New heterobimetallic Cu(I)–Pd(II)-containing polymer complexes: Electrochemical synthesis and application in catalysis

Electrochemical approach to a new electroactive heteropolynuclear catalytic system based on polyamic acids with biquinolyl (biQ) fragments in the polymer backbone capable of coordination to PdII and CuI-ions was developed using sacrificial Pd and Cu anodes. The order of anode dissolution (first Pd and then Cu) was shown to be important for the synthesis of the heteropolynuclear complex. The opposite order of dissolution resulted in the oxidation of the initially formed CuI ions to CuII. The redox properties of the obtained heteronuclear polymer complexes containing CuI and PdII coordination units were characterized by cyclic voltammetry. The catalytic properties of the resultant metal–polymer system were investigated and it showed high catalytic activity in the reaction of aryl halides with phenylacetylene (Sonogashira coupling) at a small Pd loadings (0.1 mol%) yielding 50–90% of arylphenylacetylene depending on the nature of the aryl halide. The proposed catalytic system also exhibits high catalytic activity in cascade cyclisations of 2-iodoaniline and 2-iodophenole in the presence of phenylacetylene yielding synthetically useful 2-phenylindole (90%) and 2-phenylbenzofuran (92%).