η2‑Allenyl- and η2‑Alkynylphosphonium Complexes of Platinum

The reaction of the propargylic salt [Ph3PCH2CCH]­PF6 with [Pt­(C2H4)­(PPh3)2] affords the η2-allenylphosphonium salt [Pt­(η2-CH2CCHPPh3)­(PPh3)2]­PF6 via a metal-mediated propargylic rearrangement. Isomerization of the complex occurs in solution to generate the salt [Pt­{η2-C­(PPh3)CCH2}­(PPh3)2]­PF6, wherein the allene is coordinated by the internal CC bond. Computational studies indicate that the isomerization of the propargylic cation [Ph3PCH2CCH]+ to the allenyl species [Ph3PCHCCH2]+ and the α-alkynyl isomer [Ph3PCCCH3]+ is thermodynamically favorable. The isomeric η2-alkynylphosphonium salt [Pt­{η2-C­(CH3)CPPh3}­(PPh3)2]­PF6 is formed from the reaction of [Ph3PCCCH3]­PF6 with [Pt­(C2H4)­(PPh3)2] and does not isomerize to the propargylic or allenyl forms.炔丙基盐（propargylic salt）[Ph₃PCH₂C≡CH]PF₆与乙烯双(三苯基膦（triphenylphosphine, PPh₃）)合铂[Pt(C₂H₄)(PPh₃)₂]发生反应，经由金属介导的炔丙基重排（metal-mediated propargylic rearrangement），生成η²-联烯鏻盐（η²-allenylphosphonium salt）[Pt(η²-CH₂=C=CHPPh₃)(PPh₃)₂]PF₆。 该配合物在溶液中发生异构化，得到盐[Pt{η²-C(PPh₃)=C=CH₂}(PPh₃)₂]PF₆，此产物中的联烯通过内部C=C双键完成配位。 计算研究（computational studies）表明，炔丙基阳离子（propargylic cation）[Ph₃PCH₂C≡CH]⁺异构为联烯类物种[Ph₃PCH=C=CH₂]⁺与α-炔基异构体（α-alkynyl isomer）[Ph₃PC≡CCH₃]⁺的过程均为热力学有利的。 与前述产物异构的η²-炔基鏻盐（η²-alkynylphosphonium salt）[Pt{η²-C(CH₃)≡CPPh₃}(PPh₃)₂]PF₆可由[Ph₃PC≡CCH₃]PF₆与[Pt(C₂H₄)(PPh₃)₂]反应生成，且无法异构为炔丙基或联烯型配合物。