Mechanism of metal-free hydrogen transfer between amine-boranes and aminoboranes

Show simple item record Leitao, Erin en Stubbs, NE en Robertson, APM en Helten, H en Cox, RJ en Lloyd-Jones, GC en Manners, I en 2016-10-13T03:17:45Z en 2012-10-10 en
dc.identifier.citation Journal of the American Chemical Society, 2012, 134 (40), 16805 - 16816 en
dc.identifier.issn 0002-7863 en
dc.identifier.uri en
dc.description.abstract The kinetics of the metal-free hydrogen transfer from amine-borane Me(2)NH·BH(3) to aminoborane iPr(2)N═BH(2), yielding iPr(2)NH·BH(3) and cyclodiborazane [Me(2)N-BH(2)](2) via transient Me(2)N═BH(2), have been investigated in detail, with further information derived from isotopic labeling and DFT computations. The approach of the system toward equilibrium was monitored in both directions by (11)B{(1)H} NMR spectroscopy in a range of solvents and at variable temperatures in THF. Simulation of the resulting temporal-concentration data according to a simple two-stage hydrogen transfer/dimerization process yielded the rate constants and thermodynamic parameters attending both equilibria. At ambient temperature, the bimolecular hydrogen transfer is slightly endergonic in the forward direction (ΔG(1)°((295)) = 10 ± 7 kJ·mol(-1); ΔG(1)(‡)((295)) = 91 ± 5 kJ·mol(-1)), with the overall equilibrium being driven forward by the subsequent exergonic dimerization of the aminoborane Me(2)N═BH(2) (ΔG(2)°((295)) = -28 ± 14 kJ·mol(-1)). Systematic deuterium labeling of the NH and BH moieties in Me(2)NH·BH(3) and iPr(2)N═BH(2) allowed the kinetic isotope effects (KIEs) attending the hydrogen transfer to be determined. A small inverse KIE at boron (k(H)/k(D) = 0.9 ± 0.2) and a large normal KIE at nitrogen (k(H)/k(D) = 6.7 ± 0.9) are consistent with either a pre-equilibrium involving a B-to-B hydrogen transfer or a concerted but asynchronous hydrogen transfer via a cyclic six-membered transition state in which the B-to-B hydrogen transfer is highly advanced. DFT calculations are fully consistent with a concerted but asynchronous process. en
dc.description.uri en
dc.format.medium Print-Electronic en
dc.language English en
dc.publisher American Chemical Society en
dc.relation.ispartofseries Journal of the American Chemical Society en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. Details obtained from en
dc.rights.uri en
dc.title Mechanism of metal-free hydrogen transfer between amine-boranes and aminoboranes en
dc.type Journal Article en
dc.identifier.doi 10.1021/ja307247g en
pubs.issue 40 en
pubs.begin-page 16805 en
pubs.volume 134 en
dc.description.version VoR - Version of Record en
dc.identifier.pmid 23016922 en en
pubs.end-page 16816 en
pubs.publication-status Published en
dc.rights.accessrights en
pubs.subtype Article en
pubs.elements-id 516193 en Science en Chemistry en
dc.identifier.eissn 1520-5126 en
pubs.record-created-at-source-date 2016-10-13 en 2012-09-27 en
pubs.dimensions-id 23016922 en

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