The present invention relates to catalysts of transition metal complexes of N-heterocyclic carbenes, their methods of preparation and their use in chemical synthesis. The synthesis, ease-of-use, and activity of the compounds of the present invention are substantial improvements over in situ catalyst generation. Further, the transition metal complexes of N-heterocyclic carbenes of the present invention may be used as precatalysts in metal-catalyzed cross-coupling reactions.