STRUCTURAL AND ELECTROCHEMICAL PROPERTIES OF BINUCLEAR COMPLEXES CONTAINING 1,10-PHENANTHROLINE-5,6-DIOLATE AS A BRIDGING LIGAND

Bis(triphenylphosphine)(1,10-phenanthroline-5,6-diolato)platinum(II), (PPh3)2Pt(O',O-PhD), may be prepared by treating 1,10-phenanthroline-5,6-dione with Pt(PPh3)4. The oxygen-bound diolate form of the PhD ligand can coordinate to an additional metal through the nitrogen donor atoms forming a binuclear complex with the (PPh3)2Pt(O',O-PhD) unit serving as a bipyridine-like ligand. Complexes of general form (PPh3)2Pt(O',O-PhD-N,N')ML(n) have been prepared with ML(n) = PdCl2, Ru(PPh3)2Cl2, and Pt(DBCat). The Pt,Pd and Pt,Ru complexes could not be characterized from elemental analytical data due to the presence of nonstoichiometric solvate molecules; crystallographic structure determinations provided information on both complexes. (PPh3)2Pt(O',O-PhD-N,N')PdCl2 crystallizes in the orthorhombic space group Pbcn with 2.5 molecules of benzene per complex molecule in a unit cell of dimensions a = 16.175 (5) angstrom, b = 27.792 (6) angstrom, c = 25.801 (7) angstrom, V = 11599 (5) angstrom 3, and Z = 8. (PPh3)2Pt(O',O-PhD-N,N')Ru(PPh3)2Cl2 crystallizes as a mixed toluene-dichloromethane solvate, in the triclinic space group P1BAR, with unit cell dimensions of a = 15.758 (3) angstrom, b = 15.715 (3) angstrom, c = 19.193 (3) angstrom, alpha = 82.91 (1)-degrees, beta = 80.41 (1)-degrees, gamma = 66.89 (1)-degrees, V = 4301 (1) angstrom 3, and Z = 2. Structural features of both molecules include similar, planar P2Pt(PhD)MCl2 regions, with additional axial PPh3 ligands for M = Ru, and C-O lengths for the PhD ligand that are typical of catecholate ligands. The electrochemical properties of the complexes consist of first and second electron oxidations of the PhD bridge for all three species, with an additional Ru(II)/Ru(III) couple for (PPh3)2Pt(O',O-PhD-N,N')Ru(PPh3)2Cl2 and two additional catecholate oxidations for the DBCat ligand of (PPh3)2Pt(O',O-PhD-N,N')Pt(DBCat). Similarities in bonding between L(n)M(O',O-PhD) species and the bipyridine and 1,10-phenanthroline ligands is described. However, the redox activity of the PhD bridge at potentials near the redox potentials of electroactive metal ions presents an important difference between PhD-bridged complexes and the simple nitrogen donor analogues.