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

Treatment
of the tris­(phosphinoamide) titanium precursor ClTi­(XylNPiPr2)3 (1) with
CoI2 leads to the heterobimetallic complex (η2-iPr2PNXyl)­Ti­(XylNPiPr2)2(μ-Cl)­CoI
(2). One-electron reduction of 2 affords
(η2-iPr2PNXyl)­Ti­(XylNPiPr2)2CoI (3), which can be reduced by another electron under dinitrogen to generate
the reduced diamagnetic complex (THF)­Ti­(XylNPiPr2)3CoN2 (4).
The removal of the dinitrogen ligand from 4 under vacuum
affords (THF)­Ti­(XylNPiPr2)3Co (5), which features a Ti–Co triple
bond. Treatment of 4 with hydrazine or methyl hydrazine
results in N–N bond cleavage and affords the new diamagnetic
complexes (L)­Ti­(XylNPiPr2)3CoN2 (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.