| 1. |
- Melcher, Michaela Christina, et al.
(author)
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Chiral Discrimination in Rhodium(I) Catalysis by 2,5-Disubstituted 1,3 a,4,6 a -Tetrahydropenatalene Ligands -More Than Just a Twist of the Olefins?
- 2018
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 3:3, s. 3622-3630
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Journal article (peer-reviewed)abstract
- Chiral dienes are useful ligands in a number of asymmetric transition-metal-catalyzed reactions. Here, we evaluate the efficiency of 2,5-disubstituted 1,3a,4,6a-tetrahydropentalenes as ligands to rhodium(I). 2,5-Dibenzyl and diphenyl tetrahydropentalenes were synthesized in two steps and resolved, either chromatographically, or through fractional crystallization of diastereomeric rhodium(I) salts. When evaluated in a 1,4-arylation reaction, the 2,5-dibenzyl ligand gave up to 99% ee. The use of a well-defined rhodium complex as catalyst, Cs2CO3 as the base, and toluene/water as solvent was found to have a pronounced beneficial effect on the selectivity of the reaction. The homologous 2,5-diphenyl ligand on the other hand proved to be highly prone to racemization/loss of chirality during catalysis. Control experiments reveal that this rearrangement proceeds via a rhodium-mediated 1,3-hydride shift. Implications for ligand design and catalysis are discussed.
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| 2. |
- Melcher, Michaela Christina, et al.
(author)
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Control of Enantioselectivity in Rhodium(I) Catalysis by Planar Chiral Dibenzo[a,e]cyclooctatetraenes
- 2018
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539. ; 24:10, s. 2344-2348
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Journal article (peer-reviewed)abstract
- Planar chiral 5,11-disubstiuted dibenzo[a,e]cyclo-octatetraenes (dbCOTs) have been developed as the first useful chiral homologs to dbCOT-ligands for asymmetric applications. Methods enabling the preparation of such compounds on a gram-scale in enantiomerically pure form are described. Evaluated as ligands in rhodium(I)-catalyzed 1,4- and 1,2-arylation reactions, tertiary and quarternary stereogenic centers were formed with excellent yields and selectivities of up to >99%ee. A catalytic asymmetric synthesis of a key cyclization precursor to (-)-penifulvinA highlights the system in an applied context.
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| 3. |
- Melcher, Michaela
(author)
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Design and synthesis of rhodium and iridium bis-η2 diolefin catalysts: : Applications in C–C bond formation and asymmetric catalysis
- 2018
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with the design and synthesis of rhodium and iridium bis-η2 diolefin catalysts and their applications in C–C bond formation and asymmetric catalysis.More specifically, the second chapter describes the development of inter- and intramolecular (5+2) cycloadditions catalyzed by cationic iridium(I) complexes that lead to the formation of seven-membered rings in a single step. DFT was applied to investigate the mechanism of this reaction. Based on the findings described in Chapter 2, Chapter 3 discusses the relationship between the structure and the reactivity of a set of iridium and rhodium based bis–η2 diolefin complexes with respect to their application in four selected reactions.Chapters 4-6 discuss the design and development of chiral bis–η2 diolefin ligands and their application in asymmetric catalysis. The knowledge gained from the first chapters is applied to the development of C2-symmetric bis–η2 diolefin ligands and their complexation to transition metals. More specifically, Chapters 4 and 6 focus on the design, synthesis, and resolution of such chiral complexes, while their application and reactivity are discussed in chapter 5 and partly in chapter 6.
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| 4. |
- Melcher, Michaela, et al.
(author)
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Iridium Catalyzed Carbocyclizations: Efficient (5+2) Cycloadditions of Vinylcyclopropanes and Alkynes.
- 2015
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In: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 21:2, s. 531-535
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Journal article (peer-reviewed)abstract
- Third-row transition metal catalysts remain a largely untapped resource in cycloaddition reactions for the formation of medium-sized rings. Herein, we report the first examples of iridium-catalyzed inter- and intramolecular vinylcyclopropane (VCP)-alkyne (5+2) cycloadditions. DFT modeling suggests that catalysis by iridium(I) proceeds through a mechanism similar to that previously reported for rhodium(I)-catalyzed VCP-alkyne cycloadditions, but a smaller free energy span for iridium enables substantially faster catalysis under favorable conditions. The system is characterized by up to quantitative yields and is amenable to an array of disubstituted alkynes and vinylcyclopropanes.
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| 5. |
- Tasić, Magdalena, et al.
(author)
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Electro-mechanically switchable hydrocarbons based on [8]annulenes
- 2022
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Journal article (peer-reviewed)abstract
- Pure hydrocarbons with shape and conjugation properties that can be switched by external stimuli is an intriguing prospect in the design of new responsive materials and single-molecule electronics. Here, we develop an oligomeric [8]annulene-based material that combines a remarkably efficient topological switching upon redox changes with structural simplicity, stability, and straightforward synthesis: 5,12-alkyne linked dibenzo[a,e]cyclooctatetraenes (dbCOTs). Upon reduction, the structures accommodate a reversible reorganization from a pseudo-conjugated tub-shape to a conjugated aromatic system. This switching in oligomeric structures gives rise to multiple defined states that are deconvoluted by electrochemical, NMR, and optical methods. The combination of stable electromechanical responsivity and ability to relay electrons stepwise through an extended (pseudo-conjugated) π-system in partially reduced structures validate alkyne linked dbCOTs as a practical platform for developing new responsive materials and switches based on [8]annulene cores.
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