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Keywords = Hirao reaction

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13 pages, 1539 KiB  
Article
Microwave-Assisted P–C Coupling of the Less Reactive Chlorobenzene and >P(O)H Reagents in the Absence of the Usual Mono- and Bidental P-Ligands
by Bianka Huszár, Zoltán Mucsi and György Keglevich
Molecules 2025, 30(5), 1045; https://doi.org/10.3390/molecules30051045 - 25 Feb 2025
Viewed by 632
Abstract
The so far unattended version of the Hirao reaction involving the coupling of the less reactive chloroarenes with >P(O)H reagents, such as diarylphosphine oxides, diethyl phosphite, and ethyl phenyl-H-phosphinate, was investigated in detail using Pd(OAc)2 as the catalyst precursor, and [...] Read more.
The so far unattended version of the Hirao reaction involving the coupling of the less reactive chloroarenes with >P(O)H reagents, such as diarylphosphine oxides, diethyl phosphite, and ethyl phenyl-H-phosphinate, was investigated in detail using Pd(OAc)2 as the catalyst precursor, and applying some excess of the P-reagent to provide the ligand via its trivalent tautomeric (>P-OH) form. In the presence of triethylamine, no P–C coupling took place, meaning that there was a need for a stronger base, an alkali carbonate. The solvent had a significant effect on the efficiency of the Hirao reaction. The optimum conditions (10% of the Pd(OAc)2, 1.3 equiv. of the P-reagent, 1.1 equiv. of the alkali carbonate, 135–150 °C) explored herein were applied in the synthesis of diaryl-phenylphosphine oxides, aryl-diphenylphosphine oxides, diethyl arylphosphonates, and ethyl diphenylphosphinate. Theoretical calculations performed at the M06-2X/6-31G(d,p)[PCM(MeCN)] level also justified coupling with the chloroarenes under appropriate conditions, and were in accord with the experimental results revealing the unsuitability of triethylamine as a base and the need for an alkali carbonate. The new protocol elaborated herein is more practical and “greener” than the version with bromoarenes, and embraces a wide substrate scope. Full article
(This article belongs to the Special Issue Recent Developments in Cross-Coupling Reactions)
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19 pages, 4460 KiB  
Article
Stabilized Palladium Nanoparticles from Bis-(N-benzoylthiourea) Derived-PdII Complexes as Efficient Catalysts for Sustainable Cross-Coupling Reactions in Water
by Samet Poyraz, H. Ali Döndaş, Samet Belveren, Senanur Taş, Raquel Hidalgo-León, José Trujillo-Sierra, Lesly V. Rodríguez-Flórez, Mª de Gracia Retamosa, Ana Sirvent, Mohammad Gholinejad, Sara Sobhani and José M. Sansano
Molecules 2024, 29(5), 1138; https://doi.org/10.3390/molecules29051138 - 4 Mar 2024
Cited by 4 | Viewed by 2082
Abstract
Stable palladium (II) complexes, incorporating a double (N-benzoylthiourea) arrangement bonded to a complex heterocyclic scaffold, are used as precursors of catalytic species able to promote Suzuki–Miyaura, Mizoroki–Heck, Hiyama, Buchwald–Hartwig, Hirao and Sonogashira–Hagihara cross-coupling transformations in water. These sustainable processes are chemoselective [...] Read more.
Stable palladium (II) complexes, incorporating a double (N-benzoylthiourea) arrangement bonded to a complex heterocyclic scaffold, are used as precursors of catalytic species able to promote Suzuki–Miyaura, Mizoroki–Heck, Hiyama, Buchwald–Hartwig, Hirao and Sonogashira–Hagihara cross-coupling transformations in water. These sustainable processes are chemoselective and very versatile. The nanoparticles responsible for these catalytic reactions were analyzed and studied. Their usefulness is demonstrated after several tests and analyses. The heterogeneous character of this species in water was also confirmed. Full article
(This article belongs to the Special Issue Research on Heterogeneous Catalysis)
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15 pages, 3335 KiB  
Article
Pd-Catalyzed Hirao P–C Coupling Reactions with Dihalogenobenzenes without the Usual P-Ligands under MW Conditions
by Bianka Huszár, Petra Regina Varga, Nóra Á. Szűcs, András Simon, László Drahos and György Keglevich
Catalysts 2022, 12(10), 1080; https://doi.org/10.3390/catal12101080 - 20 Sep 2022
Cited by 2 | Viewed by 2195
Abstract
A literature survey of the P–C coupling reactions of 1,4-and 1,2-bromo-iodobenzenes with diphenylphosphine oxide or diethyl phosphite under different conditions comprising Pd-, Ni-, or Cu-catalysis revealed that, depending on the experimental details, the yields of the corresponding >P(O)-bromobenzenes were rather diverse and occasionally [...] Read more.
A literature survey of the P–C coupling reactions of 1,4-and 1,2-bromo-iodobenzenes with diphenylphosphine oxide or diethyl phosphite under different conditions comprising Pd-, Ni-, or Cu-catalysis revealed that, depending on the experimental details, the yields of the corresponding >P(O)-bromobenzenes were rather diverse and occasionally contradicting. Therefore, the reactivity of a series of 1,4-, 1,3- and 1,2-dibromo- and bromo-iodobenzenes with the above mentioned P-reagents was evaluated under the “P-ligand-free” microwave (MW)-assisted conditions elaborated by us. Starting from dibromobenzenes and iodo-bromoarenes, practical and competent syntheses were developed for phosphonoyl- and phosphinoyl-bromoarenes, and, in a few instances, for arenes with two P-functions. The cheaper dibromobenzenes may be substituted for the bromo-iodo derivatives. In all, 12 products were prepared in yields of 45–82%. They were fully characterized. The method described does not require the use of traditional P-ligands. Full article
(This article belongs to the Special Issue Catalysis in Heterocyclic and Organometallic Synthesis II)
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5 pages, 1849 KiB  
Proceeding Paper
Microwave-Assisted Synthesis of Aryl Phosphonates and Tertiary Phosphine Oxides by the Hirao Reaction
by Bianka Huszár, Zoltán Mucsi and György Keglevich
Chem. Proc. 2022, 8(1), 79; https://doi.org/10.3390/ecsoc-25-11697 - 15 Nov 2021
Viewed by 1201
Abstract
Our group described a green, “P-ligand-free”, Pd(OAc)2- or NiCl2-catalyzed synthesis under MW conditions. The reactivity of a few aryl derivatives in the Pd(OAc)2-catalyzed, “P-ligand-free” P–C coupling reactions under MW condition was also studied. An induction period was [...] Read more.
Our group described a green, “P-ligand-free”, Pd(OAc)2- or NiCl2-catalyzed synthesis under MW conditions. The reactivity of a few aryl derivatives in the Pd(OAc)2-catalyzed, “P-ligand-free” P–C coupling reactions under MW condition was also studied. An induction period was observed. Finally, the less known copper(I)-promoted reactions were investigated experimentally. The mechanism was explored by quantum chemical calculations. Full article
(This article belongs to the Proceedings of The 25th International Electronic Conference on Synthetic Organic Chemistry)
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16 pages, 3156 KiB  
Article
MW-Promoted Cu(I)-Catalyzed P–C Coupling Reactions without the Addition of Conventional Ligands; an Experimental and a Theoretical Study
by Bianka Huszár, Réka Henyecz, Zoltán Mucsi and György Keglevich
Catalysts 2021, 11(8), 933; https://doi.org/10.3390/catal11080933 - 30 Jul 2021
Cited by 8 | Viewed by 2758
Abstract
An experimental and a theoretical study on the so far less investigated Cu(I) salt-catalyzed Hirao reaction of iodobenzene and diarylphosphine oxides (DAPOs) revealed that Cu(I)Br or Cu(I)Cl is the most efficient catalyst under microwave irradiation. The optimum conditions included 165 °C and a [...] Read more.
An experimental and a theoretical study on the so far less investigated Cu(I) salt-catalyzed Hirao reaction of iodobenzene and diarylphosphine oxides (DAPOs) revealed that Cu(I)Br or Cu(I)Cl is the most efficient catalyst under microwave irradiation. The optimum conditions included 165 °C and a 1:2 molar ratio for DAPOs and triethylamine. The possible ligations of Cu(I) were studied in detail. Bisligated P---Cu(I)---P (A), P---Cu(I)---N (B) and N---Cu(I)---N (C) complexes were considered as the catalysts. Calculations on the mechanism suggested that complexes A and B may catalyze the P–C coupling, but the latter one is more advantageous both according to experiments and calculations pointing out the Cu(I) → Cu(III) conversion in the oxidative addition step. The P–C coupling cannot take place with PhBr, as in this case, the catalyst complex cannot be regenerated. Full article
(This article belongs to the Special Issue Catalytic Process Intensification for Green Chemistry)
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23 pages, 6774 KiB  
Review
Microwaves as “Co-Catalysts” or as Substitute for Catalysts in Organophosphorus Chemistry
by György Keglevich
Molecules 2021, 26(4), 1196; https://doi.org/10.3390/molecules26041196 - 23 Feb 2021
Cited by 10 | Viewed by 3306
Abstract
The purpose of this review is to summarize the importance of microwave (MW) irradiation as a kind of catalyst in organophosphorus chemistry. Slow or reluctant reactions, such as the Diels-Alder cycloaddition or an inverse-Wittig type reaction, may be performed efficiently under MW irradiation. [...] Read more.
The purpose of this review is to summarize the importance of microwave (MW) irradiation as a kind of catalyst in organophosphorus chemistry. Slow or reluctant reactions, such as the Diels-Alder cycloaddition or an inverse-Wittig type reaction, may be performed efficiently under MW irradiation. The direct esterification of phosphinic and phosphonic acids, which is practically impossible on conventional heating, may be realized under MW conditions. Ionic liquid additives may promote further esterifications. The opposite reaction, the hydrolysis of P-esters, has also relevance among the MW-assisted transformations. A typical case is when the catalysts are substituted by MWs, which is exemplified by the reduction of phosphine oxides, and by the Kabachnik–Fields condensation affording α-aminophosphonic derivatives. Finally, the Hirao P–C coupling reaction may serve as an example, when the catalyst may be simplified under MW conditions. All of the examples discussed fulfill the expectations of green chemistry. Full article
(This article belongs to the Special Issue Catalysts for a Green Chemistry: A Themed Issue Honoring Professor Roger Sheldon for His Contribution in the Field of the Green Chemistry with the Introduction of the E Factor)
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14 pages, 3047 KiB  
Review
Focusing on the Catalysts of the Pd- and Ni-Catalyzed Hirao Reactions
by György Keglevich, Réka Henyecz and Zoltán Mucsi
Molecules 2020, 25(17), 3897; https://doi.org/10.3390/molecules25173897 - 26 Aug 2020
Cited by 17 | Viewed by 4499
Abstract
The Hirao reaction involving the phosphinoylation or phosphonation of aryl halides by >P(O)H reagents is a P–C bond forming transformation belonging to the recently very hot topic of cross-couplings. The Pd- or Ni-catalyzed variations take place via the usual cycle including oxidative addition, [...] Read more.
The Hirao reaction involving the phosphinoylation or phosphonation of aryl halides by >P(O)H reagents is a P–C bond forming transformation belonging to the recently very hot topic of cross-couplings. The Pd- or Ni-catalyzed variations take place via the usual cycle including oxidative addition, ligand exchange, and reductive elimination. However, according to the literature, the nature of the transition metal catalysts is not unambiguous. In this feature article, the catalysts described for the Pd(OAc)2-promoted cases are summarized, and it is concluded that the “(HOY2P)2Pd(0)” species (Y = aryl, alkoxy) is the real catalyst. In our model, the excess of the >P(O)H reagent served as the P-ligand. During the less studied Ni(II)-catalyzed instances the “(HOY2P)(−OY2P)Ni(II)Cl−” form was found to enter the catalytic cycle. The newest conclusions involving the exact structure of the catalysts, and the mechanism for their formation explored by us were supported by our earlier experimental data and theoretical calculations. Full article
(This article belongs to the Special Issue Synthesis and Structure of Heterocyclic and Organometallic Compounds)
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