Zwitterionic Mixed‐Carbene Coinage Metal Complexes: Synthesis, Structures, and Photophysical Studies

Abstract

A series of three zwitterionic mixed‐ligand bis(carbene) complexes of copper (1), silver (2) and gold (3) have been synthesized, based on a combination of ethyl‐substituted cyclic (alkyl)(amino)carbene (Et2CAAC) and an anionic methyl‐malonate‐derived N‐heterocyclic carbene (maloNHC). The crystal structures confirm the linear two‐coordinate geometry without close intermolecular contacts. The compounds show blue‐white phosphorescence consistent with a wide HOMO‐LUMO energy gap (2.87–3.07 eV) estimated by cyclic voltammetry. The excited state lifetimes of crystalline powders decrease in the series Cu > Ag > Au, from 400 µs for copper 1 to 50 µs for the gold complex 3. DFT calculations indicate a large change in the transition dipole moment on excitation, of up to 16 D.