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 the reaction of the corresponding eta(1)-allenyl- or eta(1)-propargylpalladium complexes with Pd(2)(dba)(3). The X-ray diffraction analysis indicates that the dinuclear complex has a unique structure, in which two palladium, three carbon, two phosphorus, and one halogen atoms are in the same plane. These 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 mu-eta(3)-vinylcarbenedipalladium complexes. Intramolecular reaction proceeded smoothly to give cyclization products quantitatively. Addition of a catalytic amount of a palladium(0) complex dramatically accelerated the carbon-carbon bond formation. The MO calculations on the mu-eta(3)-allenyl/propargyl complexes indicated that the reaction proceeds via orbital control.