Reactions of µ-ethynediyl complexes of transition metals: selective double insertion of isocyanides and molecular structure of [Cl(Et3P)2PdCCC(NPh)C(NPh)Pd(PEt3)2Cl]

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Abstract
The µ-ethynediyl-dipalladium complexes [X(R3P)2PdCCPd(PR3)2X]1(X = Cl or I, 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)2PdCCC(NR′)C(NR′)Pd(PR3)2X]2, selectively. Complexes 2 have been characterized by IR, mass, 1H, 13C-{1H}, and 31P-{1H} NMR spectra. Selective double insertion is peculiar to the µ-ethynediyl dinuclear complexes, and other dipalladium complexes [Cl(R3P)2PdCCYCCPd(PR3)2Cl](Y = bond or C6H4) and mononuclear acetylide complexes [Pd(PEt3)2Cl(CCR)](R = Ph or 4-MeOC6H4) give normal single-insertion products, respectively. The dicationic complex [(PhNC)(Et3P)2PdCCPd(PEt3)2(CNPh)][PF6]2 has been isolated as an intermediate, which reacts with NR4X (R = Et or C5H11; X = Cl, Br or I) to give double-insertion products 2. The structure of [Cl(Et3P)2PdCCC(NPh)C(NPh)Pd(PEt3)2Cl] has been determined by X-ray analysis: space group P21/c, a= 11.488(3), b= 24.997(5), c= 18.659(4)Å, β= 112.91(2)°, and Z= 4.