Oxidation Potential Gap (ΔEox): The Hidden Parameter in Redox Chemistry

Oxidative biaryl coupling of aryls with different electronic features generally fails. However, this has not been systematically studied via theoretical analysis, and thus, the crucial factor governing coupling efficiency remains unclear. Herein, we propose that the oxidation potential gap (Delta E-ox) is a key parameter in predicting the efficiency of an intramolecular oxidative coupling reaction, with Delta E-ox defined as a difference in the oxidation potentials of the relevant aromatic rings. Our experimental and computational analyses revealed that the efficiency of an aromatic intramolecular coupling reaction correlates with the activation energy (Delta E-not equal) of C-C bond formation of the radical cation intermediates. Furthermore, Delta E-not equal correlates with Delta E-ox. Therefore, we demonstrate the tuning of Delta E-ox by attaching cleavable extra electron-donating/-withdrawing groups, enabling the rational synthesis of a phenanthridone skeleton using aromatic rings with an electronic gap.

Automated summary

This study reveals that the synthesis efficiency of aromatic radical coupling reactions can be controlled by regulating the oxidation potential gap (ΔE-ox). The activation energy (ΔE-not equal) of C-C bond formation of radical cation intermediates is found to correlate with ΔE-not equal, which is crucial for the rational synthesis of a phenanthridone skeleton using aromatic rings with an electronic gap.