Osmium–carbon double bonds: Formation and reactions

The present review reports on the chemistry of the osmium–carbon double bond, including alkylidene or carbene, vinylidene, and allenylidene derivatives. Within the first type of compounds, we show the synthetic methods and reactivity of half-sandwich derivatives, including cyclopentadienyl and arene complexes, carbene compounds derived from alkynes, α,β-unsaturated carbene species, and osmacyclopropene, hydride–carbene, osmafurane, and osmapyrrole complexes. The vinylidene compounds include: half-sandwich, PCP “pincer”, hydride–vinylidene, azavinylidene–vinylidene, and metallaarene derivatives. For their study the allenylidene complexes have been divided into half-sandwich and non-half-sandwich compounds. In addition, the transformation from hydride–carbyne to carbene is analyzed, the preparation of butadienyl compounds via vinylidene intermediates is shown, and the assembly of organic molecules on allenylidene species to form osmacyclopentapyrrole derivatives is described.