Well-Defined Chiral Spiro Iridium/Phosphine−Oxazoline Cationic Complexes for Highly Enantioselective Hydrogenation of Imines at Ambient Pressure

• Published in: Journal of the American Chemical Society Vol. 128; no. 39; pp. 12886 - 12891
• Main Authors: Zhu, Shou-Fei, Xie, Jian-Bo, Zhang, Yong-Zhen, Li, Shen, Zhou, Qi-Lin
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 04.10.2006; Amer Chemical Soc
• Subjects: Catalysis; Catalysts: preparations and properties; Cations; Chemistry; Chemistry, Multidisciplinary; Coordination compounds; Exact sciences and technology; General and physical chemistry; Heterocyclic compounds; Heterocyclic compounds with n hetero atom and also o and/or s, se, te hetero atoms; Hydrogen - chemistry; Imines - chemistry; Inorganic chemistry and origins of life; Iridium - chemistry; Ligands; Magnetic Resonance Spectroscopy - methods; Models, Molecular; Molecular Conformation; Organic chemistry; Oxazoles - chemical synthesis; Oxazoles - chemistry; Oxidation-Reduction; Phosphines - chemistry; Physical Sciences; Preparations and properties; Pressure; Science & Technology; Stereoisomerism; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; X-Ray Diffraction; PHOSPHORUS LIGANDS; IRIDIUM COMPLEXES; PHOSPHORAMIDITES; OLEFINS; CATALYTIC ASYMMETRIC HYDROGENATION; EFFICIENT; 1,1'-SPIROBIINDANE-7,7'-DIOL; Cationic complex; Transition element complexes; Enantioselectivity; Molecular structure; Ligand; Chiral compound; NMR spectrometry; Hydrogenation; Electrospray; Characterization; Amine; Aromatic compound; Chemical synthesis; Oxazole derivatives; Oxygen nitrogen heterocycle; Molecular rigidity; Complexation; Trimer; Catalytic reaction; Stability; Organic phosphine; Iridium complex; Steric hindrance; Sodium compound; Imine; X ray diffraction; Spiran; Ketimine; Enantiomeric excess; Platinoid Complexes; Fluorine Organic compounds; Mass spectrometry; Catalyst
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja063444p

New chiral phosphine−oxazoline ligands (7, SIPHOX) with a rigid and bulky spirobiindane scaffold were synthesized, starting with optically pure 7-diphenylphosphino-7‘-trifluoromethanesulfonyloxyl-1,1‘-spirobiindane, in four steps in 40−64% overall yield. Iridium complexes of 7, the chiral analogues of the Crabtree catalyst, were generated by coordination of ligands 7 and [Ir(COD)Cl]2 in the presence of sodium tetrakis-3,5-bis(trifluoromethyl)phenylborate. The complexes were characterized by NMR, ESI-MS, and X-ray diffraction analysis. The Ir−SIPHOX complexes can catalyze the hydrogenation of acyclic N-aryl ketimines under ambient pressure with excellent enantioselectivities (up to 97% ee) and full conversions. This result represents the highest enantioselectivity and the first example of the hydrogenation of imines catalyzed by chiral analogues of the Crabtree catalyst at ambient pressure. Studies on the stability of the catalysts revealed that the catalysts Ir−SIPHOX are very stable and resistant to the formation of inactive trimers under hydrogenation conditions. On the basis of the X-ray diffraction analysis of the structures of catalysts and amine products, a rational explanation for the enantiocontrol of the chiral catalysts in the hydrogenation of imines is proposed.