Coupling of Acetylenes Held Proximate to a Metal: Alkyne-Alkyne Interactions in cis-Phosphinoacetylene Complexes, Including Structural Characterization of the Unsymmetrical Diphosphine 1-Phenyl-2,3-bis(diphenylphosphino)naphthalene and Three Platinum(II) Complexesof Ph2PPh

The diphenyl(phenylethyny1)phosphine complexes cis-PtX(Y)(Ph2PCCPh)2 [X = Y = C1, I, CF3, C6F5, Me; X(Y) = o-C6H4O2, Me(Cl)] have been synthesized, and for all of the complexes except the dimethyl complex, intramolecular coupling of the phosphinoacetylene ligands occurs on heating to form cis-PtX(Y){o-C16Hl0(PPh2)2]. A mixture of the two possible structural isomers is formed for {cis-PtMe(Cl){o-C16H10(PPh2)2T)}. The complex {cis-PtMe2(o-C16Hl0(PPh2)2)} has been obtained by reaction of the dichloro analogue with methyllithium. The unsymmetrical diphosphine l-phenyl-2,3-bis(diphenylphosphino)naphthalene [o-C16H10(PPh2)2], produced as a coordinated ligand via these intramolecular coupling reactions, has been isolated in moderate yield from the dichloro complex and its structure determined by X-ray diffraction. Crystals of O-C1610(PPh2)2 are triclinic, space group P1-bar, with a = 11.437(13) A, b = 9.628(12) A, c = 16.712(21) A, alpha = 82.31(9)O, beta = 119.08(3)', gamma = 110.03(5)O, and Z = 2. The structure was solved and refined to R = 0.058, R, = 0.070. Structure determinations of cis-PtCl2(Ph2PCCPh)2.2MeCN, cis-PtMe(Cl)(Ph2PCPh)2.0.5CH2Cl2, and cis-PtMe2(Ph2PCCPh)2 have been carried out to evaluate interligand interactions in the complexes. Crystallographic data: cis-PtC12(Ph2- PCCPh)2.2MeCN, monoclinic, space group P21/c, a = 11.604(2) A, b = 18.416(5) A, c = 19.344(3) A, beta = 98.63', Z = 4, R = 0.031, R, = 0.035; cis-PtMe(Cl)(Ph2PCCPh2)2.0.5CH2Cl2, orthorhombioc, space group Pbca, a = 16.910(2) A, b = 17.207(1) A, c = 25.300(2) A, Z = 8, R = 0.039, R, = 0.044; cis-PtMe2(Ph2PCPh)2, orthorhombic, space group Pbca, a = 11.934(2) A, b = 16.885(3) A, c = 34.098(8) A, Z = 8, R = 0.037, R, = 0.042. Factors affecting the occurrence of intramolecular coupling are assessed, together with a comparison of this reaction with related reactions of organic diacetylenes. The complex ci2-PtMe(Cl)(Ph2PCCPh)2 reacts with diphenylphosphine to form a mixture of the two structural isomers of cis-PtMe(Cl){Ph2PCH=C(Ph)PPh2]