A Theoretically-Guided Optimization of a New Family of Modular P,S-Ligands for Iridium-Catalyzed Hydrogenation of Minimally Functionalized Olefins
作者:Jèssica Margalef、Xisco Caldentey、Erik A. Karlsson、Mercè Coll、Javier Mazuela、Oscar Pàmies、Montserrat Diéguez、Miquel A. Pericàs
DOI:10.1002/chem.201402978
日期:2014.9.15
thioether‐phosphite/phosphiniteligands has been evaluated in the asymmetric iridium‐catalyzedhydrogenation of minimallyfunctionalizedolefins. The modular ligand design has been shown to be crucial in finding highly selective catalysts for each substrate. A DFT study of the transition state responsible for the enantiocontrol in the Ir‐catalyzedhydrogenation is also described and used for further optimization
Iridium-Catalyzed Enantioselective Hydrogenation of Alkenylboronic Esters
作者:Adnan Ganić、Andreas Pfaltz
DOI:10.1002/chem.201200246
日期:2012.5.29
iridium complex derived from a phosphino–imidazoline ligand is a highly efficient catalyst for the asymmetric hydrogenation of terminal vinyl boronic esters (see scheme). On the other hand, trisubstituted alkenyl‐boronates can be reduced with high activity and good to excellent enantioselectivity employing a pyridine–phosphinite ligand.
Iridium-Catalyzed Asymmetric Hydrogenation with Simple Cyclohexane-Based P/S Ligands: <i>In Situ</i> HP-NMR and DFT Calculations for the Characterization of Reaction Intermediates
We report a reduced but structurally valuable phosphite/phosphinite-thioether ligand library for the Ir-hydrogenation of 40 minimally functionalized alkenes, including relevant examples with poorly coordinative groups. We found that enantiomeric excesses are mainly dependent on the substrate structure and on some ligand parameters (i.e., the type of thioether/phosphorus moieties and the configuration of the phosphite group), whereas the substituents of the biaryl phosphite moiety had little impact. By tuning the ligand parameters we were able to find highly selective catalysts for a range of substrates (ee's up to 99%). These phosphite/phosphinite-thioether ligands have a simple backbone and thus yield simple NMR spectra that reduce signal overlap and facilitate the identification of relevant intermediates. Therefore, by combining HP-NMR spectroscopy and theoretical studies, we were also able to identify the catalytically competent Ir-dihydride alkene species, which made it possible to explain the enantioselectivity obtained.