Mimicking Transition Metals in Borrowing Hydrogen from Alcohol

Abstract

Borrowing hydrogen from alcohol, storing it on the catalyst and subsequent transfer of the hydrogen from catalyst to an in situ generated imine is the hallmark of a transition metal mediated catalytic N-alkylation of amines. However, such borrowing hydrogen mechanism with a transition metal free catalytic system which stores hydrogen molecule in the catalyst backbone is yet to be established. Herein, we demonstrate that a phenalenyl ligand can imitate the role of transition metals in storing and transferring hydrogen molecule leading to borrowing hydrogen mediated alkylation of anilines by alcohol including a wide range of substrate scope. A close inspection to the mechanistic pathway by characterizing several intermediates through various spectroscopic techniques, deuterium labelling experiments, and DFT study concluded that the phenalenyl radical based backbone sequentially adds H+, H• and an electron through a dearomatization process which are subsequently used as reducing equivalents to the C-N double bond in catalytic fashion.