A Diverse Array of Catalytic Photoredox Reactions Based on Aluminum(III)-Salen Complexes: Understanding the Enhancement of Catalytic Activity via Amine Association.

Since aluminum is an earth-abundant and environmentally benign main-group metal, the development of aluminum-complex-based photoredox catalysts remains a significant issue. Herein, we report aluminum(III)-salen complexes (Al-salens) as versatile photoredox catalysts. The combination of an Al-salen catalyst with an amine under visible-light irradiation allowed the hydrodechlorinative transformations of aryl chlorides, the reductive coupling of carbonyl compounds, and the defluoroallylation of perfluoroalkylarenes. Mechanistic studies using transient absorption spectroscopy suggested that the Al-salen complex associates with the amine via its vacant site to improve the reducing ability of its excited state. After electron transfer between the excited state of the Al-salen/amine complex and an appropriate oxidant, the generated aminium radical cation is leveraged to achieve the oxidative transformations of amines, such as α-arylation and α-cyanation. The diversity of the catalytic photoredox reactions based on Al-salen complexes is comparable to that of heavy-precious-metal-based catalysts.