Metal oxos are critical intermediates to various impactful reactions in industry and biology, such as alkane activation, carbon dioxide reduction, proton reduction, olefin epoxidation etc. Understanding the manner in which metal oxo react has a potential to impact fields related to energy storage, petrochemical industry, and catalysis in general. Typically, late transition metal oxos are employed, which are short-lived, difficult to generate, and challenging to study mechanistically. An alternative approach is to utilize stable early transition metal oxos, which can be activated by light to initiate novel reactivity. Such a light-driven pathway also provides a strategy to directly utilize solar energy to drive chemical reactivity. Towards these goals, the photoreactivity of a molybdenum dioxo complex bearing a bipyridine ligand has been investigated.<br/>This work seeks to investigate the photochemical reaction mechanism between MoO2Cl2(bpy-tBu) and various hydrocarbon substrates under irradiation with light. The photoreaction of MoO2Cl2(bpy-tBu) typically affords C–H activation of the substrate followed by C–C homocoupling over the traditional substrate hydroxylation. Photoreaction quantum yield studies were used to develop an overall rate law for the transformation, which indicates a dependence on substrate concentration and no dependence on photon flux of Mo dioxo concentration besides its role as the chromophore. Quantum yield analyses in the presence of various substrates were used to develop linear free energy relationships for the photoreaction, which shows a correlation between the overall reaction efficiency and the BDE of the substrate. Furthermore, primary kinetic isotope effects suggest a critical C–H bond cleavage in the photochemical step. However, the ability to react with specific substrates qualitatively correlates with the substrate’s ionization potential. These results are discussed in the context of the concerted or step-wise nature of the overall hydrogen atom transfer that occurs from the excited state.

Quantum yield studies of C-H bond activation by a Mo(VI) dioxo complex

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.