Lanthanocene Chemistry with [CpR]-, [Cpt]-, [Cptt]-, and[CpR′

2SiMe2]2- Ligands: Synthesis and Characterizationof Bis(cyclopentadienyl)lanthanide(III) Halides andBis(cyclopentadienyl)lanthanide(II) Complexes and

Crystal Structures of [{NdCpR2(µ-Cl)}2], [{TmCptt

2(µ-I)}2],and [Yb(CpR′

2SiMe2)(THF)2] (CpR ) η5-C5H4{CH(SiMe3)2},Cpt ) η5-C5H4(SiMe2But), Cptt ) η5-C5H3(SiMe2But)2-1,3,

and CpR′ ) η5-C5H3{CH(SiMe3)2}-3)Peter B. Hitchcock, Michael F. Lappert,* and Shun Tian

The Chemistry Laboratory, University of Sussex, Brighton BN1 9QJ, U.K.

Received April 11, 2000

The bis(substituted cyclopentadienyl)lanthanide(III) halides [{LnCpR2(µ-Cl)}2] (Ln ) Pr,

Nd, Sm, Dy, Tb, Y), [{LnCptt2(µ-X)}2] (X ) Cl, Ln ) La, Nd; X ) I, Ln ) Tm), and [Nd-

(CpR′2SiMe2)(µ-Cl)}2] and bis(substituted cyclopentadienyl)lanthanide(II) complexes [LnCpR

2-(THF)2] (Ln ) Sm, Eu, Yb), [YbCpt

2(THF)2], [LnCptt2(THF)2] (Ln ) Sm, Yb), LnCpR

2 (Ln )Sm, Eu, Yb), YbCpt

2, LnCptt2 (Ln ) Sm, Yb), and [Yb(CpR′

2SiMe2)(THF)2] (CpR ) η5-C5H4-{CH(SiMe3)2}, Cpt ) η5-C5H4(SiMe2But), Cptt ) η5-C5H3(SiMe2But)2-1,3 and CpR′ ) η5-C5H3-{CH(SiMe3)2}-3) have been synthesized from the appropriate LnCl3, TmI3, or LnI2 with theselected sodium or potassium cyclopentadienide. The complexes were characterized by 1H,13C, 29Si, and 171Yb (for Yb(II) complexes) NMR spectroscopy, elemental analysis, and massspectrometry. The molecular structures of [{NdCpR

2(µ-Cl)}2], [{TmCptt2(µ-I)}2], and [Yb(CpR′

2-SiMe2)(THF)2] have been determined by single-crystal X-ray diffraction studies. Attemptsto reduce the complexes [{NdCpR

2(µ-Cl)}2], [{NdCptt2(µ-Cl)}2], and [{TmCptt

2(µ-I)}2] aredescribed.

Introduction

The bis(cyclopentadienyl)lanthanide(III) halides andbis(cyclopentadienyl)lanthanide(II) complexes haveproved to be useful organolanthanide complexes,1 beingimportant precursors for a variety of lanthanocene(III)derivatives, such as alkyls, hydrides, and amides, whichhave been shown to exhibit unique characteristics ascatalysts in hydrogenation,2 oligomerization,3 polymer-ization,4 hydroamination,5 hydrosilylation,6 silanolyticchain transfer,7 and hydroboration.8 The lanthanocene-(II) complexes have been shown to be single-electron

reducing agents and are widely used in organic synthe-sis.9,10 The stability, solubility, and reactivities of thelanthanocene catalysts are dramatically influenced bythe modification of cyclopentadienyl ligands; cyclopen-tadienyl-free organolanthanide complexes have alsobeen studied extensively.1d In the past, we have exten-sively investigated 1,3-bis(trimethylsilyl)cyclopentadi-enyl (Cp′′)-based lanthanide chemistry. We have re-cently developed a series of new (Me3Si)2CH- andButMe2Si-substituted cyclopentadienyl ligands as theiralkali-metal compounds11 and synthesized the corre-sponding bis- and tris(cyclopentadienyl)thorium andtris(cyclopentadienyl)lanthanide(III) complexes.12 Aspreviously mentioned,11 the steric bulk exerted byelectron-withdrawing SiMe3 or SiMe2But groups is animportant effect, as is the superior solubility in nonpolarsolvents and often the crystallinity of their metalcomplexes. The new ansa-bridged ligand [CpR′

2SiMe2]2-,known only as the (K+)2 salt,11 has not previously been

(1) For recent leading organolanthanide reviews, see: (a) Anwander,R.; Herrmann, W. A. Top. Curr. Chem. 1996, 179, 1. (b) Edelmann, F.T. Top. Curr. Chem. 1996, 179, 247. (c) Edelmann, F. T.; Abel, E. W.;Stone, F. G. A.; Wilkinson, G.; Eds. Comprehensive OrganometallicChemistry, 2nd ed.; Lappert, M. F., Ed.; Pergamon: Oxford, U.K., 1995;Vol. 4, Chapter 2. (d) Edelmann, F. T. Angew. Chem., Int. Ed. Engl.1995, 34, 2466. (e) Schumann, H.; Meese-Marktscheffel, J. A.; Esser,L. Chem. Rev. 1995, 95, 865. (f) Schaverien, C. J. Adv. Organomet.Chem. 1994, 36, 283. (g) Molander, G. A. Chemtracts: Org. Chem. 1998,11, 237.

(2) (a) Roesky, P. W.; Denninger, U.; Stern, C. L.; Marks, T. J.Organometallics 1997, 16, 4486. (b) Molander, G. A.; Hoberg, J. O. J.Org. Chem. 1992, 57, 3266. (c) Jeske, G.; Lauke, H.; Mauermann, H.;Schumann, H.; Marks, T. J. J. Am. Chem. Soc. 1985, 107, 8111. (d)Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem.Soc. 1983, 105, 1401.

(3) (a) Thompson, M. E.; Baxter, S, M.; Bulls, A. R.; Burger, B. J.;Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am.Chem. Soc. 1987, 109, 203. (b) Piers, W. E.; Bercaw, J. E. J. Am. Chem.Soc. 1990, 112, 9406. (c) den Hann, K. H.; Wielstra, Y.; Teuben, J. H.Organometallics 1987, 6, 2053. (d) Jeske, G.; Schock, L. E.; Swepston,P. N.; Schumann, H.; Marks, T. J. J. Am. Chem. Soc. 1985, 107, 8103.(e) Heeres, H. J.; Teuben, J. H. Organometallics 1991, 10, 1980.

(4) (a) Watson, P. L. J. Am. Chem. Soc. 1983, 105, 6491. (b) Watson,P. L.; Roe, D. C. J. Am. Chem. Soc. 1982, 104, 6471. (c) Schaverien, C.J. Organometallics 1994, 13, 69. (d) Piers, W. E.; Shapiro, P. J.; Bunel,E. E.; Bercaw, J. E. Synlett 1990, 2, 74. (e) Shapiro, P. J.; Bunel, E.;Schaefer, W. P.; Bercaw, J. E. Organometallics 1990, 9, 867. (f) Marsh,R. E.; Schaefer, W. P.; Coughlin, E. B.; Bercaw, J. E. Acta Crystallogr.1992, C48, 1773. (g) Giardello, M. A.; Yamamoto, Y.; Brard, L.; Marks,T. J. J. Am. Chem. Soc. 1995, 117, 3276. (h) Yasuda, H.; Yamamoto,H.; Yokota, K.; Miyake, S.; Nakamura, A. J. Am. Chem. Soc. 1992,114, 4908. (i) Yang, X.; Seyam, A. M.; Fu, P.-F.; Marks, T. J.Macromolecules 1994, 27, 4625. (j) Yasuda, H.; Ihara, E. Macromol.Chem. Phys. 1995, 196, 2417. (k) Ihara, E.; Nodono, M.; Yasuda, H.Macromol. Chem. Phys. 1996, 197, 1909.

3420 Organometallics 2000, 19, 3420-3428

10.1021/om000305m CCC: $19.00 © 2000 American Chemical SocietyPublication on Web 07/21/2000

used with a wider range of metals (CpR′ ) η-C5H3{CH-(SiMe3)2}-3). We now report the synthesis and charac-terization of various bis(cyclopentadienyl)lanthanide(III)halides (1-10) and bis(cyclopentadienyl)lanthanide(II)derivatives (11-23) with these ligands, including theX-ray structures of three representative complexes.Among the Ln(II) complexes are six ytterbocene(II)compounds (13, 14, 16, 19, 22, and 23) for which 171Yb-{1H} NMR spectroscopic chemical shifts are reportedand compared with those of related compounds in theliterature.

Results and Discussion

Synthesis and Characterization of the Lantha-nocene(III) Halides 1-10. Reaction of the anhydrouslanthanide(III) chloride with 2 equiv of potassium [bis-(trimethylsilyl)methyl]cyclopentadienide (≡KCpR) orbis(tert-butyldimethylsilyl)cyclopentadienide (≡KCptt) intetrahydrofuran and subsequent sublimation underhigh vacuum afforded the crystalline, dimeric lanthano-cene(III) chlorides [{LnCpR

2(µ-Cl)}2] (1-6) and [{Ln-Cptt

2(µ-Cl)}2] (7, 8) in good yields (eqs 1 and 2).One of our objectives (not yet realized) was to syn-

thesize organothulium(II) complexes, by using stericallydemanding substituted cyclopentadienyl ligands andlarge ancillary halides or chalcogenides. A potential Tm-(III) precursor, [{TmCptt

2(µ-I)}2] (9), was synthesized byreaction of thulium(III) iodide and KCptt in THF andsubsequent sublimation (eq 3).

Treatment of NdCl3 with 1 equiv of K2[CpR′2SiMe2]

(CpR′ ≡ C5H3CH(SiMe3)2-3) in THF and subsequentsublimation yielded the green ansa-bridged bis(cyclo-pentadienyl)neodymium(III) chloride 10 (eq 4). The 1HNMR spectrum of 10 in toluene-d8 was too complicatedto be readily assigned, possibly due to the formation oftwo isomers, chelating (a) and bridging (b). However,elemental analysis and mass spectrometry confirmedthe above formulation.

The CpR-substituted complexes 1-6 were sparinglysoluble in CHCl3 and CH2Cl2, and even in benzene ortoluene but were very soluble in THF or pyridine,causing cleavage of the bridging Cl-Ln bonds. The CpR

lanthanocenes 7-9 were much less soluble, beinginsoluble in hydrocarbons such as hexane, benzene, andtoluene and only sparingly soluble in THF or pyridine.

An attempt to synthesize [{EuCpR2(µ-Cl)}2] by reac-

tion of EuCl3 with 2 equiv of KCpR in THF led insteadto the europocene(II) complex [EuCpR

2(THF)2] (12).Complexes 1-10 were characterized by C and H

elemental analysis and mass spectrometry. The dia-magnetic compounds 6 and 7 and the early-lanthanideparamagnetic complexes 1-3 and 8 were additionallyidentified by 1H NMR spectroscopy. Like their homo-leptic analogues12 [NdCpR

3], [SmCpR3], and [NdCptt

3],the paramagnetic Nd(III) and Sm(III) complexes gavevery sharp 1H NMR signals, although the chemicalshifts deviated substantially from those in the diamag-netic analogues 6 and 7. Because of the extremely lowsolubility of complexes 7 and 8 in toluene or CDCl3, their1H and 13C NMR spectra were measured in C5D5Nsolution, probably forming [LnCptt

2Cl(py-d5)] (La ) La,Nd). In the 1H NMR spectrum of the Nd compound 8, a

(5) (a) Gagne, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc.1992, 114, 275. (b) Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1996, 118,9295. (c) Giardello, M. A.; Conticello, V. P.; Brard, L.; Gagne, M. R.;Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10241. (d) Gagne, M. R.;Brard, L.; Conticello, V. P.; Giardello, M. A.; Stern, C. L.; Marks, T. J.Organometallics 1992, 11, 2003. (e) Li, Y.; Marks, T. J. Organometallics1996, 15, 3770. (f) Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1996, 118,707. (g) Molander, G. A.; Dowdy, E. D. J. Org. Chem. 1998, 63, 8983.(h) Arredondo, V. M.; McDonald, F. E.; Marks, T. J. J. Am. Chem. Soc.1998, 120, 4871. (i) Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1998, 120,1757. (j) Roesky, P. W.; Stern, C. L.; Marks, T. J. Organometallics 1997,16, 4705. (k) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J.Organometallics 1999, 18, 2568. (l) Arredondo, V. M.; Tian, S.;McDonald, F. E.; Marks, T. J. J. Am. Chem. Soc. 1999, 121, 3633.

(6) (a) Molander. G. A.; Retsch, W. H. Organometallics 1995, 14,4570. (b) Fu, P.-F.; Brard, L.; Li, Y.; Marks, T. J. J. Am. Chem. Soc.1995, 117, 7157. (c) Molander, G. A.; Julius, M. J. Org. Chem. 1992,57, 6347. (d) Sakakura, T.; Lautenschlager, H.-J.; Tanaka, M. J. Chem.Soc., Chem. Commun. 1991, 40.

(7) (a) Fu, P.-F.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 10747.(b) Koo, K.; Fu, P.-F.; Marks, T. J. Macromolecules 1999, 32, 981.

(8) (a) Harrison, K. N.; Marks, T. J. J. Am. Chem. Soc. 1992, 114,9220. (b) Bijpost, E. A.; Duchateau, R.; Teuben, J. H. J. Mol. Catal. A,Chem. 1995, 95, 121.

(9) For recent reviews on organolanthanides in organic synthesis,see: (a) Kobayashi, S., Ed. Lanthanides: Chemistry and Use in OrganicSynthesis; Springer: Berlin, 1999. (b) Imamoto, T., Ed. Lanthanidesin Organic Synthesis; Academic Press: London, 1994. (c) Molander,G. A.; Harris, C. R. Chem. Rev. 1996, 96, 307.

(10) Nair, V.; Mathew, J.; Prabharan, J. Chem. Soc. Rev. 1997, 127.(11) Edelman, M. A.; Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S.;

Tian, S. J. Organomet. Chem. 1998, 550, 397.(12) Al-Juaid, S.; Gun’ko, Y. K.; Hitchcock, P. B.; Lappert, M. F.;

Tian, S. J. Organomet. Chem. 1999, 582, 143.

Lanthanocene Chemistry with Cp Ligands Organometallics, Vol. 19, No. 17, 2000 3421

singlet at δ 5.72 is assigned to But protons; the threeCp ring protons appeared at δ 29.93 (1H) and -10.08(2H), while the Me2Si protons appeared as a pair ofsinglets at δ -2.02 and -6.10, corresponding to themagnetically inequivalent methyls on the Me2Si group.Splitting of the dimethylsilyl proton signals has alsobeen observed in other metal-Cptt complexes: [LiCptt-(TMEDA)],11 [SmCptt

2(THF)2] (15), [YbCptt2(THF)2] (16),

YbCpt2 (20), SmCptt

2 (21), and YbCptt2 (22) (see below).

The conformation of the (Cptt)- ligand, showing twomagnetically inequivalent methyl protons, is depictedin Figure 1.

The EI-MS spectra of [{LnCpR2(µ-Cl)}2] (1-6) re-

vealed them to be dimeric, the molecular ions [M]+ beingof relatively low intensity. Each of the bis(cyclopenta-dienyl)lanthanide chlorides showed the typical frag-ments [M - Cl]+, [M - CpR]+, [LnCpR

2]+, and [SiMe3]+.The lanthanocenes containing the [Cptt]- ligand were

less soluble in hydrocarbons and more air-stable thanthose containing [C5H3(SiMe3)2-1,3]- (≡Cp′′-) or [CpR]-

ligands. For instance, [{NdCptt2(µ-Cl)}2] (8) was in-

soluble in toluene and stable in air for several minutes(the green color did not change), while [{NdCpR

2(µ-Cl)}2](2) and [{NdCp′′2(µ-Cl)}2] were slightly soluble in tolu-ene and decomposed in air within 1 min. The enhancedstability of the Cptt-containing compounds is also evi-dent in organothorium(III) chemistry; thus, [ThCp′′3]13

and [ThCpR3]14 were extremely soluble in hexane or

toluene and very air-sensitive, immediately decompos-ing upon exposure to air within 1 s both in solution andin the solid, as evidenced by the disappearance of theirdeep blue color (which we regard as among the most

air-sensitive organometallic compounds we have en-countered), while [ThCptt

3]14 was less soluble in diethylether, hexane, or toluene and considerably more stablein air. The deep blue color of the solid [ThCptt

3] persistedin air for ca. 10 min! This is attributed to the greaterbulk of the [Cptt]- ligand. Thus, it is likely that it maybe serve as a useful ligand in a wider context.

Synthesis and Characterization of the Lantha-nocene(II) Complexes 11-23. The solvated bis(sub-stituted cyclopentadienyl)lanthanide(II) complexes weresynthesized by the reaction of the lanthanide(II) iodidewith the appropriate sodium or potassium cyclopenta-

(13) Blake, P. C.; Lappert, M. F.; Atwood, J. L.; Zhang, H. J. Chem.Soc., Chem. Commun. 1986, 1148.

(14) Tian, S. D. Philos. Thesis; University of Sussex, 1994.

Figure 1. Conformation of the [Cptt]- ligand showing two magnetically inequivalent methyl protons; the metal atom ispositioned above the center of the C5 ring.

3422 Organometallics, Vol. 19, No. 17, 2000 Hitchcock et al.

dienide in tetrahydrofuran. Subsequent sublimationunder high vacuum afforded the solvent-free bis(cyclo-pentadienyl)lanthanide(II) products (eq 5). Interest-

ingly, the solvent-free ytterbocenes YbCpR2 (19) and

YbCptt2 (22) were very soluble in benzene or toluene.

In contrast, YbCpt2 (20) was only soluble in THF or

pyridine; the state of molecular aggregation of 17-22was not determined; each except 20 (which also has thehighest sublimation temperature) is probably a mono-mer in solution but may be a loosely bound polymer inthe solid state, as has been established previously for[Yb{η5-C5H3(SiMe3)2-1,3}2]∞

15 and [Yb(η5-C5Me5)2]∞.16

Compounds 11, 13-16, and 19-22 gave satisfactoryC and H elemental analysis; 1H and 13C{1H} NMRspectroscopy revealed the number of THF moleculescoordinated to the metal center (0 or 2). The diamagneticYb(II) complexes have been additionally characterizedby 171Yb and 29Si{1H} NMR spectroscopy. Since samari-um(II) has a 4f6 electronic ground-state configurationand its complexes are paramagnetic, NMR spectroscopyof samarocene(II) complexes has two features: (i) largechemical shifts of the observable NMR signals and (ii)significant line-broadening effects. The 1H NMR spectraof 11, 15, and 21 showed broad signals that weresubstantially shifted compared with the values for theirdiamagnetic analogues 13, 16, and 22. As for 11, the

Me3Si groups appeared as a broad singlet at δ 9.64 andthe methyne proton at δ 3.62. The ring protons wereobserved at δ 5.54 and 22.17 for the two groups of twoequivalent protons. The peaks due to THF appeared atδ -0.64 and -1.44. In the 1H NMR spectrum of 15, theMe2Si protons signals were split into two at δ 9.00 and15.28. Two signals, at δ -8.82 and 12.69 (integrated as1:2), are assigned to the cyclopentadienyl ring protons.The THF protons were found at δ -1.01 and 1.87.

Since Yb2+ has a 4f14 electronic ground-state config-uration and, hence, its complexes are diamagnetic, the1H and 13C NMR spectra of compounds 13, 14, 16, 19,and 20 were unexceptional. Ytterbium is unique in thatits spin 1/2 isotope (171Yb) has a relatively high naturalabundance (14.27%) and the 171Yb nucleus has a recep-tivity 4 times greater than that of the 13C nucleus. Thesetwo features make possible the high-resolution directNMR spectral observation of 171Yb in the +2 oxidationstate, as originally established for ytterbium(II) amidoand pentamethylcyclopentadienyl complexes in 1989.17

Several ytterbocene(II) alkoxide, aryloxide, alkyl, amide,â-diketiminate, 1-azaallyl and stannyl complexes havebeen studied by 171Yb NMR spectroscopy.18 A review of171Yb solution state NMR spectroscopic chemical shiftswas published in 1996.19 A later paper by the sameauthors, Keates and Lawless,20 noted that such datawere then (1997) available for more than 200 organicytterbium(II) complexes, with δ(171Yb) ranging from+2500 to -500, with [Yb(η5-C5Me5)2(THF)] (δ 0) asstandard.17 It was further observed that the isotropicchemical shifts of π-bonded cyclopentadienyl derivativesare of low frequency compared with those containingσ-bonded ligands;19,20 this is consistent with our data,summarized in Table 1, together with literature valuesfor other ytterbocene(II) complexes. Each complex of theformula [YbCpx

2(THF)2] (Cpx ) CpR (13), Cpt (14)), like[Yb{η5-C5H3(SiMe3)2-1,3}2(THF)] in THF, has a δ(171Yb)value of 154 ( 20 at ambient temperature. It appearsthat 16, having the bulkiest [Cpx]- ligand ([Cptt]-), isunder these conditions largely neutral donor (THF)-free,the δ value being almost identical with that in thehomoleptic complex 22.

The europium(II) complexes [EuCpR2(THF)2] (12) and

EuCpR2 (18) were characterized by C and H elemental

analysis and IR spectroscopy. The 1H NMR spectralsignals of 12 and 18 were too broad to be assignedbecause of the significant paramagnetic effect of Eu-(II). The IR spectrum of 12 showed bands at 1031, 927,and 840 cm-1, assigned to coordinated THF.

Although Me2Si-bridged bis(cyclopentadienyl)metalcomplexes (known as ansa-metallocenes) of group 4elements and lanthanides(III) are well-known, ansa-lanthanocene(II) complexes are very rare. We now

(15) Hitchcock, P. B.; Howard, J. A. K.; Lappert, M. F.; Prashar, S.J. Organomet. Chem. 1992, 437, 177.

(16) Burns, C. J. Ph.D. Thesis, University of California, Berkeley,CA, 1987.

(17) Avent, A. G.; Edelman, M. A.; Lappert, M. F.; Lawless, G. A.J. Am. Chem. Soc. 1989, 111, 3423.

(18) (a) Hitchcock, P. B.; Lappert, M. F.; Tian, S. J. Organomet.Chem. 1997, 549, 1. (b) van den Hende, J. R.; Hitchcock, P. B.; Holmes,S. A.; Lappert, M. F.; Tian, S. J. Chem. Soc., Dalton Trans. 1995, 3933.(c) Hitchcock, P. B.; Holmes, S. A.; Lappert, M. F.; Tian, S. J. Chem.Soc., Chem. Commun. 1994, 23, 2691. (d) Keates, J. M.; Lawless, G.A. Organometallics 1997, 13, 2842. (e) van den Hende, J. R.; Hitchcock,P. B.; Lappert, M. F. J. Chem. Soc., Dalton Trans. 1995, 2251. (f) vanden Hende, J. R.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc., Chem.Commun. 1994, 1413.

(19) Keates, J. M.; Lawless, G. A. In Advanced Applications of NMRto Organometallic Chemistry; Gielen, M., Willem, R., Wrackmeyer, B.,Eds.; Wiley: Chichester, U.K., 1996; Chapter 12, pp 357-370.

(20) Keates, J. M.; Lawless, G. A. Organometallics 1997, 16, 2842.

Lanthanocene Chemistry with Cp Ligands Organometallics, Vol. 19, No. 17, 2000 3423

describe [Yb(CpR′2SiMe2)(THF)2] (23), which was syn-

thesized by the reaction of ytterbium(II) iodide with K2-(CpR′

2SiMe2) in tetrahydrofuran (eq 6). Complex 23 was

crystallized from toluene as red needles. It was char-acterized by 1H, 13C{1H}, 29Si{1H}, and 171Yb NMRspectroscopy. Successful elemental analysis data werenot obtained, possibly due to the ready loss of thecoordinated THF when the analysis was performed. Themolecular structure of 22 was determined by single-crystal X-ray diffraction.

Attempted Reduction of [{NdCpR2(µ-Cl)}2] (2),

[{NdCptt2(µ-Cl)}2] (8), and [{TmCptt

2(µ-I)}2] (9). Weare interested in organolanthanide(II) chemistry in theunusual oxidation state +2 for 4f elements other thanthe classic Eu(II), Sm(II), and Yb(II)12 and recently havereported the first thermally stable, crystalline, subva-lent organolanthanum compound, formulated as a La-(II) complex.21 We have also described attempts toreduce the Ln(III) compounds [NdCpR

3], [NdCptt3], [Nd-

{η5-C5H3(SiMe3)2-1,3}3], and [TmCpR3]12 with K or Li in

THF.12 The case of Tm(II) is noteworthy, in part becausea Tm(II) complex might have the potential of providingaccess to organothulium(I) compounds; the 169Tm nucleusis NMR active (169Tm (f 14), I ) 1/2, natural abundance100%).22

Reduction of [{NdCpR2(µ-Cl)}2] (2) or [{NdCptt

2(µ-Cl)}2] (8) with potassium in THF yielded a dark brownsolution, which gradually decomposed to precipitate the

black Nd metal and the appropriate tris(cyclopentadi-enyl)neodymium(III) complex (eq 7). Addition of a

neutral donor ligand, such as DME, TMEDA, PMDETA,or [18]-crown-6, to the reaction systems failed to stabi-lize the presumed Nd(II) intermediates. The dark brownprecipitate from 2 may have been an ionic species, sinceit was insoluble in pentane or hexane, sparingly solublein toluene, and very soluble in THF. Attempts tostabilize and isolate a Nd(II) species by adding [NBun

4]-[BF4] to the “reduced” reaction mixture from 2 were alsounsuccessful.

The reaction of the yellow [{TmCptt2(µ-I)}2] (9) with

potassium in THF gave a brown solution. As in theneodymium systems, the latter was unstable and readilydecomposed, yielding a black precipitate, presumed tobe Tm. Attempted stabilization of a Tm(II) compound,using procedures similar to those described above forNd(II), were unsuccessful.

X-ray Crystal Structures of Complexes 2, 9, and23. X-ray-quality single crystals were obtained by slowsublimation of [{NdCpR

2(µ-Cl)}2] (2) or [{TmCptt2(µ-I)}2]

(9) under high vacuum or by recrystallization of [Yb-(CpR′

2SiMe2)(THF)2] (23) from toluene. The molecularstructures and atom-numbering schemes of 2, 9, and23 are shown in Figures 2-4, respectively. Selectedbond distances and angles are presented in Table 2.

The crystalline complex 2 is a centrosymmetric dimer.The two neodymium atoms, each with two η5-bondedcyclopentadienyl groups, are bridged by two chlorides.The Nd-Cl bond lengths of 2.805(1) and 2.786(1) Å areslightly shorter than those in [{Nd(C5H3But

2-1,3)2(µ-Cl)}2]23 (2.837(1) and 2.841(1) Å). The Nd-C(Cp) dis-tances are within the range 2.826-2.671 Å, averaging2.733 Å. Each neodymium atom is at the center of adistorted tetrahedron, with the centroids of the two Cp

(21) Cassani, M. C.; Duncalf, D. J.; Lappert, M. F. J. Am. Chem.Soc. 1998, 121, 12958.

(22) Harris, R. K.; Mann, B. E. NMR and The Periodic Table;Academic Press: London, 1978.

(23) Marks, T. J.; Grynkewich, G. W. Inorg. Chem. 1976, 15, 1302.

Table 1. Solution 171Yb{1H} NMR SpectroscopicChemical Shifts (δ) for Ytterbocene(II) Complexes

13, 14, 16, 19, 22, and 23 and Related Complexes

compd171Yb{1H}

(T/K) solvent

[YbCpR2(THF)2] (13) 134.5 (304) PhH

[YbCpt2(THF)2] (14) 157.5 (298) PhMe-PhH

[YbCptt2(THF)2] (16) -7.06 (298) PhMe-PhH

YbCpR2 (19) 118.7 (295) PhMe-PhH

YbCptt2 (22) -7.02 (304) PhMe-PhH

[Yb{CpR′2SiMe2}(THF)2] (23) 306.3 (304) PhMe-PhH

[Yb{η5-C5H3(SiMe3)2-1,3}2(THF)]a 172.0 (304) THF-PhMe[Yb{η5-C5H3(SiMe3)2-1,3}2]∞a -15.7 (297) PhMe[YbCp*2(THF)2]b 0.0 (296) THF[YbCp*2(OEt2)2]b 26 (308) Et2O[YbCp*2(NC5H5)2]c 949 (338) C5H5N[YbCp*2(DME)]d 98 (298) DME-C6H6[YbCp*2]∞e -3.3 (298) PhMe[Yb(η5-C5Me4H)2(THF)2]c 131 (298) THF[Yb{η5-C5Me4(SiMe3)]2(THF)]c 6 (298) THF[Yb{η5-C5Me4(SiMe2But)}2]c 20 (298) C6H11Me-c

a Reference 15. b Reference 17. c Reference 20. d Duncalf, D. J.D. Philos. Thesis, University of Sussex. e Keates, J. M; Lawless,G. A.; Waugh, M. P. J. Chem. Soc., Chem. Commun. 1996, 1627.

Table 2. Selected Intramolecular Bond Distances(Å) and Angles (deg) with Estimated Standard

Deviations for [{NdCpR2(µ-Cl)}2] (2) and

[{TmCptt2(µ-I)}2] (9)

2 9

Bond Distancesa

Ln-X 2.805(1) 3.045(1)Ln-X′ 2.786(1) 3.050(1)Ln-Cp1 2.446 2.33Ln-Cp2 2.455 2.34

Bond AnglesCp1-Ln-Cp2 128.9 131.5X-Ln-X′ 76.76(3) 82.88(3)Ln-X-Ln′ 103.24(3) 97.12(3)

a Cp1 and Cp2 represent the centroids of the two cyclopenta-dienyl rings attached to the Ln atom.

3424 Organometallics, Vol. 19, No. 17, 2000 Hitchcock et al.

rings and two chlorides forming the apexes. The ClNd-Cl′Nd core is rhomboidal with the angle at the Nd atomssmaller (76.76(3)°) than that at Cl (103.24(3)°). Someother structurally characterized dinuclear bis(cyclopen-tadienyl)neodymium chlorides are [{Nd(η5-C5H5)2(THF)-(µ-Cl)}2],24 [Nd{η5-C5H3(SiMe3)2-1,3}2(µ-Cl)2Li(THF)2],25

and [Nd{(η5-C5H4)2SiMe2}2(µ-Cl)3Li(THF)2].3d

The structure of crystalline 9 is very similar to thatof 2, being a diiodide-bridged symmetric dimer. Weinitially expected that the molecule might be a mono-

mer, due to the bulky [Cptt]- and I- ligands, as well asthe small size of Tm(III). The Tm-I bond lengths are3.045(1) and 3.050(1) Å. The distances between each Tmand the two cyclopentadienyl centroids (Cp) are 2.33 and2.34 Å, respectively. The Cp-Tm-Cp′ angle of 131.5°in 9 is slightly larger than the Cp-Nd-Cp angle of128.9° in 2.

Although several ansa-lanthanocene(III) halides,alkyls, alkoxides, and amides have been reported,ansa-lanthanocene(II) complexes are rare. Struc-turally characterized examples of the former include[Yb{(η5-C5H3But)2CMe2-3}(µ-Cl)2Li(OEt2)2],26 [Yb{(η5-C5H3SiMe3)2SiMe2-3}Cl(THF)],26 [(Yb{(η5-C5H3But)2CMe2-3}(µ-OMe))2],26 [(Yb{(η5-C5H4)2SiMe2}(µ-X))2] (X ) Cl,27

Br28), [Yb{(η5-C5H3SiMe3)2CMe2-3}(µ-Cl)2Li(OEt2)],29 [Sm-{(η5-C5H3But)2(Me2SiOSiMe2)}(THF)2],4k [Sm{(η5-C5H2(Si-Me3)2-1,3)2SiMe2-5}(µ-Cl)2Li(THF)2],4j [Sm{(η5-C5H2(Si-Me3)2-1,3)2SiMe2-5}CH(SiMe3)2],4j [Nd{(η5-C5Me4)2Si-Me2}CH(SiMe3)2],3d [(Nd{(η5-C5Me4)2SiMe2})2(µ-Cl)3Li-(THF)2],3d [Lu{(η5-C5H4)(η5-C5Me4)SiMe2}CH(SiMe3)2],30

[Sm{(η5-C5Me4)(η5-C5H3R*)ESiMe2}CH(SiMe3)2],31 and[Y{(η5-C5Me4)(η5-C5H3R*)ESiMe2}CH(SiMe3)2]31 (R* )neomenthyl, menthyl, E ) CH, N). The few structurallycharacterized Ln(II) analogues are rac-[Sm{(η5-C5H2-(But)(SiMe3)-2,4)SiMe2}(THF)2]4j and the indenyl com-

(24) Jin, Z.; Liu, Y.; Chen, W. Sci. Sin., Ser. B 1987, 30, 1136.(25) Lappert, M. F.; Singh, A.; Atwood, J. L.; Hunter, W. E. J. Chem.

Soc., Chem. Commun. 1981, 1191.

(26) Khvostov, A. V.; Belsky, V. K.; Bulychev, B. M.; Sizov, A. I.;Ustinov, B. B. J. Organomet. Chem. 1999, 571, 243.

(27) Hock, N.; Oroschin, W.; Paolucci, G.; Fischer, R. D. Angew.Chem., Int. Ed. Engl. 1986, 25, 738.

(28) Akhnoukh, T.; Muller, J.; Qiao, K.; Li, X.-F.; Fischer, R. D. J.Organomet. Chem. 1991, 408, 47.

(29) Khvostov, A. V.; Belsky, V. K.; Sizov, A. I.; Bulychev, B. M.;Ivchenko, N. B. J. Organomet. Chem. 1998, 564, 5.

Figure 2. Molecular structure and atom-numbering schemefor [{NdCpR

2(µ-Cl)}2] (2).

Figure 3. Molecular structure and atom-numbering schemefor [{TmCptt

2(µ-I)}2] (9).

Figure 4. Molecular structure and atom-numbering schemefor [Yb(CpR′

2SiMe2)(THF)2] (23).

Lanthanocene Chemistry with Cp Ligands Organometallics, Vol. 19, No. 17, 2000 3425

plexes rac-[Yb{(η5-C9H6-1)(CH2)2(THF)2]32 and rac-[Yb-{(η5-C9H4Me2-4,7)2(CH2)2-1}(THF)2].32 The new meso-ytterbocene(II) compound 23 has a distorted-tetrahedralgeometry around the ytterbium atom, if each Cp ringis regarded as occupying a single coordination site: cf.the bond angles Cp-Yb-Cp′ (121.98(3)°), Cp-Yb-O(107.8(2)°), Cp-Yb-O′ (105.9(2)°), and O-Yb-O′ (106.5-(2)°). The molecule possesses a 2-fold axis extendingthrough the bridged Si(1) and ytterbium atoms. Theatoms C(6), C(6)′, Si(1), Yb, O, and O′ are coplanar. Asimplified bonding pattern is shown in Figure 5.

Experimental Section

General Considerations. All manipulations were carriedout under vacuum or argon using standard Schenk techniques.Solvents were dried and distilled over Na/K alloy under anatmosphere of nitrogen gas and were degassed prior to use byfreeze-pump-thaw cycling. The following compounds wereprepared by known procedures: LnCl3,33 TmI3,34 SmI2(THF)2,35

EuI2(THF)2,35 YbI2,36 KCpR,11 NaCpt,11 KCptt,11 and K2[CpR′2-

SiMe2].11 Others were purchased and purified by standardprocedures. Microanalyses were carried out by Medac Ltd.(Brunel University). NMR spectra were recorded with BrukerAC-250, WM-360, or AMX-500 instruments. Chemical shiftdata are shown in the following sequence: (i) SiMe3, CH(SiMe3)2,Cp, thf or (ii) CMe3, CMe3, SiMe2, thf. Mass spectra wererecorded on a VG Autospec mass spectrometer operating inthe EI mode at 70 eV. IR spectra were recorded as Nujol mullsbetween KBr plates, using a Perkin-Elmer 1720 FT spectrom-eter. The samples were prepared in a drybox under anatmosphere of nitrogen gas.

[{PrCpR2(µ-Cl)}2] (1). A solution of KCpR (2.5 g, 9.7 mmol)

in tetrahydrofuran (50 mL) was added to a stirred suspensionof PrCl3 (1.2 g, 4.85 mmol) in tetrahydrofuran (75 mL). Themixture was stirred at room temperature for 2 days, leavinga colorless solution and a white precipitate, which was filteredoff. Solvent was removed from the filtrate in vacuo to yield awhite solid, which was scraped from the side of the Schlenk

tube with a spatula and transferred to a horizontal sublimationtube. Sublimation at 280-300 °C/10-4 mmHg for 3 h affordedpale yellow crystals of compound 1 (2.16 g, 71.3%). Anal. Calcdfor C48H92Cl2Pr2Si8: C, 46.3; H, 7.44. Found: C, 45.8; H, 7.44.1H NMR (CDCl3, 20 °C): δ -13.58 (s, 18 H, SiMe3); 11.49 (s,1H, CH(SiMe3)2); 22.42 (s, 2H, Cp ring); 66.07 (s, 2H, Cp ring).MS: m/e 1247 ([M]+, 0.1%); 1232 ([M - Me]+, 0.9%); 1210 ([M- Cl]+, 11.5%); 1024 ([M - CpR]+, 10.0%); 588 ([CpR

2Ln]+,100%); 73 ([SiMe3]+, 61.0%).

[{NdCpR2(µ-Cl)}2] (2). The reaction of KCpR (2.1 g, 8.0

mmol) and NdCl3 (1.0 g, 3.99 mmol), using the proceduredescribed for 1, afforded green-blue crystals of compound 3(1.34 g, 53.4%). Anal. Calcd for C48H92Cl2Nd2Si8: C, 46.0; H,7.40. Found: C, 45.8; H, 7.49. 1H NMR (CDCl3, 20 °C): δ -7.33(s, 18 H, SiMe3); 3.47 (s, 1H, CH(SiMe3)2); 6.04 (s, 2H, Cp ring);25.82 (s, 2H, Cp ring). MS: m/e 1250 ([M]+, 0.001%); 1216 ([M- Cl]+, 0.001%); 1029 ([M - CpR]+, 0.23%); 590 ([CpR

2Ln]+,24%); 73 ([SiMe3]+, 100%).

[{SmCpR2(µ-Cl)}2] (3). The reaction of KCpR (1.6 g, 4.7

mmol) and SmCl3 (0.76 g, 2.96 mmol), using the proceduredescribed for 1, afforded orange crystals of compound 3 (1.28g, 68.5%). Anal. Calcd for C48H92Cl2Sm2Si8: C, 45.6; H, 7.33.Found: C, 44.9; H, 7.33. 1H NMR (CDCl3, 20 °C): δ -1.86 (s,18 H, SiMe3); 0.61 (s, 1H, CH(SiMe3)2); 12.13 (s, 2H, Cp ring);16.45 (s, 2H, Cp ring). MS: m/e 1266 ([M]+, 0.2%); 1251 ([M -Me]+, 0.1%); 1230 ([M - Cl]+, 0.25%); 1043 ([M - CpR]+, 1.1%);598 ([CpR

2Ln]+, 100%); 73 ([SiMe3]+, 70%).[{DyCpR

2(µ-Cl)}2] (4). The reaction of KCpR (1.0 g, 3.8mmol) and DyCl3 (0.51 g, 1.9 mmol), using the proceduredescribed for 1, afforded pale yellow crystals of compound 4(0.8 g, 65.4%). Anal. Calcd for C48H92Cl2Dy2Si8: C, 44.7; H,7.89. Found: C, 44.2; H, 7.20. MS: m/e 1289 ([M]+, 0.001%);1066 ([M - CpR]+, 0.12%); 608 ([CpR

2Ln]+, 18%); 73 ([SiMe3]+,100%).

[{TbCpR2(µ-Cl)}2] (5). The reaction of KCpR (1.0 g, 3.8

mmol) and TbCl3 (0.50 g, 1.9 mmol), using the proceduredescribed for 1, afforded colorless crystals of compound 5 (0.52g, 42.7%). Anal. Calcd for C48H92Cl2Tb2Si8: C, 44.9; H, 7.23.Found: C, 44.5; H, 7.28. MS: m/e 1283 ([M]+, 0.2%); 1283 ([M- Cl]+, 0.5%); 1247 ([M - Cl]+, 15.0%); 1060 ([M - CpR]+,0.05%); 606 ([CpR

2Ln]+, 85.0%); 73 ([SiMe3]+, 100%).[{YCpR

2(µ-Cl)}2] (6). The reaction of KCpR (2.97 g, 11.3mmol) and YCl3 (1.12 g, 5.7 mmol), using the proceduredescribed for 1, afforded colorless crystals of compound 6 (2.0g, 61.4%). Anal. Calcd for C48H92Cl2Y2Si8: C, 50.5; H, 8.12.Found: C, 51.0; H, 8.22. 1H NMR (CDCl3, 20 °C): δ 0.07 (s,18 H, SiMe3); 1.78 (s, 1H, CH(SiMe3)2); 6.02 (s, 2H, Cp ring);6.11 (s, 2H, Cp ring). MS: m/e 1142 ([M]+, 0.001%); 1127 ([M

(30) Stern, D.; Sabat, M.; Marks, T. J. J. Am. Chem. Soc. 1990, 112,9558.

(31) Giardello, M. A.; Conticello, V. P.; Brard, L.; Sabat, M.;Rheingold, A. L.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994,116, 10212.

(32) Khvostov, A. V.; Bulychev, B. M.; Belsky, V. K.; Sizov, A. I. J.Organomet. Chem. 1999, 584, 164.

(33) Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 24,387.

(34) (a) Haberle, N. Technol. Wiss. Abh. Osram Ges. 1973, 11, 285.(b) Haberle, N. Chem. Abstr. 1974, 81, 71961.

(35) Watson, P. L.; Tulip, T. H.; Williams, I. Organometallics 1990,9, 1999.

(36) Tilley, T. D.; Boncella, J. M.; Berg, D. J.; Burns, C. J.; Andersen,R. A. Inorg. Synth. 1990, 27, 146.

Figure 5. Simplified bonding pattern for complex 23 with selected bond distances (Å) and angles (deg).

3426 Organometallics, Vol. 19, No. 17, 2000 Hitchcock et al.

- Me]+, 0.01%); 1106 ([M - Cl]+, 1.5%); 919 ([M - CpR]+,1.4%); 536 ([CpR

2Ln]+, 100%); 73 ([SiMe3]+, 43.0%).Reaction of EuCl3 with KCpR. A solution of KCpR (1.23

g, 4.7 mmol) in tetrahydrofuran (50 mL) was added to a stirredsuspension of EuCl3 (0.6 g, 2.33 mmol) in tetrahydrofuran (100mL). As the first drop of KCpR solution was added, the solutionimmediately became blue and gradually changed to red-orangeupon completing the addition. The mixture was stirred at roomtemperature for 2 days and the resulting white precipitate wasfiltered off. Solvent was removed from the filtrate in vacuo,and the orange solid residue was extracted into pentane andfiltered. The filtrate was concentrated to ca. 5 mL. Cooling to-30 °C yielded orange crystals of [EuCpR

2(THF)2] (12; 0.8 g,46.2%). Anal. Calcd for C32H62EuO2Si4: C, 51.7; H, 8.41.Found: C, 50.7; H, 8.37. IR (Nujol, KBr): 3062 (w), 1278 (m),1125 (w), 1031 (m), 927 (m), 840 (s), 785 (w), 769 (w), 731 (m),677 (w), 657 (w) cm-1.

[{LaCptt2(µ-Cl)}2] (7). A solution of KCptt (1.2 g, 3.6 mmol)

in tetrahydrofuran (50 mL) was added to a stirred suspensionof LaCl3 (0.45 g, 1.83 mmol) in tetrahydrofuran (150 mL). Themixture was stirred at room temperature for 12 h, was refluxedfor 8 h, and then was filtered. Solvent was removed from thefiltrate in vacuo, leaving a white solid residue which waswashed with pentane (20 mL) and dried under vacuum. Thewhite solid was transferred to a horizontal sublimation tubeand was sublimed at 360 °C/10-4 mmHg for 4 h to yield whitecrystals of compound 7 (0.64 g, 51.7%). Anal. Calcd forC68H132I2La2Si8: C, 53.6; H, 8.73. Found: C, 52.7; H, 8.70. 1HNMR (C5D5N, 20 °C): δ 0.95 (s, 18 H, CMe3); 0.22 (s, 6H,SiMe2); -0.14 (s, 6H, SiMe2); 6.69 (s, 2H, Cp ring); 6.90 (s,1H, Cp ring).

[{NdCptt2(µ-Cl)}2] (8). The reaction of KCptt (2.0 g, 6.02

mmol) with NdCl3 (0.75 g, 3.0 mmol), using the proceduredescribed for 7, afforded blue crystals of compound 8 (1.3 g,56.6%). Anal. Calcd for C68H132I2Nd2Si8: C, 53.3; H, 8.67.Found: C, 53.1; H, 8.68. 1H NMR (C5D5N, 20 °C): δ 5.72 (s,18 H, CMe3); -6.10 (s, 6H, SiMe2); -2.02 (s, 6H, SiMe2); -10.08(s, 2H, Cp ring); 29.93 (s, 1H, Cp ring). MS: m/e 1532 ([M]+,0.001%); 1239 ([M - Cptt]+, 0.17%); 708 ([Cptt

2Nd - But]+,85%); 237 ([Cptt - But]+, 15%); 73 ([SiMe3]+, 100%).

[{TmCptt2(µ-I)}2] (9). The reaction of KCptt (4.3 g, 12.95

mmol) with TmI3 (3.1 g, 5.64 mmol), using the proceduredescribed for 7 except with a lower sublimation temperature(260 °C), afforded yellow crystals of compound 9 (1.3 g, 56.6%).Anal. Calcd for C68H132I2Tm2Si8: C, 46.2; H, 7.53. Found: C,46.0; H, 7.51.

[{Nd(CpR′2SiMe2)(µ-Cl)}2] (10). A solution of K2[CpR′

2-SiMe2] (0.6 g, 1.16 mmol) in tetrahydrofuran (50 mL) wasadded to a stirred suspension of NdCl3 (0.3 g, 1.19 mmol) intetrahydrofuran (100 mL). The mixture was stirred at roomtemperature for 2 days, was refluxed for 4 h, and then wasfiltered. Solvent was removed from the filtrate in vacuo,leaving a green solid, which was scraped from the side of theSchlenk flask with a spatula and transferred to a horizontalsublimation tube. Sublimation at 360 °C/10-4 mmHg yieldedgreen crystals of compound 10 (0.4 g, 50.5%). Anal. Calcd forC52H100Cl2Nd2Si10: C, 45.7; H, 7.38. Found: C, 45.5; H, 7.41.MS: m/e 1366 ([M]+, 0.5%); 1294 [M - Me3Si + 1]+, 0.65%);1086 [M - CpR - SiMe2]+, 5%); 646 [Nd(CpR′

2SiMe2)]+, 52%);73 ([SiMe3]+, 100%).

[SmCpR2(THF)2] (11). A solution of KCpR (1.5 g, 5.76 mmol)

in tetrahydrofuran (50 mL) was slowly added to a stirredsolution of SmI2(THF)2 (1.56 g, 2.85 mmol) in tetrahydrofuran(100 mL). The mixture was stirred at room temperature for36 h, leaving a purple solution and a white precipitate, whichwas filtered off. Solvent was removed from the filtrate in vacuo,yielding a purple solid which was extracted with toluene (50mL) and filtered. Toluene was removed from the filtrate invacuo, giving a green solid, which was redissolved in tetrahy-drofuran (5 mL) to yield a purple solution. The tetrahydrofuranwas carefully removed so as to retain the purple color of the

solid residue. Addition of pentane (20 mL) to the latter affordeda purple solution, the volume of which was reduced to ca. 5mL. Cooling to -30 °C yielded the purple crystalline compound11 (1.61 g, 76.3%). Anal. Calcd for C32H62O2Si4Sm: C, 51.8;H, 8.43. Found: C, 50.7; H, 8.43. 1H NMR (C6D6, 23 °C): δ9.64 (s, 18 H, SiMe3); 3.62 (s, 1H, CH(SiMe3)2); 5.42 (s, 2H, Cpring); 22.17 (s, 2H, Cp ring); -0.64 (s, 4H, THF); -1.44 (s, 4H,THF). 13C{1H} NMR (C6D6, 23 °C): δ -78.69; -77.64; -26.59;16.45; 25.14; 73.12; 120.70.

[EuCpR2(THF)2] (12). The reaction of KCpR (2.78 g, 1.06

mmol) and EuI2(THF)2 (2.75 g, 5.0 mmol), using the proceduredescribed for 11, afforded red-orange crystals of compound 12(2.36 g, 61.7%), identical with those from the reaction of EuCl3

with KCpR.[YbCpR

2(THF)2] (13). A solution of KCpR (1.5 g, 5.76 mmol)in tetrahydrofuran (80 mL) was slowly added to a stirredsolution of YbI2 (1.23 g, 2.88 mmol) in tetrahydrofuran (100mL). The mixture was stirred at room temperature for 36 h,giving a strawberry red solution and a white precipitate, whichwas filtered off. Solvent was removed from the filtrate in vacuo,yielding a red solid; this was extracted with toluene (50 mL),and the extracts were filtered. Toluene was removed from thefiltrate in vacuo, and tetrahydrofuran (5 mL) was added togive a red solution, from which volatiles were removed invacuo. Addition of pentane (20 mL) afforded a red solution,the volume of which was reduced to ca. 4 mL. Cooling to -30°C for 3 days yielded red crystals of compound 13 (1.46 g,66.3%). Anal. Calcd for C32H62O2Si4Yb: C, 50.3; H, 8.18.Found: C, 49.4; H, 8.09. 1H NMR (C6D6, 23 °C): δ 0.16 (s, 18H, SiMe3); 1.54 (s, 1H, CH(SiMe3)2); 5.97 (s, 2H, Cp ring); 5.79(s, 2H, Cp ring); 1.27 (s, 4H, THF); 3.48 (s, 4H, THF). 13C{1H}NMR (C6D6, 23 °C): δ 0.82 (SiMe3); 21.06 (CH(SiMe3)2); 106.45,108.43, 121.73 (Cp ring); 25.57, 69.75 (THF). 29Si{1H} NMR(C6D6 + PhCH3), 25 °C): δ 1.56.

[YbCpt2(THF)2] (14). The reaction of NaCpt (0.5 g, 2.25

mmol) and YbI2 (0.52 g, 1.22 mmol), using the proceduredescribed for 13, afforded red crystals of compound 14 (0.65g, 85.5%). Anal. Calcd for C30H54O2Si2Yb: C, 53.3; H, 7.99.Found: C, 53.1; H, 7.81. 1H NMR (C6D6, 23 °C): δ 1.09 (s, 9H, CMe3); 0.51 (s, 6H, SiMe2); 6.10 (s, 2H, Cp ring); 6.46 (s,2H, Cp ring); 1.25 (s, 4H, THF); 3.33 (s, 4H, THF). 13C{1H}NMR (C6D6, 23 °C): δ 17.87 (CMe3); 27.16 (C(CH3)3); -4.39(SiMe2); 109.63, 110.40, 116.73 (Cp ring); 25.35, 70.15 (THF).29Si{1H} NMR (C6D6 + PhCH3), 25 °C): δ -3.91.

[SmCptt2(THF)2] (15). The reaction of KCptt (0.5 g, 1.51

mmol) and SmI2(THF)2 (0.42 g, 0.77 mmol), using the proce-dure described for 11, afforded purple crystals of compound15 (0.64 g, 94.4%). Anal. Calcd for C42H82O2Si4Sm: C, 57.2;H, 9.37. Found: C, 56.2; H, 9.34. 1H NMR (C6D6, 23 °C): δ0.93 (s, 18 H, CMe3); 9.00 (s, 6H, SiMe2); 15.28 (s, 6H, SiMe2);-8.82 (s, 1H, Cp ring); 12.69 (s, 2H, Cp ring); -1.01 (s, 4H,THF); 1.87 (s, 4H, THF). 13C{1H} NMR (C6D6, 23 °C): δ-121.0; -51.6; -39.66; 22.7; 23.5; 24.9; 27.6; 29.5; 114.9.

[YbCptt2(THF)2] (16). The reaction of KCptt (0.8 g, 2.41

mmol) and YbI2 (0.55 g, 1.29 mmol), using the proceduredescribed for 13, afforded red crystals of compound 16 (0.89g, 81.8%). 1H NMR (C6D6, 23 °C): δ 0.95 (s, 18 H, CMe3); 0.25(s, 6H, SiMe2); 0.36 (s, 6H, SiMe2); 6.45 (s, 1H, Cp ring); 6.70(s, 2H, Cp ring); 1.33 (s, 4H, THF); 3.53 (s, 4H, THF). 13C{1H}NMR (C6D6, 23 °C): δ 17.66 (CMe3); 6.88 (C(CH3)3); -4.47(SiMe2); -4.32 (SiMe2); 118.77, 119.87, 125.90 (Cp ring); 69.39,25.62 (THF). 29Si{1H} NMR (C6D6 + PhCH3, 25 °C): δ -4.46.

SmCpR2 (17). Solid 11 (0.5 g, 0.67 mmol) was transferred

to a horizontal sublimation apparatus, which in turn wasinserted into a tubular oven. The temperature of the oven wasslowly raised until the sublimation temperature of the com-pound was reached. The compound was sublimed at 210 °C/10-4 mmHg for 3 h to yield the black-green crystallinecompound 17 (0.34 g, 84.9%). Anal. Calcd for C24H46Si4Sm: C,48.3; H, 7.86. Found: C, 48.1; H, 7.86.

EuCpR2 (18). Sublimation of 12 (0.44 g, 0.59 mmol) at 250

Lanthanocene Chemistry with Cp Ligands Organometallics, Vol. 19, No. 17, 2000 3427

°C/10-4 mmHg for 4 h, using the procedure described for 17,yielded a yellow oil, which on cooling was eventually trans-formed into the red, transparent solid 18 (0.3 g, 85%). Anal.Calcd for C24H46EuSi4: C, 48.1; H, 7.74. Found: C, 48.1; H,7.71. IR (Nujol, KBr): 3010 (w), 1243 (m), 1132 (w), 1033 (m),1010 (m), 933 (m), 757 (m), 681 (m), 656 (m) cm-1.

YbCpR2 (19). Sublimation of 13 (0.9 g, 1.18 mmol) at 180-

200 °C/10-4 mmHg for 2 h, using the procedure described for17, yielded dark red crystals of compound 19 (0.65 g, 89%).Anal. Calcd for C24H46Si4Yb: C, 46.5; H, 7.48. Found: C, 45.8;H, 7.52. 1H NMR (C6D5CD3, 23 °C): δ -0.03 (s, 18 H, SiMe3);1.17 (s, 1H, CH(SiMe3)2); 5.52 (s, 2H, Cp ring); 5.98 (s, 2H, Cpring); 13C{1H} NMR (C6D5CD3, 23 °C): δ 0.59 (SiMe3); 21.31(CH(SiMe3)2); 106.95, 107.82, 124.32 (Cp ring). 29Si{1H} NMR(C6D6 + PhCH3, 23 °C): δ 2.3.

YbCpt2 (20). Sublimation of 14 (0.3 g, 0.44 mmol) at 300

°C/10-4 mmHg for 4 h, using the procedure described for 17,yielded green crystals of compound 20 (0.2 g, 85.4%). Anal.Calcd for C22H38Si2Yb: C, 49.7; H, 7.20. Found: C, 49.1; H,7.14. 1H NMR (C5D5N, 23 °C): δ 0.88 (s, 9 H, CMe3); 0.25 (s,3H, SiMe2); -0.21 (s, 3H, SiMe2); 6.37 (s, 2H, Cp ring); 6.65(s, 2H, Cp ring).

SmCptt2 (21). Sublimation of 15 (0.4 g, 0.45 mmol) at 200

°C/10-4 mmHg for 3 h, using the procedure described for 17,yielded black-green crystals of compound 21 (0.3 g, 90.4%).Anal. Calcd for C34H66Si4Sm: C, 55.4; H, 9.02. Found: C, 54.6;H, 8.99. 1H NMR (C6D5CD3, 23 °C): δ -0.53 (s, 18 H, CMe3);8.65 (s, 6H, SiMe2); 20.06 (s, 6H, SiMe2); -14.38 (s, 1H, Cpring); 13.20 (s, 2H, Cp ring).

YbCptt2 (22). Sublimation of 16 (0.6 g, 0.66 mmol) at 180

°C/10-4 mmHg for 4 h, using the procedure described for 17,yielded black crystals of compound 22 (0.42 g, 83%). Anal.Calcd for C34H66Si4Yb: C, 53.7; H, 8.75. Found: C, 53.2; H,8.76%. 1H NMR (C6D6, 23 °C): δ 0.91 (s, 18 H, CMe3); 0.28 (s,6H, SiMe2); 0.33 (s, 6H, SiMe2); 6.42 (s, 1H, Cp ring); 6.99 (s,2H, Cp ring). 13C{1H} NMR (C6D6, 23 °C): δ 17.88 (CMe3);27.22 (C(CH3)3); -4.33 (SiMe2); 120.81, 126.97, 128.29 (Cpring). 29Si{1H} NMR (C6D6 + PhCH3), 30 °C): δ -4.09.

[Yb(CpR′2SiMe2)(THF)2] (23). A solution of K2[CpR′

2SiMe2](1.27 g, 2.18 mmol) in tetrahydrofuran (50 mL) was slowlyadded to a stirred solution of YbI2 (0.83 g, 1.94 mmol) intetrahydrofuran (100 mL). The mixture was stirred at roomtemperature for 36 h, leaving a red solution and a whiteprecipitate, which was filtered off. Solvent was removed fromthe filtrate in vacuo, yielding a red solid, which was extractedwith toluene (50 mL) and filtered. The volume of the filtratewas reduced to ca. 8 mL. Cooling to -30 °C for 3 monthsyielded red needles of compound 23 (0.84 g, 56.7%). Anal. Calcdfor C34H66O2Si3Yb: C, 53.4; H, 8.71. Found: C, 48.5; H, 8.10.1H NMR (C6D6, 23 °C): δ 0.09 (s, 18 H, SiMe3); 1.57 (s, 1H,CH(SiMe3)2); 0.12 (s, 3H, SiMe2); 5.73 (s, 1H, Cp ring); 5.77(s, 1H, Cp ring); 5.82 (s, 1H, Cp ring); 1.33 (s, 4H, THF); 3.45(s, 4H, THF). 13C{1H} NMR (C6D6, 23 °C): δ 0.98 (SiMe3); 20.73(CH(SiMe3)2); -3.80 (SiMe2); 109.97, 110.74, 111.10, 112.15,126.39 (Cp ring); 25.50, 69.27 (THF). 29Si{1H} NMR (C6D6 +PhCH3), 25 °C): δ 3.56, 2.57.

Reduction of [{NdCpR2(µ-Cl)}2] (2) with K in THF.

Reduction of 2 (0.42 g, 0.67 mmol) with a K mirror (0.025 g,0.64 mmol) in THF for 2 days yielded a dark brown mixture.

Solvent was removed in vacuo; the resulting brown residuewas extracted with toluene (30 mL), and the extracts werefiltered. The filtrate was concentrated to ca. 5 mL and cooledto -30 °C. After a period of 1 week, a black precipitate hadformed and the brown solution had changed to light blue, fromwhich crystalline [NdCpR

3]12 (0.3 g) was isolated.X-ray Structure Determination of 2, 9, and 23. Data

were measured on an Enraf-Nonius CAD4 diffractometer usingmonochromated Mo KR radiation. Crystals were sealed in acapillary under argon. Corrections for absorption were madeusing DIFABS.37 Structure solutions were made using SHELX-86.38 Refinement was on F using reflections with I > 2σ(I).Crystal data and structure refinement details are in Table 3.Tables of atom positions and thermal parameters have beendeposited at the Cambridge Crystallographic Data Center(CCDC). ORTEP drawings show 20% ellipsoids.

Acknowledgment. We thank the Chinese Govern-ment and the British Council for a studentship for S.T.and the EPSRC for other support.

Supporting Information Available: Tables of X-raycrystallographic data for 2, 9, and 23. This material isavailable free of charge via the Internet at http://pubs.acs.org.Crystallographic data for the structural analyses have alsobeen deposited with the Cambridge Crystallographic DataCenter. Copies of the information can be obtained free ofcharge from The Director, CCDC, 12 Union Road, CambridgeCB2 1EZ, U.K. (Fax, +44-1223-336-033; e-mail, deposit@acdc.cam.ac.uk; web, http://ccdc.cam.ac.uk).

OM000305M

(37) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.(38) Sheldrick, G. M., Sheldrick, G. M., Kruger, C., Goddard, R.,

Eds. Crystallographic Computing 3; Oxford University Press: Oxford,U.K., 1985; pp 175-189.

Table 3. Crystal Data and Structure Refinementfor Compounds 2, 9, and 23

2 9 23

formula C48H92Cl2Nd2Si8 C68H132I2Si8Tm2 C34H66O2Si3YbMr 1253.3 1766.2 764.2cryst syst triclinic triclinic monoclinicspace group P1h (No. 2) P1h (No. 2) C2/c (No. 15)a (Å) 8.803(4) 11.940(5) 29.866(14)b (Å) 12.331(3) 12.854(3) 10.935(3)c (Å) 15.664(2) 14.963(2) 15.387(8)R (deg) 77.99(2) 79.82(2) 90â (deg) 80.93(2) 72.67(3) 116.46(4)γ (deg) 72.69(3) 89.00(3) 90V (Å3) 1579.3 2156.2 4498.5Z 1 1 4µ(Μï ΚR) (cm-1) 18.9 29.2 21.7T (K) 295 298 293total no. of

unique rflns5546 5966 4166

no. of variables 271 361 199no. of signif rflns

(I > 2σ(I))4837 4215 2242

Ra 0.032 0.058 0.049Rw

b 0.043 0.069 0.050

a R ) (∑||Fo| - |Fc||)/∑|Fo|. b Rw ) [(∑w(|Fo| - |Fc|)2)/∑w(|Fo|2)]1/2.

3428 Organometallics, Vol. 19, No. 17, 2000 Hitchcock et al.