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

Low-temperature reaction of the tris(pyrazolyl)borate copper(II) hydroxide [iPr2TpCu]2(μ-OH)2 with triphenylsilane under a dinitrogen atmosphere gives the bridging dinitrogen complex [iPr2TpCu]2(μ-1,2-N2) (3). X-ray crystallography reveals an only slightly activated N2 ligand (N-N: 1.111(6) A) that bridges between two monovalent iPr2TpCu fragments. While DFT studies of mono- and dinuclear copper dinitrogen complexes suggest weak π-backbonding between the d10 CuI centers and the N2 ligand, they reveal a degree of cooperativity in the dinuclear Cu-N2-Cu interaction. Addition of MeCN, CNAr2,6-Me, or O2 to 3 releases N2 with formation of iPr2TpCu(L) (L=NCMe, CNAr2,6-Me2) or [iPr2TpCu]2(μ-η2:η2-O2) (1). Addition of triphenylsilane to [iPr2TpCu]2(μ-OH)2 in pentane allows isolation of a key intermediate [iPr2TpCu]2(μ-H) (5). Although 5 thermally decays under N2 to give 3, it reduces unsaturated substrates, such as CO and HC≡CPh to HC(O)H and H2C=CHPh, respectively.