Dehydrative coupling of alcohols by Iridium(III) complexes with N-Heterocyclic-Pyridine chelating ligands decorated with Naphthalene-Diimide

Abstract

A series of dimetallic and monometallic Cp*Ir(III) complexes bearing naphthalene-diimide-decorated N-heterocyclic carbene/pyridine [NDI-(NHC-pyridine)] ligands were prepared and characterized. The complexes show a C,C-chelating coordination of the NHC-pyridine ligand, with the pyridine ring of the ligand bound to the metal via cyclometallation rather than by its nitrogen atom, although the coordination by the nitrogen atom could be achieved by subjecting one of the complexes to reaction with a strong acid. The spectroelectrochemical studies of the new compounds reveal that the complexes are able to undergo two successive reduction events, associated with the sequential reduction of the NDI moiety of the ligand. The new complexes were tested in the dehydrative etherification by cross-coupling of primary alcohols, where they showed good activity and selectivity toward the cross-coupled products. The mechanistic studies allowed us to propose a reaction mechanism which likely involves a redox-neutral acid-catalyzed pathway.