Osmapyridine and Osmapyridinium from a Formal [4+2] Cycloaddition Reaction

Abstract

Metalla-cycloaddition: An unprecedented formal [4+2] cycloaddition reaction takes place when osmium hydrido alkenylcarbyne 1 reacts with acetonitrile to afford the first metallapyridinium complex 2 in high yield (see scheme). Deprotonation of 2 gives the first osmapyridine compound 3. Treatment of 3 with HBF4 can regenerate 2 in almost quantitative yield.