| 1. |
- Jorner, Kjell, et al.
(författare)
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Degradation of Pharmaceuticals through Sequential Photon Absorption and Photoionization in Amiloride Derivatives
- 2020
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Ingår i: Cell Reports Physical Science. - : Elsevier BV. - 2666-3864. ; 1:12
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Tidskriftsartikel (refereegranskat)abstract
- Haloaromatic drug molecules of the amiloride family are plagued by photodegradation with associated toxicity. Herein, we report on the photodegradation of analogs of amiloride, which are known to undergo photosubstitution in water. Model compounds built on the same scaffold undergo clean photosubstitution also in alcoholic solvent, where a certain amount of photodehalogenation is normally expected. Available evidence points to a mechanism starting with photoexcitation followed by photoionization to give a radical cation intermediate. Subsequent substitution reaction with the protic solvent is assisted by a general base, possibly strengthened by the proximal solvated electron. Recombination with the solvated electron generates the observed product. Quantum chemical computations reveal that excited state antiaromaticity is relieved when an electron is ejected from the photoexcited molecule by the second photon. The mechanism indicated here could have wide applicability to photoinduced degradation of similar heteroaromatic compounds in the environment, as well as to a class of increasingly popular synthetic photoredox methods.
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| 2. |
- Krajangsri, Suppachai, 1955-, et al.
(författare)
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Chemoselective Iridium-catalysed Peterson olefination/Asymmetric Hydrogenation of beta-Hydroxy Silaned
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Herein we report the use of Ir-N,P catalysts for the asymmetric hydrogenation of β-hydroxy silanes via an in-situ generated olefin intermediate. The reaction proceeds via an acid catalysed Peterson olefination reaction and provides hydrogenated products in excellent ee’s of up to 99% accompanied with high isolated yields under mild reaction conditions and short reaction times. Modification of the reaction conditions provides a choice to hydrogenate either an olefin or a β-hydroxy silane in a chemo-selective manner leaving the other functionality unaffected in the product.
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| 3. |
- Krajangsri, Suppachai, et al.
(författare)
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Tandem Peterson olefination and chemoselective asymmetric hydrogenation of β-hydroxy silanes
- 2019
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 10:12, s. 3649-3653
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Tidskriftsartikel (refereegranskat)abstract
- Here, we report the first Ir-N,P complex catalyzed tandem Peterson olefination and asymmetric hydrogenation of -hydroxy silanes. This reaction resulted in the formation of chiral alkanes in high isolated yields (up to 99%) and excellent enantioselectivity (up to 99% ee) under mild conditions. Modification of the reaction conditions provides a choice to transform either an olefin or the -hydroxy silane in a chemoselective manner. Additionally, based on this method, an expedient enantioselective synthesis of (S)-(+)--curcumene, from a simple ketone, was accomplished in two steps with 75% overall yield and 95% ee.
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| 4. |
- Margarita, Cristiana, et al.
(författare)
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Transition-Metal-Catalyzed Regioselective Asymmetric Mono-Hydrogenation of Dienes and Polyenes
- 2018
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 24:32, s. 8022-8028
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Tidskriftsartikel (refereegranskat)abstract
- Organic compounds containing multiple C=C bonds are attractive substrates for catalytic asymmetric hydrogenation. The full saturation of prochiral double bonds, controlling the creation of two or more stereocenters in one step, is obviously a remarkable goal. However, another fascinating and useful option is to selectively introduce a new defined stereogenic center while leaving other double bonds untouched. Thus, the retained functionalities can be further exploited in synthesis. Examples of regio- and enantioselective mono-hydrogenations of polyolefins are highlighted in this Concept article, and are divided according to the nature of the reduced double bond and the transition-metal catalyst used. Alkenes bearing coordinating functional groups are often preferentially hydrogenated by Rh- and Ru-complexes, while the more recently developed Ir-based catalysts promote the selective saturation on alkyl-substituted olefins. Relevant applications of this effective methodology in the synthesis of natural products are included to demonstrate its value in organic synthesis.
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| 5. |
- Peters, Byron K., et al.
(författare)
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An Enantioselective Approach to the Preparation of Chiral Sulfones by Ir-Catalyzed Asymmetric Hydrogenation
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:47, s. 16557-16562
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Tidskriftsartikel (refereegranskat)abstract
- Several chiral sulfonyl compounds were prepared using the iridium catalyzed asymmetric hydrogenation reaction. Vinylic, allylic and homoallylic sulfone substitutions were investigated, and high enantioselectivity is maintained regardless of the location of the olefin with respect to the sulfone. Impressive stereoselectivity was obtained for dialkyl substitutions, which typically are challenging substrates in the hydrogenation. As expected, the more bulky Z-substrates were hydrogenated slower than the corresponding E isomers, and in slightly lower enantioselectivity.
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| 6. |
- Peters, Byron K., 1986-, et al.
(författare)
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Enantio- and Regioselective Hydrogenation of Minimally and Densely Decorated Unsaturated Carbocycles
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Several cyclic prochiral olefins were successfully hydrogenated (>99 conv.,up to >99 % ee) using N,P-ligated iridium catalysts. Minimally functionalisedsubstrates (Class 1) were hydrogenated rapidly and in high ee, whichwas consistent with earlier reports. Substrates having functional groups(Class 2) and heterocycles (Class 3) attached to the unsaturated cycle, were43hydrogenated gradually over a period of time, however, high enantioselectivitywas still maintained (up to >99 % ee). This methodology is a highly practical,general and selective means of preparing chiral cyclohexanes.
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| 7. |
- Peters, Byron K., et al.
(författare)
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Enantio- and Regioselective Ir-Catalyzed Hydrogenation of Di- and Trisubstituted Cycloalkenes
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 138:36, s. 11930-11935
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Tidskriftsartikel (refereegranskat)abstract
- A number of cyclic olefins Were prepared and evaluated for the asymmetric hydrogenation reaction using novel N,P-ligated iridium imidazote-based Catalysts (Crabtree type). The diversity of these cyclic olefins spanned those having little functionality to others bearing strongly coordinating substituents and heterocycles. Excellent enantioselectivities were observed both for substrates having little functionality (up to >99% ee) and for substrates possessing functional groups several carbons away from the olefin. Substrates having functionalities such as carboxyl groups, alcohols, or heterocycles in the vicinity of the C=C bond were hydrogenated in high enantiomeric excess (up to >99% ee). The hydrogenation was also found to be regioselective, and by controlling the reaction conditions, selective hydrogenation of one of two trisubstituted olefins can be achieved: Furthermore, trisubstituted olefins can be selectively hydrogenated in the presence of tetrasubstituted olefins.
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| 8. |
- Ponra, Sudipta, et al.
(författare)
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Asymmetric synthesis of 1,2-fluorohydrin : iridium catalyzed hydrogenation of fluorinated allylic alcohol
- 2020
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 11:41, s. 11189-11194
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a simple protocol for the preparation of 1,2-fluorohydrin by asymmetric hydrogenation of fluorinated allylic alcohols using an efficient azabicyclo thiazole-phosphine iridium complex. The iridium-catalyzed asymmetric synthesis of chiral 1,2-fluorohydrin molecules was carried out at ambient temperature with operational simplicity, and scalability. This method was compatible with various aromatic, aliphatic, and heterocyclic fluorinated compounds as well as a variety of polyfluorinated compounds, providing the corresponding products in excellent yields and enantioselectivities.
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| 9. |
- Ponra, Sudipta, et al.
(författare)
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Diastereo- and Enantioselective Synthesis of Fluorine Motifs with Two Contiguous Stereogenic Centers
- 2018
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 140:42, s. 13878-13883
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of chiral fluorine containing motifs, in particular, chiral fluorine molecules with two contiguous stereogenic centers, has attracted much interest in research due to the limited number of methods available for their preparation. Herein, we report an atom-economical and highly stereoselective synthesis of chiral fluorine molecules with two contiguous stereogenic centers via azabicyclo iridium-oxazoline-phosphine-catalyzed hydrogenation of readily available vinyl fluorides. Various aromatic, aliphatic, and heterocyclic systems with a variety of functional groups were found to be compatible with the reaction and provide the highly desirable product as single diastereomers with excellent enantioselectivities.
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| 10. |
- Rabten, Wangchuk, et al.
(författare)
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A ruthenium water oxidation catalyst based on a carboxamide ligand
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:8, s. 3272-3276
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Tidskriftsartikel (refereegranskat)abstract
- Herein is presented a single-site Ru complex bearing a carboxamide-based ligand that efficiently manages to carry out the fourelectron oxidation of H2O. The incorporation of the negatively charged ligand framework significantly lowered the redox potentials of the Ru complex, allowing H2O oxidation to be driven by the mild oxidant [Ru(bpy)(3)](3+). This work highlights that the inclusion of amide moieties into metal complexes thus offers access to highly active H2O oxidation catalysts.
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| 11. |
- Rabten, Wangchuk, et al.
(författare)
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Catalytic Water Oxidation by a Molecular Ruthenium Complex : Unexpected Generation of a Single-Site Water Oxidation Catalyst
- 2015
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 54:10, s. 4611-4620
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Tidskriftsartikel (refereegranskat)abstract
- The increasing energy demand calls for the development of sustainable energy conversion processes. Here, the splitting of H2O to O-2 and H-2, or related fuels, constitutes an excellent example of solar-to-fuel conversion schemes. The critical component in such schemes has proven to be the catalyst responsible for mediating the four-electron oxidation of H2O to O-2. Herein, we report on the unexpected formation of a single-site Ru complex from a ligand envisioned to accommodate two metal centers. Surprising N-N bond cleavage of the designed dinuclear ligand during metal complexation resulted in a single-site Ru complex carrying a carboxylate amide motif. This ligand lowered the redox potential of the Ru complex sufficiently to permit H2O oxidation to be carried out by the mild one-electron oxidant [Ru(bpy)(3)](3+) (bpy = 2,2'-bipyridine). The work thus highlights that strongly electron-donating ligands are important elements in the design of novel, efficient H2O :oxidation catalysts.
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| 12. |
- Rabten, Wangchuk
(författare)
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Development of Ruthenium Complexes for Water Oxidation
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Development of a methodology to combat the world energy crisis can be one of the greatest challenges now facing mankind. Our research is focused on the development of versatile catalysts (WOCs) that oxidize water into molecular oxygen at neutral pH, driven by the mild one-electron oxidant [Ru(bpy)3]3+, using natural photosynthesis a sa model.The first part of the thesis describes the unexpected generation of a mononuclear Ru complex from a hexadentate ligand, which was envisioned to accommodate two metal atoms. The study of this mononuclear catalyst clearly demonstrated the importance of having strongly electron donating functional groups and their effect on catalytic water oxidation.The second part of thesis presents the preparation of a mononuclear Ru complex, which contains two amide groups in the ligand scaffold and the superior reactivity of this complex in catalytic water oxidation under neutral condition. When mild one-electronoxidant [Ru(bpy)3]3+ was employed, TONs of ∼ 6000 and TOFs of ∼20s-1 were achieved, which are the highest values reported so far, using this type of oxidant
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| 13. |
- Rabten, Wangchuk, et al.
(författare)
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Ir-Catalyzed Asymmetric and Regioselective Hydrogenation of Cyclic Allylsilanes and Generation of Quaternary Stereocenters via the Hosomi-Sakurai Allylation
- 2018
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 24:7, s. 1681-1685
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Tidskriftsartikel (refereegranskat)abstract
- A number of cyclic dienes containing the allylsilane moiety were prepared via Birch reduction and subjected to iridium-catalyzed regioselective and asymmetric hydrogenation, which provided chiral allylsilanes in high conversion and enantiomeric excess (up to 99 % ee). The compounds were successively used in the Hosomi-Sakurai allylation with various aldehydes employing TiCl4 as Lewis acid, providing adducts with two additional stereogenic centers in excellent diastereoselectivity.
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| 14. |
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| 15. |
- Rabten, Wangchuk, 1987-
(författare)
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The Use of N,P-Iridium and N,P-Palladium Complexes in Asymmetric Synthesis
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis concerns asymmetric catalysis using chiral N,P-ligands and iridium or palladium transition metals. The first part (Chapters 2 and 3) highlights the N,P-iridium catalyzed asymmetric hydrogenation of 1,4-cyclohexadienes having functionalized or unfunctionalized substituents, including allylsilane side chains. A series of N,P-iridium catalysts were synthesized and screened on a number of cyclohexadienes. The developed N,P-iridium catalysts have provided excellent chemo-, regio- and enantioselectivity for most of the products obtained. For substrates having an allylsilane sidechain, the chiral cyclic allylsilane products were used to induce stereocontrol in a subsequent Hosomi-Sakurai reaction using TiCl4 as Lewis acid and aldehydes as electrophiles. The corresponding homoallylic alcohols were obtained in good to excellent diastereoselectivity. The second part (Chapter 4) describes the N,P-iridium catalyzed asymmetric hydrogenation of various vinyl fluorides. A number of tri- and tetrasubstituted vinyl fluorides were synthesized and evaluated for the asymmetric hydrogenation. The corresponding saturated chiral fluoro compounds were obtained in very high enantioselectivity (up to 99% ee). The defluorination, usually known to occur under the catalytic hydrogenation conditions, were not observed for the majority of the substrates. Finally, Chapter 5 describes the application of N,P-ligands in the asymmetric cycloisomerization of 1,6-enynes using a palladium precatalyst. The enantioselectivities for the products were found to depend both on the substrate as well as the hydrogen source. These developed catalytic reactions provide attractive methods to create multiple stereogenic centers in a molecule in relatively few steps from readily available starting materials.
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| 16. |
- Shatskiy, Andrey, et al.
(författare)
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Catalyst-solvent interactions in a dinuclear Ru-based water oxidation catalyst
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:47, s. 19024-19033
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Tidskriftsartikel (refereegranskat)abstract
- Photocatalytic water oxidation represents a key process in conversion of solar energy into fuels and can be facilitated by the use of molecular transition metal-based catalysts. A novel straightforward approach for covalent linking of the catalytic units to other moieties is demonstrated by preparation of a dinuclear complex containing two [Ru(pdc)(pic)(3)]-derived units (pdc = 2,6-pyridinedicarboxylate, pic = 4-picoline). The activity of this complex towards chemical and photochemical oxidation of water was evaluated and a detailed insight is given into the interactions between the catalyst and acetonitrile, a common co-solvent employed to increase solubility of water oxidation catalysts. The solvent-induced transformations were studied by electrochemical and spectroscopic techniques and the relevant quantitative parameters were extracted.
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| 17. |
- Slanina, Tomáš, et al.
(författare)
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Impact of Excited-State Antiaromaticity Relief in a Fundamental Benzene Photoreaction Leading to Substituted Bicyclo[3.1.0]hexenes
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 142:25, s. 10942-10954
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Tidskriftsartikel (refereegranskat)abstract
- Benzene exhibits a rich photochemistry which can provide access to complex molecular scaffolds that are difficult to access with reactions in the electronic ground state. While benzene is aromatic in its ground state, it is antiaromatic in its lowest ππ∗ excited states. Herein, we clarify to what extent relief of excited-state antiaromaticity (ESAA) triggers a fundamental benzene photoreaction: the photoinitiated nucleophilic addition of solvent to benzene in acidic media leading to substituted bicyclo[3.1.0]hex-2-enes. The reaction scope was probed experimentally, and it was found that silyl-substituted benzenes provide the most rapid access to bicyclo[3.1.0]hexene derivatives, formed as single isomers with three stereogenic centers in yields up to 75% in one step. Two major mechanism hypotheses, both involving ESAA relief, were explored through quantum chemical calculations and experiments. The first mechanism involves protonation of excited-state benzene and subsequent rearrangement to bicyclo[3.1.0]hexenium cation, trapped by a nucleophile, while the second involves photorearrangement of benzene to benzvalene followed by protonation and nucleophilic addition. Our studies reveal that the second mechanism is operative. We also clarify that similar ESAA relief leads to puckering of S1-state silabenzene and pyridinium ion, where the photorearrangement of the latter is of established synthetic utility. Finally, we identified causes for the limitations of the reaction, information that should be valuable in explorations of similar photoreactions. Taken together, we reveal how the ESAA in benzene and 6π-electron heterocycles trigger photochemical distortions that provide access to complex three-dimensional molecular scaffolds from simple reactants.
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| 18. |
- Xu, Quan, et al.
(författare)
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Thiazole, Imidazole and Oxazoline Based N,P-Ligands for Palladium-Catalyzed Cycloisomerization of 1,6-Enynes
- 2016
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Ingår i: European Journal of Organic Chemistry. - : Wiley-VCH Verlagsgesellschaft. - 1434-193X .- 1099-0690. ; :20, s. 3427-3433
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Tidskriftsartikel (refereegranskat)abstract
- A series of N,P-ligands were prepared and evaluated in the asymmetric palladium-catalyzed cycloisomerization of allyl propargyl ether substrates. The reactivity and enantioselectivity of the reaction was shown to be highly dependent on the chiral skeleton of the ligand structures with ee's ranging from 22-99 %. The proton source had a significant impact on the enantioselectivity. The generation of palladium hydride from formic acid led to the highest ee. A selectivity model based on a proposed transition state was used to predict and explain the enantiomeric outcome of the reaction.
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