Decomplexation of cyclopentadienylmanganese tricarbonyls under very mild conditions: A novel route to substituted cyclopentadienes and their application in organometallic synthesis

Photolysis of cyclopentadienylmanganese tricarbonyl derivatives in the presence of a proton source leads to decomplexation and formation of the free cyclopentadiene in excellent yield. In contrast, attempted decomplexation using Ce(IV) or Fe(III) leads merely to decomposition products. It is proposed that, upon photolytic loss of a CO ligand, coordination of methanol or water facilitates an intramolecular proton transfer to the cyclopentadienyl ring. This method is applicable to polyfunctional molecules such as ethynylestradiol. In this new synthetic approach, these cymantrenes have also been used as precursors to the corresponding iron, tungsten, titanium, and rhenium complexes via the generation of the intermediate cyclopentadienes.