Abstract
We report the synthesis and characterisation of a series of M(IV) substituted cyclopentadienyl hypersilanide complexes of the general formula [M(Cp(R))(2){Si(SiMe(3))(3)}(X)] (M = Hf, Th; Cp(R) = Cp', {C(5)H(4)(SiMe(3))} or Cp'', {C(5)H(3)(SiMe(3))(2)-1,3}; X = Cl, C(3)H(5)). The separate salt metathesis reactions of [M(Cp(R))(2)(Cl)(2)] (M = Zr or Hf, Cp(R) = Cp'; M = Hf or Th, Cp(R) = Cp'') with equimolar K{Si(SiMe(3))(3)} gave the respective mono-silanide complexes [M(Cp')(2){Si(SiMe(3))(3)}(Cl)] (M = Zr, 1; Hf, 2), [Hf(Cp'')(Cp'){Si(SiMe(3))(3)}(Cl)] (3) and [Th(Cp'')(2){Si(SiMe(3))(3)}(Cl)] (4), with only a trace amount of 3 presumably formed via silatropic and sigmatropic shifts; the synthesis of 1 from [Zr(Cp')(2)(Cl)(2)] and Li{Si(SiMe(3))(3)} has been reported previously. The salt elimination reaction of 2 with one equivalent of allylmagnesium chloride gave [Hf(Cp')(2){Si(SiMe(3))(3)}(η(3)-C(3)H(5))] (5), whilst the corresponding reaction of 2 with equimolar benzyl potassium yielded [Hf(Cp')(2)(CH(2)Ph)(2)] (6) together with a mixture of other products, with elimination of both KCl and K{Si(SiMe(3))(3)}. Attempts to prepare isolated [M(Cp(R))(2){Si(SiMe(3))(3)}](+) cations from 4 or 5 by standard abstraction methodologies were unsuccessful. The reduction of 4 with KC(8) gave the known Th(III) complex, [Th(Cp'')(3)]. Complexes 2-6 were characterised by single crystal XRD, whilst 2, 4 and 5 were additionally characterised by (1)H, (13)C{(1)H} and (29)Si{(1)H} NMR spectroscopy, ATR-IR spectroscopy and elemental analysis. In order to probe differences in M(IV)-Si bonds for d- and f-block metals we studied the electronic structures of 1-5 by density functional theory calculations, showing M-Si bonds of similar covalency for Zr(IV) and Hf(IV), and less covalent M-Si bonds for Th(IV).