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Highly Enantioselective Transfer Hydrogenation of Prochiral Ketones Using Ru(II)‐Chitosan Catalyst in Aqueous Media
Author(s) -
Szőllősi György,
Kolcsár Vanessza Judit
Publication year - 2019
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201801602
Subject(s) - catalysis , transfer hydrogenation , chemistry , acetophenone , enantioselective synthesis , chitosan , biopolymer , aqueous solution , hydride , organic chemistry , polymer chemistry , ruthenium , polymer , hydrogen
Unprecedentedly high enantioselectivities are obtained in the transfer hydrogenation of prochiral ketones catalyzed by a Ru complex formed in situ with chitosan chiral ligand. This biocompatible, biodegradable chiral polymer obtained from the natural chitin afforded good, up to 86 % enantioselectivities, in the aqueous‐phase transfer hydrogenation of acetophenone derivatives using HCOONa as hydrogen donor. Cyclic ketones were transformed in even higher, over 90 %, enantioselectivities, whereas further increase, up to 97 %, was obtained in the transfer hydrogenations of heterocyclic ketones. The chiral catalyst precursor prepared ex situ was examined by scanning electron microscopy, FT‐mid‐ and ‐far‐IR spectroscopy. The structure of the in situ formed catalyst was investigated by 1 H NMR spectroscopy and using various chitosan derivatives. It was shown that a Ru pre‐catalyst is formed by coordination of the biopolymer to the metal by amino groups. This precursor is transformed in water insoluble Ru‐hydride complex following hydrogen donor addition. The practical value of the developed method was verified by preparing over twenty chiral alcohols in good yields and optical purities. The catalyst was applied for obtaining optically pure chiral alcohols at gram scale following a single crystallization.