In situ XAFS and NMR study of rhodium-catalyzed dehydrogenation of dimethylamine borane

In situ X-ray absorption fine structure spectroscopy (XAFS) and 11B NMR were used to study the rhodium-catalyzed dimerization reaction of dimethylaminoborane, (CH3)2NHBH3 or DMAB. XAFS spectra show that the active form of the rhodium catalyst is most likely composed of a six-atom Rh core surrounded by tightly bound external ligands. NMR results show the presence of monomeric dimethylamine borane (CH3)2NBH2, providing evidence that hydrogen formation from the homogeneous Rh species occurs by an intramolecular pathway. This is in contrast to thermal pathways that involve intermolecular B-N concurrent with hydrogen formation. This work shows that in situ XAFS spectroscopy offers a unique experimental tool to differentiate between heterogeneous and homogeneous catalysis. Copyright © 2005 American Chemical Society.