A series of phosphine-substituted ruthenium poly-pyridine complexes, cis(P,Cl)-[Ru(trpy)(Pqn)Cl]PF6 (cis-Cl), trans(P,MeCN)-[Ru(trpy)(Pqn)(MeCN)](PF6)(2) (trans-PN), cis(P,MeCN)-[Ru(trpy)(Pqn)(MeCN)] (PF6)(2) (cis-PN), and [Ru(trpy)(dppbz)(MeCN)] (PF6)(2) (PP), were synthesized and crystallographically characterized (trpy = 2,2':6',2 ''-terpyridine, Pqn = 8-(diphenylphosphanyl)quinoline, and dppbz = 1,2-bis(diphenylphosphanyl)benzene). In electrochemical measurements for cis-PN and PP, the reduction of cis-PN resulted in the formation of trans-PN via cis trans isomerization and that of PP proceeded via a two-electron-transfer reaction. The mechanism of the electrochemical behaviors is discussed through consideration of five-coordinated species, [Ru(trpy)(Pqn)](n+) or [Ru(trpy)(dppbz)](n+) (n = 0-2), formed by liberation of a monodentate labile ligand.