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)]

Abstract

Reaction of the carbyne complexes [M(CCH₂R){P(OMe)₃}₂(η-C₅H₅)](M = Mo or W, R = Bu^t or Prⁱ) with 2,6-xylyl isocyanide affords the complexes [M{η³-R′NCC(CH₂Bu^t)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(CCH₂Bu^t){P(OMe)₃}₂(η-C₅H₅)] with CO was also studied leading to loss of P(OMe)₃, and formation of [Mo(CCH₂Bu^t)-(CO){P(OMe)₃}(η-C₅H₅)],[Mo(CCH₂Bu^t)(CO)₂(η-C₅H₅)], and [Mo{σ-CH(CO₂Me)CH₂Bu^t}-(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(CCH₂Bu^t){P(OMe)₃}₂(η-C₅H₅)] has been examined. Treatment with [4-FC₆H₄N₂][BF₄] affords the vinylidene complex [Mo(CCHBu^t)(N₂C₆H₄Me-4){P(OMe)₃}(η-C₅H₅)], whereas reaction with CF₃l gives the X-ray crystallogra phically identified complexes [Mo(CCHBu^t)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.