Study of the evolution of η1-η2-enylpalladium complexes when the palladium-migration process is blocked

eta(1)-eta(2)-Enylpalladium complexes have been detected and/or isolated in the reaction of [PdPfBr(NCMe)(2)] (Pf = C6F5) with the dienes R-CH=CH-(CH2)(n)-Y-(CH2)(m)-CH=CH2 (R = H, Me; n, m = 0, 1; Y = CCl2, C(COOMe)(2), CO2, O, SiMe2, SO2). 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 eta(3)-allyl derivatives is blocked. The evolution and decomposition processes observed for the eta(1)-eta(2)-enyls reveal that beta-X elimination is the main operating pathway for Y = CCl2 (X = Cl) or Y = OCO, O, SiMe2 (X = YR'). When Y = C(COOMe)(2) or SO2, 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 much less than C-SO2 < C-Cl < C-O (ether) < C-O (ester) approximate to C-Si.