2g(�1-CH2COMe)Cl] as the final product297. Some intermediates of this process have beenisolated (Scheme 24) and the C�H activation of other ketones has also been studied342.Like the diaryl complexes described above, the aryl acetonyl complexes can bederivatized in various ways, either by substitution of the chloride ligand or by cleavageof the gold–nitrogen bond with other donor ligands343. Some of these chloro ortriphenylphosphine derivatives undergo a reductive elimination of both aryl and acetonylligands in a similar way as shown in equation 74344.

Several diarylgold(III) complexes with monodentate alkyldiphenylphosphonio(diphe-nylphosphino)methanide ligands have been prepared. These compounds react withsodium hydride to give the corresponding methanide complexes, which in turn maybe transformed into polynuclear gold(III)/gold(I) complexes upon treatment with gold(I)reagents containing labile ligands (Scheme 25)320.

Most other reported diorganylgold(III) complexes with phosphorus donor ligands con-tain difunctional phosphines such as bis(diphenylphosphino)methane (dppm) or closelyrelated species56,239,320,345– 347. Dimeric [Au2(�-Cl)2(C6F5)4] may be cleaved with dppmto give [Au(C6F5)2Cl(dppm)], which upon reaction with AgClO4 forms the cationiccomplex [Au(C6F5)2(dppm)]ClO4. This is transformed into the deprotonated complex[Au(C6F5)2(Ph2PCHPPh2)] by treatment with sodium hydride. This compound as wellas the related complex with tris(diphenylphosphino)methane can be alternatively pre-pared by direct reaction of the phosphine with [Au(C6F5)2(acac)] under mild reaction

58



C

Au

Cl

Cl

N

iC

Au

Cl

X

N

ii

C

Au

Cl

X

O

Me

H2C

H

N

C

Au

Cl

X

O

Me

H2C

HN

C

Au

Cl

X

Me

O

NH

C

Au

Cl

N

Me

O

−

++

iii

NN

Ph

Au

Cl

Cl

−

SCHEME 24. Proposed mechanism for the C�H activation of ketones with 2-(phenylazo)-phenyl-gold(III) complexes; (i) CHX; X D acac-C, CN, C6H4(NDNPh)-2, C6F5 or C6H4NO2-2; (ii) CMe2CO;(iii) - HX

+ [Ph2PCH2PPh2CH2Ph]ClO4

F5C6

Au

P

ClF5C6

C

PPh2

CH2Ph

HH

ClO4NaH

−H2, −NaClO4

P C

PPh2

CH2Ph

H

[Au(C6F5)(SC4H8)]P C

PPh2

CH2Ph

H

1/2

Ph2

−SC4H8

Au(C6F5)

F5C6

Au

F5C6

Cl

Cl

Au

C6F5

C6F5

F5C6

Au

ClF5C6

Ph2F5C6

Au

ClF5C6

Ph2

SCHEME 25. Synthesis of alkyldiphenylphosphonio(diphenylphosphino)methanide complexes ofgold(III)

59



conditions345. The methanide derivatives can then react further with gold(I) or gold(III)complexes to yield di- or trinuclear complexes such as [(C6F5)2Auf(Ph2P)2CHAu(C6F5)g]or cis-[f(C6F5)2Auf(Ph2P)2CPPh2gg2Au(C6F5)2]ClO4. The preparation of the latter issummarized in Scheme 26. A hexanuclear gold(III)/gold(I) complex with four methanidebridging units has also been described353. Deprotonation and metallation to give polynu-clear methanediide derivatives is also possible with dppm. A comprehensive review ofthese complexes has appeared320.

O

Au

O

C

CH + (Ph2P)3CH

C

F5C6

F5C6

−acacHP

Au

P

C PPh2

F5C6Ph2

Ph2

1/2 [Au(C6F5)2(OEt2)2]ClO4

−2 OEt2

P

Au

P

C P

F5C6Ph2

Ph2P

C

P

Au

Ph2

Ph2

Au

F5C6 C6F5

PPh2 Ph2

C6F5

C6F5

ClO41/2

CH3

CH3

F5C6

F5C6

SCHEME 26. Synthesis of polynuclear diarylgold(III) complexes containing diphosphinomethanideligands

G. Gold(III) Complexes with Three Gold–Carbon Bonds

The principal methods available for the synthesis of compounds containing threealkyl and/or aryl ligands are the reactions of suitable gold(III) halide complexes withorganolithium or Grignard reagents and the oxidative arylation of gold(I) complexes withorganothallium(III) compounds11–13. Specific examples for these reactions are given inequations 75348, 76349 and 77350 and a selection of complexes of this type is presentedin Table 13.

Au2Br61. 6 MeLi; �6 LiBr��!

2. 2 PMe32[AuMe3�PMe3�] �75�

cis-[AuIMe2�PPh3�]C PhMgBr ��! cis-[AuMe2Ph�PPh3�]CMgBrI �76�

[Au�C6F5��SC4H8�]C [Tl�C6F5�2Cl] ��! [Au�C6F5�3�SC4H8�]C TlCl �77�

Some tris(trifluoromethyl)gold(III) complexes are also known. [Au(CF3)3(PMe3)] canbe synthesized in high yield by treatment of [AuI(CF3)2(PMe3)] with [Cd(CF3)2] Ð DME(DME D 1, 2-dimethoxyethane) in the presence of an excess of trifluoromethyl iodide(equation 78)21. The complex has also been obtained by donor ligand stabilizationof [Au(CF3)3], which can be generated by cocondensation of gold atoms with CF3radicals356. The related complex [Au(CF3)3(PEt3)] is reported to form when CF3I and

60



TABLE 13. Some gold(III) complexes of the types [AuR3L] and [AuR2R0L]


[AuMe3(PMe3)] — 348

[Au(CF3)3(PMe3)] — 21

[Au(CF3)3(PEt3)] — 22

cis-[AuMe2Et(PPh3)] — 351

cis-[AuMe2f�1-CH2C(Me)DCH2g(PPh3)] — 352

cis-[AuMe2 (trans-MeCHDCH)(PPh3)] — 351

cis-[AuMe2(C�CPh)(PPh3)] — 351

cis-[AuMe2Ph(PPh3)] 101(d) 351

cis-[AuMe2PhfP(C6H4OMe-4)3g] 113(d) 349

cis-[AuMe2PhfP(C6H4F-4)3g] 115(d) 349

cis-[AuMe2(COOMe)(PPh3)] 124(d) 353

cis-[AuMe2(COOEt)(PPh3)] 130(d) 353

cis-[AuMe2(COOPr-i)(PPh3)] 120(d) 353

[Au(C6F5)3(SC4H8)] 190 350

[Au(C6F5)3fS(MeS)CNH(C6H4Me-4)g] 131 100

[Au(C6F5)3(OEt2)] — 354

[Au(C6F5)3(ODCMe2)] — 354

[Au(C6F5)3(OAsPh3)] 157 354

[Au(C6F5)3(�1-Ph2AsCH2AsPh2)] 197 107

[Au(C6F5)3(�1-SPh2PCH2PPh2Me)]C 138 331

[Au2(C6F5)6(�-Ph2P-fFc0g-PPh2)]a 260 114

[Au2(C6F5)6(�-S2CNEt2)]� 203 318

[Au2(C6F5)6(�-S2CPBu3)] 152 117

[f(C6F5)3Au(�-Ph2PCHPPh2)g2Au]� 80(d) 196

[f(C6F5)3Auf�-Ph2PC(AuPPh3)2PPh2gg2Au]C 99(d) 196

[Au(C6Cl5)3(SC4H8)] 150(d) 355

[Au(C6Cl5)3Cl]� 145(d) 355

afFc0g; 1,10-ferrocenediyl.

[Au(CF3)(PEt3)] are reacted over extended periods of time (>10 days)22.

2[AuI�CF3��PMe3�]C [Cd�CF3�2] žDMEC 2 CF3I ��! 2[Au�CF3�3�PMe3�]CCDMEC CdI2 �78�

The mixed compounds of the type [AuMe2R(PR03)] (R D alkyl, alkenyl, alkynyl, aryl;R0 D alkyl, aryl) often have cis stereochemistry, as indicated by NMR data349,352,357,358.When heated, both the trimethyl- and the mixed cis-dimethyl(organyl)(phosphine)gold(III)complexes undergo reductive elimination of two organic groups after dissociation of thephosphine ligand, a reaction which is important for the catalytic coupling between alkyl-lithium reagents and alkyl halides348. As illustrated in Scheme 27, two types of productmay form in the case of the mixed complexes. While reductive elimination of R�Me ispredominant when R D alkenyl or aryl, the formation of ethane is favoured when R is

61



Me Au

Me

R

L Me Au + L

Me

R

RMe + [AuMeL]

C2H6 + [AuRL]

SCHEME 27. Mechanism of thermolysis of cis-dimethylorganylgold(III) compounds

an alkynyl or an electron-withdrawing alkyl group351. In addition to electronic effects,the selectivity of the process also depends on the steric demand of both the phosphineligand and R349,357. In another type of reaction, dimethylarylgold(III) complexes undergoselective cleavage of the gold–aryl bond when treated with electrophiles such as HCl,HgCl2 or [PtI2(PMe2Ph)2], the gold-containing products being complexes of the typecis-[AuXMe2(PPh3)] (X D Cl or I)358. Similar processes take place with dimethylal-lylgold(III) derivatives and their reaction with aldehydes and ketones gives homoallylalcohols, with C�C bond formation selectively at the �-position of the �1-allyl moiety352.An example of these reactions is represented in equation 79.

PPh3

Au

Me

Me

Ph

H

C O

Ph

OH

AuMe R

Me

PPh3

+

+ + HR

R = CH(CN)2, C CPh

(79)

A related group of compounds is that of the gold(III) dimethyl(alkoxycarbonyl) com-plexes, accessible by the reaction of carbon monoxide with dimethyl(alkoxy)(triphenyl-phosphine)gold(III), which is prepared in situ from cis-[AuIMe2(PPh3)] and sodiumalkoxide in methanol (equation 80)353,359. Thermolysis of the methoxycarbonyl complexin benzene leads to the reductive elimination of methyl acetate and ethane, indicatingcompetition between the two modes of decomposition illustrated in Scheme 27. The reac-tion of the same complex with electrophiles such as hydrogen chloride proceeds withliberation of carbon monoxide and methanol, as illustrated in equation 81.

cis-[AuIMe2�PPh3�]C NaOMe/MeOHC CO ��! cis-[AuMe2�COOMe��PPh3�] �80�

cis-[AuMe2�COOMe��PPh3�]C HCl ��! cis-[AuClMe2�PPh3�]CMeOHC CO �81�

As regards triarylgold(III) complexes, only polyhalophenyl derivatives are known.[Au(C6F5)3(SC4H8)] is a useful precursor for the preparation of a wide variety of othercompounds by ligand substitution. It reacts with neutral [L D NH3, C5H5N, P(OPh)3,

62



[NBu4]

(F5C6)3AuS

C

(F5C6)3AuS

N

Et

Et

(11)

(F5C6)3AuS

C

(F5C6)3AuS

PEt3

(12)

Ph2P

Au Au

PPh2

C

Ph2PC

PPh2

AuR

R

R

R

R

R

HH

H H

ClO4

2 [AuR3(Ph2PCH2PPh2)]

R = C6F5

[Au(SC4H8)2]ClO4

−2 SC4H81/2

4 [Au(acac)(PPh3)]−4 acacH

Ph2P

Au Au

PPh2

C

Ph2PC

PPh2

AuR

R

R

R

R

R

AuPPh3Ph3PAu

Ph3PAu AuPPh3

ClO4

SCHEME 28. Preparation of a heptanuclear trialkylgold complex with two C(AuPPh3)2 units

AsPh3, SbPh3, CNC6H4Me-4]350 or anionic ligands (X D Cl, Br, I, SCN, N3)350,355 togive complexes of the types [Au(C6F5)3L] and [Au(C6F5)3X]�, and dinuclear deriva-tives (for example 11 and 12117) have been similarly obtained from the reaction withbridging ligands107,114,117,350. The diphosphine complex [Au(C6F5)3(Ph2PCH2PPh2)]can be used as a precursor for the preparation of polynuclear gold(III)/gold(I) phos-phino and methanide complexes53,196. The synthesis of a heptanuclear product with two[C(AuPPh3)2] units is illustrated in Scheme 28. The complex [Au(C6F5)3(OEt2)]354, pre-pared according to equation 82, is another useful starting material as the ether molecule isdisplaced even more readily, allowing the synthesis of compounds which are inaccessible

63



P

Au

Cl

C

PPh2

F5C6

F5C6

CH COOMe

H

H

Ph2

ClO4Na2CO3

PPh2

CP

C

HH

H COOMe

−NaCl, −NaClO4

−2 H22 NaH

PPh2

CP

C

H

H COOMe

Ph2

Ph2

[Au(PPh3)(SC4H8)]ClO4

−SC4H8 PPh2

CP

C

HAuPPh3

H COOMe

Ph2

ClO4

ClO4

−NaClO4

−H2

NaH

PPh2

CP

C

AuPPh3

H COOMe

Ph2

[Au(PPh3)(SC4H8)]ClO4

−SC4H8PPh2

CP

C

AuPPh3AuPPh3

H COOMe

Ph2

S

Cl

P

ClO4 −AgCl

−HClO4

AgClO4

S

C

PPh2

H PPh2CH2COOMe

ClO4

−2 H22 NaH

S

C P

P

COOMe

Ph2

[Au(C6F5)(SC4H8)]

−SC4H8

C H

Ph2

S

C P

PPh2

C

Ph2

Au(C6F5)

H

H

or AgClO4

ClO4

C

PPh2

C

H

H

HCOOMe

H

Ph2

−NaCl, −NaClO4

COOMeHH

Au

F5C6

F5C6

Au

F5C6

F5C6

Au

F5C6

F5C6

Au

F5C6

F5C6

Au

F5C6

F5C6

Au

F5C6

F5C6

Au

F5C6

F5C6

Au

F5C6

F5C6

Au

F5C6

F5C6

SCHEME 29. Preparation of methanide auracycles from different diarylgold(III) phosphinophospho-nium salts

64



from the thiophene adduct (equation 83)100,119,231.

[NBu4][Au�C6F5�3Br]C AgClO4

Et2O��!� AgBr

�[NBu4]ClO4

[Au�C6F5�3�OEt2�] �82�

[Au(C6F5)3(OEt2)] + C5H5NS −Et2ON

SAu

C6F5

F5C6

C6F5

H

(83)

Gold(III) complexes with two aryl ligands and one methanide ligand have also beenprepared, as illustrated in Scheme 29320,360,361. The synthesis starts from diarylgold(III)precursors containing substituted phosphinophosphonium ligands, which adopt a chelat-ing bonding mode upon deprotonation. Depending on the reaction conditions, chelaterings of varying size may be obtained. Thus, Na2CO3 or AgClO4 as deprotonating agentseffect single deprotonation and simultaneous halide abstraction, leading to cationic four-or five-membered auracycles, while NaH deprotonates both CH2 groups to give neu-tral complexes containing five- or six-membered rings, whose methanide carbon atomscan serve as electron donors to other metal centres, thus forming polynuclear deriva-tives. Sequential deprotonation and metallation of the same methylene group is alsopossible, giving five-membered methanediide auracycles with a [>C(AuPPh3)2] struc-tural unit which resembles that found in certain diauriomethanes362. Analogous reactionshave also been carried out with gold(III) complexes of bis(diphenylphosphino)methanedisulphide118.

H. Gold(III) Complexes with Four Gold–Carbon Bonds

The simplest compounds of this type are the tetraalkylaurates(III), prepared by the reac-tion of trialkyl(triphenylphosphine)gold(III) complexes with alkyllithiums, which proceedsby phosphine displacement as illustrated in equation 84. Recent studies have shown thereaction to be stereoselective, with cis- (or trans-) dimethylalkylgold(III) complexes giv-ing square planar cis- (or trans-) tetraalkylaurates and an associative mechanism involvinga pentacoordinate gold(III) intermediate has been postulated363.

cis-[AuMe2Et�PPh3�]C LiEt ��! Lifcis-[AuMe2Et2]g C PPh3 �84�

The novel tetrakis(trifluoromethyl)aurate(III) anion has been employed to prepare twodistinct phases of �-(ET)2Au(CF3)4 ž (TCE) [ET D bis(ethylenedisulphanyl) tetrathiaful-valene, TCE D 1,1,2-trichloroethane], which are superconductors at ambient pressure atlow temperatures363.

Several tetraarylaurates(III) are known364,256. Tetraarylaurate(III) complexes containingpolyhalophenyl ligands11,12 are best prepared by further arylation of triarylhaloaurates(III)with Ag(C6F5) (equation 85)350.

[N�PPh3�2][Au�C6F5�3Cl]C Ag�C6F5� ��! [N�PPh3�2][Au�C6F5�4]C AgCl �85�

The stable hydrogen dimethyl-bis(2-pyridyl)-aurate(III) is prepared by the reaction ofcis-dimethyliodo(triphenylphosphine)gold(III) with 2-pyridyllithium at low temperature

65



and subsequent hydrolysis (equation 86)365.

Me

Au

PPh3

N

2 Li

H2O

1.

2.

− PPh3, − LiCl, − LiOH

N

NAu H

Me

Me

Me I (86)

III. HOMO- AND HETEROMETALLIC GOLD CLUSTERS CONTAININGGOLD–CARBON BONDS

Of the many gold cluster compounds in which the metal has an oxidation state between0 and C1, only very few also feature bonds between gold and carbon4,13. A recentexample is the neutral cluster [Au10(C6F5)4(PPh3)5], prepared selectively by the reactionof [Au9(PPh3)8](NO3)3 with [NBu4][Au(C6F5)2] in a 1 : 3 molar ratio366.

Species such as [Au8(PPh3)7(CNBu-t)](NO3)2 and [Au9(PPh3)6(CNBu-t)2](NO3)3have been prepared by the addition of one equivalent of isocyanide to the starting material[Au8(PPh3)7](NO3)2 and by isocyanide-induced displacement of phosphine ligands in[Au9(PPh3)8](NO3)3, respectively. The reactivity of the products towards halide ions andamines has been studied367. Ligand displacement in related platinum–gold clusters hasled to species such as [PtAu8(PPh3)7(CNBu-t)2](NO3)2

368.

Ph3P

Au

AuPh3P Ir

C C

Fe(CO)3

OCPh3P Fe

(CO)3

H

H

Mo Mn(CO)3

P

H

Me

Au

Co(CO)3

C

Fe(CO)3

Fe(CO)3

Fe(CO)3

Ph3P

AuPPhMe2

Ph2

Ph(CO)4Os Os(CO)4

Au

C(CO)3Os Os(CO)3

(CO)3Os Os(CO)3

OMe

FIGURE 12. Heterometallic cluster compounds of monovalent gold containing gold– carbon bonds

66



Heterometallic cluster compounds of gold can often be prepared by treating suitable sub-strates with aurating agents such as [AuCl(PPh3)] or [O(AuPPh3)3][BF4]369. The reactionhas served to determine the extent of structural analogies between isolobal hydrido andL�Au clusters. A variety of substrates has been studied in this context, some of themcontaining alkyne370 or carbido ligands371. Auration may involve the metal frameworkand/or the organic ligand372. In a related reaction, it was possible to replace an agostichydrogen atom of a metal-coordinated allyl group by an isolobal gold ligand373. Examplesof the various kinds of compounds which have recently been prepared are collected inFigure 12370,371,373,374.

IV. SYNTHESIS AND PROPERTIES OF ALKENE, ALKYNE, CARBENE ANDRELATED COMPLEXES OF GOLD

Complexes of zero valent gold (in the form of atoms or at the surface of the bulkmetal) and unsaturated molecules such as alkenes375,376, alkynes376,377, allenes378,arenes379 or fullerenes380 were the subject of a number of experimental studies. Molecularspecies which are formed by low-temperature cocondensation of gold atoms withunsaturated organic substrates have been characterized by their infrared/Raman, UV-visible absorption and ESR spectra, but the interpretation of these data is not withoutcontradictions377,378,381.

Olefin complexes of gold(I) can be prepared either by the reaction of tetrachloroau-ric acid with the olefin or directly from the olefin and gold(I) halide13,15. While suchspecies usually have poor stability and decompose in solution at room temperature, the cis-cyclooctene and norbornene complexes of AuCl, obtained from the reaction of [AuCl(CO)]with the corresponding olefin by a CO displacement reaction, have been found to be lessprone to decomposition382. An (olefin)gold(I) complex featuring a tetracoordinate envi-ronment for the gold centre bonded to the olefin has recently been obtained according tothe procedure shown in equation 87383.

ClAu P

PClAu

H

H

2

NC

NC

SNa

SNa

+ − 2 NaCl

CNNC

SS

Au HH

Ph2P PPh2

Au

PPh2Ph2P

HH

Au

Cl

Au

Cl

Ph2

Ph2

(87)

It has been noted that metal–carbon triple bonds behave in a similar way as alkynes withrespect to -complex formation13,15. Various heterometallic gold complexes with bridgingcarbyne ligands reflect this analogy. Alkylidyne complexes like [W(�CR)(CO)2(�5-C5H5)], [W(�CR)(CO)2(�5-C2B9H9R02)]� (R D alkyl, aryl, amino; R0 D H, Me) readily

67



Me

C

W Au

COOC

+

[PF6]−

N

C

W Au

COOC

Me Et

C

W Au

COOC

W

C

CO

Au

W

C

OC

CO

OC

−

[η5−C2B9H9Me2]−: • = CMe

[NEt4]+

PPh3

C6F5

Me

Me

Me

Me

FIGURE 13. Dimetallacyclopropene complexes obtained in the addition of gold(I) fragments to metalalkylidyne complexes

react with [AuCl(PPh3)] or [AuX(SC4H8)]n� (n D 0, X D Cl, C6F5; n D 1, X DC2B9H9Me2) to give cationic, neutral or anionic dimetallacyclopropene species, formedby addition of a gold(I) fragment to the metal– ligand multiple bond (Figure 13)384– 387.Trinuclear compounds in which an alkylidyne ligand caps a triangle of metal atoms havebeen obtained in an analogous way386– 388. A review of these gold complexes and relatedcopper species has appeared389.

Four main methods have been established for the preparation of gold carbene complexesand a large number of compounds are known.

(a) The most important preparation uses the nucleophilic addition of alcohols or aminesto gold-coordinated isocyanides (equation 88)390:

+

CH3O

C-Au-Cl

p-MeC6H4NH

p-MeC6H4NCAuCl CH3OH (88)

68



Similarly, diisocyanide compounds, [Au(R1NC)2]C (R1 D aryl), give cationic bis(carbene)complexes, which can be further oxidized with I2 to gold(III) carbene complexes(equation 89)391– 394:

X

C

R′HN

Au C

X

NHR′I2

X

C

R′HN

Au C

X

NHR′

+I

I

+

+

(89)

where X D NR2R3 or OR4 and R2, R3 and R4 are organic groups.Amines react in general more readily than alcohols and aromatic isocyanides are more

reactive than aliphatic ones. The ionic diisocyanide complexes react under milder condi-tions than the neutral monoisocyanide complexes395,396. No reactions with mercaptaneshave been reported. Acyclic aminocarbene complexes occur as isomers when R1 6D R2

due to restricted rotation around the C(carbene)�N bond397. Dinuclear carbene complexesare formed when the amine complexes [Au(C6F5)NH2(CH2)nNH2] (n D 1 or 2) or thecarbene complexes [(C6F5)mAuC(NHR)NH(CH2)nNH2] (m D 1 or 3) are treated withthe isocyanide compound [(C6F5)mAuCNR] (R D Ph or p-tolyl)398.

The same principle is also utilized, albeit in somewhat modified form, when [AuCl4]�is treated with isocyanides and an excess of amine to yield bis(carbene) complexes(equation 90)399.

AuCl4− + R′ΝC + R′′NH2

NHR′′

C

NHR′

Au

2

+

+ . . . (90)

The aliphatic derivatives have been oxidized with I2 to their gold(III) analogues. In afurther unique application of this method, isocyanides with OH groups in position 2 or 3become activated by [AuCl4]� and undergo an internal attack by the OH group on theisocyanide to give heterocyclic carbene complexes. Excess isocyanide leads to reductionof the initially formed gold(III) complex to afford both mono- and bis(carbene) complexesof gold(I) (Scheme 30)400.

In a modification of this reaction, the use of isocyanide becomes unnecessary whenH[Au(CN)2] reacts with propene oxide or styrene oxide to yield (cyano)carbene complexesof the same family (Scheme 31)401.

Organogold carbene compounds [Au(carbene)(CN)m�1Rn] can be obtained from com-plexed cyanides [Au(CN)m(C6F5)n]� (n D 1 or 3, m D 1 and n D m D 2) by sequentialalkylation (to form isocyanide complexes) and nucleophilic attack of amine402. Gold(III)diisocyanides [Au(CNR)2(C6F5)2]C (R D Ph or p-tolyl), which can also be obtainedby isocyanide substitution of ether in [Au(C6F5)2(OEt2)2]C, react with hydrazobenzeneNH(Ph)NHPh and hydrazine or phenylhydrazine according to the reactions in Scheme 32to furnish cyclic bis(carbene) and cyclic carbene-imidoyl compounds403.

The amine addition to a coordinated isocyanide finds application for a cyclizationreaction404. �-(1,2-Diisocyanobenzene)bis(chlorogold) reacts with methylamine, aniline

69



AuCl4− + HO(CH2)nNC Cl3Au C

NH

O CH2

(CH2)n

n = 2 or 3 n = 1 or 2

excessisocyanide

ClAu C

NH

O CH2

(CH2)n

Cl2Au C

NH

O CH2

(CH2)n+

2

+

SCHEME 30. Carbene complexes from ω-hydroxyisocyanides

CNAu C

NH

O CHR′

CHR

CNAuCNH +

O

R R′

NCCNAu CHR CHR′OH

R = Me and R′ = H

R = H and R′ = Ph

SCHEME 31. Carbene complexes from epoxides

Au

C6F5 CNR

C6F5 CNR

+NHPh

NHPh NPh

NPhC

Au

C

NHR

NHR

C6F5

C6F5

+

+

N

NR'C

Au

C

NHR

+ Η+

+

C6F5

C6F5

NHR′

NH2

. . .

NHR

SCHEME 32. Cyclic bis(carbenes)

70



NCAuCl

NCAuCl

+ PhNH2

N

N

CAuClPhH2N

+

••

CAuCl

N

CH

N

AuCl

C

H

PhHN

ClAuCNPh+

N

C

N

AuCl

H

H

AuCl

SCHEME 33. Cyclic carbene complexes from bis(isocyanides)

(see Scheme 33), 1,2-diaminobenzene or 1,8-diaminonaphthalene to form benzimidazolin-2-ylidene(chloro)gold complexes.

In the process the nucleophilic attack by the amine is followed by an imine attackon the second isocyanide functionality to give a heterocyclic ring by the elimination of[Au(Cl)CNPh].

(b) Electron-rich olefins can be used as nucleophilic carbene transfer reagents to give,e.g., bis(imidazolinylidene) complexes (equation 91)405.

N

C

N N

C

N

Me Me

Me Me

ClAuPPh3

N

C

N

Me

Me

+Au

+

+

2

. . . (91)

(c) Carbene groups can also be introduced via a transfer from group 6 metals. TypicalFischer-type alkoxy-organo or amino-organo carbene complexes of gold(I) and gold(III)are formed when H[AuCl4] reacts with pentacarbonyl carbene complexes of chromium,molybdenum or tungsten (equation 92)406,407.

(CO)5M=C(Y)R + H[AuCl4] ClAu=C(Y)R + Cl3Au=C(Y)R

Y = OMe, NH2, NHMe, NMe2

(92)

71



The carbene transfer occurs with retention of the aminocarbene configuration, indicatingthat an sp3 transition state is not formed. With H[AuBr4] and [W(CO)5fC(NMe2)Phg],only the reductive substitution reaction occurs to give the gold(I) compound[Au(Br)C(NMe2)Ph].

(d) Protonation or alkylation of gold azolyl compounds is another straightforwardapproach to carbene complexes. An azolyl lithium is used to substitute one or more ligandsof gold and then one or two of these is protonated or alkylated408–411 (Scheme 34).

C

N

X

−ClAu(SC4H8) + 2 C

N

X

−

2

Au

C

N

X

C

N

X

R

Au

R +

C

N

X

C

N

X

Au

+ 2 R+

+R+

R = H or MeX = N or S

R

SCHEME 34. Carbene complexes via azolyl lithium reagents

With lithiated imidazoles, only bis(carbene) complexes are formed, although carefuladjustment of the conditions can lead to a compound which contains carbene ligandsresulting from both alkylation and protonation411. A similar methodology is applicablewith isothiazolyl lithium. In the product the nitrogen atom occupies a position remotefrom the coordinated carbon (equation 93)412.

NS Li

C6F5Au(SC4H8) + NS AuC6F5

Li

NS AuC6F5Me

CF3SO3Me (93)

Sequential transmetallation and protonation of 2-(20-oxazolinyl)thien-3-yl lithiumaffords the mono- and bis-carbene complexes 13, 14 and 15. These complexes containonly distant (albeit conjugated) heteroatoms413.

72



N OH

SPh3PAu

+

N OH

S(C6F5)Au

O N

S

N O

S

H H

Au

+

(13) (14) (15)

Other compounds belonging to this family are formed when a stable gold trimer istreated, for example, with ClCOOEt or EtI (equation 94)414,415.

N

C

N

Au

R

EtIN

C

N

Au

R

I

Et

3

1/3 (94)

The general pattern is the same if a gold halide is reacted with 2-lithiated pyridinefollowed by a protonating or an alkylating agent416. Both the gold pyridyl trimer417,418

which precipitates upon treatment with one molar amount and the aurate which forms withan excess of 2-pyridyl lithium may be protonated, but only the latter can be alkylatedreadily (Scheme 35).

Mixed ligand gold(I) complexes are prone to homoleptic rearangement. This reactionmay either occur in solution or during crystallization (equation 95)412.

SN

(Ph3P)Au Me

+

SN

Au Me

+

Au(PPh3)2+

2

+2

(95)

Treatment of [Au(Cl)[C(OEt)NMe2] with Lewis acids does not lead to carbynecomplex formation. Reactions with BBr3 and BI3 yield only the substitution products[Au(X)fC(OEt)NMe2g]419,420.

Liquid-crystalline gold isocyanide complexes [CnH2nC1O�(C6H4)�O�C(O)�(C6H4)�NCAuCl] react with alcohols CmH2mC1OH (n D 10 or 11; m D 2 to 5) to formZ/E isomeric mixtures of carbene complexes [isomerism occurs around the C(carbene)�Nbond] with mesomorphic properties and provide the first examples of liquid-crystallinemetal–carbene complexes421. The isomers can also be separated, with the E form beingslightly more stable than the Z form.

73



Cl Au SC4H8N

Li2

N

Li

N

N

Au Li

2 RX

N

N

Au X

R

R

N

Au

HCl

N

Au Cl

H

R = H, X = Cl or

R = Me, X = CF3SO3

3

1/3

SCHEME 35. Pyridyl and pyridinium complexes of gold(I)

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