Valence tautomerism and metal-mediated catechol oxidation for complexes ofcopper prepared with 9,10-phenanthrenequinone

Bis (pyridine) (9, 10-phenanthrenequinone) (9, 10-phenanthrenediolato)coppe r(II), Cu(py)(2)(PhenCat)(PhenBQ), has been prepared by treating copper met al with 9,10-phenanthrenequinone in pyridine solution. In dilute solution, both Cu(py)(2)(PhenCat)(PhenBQ) and the related complex Cu(tmeda)(PhenCat)( PhenBQ) lose PhenBQ to form (CuL2)-L-II(PhenCat), where L-2= tmeda, 2 py. E PR spectra recorded at temperatures between 300 and 77 K reveal the presenc e of species with radical and metal localized spins together at equilibrium . Equilibria between (CuL2)-L-II(PhenCat) and (CuL2)-L-I(PhenSQ) redox isom ers are solvent dependent, with a shift to higher temperature for polar sol vents. Both complexes are oxygen sensitive, reacting with dioxygen to give complexes of diphenic acid. Structural characterization on products obtaine d with tmeda show that dioxygen insertion across the C-C bond within the ch elate ring leads to dimeric products with adjacent Cu(II) ions bridged by d iphenate ligands. The addition Of O-2 to Cu(tmeda)(PhenCat) in acetonitrile solution at 0 degreesC appears to form a peroxo complex, tentatively ident ified as Cu(tmeda)(O-2)(PhenQ) on the basis of iodometric titration, as the precursor to the diphenate complex.