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

High Resolution Image Download MS PowerPoint Slide Reduction of (depe) 2 CrCl 2 (depe = 1,2-bis(diethylphosphino)ethane) and (dep-benz) 2 CrCl 2 (dep-benz = 1,2-bis(diethylphosphino)benzene) under 1 atm of N 2 furnished the dinitrogen complexes (depe) 2 Cr(N 2 ) 2 and (dep-benz) 2 Cr(N 2 ) 2, respectively. One-electron oxidation of these products with FcBAr F 4 (Fc = ferrocenium, BAr F 4 = B(3,5-(CF 3 ) 2 C 6 H 3 ) 4 ) yielded the unusual, high-spin tetrahedral complexes [(depe) 2 Cr][BAr F 4 ] and [(dep-benz) 2 Cr][BAr F 4 ] with concomitant loss of dinitrogen. Reaction of the chromium(I) derivatives with Ph 3 CN 3 furnished rare examples of chromium(IV) nitrides as confirmed spectroscopically and by X-ray crystallography. While [(depe) 2 Cr(≡N)][BAr F 4 ] underwent association of isocyanides accompanied by partial ligand dissociation, neither chromium nitride was reactive toward H 2 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.