Umpolung in a Pair of Cobalt(III) Terminal Imido/Imidyl Complexes
Weiqing Mao, Dominik Fehn, Frank W. Heinemann, Andreas Scheurer, Maurice van Gastel, Sergio A. V. Jannuzzi, Serena DeBeer, Dominik Munz, Karsten Meyer
Abstract
Abstract Reaction of the Co I complex [(TIMMN mes )Co I ](PF 6 ) ( 1 ) (TIMMN mes = t ris ‐[2‐(3‐mesityl‐ im idazolin‐2‐ylidene)‐ m ethyl]ami n e) with mesityl azide yields the Co III imide [(TIMMN mes )Co III (NMes)](PF 6 ) ( 2 ). Oxidation of 2 with [FeCp 2 ](PF 6 ) provides access to a rare Co III imidyl [(TIMMN mes )Co(NMes)](PF 6 ) 2 ( 3 ). Single‐crystal X‐ray diffractometry and EPR spectroscopy confirm the molecular structure of 3 and its S = ground state. ENDOR, X‐ray absorption spectroscopy and computational analyses indicate a ligand‐based oxidation; thus, an imidyl‐radical electronic structure for 3 . Migratory insertion of one ancillary NHC to the imido ligand in 2 gives the Co I N ‐heterocyclic imine ( 4 ) within 12 h. Conversely, it takes merely 0.5 h for 3 to transform to the Co II congener ( 5 ). The migratory insertion in 2 occurs via a nucleophilic attack of the imido ligand at the NHC to give 4 , whereas in 3 , a nucleophilic attack of the NHC at the electrophilic imidyl ligand yields 5 . The reactivity shunt upon oxidation of 2 to 3 confirms an umpolung of the imido ligand.