Metal–Ligand Cooperation of Ir(III) Catalysts Bearing a β‐Protic Pyrazole Chelate in Carboxylative Cyclization of Propargylic Amine with CO₂

Bifunctional iridium complexes having a β‐protic C–N chelating pyrazole ligand catalyze the carboxylative cyclization of 1‐methylamino‐2‐butyne under atmospheric CO 2 . This reaction affords a five‐membered cyclic urethane, along with a six‐membered regioisomer. Alkenyliridium(III) complexes as catalytic intermediate models are formed by stoichiometric reaction of related nonprotic pyrazole complexes with 1‐methylamino‐2‐butyne and CO 2 in the presence of Ag 2 O, although the protic pyrazole analog is too unstable to be detected. In particular, the isolable N ‐phenylpyrazole‐ligated alkenyliridium(III) complex with a cyclic urethane framework is characterized by X‐ray crystallography. The β‐protic pyrazole ligand would be capable of accelerating protonolysis of the alkenyl carbon–iridium bond in the key intermediate, releasing the cyclic urethane product, and being responsible for the catalytic function.