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A Cationic Unsaturated Platinum(II) Complex that Promotes the Tautomeration of Acetylene to Vinylidene


L. Ortega-Moreno, R. Peloso, J. López-Serrano, J. Iglesias-Sigüenza, C. Maya, E. Carmona Angew. Chem. Int. Ed. 2017, Vol. 56, 2772-2775

Complex [PtMe2 (PMe2 ArDipp2)] (1), which contains a tethered terphenyl phosphine (ArDipp2 =2,6-(2,6-(i) Pr2 C6 H3)2 C6 H3), reacts with [H(Et2 O)2 ]BArF (BArF(-) =B[3,5-(CF3 )2 C6 H3 ]4(-) ) to give the solvent (S) complex [PtMe(S)(PMe2 ArDipp2)](+) (2⋅S). Although the solvent molecule is easily displaced by a Lewis base (e.g., CO or C2 H4 ) to afford the corresponding adducts, treatment of 2⋅S with C2 H2 yielded instead the allyl complex [Pt(η(3) -C3 H5 )(PMe2 ArDipp2 )](+) (6) via the alkyne intermediate [PtMe(η(2) -C2 H2 )(PMe2 ArDipp2 )](+) (5). Deuteration experiments with C2 D2, and kinetic and theoretical investigations demonstrated that the conversion of 5 into 6 involves a Pt(II) -promoted HC≡CH to :C=CH2 tautomerization in preference over acetylene migratory insertion into the Pt-Me bond.