Study of the Evolution of η<SUP>1</SUP>-η<SUP>2</SUP>-Enylpalladium Complexes When the Palladium-Migration Process Is Blocked

η¹−η²-Enylpalladium complexes have been detected and/or isolated in the reaction of [PdPfBr(NCMe)<INF>2</INF>] (Pf = C<INF>6</INF>F<INF>5</INF>) with the dienes R−CH&dbd;CH−(CH<INF>2</INF>)<INF>n</INF><INF></INF>−Y−(CH<INF>2</INF>)<INF>m</INF><INF></INF>−CH&dbd;CH<INF>2</INF> (R = H, Me; n, m = 0, 1; Y = CCl<INF>2</INF>, C(COOMe)<INF>2</INF>, CO<INF>2</INF>, O, SiMe<INF>2</INF>, SO<INF>2</INF>). Insertion of one double bond into the Pd−aryl bond and coordination of the remaining double bond gives the above-mentioned organometallic derivatives. The dienes tested have a non-hydrogen-containing link (Y), so Pd migration to give η³-allyl derivatives is blocked. The evolution and decomposition processes observed for the η¹-η²-enyls reveal that β-X elimination is the main operating pathway for Y = CCl<INF>2</INF> (X = Cl) or Y = OCO, O, SiMe<INF>2</INF> (X = YR‘). When Y = C(COOMe)<INF>2</INF> or SO<INF>2</INF>, C−X cleavage is not observed and intramolecular insertion to give cyclic products or Pd−H elimination to generate a substituted diene predominates, respectively. From these results, a trend in C−X cleavage easiness in the presence of palladium can be estimated:  C−C ≪ C−SO<INF>2</INF> &lt; C−Cl &lt; C−O (ether) &lt; C−O (ester) ≈ C−Si.