A π -Bonded Azo-Transition Metal Complex. The Structure of Bis(tert-butyl isocyanide) (azobenzene) nickel (0)

The structure of bis(tert-butyl isocyanide)(azobenzene)nickel(0), Ni(C₆H₅N=NC₆H₅)((CH₃)₃C—N≡C)₂, has been determined from three-dimensional X-ray data collected by counter methods. The compound crystallizes in space group C_2h⁵-P2₁/c of the monoclinic system, with four molecules in a cell of dimensions a = 12.404 (8), b = 17.154 (8), c = 12.487 (6)Å, β = 117.46 (6)°. The structure has been refined by least-squares techniques to a final R factor on F of 7.0% based on 2694 observations above background. The coordination about the Ni atom is trigonal if the azobenzene is regarded as a monodentate ligand. The molecule possesses essentially C₂ symmetry. The dihedral angle between the Ni-NN (of azobenzene) and Ni-CC (of tert-butyl isocyanide) planes is 1.2 (3)° and the inner coordination sphere is essentially planar. The tert-butyl isocyanide ligands are very nearly linear, and the average Ni-C distance is 1.841 (5)Å. The azobenzene nitogen atoms are equidistant from the metal, with an average Ni-N bond length of 1.898 (4)Å. The N-N distance of 1.385 (5) Åis very close to an N-N single bond distance. The phenyl rings of the coordinated azobenzene are twisted 14° from ideal planarity, and there is a dihedral angle of 26.8 (4)° between the two N-N-C (phenyl) planes. The bond lengthening and the geometry within the coordinated azobenzene are both consistent with the usual description of πbonding of olefinic-type ligands to transition metals. The complex is suggested as a suitable model for consideration of the possible role of π-bonded diimide in the biological fixation of nitrogen.