CHARGE-DISTRIBUTION IN THE QUINONE COMPLEXES OF OSMIUM - SYNTHESIS AND CHARACTERIZATION OF THE OS(PPH3)2(Q)CL2 AND OS(PPH3)2(Q)2 (Q = 3,5-DI-TERT-BUTYL-1,2-QUINONE, TETRACHLORO-1,2-QUINONE) SERIES

Members of the Os(PPh3)2(Q)Cl2 and Os(PPh3)2(Q)2 (Q = DBQ, Cl4Q) families have been studied in order to understand the charge distribution in the neutral quinone complexes of osmium. The Os(PPh3)2(Q)Cl2 complexes have been synthesized by the reaction of Os(PPh3)3Cl2 with BQ (BQ = DBBQ, Cl4BQ). Os(PPh3)2(DBQ)Cl2 has been characterized structurally. Crystals of Os(PPh3)2(DBQ)Cl2 form in the monoclinic space group P2(1)/c with Z = 4 in a unit cell of dimensions, a = 16.504 (3) angstrom, b = 12.206 (3) angstrom, c = 22.563 (3) angstrom, and beta = 100.63 (10)-degrees. Structural features of the quinone ligand indicate that in the solid state it is intermediate between semiquinone and catechol. Treatment of Os(PPh3)2(Q)Cl2 with a second catecholate ligand leads to displacement of the chloro ligands with formation of the bis(quinone) product. The Os(PPh3)2(Q)2 complexes have also been synthesized by the reaction of Os(PPh3)3Cl2 with H2Cat (H2Cat = H2DBCat, H2Cl4Cat). Os(PPh3)2(DBQ)2 has been characterized crystallographically. Crystals of this compound form in the monoclinic space group P2(1)/n with Z = 4 in a unit cell of dimensions a = 13.539 (2) angstrom, b = 15.629 (4) angstrom, c = 27.105 (7) angstrom, and beta = 100.21 (2)-degrees. Structural features of the quinone ligands are both typically catecholate. Electrochemical characterization has shown that each of the two Os(PPh3)2(Q)Cl2 complexes undergoes one oxidation and one reduction at potentials similar to those observed for the Ru(PPh3)2(SQ)Cl2 complex. The bis(quinone)osmium complexes show redox behavior similar to that of the Ru(PPh3)2(SQ)2 complexes. This similarity indicates that in solution the Os(PPh3)2(Q)Cl2 and Os(PPh3)2(Q)2 complexes have electronic structures similar to those of members of the Ru(PPh3)2(SQ)Cl2 and Ru(PPh3)2(SQ)2 series, respectively.