Molybdenum-mediated cocyclisation reactions involving prop-2-ynyl, alkyne and carbon monoxide ligands

Abstract

Reaction of the σ,η²(3e)-prop-2-ynyl/η²(4e)-alkyne complex [Mo{σ,η²(3e)-CH₂C₂Me}{η²(4e)-MeC₂Me}-(η-C₅H₅)] with hexafluorobut-2-yne led to a novel cyclisation reaction affording an X-ray crystallographically identified complex containing an (η-C₅H₅)Mo fragment η³, η⁴ bonded to a bicyclo[4.3.0]nonyl ring system formed by the cocyclisation of two molecules of CF₃C₂CF₃, a but-2-yne molecule and a prop-2-ynyl fragment. A mechanism of formation is proposed involving, in the final step, the placement of a hydrogen substituent on the opposite face of the bicyclo-ring system to which the molybdenum is attached, via the ionisation of an acidic Mo–H bond. The reactions of [Mo{σ,η²(3e)-CH₂C₂R}{η²(4e)-MeC₂R}(η-C₅H₅)](R = Me or Ph) with carbon monoxide led to novel cocyclisation reactions and the formation of the X-ray crystallographically identified complexes [Mo{η²,η³-[graphic omited]CH₂}(CO)(η-C₅H₅)]. Protonation (HBF₄·Et₂O) of the methyl-substituted system was shown by X-ray crystallography to involve protonation of the keto-group, rather than the η³-allylic CH₂ group, to give the cationic complex [Mo{η³,η³-[graphic omited]CH₂}-(CO)(η-C₅H₅)][BF₄].