In organometallic chemistry, sigma-bond metathesis is a chemical reaction wherein a metal-ligand sigma bond undergoes metathesis (exchange of parts) with the sigma bond in some reagent.
The reaction is illustrated by the exchange of lutetium(III) methyl complex with a hydrocarbon (R-H):[1] This reactivity was first observed by Patricia Watson, a researcher at duPont.
Indeed, the rate of the reaction is characterized by a highly negative entropy of activation, indicating an ordered transition state.
For metals unsuited for redox, sigma bond metathesis provides a pathway for introducing substituents.
The reaction attracted much attention because hydrocarbons are normally unreactive substrates, whereas some sigma-bond metatheses are facile.