Cationic Iron Aminocarbene Complexes as Dienophiles in Diels‐Alder Reaction with Cyclopentadiene

The cationic iron (alkynyl)aminocarbene complexes [Cp(CO) 2 Fe(C(NHR)CCSiMe 3 ][PF 6 ], (R C 6 H 5 , p ‐CH 3 C 6 H 4 ) 1 derived from aromatic amines smoothly react with cyclopentadiene in dichloromethane to yield the cycloadducts 2 . No reaction was observed for complexes derived from sterically demanding aliphatic amines, like L ‐alanine tert ‐butyl ester. For comparison, the alkynyl‐substituted acyl iron compounds Cp(CO) 2 Fe(CO)CC̊ (R SiMe 3 , C 6 H 5 ) 3 were investigated, requiring TiCl 4 catalysis to undergo the cycloaddition reaction. The structures of the cycloadducts 4 were determined by X‐ray crystallography.