Cupric superoxide species (η1) CuII(O2●–) are likely key intermediates in the catalytic cycle of copper-containing monooxygenases (like PHM, DβM, TβM and LPMOs), which carry out hydroxylation reactions with varying substrates. Since this species was observed for the first time, in a model complex, many efforts have been done on ligand design in order to make this species more stable and susceptible to deeper investigation. Neutral ligands containing strongly electron-donating groups, sterically bulky groups, and substituents that can participate in hydrogen bonding (H-bonding) interactions, are found among these strategies. In particular there are few examples concerning the role of H-bonding interactions. Here, we report on the synthesis of a series of ligand-copper(I) complexes, those with and without ligand H-bonding groups. Dioxygen reactivity studies at -135 °C in 2-methyltetrahydrofuran (MeTHF) have been carried out. Interestingly, the LCuI complexes show varying reactivity with O2, leading to differing types of LCuII(O2●–), LCuII(O22-)CuIIL, or LCuIII(μ-O2-)2CuIIIL species, depending on the presence of an H-bonding group, despite having similar reduction potentials as indicated by electrochemical data obtained from analog azido [LCuII-N3]+ complexes. Further, for those complexes able to form LCuII(O2●–), there is an enhancement in reactivity toward substrates, compared to the parent system [CuII(TMPA)(O2●–)]+, that seems to correlate with H-bonding interactions.

Stabilization of cupric superoxide species with intramolecular hydrogen bonding moieties

254th National Meeting (2017)

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