Reactions of co-ordinated ligands. Part 45. Ligand displacement and oxidative reactions of the carbyne complex [Mo(CCH2But){P(OMe)3}2(η-C5H5)]; crystal and molecular structures of [Mo{η3-RNCC(CH2But)CNR}-(CNR)2(η-C5H5)](R = 2,6-Me2C6H3), [Mo(CCHBut)I{P(OMe)3}2(η-C5H5)], and [M o{C(CH2But)P(O)(OMe)2}{P(OMe)3}(η-C5H5)]

Reaction of the carbyne complexes [M(CCH2R){P(OMe)3}2(η-C5H5)](M = Mo or W, R = But or Pri) with 2,6-xylyl isocyanide affords the complexes [M{η3-R′NCC(CH2But)CNR′}(CNR′)2(η-C5H5)](R′= 2,6-Me2C6H3), the molybdenum complex being identified by X-ray crystallography. In the 1,3-di-imino-substituted η3-allyl fragment the nitrogen atoms are bent back away from the allyl plane to subtend C–C–N angles of 135.2(9) and 133.1 (9)°. The central carbon atom of the allyl is also tilted away from the metal possibly due to intramolecular interactions. These complexes show temperature-dependent n.m.r. spectra which are discussed in terms of rotation about C–NR bonds and endo/exo isomerism. In attempting to understand the mechanism of formation of these complexes the solution 31P-{1H} n.m.r. spectra of the carbyne in the presence of free P(OMe)3 was studied. A DANTE pulse sequence suggested that dissociative loss of P(OMe)3 is not a rate-determining step in the reaction with isocyanide. The reaction of [Mo(CCH2But){P(OMe)3}2(η-C5H5)] with CO was also studied leading to loss of P(OMe)3, and formation of [Mo(CCH2But)-(CO){P(OMe)3}(η-C5H5)],[Mo(CCH2But)(CO)2(η-C5H5)], and [Mo{σ-CH(CO2Me)CH2But}-(CO)2{P(OMe)3}(η-C5H5)]. The mechanism of formation of these complexes is discussed. In addition the reaction of potential one-electron oxidants with [Mo(CCH2But){P(OMe)3}2(η-C5H5)] has been examined. Treatment with [4-FC6H4N2][BF4] affords the vinylidene complex [Mo(CCHBut)(N2C6H4Me-4){P(OMe)3}(η-C5H5)], whereas reaction with CF3l gives the X-ray crystallogra phically identified complexes [Mo(CCHBut)I{P(OMe)3}2(η-C5H5)] and [[graphic omitted]-(OMe)2}I{P(OMe)3}(η-C5H5)]. It is suggested that the latter complex is formed via the migration of a phosphonate group from molybdenum onto a carbyne carbon atom.