In the presence of a base such as KO-t-Bu, generates the imidazol-2-ylidene, an example of an N-heterocyclic carbene (NHC). NHCs are relatively strong bases, and valuable replacements for phosphine ligands in transition metal chemistry. They are relatively stable to dimerization, but sensitive to air and moisture, so are best generated in situ. Review: Angew. Chem. Int. Ed., 36, 2163 (1997). For a review of stable carbenes, see: Chem. Rev., 100, 39 (2000).Used as a phosphine-free ligand in various metal-catalyzed coupling reactions, often with advantageous results in difficult cases. For use in the Pd-catalyzed cross-coupling of aryl Grignards with aryl chlorides (Kumada reaction), see: J. Am. Chem. Soc., 121, 9889 (1999). For Pd-catalyzed coupling of trimethoxysilanes with electron-deficient aryl chlorides, see: Org. Lett., 2, 2053 (2000). Many examples have been recorded of the use of NHC ligands in the Suzuki coupling reaction, for examples utilizing 1,3-bis(2,6-diisopropylphenyl)imiazol-2-ylidene, enabling otherwise difficult coupling reactions of aryl chlorides with aryl and alkyl boronic acids, see: Synlett, 292 (2001) (includes alkylboronic acids: better yields than 1,3-dimesitylimidazol-2-ylidene); Org. Lett., 6, 4435 (2004); Tetrahedron Lett., 45, 3511 (2004).
