Sigma-bond metathesis

In <a href="/facts/Organometallic_chemistry/bhqFz2P0">organometallic chemistry</a>, sigma-bond metathesis is a <a href="/facts/Chemical_reaction/GpqWlKrz">chemical reaction</a> wherein a metal-ligand <a href="/facts/Sigma_bond/CSyEe5CY">sigma bond</a> undergoes metathesis (exchange of parts) with the sigma bond in some reagent. The reaction is illustrated by the exchange of <a href="/facts/Lutetium/URlmnYG8">lutetium</a>(III) methyl complex with a hydrocarbon (R-H):

(C5Me5)2Lu-CH3 + R-H → (C5Me5)2Lu-R + CH4
This reactivity was first observed by Patricia Watson, a researcher at duPont. 
The reaction is mainly observed for complexes of metals with d0 configuration, e.g. complexes of Sc(III), Zr(IV), Nb(V), Ta(V), etc. f-Element complexes also participate, regardless of the number of f-electrons. The reaction is thought to proceed via <a href="/facts/Cycloaddition/Gme6TDFP">cycloaddition</a>. Indeed, the rate of the reaction is characterized by a highly negative entropy of activation, indicating an ordered <a href="/facts/Transition_state/34PsdqRd">transition state</a>. 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. Unfortunately the reaction does not readily allow the introduction of functional groups. It has been suggested that dehydrocoupling reactions proceed via sigma-bond metathesis.

Sigma-bond metathesis open-in-new

Sigma-bond metathesis