Stereochemical Control of Chirally Flexible Phosphepines

Žalubovskis, Raivis; Fjellander, Ester; Szabó, Zoltán; Moberg, Christina

doi:10.1002/ejoc.200600717

Cited by 10 publications

(6 citation statements)

References 38 publications

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“…Upon cooling, the signals broadened but, whereas the central methylene proton started to split at −79 °C (194 K), the NH and phosphorus signals did not split even at this low temperature, suggesting a barrier to inversion ≤10 kcal mol –1 (Figures S1 and S2). This behavior is similar to that of other ligands containing the same biphenyl phosphite moiety, which have inversion barriers around 10 kcal mol –1 . , An analogous phosphine ligand has been found to have a considerably higher barrier, 19.3 kcal mol –1 at 298 K; the ability to undergo rapid configurational change might render flexible phosphites more useful than their phosphine analogues for catalytic applications.…”

Section: Resultssupporting

confidence: 70%

Cofactor-Controlled Chirality of Tropoisomeric Ligand

et al. 2016

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A new tropos ligand with an integrated anion receptor site has been prepared. Chiral carboxylate and phosphate anions that bind in the anion receptor unit proved capable of stabilizing chiral conformations of the achiral flexible bidentate biaryl phosphite ligand, as shown by variable temperature 1 H and 31 P NMR spectroscopical studies of palladium(0) olefin complexes. Palladium allyl complexes of the supramolecular ligand-chiral cofactor assemblies catalyzed asymmetric allylic substitutions of rac-(E)-1,3-diphenyl-2propenyl carbonate and rac-3-cyclohexenyl carbonate with malonate and benzylamine as nucleophiles to provide nonracemic products. Although moderate enantioselectivities were observed, (ee:s up to 66%), the results confirm the ability of the anionic guests to affect the conformation of the ligand.

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Section: Resultssupporting

confidence: 70%

Cofactor-Controlled Chirality of Tropoisomeric Ligand

et al. 2016

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“…28 In phosphenines, pyramidal inversion at phosphorus is required, but since P is not a stereogenic center, this does not affect the chirality (Scheme 1). 17 In metal complexes, tropoisomerization may occur "onmetal", without decoordination of a ligand arm, but one-arm decoordination may also be required for configurational change to occur.…”

Section: Mechanism Of Tropoinversionmentioning

confidence: 99%

“… Barriers for tropoisomerization of bridged biaryl derivatives. Data were taken from (a) ref ( 14 ), (b) ref ( 15 ), (c) ref ( 16 ), or (d) ref ( 17 ). …”

Section: Introductionmentioning

confidence: 99%

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Self-Adaptable Tropos Catalysts

2021

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Conspectus Biological systems have often served as inspiration for the design of synthetic catalysts. The lock and key analogy put forward by Emil Fischer in 1894 to explain the high substrate specificity of enzymes has been used as a general guiding principle aimed at enhancing the selectivity of chemical processes by optimizing attractive and repulsive interactions in molecular recognition events. However, although a perfect fit of a substrate to a catalytic site may enhance the selectivity of a specific catalytic reaction, it inevitably leads to a narrow substrate scope, excluding substrates with different sizes and shapes from efficient binding. An ideal catalyst should instead be able to accommodate a wide range of substrates—it has indeed been recognized that enzymes also are often highly promiscuous as a result of their ability to change their conformation and shape in response to a substrate—and preferentially be useful in various types of processes. In biological adaptation, the process by which species become fitted to new environments is crucial for their ability to cope with changing environmental conditions. With this in mind, we have been exploring catalytic systems that can adapt their size and shape to the environment with the goal of developing synthetic catalysts with wide scope. In this Account, we describe our studies aimed at elucidating how metal catalysts with flexible structural units adapt their binding pockets to the reacting substrate. Throughout our studies, ligands equipped with tropos biaryl units have been explored, and the palladium-catalyzed allylic alkylation reaction has been used as a suitable probe to study the adaptability of the catalytic systems. The conformations of catalytically active metal complexes under different conditions have been studied by both experimental and theoretical methods. By the design of ligands incorporating two flexible units, the symmetry properties of metal complexes could be used to facilitate conformational analysis and thereby provide valuable insight into the structures of complexes involved in the catalytic cycle. The importance of flexibility was convincingly demonstrated when a phosphine group in a privileged ligand that is well-known for its versatility in a number of processes was exchanged for a tropos biaryl phosphite unit: the result was a truly self-adaptive ligand with dramatically increased scope.

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“…To demonstrate this, we decided to attach a stereochemically flexible phosphepine unit to alcohols 2a and 2b, hoping that the flexible unit would adopt the most suitable configuration in the catalytic reaction. Transformation of 2a and 2b to their lithium alcoholates followed by reaction of chlorophosphine 3 12 and BH 3 -protection gave access to 1e and 1f, respectively (Scheme 2).…”

Section: Preparation Of Ligandsmentioning

confidence: 99%

Iridium-catalyzed asymmetric hydrogenation of olefins using pyridine-phosphinites derived from the chiral pool

Žalubovskis¹,

Hörmann²,

Pfaltz³

et al. 2008

Arkivoc

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Cationic iridium complexes containing chiral pyridine-phosphinites, with their chirality derived from menthol or mandelic acid, were assessed in hydrogenations of trisubstituted nonfunctionalized olefins. Complexes with the new ligands showed high reactivity towards most of the olefins tested. The enantioselectivities varied with the structures of the substrate and the ligand. Best results were obtained in the hydrogenation of 3-hydroxy-2-methyl-1-phenylpropene using a ligand prepared from (-)-menthol, pyridyllithium and diphenylchlorophosphine (>99% conversion, 92% ee).

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Stereochemical Control of Chirally Flexible Phosphepines

Cited by 10 publications

References 38 publications

Cofactor-Controlled Chirality of Tropoisomeric Ligand

Cofactor-Controlled Chirality of Tropoisomeric Ligand

Self-Adaptable Tropos Catalysts

Iridium-catalyzed asymmetric hydrogenation of olefins using pyridine-phosphinites derived from the chiral pool

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