Synthesis and structure of bimetallic complexes with σ,π-bridged monocarbene ligands

Abstract

The Fischer method was employed to synthesize bimetallic monocarbene complexes from lithiated [Cr(SC ₄ H ₄ )(CO) ₃ ] and metal hexacarbonyls. In addition to the formation of [M{C[η ⁵ -C ₄ H ₃ SCr(CO) ₃ ]OEt}(CO) ₅ ] (M = Cr 1 or W 2) the complexes [M{C[η ⁵ -C ₄ H ₃ SCr(CO) ₃ ]O(CH ₂ ) ₄ OEt}(CO) ₅ ] (M = Cr 3 or W 4), were also obtained. The formation of 3 and 4 is ascribed to the activation of tetrahydrofuran (thf) by a σ,π-co-ordinated acyl metalate, which triggers the cleavage of the thf ring and leads to its inclusion into the alkoxy substituent of the resulting carbene moiety. In polar solvents the Cr(CO) ₃ fragments are displaced to give known pentacarbonyl[ethoxy(thienyl)carbene] complexes and the new mononuclear carbene complexes [M{C(C ₄ H ₃ S)O(CH ₂ ) ₄ OEt }(CO) ₅ ] (M = Cr 5 or W 6). The analogous benzo[b]thienyl carbene complex [Cr{C[η ⁶ -C ₈ H ₅ SCr(CO) ₃ ]OEt}(CO) ₅ ] 7 was prepared similarly, but did not afford the thf-inserted product and the corresponding conversion into the mononuclear carbene complex [Cr{C(C ₈ H ₅ S)OEt}(CO) ₅ ] 8, was much slower.