Simple Synthetic Routes to Carbene-M-Amido (M=Cu, Ag, Au) Complexes for Luminescence and Photocatalysis Applications

Abstract

The development of novel and operationally simple synthetic routes to carbene-metal-amido (CMA) complexes of copper, silver and gold relevant for photonic applications are reported. A mild base and sustainable solvents allow all reactions to be conducted in air and at room temperature, leading to high yields of the targeted compounds even on multigram scales. The effect of various mild bases on the N-H metallation was studied in silico and experimentally, while a mechanochemical, solvent-free synthetic approach was also developed. Our photophysical studies on [M(NHC)(Cbz)] (Cbz=carbazolyl) indicate that the occurrence of fluorescent or phosphorescent states is determined primarily by the metal, providing control over the excited state properties. Consequently, we demonstrate the potential of the new CMAs beyond luminescence applications by employing a selected CMA as a photocatalyst. The exemplified synthetic ease is expected to accelerate the applications of CMAs in photocatalysis and materials chemistry.

Keywords: carbene-metal-amides; coinage metal-N-heterocyclic carbene complexes; mechanochemistry; photocatalysis; synthetic methods.

Scheme 1

Scope of the CMA synthetic route. The X‐ray molecular structure of complexes 4 b, 4 e, 4 f, 5 c and 6 c are presented, showing thermal displacement ellipsoids at the 50 % probability level and hydrogen atoms omitted for clarity (see Supporting Information for more detailed structural information).

Scheme 2

Scope of amines in the case of gold.

Scheme 3

Large scale synthesis, one‐pot synthesis and mechanochemical synthesis of CMA complexes.

Figure 1

Absorption spectra of 4 a, b and 5 a, b in THF solution at room temperature.

Figure 2

Normalized emission (blue) and excitation (black for λ_em=430 nm, grey for λ_em=540 nm) spectra of 4 b in THF solution and in the solid state (inset) at room temperature.