Unprecedented phosphino copper(I) derivatives oftris(pyrazolyl)methanesulfonate ligand co-ordinated to metal in

an unusual j3-N;N0;O fashion

Carlo Santini a,*, Maura Pellei a, Giancarlo Gioia Lobbia a, Augusto Cingolani a,Riccardo Spagna b,1, Mercedes Camalli b

a Dipartimento di Scienze Chimiche, Universit�aa degli Studi di Camerino, via S. Agostino 1, 62032 Camerino, Macerata, Italyb Istituto di Cristallografia – CNR, Sezione di Monterotondo C.P. No. 10, 00016 Monterotondo Stazione (Roma), Italy

Received 18 March 2002; accepted 9 April 2002

Abstract

New copper(I) triorganophosphine derivatives [CuðR3PÞ(Tpms)] have been synthesised from the reaction of CuCl with PR3

(R ¼ phenyl or p-tolyl) and lithium tris(pyrazolyl)methanesulfonate (Tpms). The complexes obtained have been characterised by

elemental analyses and FT-IR in the solid state and by NMR (1H and 31Pf1Hg) spectroscopy and conductivity measurements in

solution. Single crystal structural characterisations were undertaken for [Cu(Ph3P)(Tpms)] which is the first example of structurally

characterised complex containing the [Tpms] ligand co-ordinated to a metal ion in an unusual j3-N;N0;O fashion. � 2002 Published

by Elsevier Science B.V.

Keywords: Copper(I) complexes; Tris(pyrazolyl)methanesulfonate ligand; Crystal structure

1. Introduction

Since the initial development of tris(pyrazolyl)borateor ‘‘scorpionate’’ ligands by Trofimenko in the 1966 [1],a significant number of complexes, using various maingroup elements as well as numerous transition metals,lanthanoids and actinoids, have been prepared withthese ligands and they have found wide application incoordination, organometallic, and bioinorganic chem-istry [2].

In this research field several recent contributions arerelated to the polyfunctional bis(pyrazol-1-yl)methanesystem, containing carboxylate or ethoxy group to give asmall degree of steric hindrance and considerable co-ordinative flexibility [3,4]. Some recent papers by Kl€aauiet al. [5] as well as Mews and co-workers [6] provide toincrease the number of potentially useful functionalised

tris(pyrazol-1-yl)methane ligands which offer the op-portunity of a new and interesting chemistry parallelingthat of the poly(pyrazolyl)borate arrays [7].

In the last years we have initiated an investigation intothe coordination chemistry of new ‘‘heteroscorpionate’’monoanionic ligands, N- or S-donor, towards earlytransition metal centres [8]. Since one goal of our re-search is the introduction of a hydrophilic moiety toobtain complexes that are soluble and stable underphysiological condition, the tris(pyrazol-1-yl)methane-sulfonate ligand (Tpms) seems to be a suitable candidate:it is highly water-soluble and the solutions are stable overa wide pH range. On this basis, the ligand Tpms can offerthe opportunity for the development of new systemswhich improve copper(I) catalysis [9] in aqueous or inprotic media or having relevant biological activity [10].

This paper, as part of our initial investigations into thetransition metal coordination chemistry of this new classof ligands, describes the synthesis and the spectroscopiccharacterisation of new tris(pyrazol-1-yl)methanesulfo-nate complexes containing copper(I) acceptors. TheX-ray crystal structure of [CuðPh3PÞ(Tpms)] is the first

Inorganic Chemistry Communications 5 (2002) 430–433

www.elsevier.com/locate/inoche

*Corresponding author. Fax: +39-0737-637345.

E-mail addresses: carlo.santini@unicam.it (C. Santini), riccardo.

spagna@mlib.cnr.it (R. Spagna).1 Fax: +39-06-90672-630.

1387-7003/02/$ - see front matter � 2002 Published by Elsevier Science B.V.

PII: S1387-7003(02 )00444 -6

example of j3-N;N0;O coordination mode of thetris(pyrazol-1-yl)methanesulfonate ligand.

2. Experimental

2.1. General procedures

All syntheses and handling were carried out under anatmosphere of dry oxygen-free dinitrogen, using stan-dard Schlenk techniques or a glove box. All solventswere dried, degassed and distilled prior to use. Thephysical measurements were performed as previouslyreported [8].

2.2. Syntheses

All reagents were purchased from Aldrich and usedas received. Tris(pyrazolyl)methane was synthesised inaccordance with the procedure previously reported [11].

2.2.1. Li½Tpms�The lithium salt of tris(pyrazolyl)methanesulfonate

(LiTpms) was synthesised in accordance with the stan-dard procedure reported by Kl€aaui [5]. Yield 51%. M.P.:>300 �C. 1H NMR (CD3OD, 293 K): d 6.41 (dd, 3H, 4-CH ), 7.58 (d, 3H, 5-CH ), 7.91 (d, 3H, 3-CH ). IR: 3161w,3129w (C–H), 1524m (C@Cþ C@N), 1107s, 1061s,1057s, 1044s, 606m, 574m, 537m (SO3). Calcd forC10H9LiN6O3S: C, 40.0%; H, 3.0%; N, 28.0%; S, 10.7%.Found: C, 39.8%; H, 3.1%; N, 28.2%; S, 10.5%.

2.2.2. ½CuðPh3PÞðTpmsÞ� ð1ÞTo a methanol solution (50 ml) of CuCl (0.099 g, 1.0

mmol) and Ph3P (0.262 g, 1.0 mmol), LiTpms (0.300 g,1.0 mmol) was added at room temperature. The solutionwas stirred for 5 h and the solvent subsequently removedwith a rotary evaporator. CHCl3 (50 ml) was added; thesuspension was filtered and concentrated under reducedpressure. A colourless precipitate was formed which wasfiltered off and washed with diethyl ether. Re-crystalli-sation from CH2Cl2–petroleum ether gave complex 1 asa microcrystalline solid in 72% yield. M.P.: 101 �C dec.1H NMRðCDCl3, 293 K): d 6.32 (s, 3H, 4-CH ), 7.28–7.44 (m, 18H, C6H5 and 5-CH ), 8.25 (s, 3H, 3-CH ).1H NMR (CDCl3, 193 K): d 6.61 (s, 1H, 4-CH ), 6.80 (s,2H, 4-CH ), 7.20–7.51 (m, 15H, C6H5Þ, 7.68 (s, 1H, 5-CH ), 7.93 (s, 2H, 5-CH ), 8.84 (s, 1H, 3-CH), 8.96 (s, 2H,3-CH ). 31Pf1Hg NMR ðCDCl3, 293 K): d 8.54 (sbr);31Pf1Hg NMR (CDCl3, 218 K): d )4.60 (s), )1.82 (s),7.63 (s), 9.30 (s). IR: 3161w, 3131w, 3118w (C–H), 1520s(C@Cþ C@N), 1114m, 1094s, 1064s, 1038s, 608m,599w, 518w ðSO3Þ, 533s, 496m, 442m (PPh3), 409m,338m. Calcd for C28H24CuN6O3PS: C, 54.3%; H, 3.9%;N, 13.6%; S, 5.2%. Found: C, 54.3%; H, 3.8%; N, 13.8%;S, 5.4%.

2.2.3. ½CuððC6H4Me-pÞ3P ÞðTpmsÞ� ð2ÞCompound 2 was prepared similarly to compound 1,

by using CuCl (0.099 g, 1.0 mmol), ðC6H4Me-pÞ3P(0.304 g, 1.0 mmol) and LiTpms (0.300 g, 1.0 mmol) inCH3CN/methanol (1:3) solution. Re-crystallisationfrom CHCl3/petroleum ether (1:3) gave complex 2 as amicro-crystalline solid in 75% yield. M.P.: 265–267 �C.1H NMR (CDCl3, 293 K): d 2.37 (s, 9H, CH3), 6.31 (dd,3H, 4-CH ), 7.18–7.41 (m, 15H, 5-CH and C6H4), 8.25 (s,3H, 3-CH ). 1H NMR (CDCl3, 193 K): d 2.39 (br, 9H,CH3), 6.62 (br, 1H, 4-CH ), 6.81 (br, 2H, 4-CH ), 7.07–7.46 (m, 12H, C6H4), 7.69 (br, 1H, 5-CH ), 7.93 (br, 2H,5-CH ), 8.86 (br, 1H, 3-CH ), 9.94 (br, 2H, 3-CH ).31Pf1Hg NMR (CDCl3, 293 K): d 6.60 (sbr);31Pf1Hg NMR (CDCl3, 218 K): d )6.42 (s), 5.45 (s),6.84 (s), 32.07 (s). IR: 3129w, 3160w, 3102w (C–H),1515m, 1497w (C@Cþ C@N), 1110m, 1099s, 1062s,1047s, 1036s, 604m, 524s (SO3), 513s, 504s, 432m(PPh3), 405m, 340w. Calcd for C31H30CuN6O3PS; C,56.3%; H; 4.6%; N, 12.7%; S, 4.8%. Found: C, 56.4%; H;4.5%; N, 12.6%; S, 5.0%.

2.2.4. ½CuðTpmsÞ2� ð3ÞTo a CH3CN/methanol (3:1) solution (50 ml) of CuCl

(0.099 g, 1.0 mmol) and cy3P (0.262 g, 1.0 mmol),LiTpms (0.300 g, 1 mmol) was added at room temper-ature. The solution was stirred for 1 h and a blue-skycolour appeared. The solvent was subsequently removedwith a rotary evaporator. CHCl3 (50 ml) was added; thesuspension was filtered and concentrated under reducedpressure. A blue-sky crystalline precipitate was formedwhich was filtered off and washed with diethyl ether.Yield: 78%. M.P.: 296 �C dec. IR: 3128w, 3100w (C–H),1531m (C@Cþ C@N), 1103s, 1078s, 1053s, 1031s,767m, 722m, 650m, 633m, 600m, 534m (SO3). Calcd forC20H18CuN12O6S2; C, 36.9%; H; 2.8%; N, 25.8%; S,9.9%. Found: C, 37.0%; H; 2.9%; N, 26.0%; S, 9.7%.

2.3. X-ray crystallography

The crude complex 1 was dissolved in a methanolsolution containing a small amount of acetonitrile; asingle crystal of 1 suitable for X-ray diffraction analysiswas obtained and mounted on a Rigaku AFC5R dif-fractometer using graphite-monochromated Cu-Ka ra-diation (1.54178 �AA) and a rotating anode generator.

The crystals are monoclinic, a ¼ 15:247ð6Þ �AA, b ¼12:333ð5Þ �AA, c ¼ 16:237ð4Þ �AA, b ¼ 114:37ð2Þ�, U ¼2781ð1Þ �AA3

, T ¼ 296 K, space group P21=n (no. 14),Z ¼ 4, lðCu-KaÞ ¼ 2:7 mm1, 4814 reflections mea-sured, 4384 unique (Rint ¼ 0:051), 3894 observedðI > 3rðIÞÞ were used in all calculations. The final RðF Þand wRðF 2Þ were 0.034 and 0.038, respectively. The cellparameters were refined by least squares from the an-gular positions of 24 reflections in the range78:56� < 2h < 79:92�. The data were measured at room

C. Santini et al. / Inorganic Chemistry Communications 5 (2002) 430–433 431

temperature for 6:7� < 2h < 124:14� using a h=2h scantechnique. The data were processed to yield values of Iand rðIÞ corrected for Lorentz, polarisation and shapeanisotropy effects. The observed reflections were pro-cessed by the direct methods program SIR97 [12], whichprovided the complete structure. All non-hydrogen at-oms were refined by full-matrix least squares methodwith anisotropic thermal parameters. The hydrogen at-oms were idealised (C–H ¼ 0:96 �AA). Each H atom wasassigned the equivalent isotropic temperature factor ofthe parent atom and allowed to ride on it. The finaldifference Fourier map, with a root-mean-square devi-

ation of electron density of 0.06 e �AA3showed no sig-

nificant features. Calculations were performed using theSIR97 and CAOS structure determination package [13].Crystallographic data have been deposited at the CCDCand allocated the deposition number CCDC 176067.

3. Results and discussion

From the interaction of one equivalent of the lithiumsalt Li(Tpms) with one equivalent of CuCl and of thetertiary monophosphine in methanol or acetonitrile atroom temperature, the complexes 1 and 2 have beenobtained in high yield (Scheme 1). The same compounds1 and 2 have been obtained also when this reaction wascarried out with an excess of the phosphorus donor ð>2equivalents).

Only [CuðTpmsÞ2] adduct 3 has been obtained byusing sterically hindered cy3P, also in presence of anexcess of the phosphorus donor. Decomposition occursin two stages: first, breaking of the copper(I)–phosphinebond with consequent formation of the dinuclear cop-per(I) complex ½CuðTpmsÞ�2 followed by the dispro-portionation to copper(0) and the copper(II) complex 3

½CuðTpmsÞ2� [14].Both of the colourless compounds 1 and 2 are soluble

in chlorinated or protic solvents and air stable even assolutions. They are non-electrolytes in CHCl3 in which anon-ionic dissociation equilibrium such as thatproposed in Eq. (a) is likely, not only on the basis of

vaporimetric molecular weight determinations (the ratiobetween calculated and vaporimetric molecular weight is0.71 at conc. 0.01 M and 0.62 at 0.005 M for compound1 and 0.67 at conc. 0.01 M and 0.59 at 0.005 M forcompound 2), but also on the basis of the31Pf1Hg NMR variable temperature study

½CuðPR3ÞnðTpmsÞ�¡½CuðPR3Þn1ðTpmsÞ� þ PR3 ðaÞThe 1H NMR spectra at 298 K of 1 and 2, in chlo-

roform or methanol solution, show one set of reso-nances for H(3), H(5) and H(4), indicating that allpyrazole rings are equivalent. In addition, all the reso-nances are shifted to lower field in comparison withthose of lithium compound Li[Tpms]. Variable temper-ature 1H NMR studies have been done for both thecomplexes: it was possible to slow down the rate of thedynamic process responsible for the spectrum obtainedat room temperature and at 193 K a static spectrum wasobtained. This pattern indicates that the three pyrazolylrings are magnetically different according to the solidstate structure.

The room temperature 31P NMR spectra of com-plexes 1 and 2 show a single broad resonance, ascribedto some fluxional behaviour in these complexes. Avariable-temperature 31P NMR study was performedfrom 293 to 193 K, in approximately 10 K decrements.For compound 1 at 218 K the broad resonance splitsinto four, one of them being assignable to the free Ph3P;similarly in the spectrum of 2 recorded at 218 K fourpeaks appeared, one of these signals being due to thefree triorgano-phosphine, which rapidly converts to itsoxidised form.

Crystal structure of complex 1 has been determinedby X-ray crystallographic analysis [12,13], as shown inFig. 1. This is the first complex of this new ligand ana-logue of Tp to be structurally characterised and the firstcomplex of copper(I) with a PCuðON2Þ arrays. The

Scheme 1.

Fig. 1. Crystal structure of ½CuðPh3PÞ(Tpms)] showing the atom

numbering schemes, with thermal ellipsoid drawn at 50% level.

432 C. Santini et al. / Inorganic Chemistry Communications 5 (2002) 430–433

structure consists of a heteroscorpionate ligand bondedto the copper centre through two nitrogen atoms fromthe pyrazolyl rings and the oxygen from the sulfonatogroup. The third pyrazolyl ring acts as a pendant un-coordinated pyrazolate group. In addition the coppercentre is coordinated to one phosphorus atom of thePh3P co-ligand; with this disposition the coordinationgeometry around the copper atom is best described as atrigonally distorted tetrahedron. The Cu(1)–P(1) bonddistance is 2.147(1) �AA with P(1)–Cu(1)–N(1), P(1)–Cu(1)–N(3) and P(1)–Cu(1)–O(1) angles of 134.32(7),131.55(6) and 113.98(8)�, respectively. The two distancesCu(1)–N(1) and Cu(1)–N(3) are 2.003(3) and 2.032(2) �AA,respectively. The intraligand N(3)–Cu–N(1) angle is re-strained by the chelate rings to 90.1(1)�, and the averageangles from these nitrogen atoms to the Ph3P donoratom open to 133�. These values are comparable tothose previously reported in (unidentate phos-phine)(bidentate pyrazolate)metal(I) arrays of the type½Tp�MIðR3PÞn ðMI ¼ CuI or AgI; n ¼ 1 or 2; Tp ¼ bis-or tetrakis(pyrazolyl)borate) [14]. The Cu–O bond dis-tance (2.341(3) �AA) is significantly longer that the meanvalue observed in complexes containing CuI–OSO2

(2.136 �AA) [15], CuI–ONO2 (2.11 �AA) [16] as well as incopper(I) complexes containing O-donors ligands [17].

In view of our result the Tpms ligand can exhibitdifferent donor/acceptor properties, in comparison withthe analogous poly(pyrazolyl)borate ligands, havinggreat potential for tuning the electron density at themetal centre and hence the redox properties, a factorwhich is of great importance when exploiting the coor-dination chemistry of compounds in catalysis and en-zyme models.

Acknowledgements

We are grateful to the University of Camerino and‘‘CARIMA Foundation’’ for financial support.

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