General Principles and Trends

Nucleophilic attack on unsaturated u-bound ligands, such as acyl groups, is faster than attack on saturated alkyl ligands. Because the metal-bound carbon of these ligands can possess a partial negative charge, acyl, alkoxycarbonyl, and aminocarbonyl complexes 

In contrast to these slow reactions of (r-bound ligands, many complexes of anionic T7-bound ligands react readily with nucleophiles. Reactions of Ti-allyl complexes with nucleophiles are most common, and these reactions have become a staple for the development of catalytic transformations of allyUc alcohol derivatives, dienes, and allenes. Attack on electron-poor, often cationic, allyl complexes with relatively weak nucleophiles can occur rapidly below room temperature.  

Nucleophilic attack of transition metal centers on a-bound ligands occurs as readily as reaction with the common nucleophiles of organic chemistry. Degenerate exchange of alkyl groups from one metal to another, as exemplified by the reactions in Equations 11.11 and 11.12, is proposed to occur by nucleophilic attack. This exchange of alkyl groups has been proposed as a mechanism to racemize chiral alkylmetal complexes. -  

The attack of a nucleophile, such as an amine, alkoxide, thiolate, or halide on an alkyl group is most common when the alkyl group is bound to an electron-poor, often high-valent, metal center. These reactions occur by mechanisms that are similar to the Sjj2 process of organic electrophiles. The reactions are sensitive to the polarity of the solvent, are sensitive to the steric effects at the point of attack, and lead to inversion of configuration at the carbon at the metal that is subject to the attack. 

This reaction is part of the mechanism for reductive eliminations of alkyl halides from Pt(IV). As noted in Chapter 8 (reductive elimination), this reaction occurs by initial dissociation of iodide to generate a cationic Pt(IV) methyl complex and subsequent attack of iodide on the platinum(IV) methyl group to generate methyl iodide (Equation 11.13). The reductive elimination of methyl aryl ethers, methyl acetate, and methyl trifluoroacetate 

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