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A combined computational and experimental approach allowed us to develop overall the most selective catalyst for the direct hydrogenation of N‐methyl, N‐alkyl and N‐aryl imines described to date. Iridium catalysts with a cyclometallated cyclic imide group provide selectivity of up to 99 % enantiomeric excess. Computational studies show that the selectivity results from the combined effect of H‐bonding of the imide C=O with the substrate iminium ion and a stabilizing π–π interaction with the cyclometallated ligand. The cyclometallated ligand thus exhibits a unique mode of action, serving as a template for the H‐bond directed approach of the substrate which results in enhanced selectivity. The catalyst (2) has been synthesized and isolated as a crystalline air‐stable solid. X‐ray analysis of 2 confirmed the structure of the catalyst and the correct position of the imide C=O groups to engage in an H‐bond with the substrate. 19F NMR real‐time monitoring showed the hydrogenation of N‐methyl imines catalyzed by 2 is very fast, with a TOF of approx. 3500 h−1. [ABSTRACT FROM AUTHOR]

Chiral compounds containing nitrogen heteroatoms are fundamental substances for the chemical, pharmaceutical and agrochemical industries. However, the preparation of some of these interesting scaffolds is still underdeveloped. Herein we present the synthesis of a family of P‐stereogenic phosphinooxazoline iridium catalysts from L‐threonine methyl ester and their use in the asymmetric hydrogenation of N‐Boc‐2,3‐diarylallyl amines, achieving very high enantioselectivity. Furthermore, the synthetic utility of the 2,3‐diarylpropyl amines obtained is demonstrated by their transformation to 3‐aryl‐tetrahydroquinolines and 4‐benzyl‐tetrahydroisoquinolines, which have not yet been obtained in an enantioselective manner by direct reduction of the corresponding aromatic heterocycles. This strategy allows the preparation of these types of alkaloids with the highest enantioselectivity reported up to date. [ABSTRACT FROM AUTHOR]

The MaxPHOX-Ir catalyst system provided the highest selectivity ever reported for the reduction of cyclic enamides derived from α- and β-tetralones. This result indicates that iridium catalysts are also proficient in reducing alkenes bearing metal-coordinating groups. In the present system, selectivity was pressure-dependent: In most cases, a decrease in the H2 pressure to 3 bar resulted in an increase in enantioselectivity. Moreover, the process can be carried out in environmentally friendly solvents, such as methanol and ethyl acetate, with no loss of selectivity. [ABSTRACT FROM AUTHOR]

The synthesis of optically and diastereomerically pure P-stereogenic phosphine-imidazole ligands is reported. The new ligands contain either a benzoimidazole or a 4-phenylimidazole as a N -donor fragment. The ligands have been coordinated to iridium and the structure of the corresponding cationic COD complexes has been determined by X-ray analysis. The combination of the chiral phosphorus atom and the imidazole substituents generate a strong chiral environment around the metal center. Preliminary hydrogenation reactions with a model cyclic β-enamide are also reported. Image 1 [ABSTRACT FROM AUTHOR]

A threonine-derived phosphine-oxazoline iridium catalyst is reported, showcasing excellent selectivity in the hydrogenation of N -Boc-2,3-diarylallylamines. The reversible cyclometallation process between the square planar Ir(I) complex and the corresponding octahedral Ir(III) species is thoroughly investigated, while considering the influence of substitution at the phenyl group of the oxazoline on this equilibrium. X-Ray analysis reveals that the cyclometallated tridentate ligand adopts a fac coordination mode. Furthermore, the catalytic performance of these complexes in the asymmetric hydrogenation is evaluated and the utilization of Ir(III) pre-catalysts or Ir(I)/Ir(III) mixtures in hydrogenation reactions is proposed based on the observed equilibrium dynamics. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Here we report the synthesis of a new N-di-tert-butylphosphino-tert-butylsulfinamide (PNSO) ligand and its corresponding p-tolylsulfinamide analog. The coordination of these compounds to rhodium to form a neutral and apolar complex is described, followed by the subsequent protonation of said complexes to quantitively form the more orthodox, cationic rhodium species containing a tetrafluoroboric counterion. The crystallographic structure of the tert-butylsulfinamide-derived cationic species was obtained and is elucidated. It outlines coordination from the sulfinamide group to the rhodium atom and shows no preference between O- and S-coordination as both complexes can be seen in one unit cell of the crystal. The efficacies of the neutral species and the salt species were tested in the asymmetric hydrogenation of methyl (Z)-α-acetamido cinnamate (Z-MAC). The p-tolylsulfinamide-derived complexes gave no hydrogenation while the tert-butylsulfinamide-derived ones produced hydrogenation with complete conversion but low enantioselectivities. The stereochemical outcome of the reaction was analyzed by means of the quadrant method. [Copyright &y& Elsevier]