Novel coordination behavior of unsaturated hydrocarbon ligands on Pd–Pd bonds*

Abstract: The dinuclear Pd(I) complexes containing substitutionally labile acetonitrile lig-ands [Pd2(CH3CN)2(L)2](BF4)2 [L = CH3CN (1), PPh3 (2)] were prepared. The complex 1 was demonstrated to serve as a versatile building block for synthesizing sandwich chain com-plexes made of conjugated polyenes and linear polypalladium chains. The complex 2 react-ed with 2 equiv arylacetylenes to give dinuclear organopalladium complexes arising from formal [2σ + 2π + 2π] addition with the Pd–Pd σ bond participating as one component. The reaction of 2 with 1,3-butadiene afforded a complex regarded as an intermediate lying halfway on the [2σ + 4π] reaction coordinate