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Uncovering the Synchronous Role of Bis‐borane with Nucleophilic Solvent as Frustrated Lewis Pair in Metal‐Free Catalytic Dehydrogenation of Ammonia‐borane

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Effective metal-free dehydrogenation of ammonia-borane (AB). A metal-free bis-borane based catalyst, 9,10-dichlorodiboraanthracene, containing two Lewis acidic boron centers, dehydrogenate AB successfully when it is conjugated with an ethereal solvent, diglyme. The activation barrier becomes formidably high in absence of solvent molecule. Hence, the active participation of the solvent molecule plays a crucial role for facilitating the dehydrogenation process.


Abstract

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 moderate conditions. The mechanistic channels thus uncovered reveal that the boron catalyst abstracts a hydride from NH3BH3 followed by crucial stabilization 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.

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