Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction

Storing and transferring electrons for multi-electron reduction processes are considered as the key steps in various important chemical and biological transformations. In this work, we accomplished multi-electron reduction of carboxylic acid via hydrosilylation pathway where a redox-active phenalenyl backbone in Co(PLY-O,O)2(THF)2, stores electrons and plays a preponderant role in the entire process. This reduction proceeds by a single electron transfer (SET) from the mono-reduced ligand backbone leading to the cleavage of Si–H bond. Several important intermediates along the catalytic reduction have been isolated and well characterized to prove that the redox equivalent is stored in the form of a C–H bond in the PLY backbone via a ligand dearomatization process. Ligand’s extensive participation in storing a hydride equivalent has been conclusively elucidated by deuterium labelling experiment. This is a rare example where ligand orchestrates the multielectron reduction process leaving the metal only to maintain conformational requirement and fine tune the electronics of the catalyst.