β-Heteroatom versus β-hydrogen elimination:: A theoretical study

beta-Heteroatom and beta-hydrogen eliminations of the model complexes [L2PdCH2CH2X](+) (L-2 = H2PCH2-CH2PH2; X = halides, OMe, OH, OAc) were studied using density function theory calculations at the B3LYP level. Our calculations indicate that for the complexes where X = Cl, Br, and Ib beta-heteroatoin eliminations are thermodynamically and kinetically more favorable. For the complexes where X = F, OH, ONle, and OAc, beta-hydrogen elimination is kinetically more favorable than beta-heteroatom elimination. However, the products (hydride-olefin complexes) formed from the kinetically favorable P-hydrogen elimination are thermodynamically unstable relative to the pre-eliminated species (Pd-alkyl containing a beta-X to metal dative bond). Implications of these results on the palladium-catalyzed reactions have been discussed.