Dinitrogen Activation at Iron and Cobalt Metallalumatranes

Anionic cobalt and iron metallalumatranes that bind dinitrogen in an end-on fashion were prepared and characterized by X-ray crystallography. Along with literature-known neutral cobalt and iron metallalumatranes, they form a quartet of low-valent coordination complexes for comparing dinitrogen activation and functionalization at cobalt versus iron centers. In the anionic metallalumatranes, the metal atoms are proposed to have subvalent oxidation states of -1. The electronic structure of the anionic iron alumatrane, which was probed by electron paramagnetic resonance spectroscopy, Mossbauer spectroscopy, and density functional theory, is most consistent with Fe(-1)Al(+3). Functionalization of dinitrogen was achieved by reaction of the ferrate alumatrane with 1,2-bis(chlorodimethylsilyl)ethane and KC8 (1 equiv.) to generate an iron(II) disilylhydrazido complex. The transformation of dinitrogen to disilylhydrazido(2-) is an overall four-electron process.