A Dinitrogen Dicopper(I) Complex via a Mixed-Valence Dicopper Hydride

Low-temperature reaction of the tris(pyrazolyl) borate copper(II) hydroxide [(iPr2)TpCu](2)(m-OH)(2) with triphenylsilane under a dinitrogen atmosphere gives the bridging dinitrogen complex [(iPr2)TpCu](2)(mu-1,2-N-2) (3). X-ray crystallography reveals an only slightly activated N-2 ligand (N-N: 1.111(6) angstrom) that bridges between two monovalent (iPr2)TpCu fragments. While DFT studies of mono-and dinuclear copper dinitrogen complexes suggest weak pi-backbonding between the d(10) Cu-I centers and the N-2 ligand, they reveal a degree of cooperativity in the dinuclear Cu-N-2-Cu interaction. Addition of MeCN, CNAr2,6-Me, or O-2 to 3 releases N-2 with formation of (iPr2)TpCu(L) (L= NCMe, CNAr2,6-Me2) or [(iPr2)TpCu](2)(mu-eta(2):eta(2)-O-2) (1). Addition of triphenylsilane to [(iPr2)TpCu](2)(mu-OH) 2 in pentane allows isolation of a key intermediate [(iPr2)TpCu](2)(mu-H) (5). Although 5 thermally decays under N-2 to give 3, it reduces unsaturated substrates, such as CO and HC CPh to HC(O)H and H2C=CHPh, respectively.