Vinylic Deprotonation in the Coordination Sphere of Platinum( II ): Regioselective Formation of Alkenyl Complexes

Reaction of [PtCl(η 2 ‐CH 2 =CHAr)(tmeda)](ClO 4 ) ( 1 ) [Ar = C 6 H 5 ( 1a ), 4‐CH 3 OC 6 H 4 ( 1b ), 3‐NO 2 C 6 H 4 ( 1c ); tmeda = N , N , N′ , N′ ‐tetramethylethylenediamine) with triethylamine, or even with inorganic carbonate, leads to the abstraction of a vinylic proton and formation of the (alkenyl)platinum species [PtCl{( E )‐CH=CHAr}(tmeda)] ( 2 ) in high yield. The initially formed ( E ) isomer, in solution of chlorinated solvents, partly isomerizes into the ( Z ) form [equilibrium ratio ( E )/( Z ) ≈ 4:1]; the isomerization reaction is rather slow and is catalyzed by visible light. The nature of the phenyl substituent (electron donor OMe or electron‐withdrawing NO 2 group) does not appear to affect the rate of deprotonation. The nature and stereochemistry of the formed (alkenyl)platinum species has been elucidated through 1D and 2D 1 H and 13 C NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)