SYNTHESIS, CYCLIC VOLTAMMETRY, AND X-RAY CRYSTAL-STRUCTURES OF COPPER(I) AND COPPER(II) COMPLEXES OF TRIS((6-PHENYL-2-PYRIDYL)METHYL)AMINE (TPPA)

The synthesis and characterization of a new ligand, tris((6-phenyl-2-pyridyl)methyl)amine (TPPA) and some of its copper complexes are described. The complexes [Cu(TPPA)]BPh(4) (7) and [Cu(TPPA)(AN)](ClO4)(2) (8) (AN = acetonitrile) were prepared and their X-ray crystal structures and redox potentials were determined. The X-ray structure of 7 (triclinic space group, P ($) over bar 1; a = 14.603(3), b = 15.137(3), c = 12.974(3) Angstrom A, alpha = 91.76(3), beta = 105.87(3), gamma = 117.00(3)degrees, V = 2417.4(12) A Angstrom(3), Z = 2) displays a copper(I) atom with a distorted trigonal pyramidal coordination sphere, but the X-ray structure of 8 (triclinic space group, P ($) over bar 1; a 13.458(3), b = 13.586(3) c = 11.082(2) Angstrom A, alpha = 113.00(3), alpha = 94.48(3), gamma = 90.53(3)degrees, V = 1857.7(9) Angstrom A(3), Z = 2) indicates that the copper(II) atom has the expected trigonal bipyramid geometry. The reduction potential of 8 in dimethylformamide, dimethylacetamide, acetonitrile, and isobutyronitrile is quite positive compared to [Cu(TPA)](ClO4)(2) (TPA = tris(2-pyridylmethyl)amine) under identical conditions. The various factors that may contribute to the difference in oxidation potential are discussed. The positive redox potential combined with steric factors accounts for the lack of reactivity of [Cu(TPPA)]PF6 with molecular O-2.