Cobalt–Magnesium and Cobalt–Calcium Heterotrimetallic Dinitrogen Complexes

We report the use of alkaline earth metals magnesium and calcium for the reduction of the cobalt(II) complex [iPr2NN]Co(μ–Cl)2Li(thf)2 (iPr2NN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) (1) resulting in heterotrimetallic dinitrogen complexes 2 and 3 with a rare example of [Co–N2–M–N2–Co] core where M = Mg (complex 2) and Ca (complex 3). The dinitrogen ligands in complexes 2 and 3 showed weakened N–N bonds, as judged by infrared spectroscopy and the structures of 2 and 3 were confirmed by X-ray crystallography. These cobalt complexes can be isolated as pure solids that are stable in solution of non-coordinating solvents such as n-pentane or cyclohexane, as well as THF. These results demonstrate the correlation between the binding mode of the Lewis acid and N–N weakening in heterotrimetallic dinitrogen complexes.