A New Phenoxide Chelated Ir^IIIN-Heterocyclic Carbene Complex and Its Application in Reductive Amination Reactions

Abstract

A new phenoxide chelated [Ir(NHC)Cp*Cl] (NHC = Nheterocyclic carbene; Cp* = pentamethylcyclopentadienyl) complex (3) has been prepared by reaction of [IrCp*Cl 2 ] 2 with an in situ prepared NHC−Ag complex in dichloromethane at ambient temperature. The Ir III complex was stable toward air and moisture and was fully characterized by 1 H, 13 C 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 H 2 . 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 H 2 is faster and permits higher molar ratios of the substrate to the catalyst (S/ C).

Enhanced Catalytic Activity of Oxygen‐Tethered IrIII NHC Complexes in Aqueous Transfer Hydrogenative Reductive Amination Reactions: Experimental Kinetic and Mechanistic Study

“…The NHCÀAg species were not isolated, however. The IrÀC carbene and IrÀO bond distances and ligand bite angles are within the typical ranges [9,12] and shows little variation as may be expected. Formation of 3 a-g were confirmed by HRMS analysis and NMR spectroscopic analysis, which showed the characteristic IrÀC carbene signals at d = 159.5-175.9 ppm in the 13 C NMR spectrum.…”

“…[10] Following the procedures as described previously by our group, [9] the new neutral aryloxide chelated NHCÀIr III complexes (3 a-g) were synthesized by transmetalation [11] from the in-situ formed NHCÀAg derivatives by employing a two-step process (Scheme 1). [10] Following the procedures as described previously by our group, [9] the new neutral aryloxide chelated NHCÀIr III complexes (3 a-g) were synthesized by transmetalation [11] from the in-situ formed NHCÀAg derivatives by employing a two-step process (Scheme 1).…”

“…NHCs often form stable complexes with many transition metals irrespective of their oxidation states. [9] This complex was found, for the first time, to efficiently catalyze both transfer hydrogenative and hydrogenative RA of various ketones and aldehydes with aniline derivatives (Figure 1). An example is NHCÀiridium complexes, which have been successfully employed as catalysts for a number of transfer hydrogenation (TH) rections.…”

Hofmann N‐alkylation of aniline derivatives with alcohols using ferric perchlorate immobilized on SiO2 as a catalyst through Box–Behnken experimental design

“…The [24] 6 5 8 5 6 9 -72 (68-71) [24] (Continues) produced pink crystals were filtered and washed with 5 ml of perchloric acid. [27] 10 4 8 5 9 7 -100 (98-99) [28] 11 5 82 Liquid (liquid) [29] 12 5.5 85 84-86 (82-84) [30] 13 6 8 0 9 2 -95 (93-95) [31] 14 5 84 119-121 (120-121) [32] (Continues) [27] 10 4 8 5 9 7 -100 (98-99) [28] 11 5 82 Liquid (liquid) [29] 12 5.5 85 84-86 (82-84) [30] 13 6 8 0 9 2 -95 (93-95) [31] 14 5 84 119-121 (120-121) [32] (Continues) …”

Imino Transfer Hydrogenation Reductions

“…[204] A phenoxide-chelated Ir complex -16 in Figure 54 has also been prepared and demonstrated to be capable of C=N bond reduction by both hydrogenation and transfer hydrogenation via reductive amination. [205] 36…”