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].