Construction of a Metallacyclopentadiene Ring through the Attack of Carbanions to M≡C Bond Followed by C—H Activation†

Comprehensive Summary Metallacyclopentadienes are important metallacycles and regarded as intermediates in many reactions, therefore, new methods to achieve them are anticipated. In this study, a formal [3+2] method, through the reactions of an osmapentalyne with benzyl carbanions, was developed. The reactions underwent a nucleophilic attack of carbanions to the Os≡C bond, followed by C—H activation to form the five‐membered osmacyclopentadiene ring. Most of the reactions were carried out at room temperature, the substituents on the aromatic rings of benzyl carbanions are diverse, and the resulting products contain an Os—H bond, representing a novel type of 10C‐carbolong complexes. This work provides a new convenient route to construct metallacyclopentadienes, which is expected to further promote the development of such a type of substances.