644995-50-6Relevant articles and documents
Mechanistic insights into iridium-catalyzed asymmetric hydrogenation of dienes
Cui, Xiuhua,Fan, Yubo,Hall, Michael B.,Burgess, Kevin
, p. 6859 - 6868 (2005)
Hydrogenation of 2,3-diphenylbutadiene (1) with the chiral carbene-oxazoline-iridium complex C has been studied by means of a combined experimental and computational approach. A detailed kinetic profile of the reaction was obtained with respect to consumption of the substrate and formation of the intermediate half-reduction products, 2,3-diphenylbut-1-ene (2) and the final product, 2,3-diphenylbutane (3). The data generated from these analyses, and from NMR experiments, revealed several facets of the reaction. After a brief induction period (presumably involving reduction of the cyclooctadiene ligand on C), the diene concentration declines in a zero-order process primarily to give mono ene intermediates. When all the diene is consumed, the reaction accelerates and compound 3 begins to accumulate. Interestingly, the prevalent enantiomer of the monoene intermediate 2 is converted mostly to meso-3 so the enantioselectivity of the reaction appears to reverse. The reaction seems to be first-order with respect to the catalyst when the catalyst concentration is less than 0.0075 M; diffusion of hydrogen across the gas-liquid interface complicates the analysis at higher catalyst concentra tions. Similarly, these diffusion effects complicated measurements of reaction rate versus applied pressure of dihydrogen; other factors like stir speed and flask geometry come into play under some, but not all, the conditions examined. Density functional theory (DFT) calculations, using the PBE method, were used to probe the reaction. These studies indicate a transoid-η 4-diene-di-hydride complex forms in the first stages of the catalytic cycle. Further reaction requires dissociation of one alkene ligand to give a η4-diene-dihydride-dihydrogen intermediate. A catalytic cycle that features Ir3+/Ir5+ seems to be involved thereafter.
Iridium-Mediated Asymmetric Hydrogenation of 2,3-Diphenylbutadiene: A Revealing Kinetic Study
Cui, Xiuhua,Burgess, Kevin
, p. 14212 - 14213 (2007/10/03)
Hydrogenation of 2,3-diphenylbutadiene mediated by a chiral iridium carbene oxazoline complex was studied. The kinetics of the reaction showed that it occurred in two distinct stages. The first corresponded to slow consumption of the diene to form half-hydrogenated products, i.e., monoenes. After all the diene was consumed, however, the reaction was much faster and more stereoselective. These data were interpreted in terms of possible catalytic intermediates. Copyright
