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(CCHPh)Br{P(OMe)3}2(η-C5H5)]

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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 = But 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[BHBus 3] or Li[CuMe2] affords the η2-vinyl complexes [[graphic omitted](SMe)R′{P(OMe)3}2(η-C5H5)](R = But 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- ButC2Br){P(OMe)3}2(η-C5H5)][BF4] with K[BHBus 3] gives the carbyne [Mo(CCH2But){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[BHBus 3] 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[BHBus 3] to give a carbyne complex.

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