ELECTROCHEMICAL OXIDATION OF DIAQUARUTHENIUM(II) COMPLEXES OF QUATERPYRIDINES AND CRYSTAL-STRUCTURE OF [RUL1(PPH3)2][CLO4]2 (L1 = 3'',5,5',5'''-TETRAMETHYL-2,2',6',2'',6'',2'''-QUATERPYRIDINE)

The perchlorate salts of (RuL2(OH2)2]2+ 1 and [RuL1(OH2)2]2+ 2 (L2 = 2,2':6',2'':6'',2'''-quaterpyridine, L1 = 3'',5,5',5'''-tetramethyl-2,2':6',2'':6'',2'''-quaterpyridine) have been isolated. In acidic solutions both 1 and 2 exhibit reversible Ru(VI)-Ru(IV) and Ru(III)-Ru(II) couples, though the Ru(IV)-Ru(III) couples are only quasireversible. The effect of pH on the E 1/2 of these couples has been investigated. At pH 1, the E-degrees values of the ([RuLO2]2+)-O-2-[RuL2(O)(OH2)]2+ and [RuLO-1(2)]2+-[RuL1(O)(OH2)]2+ couples are 1.12 and 1.05 V vs. saturated calomel electrode respectively. The crystal structure of [RuL1(PPh3)2][ClO4]2. MeCN.H2O has been determined: monoclinic space group P2(1)/n, a = 13.210(4), b = 29.711(7) c =14.878(3) angstrom, beta = 98.89(2)-degrees, Z = 4. In this complex the quaterpyridine ligand adopts a non-planar conformation with a dihedral angle of 28.3-degrees between the two central pyridyl rings. The two triphenyl-phosphine ligands are in a trans configuration [P(l)-Ru-P(2) 177.6-degrees]. The complex (RuL2(OH2)2]2+ is an active catalyst for the electrochemical oxidation of propan-2-ol.