Nickel‐Catalyzed Asymmetric Hydrogenation of N‐Sulfonyl Imines

Abstract

An efficient nickel‐catalyzed asymmetric hydrogenation of N‐tBu‐sulfonyl imines was developed with excellent yields and enantioselectivities using (R,R)‐QuinoxP* as a chiral ligand. The use of a much lower catalyst loading (0.0095 mol %, S/C=10500) represents the highest catalytic activity for the Ni‐catalyzed asymmetric hydrogenations reported so far. Mechanistic studies suggest that a coordination equilibrium exists between the nickel salt and its complex, and that excess nickel salt promotes the formation of the active Ni‐complex, and therefore improved the efficiency of the hydrogenation. The catalytic cycle was also investigated by calculations to determine the origin of the enantioselectivity. An extensive network of numerous weak attractive interactions was found to exist between the catalyst and substrate in the transition state and may also contribute to the high catalytic activity.

Nickel‐Catalyzed Asymmetric Hydrogenation of 2‐Amidoacrylates

“…The existence of Complex‐1 in solution was confirmed by HRMS (see Figure S1 for details). It is very interesting to note that only Complex‐1 was observed, without any Complex‐2 , which differs from that of Ni‐QuinoxP* . The content of Complex‐1 is approximately 50 % when the L/M ratio is 1:1, and it increases to 65 % and 68 % when the L/M ratios are 2:1 or 1:2, respectively (Figure , traces a–d, 25 °C).…”

“…Recently, a few examples of Ni‐catalyzed asymmetric hydrogenation of alkenes have been reported by the Chirik and Zhang groups with excellent results . Along with our interest in asymmetric hydrogenation, we have developed the first efficient Ni‐catalyzed asymmetric hydrogenation of imines for the synthesis of chiral amines . It was found that some interactions between the substrate and catalyst improved the catalytic activity, and an appropriate metal/ligand ratio increased the catalyst efficiency.…”

“…It is believed that this is due to the activating effect on the protonolysis step and the solubilizating effect to the ligand. On the other hand, inspired by the discovery in our previous work, the ratios of metal/ligand were investigated in order to increase the catalyst efficiency. The coordination behavior of ( S )‐DM‐MeO‐BIPHEP with Ni(OAc) 2 ⋅4 H 2 O in a mixed solvent of CF 3 CD 2 OD and CD 3 COOD was studied in different ratios and at different temperatures using 1 H NMR spectroscopy (Figure , top).…”

A diversity of recently reported methodology for asymmetric imine reduction

“…This journal is © the Partner Organisations 2020 N-sulfonyl imines. 43 Exhibiting one of the highest catalytic activities and an ee of 97% was the complex of the (R,R)-QuinoxP* ligand 27 (Fig. 37) in the reduction of 2-methyl-N-(1phenylethylide-ne)propane-2-sulfonamides.…”

Platinum Nanoparticle Based Dip‐Catalyst for Facile Hydrogenation of Quinoline, Unfunctionalized Olefins, and Imines

“…Noteworthy developments have been made in recent years in the area of metal-catalyzed hydrogenation of N-bearing heterocyclic compounds, [1] alkenes, [2] and imines [3] to produce pharmaceuticals, petrochemicals, and polymers from natural products on an industrial scale. In this context, researchers have studied many unique homogeneous catalysts based on Mn, [4][5][6] Fe, [7][8][9][10][11] Co, [12][13][14] Ni, [15][16] Rh, [17][18][19][20][21] Ir, [22] Ru, [23,24] and Pd [25,26] with excellent performance. However, owing to the complex multi-step procedures, use of toxic solvents, harsh reaction conditions, and a tedious and cumbersome process of separating the spent catalyst, the currently available methods are not commercially viable.…”