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Thermodynamic Studies and Hydride Transfer Reactions from a Rhodium Complex to BX3 Compounds

Journal Article · · Journal of the American Chemical Society
DOI:https://doi.org/10.1021/ja905287q· OSTI ID:973723
This study examines the use of transition-metal hydride complexes that can be generated by the heterolytic cleavage of H2 gas to form B–H bonds. Specifically, these studies are focused on providing a reliable and quantitative method for determining when hydride transfer from transition-metal hydrides to three-coordinate BX3 compounds will be favorable. This involves both experimental and theoretical determinations of hydride transfer abilities. Thermodynamic hydride donor abilities (ΔG°H-) were determined for HRh(dmpe)2 and HRh(depe)2, where dmpe = 1,2-bis(dimethylphosphinoethane) and depe = 1,2-bis(diethylphosphinoethane), on a previously established scale in acetonitrile. This hydride donor ability was used to determine the hydride donor ability of [HBEt3]⁻ on this scale. Isodesmic reactions between [HBEt3]⁻ and various BX3 complexes to form BEt3 and [HBX3]⁻ were examined computationally to determine the relative hydride affinities of various BX3 compounds. The use of these scales of hydride donor abilities and hydride affinities for transition-metal hydrides and BX3 compounds is illustrated with a few selected reactions relevant to the regeneration of ammonia borane. Our findings indicate that it is possible to form B-H bonds from B-X bonds, and the extent to which BX3 compounds are reduced by transition-metal hydride complexes forming species containing multiple B-H bonds depends on the heterolytic B-X bond energy. An example is the reduction of B(SPh)3 using HRh(dmpe)2 in the presence of triethylamine to form Et3N-BH3 in high yields. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.
Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC05-76RL01830
OSTI ID:
973723
Report Number(s):
PNNL-SA-67143; EB4202000
Journal Information:
Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 40 Vol. 131; ISSN JACSAT; ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English

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