SYNTHESIS OF (ALLYLOXY)(ALKYNYL)CARBENE COMPLEXES AND THEIR REACTION WITH OCTACARBONYLDICOBALT - AN UNPRECEDENTED RETRO-FISCHER REACTION

allyloxy)((4-methylphenyl)ethynyl)carbene]chromium and tungsten comple xes 1 and 2 have been prepared in moderate yields from the correspondi ng metal hexacarbonyl in a two-step, one-pot, Fischer type nucleophili c/electrophilic addition methodology using allyl triflate as alkylatin g reagent. As a consequence of its pronounced electrophilicity it also attacks the solvent THF, which results in the formation of the (((all yloxy)butyl)oxy)carbene complex 3 as a byproduct. Both the alkene-alky ne complexes 1 and 2 and their Co-2(CO)(6) adducts fail to undergo int ramolecular Pauson-Khand reactions; instead, at room temperature, a 1, 2-elimination within the carbene ligand occurs, regenerating the metal hexacarbonyl with predominant formation of the 1,4-enynes and 8-10. T his process corresponds to an unprecedented retroversion,of the custom ary Fischer carbene complex synthesis.