Aluminum Redox Catalysis: Cyclotrimerization of Alkynes

Aluminum catalysis has conventionally been limited to exploiting the Lewis acidic properties of the metal in its +III oxidation state. Herein, we show a low-valent aluminum species, specifically carbazolylaluminylene, which is capable of undergoing oxidative addition, twofold insertion, isomerization and reductive elimination processes via an Al(I)/Al(III) redox cycle—mimicking the quintessential steps characteristic of transition metal catalysis. This innovation enables effective, regioselective Reppe cyclotrimerization of alkynes to form a variety of benzene derivatives, achieving the highest turnover number of 2290. Through X-ray crystallography and quantum chemical analyses, we reveal that the adaptable nitrogen geometry of the carbazolyl ligand modulates the coordination environments at aluminum, thereby facilitating the catalytic cycle. Our work provides insights for further design and application of catalysis based on the main group redox cycle.