The discovery of mild methods for metal mediated cleavage of the dinitrogen triple bond to produce metal nitride derivatives is a fundamental aspect of nitrogen fixation. This presentation will describe the synthesis and structural characterization of a new chromium dinitrogen complex, namely [Cp*Cr(dmpe)]2(µ-N)2 (1). Compound 1 can be reduced and oxidized. The effect of these transformations on the N2 ligand was monitored by structural studies. Upon reduction of compound 1, another dinitrogen compound with the oxidation state of 0 was produced, namely [Cp*(dmpe)Cr(µ-N2)Na(TMEDA)2] (2). Unexpectedly, formal reduction of chromium decreased the bond distance from 1.195(3)A° in 1 to 1.175(4)A° in 2. Upon oxidation of 1, a mixed valent (CrI/CrII) dinitrogen compound was formed, namely [(Cp*(dmpe)Cr)2(µ-N2)]BArF4 (3). The N-N bond distance in compound 3 show an increase to 1.241 A°. The desired cleavage product, i.e. [Cp*(dmpe)Cr≡N] (4), was prepared by an independent method. Compounds 1 and 4 do not interconvert, suggesting a large intrinsic activation barrier for the cleavage/formation of the N2 molecule.

Correlation of formal oxidation state with the N-N bond distance of chromium dinitrogen complexes

2019 Fall National Meeting

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