Abstract
The synthesis of chelating N-heterocyclic carbene (NHC) complexes with considerable π-acceptor properties can be a challenging task. This is due to the dimerization of free carbene ligands, the moisture sensitivity of reaction intermediates or reagents, and challenges associated with the workup procedure. Herein, we report a general route using transmetalation from magnesium–NHCs. Notably, this route gives access to transition-metal complexes in quantitative conversion without the formation of byproducts. It therefore produces transition-metal complexes outperforming the conventional routes based on free or lithium-coordinated carbene, silver complexes, or in situ metalation in dimethyl sulfoxide (DMSO). We therefore propose transmetalation from magnesium–NHCs as a convenient and general route to obtain NHC complexes.
Highlights
N-heterocyclic carbene (NHC) ligands have become the powerhouse of modern transition metal chemistry [1,2,3,4,5,6,7,8,9,10,11,12,13]
This led to the design of π-electron-withdrawing carbenes such as Bertrand’s cyclic(amino) carbenes (CAACs) [16,17,18,19,20,21], diamido carbenes (DACs) [22,23,24,25], or ferrocenium-decorated
We reported that transmetalation from magnesium complexes with pincer-type NHC ligands
Summary
N-heterocyclic carbene (NHC) ligands have become the powerhouse of modern transition metal chemistry [1,2,3,4,5,6,7,8,9,10,11,12,13] This is largely due to the ease of tuning their electronic and steric properties targeting a specific application. NHCs with saturated backbones (saNHCs, imidazolidin-2-ylidenes) as well as benzannulated congeners (benzNHCs, benzimidazolin-2-ylidenes) show considerable backbonding capabilities. This is either due to the pyramidalization of the amino groups, which reduces the overlap with the π-system within the N-heterocycle, or to the π-acidic character of the benzannulated π-system
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