When is a Nanoparticle a Cluster? An Operando EXAFS Study of Amine Borane Dehydrocoupling by Rh4-6 Clusters
Journal Article
·
· Journal of the American Chemical Society
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Univ. of Oregon, Eugene, OR (United States)
X-ray absorption fine structure (XAFS) is used to determine the structure of the rhodium cluster present during the catalyzed dehydrocoupling of amine boranes under operando conditions. Analysis of the in-situ XAFS spectra using a series of amine boranes (NH3BH3, R2NHB3 and RNH2BH3 where R = methyl, isopropyl, tert-butyl and cyclohexyl) and rhodium catalyst precursor compounds ((including chloro-(1,5-cyclooctadiene)rhodium (I) dimer, bis(1,5- cyclooctadiene)rhodium (I) trifluoromethanesulfonate, chlorodicarbonylrhodium (I) dimer, dichloro(pentamethylcylcopentadienyl) rhodium (III) dimer, hexarhodium hexadecacarbonyl, and tetrarhodium dodecacarbonyl) strongly suggest that the active catalyst species for this reaction is a homogeneous rhodium complex. Rhodium clusters containing four or six rhodium atoms (Rh4-6) bound to amine boranes are observed as the major (>98%) rhodium containing species during and after the catalyzed anaerobic dehydrocoupling. During the later stages of the reaction, a non-metallic rhodium complex precipitate forms in which individual Rh4-6 clusters likely form polymer chains ligated by the reaction products that have two or more ligating sites. The best FEFF fits of the XAFS data show that the major rhodium species (80%) has each rhodium atom directly bound to three rhodium atoms with an observed bond distance of 2.73 Å and to two boron atoms at 2.095 Å. A minor (20%) rhodium species has each rhodium atom bound to four rhodium atoms with a bond distance of about 2.73 Å and a single rhodium atom at a non-bonding distance of 3.88 Å. No metallic rhodium was observed at any time during the anaerobic reaction.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
- DOE Contract Number:
- AC05-76RL01830; AC02-06CH11357
- OSTI ID:
- 985047
- Report Number(s):
- PNNL-SA--55184; KC0302010
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 39 Vol. 129; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- United States
- Language:
- English
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