Mononuclear and binuclear copper( I)-diazene complexes: A new chapter of copper coordination chemistry

Starting from copper( II) hydrotris( pyrazolyl) borate precursors and substituted hydrazines, we were able to synthesize mononuclear and binuclear copper( I) - diazene complexes for the first time. The mechanism of these reactions corresponds to a simple hydrazine oxidation by the copper( II) centers. Binuclear diazene complexes contain the central Cu( I) - NR=NR - Cu( I) unit, which we have structurally and spectroscopically characterized. Interestingly, usage of a sterically demanding hydrotris( pyrazolyl) borate ligand that prevents the dimer formation, leads to decomposition of the diazene complex and the isolation of a copper( I) - hydrazine complex. The same is observed when a tris( pyrazolyl) methane ligand is applied. Finally, using 1,1-diphenylhydrazine or the corresponding monophenyl derivative, we were able to obtain mononuclear Cu( I) - diazene complexes. In this case, the phenyl substituent( s) prevent the dimerization, but also stabilize the diazene ligand. Mononuclear and binuclear Cu( I) - diazene complexes are characterized by their intense reddish to purple color, which is caused by an intense Cu-d to diazene-pi* transition in the visible region. Resonance Raman spectra of the diazene complexes show the Cu -N and N - N stretching vibrations in the 500 cm (-1) and 1350 - 1400 cm(-1) energy regions, respectively, in agreement with the diazene description of the complexes. The copper( I) - diazene bond in these complexes is dominated by p backbonding. (c) 2007 Elsevier B. V. All rights reserved.