19262-20-5Relevant articles and documents
Indene Derived Phosphorus-Thioether Ligands for the Ir-Catalyzed Asymmetric Hydrogenation of Olefins with Diverse Substitution Patterns and Different Functional Groups
Margalef, Jèssica,Biosca, Maria,de la Cruz-Sánchez, Pol,Caldentey, Xisco,Rodríguez-Escrich, Carles,Pàmies, Oscar,Pericàs, Miquel A.,Diéguez, Montserrat
supporting information, p. 4561 - 4574 (2021/04/05)
A family of phosphite/phosphinite-thioether ligands have been tested in the Ir-catalyzed asymmetric hydrogenation of a range of olefins (50 substrates in total). The presented ligands are synthesized in three steps from cheap indene and they are air-stable solids. Their modular architecture has been crucial to maximize the catalytic performance for each type of substrate. Improving most Ir-catalysts reported so far, this ligand family presents a broader substrate scope, covering different substitution patterns with different functional groups, ranging from unfunctionalized olefins, through olefins with poorly coordinative groups, to olefins with coordinative functional groups. α,β-Unsaturated acyclic and cyclic esters, ketones and amides werehydrogenated in enantioselectivities ranging from 83 to 99% ee. Enantioselectivities ranging from 91 to 98% ee were also achieved for challenging substrates such as unfunctionalized 1,1′-disubstituted olefins, functionalized tri- and 1,1′-disubstituted vinyl phosphonates, and β-cyclic enamides. The catalytic performance of the Ir-ligand assemblies was maintained when the environmentally benign 1,2-propylene carbonate was used as solvent. (Figure presented.).
Synthesis and Asymmetric Alkene Hydrogenation Activity of C2-Symmetric Enantioenriched Pyridine Dicarbene Iron Dialkyl Complexes
Viereck, Peter,Rummelt, Stephan M.,Soja, Natalia A.,Pabst, Tyler P.,Chirik, Paul J.
supporting information, p. 1053 - 1061 (2021/05/07)
Enantioenriched N-alkyl-imidazole-substituted pyridine dicarbene iron dialkyl complexes have been synthesized and characterized by 1H NMR and zero-field 57Fe M?ssbauer spectroscopies as well as single-crystal X-ray diffraction. In benzene-d6, reversible coordination of N2 was observed establishing an equilibrium between a five-coordinate, S = 1 iron dialkyl derivative and the corresponding six-coordinate, diamagnetic dinitrogen complex. A modest enantioselectivity of 45% enantiomeric excess (ee) was observed for the catalytic asymmetric hydrogenation of 1-isopropyl-1-phenyl ethylene at 4 atm of H2 using 10 mol % of an enantioenriched iron dialkyl precatalyst, (ACNC)Fe(CH2SiMe3)2 ((ACNC) = bis(alkylimidazol-2-ylidene)pyridine). Decreasing the H2 pressure to 1 atm increased the ee to 70%. Incubation experiments established that the reaction of the iron dialkyl precatalysts with H2 initiates a background reaction leading to the generation of a less selective catalyst; suppressing this pathway is crucial for obtaining high enantioselectivity. The attempted hydrogenation of methyl-2-acetamidoacrylate identified a deactivation pathway where N-H bond activation generated an iron alkyl κ2-amidate alkyl. For productive catalytic reactions, deuterium labeling studies are consistent with a pathway for hydrogenation involving fast, reversible [2,1]-alkene insertion and a slow, enantiodetermining [1,2]-insertion. Monitoring the catalytic alkene hydrogenation reaction by NMR spectroscopy supports a homogeneous active catalyst that also undergoes C-H activation of the ACNC ligand backbone as a competing reaction.
Ir/Thioether-Carbene, -Phosphinite, and -Phosphite Complexes for Asymmetric Hydrogenation. A Case for Comparison
Cruz-Sánchez, Pol De La,Faiges, Jorge,Mazloomi, Zahra,Borràs, Carlota,Biosca, Maria,Pàmies, Oscar,Diéguez, Montserrat
, p. 4193 - 4205 (2019/10/16)
We studied for the first time the potential of novel and simple Ir/thioether-NHC complexes in the asymmetric hydrogenation of unfunctionalized olefins and cyclic β-enamides. For comparison, we prepared and applied the analogues thioether-phosphinite/phosphite complexes. We found that the efficiency of the new Ir/thioether-NHC catalyst precursors varies with the type of olefin. Thus, while the Ir/thioether-NHC catalyst precursors provided lower catalytic performance than their related Ir/thioether-P complexes in the hydrogenation of olefins lacking a coordinating group, the catalysts had similar good performance for the reduction of functionalized olefins (e.g., tri- and disubstituted enol phosphonate derivatives). Catalytic results together with the studies of the reactivity toward H2 indicated that the thioether-carbene design favors the formation of inactive trinuclear species, which are responsible for the low activities obtained with these carbene-type catalysts. Nevertheless, this catalyst deactivation can be avoided by using functionalized olefins such as enol phosphonates. We also report the discovery of simple-to-synthesize Ir/thioether-P catalysts containing a simple backbone that gave high enantioselectivities for some trisubstituted olefins, some challenging 1,1′-disubstituted olefins, and cyclic β-enamides.
