Metal free catalysis has emerged as a viable alternative for transition metal based catalysts for enabling different chemical processes, particularly for de/hydrogenation reactions. Herein, employing theoretical studies we reveal the unexpected Frustrated Lewis Pair like reactivity of a boron based catalyst, 9,10-dichlorodiboraanthracene and the ethereal solvent to enable dehydrogenation of ammonia-borane (NH3BH3, AB) under mild conditions. The mechanistic channels thus uncovered reveal that the boron catalyst abstracts a hydride from NH3BH3 followed by crucial stabilisation of the NH3BH2+ moiety by the nucleophilic action of the solvent. H2 is released by the combination of hydride and proton from the borohydride moiety and the solvated NH3BH2+ respectively. Catalysis becomes unfeasible if the Lewis base-like action of the ethereal solvent is not taken into consideration. Thus it is suggested that the clandestine partnership of the Lewis Acid, Boron catalyst and the Lewis Base, ethereal solvent, i.e. FLP like action enables dehydrogenation of NH3BH3 in the instant case.
Uncovering the Synchronous Role of Bis-borane with Nucleophilic Solvent as Frustrated Lewis pair in Metal-free Catalytic Dehydrogenation of Ammonia-borane
representative mechanistic scheme for the activation of catalyst 1HCl and the dehydrogenation of AB by the corresponding activated catalyst 1HH; different models of Lewis acid base adducts formed between 1ClCl and Dg; Gibbs free energy profile and representative mechanistic scheme for solvent assisted activation of catalyst 2HCl; Gibbs free energy profile and representative mechanistic scheme for the dehydrogenation of AB by the corresponding active catalyst 2HH; rate determining barriers at different level of theory; concerted pathway of catalyst activation by one Dg molecule which involves relatively higher free energy barrier; 2HCl and 2HH catalyzed concerted pathways of H2 release involving one diglyme (Dg) molecule which involve relatively higher free energy barrier;alternative pathway of AB dehydrogenation by one Dg molecule which involves relatively higher free energy barrier;