Iron‐Catalyzed Highly Enantioselective Reduction of Aromatic Ketones with Chiral P₂N₄‐Type Macrocycles

Abstract

Novel P 2 N 4 -donors containing chiral 22membered macrocyclic ligands have been synthesized and the structures have been determined by an X-ray diffraction study. The catalytic systems in situ generated from triiron dodecarbonyl, Fe 3 (CO) 12 , and the chiral macrocyclic ligand exhibited high activity (TOF up to 1940 h À1 ) and excellent enantioselectivity with up to 99% ee in the asymmetric transfer hydrogenation of various aromatic ketones.

Self‐Assembly of Chiral 1,8‐Diaza‐3,6,10,13‐tetraphosphacyclotetradecanes via Dynamic Transformation of 7‐ and 14‐Membered Aminomethylphosphines

“…Some chiral macrocycles containing O,N,S donor centres have been successfully applied as pre‐catalysts in different asymmetric organic reactions . However, chiral macrocycles with P,N donors have rarely been employed in asymmetric reactions, due to the difficult synthesis of phosphorus‐based macrocycles and the formation of diastereomeric mixtures when two or more phosphorus atoms are present . A synthetic strategy based on the dynamic covalent chemistry of macrocyclic aminomethylphosphines was developed for numerous 14‐, 16‐, 18‐ and 20‐membered P 4 N 2 macrocycles .…”

Iron Complexes with Chiral N/P Macrocycles as Catalysts for Asymmetric Transfer Hydrogenation

“…Macrocycle 7 was tested in situ in the asymmetric transfer hydrogenation of propiophenone with a number of iron precursors. Mono‐ and dinuclear carbonyl complexes, as well as Fe(II) and Fe(III) salts gave poorly active ATH catalysts, whereas trinuclear Fe(0) carbonyl complexes such as [Fe 3 (CO) 12 ] and [Fe 3 H(CO) 11 ] − reduced propiophenone with 98 % ee and good activity with NH 4 Cl as promoter . In contrast, the imino analogue of 7 (not shown above) was inefficient in terms of activity and enantioselectivity.…”

“…In 2012, Gao prepared the potentially hexadentate, 22‐membered chiral macrocycle 7 with an N 4 P 2 donor set by cyclocondensation of a chiral diamine with 2,2′‐(phenylphosphinediyl)dibenzaldehyde, an achiral and readily prepared phosphine, followed by reduction with NaBH 4 of the imino intermediate. Notably, 7 is the first example of a C 2 ‐symmetric P/N macrocycle (Scheme ) …”

Asymmetric Transfer Hydrogenation of Ketones Using New Iron(II) (P‐NH‐N‐P′) Catalysts: Changing the Steric and Electronic Properties at Phosphorus P′

“…The use of abundant metals such as iron for this transformation is attractive due to their lower cost and toxicity, and this has been a topic of much interest in the last decade . Recently discovered iron catalysts stand out for their high enantioselectivity and activity in the asymmetric transfer hydrogenation of ketones ,,,…”