Chemistry Chat

Carbene complexes are organometallic complexes with the carbene coordinated on the carbon atom to the metal center. There are two types which can be categorized as Fischer type carbene complexes and Schrock type carbene complexes.
Fischer carbene complexes show electrophilicity　because the center metal is in an electron poor state. Therefore, the reactivity of it is similar to carbonyl compounds in which nucleophilic substitution of it with various nucleophiles proceeds. In addition one of substituents has to be an alkoxy group because of its electronic structure.
The chemical character of Schrock type carbene complexes is nucleophilic because of an electron rich state at the metal center. It shows especially high reactivities towards carbon-carbon and carbon-heteroatom multiple bonds. As typical chemical examples of Schrock type carbene complex usage, olefin metathesis and carbonyl olefination are well known. These synthetic characteristics are very useful so many suppliers have Schrock type carbene complexes as reagents.

Olefin metathesis is a chemical reaction between double bonds of two separate olefin units in which double bonds exchange with each other to form two new olefin units.  A Schrock type carbene complex is usually used for such a synthesis and Mo, Ru and Ti metals are generally used as active metals.  The bulkiness of substituents on the olefins affects their reactivity in olefin metathesis, so the development of new carbene complexes showing higher reactivity has been studied since the 1990’s.