Direct Activation of Oxygen by Early Transition Metal Complexes: From Fundamental Science to Application in Oxidation Catalysis
01 / 2012 - 01 / 2015
The direct use of dioxygen (O2) in catalytic oxidation processes is a major challenge and is of substantial economic importance in bulk and fine chemical production, e.g. adipic acid. I propose to develop a new class of compounds that will activate dioxygen and mediate O-transfer to (organic) substrates. The compounds to be studied will be based on early transition metals, which normally do not interact readily with O2 in a controllable fashion. The fundamental problem is the strong tendency for early transition metals to form complexes in high oxidation states that lack the electrons required for O2 activation. The approach taken in this project will utilize redox-active ligands to overcome this problem. Redox-active ligands can facilitate unusual oxidation/reduction events at metal centers that are otherwise reluctant to participate in redox reactions. The interaction between early transition metal complexes bearing new redox-active ligands and dioxygen is largely unexplored. This project will focus on the chemistry of formally low-valent early transition metal complexes in which the metal d-electrons are (partially) delocalized into the ligand framework. These electrons are available for interaction with dioxygen, which will allow for its activation to give metal-peroxo species. The subsequent selective O-atom transfer to (organic) substrates will be investigated and form the basis for the development of a new paradigm in oxidation catalysis, in which dioxygen is the terminal oxidant.