The transmetallation of the palladacyclopentadiene complex Pd{C(COOMe) C(COOMe) C( COOMe) C(COOMe)}(bipy) with the dicationic Pd-II complex [Pd(bipy)(CH3CN)(2)][BF4](2) afforded a terminally sigma-palladated diene complex [Pd-2{mu-eta(1):eta(1)-C(COOMe)C(COOMe) C(COOMe) C(COOMe)}-(bipy)(2)(CH3CN)(2)][BF4](2). It was revealed by X-ray crystallographic analysis that replacement of the acetonitrile ligands in a terminally sigma-palladated diene complex with PPh3 ligands resulted in the conformation change of the sigma-palladated diene moiety from skewed s-cis to planar s-trans. Treatment of a bis-triphenylphosphine dipalladium complex [Pd-2(PPh3)(2)(CH3CN)(4)][PF6](2) with dimethoxyacetylene dicarboxylate (DMAD) (1 equiv.) in acetonitrile resulted in the insertion of DMAD to the Pd-Pd bond to afford [Pd-2{mu-eta(1):eta(1)-C(COOMe)C(COOMe)}(PPh3)(2)(CH3CN)(4)][PF6](2). Addition of the second DMAD gave the ylide-type complex [Pd-2{mu-eta(2):eta(3)-C(COOMe)C(COOMe) C(COOMe)C(COOMe)- (PPh3)}(PPh3)(2)(CH3CN)(3)][PF6](2) of which the structure was determined by X-ray crystallographic analysis.