Chromium dinitrogen compounds

Compared to Mo and W, only a Hmited number of chromium dinitrogen compounds are known and most of them contain weakly activated N2 ligands that can readily be displaced by stronger Ugands. In early, rather alchemistic studies, it was shown that CrCla promotes the sdylation of N2 at ambient conditions in the presence of MeaSiCl and Li forming N(SiMe3)3 (5.4 equiv.), but no details regarding the reaction mechanism or the intermediates involved were revealed. 

Highly reduced chromium binds dinitrogen, for example in fra i -[Cr(dmpe)2(N2)2] (4). Its crystal structure shows linearly bound N2 ligands (Cr-N, 187.4 pm, N-N, 112.2pm) and relatively short Cr-P distances (Cr-Pav, 229.6 pm). The related Cr(dmpe)3 exhibits similarly short Cr-P bonds (231.7 pm). These short Cr-P distances are thought to be due to n-Back Bonding to the phosphine ligand. Both Cr(dmpe)3 and Cr[P(OMe)3]6 were prepared by metal vapor synthesis see Metal Vapor Synthesis of Transition Metal Compounds). The same technique may also be used to prepare... 

Burdett JK, Graham MA, Turner JJ. Binary compounds of dinitrogen with nickel, chromium, platinum, and copper a vibrational investigation of the metal-dinitrogen linkage. J Chem Soc Dalton Trans. 1972 1620-1625. 

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