N,O- vs N,C-Chelation in Half-Sandwich Iridium Complexes: A Dramatic Effect on Enantioselectivity in Asymmetric Transfer Hydrogenation of Ketones

Zhou, Gang, Aboo, Ahmed H, Robertson, Craig M ORCID: 0000-0002-4789-7607, Liu, Ruixia, Li, Zhenhua, Luzyanin, Konstantin ORCID: 0000-0001-9312-7139, Berry, Neil G ORCID: 0000-0003-1928-0738, Chen, Weiping and Xiao, Jianliang ORCID: 0000-0003-2010-247X (2018) N,O- vs N,C-Chelation in Half-Sandwich Iridium Complexes: A Dramatic Effect on Enantioselectivity in Asymmetric Transfer Hydrogenation of Ketones. ACS CATALYSIS, 8 (9). pp. 8020-8026.

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Official URL: http://dx.doi.org/10.1021/acscatal.8b02068

Abstract

Cyclometalation of [Cp∗IrCl2]2 with methyl (S)-2-phenyl-4,5-dihydrooxazole-4-carboxylate in the presence of NaOAc selectively led to a N,C- or N,O-chelated Cp∗Ir(III) complex, depending on whether or not water was present in the reaction. While derived from the same precursor, these two complexes behaved in a dramatically different manner in asymmetric transfer hydrogenation (ATH) of ketones by formic acid, with the N,O-chelated complex being much more selective and active. The sense of asymmetric induction is also different, with the N,O-complex affording S while the N,C-analogue R alcohols. Further study revealed that the nature of the base additive considerably impacts the enantioselectivity and the effective HCOOH/amine ratios. These observations show the importance of ligand coordination mode and using the right base for ATH reactions.

Item Type:	Article
Uncontrolled Keywords:	N,O-chelation, N,C-chelation, half-sandwich iridium complexes, cyclometalation, asymmetric transfer hydrogenation
Depositing User:	Symplectic Admin
Date Deposited:	02 Aug 2018 09:56
Last Modified:	19 Jan 2023 01:29
DOI:	10.1021/acscatal.8b02068
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3024497