Issue 11, 2017

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.

Graphical abstract: Bond dissociation energy controlled σ-bond metathesis in alkaline-earth-metal hydride catalyzed dehydrocoupling of amines and boranes: a theoretical study

Supplementary files

Article information

Article type
Research Article
Submitted
02 aug 2017
Accepted
05 sep 2017
First published
15 sep 2017

Inorg. Chem. Front., 2017,4, 1813-1820

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, 4, 1813 DOI: 10.1039/C7QI00459A

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