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) Å) 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. Caught between two coppers: A tris(pyrazolyl)borate (Tp) dicopper N2 complex [CuI]2(μ‐N2) forms through the intermediacy of a mixed‐valence dicopper hydride [Cu1⋅5]2(μ‐H). Besides allowing a direct comparison between N2 and O2 binding at copper(I), this [CuI]2(μ‐N2) complex represents a key member in a family of TpCu complexes [CuI]2(μ‐NH=NH) and [CuI](NH2NH2) featuring reduced N2 ligands.