Retention of Stereochemistry in the Formation and Fragmentation of Diosmacyclobutanes, and Other Evidence against a Diradical Mechanism

Two results argue against a diradical intermediate in the exchange of diosmacyclobutanes with free olefins. The diosmacyclobutane Os[sub 2](CO)[sub 8]([mu]-propene) reacts with vinylcyclopropane to give as the sole product a diosmacyclobutane bearing an intact cyclopropane ring. Repeated exchange of trans-ethylene-1,2-d[sub 2] with the same ligand in a diosmacyclobutane shows >99.1% stereochemical excess per exchange half-life. These exchange reactions do not involve mononuclear olefin complexes. 36 refs.