Group 4 metal substituents carbene insertion reactions

Carbenes, in general, are very reactive electrophilic species. Their activity depends to some extent on the method and conditions of preparation, on the nature of the substituent groups and also on the presence or absence of metals or metallic salts. Carbenes undergo a variety of reactions, including insertion into C—H bonds, addition to multiple bonds and skeletal rearrangements. The simplest carbene, methylene itself, attacks primary, secondary and tertiary C—H bonds indiscriminantly. However, alkyl carbenes can undergo selective intramolecular C—H, N—H or O—H insertion to provide useful synthetic transformations. In general, no intermolecular reactions are observed when intramolecular insertion is possible. 

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