Rhodium versus ruthenium catalysis: From carbene transfer to olefin metathesis.

Abstract

An review with 30 refs. of the possible types of bonding in transition-metal carbene complexes is presented. The different modes of carbene reactivity seem to reflect a dramatic difference in the type of bonding. Comparison between dirhodium(II) and diruthenium(II) tetracarboxylates illustrate the diversity in the chem. When activated by addn. of a diazo compd., rhodium compds. only catalyze carbene transfer reactions to olefins (i.e. cyclopropanation), while the corresponding ruthenium complexes initiate both olefin metathesis and carbene transfer reactions. With ruthenium complexes, modification of the metal coordination sphere can direct the reaction toward metathesis or carbene transfer. New catalyst systems, based on ruthenium, are highly efficient for promoting the ROMP of cycloolefins. [on SciFinder(R)]