CHEMISTRY OF BIS(O-BENZOSEMIQUINONATO)BIS(TRIPHENYLPHOSPHINE)RUTHENIUM(II) COMPLEXES - CRYSTAL AND MOLECULAR-STRUCTURE OF [RU(O2C6CL4)2(PPH3)2]

The green complexes [Ru(L(s))2(PPh3)2].2H2O (L(s) = o-benzosemiquinonate) are obtained in excellent yields by the reaction of catechols H2L1-H2L4 with [RuH(Hsa)(PPh3)3] {H-2L1 = C6H4(OH)2-1,2; H-2L2 = 4 ButC6H3(OH)2-1,2; H-2L3 = 3,5-But2C6H-2(OH)2-1,2; H2L4 = C6Cl4(OH)2-1,2; H2sa = salicyclic acid}. The crystals of the tetrachloro complex are triclinic, space group P1BAR with a = 9.430(5), b = 11.689(4), c = 12.551 (6) angstrom, alpha = 68.58(3), beta = 72.07(4), gamma = 79.92(4)-degrees and Z = 1; the final R factor is 0.0406 for 4741 observed reflections. The complex is centrosymmetric with a trans-RuO4P2 co-ordination sphere; the average C-O distance is 1.310(5) angstrom. Significant d(pi-p(pi)* back-bonding occurs within the Ru(II)(L(s))2 fragment and metal-to-ligand charge-transfer (m.l.c.t.) transitions are observed in the near-IR region (900-1300 nm). In dichloromethane solution four successive one-electron cyclic voltammetric couples are observed. The product of the first one-electron reduction has been identified as [Ru(III)(L(c))2]- (L(c) = catecholate) from ESR spectra. The probable nature of the other members of the redox series is discussed.