Mixed-sandwich complexes of zirconium(III) and hafnium(III): Potential analogues of [U(η-C 8H 6{Si iPr 3-1,4} 2)(η-Cp ∗)] for cyclooligomerisation of CO

Abstract

Reaction of ZrCl 4 or HfCl 4 with 2 equivalents of K 2(COT{Si i Pr 3-1,4} 2), followed by in situ treatment of the resultant sandwich complexes M(COT{Si i Pr 3-1,4} 2) with a further equivalent of MCl 4 affords the mono-COT chloro-bridged dimers [M(η-COT{Si i Pr 3-1,4} 2)(μ-Cl)Cl] 2, M = Zr ( 1); M = Hf ( 4). Further reaction of the latter with 2 equivalents of KCp ∗ yields the crystallographically characterised M(IV) mixed-sandwich complexes [M(η-COT{Si i Pr 3-1,4} 2)(η-Cp ∗)Cl], M = Zr ( 2); M = Hf ( 5). Reduction of 2 with KC 8 in toluene affords the monomeric Zr(III) mixed-sandwich complex [Zr(η-COT{Si i Pr 3-1,4} 2)(η-Cp ∗)], whereas the analogous reaction with 5 results in coupling of the COT rings to give dimeric [Hf(η-Cp ∗)] 2(μ-η 7,η 7-(C 8H 6{Si i Pr 3-3,6} 2C 8H 6{Si i Pr 3-3,6} 2)); both 2 and 5 have been structurally characterised.