Stereochemical Control of Tricoordinate Copper(I) Complexes Based on N-(9-Alkyl-9-fluorenyl)-Substituted Heterocyclic Carbenes

Abstract

A series of tricoordinate copper(I) complexes of general formula [Cu(Et F-NHC)(2,2′-dipyridylamine)][BF4], in which Et F-NHC represents an imidazol-2-ylidene ligand bearing a 9-ethyl-9-fluorenyl N-substituent have been synthesised stepwise from appropriate N-arylimidazoles. All complexes are remarkably air-stable, both in solution and in the solid state. X-ray diffraction studies revealed that in three of the complexes the fluorenylidene plane and the dipyridylamine (dpa) unit undergo intramolecular π–π stacking. The resulting bending of the fluorenilydene plane towards the metal atom is likely to contribute to maintain the trigonal planar geometry of the [Cu–C,N,N] unit upon binding of exogenous substrates, thereby considerably increasing complex stability.

Investigations of a Copper(II) Bipyridyl-N-Heterocyclic Carbene Macrocycle for CO2 Reduction: Apparent Formation of an Imidazolium Carboxylate Intermediate Leading to Demetalation

“…It is worth noting that a number of three-coordinate Cu(I) compounds supported by carbene-based ligands are known in the literature. − In these examples, trigonal planar geometries are typically observed with either one or two coordinated NHC donors. − Relevant examples of copper complexes in different oxidation states bearing macrocyclic tetradentate NHC based ligands have also been reported. , In the report by Kühn and co-workers using a tetraNHC ligand, a Cu(III) complex was accessed via a disproportionation reaction starting from a Cu(II) salt even under anaerobic conditions . Interestingly, the copper(III) metal center can react with acetate to cause decoordination of the macrocycle along with oxidation of an NHC donor .…”