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

Complex [PtMe 2 (PMe 2 ArDipp2)] ( 1 ), which contains a tethered terphenyl phosphine (ArDipp2=2,6‐(2,6‐ i Pr 2 C 6 H 3 ) 2 C 6 H 3 ), reacts with [H(Et 2 O) 2 ]BAr F (BAr F − =B[3,5‐(CF 3 ) 2 C 6 H 3 ] 4 − ) to give the solvent (S) complex [PtMe(S)(PMe 2 ArDipp2)] + ( 2⋅S ). Although the solvent molecule is easily displaced by a Lewis base (e.g., CO or C 2 H 4 ) to afford the corresponding adducts, treatment of 2⋅S with C 2 H 2 yielded instead the allyl complex [Pt(η 3 ‐C 3 H 5 )(PMe 2 ArDipp2)] + ( 6 ) via the alkyne intermediate [PtMe(η 2 ‐C 2 H 2 )(PMe 2 ArDipp2)] + ( 5 ). Deuteration experiments with C 2 D 2 , and kinetic and theoretical investigations demonstrated that the conversion of 5 into 6 involves a Pt II ‐promoted HC≡CH to :C=CH 2 tautomerization in preference over acetylene migratory insertion into the Pt−Me bond.