Editorial

2 pages, 177 KiB

Open AccessEditorial

Organocatalysis in the Chemical Transformations

by Adriana Maria da Silva

Catalysts 2023, 13(9), 1282; https://doi.org/10.3390/catal13091282 - 07 Sep 2023

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Organocatalysis has been a breakthrough in chemical transformations becoming viable the conversion of challenging reactions through the sustainable use of small organic molecules as catalysts [...] Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

Research

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10 pages, 1323 KiB

Open AccessArticle

by Or Fleischer, Tom Targel, Fatma Saady and Moshe Portnoy

Catalysts 2023, 13(2), 361; https://doi.org/10.3390/catal13020361 - 07 Feb 2023

Cited by 3 | Viewed by 1053 | Correction

Abstract

We demonstrated recently that organocatalysts, based on a nucleophilic core (N-alkylimidazole or 4-aminopyridine) and decorated with an extensive secondary-sphere envelope (connected to the core through a benzyl substituent), strongly affect the site selectivity in acylation and phosphorylation of amphiphilic diols, sometimes entirely overriding [...] Read more.

We demonstrated recently that organocatalysts, based on a nucleophilic core (N-alkylimidazole or 4-aminopyridine) and decorated with an extensive secondary-sphere envelope (connected to the core through a benzyl substituent), strongly affect the site selectivity in acylation and phosphorylation of amphiphilic diols, sometimes entirely overriding the innate predisposition of the substrate. Preliminary studies pointed out that, despite some similarities, there are differences between the two transformations, regarding the influence of various catalyst features on the selectivity. To fully elucidate this, extended families of organocatalysts of the said design were examined, activity- and selectivity-wise, in the abovementioned transformations of model alcohol and amphiphilic diol substrates. A comparison of the influence of the catalyst design on the two reactions revealed that while the inductive electron donation of the o,o-dialkoxybenzyl substituent of the core, combined with the catalytic intermediate-stabilizing influence of some of the secondary-sphere components, causes an increase in the catalyst activity in both reactions and in the site selectivity in phosphorylation, its effect on the site selectivity in acylation is opposite. On the other hand, the lipophilicity of the secondary-sphere appendages improves the apolar site-favoring selectivity in both reactions. Thus, both factors work in concert in phosphorylation, but in opposite directions in acylation. Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

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26 pages, 5668 KiB

Open AccessEditor’s ChoiceArticle

Ring-Opening Polymerization of rac-Lactide Catalyzed by Octahedral Nickel Carboxylate Complexes

by Alexey Nikiforov, Natalia Panina, Daniil Blinou, Vladislav Gurzhiy, Juliya Nashchekina, Evgenia Korzhikova-Vlakh, Alexey Eremin and Mariia Stepanova

Catalysts 2023, 13(2), 304; https://doi.org/10.3390/catal13020304 - 29 Jan 2023

Cited by 4 | Viewed by 2113

Abstract

To date, nickel(II) complexes have not been practically investigated as catalysts in ring-opening polymerization (ROP) of lactide to produce biodegradable poly(lactic acid), which is in demand in biomedicine and industry. In this study, carboxylate complexes of nickel(II) containing various N-donor ligands with different [...] Read more.

To date, nickel(II) complexes have not been practically investigated as catalysts in ring-opening polymerization (ROP) of lactide to produce biodegradable poly(lactic acid), which is in demand in biomedicine and industry. In this study, carboxylate complexes of nickel(II) containing various N-donor ligands with different nuclearity, metal core rigidity and nature of carboxylate ligands were synthesized and studied by infrared spectroscopy, X-ray diffraction, elemental and thermogravimetric analyses. The obtained complexes were examined in the ROP of the rac-lactide in bulk and in toluene solution with and without the addition of a benzyl alcohol initiator. In the series of complexes studied, the complex [Ni(DBED)₂(O₂CC(CH₃)₃)₂]·(CH₃)₃CCO₂H (DBED is N,N′-dibenzylethylenediamine) was a syndioselective catalyst and showed the highest catalytic ability in the polymerization without the addition of benzyl alcohol. For this complex, according to 1D DOSY ¹H NMR spectroscopy and mass spectrometry with electrospray ionization, polymerization is initiated by a free secondary amine, DBED, leaving the metal’s inner coordination sphere. Based on the experimental data obtained, a comprehensive density functional theory (DFT) study of the ROP pathways including the initiation and first chain growth cycle steps with a detailed description of the intermediates and evaluation of the energy barriers of the steps was carried out. It was shown that one of the key roles in the reaction process is played by carboxylate ligands, which act as proton carriers from the initiator molecule and have a significant influence on the reactivity of the catalytic metal complexes. Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

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16 pages, 1745 KiB

Open AccessArticle

Development of L-Proline-Based Chiral Ionic Liquids for Asymmetric Michael Reaction

by Karolina Zalewska, Isabel Pinto, Luis Cabrita, Małgorzata E. Zakrzewska, João P. Noronha, M. Nunes da Ponte and Luis C. Branco

Catalysts 2023, 13(2), 270; https://doi.org/10.3390/catal13020270 - 25 Jan 2023

Cited by 2 | Viewed by 1607

Abstract

Different Chiral Ionic Liquids (CIL) based on L-proline have been developed. Simple and efficient synthetic methodologies are used, allowing preparation in good yields for twelve novel CILs using L-proline as a cation or anion combined with suitable counter-ions. A detailed physical and chemical [...] Read more.

Different Chiral Ionic Liquids (CIL) based on L-proline have been developed. Simple and efficient synthetic methodologies are used, allowing preparation in good yields for twelve novel CILs using L-proline as a cation or anion combined with suitable counter-ions. A detailed physical and chemical characterization of the CILs was performed to evaluate the influence of counter-ions on the final properties. The most promissory CILs were tested as efficient chiral catalysts in IL media for asymmetric Michael addition reactions of ketones and aldehydes to nitro-olefins. Similar or even better conversions and enantioselectivities (ee up to 95%) compared to the original L-proline were achieved. Additionally, a good product extraction performance using supercritical CO₂ processes was obtained. Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

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14 pages, 3868 KiB

Open AccessFeature PaperArticle

Poly(ε-caprolactones) Initiated by Chiral Compounds: A New Protocol to Support Organocatalysts

by Caroline Gross Jacoby, Jorge Hugo Sbardelotto, Tales da Silva Daitx, Bianca Thaís Dalberto, Raquel Santos Mauler and Paulo Henrique Schneider

Catalysts 2023, 13(1), 164; https://doi.org/10.3390/catal13010164 - 10 Jan 2023

Cited by 2 | Viewed by 1104

Abstract

This work investigates the support of organocatalysts in polyesters, a class of polymers seldom used for this purpose. The proposal is to use the hydroxyl groups present in the structure of the chosen chiral compounds to promote the polymerization of ε-caprolactone, generating the [...] Read more.

This work investigates the support of organocatalysts in polyesters, a class of polymers seldom used for this purpose. The proposal is to use the hydroxyl groups present in the structure of the chosen chiral compounds to promote the polymerization of ε-caprolactone, generating the support and anchoring the organocatalyst in a single step. A very simple method, with acid catalysis, was employed, that showed versatility in generating supported catalysts with different structures and functional groups and modulating the mass of the materials to generate specific solubility characteristics. In this way, the catalysts can be solubilized in some organic solvents, such as dichloromethane, but at the end of the reaction, they can be recovered in a heterogeneous way, through precipitation in more apolar solvents. The materials were applied as organocatalysts on an aldol addition test reaction and the product could be obtained in excellent yields and good stereoselectivity. The polymer did not show signs of degradation after the reaction, proving to be robust and suitable for use in catalysis; however, a recycling process appears to be necessary for its reuse. Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

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Review

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27 pages, 6778 KiB

Open AccessFeature PaperReview

Organocatalytic Transformations from Sulfur Ylides

by Marcio Hayashi and Antonio C. B. Burtoloso

Catalysts 2023, 13(4), 689; https://doi.org/10.3390/catal13040689 - 31 Mar 2023

Cited by 5 | Viewed by 1836

Abstract

Sulfur ylides are an important class of organic compounds due to their ability to perform many different transformations that can give diverse and interesting products with a high degree of complexity. Although metal-catalyzed transformations are frequent in this class of compounds, organocatalyzed transformations [...] Read more.

Sulfur ylides are an important class of organic compounds due to their ability to perform many different transformations that can give diverse and interesting products with a high degree of complexity. Although metal-catalyzed transformations are frequent in this class of compounds, organocatalyzed transformations remain scarce. From initial works, this review aims to show organocatalyzed transformations from sulfur ylides, involving cyclopropanation and formal N–H, S–H, and C–H insertion reactions, including enantioselective versions. The proposed mechanisms and the modes of activation of these organocatalysts will be covered. Furthermore, advances in this area and potential challenges to be circumvented in the near future will also be discussed. Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

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52 pages, 13982 KiB

Open AccessFeature PaperReview

Recent Advances in Greener Asymmetric Organocatalysis Using Bio-Based Solvents

by Lorena S. R. Martelli, Ingrid V. Machado, Jhonathan R. N. dos Santos and Arlene G. Corrêa

Catalysts 2023, 13(3), 553; https://doi.org/10.3390/catal13030553 - 09 Mar 2023

Cited by 5 | Viewed by 1703

Abstract

Efficient synthetic methods that avoid the extensive use of hazardous reagents and solvents, as well as harsh reaction conditions, have become paramount in the field of organic synthesis. Organocatalysis is notably one of the best tools in building chemical bonds between carbons and [...] Read more.

Efficient synthetic methods that avoid the extensive use of hazardous reagents and solvents, as well as harsh reaction conditions, have become paramount in the field of organic synthesis. Organocatalysis is notably one of the best tools in building chemical bonds between carbons and carbon-heteroatoms; however, most examples still employ toxic volatile organic solvents. Although a portfolio of greener solvents is now commercially available, only ethyl alcohol, ethyl acetate, 2-methyltetrahydrofuran, supercritical carbon dioxide, ethyl lactate, and diethyl carbonate have been explored with chiral organocatalysts. In this review, the application of these bio-based solvents in asymmetric organocatalytic methods reported in the last decade is discussed, highlighting the proposed mechanism pathway for the transformations. Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

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Other

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2 pages, 157 KiB

Open AccessCorrection

Correction: Fleischer et al. Similarities and Differences between Site-Selective Acylation and Phosphorylation of Amphiphilic Diols, Promoted by Nucleophilic Organocatalysts Decorated with Outer-Sphere Appendages. Catalysts 2023, 13, 361

by Or Fleischer, Tom Targel, Fatma Saady and Moshe Portnoy

Catalysts 2023, 13(7), 1098; https://doi.org/10.3390/catal13071098 - 14 Jul 2023

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Abstract

The authors wish to make the following corrections to this paper [...] Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

10 pages, 949 KiB

Open AccessPerspective

Usefulness of the Global E Factor as a Tool to Compare Different Catalytic Strategies: Four Case Studies

by Achille Antenucci and Stefano Dughera

Catalysts 2023, 13(1), 102; https://doi.org/10.3390/catal13010102 - 03 Jan 2023

Cited by 3 | Viewed by 1295

Abstract

The global E factor (E_G factor) has recently been introduced, in the context of asymmetric organocatalysis, as a new green chemistry metric to take into consideration the synthesis of the catalyst in the overall economy of the synthetic process of a [...] Read more.

The global E factor (E_G factor) has recently been introduced, in the context of asymmetric organocatalysis, as a new green chemistry metric to take into consideration the synthesis of the catalyst in the overall economy of the synthetic process of a given chiral molecule in optically pure form. Herein, its further usefulness in comparing diverse catalytic systems, even different from organocatalysts, is shown by the analysis of four case studies. Full article

(This article belongs to the Special Issue Organocatalysis in the Chemical Transformations)

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