Journal of the Chemical Society, Dalton Transactions p. 415 - 430 (1996)
Update date:2022-08-04
Topics:
Carfagna, Carla
Carr, Nicholas
Deeth, Robert J.
Dossett, Stephen J.
Green, Michael
Mahon, Mary F.
Vaughan, Corrine
Reaction of cis-/trans-[ReBr2(CO)2(η-C5H5)] with PhC2Ph and MeC2Ph in refluxing toluene afforded good yields of the n2(4e)-donor alkyne complexes [ReBr2(η2-PhC2Ph)(η-C5H 5)] 1 and [ReBr2(η2-MeC2Ph)(η-C5H 5)] 2, respectively. Treatment of 1 and 2 with either AgBF4 or TlPF6 in the presence of PPh3, PMePh2 or P(OMe)3 (L) gave monocations [ReBr{η2(4e)-alkyne}L(η-C5H5)] +, whereas a similar reaction with 2 equivalents of AgBF4 and 1 equivalent of Ph2PCH2CH2PPh2 (dppe) afforded dications [Re(η2-PhC2Ph)(dppe)(η-C5H 5)][BF4]2 and [Re(η2-MeC2Ph)(dppe)(η-C5H 5)][BF4]2. The structural identity of [ReBr(η2-PhC2Ph)(PMePh2)(η-C 5H5)][PF6] was confirmed by single-crystal X-ray crystallography. The alkyne C-C vector lies parallel to the Re-Br bond and the alkyne C-C bond length [C(1)-C(2) 1.26(4) A] is relatively short. Treatment of [ReBr(η2-PhC2Ph)(PPh3)(η-C 5H5)][BF4] and [ReBr(η2-PhC2Ph)(PMePh2)-(η-C 5H5)][PF6] with K[BHBus3] in dichloromethane at -78°C led to neutral η2(3e)-vinyl complexes [Re{=C(Ph)CHPh}Br(PPh3)(η-C5H5)] and [Re{=C(Ph)CHPh}Br(PMePh2)(η-C5H5)]. The crystal structure of the latter showed that the C-C vector of the vinyl moiety lies almost parallel to the Re-Br bond. The stereochemistry of these reactions is discussed in the light of extended-Hueckel molecular orbital calculations. Reaction (-78°C) of [Re(η2-PhC2Ph)(dppe)(η-C5H 5)][BF4]2 with 1 equivalent of K[BHBus3] in tetrahydrofuran afforded the X-ray crystallographically identified monocationic η2(3e)-vinyl complex [Re{=C(Ph)CHPh}(dppe)(η-C5H5)][BF4], which reacted at room temperature with a further equivalent of K[BHBus3] to give the cis-stilbene-substituted complex [Re(η2-Z-PhCH=CHPh)(dppe)(η-C5H5)]. The crystal structure of the latter showed that the alkene phenyl substituents are orientated towards the cyclopentadienyl ring. In contrast, a similar reaction between K[BHBus3] and [Re(η2-MeC2Ph)(dppe)(η-C5H 5)][BF4]2 gave initially the η2(3e)-vinyl complex [Re{=C(Me)CHPh}(dppe)(η-C5H5)][BF4]; a further equivalent of K[BHBus3] led to deprotonation and formation of the η2-allene complex [Re{η2-CH(Ph)=C=CH2}(dppe)-(η-C5H 5)], in which the substituted allenic bond is co-ordinated to the rhenium. The dinuclear complex [Re2Br2(PPh3)2(μ-O)(η-C 5H5)2][BF4]2 was also prepared and shown crystallographically to possess a single rhenium-rhenium bond [2.731(5) A].
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