Cyclic (alkyl)(amino)carbenes with a six-membered backbone were prepared. Compared to their five-membered analogues, they feature increased % V and enhanced donor and acceptor properties, as evidenced by the observed n → π* transition trailing into the visible region. The high ambiphilic character even allows for the intramolecular insertion of the carbene into an unactivated C(sp)-H bond. When used as ligands, they outcompete the five-membered analogues in the palladium-mediated α-arylation of ketones with aryl chlorides.

Cyclic (alkyl)(amino)carbene (CAAC) metal complexes can also engage in asymmetric transformations, thereby expanding the toolbox of available chiral carbene ligands.

Selenium NMR has become a standard tool for scaling the p-accepting character of carbenes. Herein, we highlight that non-classical hydrogen bonding (NCHB), likely resulting from hyperconjugation, can play a significant role in the carbene-selenium 77 Se NMR chemical shift, thus triggering a non-linear behavior of the Se-Scale.

Through kinetic measurements, catalytic and stoichiometric experiments, as well as DFT calculations, we compare the catalytic activity of gold complexes supported by a variety of ligands (R3P, NHC, CAAC-5, CAAC-6, BiCAAC) in the hydroamination and hydrohydrazination of alkynes. This study provides a rationale for the superior efficiency of a gold complex bearing a bicyclic (alkyl)(amino)carbene (BiCAAC). We demonstrate that this ligand motif, which is readily available, provides a durable gold catalyst able to compete with sophisticated state-of-the-art phosphine and NHC ligands, which feature secondary interaction capabilities.