Reactions of co-ordinated ligands. Part 41. Synthesis and reactions of cationic functionalised alkyne molybdenum complexes; formation of carbyne and vinylidene complexes and crystal structure of [Mo(CCHPh)Br{P(OMe)3}2(η-C5H5)]

Abstract

Treatment of a solution of [Mo₂(CO)₆(η-C₅H₅)₂] in CH₂Cl₂, with AgBF₄ in the presence of the substituted alkynes RC₂X (R = Bu^t or Ph, X = SMe or Br) gives the cations [Mo(η²-RC₂X)₂(CO)(η-C₅H₅)][BF₄], which react with P(OMe)₃ to form the highly coloured monoalkyne cations [Mo(η²-RC₂X){P(OMe)₃}₂(η-C₅H₅)][BF₄]. Reaction of the thiosubstituted cations with K[BHBu^s₃] or Li[CuMe₂] affords the η²-vinyl complexes [[graphic omitted](SMe)R′{P(OMe)₃}₂(η-C₅H₅)](R = Bu^t or Ph, R′= H or Me), which react with AgBF₄ in CH₂Cl₂ to form the alkyne cations [Mo(η²-RC₂R′){P(OMe)₃}₂(η-C₅H₅)][BF₄]. Treatment of the bromo-substituted cation [Mo(η²- Bu^tC₂Br){P(OMe)₃}₂(η-C₅H₅)][BF₄] with K[BHBu^s₃] gives the carbyne [Mo(CCH₂Bu^t){P(OMe)₃}₂(η-C₅H₅)], whereas the phenyl-substituted cation affords a mixture of [Mo(CCH₂Ph){P(OMe)₃}₂(η-C₅H₅)] and the vinylidene complex [Mo(CCHPh)Br{P(OMe)₃)₂(η-C₅H₅)], the latter being identified by single-crystal X-ray crystallography. The molecule has a typical ML₄(η-C₅H₅)‘piano-stool’ geometry, the MoCCHPh moiety adopting an essentially linear arrangement [Mo–C(7)–C(8) 177.9(5)°] with C(7)–C(8) and Mo–C(7) bond lengths of 1.327(7)Å and 1.917(5)Å respectively. Treatment of the bromo-vinylidene complex with K[BHBu^s₃] or Li[CuPh₂] affords the carbynes [Mo(CCH₂Ph)(P)OMe)₃)₂(η-C₅H₅)] and [Mo(CCPh₂){P(OMe)₃}₂(η-C₅H₅)]. Reaction of [Mo(η²-PhC₂Br){P(OMe)₃}₂(η-C₅H₅)][BF₄] with Li[CuPh₂] affords the η²-vinyl complex [[graphic omitted]Ph₂}{P(OMe)₃}₂(η-C₅H₅)], which reacts with Li[CuMe₂] or Li[CuPh₂] to give [[graphic omitted]Ph₂}{P(OMe)₃}₂(η-C₅H₅)](R = Me or Ph). The bromo-vinylidene complex also reacts with PEt₃ to give [Mo(CCHPh)Br{P(OMe)₃}(PEt₃)(η-C₅H₅)], which in turn reacts with K[BHBu^s₃] to give a carbyne complex.