REACTIONS OF COORDINATED LIGANDS .52. FORMATION AND REACTIVITY OF MOLYBDENUM VINYLIDENE ANIONS - CRYSTAL-STRUCTURES OF [MOI(ETA-4-CH2 = CHCH = CHCH2BUT)(P(OME)3)(ETA-C5H5)] AND [MO(ETA-3-CBUTCHCHCME2CO)(P(OME)3)2(ETA-C5H5)]

Reaction of LiBu(n) with the carbyne complexes [Mo(= CCH2R){P(OMe)3}2(eta-C5H5)](R = Ph or Bu(t)) affords the red lithium species Li[Mo(CCHR){P(OMe)3}2(eta-C5H5)] characterised in solution by C-13 and P-31 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, activated CH2CH2O, Bu(t)COCl and CH2 = CHCH2Cl results in attack on the beta-carbon atom of the vinylidene with formation of a range of beta-substituted carbyne complexes isolated as crystalline materials. In the case of the benzyl-substituted systems there was also evidence for the formation of beta,beta'-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(eta-4-CH2 = CHCH = CHCH2Bu(t)){P(OMe)3}(eta-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(eta-C5H5)] affords the eta-3-allyl complex [Mo{activated eta-3-CBu(t)CHCMe2CO}{P(OMe)3}2(eta-C5H5)] in a reaction involving an unusual C-H activation.