Study of the Evolution of η1-η2-Enylpalladium Complexes When the Palladium-Migration Process Is Blocked

η 1 −η 2 -Enylpalladium complexes have been detected and/or isolated in the reaction of [PdPfBr(NCMe) 2 ] (Pf = C 6 F 5 ) with the dienes R−CH CH−(CH 2 ) n −Y−(CH 2 ) m −CH CH 2 (R = H, Me; n, m = 0, 1; Y = CCl 2, C(COOMe) 2, CO 2, O, SiMe 2, SO 2 ). 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 η 3 -allyl derivatives is blocked. The evolution and decomposition processes observed for the η 1 -η 2 -enyls reveal that β-X elimination is the main operating pathway for Y = CCl 2 (X = Cl) or Y = OCO, O, SiMe 2 (X = YR‘). When Y = C(COOMe) 2 or SO 2, 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 2 < C−Cl < C−O (ether) < C−O (ester) ≈ C−Si.