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Probing the second dehydrogenation step in ammonia-borane dehydrocoupling: characterization and reactivity of the key
Hassan A Kalviri1, Felix Gärtner1,2, Gang Ye1
1Department of Chemistry and Centre for Catalysis Research and Innovation (CCRI) , University of Ottawa , 10 Marie Curie , Ottawa , Ontario K1N 6N5 , Canada . Email: rbaker@uottawa.ca ; ; Tel: +1 613 5625698.
Abstract:
While thermolysis of ammonia-borane (AB) affords a mixture of aminoborane- and iminoborane oligomers, the most selective metal-based catalysts afford exclusively cyclic iminoborane trimer (borazine) and its B-N cross-linked oligomers (polyborazylene). This catalysed dehydrogenation sequence proceeds through a branched cyclic aminoborane oligomer assigned previously as trimeric B-(cyclodiborazanyl)amine-borane (BCDB). Herein we utilize multinuclear NMR spectroscopy and X-ray crystallography to show instead that this key intermediate is actually tetrameric B-(cyclotriborazanyl)amine-borane (BCTB) and a method is presented for its selective synthesis from AB. The reactivity of BCTB upon thermal treatment as well as catalytic dehydrogenation is studied and discussed with regard to facilitating the second dehydrogenation step in AB dehydrocoupling.
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