Oxidocobalt(IV) Cores Based on Oxidation Resistant Guanidine Donors

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The selective transformation of methane to methanol has generated great interest in industry and academia, since it has been deemed as the future industrial carbon feedstock substituting mineral oil. The industrial scale functionalization of methane will obviously require an inexpensive and highly abundant reagent, i.e. dioxygen, O2. Based on previous experimental investigations and DFT calculations, it is anticipated that the rare class of monomeric, late transition metal complexes with a terminal M=O unit, LnM=O, where M is a late transition metal like cobalt, nickel or copper are perfectly suited as catalysts. The synthetic access to the LnCoIV=O core involves the main theme of this project. Notably, isolation of terminal late transition metal-oxo species to the right of group 8 (also known as “the oxo wall” for C4v symmetry) has only been achieved in extremely rare cases in ligand fields that are not tetragonal. The main strategies that have been employed here for the stabilization of such elusive intermediates are : a) attenuation of equatorial ligand donation in a tetragonal field so as to achieve a unique 1:3:1 d-orbital splitting pattern that can support metal-oxo cores with high d-electron count; b) incorporation of stabilizing Hydrogen bonding interaction in order to reduce the anticipated strong repulsion between the electron-rich oxo and late transition metal centers; and c) utilization of oxidatively robust guandine ligand donors. Detailed reactivity studies, including C-H bond activation and oxygen atom transfer reactions, in conjunction with spectroscopy and theory on these long sought-after LnCoIV=O intermediates may help us to understand how the steric and electronic properties of the metal centers modulate their reactivities. This will provide vital insights into the field of abundant metal catalysis.