Tuning Redox States of Phenalenyl-Based Molecules by Consecutive Reduction toward Transition Metal-Free Heck-Type C–C Cross-Coupling

Phenalenyl-based molecules can switch their redox states on successive addition of electrons from a cation to a radical to an anion. Utilizing this phenomenal ability, we have designed the first example where all three redox states have been utilized to design a Heck-type coupling reaction. In this work, we have developed a protocol where a phenalenyl moiety tunes its redox states and acts as a catalyst in Matsuda–Heck-type and Mizoroki–Heck-type coupling reactions. A wide range of substrate scopes was successfully achieved in both processes under ambient reaction conditions. Moreover, the characterization of active catalysts for both Heck-type couplings was accomplished with the help of different spectroscopic techniques. The control experiments unveiled that these catalytic processes follow a radical mechanism, and several key radical intermediates have been arrested and characterized. It was realized that the catalytic reactions are selective toward the use of mono- and doubly reduced phenalenyl species. This study implies that tuning the energy of the frontier orbital (singly occupied molecular orbital (SOMO) or highest occupied molecular orbital (HOMO)) of the reduced phenalenyl moiety plays a key role in accomplishing these reactions.