COORDINATION CHEMISTRY OF PERHALOGENATED CYCLYOPENTADIENES AND ALKYNES .21. STUDIES ON THE SUBSTITUTION-REACTIONS OF PT(PPH3)(2)(C2CL2) ANDTRANS-PT(PPH3)(2)(CL)(C2CL) WITH TRIPHENYLPHOSPHITE

The reactions of the Pt(0) pi-alkyne complex Pt(PPh3)(2)(CI C equivale nt to CCl) and the Pt-II alkynyl complex Pt(PPh3)(2)(Cl)(C equivalent to CCl) with P(OPh)(3) lead to either the pi-alkyne complexes Pt(PPh3) (n)(P(OPh)(3))(2-n)(Cl C equivalent to CCl) (n = 0, 1) or the cis and trans isomers of Pt(PPh3)(n)[P(OPh)(3)](2-n) (Cl)(C equivalent to CCl) (n = 0, 1), depending on the reaction conditions. The course of the r eaction was followed by P-31-NMR spectroscopy, from which a plausible mechanism for the oxidative addition reaction can be derived: key step s are phosphine dissociation from the Pt(0) species to a two-coordinat e intermediate, which undergoes oxidative addition of a C-Cl bond to g ive a three-coordinate Pt-II species, which might be stabilized by dim erization. (C) 1997 Elsevier Science Ltd.