Improving the Configurational Stability of Chiral-at-Iron Catalysts Containing Two N-(2-Pyridyl)-Substituted N-Heterocyclic Carbene Ligands

Organometallics. 2022 Dec 26;41(24):3852-3860. doi: 10.1021/acs.organomet.2c00492. Epub 2022 Nov 25.

ABSTRACT

Recently, we introduced the first example of chiral-at-iron catalysts in which two achiral N-(2-pyridyl)-substituted N-heterocyclic carbene (NHC) ligands in addition to two labile acetonitriles are coordinated around a central iron, to generate a stereogenic metal center [Hong Y.Chiral-at-Iron Catalyst: Expanding the Chemical Space for Asymmetric Earth-Abundant Metal Catalysis. J. Am. Chem. Soc.2019, 141, 4569-4572]. A more facile synthesis of such chiral-at-iron catalysts was developed, which omits the use of expensive silver salts and an elaborate electrochemical setup. Configurational robustness was improved by replacing the imidazol-2-ylidene carbene moieties with benzimidazol-2-ylidenes. The π-acceptor properties of the altered NHCs were investigated by Ganter’s 77Se NMR method. The obtained benzimidazol-2-ylidene chiral-at-iron complex is an excellent catalyst for an asymmetric hetero-Diels-Alder reaction under open-flask conditions.

PMID:36590905 | PMC:PMC9795549 | DOI:10.1021/acs.organomet.2c00492

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