Carbon-carbon bond formation by electrophilic addition at the central carbon of the mu-eta(3)-allenyl/propargyl ligand on the Pd-Pd bond

The mu-eta (3)-allenyl/propargyldipalladium complexes were synthesized by t he reaction of the corresponding eta (1)-allenyl- or eta (1)-propargylpalla dium complexes with Pd-2(dba)(3) The X-ray diffraction analysis indicates t hat the dinuclear complex has a unique structure, in which two palladium, t hree carbon, two phosphorus, and one halogen atoms are in the same plane. T hese dinuclear complexes react with electrophiles, such as HCl or AcCl, at the central carbon of the mu-eta (3)-allenyl/propargyl ligand to give the m u-eta (3)-vinylcarbenedipalladium complexes. Intramolecular reaction procee ded smoothly to give cyclization products quantitatively. Addition of a cat alytic amount of a palladium(0) complex dramatically accelerated the carbon -carbon bond formation. The MO calculations on the mu-eta (3)-allenyl/propa rgyl complexes indicated that the reaction proceeds via orbital control.