Wang and Lin developed a method of synthesizing metal complexes containing these compounds, where these compounds are first reacted with silver before undergoing transmetalation. Pyridines and these compounds are ligands in the PEPPSI (“pepsi”) catalysts used for cross-coupling reactions. Bertrand et al. discovered the mesoionic type of these compounds, which unlike other types of these compounds do not dimerize in an equilibrium named for (*) Wanzlick. (10[2])Two adamantyl groups were attached to an imidazolium in the synthesis of one of these compounds by Arduengo et al. These compounds were used in place of a phosphine ligand in second and third generation Grubbs catalysts. The best-known subgroup of the persistent type of these compounds contains nitrogen heterocycles. For 10 points, what compounds contain a neutral carbon with six valence electrons? ■END■