Heterobimetallic Ti/Co Complexes That Promote Catalytic N-N Bond Cleavage

Treatment of the tris(phosphinoamide) titanium precursor ClTi(XylNP(i)Pr(2))(3) (1) with CoI2 leads to the heterobimetallic complex (eta(2)-(i)Pr(2)PNXyl)Ti(XylNP(i)Pr(2))(2)(mu-Cl)CoI (2). One-electron reduction of 2 affords (eta(2)-(i)Pr(2)PNXyl)-Ti(XylNP(i)Pr(2))(2)CoI (3), which can be reduced by another electron under dinitrogen to generate the reduced diamagnetic complex (THF)Ti(XylNP(i)Pr(2))(3)CoN2 (4). The removal of the dinitrogen ligand from 4 under vacuum affords (THF)Ti-(XylNP(i)Pr(2))(3)Co (5), which features a TiCo triple bond. Treatment of 4 with hydrazine or methyl hydrazine results in NN bond cleavage and affords the new diamagnetic complexes (L)Ti(XylNP(i)Pr(2))(3)CoN2 (L = NH3 (6), MeNH2 (7)). Complexes 4, 5, and 6 have been shown to catalyze the disproportionation of hydrazine into ammonia and dinitrogen gas through a mechanism involving a diazene intermediate.