Reactivity of Cyclic Osmium Vinylidenes: Shuttle of Osmium Vinylidene Unit, Electrophilic Substitution, and Cycloaddition Reactions ^†

Comprehensive Summary Metal vinylidene complexes exhibit rich reactivity and play pivotal roles in catalytic alkyne transformations; however, the reactivity of cyclic metal vinylidene complexes has been scarcely explored, largely due to the limited availability of such species caused by high ring strain. In this work, we report the diverse reactivity of a cyclic osmium vinylidene embedded in a CNC pincer framework. The cyclic osmium vinylidene complex reacts with aryl alkynes to unveil the first shuttle reaction of a metal vinylidene unit. In contrast, halogenation is observed upon treatment with N ‐halosuccinimides, occurring electrophilic substitution at an alternative site rather than electrophilic addition at the osmium vinylidene carbon, as further rationalized by Fukui function analysis for regioselectivity. Moreover, the reaction of the cyclic osmium vinylidene complexes with isocyanides affords the rarely crystallographically characterized metallacyclopropanimine. Collectively, these findings not only expand the distinctive reactivity of metal vinylidenes but also enrich the chemistry of CNC pincer complexes.