Electrochemical behavior of phosphine-substituted ruthenium(II) polypyridine complexes with a single labile ligand.

A series of phosphine-substituted ruthenium polypyridine complexes, cis(P,Cl)-[Ru(trpy)(Pqn)Cl]PF6 (cis-Cl), trans(P,MeCN)-Ru(trpy)(Pqn)(MeCN)2 (trans-PN), cis(P,MeCN)-Ru(trpy)(Pqn)(MeCN)2 (cis-PN), and Ru(trpy)(dppbz)(MeCN)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) or Ru(trpy)(dppbz) (n = 0-2), formed by liberation of a monodentate labile ligand.