Fundamental Palladium Catalyzed Oxidative Addition Reactions

This thesis focuses on investigating fundamental oxidative addition (OA) reactions catalysed by palladium. OA, being the first and rate determining step in cross-coupling reactions, is a reaction of vital importance in synthetic chemistry. The findings in this thesis were successfully obtained using the Activation Strain Model of chemical reactivity in combination with computations based on Density Functional Theory (DFT) as implemented in the ADF program. The ASM model is a fragment-based approach that characterizes reactions in terms of the rigidity and the bonding capabilities of the original reactants, and the extent to which the reactants must deform along the reaction pathway of a particular reaction mechanism. Thus, the total energy profile of a particular chemical reaction can be decomposed into contributions from the deformation of the reactants (the strain energy) and their mutual interaction (the interaction energy). The interaction energy can then be further decomposed using the canonical energy decomposition analysis of ADF into electrostatic interactions, destabilizing Pauli repulsion, and stabilizing orbital interactions. In Chapter 3, with the aim of understanding the underlying mechanism and trends found by the OA, we detailed our quantum chemical exploration of the palladium-mediated activation of C(spn)–X bonds (n = 1–3; X = F, Cl, Br, I) in the archetypal model substrates H3C–CH2–X, H2C=CH–X, and HC≡C–X by a model bare palladium catalyst. First and foremost, we investigated the bond dissociation enthalpies (BDEs) of the bonds to be activated. So, we started from the C(sp3)–X moving to C(sp2)–X and then to C(sp)–X bonds for each of the selected set of X atoms above. We found that as we move down group 17, the C(spn)–X bond becomes weaker and as such easier to break.