Synthetic Routes to Late Transition Metal–NHC Complexes

The growing interest in the use of late transition metal–N-heterocyclic carbene ligand (NHC) complexes in catalysis, medicinal chemistry, and materials science has stimulated the development of various synthetic strategies, leading to the isolation of these compounds. A recent procedure for the preparation of metal–NHC complexes consists of the use of weak bases and green solvents, operating in air and under generally mild conditions. The weak base approach has allowed for synthesis in high yields and purity of many metal complexes in recent years, some of which have proven to be powerful synthons as well as efficient homogeneous catalysts and promising bioactive compounds. Mechanistic studies have provided some important evidence on the role of both the weak base and the nature of the metal precursor used to obtain the target compounds. Transition metal complexes bearing N-heterocyclic carbene ligands (NHCs) have gained a place of crucial importance in numerous areas of research such as medicinal chemistry, material sciences, and homogeneous/heterogeneous catalysis. In the present review, an updated overview of the main synthetic routes used for the preparation of this broad class of compounds along with their main applications are reported. Particular attention will be paid to the synthesis of late transition metal–NHC complexes using weak bases, eco-friendly solvents, and mild operating conditions. This simple synthetic approach, also known as the ‘weak base route’, represents a recent development with yet unrealized potential. Transition metal complexes bearing N-heterocyclic carbene ligands (NHCs) have gained a place of crucial importance in numerous areas of research such as medicinal chemistry, material sciences, and homogeneous/heterogeneous catalysis. In the present review, an updated overview of the main synthetic routes used for the preparation of this broad class of compounds along with their main applications are reported. Particular attention will be paid to the synthesis of late transition metal–NHC complexes using weak bases, eco-friendly solvents, and mild operating conditions. This simple synthetic approach, also known as the ‘weak base route’, represents a recent development with yet unrealized potential. salts obtained for the protonation or substitution at nitrogen of imidazoles and their derivatives. a complex with two or more types of ligands. a complex with all ligands identical. the exchange of one ligand for another, with no change in oxidation state at the metal center. a structural unit within a molecule, which, by means of a chemical reaction, can be converted into the desired product. a reaction that involves the transfer of a ligand from a metal to another. a base that does not ionize fully in an aqueous solution. use of weak bases, mild conditions, and green solvents for the preparation of metal–NHC complexes.