Synthesis of Chromium(IV) Nitrides Through High-Spin Tetrahedral Chromium(I) Intermediates.

Reduction of (depe)2CrCl2 (depe = 1,2-bis(diethylphosphino)ethane) and (dep-benz)2CrCl2 (dep-benz = 1,2-bis(diethylphosphino)benzene) under 1 atm of N2 furnished the dinitrogen complexes (depe)2Cr(N2)2 and (dep-benz)2Cr(N2)2, respectively. One-electron oxidation of these products with FcBArF4 (Fc = ferrocenium, BArF4 = B(3,5-(CF3)2C6H3)4) yielded the unusual, high-spin tetrahedral complexes [(depe)2Cr][BArF4] and [(dep-benz)2Cr][BArF4] with concomitant loss of dinitrogen. Reaction of the chromium(I) derivatives with Ph3CN3 furnished rare examples of chromium(IV) nitrides as confirmed spectroscopically and by X-ray crystallography. While [(depe)2Cr(≡N)][BArF4] underwent association of isocyanides accompanied by partial ligand dissociation, neither chromium nitride was reactive toward H2 or diphenylsilane under thermal or photochemical conditions. These results distinguish the unique properties of the chromium(IV) nitrides as compared to heavier group 6 congeners and demonstrate both the feasibility of nitride synthesis and the limitations of dinitrogen cleavage and subsequent N-H bond formation.