Synthesis and characterization of a metal coordination polymer consisting of ruthenium(III) β-diketone units linked by butadiyne bridges

Abstract

A new metal coordination polymer consisting of ruthenium(III) β-diketone units linked by butadiyne bridges was synthesized, and two mononuclear complexes, [Ru(mESima)3] and [Ru(mEma)3] (mESima−=3-(trimethylsilyl)ethynyl-2,4-pentanedionate ion and mEma−=3-ethynyl-2,4-pentanedionate ion), were also prepared as starting materials for the polymerization. The polymer was soluble in dichloromethane, chloroform, and benzene. The number-average molecular weight, 5400, corresponding to about 11 monomer units, was obtained from the FT-NMR integrated intensities for the protons on the ethynyl group of the mEma ligand end-group relative to the methyl protons of the entire chains. The NMR spectra also showed that the polymer structure was not a star-burst type but a chain-like type. The polymer exhibited one oxidation peak and one reduction peak on differential pulse voltammograms at 25°C; however, the one anodic peak separated into two peaks at −36°C. The difference in peak potentials between the first and the second oxidation waves was 0.23 V, which was very similar to the difference (0.22 V) in peak potentials for the corresponding binuclear complex. This indicated that metal–metal interactions in the polymer operate between only the closest neighboring units. Results of the controlled potential coulometry of the polymer in dichloromethane medium indicated that each monomer unit underwent a one-electron reduction.