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Redox‐Switchable Cycloisomerization of Alkynoic Acids with Napthalenediimide‐Derived N‐Heterocyclic Carbene Complexes
Author(s) -
RuizZambrana César,
GutiérrezBlanco Ana,
Gonell Sergio,
Poyatos Macarena,
Peris Eduardo
Publication year - 2021
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202107973
Subject(s) - cycloisomerization , carbene , iridium , catalysis , chemistry , rhodium , ligand (biochemistry) , redox , metal , medicinal chemistry , photochemistry , organic chemistry , receptor , biochemistry
Abstract Two naphthalene‐diimide (NDI) bis‐imidazolium salts have been used as N‐heterocyclic carbene (NHC) precursors for the preparation of NDI‐functionalized complexes of rhodium and iridium of general formula [MCl(NDI‐NHC)(COD)] (M=Rh, Ir; NDI‐NHC=NDI‐functionalized NHC ligand). Comparison of the IR spectra of the complexes [IrCl(NDI‐NHC)(CO) 2 ] and their related one‐ and two‐electron reduced forms, reveal that each one‐electron reduction produces a decrease of the average ν(CO) of 9–10 cm −1 , indicating a significant enhancement of the electron‐richness of the metal. The [MCl(NDI‐NHC)(COD)] complexes were tested in the catalytic cycloisomerization of alkynoic acids. The one‐electron reduced forms showed greatly enhanced activities. For the cyclization of 5‐hexynoic acid, the two‐electron reduction of the ligand produced further enhancement of the catalytic activity, therefore showing that the catalyst can switch between three redox species with three distinct catalytic activities.