A New Phenoxide Chelated IrIII N‑Heterocyclic Carbene Complex and Its Application in Reductive Amination Reactions

A new phenoxide chelated [Ir­(NHC)­Cp*Cl] (NHC = N-heterocyclic carbene; Cp* = pentamethylcyclopentadienyl) complex (3) has been prepared by reaction of [IrCp*Cl2]2 with an in situ prepared NHC–Ag complex in dichloromethane at ambient temperature. The IrIII complex was stable toward air and moisture and was fully characterized by 1H, 13C NMR, HRMS, and single-crystal X-ray diffraction. The new complex was found to be an active catalyst for transfer hydrogenative reductive amination under aqueous conditions with formate as hydrogen source as well as hydrogenative reductive amination reactions using H2. Various carbonyl compounds such as aliphatic and aromatic ketones and aldehydes were successfully reacted with amines to give new amines. In comparison with transfer hydrogenative reductive amination, the reductive amination with H2 is faster and permits higher molar ratios of the substrate to the catalyst (S/C).

一种新型苯氧基螯合的[Ir(NHC)Cp*Cl]（NHC = 氮杂环卡宾（N-heterocyclic carbene；Cp* = 五甲基环戊二烯基（pentamethylcyclopentadienyl））配合物（3），可通过二聚体[IrCp*Cl₂]₂与原位制备的NHC-银配合物在二氯甲烷中于室温下反应制得。该三价铱（IrIII）配合物对空气与湿气均具有良好稳定性，并通过¹H核磁共振（¹H NMR）、¹³C核磁共振（¹³C NMR）、高分辨质谱（HRMS）以及单晶X射线衍射（single-crystal X-ray diffraction）完成了完整表征。研究发现，该新型配合物可作为活性催化剂，在以甲酸盐为氢源的水相转移氢化还原胺化反应，以及以氢气（H₂）为氢源的氢化还原胺化反应中均表现出催化活性。多种羰基化合物，如脂肪族酮、芳香族酮及醛，均可与胺类底物顺利反应得到新型胺类产物。相较于转移氢化还原胺化反应，以氢气为氢源的还原胺化反应速率更快，且可实现更高的底物与催化剂摩尔比（S/C）。