Frontier molecular orbital effects control the hole-catalyzed racemization of atropisomeric biaryls

Tan, Jacqueline S. J.; Paton, Robert S.

doi:10.1039/c8sc05066j

Cited by 22 publications

(29 citation statements)

References 35 publications

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“…The energy barrier for the rotation of one arm was studied by conformational search (Figure S31, detailed method was summarized in SI), which was calculated as 72.44 kJ·mol –1 . It is higher than the rotational energy of C—C in freely rotating n ‐butane (19 kJ·mol –1 ), but lower than that of conformationally stabilized 1,1'‐bi‐2‐naphthol (167 kJ·mol –1 ) . Compared to the reported longer version of tetratopic tpy‐porphyrin ligand, our design introduced more restriction to the rotation of tpy with a short arm, and constructed more compact structures with higher stability …”

Section: Resultsmentioning

confidence: 91%

Order from Chaos: Self‐Assembly of Nanoprism from a Mixture of Tetratopic Terpyridine‐Porphyrin Conformers

Filosa

Wang

et al. 2019

Chin. J. Chem.

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Summary of main observation and conclusion Porphyrins have been widely used in the self‐assembly of metallo‐supramolecules. In this study, we introduced 2,2':6,2"‐terpyridine (tpy) into a porphyrin core to synthesize a tetratopic building block with multiple conformers. During the self‐assembly with Zn(II), such a mixture of conformers was able to form a discrete nanoprism with all building blocks in one conformation. Detailed characterizations, including NMR, ESI‐MS and traveling‐wave ion mobility‐mass spectrometry (TWIM‐MS), all supported the formation of the desired assemblies. AFM and TEM further confirmed the dimensions of assembled nanoprisms. Moreover, the photophysical properties of the ligands and complexes were noticeably different depending upon size and metal ion center.

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Section: Resultsmentioning

confidence: 91%

Order from Chaos: Self‐Assembly of Nanoprism from a Mixture of Tetratopic Terpyridine‐Porphyrin Conformers

Filosa

Wang

et al. 2019

Chin. J. Chem.

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“…[34][35][36] The greater racemization of 3 a may indicate that this intermediate is longer-lived for this substrate, allowing more time for racemization to occur. The formation of radical intermediates may also account for the loss of ee, as has been noted by Pappo [37] and further investigated by Paton [38] for BINOL atropisomers. DFT studies indicate that single electron transfer to 2 (forming 2 * À ) causes a reduction in rotational barrier of 15-20 kcal mol À 1 , sufficient to enable significant racemization (see ESI for further discussion).…”

mentioning

confidence: 74%

Atroposelective Synthesis, Structure and Properties of a Novel Class of Axially Chiral N‐Aryl Quinolinium Salt

et al. 2021

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Inspired by naturally occurring molecules containing atropisomeric N+‐C axes, we have developed a novel synthetic approach to generate a library of axially chiral N‐aryl quinolinium salts. Enantiopurities up to 93 % ee were obtained via a four‐step route from commercially available precursors. Axial stereochemistry was controlled through an enantioselective ring‐closing Buchwald–Hartwig coupling reaction. The structure and properties of the salts were examined by X‐ray crystallography, DFT, UV‐Vis, and fluorescence spectroscopy, revealing high rotational barriers and solvatochromic behaviour.

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“…[55] Ta na nd Paton have shown that the hole-catalysedr acemization of atropisomericb iaryls occurs throughatwo-step mechanism in aprocess controlled by frontier molecular orbitals. [56] 2.6.5 Mechanism not known…”

Section: Rotationa Bout Single Bondsmentioning

confidence: 99%

Racemisation in Chemistry and Biology

Ballard

Narduolo

Ahmed

et al. 2020

Chemistry A European J

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The two enantiomers of a compound often have profoundly different biological properties and thus their liability to racemisation in aqueous solutions is an important piece of information. The authors reviewed the available data concerning the process of racemisation in vivo, in the presence of biological molecules (e.g., racemase enzymes, serum albumin, cofactors and derivatives) and under purely chemical but aqueous conditions (acid, base and other aqueous systems). Mechanistic studies are described critically in light of reported kinetic data. The types of experimental measurement that can be used to effectively determine rate constants of racemisation in various conditions are discussed and the data they provide is summarised. The proposed origins of enzymatic racemisation are presented and suggest ways to promote the process that are different from processes taking place in bulk water. Experimental and computational studies that provide understanding and quantitative predictions of racemisation risk are also presented.

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Frontier molecular orbital effects control the hole-catalyzed racemization of atropisomeric biaryls

Abstract: Biaryl atropisomerization is dramatically accelerated by the removal of an electron. The planar transition state is preferentially stabilized from depopulation of the highest occupied molecular orbital.

Cited by 22 publications

References 35 publications

Order from Chaos: Self‐Assembly of Nanoprism from a Mixture of Tetratopic Terpyridine‐Porphyrin Conformers

Order from Chaos: Self‐Assembly of Nanoprism from a Mixture of Tetratopic Terpyridine‐Porphyrin Conformers

Atroposelective Synthesis, Structure and Properties of a Novel Class of Axially Chiral N‐Aryl Quinolinium Salt

Racemisation in Chemistry and Biology

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