Preparation of Osmium η5-Phospholide Complexes and Their Reactions with Acyl Electrophiles: CO Bond Cleavage and C−C Bond Formation within the Metal Coordination Sphere

Two diphosphaosmocene species have been pre pared in excellent yields by the reaction of a lithium 2,5-dialkylphospholide (alkyl = cyclohexyl, (−)-menthyl) and [(η6-cymene)OsCl2]2 in THF. These are the first examples of phosphametallocenes with an osmium core. For the success of the phosphaosmocene synthesis, the use of a sterically demanding phospholide is crucial. A treatment of the 2,2′,5,5′-Cy4-diphosphaosmocene with an AcCl/AlCl3 mixture in dichloromethane gives a novel (μ-vinylidene)osmium complex via activation of the acetyl CO double bond. In the osmium complex, a μ-vinylidene moiety bridges between the osmium atom and a phosphorus of the η4-(P-oxophospholide). In the presence of excess acetyl electrophile, the μ-vinylidene complex is subjected to further acetylation at the CH2 terminus of the μ-vinylidene moiety to give a (μ-acetylvinylidene)osmium complex. A stepwise application of acetyl chloride and phenylacetyl chloride to this transformation enabled production of a [μ-(phenylacetyl)vinylidene]osmium species by C−C bond formation between the two different acyl chlorides.