title: A Rhodium Catalyst Superior to Iridium Congeners for Enantioselective Radical Amination Activated by Visible Light.
abstract: A bis-cyclometalated rhodium(III) complex catalyzes a visible-light-activated enantioselective α-amination of 2-acyl imidazoles with up to 99 % yield and 98 % ee. The rhodium catalyst is ascribed a dual function as a chiral Lewis acid and, simultaneously, as a light-activated smart initiator of a radical-chain process through intermediate aminyl radicals. Notably, related iridium-based photoredox catalysts reported before were unsuccessful in this enantioselective radical C-N bond formation. The surprising preference for rhodium over iridium is attributed to much faster ligand-exchange kinetics of the rhodium complexes involved in the catalytic cycle, which is crucial to keep pace with the highly reactive and thus short-lived nitrogen-centered radical intermediate.
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Shen
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Harms
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Marsch
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany. meggers@chemie.uni-marburg.de.|College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China. meggers@chemie.uni-marburg.de.
authors.forename: Eric
authors.initials: E
authors.lastname: Meggers
keywords: asymmetric; catalysis; photoredox; visible light