Electrochemical oxidation of methanol with Ru/Pd, Ru/Pt, and Ru/Au heterobimetallic complexes

The heterobimetallic complexes CpRu(PPh3)(mu-Cl)(mu-dppm)PdCl2 (1) [dppm = bis(diphenylphosphino)methane], CpRu(PPh3)Cl(mu-dppm)AuCl (2), and CpRu(PPh3)(mu-Cl)(mu-dppm)PtCl2 (3) were synthesized by the reaction of CpRu(PPh3)Cl(eta(1)-dppm) (4) with Pd(COD)Cl-2, AuPPh3Cl, and Pt(COD)Cl-2, respectively. Compounds 1 and 2 were characterized by X-ray crystallography. Electrochemical oxidation of CH3OH in the presence of 1, 2, or 3 leads to considerable enhancement of the oxidative currents and formation of the organic products CH2(OCH3)(2) and HCOOCH3. Addition of water increases both the current and the proportion of the more highly oxidized product, HCOOCH3. Current efficiencies obtained with heterobinuclear complexes 1-3 were significantly higher than those obtained using the model compound CpRuCl(eta(2)-dppm) (5) as catalyst.