Topochemical Polymerization of a Diacetylene in a Chalcogen‐Bonded (ChB) Assembly

Dhaka, Arun; Jeon, Ie‐Rang; Jeannin, Olivier; Aubert, Emmanuel; Espinosa, Enrique; Fourmigué, Marc

doi:10.1002/ange.202116650

Cited by 5 publications

(2 citation statements)

References 45 publications

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“…Because anion–π catalysis was so impactful, the integration of unorthodox interactions into catalysis was continued with chalcogen bonds in 2017, [9] followed by pnictogen bonds in 2018 [10] . Since then, chalcogen‐ and pnictogen‐bonding catalysis have received increasing attention in the community [11–39] …”

Section: Figurementioning

confidence: 99%

Pnictogen‐Bonding Catalysts, Compared to Tetrel‐Bonding Catalysts: More Than Just Weak Lewis Acids

Chen

Frontera

López

et al. 2022

Helvetica Chimica Acta

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A hyperresponsive tool to assess supramolecular catalysis, the cyclization of di-epoxides into cyclic ethers is used to elucidate the difference between pnictogen-bonding and Lewis acid catalysis systematically. For all stereoisomers, most tested catalysts follow the Baldwin rules. Brønsted acid and anion-π catalysis afford almost only Baldwin products. Lewis acids such as SbCl 3 , BF 3 and BiCl 3 give the poorest selectivity, with at least 50 % Baldwin (B) products for all stereoisomers. In clear contrast, optimized pnictogen-bonding catalysts operating on the Sb(III) and the Sb(V) level give the fused anti-Baldwin (A) bicycles as the main product of trans epoxides, independent of syn or anti relation of the two epoxides. In the cis series, Sb(III) pnictogen-bonding catalysts afford BA products almost exclusively for syn diastereomers, while anti diastereomers give equal amounts of BA and AB products. Sb(V) pnictogen-bonding catalysts show similarly special trends. These unique characteristics support that pnictogen-bonding catalysis differs from Lewis acid catalysis and can arguably be defined as its non-covalent counterpart, just like hydrogen-bonding catalysis is understood and appreciated as the noncovalent counterpart of Brønsted acid catalysis. Computational studies on the origin of anti-Baldwin selectivity reveal Sb(V) catalysts with an introvert deep σ hole surrounded by an almost planar ring of ligands. Central pnictogen-bond attraction against peripheral steric repulsion then forces the epoxide to break open. In contrast, transient antimony oxidation in cyclic intermediates accounts for the chemoselectivity of Sb(III) catalysts. Presumably due to insufficient accessibility of their σ holes, the activity of tetrel-bonding catalysts is negligible. The division between powerful pnictogen-bonding and irrelevant tetrel-bonding catalysts does not exist with the respective orthodox Lewis acids and thus supports that σ-hole and Lewis acid catalysis are not the same.

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Section: Figurementioning

confidence: 99%

Pnictogen‐Bonding Catalysts, Compared to Tetrel‐Bonding Catalysts: More Than Just Weak Lewis Acids

Chen

Frontera

López

et al. 2022

Helvetica Chimica Acta

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“…Pnictogen-bonding catalysis [1][2][3][6][7][8][9][10][11][12][13][14][15] is the so far most performant expression of σ-hole catalysis, which today covers also halogen-bonding, [16][17][18][19][20][21][22][23] chalcogenbonding [13,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] and tetrel-bonding catalysis. [3] σ Holes describe the highly localized area of extreme electron deficiency that appears at the place of antibonding σ* orbitals opposite to covalent bonds on the respective atoms.…”

Section: Introductionmentioning

confidence: 99%

A Fluorogenic Substrate for Quinoline Reduction: Pnictogen‐Bonding Catalysis in Aqueous Systems

Renno,

Zhang,

Frontera

et al. 2024

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It is often said that pnictogen‐bonding catalysis, and s‐hole catalysis in general, would not work in aqueous systems because the solvent would interfere as an overcompetitive pnictogen‐bond acceptor. In this study, we show that the transfer of pnictogen‐bonding catalysis from hydrophobic solvents to aqueous systems is possible by replacing only hydrophobic with hydrophilic substrates, without changing catalyst or reaction. This differs from conventional covalent Lewis acid catalysts, which are instantaneously destroyed by ligand exchange. With their water‐proof substituents in place of exchangeable ligands, pnictogen‐bonding catalysts, the supramolecular counterpart of Lewis acid catalysts, are evinced to catalyze transfer hydrogenation of quinolines in neutral aqueous systems. To secure these results, we introduce a water‐soluble fluorogenic substrate that releases a coumarin upon the reduction of quinolines instead of activated quinolidiniums, and stiborane catalysts with deepened s holes. They demonstrate that pnictogen‐bonding catalysts can operate in higher‐order architectures for supramolecular systems catalysis under biologically relevant conditions, and provide an operational assay for high‐throughput catalyst screening by fluorescence imaging, in situ under relevant aqueous conditions.

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Tuning the Regioselectivity of Topochemical Polymerization through Cocrystallization of the Monomer with an Inert Isostere

et al. 2022

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Regiochemistry of topochemical reactions depends on the crystal packing and biasing the regiochemistry necessitates precise crystal engineering. The pristine crystals of monomer 1 upon topochemical azidealkyne cycloaddition (TAAC) reaction give a 1 : 1 blend of 1,4-and 1,5-triazole-linked polymers due to the presence of two self-sorted reactive conformers in the crystal. We designed a binary isomorphous cocrystal of monomer 1 and a structurally similar dummy molecule 2 to limit the number of reactive conformers of 1 to one and thus to get one type of polymer. Equimolar solution of 1 and 2 in chloroform-acetone mixture gave two 1 : 1 cocrystals Co-I and Co-II. The Co-II, a chloroform adduct, on heating undergoes desolvation and polymorphic transition to Co-I. Co-I is isomorphic to 1 and 2 and possess self-sorted arrays of 1 and 2. Heating Co-I results in the TAAC polymerization giving 1,4-triazolyllinked polymer of 1 selectively, showing the power of crystal engineering in regiocontrol. Chemical reactions governed by the molecular arrangementin crystals-topochemical reactions-are attractive in terms of greener, catalyst-free and solvent-free reaction conditions, nonnecessity of chromatographic purification, and their ability to form unique products that are not accessible by the conventional solution-phase methods. [1][2][3][4][5][6] However unlike solution-state reactions that are well-explored, factors that influence topochemical reactions are still poorly understood. [7][8][9][10] The solution-state reactivity of molecules could be easily regulated by altering the reaction conditions such as solvent, reagents, catalyst, etc. However in the case

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Topochemical Polymerization of a Diacetylene in a Chalcogen‐Bonded (ChB) Assembly

Cited by 5 publications

References 45 publications

Pnictogen‐Bonding Catalysts, Compared to Tetrel‐Bonding Catalysts: More Than Just Weak Lewis Acids

Pnictogen‐Bonding Catalysts, Compared to Tetrel‐Bonding Catalysts: More Than Just Weak Lewis Acids

A Fluorogenic Substrate for Quinoline Reduction: Pnictogen‐Bonding Catalysis in Aqueous Systems

Tuning the Regioselectivity of Topochemical Polymerization through Cocrystallization of the Monomer with an Inert Isostere

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