Towards the design of novel boron- and nitrogen-substituted ammonia-borane and bifunctional arene ruthenium catalysts for hydrogen storage
Article first published online: 5 FEB 2014
Copyright © 2014 Wiley Periodicals, Inc.
Journal of Computational Chemistry
Volume 35, Issue 12, pages 891–903, 5 May 2014
How to Cite
How to cite this article: J. Comput. Chem. 2014, 35, 891–903. DOI: 10.1002/jcc.23534, , , , .
- Issue published online: 2 APR 2014
- Article first published online: 5 FEB 2014
- Manuscript Accepted: 20 DEC 2013
- Manuscript Revised: 27 NOV 2013
- Manuscript Received: 22 AUG 2013
- Science Foundation Ireland (SFI). Grant Number: 07/SRC/B1160.
- density functional theory;
Electronic-structure density functional theory calculations have been performed to construct the potential energy surface for H2 release from ammonia-borane, with a novel bifunctional cationic ruthenium catalyst based on the sterically bulky β-diketiminato ligand (Schreiber et al., ACS Catal. 2012, 2, 2505). The focus is on identifying both a suitable substitution pattern for ammonia-borane optimized for chemical hydrogen storage and allowing for low-energy dehydrogenation. The interaction of ammonia-borane, and related substituted ammonia-boranes, with a bifunctional η6-arene ruthenium catalyst and associated variants is investigated for dehydrogenation. Interestingly, in a number of cases, hydride-proton transfer from the substituted ammonia-borane to the catalyst undergoes a barrier-less process in the gas phase, with rapid formation of hydrogenated catalyst in the gas phase. Amongst the catalysts considered, N,N-difluoro ammonia-borane and N-phenyl ammonia-borane systems resulted in negative activation energy barriers. However, these types of ammonia-boranes are inherently thermodynamically unstable and undergo barrierless decay in the gas phase. Apart from N,N-difluoro ammonia-borane, the interaction between different types of catalyst and ammonia borane was modeled in the solvent phase, revealing free-energy barriers slightly higher than those in the gas phase. Amongst the various potential candidate Ru-complexes screened, few are found to differ in terms of efficiency for the dehydrogenation (rate-limiting) step. To model dehydrogenation more accurately, a selection of explicit protic solvent molecules was considered, with the goal of lowering energy barriers for H-H recombination. It was found that primary (1°), 2°, and 3° alcohols are the most suitable to enhance reaction rate. © 2014 Wiley Periodicals, Inc.