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

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.