Comparison of group 4 and thorium M(iv) substituted cyclopentadienyl silanide complexes

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).