Sterically controlled formation of monodentate versus chelating carbene ligands from phenylhydrazine

Palladium-templated addition of phenylhydrazine to methylisocyanide led to a Chugaev-type chelating dicarbene–palladium complex that is an effective catalyst for Suzuki-Miyaura cross-coupling reactions of aryl bromides and activated aryl chlorides. In contrast, the use of isopropylisocyanide resulted in an unprecedented complex containing aminohydrazinocarbene ligands, which was characterized by X-ray crystallography. The latter complex represents a possible intermediate in the formation of chelating carbene ligands.