The reaction of [Yb(q-CSMes)2(OEt2)] with 1 equiv. of [Li{Si(SiMe3)3)(thf)3] in toluene affords [Yb(q-C5MeS){Si-(SiMe3)3)(thf)2] 1 in high yield; a single-crystal X-ray analysis and multinuclear 1 7 l Y b and 29Si NMR spectroscopic data for 1 are reported.Since their proposed role in the catalytic dehydrocoupling of primary silanes to polysilanes, much interest has recently focused on the exploration of chemistry of lanthanide-siliconbonded species.' Nevertheless only three routes to such compounds are known, and four complexes have been structurally characterised (Scheme 1, Table l).2-5We now report the synthesis and molecular structure of [Yb(q-CSMeS)( Si(SiMe3)3}(thf)2] 1. The reaction of [Yb(q-C5Me5)2(OEt2)] with 1 equiv. of [Li( Si(SiMe&}(thf)3] in toluene afforded 1 in high yield (75%).t The elimination of LiC5Me5 has been previously employed for complexes of main-group697 and lanthanides elements in substitution reactions in which the CSMeS-group was replaced by alkyl, alkoxide or amide but not, to our knowledge, by silyl derivatives. 1 was initially characterised by its 17lYb NMR spectrum, in toluene solution, which displayed a single resonance at 6 421 with satellites corresponding to 1J(171Yb_29Si) 829 Hz [Fig. l(a)]. The 29Si NMR spectrum (Fig. l(b)] comprised two resonances at 6 -2.9 and -158, the latter assigned to Si(SiMe)3 possessing satellites confirming the previously measured 1J(171Yb-29Si) coupling and also displaying IJ(29Si-29Si) 26 Hz; the former, assigned to Si(SiMe)3 showed a 2J(29Si-171Yb) coupling of 11.5 Hz and a 1J(29Si-13C) coupling of 40 Hz. The 13C NMR spectrum of 1 revealed 2J(13C-29Si) of 8 Hz for Si(SiMe)3 and a lJ(l3C-171Yb) coupling of 10 Hz for C5Me5.Recry stallisation of 1 from hexane afforded orange needles. The molecular structure was determined from a single-crystal X-ray diffraction study (Fig. 2).$ The ligand geometry about the Yb atom is distorted tetrahedral, with the angle between the Compound Ln-SilA Ref.

The reduction of CpRZrCl3(dme) (CpR = Cp (a), C5H4SiMe3 (b), C5H4Me (c), Ind (d)) with sodium amalgam in the presence of isoprene, followed by the addition of allylmagnesium chloride, gives the diene complexes CpRZr(η3-allyl)(η4-isoprene) (2a−d). The preparations are conveniently carried out as one-pot reactions. The reaction of 2a−d with B(C6F5)3 in toluene solution at −78 °C proceeds quantitatively to give the thermally unstable zwitterionic complexes CpRZr(η3-allyl){η1:η3-CH2CMeCHCH2B(C6F5)3} (3a−d), which on warming decompose under C−H activation and propene elimination to give CpRZr(C6F5){η4-CH2CMeCHCHB(C6F5)2} (4a−d). The complexes are stabilized by the coordination of one o-F atom of a boryl−C6F5 ring to the metal center. Compounds 4 are fluxional. The rotation of the Zr−C6F5 ligand is influenced by the steric demand of the Cp ligands (ΔG ⧧ = 43−49 kJ mol-1), while there is little variation in the rotational barriers of the B−C6F5 substituents (ΔG ⧧ = ca. 47 kJ mol-1). Recrystallization of 4a from diethyl ether affords the 16-electron complex 4a·OEt2, in which fluorine coordination is replaced by an ether ligand. The structure of this complex has been determined; unlike its C5Me5 and C5H3(SiMe3)2 congeners, it shows the boryldiene moiety to occupy a prone (endo) conformation. Propene inserts into the CH2 terminus of the boryldiene ligand under ambient conditions to give the metallacycles CpRZr(C6F5){η1:η3-CH2CH(Me)−CH2C(Me)CHCHB(C6F5)2} (5a−d), with complete regioselectivity and very high stereoselectivity. The insertion process is reversible; propene extrusion occurs via β-alkyl elimination from the major chair conformation isomer.

The reaction of YCl3 with 2 or 3 equiv. of NaC5H4CH([CH2]2)2NMe in toluene affords [{Y[η‐C5H4CH([CH2]2)2NMe]2(μ‐Cl)}2] (1) and [Y{η‐C5H4CH([CH2]2)2NMe}3] (2), respectively, in high yield; the three amino‐functionalised cyclopentadienyl units of 2 are fluxional at room temperature, giving us a rare example of stabilisation of an yttrium centre without the use of extraneous ligands. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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