REACTIONS OF MU-ETHYNEDIYL COMPLEXES OF TRANSITION-METALS - SELECTIVE DOUBLE INSERTION OF ISOCYANIDES AND MOLECULAR-STRUCTURE OF [CL(ET3P)2PDC=CC(=NPH)C(=NPH)PD(PET3)2CL]

The mu-ethynediyl-dipalladium complexes [X(R3P)2PdC = CPd(PR3)2X] 1 (X = Cl or l, R = Et or Bu) react with aryl isocyanides R'NC(R' = Ph, 4-NO2C6H4, or 2,6-Me2C6H3) to give double-insertion products [X(R3P)2PdC = CC(= NR')C(= NR')Pd(PR3)2X] 2, selectively. Complexes 2 have been characterized by IR, mass, H-1, C-13-{H-1}, and P-31-{H-1} NMR spectra. Selective double insertion is peculiar to the mu-ethynediyl dinuclear complexes, and other dipalladium complexes [Cl(R3P)2PdC = CYC = CPd(PR3)2Cl] (Y = bond or C6H4) and mononuclear acetylide complexes [Pd(PEt3)2Cl(C = CR)] (R = Ph or 4-MeOC6H4) give normal single-insertion products, respectively. The dicationic complex [(PhNC)(Et3P)2PdC = CPd(PEt3)2(CNPh)][PF6]2 has been isolated as an intermediate, which reacts with NR4X (R = Et or C5H11; X = Cl, Br or l) to give double-insertion products 2. The structure of [Cl(Et3P)2PdC = CC(= NPh)C(= NPh)Pd(PEt3)2Cl] has been determined by X-ray analysis: space group P2(1)/c, a = 11.488(3), b = 24.997(5), c = 18.659(4) angstrom, beta = 112.91(2)-degrees, and Z = 4.