Photocatalytic Vanadium-Mediated Amination of Benzene With Hydroxylamine

The synthesis of aromatic amines, especially anilines, is crucial in organic chemistry because of their significance in pharmaceuticals and high-value chemicals. However, traditional methods for producing aniline involve pre-functionalization and/or several high-energy-demanding steps. Therefore, the development of direct protocols towards aniline has attracted significant interest. We introduce a direct photocatalytic method for synthesizing aniline using hydroxylamine and vanadium complexes. While previous studies describe vanadium complexes and hydroxylamine in thermally driven reactions, our research utilizes photochemistry, providing milder reaction conditions for the efficient benzene amination. Mechanistic investigations using ⁵¹V-NMR support coordination of hydroxylamine to vanadium and the multifaceted role of acetic acid as solvent, acid, and ligand. X-band EPR and ⁵¹V-NMR demonstrated the time-dependent reduction of vanadium by hydroxylamine. The same excess experiments and ¹⁵N-NMR coordination studies identified product inhibition by aniline. ¹H-NMR kinetic experiments, enabled through a broad peak suppression, suggest a paramagnetic V⁺⁴-hydroxylamine complex as the key intermediate, and ⁵¹V-NMR kinetics support the photocatalyst's role in maintaining the redox cycle and reducing the active V⁺⁴-hydroxylamine intermediate. Our direct photocatalytic method not only enables the selective synthesis of aniline under mild conditions, but also allows easy scaling through its compatibility with flow systems.