Reactions of co-ordinated ligands. Part 39. The synthesis of carbyne complexes from alkyne molybdenum and tungsten cations; formation and crystal structures of [Mo(CCH2But){P(OMe)3}2(η-C5H5)] and [Mo{C(SiMe3)CH2}{P(OMe)3}2(η5-C9H7)]

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Abstract
Thermolysis of the σ-vinyl complexes [M{σ-(E)-CHCHBut}{P(OMe)3}3(η5-CmHn)](M = Mo or W; m=n= 5; m= 9, n= 7), formed by reaction of hydride-anion donors with the cations [M(η2-ButC2H){P(OMe)3}2(η5-CmHn)][BF4], leads to formation of the carbyne complexes [M(CCH2But){P(OMe)3}2(η5-CmHn)]. The η-cyclopentadienylmolybdenum carbyne complex was structurally characterised by X-ray crystallography. The molecule adopts a ‘three-legged piano-stool’ geometry with one of the legs being a MoC triple bond [1.796(2)Å]. A similar reaction (–78 °C) between [Mo(η2-PriC2H){P(OMe)3}2(η-C5H5)][BF4] and K[BHBus 3] in the presence of P(OMe)3 afforded the η3-allyl complex [Mo(η3-CH2 CH CMe2){P(OMe)3}2(η-C5H5)], whereas the same cation with NaBH4–P(OMe)3 gave the carbyne complex [Mo(CCH2Pri){P(OMe)3}2(η-C5H5)]. Possible mechanisms for these carbyne-forming reactions are discussed. In contrast, reaction of the trimethylsilyl-substituted cation [Mo(η2-Me3SiC2H){P(OMe)3}2(η5-C9H7)][BF4] with K[BHBus 3] or Li(CuPh2) affords the η2-vinyl complexes [[graphic omitted]HR}{P(OMe)3}2(η5-C9H7)](R = H or Ph). The phenyl-substituted η2-vinyl is also formed on reaction of [Mo(η2-Me3SiC2Ph){P(OMe)3}2(η5-C9H7)][BF4] with K[BHBus 3], the corresponding reaction with Li(CuPh2) affording [[graphic omited]Ph2}{P(OMe)3}2(η5-C9H7)]. The η2-vinyl species [graphic omitted]HR}(R = H or Ph) thermally rearrange to the carbyne complexes [Mo(CCH2SiMe3){P(OMe)3}2(η5-C9H7)] and [Mo{CCH(Ph)SiMe3}{P(OMe)3}2(η5-C9H7)]. These trimethylsilyl-substituted carbynes are desilylated in NaF–H2O–MeCN to form [Mo(CCH3){P(OMe)3}2(η5-C9H7)] and [Mo(CCH2Ph){P(OMe)3}2(η5-C9H7)]. The molecular geometry of [[graphic omitted]H2}{P(OMe)3}2(η5-C9H7)] was established by X-ray crystallography. The η2-vinyl C–C bond lies nearly parallel to the Mo–P(1) vector the P(1)–Mo–C(8)–C(7) torsion angle being 13.8(2)°, with the carbene carbon C(8) nearer than C(7) to the plane of the indenyl ligand. The Mo–C(8) bond length is 1.955(3)Å, whereas Mo–C(7) is 2.258(4)Å.

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