Overview and Basic Principles

The electrophile ftat modifies a coordinated ligand can be a proton, a strong Lewis acid, or an unsaturated electrophile. Examples of Lewis acids include tiityl cahon or per-fluoroarylboranes, and examples of unsaturated electrophiles include CO, SO, isocyanates, aldehydes, ketones, and related compoimds. Reactions of these electrophiles can lead to the formation of catioruc metal complexes by abstraction of a hydride or hydrocarbyl group by the Lewis acid, or they can lead to products from insertion of the unsaturated electrophile into the metal-carbon bond. These reactions are sho-wn generically in Equations 12.1-12.3. 

Electrophilic Cleavage of Metal-Carbon and Metal-Hydride cr-Bonds 

A proton is the electrophile most commonly used to remove an organic ligand from a transition metal. These protonolyses typically occur by mechanisms that retain the stereochemistry of the organic ligand. For example, the deuterium in the product of the reaction in Equation 12.4 occupies the same position about the double bond as did the ruthenium in the initial vinyl complex. Olefin stereochemistry was also shown to be retained during cleavage of a vinyl-paUadium bond with Qeavage of a metal-alkyl bond has also been shown to occur with retention of stereochemistry (Equation 12.5).  

Metal-carbon bonds are not only cleaved by protons but by halogens or mercuric halides as the electrophile. These reactions typically lead to the formation of alkyl halides or alkylmercury products (Equation 12.6). In contrast to the more common reactions with protons, these reactions generate functionalized organic products. 

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