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Bond Dissociation Energy Controlled σ-Bond Metathesis in Alkaline-Earth-Metal Hydride Catalyzed Dehydrocoupling of Amines and Boranes: A Theoretical Study

Abstract

Dehydrocoupling of amines and boranes is an efficient method for the formation of N–B bonds; however, the strong B–H bond dissociation energy (BDE) always restricts non-catalytic reaction pathways. Therefore, alkaline-earth-metal (Ae) hydrides are used as catalysts for this type of reaction because of their lower Ae–H bond energy. A theoretical study was performed to study the mechanism of Ae-catalyzed dehydrocoupling reactions. The computational results show that such reactions are initiated from σ-bond metathesis between Ae hydride catalysts and amines to release molecular hydrogen, followed by borane bonding with amino Ae intermediates. Subsequent hydride transfer yields an amino-borane product and, in the process, regenerates the Ae hydride catalyst. Our theoretical calculations revealed that dehydrogenation is the rate-determining step during σ-bond metathesis in the presence of a magnesium hydride catalyst. We predicted that beryllium hydride could not function as a catalyst because the apparent activation free energy is significantly high. Furthermore, we observed that in calcium or strontium hydride-catalyzed reactions, the rate-limiting step changed to the hydride transfer step. Further density functional theory calculations showed that the BDEs of the Ae–H bond controlled the reactivity of the σ-bond metathesis step.

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Publication details

The article was received on 02 Aug 2017, accepted on 05 Sep 2017 and first published on 15 Sep 2017


Article type: Research Article
DOI: 10.1039/C7QI00459A
Citation: Inorg. Chem. Front., 2017, Accepted Manuscript
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    Bond Dissociation Energy Controlled σ-Bond Metathesis in Alkaline-Earth-Metal Hydride Catalyzed Dehydrocoupling of Amines and Boranes: A Theoretical Study

    D. Xu, C. Shan, Y. Li, X. Qi, X. Luo, R. Bai and Y. Lan, Inorg. Chem. Front., 2017, Accepted Manuscript , DOI: 10.1039/C7QI00459A

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