Synthesis and properties of carboxy-substituted half-sandwich ruthenium complexes with chelating bisphosphine ligands (η5-C5H4CO2H)Ru(η2-L)X (X = I, H)

Several Ru(II) complexes (η5-C5H4CO2H)Ru(η2-L)I have been prepared by the hydrolysis of the ester linkage in (η5-C5H4CO2t-Bu)Ru(η2-L)Cl with trimethylsilyl iodide. The hydrides (η5-C5H4CO2H)Ru(η2-L)H may be prepared by reduction of the iodide complexes in KOH/MeOH solutions followed by acidification. Complexes with several chelating bisphosphine ligands have been prepared in this way. The carboxylate anions [(η5-C5H4CO2)Ru(η2-L)H]− are readily protonated by weak acids to give the carboxyCp complexes. The pKa of the carboxy proton of (η5-C5H4CO2H)Ru(dppe)H (dppe = 1,2-bis(diphenylphosphino)ethane) is 11.3 in DMSO. Protonation of the neutral hydride complex (η5-C5H4CO2H)Ru(dppf)H gives the cationic dihydride (η5-C5H4CO2H)Ru(dppf)H+2; the dihydride structure has been confirmed by measuring the T1 of its 1H NMR hydride resonance over a range of temperatures. The oxidations of the halide complexes (η5-C5H4CO2H)Ru(dppf)I and (η5-C5H4CO2t-Bu)Ru(dppf)Cl (dppf = 1,1′-bis(diphenylphosphino)ferrocene) have been studied by cyclic voltammetry.