Carbon-Carbon Bond Cleavage by Osmium Clusters. Ring Opening of a Cyclobutenyl Ligand by a Triosmium Cluster

Abstract

The reaction of 1-iodo-2-methylcyclobutene with the triosmium cluster complex has yielded four new osmium cluster compounds: 1 (5% yield), 2 (8% yield), 3 (16% yield), and 4 (33% yield). Compounds 1-3 were characterized by single-crystal X-ray diffraction analysis. Compounds 1 and 4 contain a {delta},{pi}-coordinated 2-methylcyclobutenyl ligand. Compounds 2 and 3 are isomers. Both contain open triosmium clusters with a metalated acyclic {delta},{pi}-coordinated bridging alkenylidene ligand formed by the cleavage of one of the carbon-carbon bonds of the cyclobutenyl ring. An iodo ligand bridges one of the two metal-metal bonds in 2 and the nonbonded Os-Os pair of metal atoms in 3. Compound 2 is an intermediate to 3 and is converted to 3 in 90% yield in solution at 25{degree}C in 48 h. From the structure of 2 it can be inferred that the C-C bond cleavage process involves a direct oxidative addition of the C-CH{sub 2} carbon-carbon {delta}-bond of the {delta},{pi}-coordinated bridging cyclobutenyl ligand in 4 adjacent to the {pi}-coordinated C-C double bond and occurs at the same metal atom. Crystal data for the compounds are given. 10 refs., 3 figs., 9 tabs.