Quantum chemical investigation of dioxygen activation by Ni-bearing transition metal complexes

In this study, quantum chemical methods are used to examine the activationmechanism of dioxygen with [Ni(H)(OH)]+ complex. The activation of dioxygenmolecule with [Ni(H)(OH)]+ complex is performed by previous experimentalworks and following theoretical studies express the fact that the quartet state ofthe complex is reactive in the reaction while dublet state is inert. In this thesis,the process up to hydroperoxide byproduct which has a key role on formationof the products of activation mechanism is tried to be enligthened. Initialencounter complex having sextet, quartet and doublet spin symmetry isanalysed at complexation step of the reactants. It is investigated at the latterstep that on the surface of quartet and doublet spins electrons are transferredfrom the center of nickel to the redox active OH ligand. However, from this newmolecule via transition state formation of hydroperoxite byproduct is observed.Effective spin surface of the reaction has consistent energy barrier so that it isspecified as quartet, conversely dublet state is not the one that performs thereaction. Crossing point calculations are done between potential energy surfacesof different spin surfaces which are close eachother energetically. According tothese results an crossing point is identified between initial encounter complexeson sextet and quartet spin surfaces. Spin-orbit coupling calculations are thencarried out in order to get an idea about transformation of spin surfaces to oneanother. Very low value of spin-orbit coupling constant indicates that thetransformation of spin surfaces is not possible for the system. By this result, ithas been concluded the quartet spin surface which fulfills the reaction is thequartet spin state obtained at the complexation step of reactants.