Reactions of co-ordinated ligands. Part 52. Formation and reactivity of molybdenum vinylidene anions; crystal structures of [Mol(η4-CH2CHCHCHCH2But){P(OMe)3}(η-C5H5)] and [Mo(η3-CButCHCHCMe2CO){P(OMe)3}2(η-C5H5)]

Abstract

Reaction of LiBuⁿ with the carbyne complexes [Mo(CCH₂R){P(OMe)₃}₂(η-C₅H₅)](R = Ph or Bu^t) affords the red lithium species Li[Mo(CCHR){P(OMe)₃}₂(η-C₅H₅)] characterised in solution by ¹³C and ³¹P NMR spectroscopy as vinylidene complexes with the negative charge localised on the metal centre. The reactions of the potentially ambident nucleophiles with a wide range of organic electrophilic reagents have been studied. Quenching with Mel, EtBr, SiMe₃Cl, EtOCH₂Cl, MeSSMe, [graphic omitted], Bu^tCOCl and CH₂CHCH₂Cl results in attack on the β-carbon atom of the vinylidene with formation of a range of β-substituted carbyne complexes isolated as crystalline materials. In the case of the benzyl-substituted systems there was also evidence for the formation of β,β′-disubstituted carbynes. In contrast, quenching with allyl iodide leads to an unusual reaction and formation of 1,3-diene complexes, this being confirmed by a single-crystal X-ray diffraction study on [Mol(η⁴-CH₂CHCHCHCH₂Bu^t){P(OMe)₃}-(η-C₅H₅)]. This is explained in terms of a competing allylation reaction at the molybdenum centre. Ultraviolet irradiation of [Mo{CCH(COBu^t)Bu^t}{P(OMe)₃}₂(η-C₅H₅)] affords the η³-allyl complex [Mo{η³-[graphic omitted]O}{P(OMe)₃}₂(η-C₅H₅)] in a reaction involving an unusual C–H activation.