Ligand-to-metal ratio controls stereoselectivity: Highly functional-group-tolerant, iridium-based, (E)-selective alkyne transfer semihydrogenation
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Date
2022
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Elsevier
Abstract
Herein, we present (E)-selective transfer semihydrogenation of al kynes based on an iridium complex in situ generated from [Ir(COD)Cl]2 and an unsymmetrical (bearing two different phosphorous cen ters), ferrocene-based phosphine ligand utilizing formic acid as a hydrogen donor. Interestingly, a ligand-to-metal ratio may be used to control the stereoselectivity of the semihydrogenation pro cess: a ratio of 1:1 iridium to ligand led to the formation of (Z)-alkene as a major product, whereas a ratio of 1:2 gave exclusively (E)-alkene. The latter 1:2 catalytic system is distinguished by its unprec edented chemoselectivity and exceptional stereoselectivity, which is substantiated by the broad scope of tested substrates, including natural product derivatives. The intriguing difference in catalytic ac tivity between unsymmetrical and symmetrical ferrocene-based li gands was attributed to divergent coordination and steric hin drance. The presented methodology constitutes a solution to the common limitations of the known catalytic systems for semihydro genation.
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Kusy et al., Chem Catalysis 2, 1346—1361 June 16, 2022. https://doi.org/10.1016/j.checat.2022.04.014