Photoredox catalysts and photosensitizers take advantage of the excited states by rapid quenching via single electron transfer (SET) reactions. An emerging class of the compounds can couple these (SET) processes and bond making/breaking events through the inclusion of reactive ligand motifs (i.e. hydrides, halides, aryls, amidos). However, such photoreactive systems can often be prone to photo-decomposition due to bond homolysis of the ligands in the excited state. Inspired by these complexes, metal oxos bearing metal-ligand multiple bonds are the scope of our study for their excited state reactivity. Our hypothesis is to alter the π-bonding between the metal and oxo in a stable metal oxo to open new reaction pathways for it. This work evaluates photoreactive systems based on Mo(VI) dioxo platform with a general formula MoO2X2bpy; where X= -Cl, -Br, -F, -CH3, -OPh, -OtBu, pyrrolide. These compounds, while typically showing great stability in the ground state, have accessible excited states that are reactive towards C–H bonds of hydrocarbons, including allyls, benzyls, aldehydes, and alkanes. However, in some examples, irradiation results in significant photo-decomposition of the complexes. Our experimental studies combined with TD-DFT calculations reveal key structural and electronic criteria to achieving photoreactivity within oxo complexes while minimizing photo-decomposition. In parallel efforts to better understand the electronic effects of the anionic ligands in MoO2X2bpy system, structural modifications are pursued. Mo(VI) dioxo complexes with the general formula MoO2(LX)2; where LX= 8-Quinolinolate and 2-(3,5-Dimethyl-2-pyrrolide)pyridine are synthesized. The extended π-system of these ligands would make the generated radical-cation by LMCT, more stable and less prone to bond homolysis.

Photoreactivity of Mo(VI) dioxo complexes in C–H bond activations and O-atom transfer, electronic and structural requirements

ACS Fall 2021

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