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.

Carbene-metal complexes as molecular scaffolds for construction of through-space TADF emitters

“…This is a contrasting behavior to IPr-Cu-Cz and some other related structural analogues, which show structured emission bands due to the phosphorescence from 3 LE states. 30,31 In agreement with the theoretical predictions, which reveal more stabilized lowest energy CT states for imidazoline-based complexes 2 and 4, these compounds show bathochromic PL shifts of 20−24 nm. The PL bands exhibit a characteristic positive solvatochromism, which arises due to the 1 CT state stabilization by the solvation shell, as evident by the emission spectra in toluene and chlorobenzene (Fig.…”

“…This process can be related to a formal hybridization change of the carbazolide nitrogen from the typical sp 2 to the sp 3 -like state, as indicated by the apparent structural pyramidalization at N2 atom and by the carbazolide N2-C2 bond lengthening, from 1.374 to 1.406 Å. The release of 13 the sterical strain by the 90° rotation of the carbazolide plane, like in several other reported CMAs, 17,30,31 in this case is not possible due to the repulsion between the carbazolide methyls and the isopropyl groups of two Dipp fragments. In comparison to complex 1, the interligand bridge in 4 (C1-Cu-N2) is slightly extended (by 0.081 Å).…”

Continuous Flow Synthesis of NHC‐Coinage Metal Amido and Thiolato Complexes: A Mechanism‐based Process Development

“…Comparable to the batch synthesis, [12] complex 7 b bearing an N ‐alkyl substituted NHC was readily afforded in high yields, and significantly shorter reaction times were sufficient to reach these results. Of significant note, great improvements with respect to reaction time were obtained in the synthesis of 7 c and 7 d , complexes whose respective batch syntheses required 24 and 48 h, respectively [12] . Especially the synthesis of complex 7 d is notable as it clearly indicates that the presence of excessive steric bulk on the supporting ligand – a feature rendering batch synthesis often cumbersome – is not an impediment in this continuous flow synthesis.…”

“…The necessity for different solvents at the separate stages of the reaction presents no issues since the second reaction step is fully operational with one‐to‐one ethanol/acetone solvent mixtures. Again, marked improvements have been established when compared to the batch version of the syntheses [12] …”

“…Several equivalents of base are required to drive reactions towards completion, while additionally necessitating reactions to stir for extended periods of time. Via solventless mechanochemical approaches, reaction times have already been greatly reduced, yet substantial excess of base and amine substrates are still required [12,16] . Continuous flow technology offers opportunities to address poor reaction kinetics simply by the nature of its small reactor dimensions which allows for enhanced mass and heat transfer [17] .…”