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.

将三(膦酰胺)钛前驱体(tris(phosphinoamide) titanium precursor) ClTi(XylNPiPr₂)₃（1）与二碘化钴(CoI₂)反应，得到异双金属配合物(heterobimetallic complex) (η²-iPr₂PNXyl)Ti(XylNPiPr₂)₂(μ-Cl)CoI（2）。对配合物2进行单电子还原(one-electron reduction)，得到(η²-iPr₂PNXyl)Ti(XylNPiPr₂)₂CoI（3）；在氮气氛围下对3进行第二次单电子还原，可生成还原得到的反磁性(diamagnetic)配合物(四氢呋喃, THF)Ti(XylNPiPr₂)₃CoN₂（4）。将配合物4在真空条件下脱去氮气配体，得到(四氢呋喃, THF)Ti(XylNPiPr₂)₃Co（5），该配合物具有Ti-Co三键。将配合物4与肼(hydrazine)或甲基肼(methyl hydrazine)反应，可发生N-N键断裂(N–N bond cleavage)，得到新型反磁性配合物(L)Ti(XylNPiPr₂)₃CoN₂（其中L分别为NH₃（6）、MeNH₂（7））。研究表明，配合物4、5与6可催化肼歧化为氨与氮气，其反应机理涉及二亚胺(diazene)中间体。