Structural and thermochemical studies of pyrrolidine borane and piperidine borane by gas electron diffraction and quantu
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ORIGINAL RESEARCH
Structural and thermochemical studies of pyrrolidine borane and piperidine borane by gas electron diffraction and quantum chemical calculations Aliyu M. Ja’o 1 & Derek A. Wann 2 & Conor D. Rankine 2 & João P. F. Nunes 2 & Jean-Claude Guillemin 3 & Sarah L. Masters 1 Received: 23 July 2020 / Accepted: 21 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The gaseous structures, thermochemical properties and dehydrogenation reaction energy profiles of the borane complexes of pyrrolidine and piperidine have been investigated using gas electron diffraction (GED) and state-of-the-art computational methods. These complexes are of interest because of their potential as hydrogen storage materials for future onboard transport applications. A comparative structural and thermochemical analysis revealed structures with a slight difference in the essential B– N bond length, with the piperidine borane having a longer bond even though it has a stronger B–N bond according to predicted bond dissociation energies, a trend common with amine boranes. To identify the most favourable dehydrogenation pathway, BH3-catalysed and BH3-uncatalysed dehydrogenation channels have been explored, where the former has been shown to be the favourable process for both complexes. The energy requirements for the hydrogen release reactions are expected to be minimal as evidenced from the calculated dehydrogenation reaction energies, implying their suitability for onboard chemical hydrogen storage. Keywords Hydrogen storage . Dehydrogenation . Amine boranes . Gas electron diffraction
Introduction Cyclic amine boranes (CABs) represent a class of singlenitrogen-containing donor-acceptor saturated complexes with the general formula CnH2n+1N·BX3 (n = 2–7, X = H, CH3, F, Cl, Br, I). They are formed by coordinating a cyclic amine with a borane group, resulting in the formation of a dative B– N bond. They have found application as precursors in ceramic production [1, 2] and as candidates for onboard chemical hydrogen storage [3–7]. Although closely related linear Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11224-020-01647-0) contains supplementary material, which is available to authorized users. * Sarah L. Masters [email protected] 1
School of Physical and Chemical Sciences, University of Canterbury, Private Bag 4100, Christchurch 8140, New Zealand
2
Department of Chemistry, University of York, Heslington, York YO10 5DD, UK
3
Univ Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, ISCR – UMR6226, F-35000 Rennes, France
analogues, such as ammonia borane (NH3BH3) [8–16] and alkyl amine boranes [17–28], are well characterised, very few CABs have been studied both in terms of their structure and chemical properties. The first CAB to be synthesised was the three-membered aziridine borane [29–31]; the crystal structure was determined subsequently [32], and the complex was later characterised by NMR and IR techniques [33] as
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