Reactions of Carbenes with Nucleophiles

Dichlorocarbene ( CH2) to benzene, but does attack the electron-rich 

In the vapor phase, there are two additional considerations that are very important in understanding of carbene chemistry. The first point reflects the fact that carbene reactions are normally highly exothermic (about 90kcal mol for insertions or additions). Thus, a product molecule is frequently produced with a large amount of excess internal energy. In the vapor phase without solvent molecules to help dissipate the excess vibrational energy, the molecule may be subject to further reactions. Such reactions are often called hot molecule reactions. Cyclopropanes from cycloaddition reactions are particularly susceptible to hot molecule decomposition to the thermodynamically more stable olefin, since for cyclopropane isomerization is only 64kcal mol .  

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Many carbene complexes undergo nucleophilic attack at the carbene carbon. This chemistry is presented in more detail in Chapter 13 on metal-ligand multiple bonds. In brief, cationic carbene complexes tend to imdergo simple addition processes to generate neutral products (Equation 11.8), whereas neutral complexes can react by either addition (Equation 11.9) or by a sequence of addition and elimination reactions (Equation 11.10). Fischer has shown that the aminolysis of alkoxycarbene complexes occurs by initial attack at the carbene carbon by a mechanism similar to that for the aminolysis of organic esters. Although less studied than reactions of carbenes with nucleophiles, reactions of carbyne complexes with nucleophiles are also known, and these reactions generate carbene complexes. ... 

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