Researchers have found an unusual transformation of an N-heterocyclic carbene (NHC) that could have implications for the design of new catalyst ligands. When NHCs act as ligands and form complexes with metals, the carbene carbon typically remains nonreactive. The carbene carbon has been known to react in some circumstances, and a group led by LeGrande M. Slaughter of Oklahoma State University, Stillwater, has found an extreme example of such a reaction (Chem. Commun. 2015, DOI: 10.1039/c5cc01560j). To carry out the reaction, Slaughter, now at the University of North Texas, and his team first converted a stable imidazolium cation to an imino-NHC intermediate. When the researchers added tetrabenzylhafnium, the intermediate was “decarbonized.” In this process, hafnium displaced the carbene carbon, but the latter didn’t flee the scene entirely. Instead, it jumped on hafnium’s back and hijacked three of hafnium’s benzyl groups (shown above). The reaction converted the neutral imino-NHC intermediate into a dianionic chelate ligand with three hafnium-linked nitrogens. The researchers demonstrated that the decarbonized chelate complex can catalyze ethylene polymerization. They now hope to find out whether similar rearrangements could play a role in activating other metal-based catalysts.