Preparation and properties of trans-Pd(Ar)(C CPh)(PEt3)(2). Intermolecular alkynyl ligand transfer between copper(I) and palladium(II) complexes relevant to palladium complex catalyzed cross-coupling of terminal alkyl with haloarene in the presence of CuI cocatalyst

trans-Pd(C6H4Me-P)(I)(PEt3)(2) (2a) reacts with [Cu(C=CPh)(PPh3)](4) (Pd:Cu = 1:1) at room temperature to give the cross-coupling product PhC=CC6N4Me-p (3a) in 74% yield. Reactions of 2a with [Cu(C=CPh)(PPh3)](4) at -30 degrees C as well as of trans-Pd(C6H4X-p)(I)(PEt3)(2) (2a, X = Me; 2b, X = OMe; 2c, X = F) with the alkynylcopper complex and additional PPh3 (2 moll mol of Cu) at room temperature give mixtures of PhC=CC6H4X-p (3a, X = Me; 3b, X = OMe; 3c, X = F) and trans-Pd(C6H4X-p)(C=CPh)(PEt3)(2) (4a, X = Me; 4b, X = OMe; 4c, X = F). Complexes 4a,b have been isolated from the latter reaction mixtures and fully characterized. Pd-C(alkynyl) and Pd-C(aryl) bond distances in 4a are 2.016(8) and 2.062(7) Angstrom, respectively. Addition of CuI to a solution of 4a at room temperature causes complete conversion of 4a into 2a and 3a in 1 h. The relative molar ratio between 2a and 4a after reaction for 2 h varies, depending on the amount of added PPh3. Reactions of trans-Pt(C6H4X-p)(I)(PEt3)(2) (5b, X = OMe; 5c, X = F) with [Cu(C=CPh)(PPh3)](4) at room temperature afford trans-Pt(C6H4X-p)(C=CPh)(PEt3)(2) (6b, X = OMe; 6c, X = F), respectively. Heating an equimolar mixture of 4a and 5b at 35-50 degrees C leads to inter-metal exchange of the alkynyl sand iodo ligands, giving 2a and 6b quantitatively. The reaction follows the kinetics that is first order in concentration of 4a and in that; of 5b. The kinetic parameters are obtained as Delta H-not equal = 110 kJ mol(-1), Delta S-not equal = -58 J mol(-1) deg(-1), and Delta G(not equal) = 127 kJ mol(-1) at 298 K. The alkynyl ligand migration from Pd(II) to Pt(II) is enhanced by addition of a catalytic amount of CuI.