Copper carbene complexes: advanced catalysts,new insights

Controlling the selectivity of reactive intermediates is a major goal of organic chemists. Carbenes generated by thermal or photochemical extrusion of nitrogen from diazo compounds defy external control and tend to give complex product mixtures. However, the catalyzed decomposition of diazo compounds gives rise to highly selective "carbenoids" which have found extensive application in synthesis although little is known of their precise nature. On the other hand, a large variety of carbene metal complexes have been prepared and characterized which more or less lack carbenoid reactivity. Structural evidence for the transients of catalyzed diazo decomposition is becoming available through experiment and computation. Although the present report focuses on copper complexes, outstanding results with other metals are also covered.