Synthesis, electrochemistry, and ligand substitution reactions of conducting copolymer films of ruthenium polypyridine complexes and aromatic heterocycles

Conducting films containing ruthenium complexes of the general formula [Ru(2,2′-bipyridine)2(pmp)X]2+ (pmp = 3-(pyrrol-1-ylmethyl)pyridine, X = Cl−, ClO4−, pmp, CH3CN, or H2O) have been prepared by copolymerization of the Ru complex monomer with pyrrole, 3-methylthiophene, 1-methyl-3-(pyrrol-1-ylmethyl)pyridinium(1+), or 2,2′-bithiophene. The immobilized complexes exhibit rapid and reversible electrochemistry in acetonitrile. The perchlorate and water ligands are rapidly substituted to give the acetonitrile complex, while the chloride ligand is replaced more slowly. In aqueous media, both the perchlorate complex and chloride yield an aqua complex. The substitution rate of the chloride ligand is again low but is enhanced by photolysis. No substitution reactions were observed for the acetonitrile or pmp ligands under a variety of conditions tested. Infrared spectroscopy and fast atom bombardment mass spectroscopy indicate that attempts to isolate [Ru(bp)2(pmp)(ClO4)]+ as a solid in fact give the aqua complex. The perchlorate complex may also rearrange to the aqua complex in polymer films. Films containing the aqua complex were not useful for electrocatalytic oxidation because of the instability of the conducting polymer matrix at low pH and the inactivity of the complex at higher pH values. Key words: polythiophene, polypyrrole, electropolymerization, metallopolymer.