VINYLPLATINUM CARBENES AND NITRILES, PLATINOXACYCLIC COMPLEXES, AND HECK-TYPE COUPLING PRODUCTS FORMED VIA REACTION OF (SIGMA-2-PROPENYL)BIS(TRIPHENYLPHOSPHINE)PLATINUM(II) TRIFLATE WITH ALKYNOLS, NITRILES, AND ACRYLATE ESTERS - MOLECULAR-STRUCTURE OF [(PPH3)2PTCH2C(O)OCH3][OTF]

The reaction of (2-propenyl)bis(triphenylphosphine)platinum(II) triflate (1a) with several unsaturated organic substrates such as alkynols, nitriles, and acrylate esters has been examined. Alkynols 3a (3-butyn-1-ol) and 3b ((+/-)-4-pentyn-2-ol) provide the vinyl carbene species [trans-Pt(=C(CH2)3O)(2-propenyl)(PPh3)2[OTf] (4a) and [trans-Pt(=C(CH2)2CH(CH3)O)(2-propenyl)-(PPh3)2][OTf] (4b). Reaction with nitriles 5a (acrylonitrile) and 5b (ethyl cyanoacetate) provide [(acrylonitrile) (2-propenyl) (PPh3)2Pt] [OTf] (6a) and [(ethyl cyanoacetate)(2-propenyl)(PPh3)2-Pt][OTf] (6b), each of which is bonded through the nitrogen lone pair. Reaction with methyl and ethyl acrylates (7a and 7b, respectively) results in the formation of the ''chelated'' platinum acrylate complexes [(PPh3)2PtCH2CH2C(O)OCH3] [OTf] (8a) and [(PPh3)2PtCH2CH2C(O)OCH2-CH3][OTf] (8b) in 63 and 58% isolated yields, respectively. The structure of complex 8a was unambiguously determined by X-ray analysis of a single crystal. Complex 8a crystallizes in the orthorhombic space group C222(1) with a = 17.433(3) angstrom, b = 17.964(4) angstrom, c = 25.047(4) angstrom, and Z = 8.0. The structure was solved and refined to R = 0.0521 and R(w) = 0.0674 with 5645 observed reflections. The formation of 8a and 8b involves cleavage of the original sigma-vinyl bond, transfer of a hydride to the acrylate, and release of the Heck-type coupling products CH2=C(CH3)-CH-CHCO2R (10a, R = CH3; 10b, R = CH2CH3). We present a mechanism of formation for complexes 8a, 8b, 10a, and 10b as well as reactions of 8a with carbon monoxide.