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Relevant academic research and scientific papers

Iridium-Catalyzed Enantioselective Hydrogenation of Vinylsilanes

We have screened a diverse array of iridium complexes derived from chiral N,P ligands as catalysts for the asymmetric hydrogenation of vinylsilanes, a transformation for which generally applicable catalysts were lacking. Several catalysts emerged from thi

Extending the substrate scope of bicyclic p-oxazoline/thiazole ligands for ir-catalyzed hydrogenation of unfunctionalized olefins by introducing a biaryl phosphoroamidite group

This study identifies a series of Ir-bicyclic phosphoroamidite-oxazoline/thiazole catalytic systems that can hydrogenate a wide range of minimally functionalized olefins (including E- and Z-tri- and disubstituted substrates, vinylsilanes, enol phosphinates, tri- and disubstituted alkenylboronic esters, and ?±,?2-unsaturated enones) in high enantioselectivities (ee values up to 99%) and conversions. The design of the new phosphoroamidite-oxazoline/thiazole ligands derives from a previous successful generation of bicyclic N-phosphane-oxazoline/thiazole ligands, by replacing the N-phosphane group with a p-acceptor biaryl phosphoroamidite moiety. A small but structurally important family of Ir-phosphoroamidite-oxazoline/thiazole precatalysts has thus been synthesized by changing the nature of the Ndonor group (either oxazoline or thiazole) and the configuration at the biaryl phosphoroamidite moiety. The substitution of the N-phosphane by a phosphoroamidite group in the bicyclic N-phosphane-oxazoline/thiazole ligands extended the range of olefins that can be successfully hydrogenated.

A theoretically-guided optimization of a new family of modular P,S-ligands for iridium-catalyzed hydrogenation of minimally functionalized olefins

A library of modular iridium complexes derived from thioether-phosphite/phosphinite ligands has been evaluated in the asymmetric iridium-catalyzed hydrogenation of minimally functionalized olefins. 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-catalyzed hydrogenation is also described and used for further optimization of the crucial stereodefining moieties. Excellent enantioselectivities (enantiomeric excess (ee) values up to 99%) have been obtained for a range of substrates, including E- and Z-trisubstituted and disubstituted olefins, α,β-unsaturated enones, tri- and disubstituted alkenylboronic esters, and olefins with trifluoromethyl substituents.

Expanded scope of the asymmetric hydrogenation of minimally functionalized olefins catalyzed by iridium complexes with phosphite-thiazoline ligands

We have replaced the oxazoline group with a thiazoline moiety in one of the most successful of the phosphite-oxazoline ligand families for the Ir-catalyzed hydrogenation of minimally functionalized olefins. A small but structurally important library of Ir phosphite-thiazoline precatalysts (Ir-L1-L2a-e) has been developed by changing the substituents/configurations at the biaryl phosphite group. We found that the replacement of the oxazoline with a thiazoline moiety in the ligand design is beneficial in terms of substrate scope.

A phosphite-pyridine/iridium complex library as highly selective catalysts for the hydrogenation of minimally functionalized olefins

A modular library of readily available phosphite-pyridine ligands has been successfully applied for the first time in the iridium-catalyzed asymmetric hydrogenation of a broad range of minimally functionalized olefins. The modular ligand design has been shown to be crucial in finding highly selective catalytic systems for each substrate. Excellent enantioselectivities (ees up to 99%) have therefore been obtained in a wide range of E- and Z-trisubstituted alkenes, including more demanding triaryl-substituted olefins and dihydronaphthalenes. This good performance extends to the very challenging class of terminal disubstituted olefins, and to olefins containing neighbouring polar groups (ees up to 99%). Both enantiomers of the reduction product can be obtained in excellent enantioselectivities by simply changing the configuration of the carbon next to the phosphite moiety. The hydrogenations were also performed using propylene carbonate as solvent, which allowed the iridium catalyst to be reused and maintained the excellent Copyright

Enantioselective Ir-catalyzed hydrogenation of minimally functionalized olefins using pyranoside phosphinite-oxazoline ligands

Pyranoside phosphinite-oxazoline ligands prepared from readily available (+)-D-glucosamine were applied to the Ir-catalyzed asymmetric hydrogenation of minimally functionalized olefins. Our results show that the enantioselectivity is dependent on the ozaxoline and the phosphinite moieties and the substrate structure. By carefully selecting the ligand components, enantioselectivities up to 99 % were obtained in the asymmetric reduction of several (E)- and (Z)-trisubstituted and 1,1-disubstituted olefins. The asymmetric hydrogenation was also performed using propylene carbonate as solvent, which allowed the iridium catalysts to be reused and maintained the high enantioselectivities. Copyright

A modular furanoside thioether-phosphite/phosphinite/ phosphine ligand library for asymmetric iridium-catalyzed hydrogenation of minimally functionalized olefins: Scope and limitations

A highly modular furanoside thioether-phosphite/phosphinite/phosphine ligand library has been synthesized for the iridium-catalyzed asymmetric hydrogenation of minimally functionalized olefins. These ligands can be prepared efficiently from easily accessible D-(+)-xylose. We found that their effectiveness at transferring the chiral information in the product can be tuned by correctly choosing the ligand components. Enantioselectivities were therefore excellent (ees up to 99%) in a wide range of E- and Z-trisubstituted alkenes using 5-deoxyribofuranoside thioether-phosphite ligands. It should be pointed out that these catalysts are also very tolerant to the presence of a neighbouring polar group. For 1,1-disubstituted substrates, both enantiomers of the hydrogenation product can be obtained in high enantioselectivities simply by changing the configuration of the biaryl phosphite moiety. The asymmetric hydrogenation was also performed using propylene carbonate as solvent, which allowed the iridium catalysts to be reused while maintaining the excellent enantioselectivities. Copyright

Pyranoside phosphite-oxazoline ligands for the highly versatile and enantioselective Ir-catalyzed hydrogenation of minimally functionalized olefins. A combined theoretical and experimental study

A modular set of phosphite-oxazoline (P,N) ligands has been applied to the title reaction. Excellent ligands have been identified for a range of substrates, including previously challenging terminally disubstituted olefins, where we now have reached enantioselectivities of 99% for a range of substrates. The selectivity is best for minimally functionalized substrates with at least a moderate size difference between geminal groups. A DFT study has allowed identification of the preferred pathway. Computational prediction of enantioselectivities gave very good accuracy.

Adaptative biaryl phosphite-oxazole and phosphite-thiazole ligands for asymmetrie Ir-catalyzed hydrogenation of alkenes

A library of readily available phosphite-oxazole/thiazole ligands (L1a-g-L7a-g) was applied in the Ir-catalyzed asymmetric hydrogenation of several largely unfunctionalized E- and Z-trisubstituted and 1,1-disubstituted terminal alkenes. The ability of the catalysts to transfer chiral information to the product could be tuned by choosing suitable ligand components (bridgelength, the substituents in the heterocyclic ring and the alkyl backbone chain, the configuration of the ligand backbone, and the substituents/ configurations in the biaryl phosphite moiety),so that enantioselectivities could be maximized for each substrate as required. Enantioselectivities were therefore excellent (enantiomeric excess (ee) values up to >99%) for a wide range of E- and Z-trisubstituted and 1,1-disubstituted terminal alkenes. The biaryl phosphite moiety was a very advantageous ligand component in terms of substrate versatility.

Iridium-catalysed asymmetric hydrogenation of vinylsilanes as a route to optically active silanes

The first use of vinylsilanes as substrates in the asymmetric iridium-catalysed hydrogenation is reported, providing products with enantioselectivities of up to 98%.