Recent Developments in N-Heterocyclic Carbene and Transition-Metal Cooperative Catalysis

Recently, N-heterocyclic carbene (NHC) catalysis has achieved significant achievement in the field of cooperative catalysis. With the combination of other established catalysis modes (e.g., Lewis acid, Bronsted acid/base, hydrogen-bond donor), great improvement has been made in the enhancement of reactivity and stereoselectivity, and this strategy has emerged as a powerful instrument in organic synthesis to construct complex molecules. However, owing to the strong propensity of NHCs to bind to transition metals, the development of cooperative catalysis of NHCs and transition metals remains a longstanding and challenging work. At present, some important progress has been made in the combination of NTICs with palladium, copper and ruthenium, and the coordination of NTICs and transition metals can be controlled by the modulation of ligand and alkalinity in reaction system, which not only avoiding the deactivation of the catalysts, but also improving the reaction activity efficiently. This strategy has also been used in the asymmetric construction of bioactive molecular scaffolds. In this perspective, the achievements on NHC and transition metals cooperative catalysis will be discussed.