Synthesis, structure and catalytic activity of dicarbene dipalladium complexes with different alkane bridge

A series of di-NHC dipalladium complexes Pd2LPy2Cl4 (L = L-C3, L-C5, L-C6 and L-C10) with alkyl bridges of different chain lengths were prepared. The molecular structures of (Pd2LPy2Cl4)-Py-C3 (1) and (Pd2LPy2Cl4)-Py-C6 (3) were determined by X-ray diffraction studies. The influence of the different bridges on the structure and reactivity of the complexes was studied. The structure of complex 3 consists of two pseudo-square-planar subunits in a trans configuration, however complex 1 shows an X configuration due to pi-pi stacking of both imidazole rings and pyridine rings. The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki-Heck reaction of styrene with aryl bromides. The length of the bridged ligands had some effect on the yield and regioselectivity of the products. (C) 2012 Elsevier B.V. All rights reserved.