Lanthanocene Chemistry with [CpR

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Organometallics 2000, 19, 3420-3428

Lanthanocene Chemistry with [CpR]-, [Cpt]-, [Cptt]-, and [CpR′2SiMe2]2- Ligands: Synthesis and Characterization of Bis(cyclopentadienyl)lanthanide(III) Halides and Bis(cyclopentadienyl)lanthanide(II) Complexes and Crystal Structures of [{NdCpR2(µ-Cl)}2], [{TmCptt2(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 [LnCpR2(THF)2] (Ln ) Sm, Eu, Yb), [YbCpt2(THF)2], [LnCptt2(THF)2] (Ln ) Sm, Yb), LnCpR2 (Ln ) Sm, Eu, Yb), YbCpt2, 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 the selected sodium or potassium cyclopentadienide. The complexes were characterized by 1H, 13 C, 29Si, and 171Yb (for Yb(II) complexes) NMR spectroscopy, elemental analysis, and mass spectrometry. The molecular structures of [{NdCpR2(µ-Cl)}2], [{TmCptt2(µ-I)}2], and [Yb(CpR′2SiMe2)(THF)2] have been determined by single-crystal X-ray diffraction studies. Attempts to reduce the complexes [{NdCpR2(µ-Cl)}2], [{NdCptt2(µ-Cl)}2], and [{TmCptt2(µ-I)}2] are described. Introduction The bis(cyclopentadienyl)lanthanide(III) halides and bis(cyclopentadienyl)lanthanide(II) complexes have proved to be useful organolanthanide complexes,1 being important precursors for a variety of lanthanocene(III) derivatives, such as alkyls, hydrides, and amides, which have been shown to exhibit unique characteristics as catalysts in hydrogenation,2 oligomerization,3 polymerization,4 hydroamination,5 hydrosilylation,6 silanolytic chain transfer,7 and hydroboration.8 The lanthanocene(II) complexes have been shown to be single-electron (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 Organometallic Chemistry, 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.

reducing agents and are widely used in organic synthesis.9,10 The stability, solubility, and reactivities of the lanthanocene catalysts are dramatically influenced by the modification of cyclopentadienyl ligands; cyclopentadienyl-free organolanthanide complexes have also been studied extensively.1d In the past, we have extensively investigated 1,3-bis(trimethylsilyl)cyclopentadienyl (Cp′′)-based lanthanide chemistry. We have recently developed a series of new (Me3Si)2CH- and ButMe2Si-substituted cyclopentadienyl ligands as their alkali-metal compounds11 and synthesized the corresponding bis- and tris(cyclopentadienyl)thorium and tris(cyclopentadienyl)lanthanide(III) complexes.12 As previously mentioned,11 the steric bulk exerted by electron-withdrawing SiMe3 or SiMe2But groups is an important effect, as is the superior solubility in nonpolar solvents and often the crystallinity of their metal complexes. The new ansa-bridged ligand [CpR′2SiMe2]2-, known only as the (K+)2 salt,11 has not previously been (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.

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Lanthanocene Chemistry with Cp Ligands

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used with a wider range of metals (CpR′ ) η-C5H3{CH(SiMe3)2}-3). We now report the synthesis and characterization of various bis(cyclopentadienyl)lanthanide(III) halides (1-10) and bis(cyclopentadienyl)lanthanide(II) derivatives (11-23) with these ligands, including the X-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 reported and compared with those of related compounds in the literature. Results and Discussion Synthesis and Characterization of the Lanthanocene(III) Halides 1-10. Reaction of the anhydrous lanthanide(III) chloride with 2 equiv of potassium [bis(trimethylsilyl)methyl]cyclopentadienide (≡KCpR) or bis(tert-butyldimethylsilyl)cyclopentadienide (≡KCptt) in tetrahydrofuran and subsequent sublimation under high vacuum afforded the crystalline, dimeric lanthanocene(III) chlorides [{LnCpR2(µ-Cl)}2] (1-6) and [{LnCptt2(µ-Cl)}2] (7, 8) in good yields (eqs 1 and 2). One of our objectives (not yet realized) was to synthesize organothulium(II) complexes, by using sterically demanding substituted cyclopentadienyl ligands and large ancillary halides or chalcogenides. A potential Tm(III) precursor, [{TmCptt2(µ-I)}2] (9), was synthesized by reaction of thulium(III) iodide and KCptt in THF and subsequent sublimation (eq 3). Treatment of NdCl3 with 1 equiv of K2[CpR′2SiMe2] (CpR′ ≡ C5H3CH(SiMe3)2-3) in THF and subsequent sublimation yielded the green ansa-bridged bis(cyclopentadienyl)neodymium(III) chloride 10 (eq 4). The 1H NMR spectrum of 10 in toluene-d8 was too complicated to be readily assigned, possibly due to the formation of two isomers, chelating (a) and bridging (b). However, elemental analysis and mass spectrometry confirmed the above formulation. (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. Organometallics 1996, 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 Organic Synthesis; Springer: Berlin, 1999. (b) Imamoto, T., Ed. Lanthanides in 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.

The CpR-substituted complexes 1-6 were sparingly soluble in CHCl3 and CH2Cl2, and even in benzene or toluene 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, being insoluble in hydrocarbons such as hexane, benzene, and toluene and only sparingly soluble in THF or pyridine. An attempt to synthesize [{EuCpR2(µ-Cl)}2] by reaction of EuCl3 with 2 equiv of KCpR in THF led instead to the europocene(II) complex [EuCpR2(THF)2] (12). Complexes 1-10 were characterized by C and H elemental analysis and mass spectrometry. The diamagnetic compounds 6 and 7 and the early-lanthanide paramagnetic complexes 1-3 and 8 were additionally identified by 1H NMR spectroscopy. Like their homoleptic analogues12 [NdCpR3], [SmCpR3], and [NdCptt3], the paramagnetic Nd(III) and Sm(III) complexes gave very sharp 1H NMR signals, although the chemical shifts deviated substantially from those in the diamagnetic analogues 6 and 7. Because of the extremely low solubility of complexes 7 and 8 in toluene or CDCl3, their 1H and 13C NMR spectra were measured in C D N 5 5 solution, probably forming [LnCptt2Cl(py-d5)] (La ) La, Nd). In the 1H NMR spectrum of the Nd compound 8, a

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

singlet at δ 5.72 is assigned to But protons; the three Cp ring protons appeared at δ 29.93 (1H) and -10.08 (2H), while the Me2Si protons appeared as a pair of singlets at δ -2.02 and -6.10, corresponding to the magnetically inequivalent methyls on the Me2Si group. Splitting of the dimethylsilyl proton signals has also been observed in other metal-Cptt complexes: [LiCptt(TMEDA)],11 [SmCptt2(THF)2] (15), [YbCptt2(THF)2] (16), YbCpt2 (20), SmCptt2 (21), and YbCptt2 (22) (see below). The conformation of the (Cptt)- ligand, showing two magnetically inequivalent methyl protons, is depicted in Figure 1. The EI-MS spectra of [{LnCpR2(µ-Cl)}2] (1-6) revealed them to be dimeric, the molecular ions [M]+ being of relatively low intensity. Each of the bis(cyclopentadienyl)lanthanide chlorides showed the typical fragments [M - Cl]+, [M - CpR]+, [LnCpR2]+, and [SiMe3]+. The lanthanocenes containing the [Cptt]- ligand were less soluble in hydrocarbons and more air-stable than those containing [C5H3(SiMe3)2-1,3]- (≡Cp′′-) or [CpR]ligands. For instance, [{NdCptt2(µ-Cl)}2] (8) was insoluble in toluene and stable in air for several minutes (the green color did not change), while [{NdCpR2(µ-Cl)}2] (2) and [{NdCp′′2(µ-Cl)}2] were slightly soluble in toluene and decomposed in air within 1 min. The enhanced stability of the Cptt-containing compounds is also evident in organothorium(III) chemistry; thus, [ThCp′′3]13 and [ThCpR3]14 were extremely soluble in hexane or toluene and very air-sensitive, immediately decomposing upon exposure to air within 1 s both in solution and in the solid, as evidenced by the disappearance of their deep blue color (which we regard as among the most (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.

air-sensitive organometallic compounds we have encountered), while [ThCptt3]14 was less soluble in diethyl ether, hexane, or toluene and considerably more stable in air. The deep blue color of the solid [ThCptt3] persisted in air for ca. 10 min! This is attributed to the greater bulk of the [Cptt]- ligand. Thus, it is likely that it may be serve as a useful ligand in a wider context. Synthesis and Characterization of the Lanthanocene(II) Complexes 11-23. The solvated bis(substituted cyclopentadienyl)lanthanide(II) complexes were synthesized by the reaction of the lanthanide(II) iodide with the appropriate sodium or potassium cyclopenta-


dienide in tetrahydrofuran. Subsequent sublimation under high vacuum afforded the solvent-free bis(cyclopentadienyl)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 17-22 was not determined; each except 20 (which also has the highest sublimation temperature) is probably a monomer in solution but may be a loosely bound polymer in the 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 satisfactory C and H elemental analysis; 1H and 13C{1H} NMR spectroscopy revealed the number of THF molecules coordinated to the metal center (0 or 2). The diamagnetic Yb(II) complexes have been additionally characterized by 171Yb and 29Si{1H} NMR spectroscopy. Since samarium(II) has a 4f6 electronic ground-state configuration and its complexes are paramagnetic, NMR spectroscopy of samarocene(II) complexes has two features: (i) large chemical shifts of the observable NMR signals and (ii) significant line-broadening effects. The 1H NMR spectra of 11, 15, and 21 showed broad signals that were substantially shifted compared with the values for their diamagnetic analogues 13, 16, and 22. As for 11, the (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.


Me3Si groups appeared as a broad singlet at δ 9.64 and the methyne proton at δ 3.62. The ring protons were observed at δ 5.54 and 22.17 for the two groups of two equivalent protons. The peaks due to THF appeared at δ -0.64 and -1.44. In the 1H NMR spectrum of 15, the Me2Si protons signals were split into two at δ 9.00 and 15.28. Two signals, at δ -8.82 and 12.69 (integrated as 1:2), 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 configuration and, hence, its complexes are diamagnetic, the 1H and 13C NMR spectra of compounds 13, 14, 16, 19, and 20 were unexceptional. Ytterbium is unique in that its spin 1/2 isotope (171Yb) has a relatively high natural abundance (14.27%) and the 171Yb nucleus has a receptivity 4 times greater than that of the 13C nucleus. These two features make possible the high-resolution direct NMR spectral observation of 171Yb in the +2 oxidation state, as originally established for ytterbium(II) amido and pentamethylcyclopentadienyl complexes in 1989.17 Several ytterbocene(II) alkoxide, aryloxide, alkyl, amide, β-diketiminate, 1-azaallyl and stannyl complexes have been studied by 171Yb NMR spectroscopy.18 A review of 171Yb solution state NMR spectroscopic chemical shifts was published in 1996.19 A later paper by the same authors, Keates and Lawless,20 noted that such data were then (1997) available for more than 200 organic ytterbium(II) complexes, with δ(171Yb) ranging from +2500 to -500, with [Yb(η5-C5Me5)2(THF)] (δ 0) as standard.17 It was further observed that the isotropic chemical shifts of π-bonded cyclopentadienyl derivatives are of low frequency compared with those containing σ-bonded ligands;19,20 this is consistent with our data, summarized in Table 1, together with literature values for other ytterbocene(II) complexes. Each complex of the formula [YbCpx2(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 appears that 16, having the bulkiest [Cpx]- ligand ([Cptt]-), is under these conditions largely neutral donor (THF)-free, the δ value being almost identical with that in the homoleptic 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 spectral signals of 12 and 18 were too broad to be assigned because 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)metal complexes (known as ansa-metallocenes) of group 4 elements and lanthanides(III) are well-known, ansalanthanocene(II) complexes are very rare. We now (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) van den 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 NMR to 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.

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Table 1. Solution 171Yb{1H} NMR Spectroscopic Chemical Shifts (δ) for Ytterbocene(II) Complexes 13, 14, 16, 19, 22, and 23 and Related Complexes 171Yb{1H}

compd [YbCpR

2(THF)2] (13) [YbCpt2(THF)2] (14) [YbCptt2(THF)2] (16) YbCpR2 (19) YbCptt2 (22) [Yb{CpR′2SiMe2}(THF)2] (23) [Yb{η5-C5H3(SiMe3)2-1,3}2(THF)]a [Yb{η5-C5H3(SiMe3)2-1,3}2]∞a [YbCp*2(THF)2]b [YbCp*2(OEt2)2]b [YbCp*2(NC5H5)2]c [YbCp*2(DME)]d [YbCp*2]∞e [Yb(η5-C5Me4H)2(THF)2]c [Yb{η5-C5Me4(SiMe3)]2(THF)]c [Yb{η5-C5Me4(SiMe2But)}2]c

(T/K) 134.5 (304) 157.5 (298) -7.06 (298) 118.7 (295) -7.02 (304) 306.3 (304) 172.0 (304) -15.7 (297) 0.0 (296) 26 (308) 949 (338) 98 (298) -3.3 (298) 131 (298) 6 (298) 20 (298)

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)

solvent

2

PhH PhMe-PhH PhMe-PhH PhMe-PhH PhMe-PhH PhMe-PhH THF-PhMe PhMe THF Et2O C5H5N DME-C6H6 PhMe THF THF C6H11Me-c

Distancesa

Bond Ln-X Ln-X′ Ln-Cp1 Ln-Cp2 Cp1-Ln-Cp2 X-Ln-X′ Ln-X-Ln′

2.805(1) 2.786(1) 2.446 2.455 Bond Angles 128.9 76.76(3) 103.24(3)

9 3.045(1) 3.050(1) 2.33 2.34 131.5 82.88(3) 97.12(3)

a Cp1 and Cp2 represent the centroids of the two cyclopentadienyl rings attached to the Ln atom.

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

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.

describe [Yb(CpR′2SiMe2)(THF)2] (23), which was synthesized 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 characterized by 1H, 13C{1H}, 29Si{1H}, and 171Yb NMR spectroscopy. Successful elemental analysis data were not obtained, possibly due to the ready loss of the coordinated THF when the analysis was performed. The molecular structure of 22 was determined by singlecrystal X-ray diffraction. Attempted Reduction of [{NdCpR2(µ-Cl)}2] (2), [{NdCptt2(µ-Cl)}2] (8), and [{TmCptt2(µ-I)}2] (9). We are interested in organolanthanide(II) chemistry in the unusual oxidation state +2 for 4f elements other than the classic Eu(II), Sm(II), and Yb(II)12 and recently have reported the first thermally stable, crystalline, subvalent organolanthanum compound, formulated as a La(II) complex.21 We have also described attempts to reduce the Ln(III) compounds [NdCpR3], [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 because a Tm(II) complex might have the potential of providing access to organothulium(I) compounds; the 169Tm nucleus is NMR active (169Tm (f 14), I ) 1/2, natural abundance 100%).22 Reduction of [{NdCpR2(µ-Cl)}2] (2) or [{NdCptt2(µCl)}2] (8) with potassium in THF yielded a dark brown solution, which gradually decomposed to precipitate the

neutral donor ligand, such as DME, TMEDA, PMDETA, or [18]-crown-6, to the reaction systems failed to stabilize the presumed Nd(II) intermediates. The dark brown precipitate from 2 may have been an ionic species, since it was insoluble in pentane or hexane, sparingly soluble in toluene, and very soluble in THF. Attempts to stabilize and isolate a Nd(II) species by adding [NBun4][BF4] to the “reduced” reaction mixture from 2 were also unsuccessful. The reaction of the yellow [{TmCptt2(µ-I)}2] (9) with potassium in THF gave a brown solution. As in the neodymium systems, the latter was unstable and readily decomposed, yielding a black precipitate, presumed to be Tm. Attempted stabilization of a Tm(II) compound, using procedures similar to those described above for Nd(II), were unsuccessful. X-ray Crystal Structures of Complexes 2, 9, and 23. X-ray-quality single crystals were obtained by slow sublimation of [{NdCpR2(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 molecular structures and atom-numbering schemes of 2, 9, and 23 are shown in Figures 2-4, respectively. Selected bond distances and angles are presented in Table 2. The crystalline complex 2 is a centrosymmetric dimer. The two neodymium atoms, each with two η5-bonded cyclopentadienyl groups, are bridged by two chlorides. The Nd-Cl bond lengths of 2.805(1) and 2.786(1) Å are slightly shorter than those in [{Nd(C5H3But2-1,3)2(µCl)}2]23 (2.837(1) and 2.841(1) Å). The Nd-C(Cp) distances are within the range 2.826-2.671 Å, averaging 2.733 Å. Each neodymium atom is at the center of a distorted 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.



Figure 2. Molecular structure and atom-numbering scheme for [{NdCpR2(µ-Cl)}2] (2). Figure 4. Molecular structure and atom-numbering scheme for [Yb(CpR′2SiMe2)(THF)2] (23).

Figure 3. Molecular structure and atom-numbering scheme for [{TmCptt2(µ-I)}2] (9).

rings and two chlorides forming the apexes. The ClNdCl′Nd core is rhomboidal with the angle at the Nd atoms smaller (76.76(3)°) than that at Cl (103.24(3)°). Some other structurally characterized dinuclear bis(cyclopentadienyl)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 that of 2, being a diiodide-bridged symmetric dimer. We initially expected that the molecule might be a mono(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.

mer, due to the bulky [Cptt]- and I- ligands, as well as the small size of Tm(III). The Tm-I bond lengths are 3.045(1) and 3.050(1) Å. The distances between each Tm and the two cyclopentadienyl centroids (Cp) are 2.33 and 2.34 Å, respectively. The Cp-Tm-Cp′ angle of 131.5° in 9 is slightly larger than the Cp-Nd-Cp angle of 128.9° in 2. Although several ansa-lanthanocene(III) halides, alkyls, alkoxides, and amides have been reported, ansa-lanthanocene(II) complexes are rare. Structurally characterized examples of the former include [Yb{(η5-C5H3But)2CMe2-3}(µ-Cl)2Li(OEt2)2],26 [Yb{(η5C5H3SiMe3)2SiMe2-3}Cl(THF)],26 [(Yb{(η5-C5H3But)2CMe23}(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(SiMe3)2-1,3)2SiMe2-5}(µ-Cl)2Li(THF)2],4j [Sm{(η5-C5H2(SiMe3)2-1,3)2SiMe2-5}CH(SiMe3)2],4j [Nd{(η5-C5Me4)2SiMe2}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 structurally characterized Ln(II) analogues are rac-[Sm{(η5-C5H2(But)(SiMe3)-2,4)SiMe2}(THF)2]4j and the indenyl com(26) Khvostov, A. V.; Belsky, V. K.; Bulychev, B. M.; Sizov, A. I.; Ustinov, B. B. J. Organomet. Chem. 1999, 571, 243. (27) Ho¨ck, N.; Oroschin, W.; Paolucci, G.; Fischer, R. D. Angew. Chem., Int. Ed. Engl. 1986, 25, 738. (28) Akhnoukh, T.; Mu¨ller, 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.

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

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 mesoytterbocene(II) compound 23 has a distorted-tetrahedral geometry around the ytterbium atom, if each Cp ring is 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 extending through the bridged Si(1) and ytterbium atoms. The atoms C(6), C(6)′, Si(1), Yb, O, and O′ are coplanar. A simplified bonding pattern is shown in Figure 5. Experimental Section General Considerations. All manipulations were carried out under vacuum or argon using standard Schenk techniques. Solvents were dried and distilled over Na/K alloy under an atmosphere of nitrogen gas and were degassed prior to use by freeze-pump-thaw cycling. The following compounds were prepared 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′2SiMe2].11 Others were purchased and purified by standard procedures. Microanalyses were carried out by Medac Ltd. (Brunel University). NMR spectra were recorded with Bruker AC-250, WM-360, or AMX-500 instruments. Chemical shift data are shown in the following sequence: (i) SiMe3, CH(SiMe3)2, Cp, thf or (ii) CMe3, CMe3, SiMe2, thf. Mass spectra were recorded on a VG Autospec mass spectrometer operating in the EI mode at 70 eV. IR spectra were recorded as Nujol mulls between KBr plates, using a Perkin-Elmer 1720 FT spectrometer. The samples were prepared in a drybox under an atmosphere 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 suspension of PrCl3 (1.2 g, 4.85 mmol) in tetrahydrofuran (75 mL). The mixture was stirred at room temperature for 2 days, leaving a colorless solution and a white precipitate, which was filtered off. Solvent was removed from the filtrate in vacuo to yield a white solid, which was scraped from the side of the Schlenk (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) Ha¨berle, N. Technol. Wiss. Abh. Osram Ges. 1973, 11, 285. (b) Ha¨berle, N. Chem. Abstr. 1974, 81, 71961. (35) Watson, P. L.; Tulip, T. H.; Williams, I. Organometallics 1990, 9, 1999.

tube with a spatula and transferred to a horizontal sublimation tube. Sublimation at 280-300 °C/10-4 mmHg for 3 h afforded pale yellow crystals of compound 1 (2.16 g, 71.3%). Anal. Calcd for C48H92Cl2Pr2Si8: C, 46.3; H, 7.44. Found: C, 45.8; H, 7.44. 1H NMR (CDCl , 20 °C): δ -13.58 (s, 18 H, SiMe ); 11.49 (s, 3 3 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 ([CpR2Ln]+, 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 procedure described 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 ([CpR2Ln]+, 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 procedure described for 1, afforded orange crystals of compound 3 (1.28 g, 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 ([CpR2Ln]+, 100%); 73 ([SiMe3]+, 70%). [{DyCpR2(µ-Cl)}2] (4). The reaction of KCpR (1.0 g, 3.8 mmol) and DyCl3 (0.51 g, 1.9 mmol), using the procedure described 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 ([CpR2Ln]+, 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 procedure described for 1, afforded colorless crystals of compound 5 (0.52 g, 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 ([CpR2Ln]+, 85.0%); 73 ([SiMe3]+, 100%). [{YCpR2(µ-Cl)}2] (6). The reaction of KCpR (2.97 g, 11.3 mmol) and YCl3 (1.12 g, 5.7 mmol), using the procedure described for 1, afforded colorless crystals of compound 6 (2.0 g, 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 (36) Tilley, T. D.; Boncella, J. M.; Berg, D. J.; Burns, C. J.; Andersen, R. A. Inorg. Synth. 1990, 27, 146.

Lanthanocene Chemistry with Cp Ligands - Me]+, 0.01%); 1106 ([M - Cl]+, 1.5%); 919 ([M - CpR]+, 1.4%); 536 ([CpR2Ln]+, 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 stirred suspension of EuCl3 (0.6 g, 2.33 mmol) in tetrahydrofuran (100 mL). As the first drop of KCpR solution was added, the solution immediately became blue and gradually changed to red-orange upon completing the addition. The mixture was stirred at room temperature for 2 days and the resulting white precipitate was filtered off. Solvent was removed from the filtrate in vacuo, and the orange solid residue was extracted into pentane and filtered. The filtrate was concentrated to ca. 5 mL. Cooling to -30 °C yielded orange crystals of [EuCpR2(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 suspension of LaCl3 (0.45 g, 1.83 mmol) in tetrahydrofuran (150 mL). The mixture was stirred at room temperature for 12 h, was refluxed for 8 h, and then was filtered. Solvent was removed from the filtrate in vacuo, leaving a white solid residue which was washed with pentane (20 mL) and dried under vacuum. The white solid was transferred to a horizontal sublimation tube and was sublimed at 360 °C/10-4 mmHg for 4 h to yield white crystals of compound 7 (0.64 g, 51.7%). Anal. Calcd for C68H132I2La2Si8: C, 53.6; H, 8.73. Found: C, 52.7; H, 8.70. 1H NMR (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 procedure described 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 ([Cptt2Nd - 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 procedure described 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′2SiMe2] (0.6 g, 1.16 mmol) in tetrahydrofuran (50 mL) was added to a stirred suspension of NdCl3 (0.3 g, 1.19 mmol) in tetrahydrofuran (100 mL). The mixture was stirred at room temperature for 2 days, was refluxed for 4 h, and then was filtered. Solvent was removed from the filtrate in vacuo, leaving a green solid, which was scraped from the side of the Schlenk flask with a spatula and transferred to a horizontal sublimation tube. Sublimation at 360 °C/10-4 mmHg yielded green crystals of compound 10 (0.4 g, 50.5%). Anal. Calcd for C52H100Cl2Nd2Si10: 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 stirred solution of SmI2(THF)2 (1.56 g, 2.85 mmol) in tetrahydrofuran (100 mL). The mixture was stirred at room temperature for 36 h, leaving a purple solution and a white precipitate, which was filtered off. Solvent was removed from the filtrate in vacuo, yielding a purple solid which was extracted with toluene (50 mL) and filtered. Toluene was removed from the filtrate in vacuo, giving a green solid, which was redissolved in tetrahydrofuran (5 mL) to yield a purple solution. The tetrahydrofuran was carefully removed so as to retain the purple color of the

Organometallics, Vol. 19, No. 17, 2000 3427 solid residue. Addition of pentane (20 mL) to the latter afforded a purple solution, the volume of which was reduced to ca. 5 mL. Cooling to -30 °C yielded the purple crystalline compound 11 (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): δ 9.64 (s, 18 H, SiMe3); 3.62 (s, 1H, CH(SiMe3)2); 5.42 (s, 2H, Cp ring); 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 procedure described for 11, afforded red-orange crystals of compound 12 (2.36 g, 61.7%), identical with those from the reaction of EuCl3 with KCpR. [YbCpR2(THF)2] (13). A solution of KCpR (1.5 g, 5.76 mmol) in tetrahydrofuran (80 mL) was slowly added to a stirred solution of YbI2 (1.23 g, 2.88 mmol) in tetrahydrofuran (100 mL). The mixture was stirred at room temperature for 36 h, giving a strawberry red solution and a white precipitate, which was 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 the filtrate in vacuo, and tetrahydrofuran (5 mL) was added to give a red solution, from which volatiles were removed in vacuo. 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, 18 H, 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 procedure described for 13, afforded red crystals of compound 14 (0.65 g, 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, 9 H, 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 (C D + PhCH ), 25 °C): δ -3.91. 6 6 3 [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 procedure described for 11, afforded purple crystals of compound 15 (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): δ 0.93 (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 procedure described for 13, afforded red crystals of compound 16 (0.89 g, 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 was inserted into a tubular oven. The temperature of the oven was slowly raised until the sublimation temperature of the compound was reached. The compound was sublimed at 210 °C/ 10-4 mmHg for 3 h to yield the black-green crystalline compound 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

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°C/10-4 mmHg for 4 h, using the procedure described for 17, yielded a yellow oil, which on cooling was eventually transformed 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 180200 °C/10-4 mmHg for 2 h, using the procedure described for 17, 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, Cp ring); 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, Cp ring); 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 (Cp ring). 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 slowly added to a stirred solution of YbI2 (0.83 g, 1.94 mmol) in tetrahydrofuran (100 mL). The mixture was stirred at room temperature for 36 h, leaving a red solution and a white precipitate, which was filtered off. Solvent was removed from the filtrate in vacuo, yielding a red solid, which was extracted with toluene (50 mL) and filtered. The volume of the filtrate was reduced to ca. 8 mL. Cooling to -30 °C for 3 months yielded red needles of compound 23 (0.84 g, 56.7%). Anal. Calcd for C34H66O2Si3Yb: C, 53.4; H, 8.71. Found: C, 48.5; H, 8.10. 1H NMR (C D , 23 °C): δ 0.09 (s, 18 H, SiMe ); 1.57 (s, 1H, 6 6 3 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.

Hitchcock et al. Table 3. Crystal Data and Structure Refinement for Compounds 2, 9, and 23 formula Mr cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z µ(Μο ΚR) (cm-1) T (K) total no. of unique rflns no. of variables no. of signif rflns (I > 2σ(I)) Ra Rw b a

2

9

23

C48H92Cl2Nd2Si8 1253.3 triclinic P1h (No. 2) 8.803(4) 12.331(3) 15.664(2) 77.99(2) 80.93(2) 72.69(3) 1579.3 1 18.9 295 5546

C68H132I2Si8Tm2 1766.2 triclinic P1 h (No. 2) 11.940(5) 12.854(3) 14.963(2) 79.82(2) 72.67(3) 89.00(3) 2156.2 1 29.2 298 5966

C34H66O2Si3Yb 764.2 monoclinic C2/c (No. 15) 29.866(14) 10.935(3) 15.387(8) 90 116.46(4) 90 4498.5 4 21.7 293 4166

271 4837

361 4215

199 2242

0.032 0.043

0.058 0.069

0.049 0.050

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

Solvent was removed in vacuo; the resulting brown residue was extracted with toluene (30 mL), and the extracts were filtered. The filtrate was concentrated to ca. 5 mL and cooled to -30 °C. After a period of 1 week, a black precipitate had formed and the brown solution had changed to light blue, from which crystalline [NdCpR3]12 (0.3 g) was isolated. X-ray Structure Determination of 2, 9, and 23. Data were measured on an Enraf-Nonius CAD4 diffractometer using monochromated Mo KR radiation. Crystals were sealed in a capillary under argon. Corrections for absorption were made using DIFABS.37 Structure solutions were made using SHELX86.38 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 been deposited at the Cambridge Crystallographic Data Center (CCDC). ORTEP drawings show 20% ellipsoids.

Acknowledgment. We thank the Chinese Government and the British Council for a studentship for S.T. and the EPSRC for other support. Supporting Information Available: Tables of X-ray crystallographic data for 2, 9, and 23. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data for the structural analyses have also been deposited with the Cambridge Crystallographic Data Center. Copies of the information can be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 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., Kru¨ger, C., Goddard, R., Eds. Crystallographic Computing 3; Oxford University Press: Oxford, U.K., 1985; pp 175-189.

Lanthanocene Chemistry with [CpR

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