Dinitrogen activation by a phosphido-bridged binuclear cobalt complex

Abstract

By reacting the semi-rigid PNP ligand with CoBr₂, the corresponding complex PNPCoBr (1) was obtained. The reduction of 1 with excess amounts of KC₈ in THF under a N₂ atmosphere yielded a binuclear cobalt dinitrogen anion complex [Co(μ-Cy₂P)PCyN₂]₂K (2) via the C–P bond cleavage of the PNP ligand. By adding 2,2,2-cryptand into complex 2, an ion pair Co complex, [Co(μ-Cy₂P)PCyN₂]₂K(crypt-222) (3), could be effectively prepared. The structures of 1, 2, and 3 have been determined by single-crystal X-ray diffraction analysis, and N₂ is moderately activated in complexes 2 and 3. There is a Co–Co bond in 2 and 3 suggested by DFT calculations. Compounds 1 and 2 display catalytic activity for the transformation of N₂ into N(SiMe₃)₃.