Air Stable Iridium Catalysts for Direct Reductive Amination of Ketones

Abstract

Half‐sandwich iridium complexes bearing bidentate urea‐phosphorus ligands were found to catalyze the direct reductive amination of aromatic and aliphatic ketones under mild conditions at 0.5 mol % loading with high selectivity towards primary amines. One of the complexes was found to be active in both the Leuckart–Wallach (NH4CO2H) type reaction as well as in the hydrogenative (H2/NH4AcO) reductive amination. The protocol with ammonium formate does not require an inert atmosphere, dry solvents, as well as additives and in contrast to previous reports takes place in hexafluoroisopropanol (HFIP) instead of methanol. Applying NH4CO2D or D2 resulted in a high degree of deuterium incorporation into the primary amine α‐position.

Recent advances of Cp*Ir complexes for transfer hydrogenation: focus on formic acid/formate as hydrogen donors

“…Recently, Rueping's group designed a new kind of Cp*Ir complex bearing P,N-chelating ligands which were broadly utilized in catalytic direct reductive amination (Scheme 23a). 64 With these [Cp*Ir(N^P)] complexes in hand, lots of primary amines were Scheme 20 General procedure of direct reductive amination.…”

Synthesis of Chiral Primary Amines via Enantioselective Reductive Amination: From Academia to Industry

“…Besides using H2 gas as the reductant, iridium catalysts have also been widely used in hydrogen-transfer reductive amination reactions featuring broad substrate scope and high efficiency. [31][32][33][34] By taking HCOOH or HCOONH4 as the reductant, the transfer hydrogenation reactions exhibit unique advantages in avoiding the use of explosive hydrogen gas and high-pressure equipment, which is safer and operationally friendly. Several representative iridium catalysts based on stable Cp* skeleton are shown in Scheme 22.…”

“…35 The main challenge lies in the enantiocontrol under usually heating conditions. Scheme 22 Representative iridium catalysts used in hydrogentransfer reductive amination reactions with NH4 + as amine source Inspired by the aforementioned works [31][32][33][34] and Cramer's work on asymmetric hydrogenation of oximes using chiral cyclopentadienyl iridium complexes, 36 our group recently evaluated a series of novel chiral Cp-Ir(III) catalysts in the hydrogen-transfer reductive amination of ketones, where HCOONH4 was used as both reductant and amine source. 37 Although high efficiency and broad substrate scope were achieved, the enantio-control was not satisfied and only 16% ee was obtained when the optimal catalyst Cat.5 was used (Scheme 23).…”

“…Besides using H 2 gas as the reductant, iridium catalysts have also been widely used in hydrogen-transfer reductive amination reactions featuring broad substrate scope and high efficiency. 31 32 33 34 The use of explosive hydrogen gas and high pressure equipment can be avoided in transfer hydrogenation reactions by using HCOOH or HCOONH 4 as the reductant, which is safer and operationally friendly. Several representative iridium catalysts based on the stable Cp* skeleton are shown in Scheme 22 .…”

ZIF‐67 Derived Co/NC Nanoparticles Enable Catalytic Leuckart‐type Reductive Amination of Bio‐based Carbonyls to N‐Formyl Compounds

“…In recent years, many catalytic systems of reduction‐amination of carbonyl compounds to construct C−N bonds have been reported [14–19] . However, only a few precious metal (e. g., Rh, Ru, and Ir) catalytic systems have been reported for Leuckart‐type reductive amination of carbonyl compounds, usually using ammonium formate or formamide as nitrogen source [20–23] . Although noble metal catalysts have achieved satisfactory results in the Leuckart‐type reactions, it is desirable to replace them with non‐noble metals (e. g., Cu, Ni, Co, Fe, and Mn) to reduce the overall production costs.…”