Organophosphates as Versatile Substrates in Organic Synthesis

This review summarizes the applications of organophosphates in organic synthesis. After a brief introduction, it discusses cross-coupling reactions, including both transition-metal-catalyzed and transition-metal-free substitution reactions. Subsequently, oxidation and reduction reactions are described. In addition, this review highlights the applications of organophosphates in the synthesis of natural compounds, demonstrating their versatility and importance in modern synthetic chemistry.

Mechanically Robust Hybrid Gel Beads Loaded with "Naked" Palladium Nanoparticles as Efficient, Reusable, and Sustainable Catalysts for the Suzuki-Miyaura Reaction

The increase in demand for Pd and its low abundance pose a significant threat to its future availability, rendering research into more sustainable Pd-based technologies essential. Herein, we report Pd scavenging mechanically robust hybrid gel beads composed of agarose, a polymer gelator (PG), and an active low-molecular-weight gelator (LMWG) based on 1,3:2,4-dibenzylidenesorbitol (DBS), DBS-CONHNH ₂ . The robustness of the PG and the ability of the LMWG to reduce Pd(II) in situ to generate naked Pd(0) nanoparticles (PdNPs) combine within these gel beads to give them potential as practical catalysts for Suzuki-Miyaura cross-coupling reactions. The optimized gel beads demonstrate good reusability, green metrics, and most importantly the ability to sustain stirring, improving reaction times and energy consumption compared to previous examples. In contrast to previous reports, the leaching of palladium from these next-generation beads is almost completely eliminated. Additionally, for the first time, a detailed investigation of these Pd-loaded gel beads explains precisely how the nanoparticles are formed in situ without a stabilizing ligand. Further, detailed catalytic investigations demonstrate that catalysis occurs within the gel beads. Hence, these beads can essentially be considered as robust "nonligated" heterogeneous PdNP catalysts. Given the challenges in developing ligand-free, naked Pd nanoparticles as stable catalysts, these gel beads may have future potential for the development of easily used systems to perform chemical reactions in "kit" form.

Suzuki C-C Coupling in Paper Spray Ionization: Microsynthesis of Biaryls and High-Sensitivity MS Detection of Aryl Bromides

Suzuki-Miyaura cross-coupling is one of the most powerful strategies for constructing biaryl compounds. However, classic Suzuki-Miyaura coupling suffers from hour-scale reaction time and competitive protodeboronation. To address these problems, a mild nonaqueous potassium trimethylsilanolate (TMSOK)-assisted Suzuki-Miyaura coupling strategy was designed for the microsynthesis of biaryls in paper spray ionization (PSI). Due to the acceleration power facilitated by microdroplet chemistry in reactive PSI, the microsynthesis of biaryls by reactive PSI was accomplished within minutes with comparable yields to the bulk, showing good substrate applicability from 32 Suzuki-Miyaura reactions of aryl bromides and aryl boronic acid/borates bearing different substituents. Based on the above TMSOK-assisted Suzuki-Miyaura coupling strategy, we further developed a high-sensitivity and selective PSI mass spectrometry (MS) method for quantitative analysis of aryl bromides, a class of environmentally persistent organic pollutants that cannot be directly detected by ambient mass spectrometry due to their low ionization efficiency. In situ derivatization of aryl bromides was achieved with aryl borates bearing quaternary ammonium groups in PSI. The proposed PSI-MS method shows good linearity over the 0.01-10 μmol L^-1 range with low detection limits of 1.8-4.8 nmol L^-1 as well as good applicability to the rapid determination of six aryl bromides in three environmental water samples. The proposed PSI-MS method also shows good applicability to brominated flame retardants (polybrominated diphenyls/diphenyl esters). Overall, this study provides a simple, rapid, low-cost, high-sensitivity, and high-selectivity strategy for trace aryl bromides and other brominated pollutants in real samples with minimal/no sample pretreatment.

Aqueous Suzuki couplings mediated by a hydrophobic catalyst

The catalytic activity of [(Ph₂P-o-C₆H₄)₂N]PdCl in aerobic aqueous Suzuki couplings is described. Though hydrophobic, this molecular catalyst is competent in cross-coupling reactions of arylboronic acids with a variety of electronically activated, unactivated, and deactivated aryl iodides, bromides, and chlorides upon heating in aqueous solutions under aerobic conditions to give biphenyl derivatives without the necessity of amphiphiles even in the presence of an excess amount of mercury.

Appealing Renewable Materials in Green Chemistry

In just a few years, chemists have significantly changed their approach to the synthesis of organic molecules in the laboratory and industry. Researchers are encouraged to approach “greener” reagents, solvents, and methodologies, to go hand in hand with the world’s environmental matter, such as water, soil, and air pollution. The employment of plant and animal derivates that are commonly regarded as “waste material” has paved the way for the development of new green strategies. In this review, the most important innovations in this field have been highlighted, paying due attention to those materials that have played a crucial role in organic reactions: wool, silk, and feather. Moreover, we decided to focus on the other most important supports and catalysts in green syntheses, such as proteins and their derivates. Different materials have shown prominent activity in the adsorption of metals and organic dyes, which has constituted a relevant scope in the last two decades. We intend to furnish a complete screening of the application given to these materials and contribute to their potential future utilization.

An Active Catalyst System Based on Pd (0) and a Phosphine-Based Bulky Ligand for the Synthesis of Thiophene-Containing Conjugated Polymers

To address the limitations of conventional Pd catalysts in the polymerization of thiophene-containing conjugated polymers, an active catalyst system based on Pd (0) and a phosphine-based bulky ligand, L1, is explored systematically in Suzuki–Miyaura polymerizations using thiophene boronic acid pinacol ester as one of the monomers. This active catalyst is found very efficient in synthesizing a series of thiophene-containing linear and hyperbranched conjugated polymers. First, as a model example, coupling reactions between electron-rich/moderately hindered aryl or thienyl halides and thiophene boronic acid pinacol ester give excellent yields with lower catalyst loading and can be completed in a shorter reaction time relative to Pd(PPh₃)₄. Notably, high molecular weight thiophene-containing polymers are successfully synthesized by Suzuki–Miyaura polycondensation of 2,5-thiophene bis(boronic acid) derivatives with different dibromo- and triple bromo-substituted aromatics in 5–15 min.

Immobilized Palladium Nanoparticles on Phosphanamine-grafted Cellulose for Arylation of Uracil

Background:

The synthesis of 5-arylation uracil nucleosides is an imperative challenge, especially for the method of Suzuki reaction using N-unprotected uracil as materials, which holds the potential to enhance the yield.

Objective:

The objective of the study was to find a more efficient catalyst to increase the yield of aryluracils and aryluridines.

Methods:

We first constructed the phosphanamine-grafted cellulose (PAGC) from cellulose material. Then, we prepared the nanocatalyst PAGC/Pd(0) through heating and reducing the mixture of PAGC and Pa(OAc)2.

Results:

When using this nanocatalyst to catalyze the Suzuki reaction of 5-iodouracil or 5-iodouridine and aryl heterocyclic boronic acids, the arylation yields have been significantly improved.

Conclusion:

This means that the resultant nanocatalyst exhibits a remarkable catalytic efficacy for Suzuki arylation of 5-iodouracil and 5-iodouridine.

A magnetically retrievable mixed-valent Fe3O4@SiO2/Pd0/PdII nanocomposite exhibiting facile tandem Suzuki coupling/transfer hydrogenation reaction

Herein, we report a magnetically retrievable mixed-valent Fe3O4@SiO2/Pd0/PdIINP (5) nanocomposite system for tandem Suzuki coupling/transfer hydrogenation reaction. The nanocomposite 5 was prepared first by making a layer of [Formula: see text] on [Formula: see text] followed by deposition of [Formula: see text] and sorption of [Formula: see text] ions successively onto the surface of Fe3O4@SiO2NP. The nanocomposite was characterized by powder XRD, electron microscopy (SEM-EDS and TEM-EDS) and XPS spectroscopy techniques. The mixed-valent [Formula: see text] present onto the surface of nanocomposite 5 was confirmed by XPS technique. Interestingly, the mixed-valent nanocomposite Fe3O4@SiO2/Pd0/PdIINP (5) exhibited tandem Suzuki coupling/transfer hydrogenation reaction during the reaction of aryl bromide with aryl boronic acid (90% of C). The nanocomposite 5 displayed much better reactivity as compared to the monovalent Fe3O4@SiO2/Pd0NP (3) (25% of C) and Fe3O4@SiO2/PdIINP (4) (15% of C) nanocomposites. Further, because of the presence of magnetic [Formula: see text], the nanocomposite displayed its facile separation from the reaction mixture and reused at least for five catalytic cycles.

Porous Organic Polymers Containing Active Metal Centers for Suzuki-Miyaura Heterocoupling Reactions

A new generation of confined palladium(II) catalysts covalently attached inside of porous organic polymers (POPs) has been attained. The synthetic approach employed was straightforward, and there was no prerequisite for making any modification of the precursor polymer. First, POP-based catalytic supports were obtained by reacting one symmetric trifunctional aromatic monomer (1,3,5-triphenylbenzene) with two ketones having electron-withdrawing groups (4,5-diazafluoren-9-one, DAFO, and isatin) in superacidic media. The homopolymers and copolymers were made using stoichiometric ratios between the functional groups, and they were obtained with quantitative yields after the optimization of reaction conditions. Moreover, the number of chelating groups (bipyridine moieties) available to bind Pd(II) ions to the catalyst supports was modified using different DAFO/isatin ratios. The resulting amorphous polymers and copolymers showed high thermal stability, above 500 °C, and moderate-high specific surface areas (from 760 to 935 m² g^-1), with high microporosity contribution (from 64 to 77%). Next, POP-supported Pd(II) catalysts were obtained by simple immersion of the catalyst supports in a palladium(II) acetate solution, observing that the metal content was similar to that theoretically expected according to the amount of bipyridine groups present. The catalytic activity of these heterogeneous catalysts was explored for the synthesis of biphenyl and terphenyl compounds, via the Suzuki-Miyaura cross-coupling reaction using a green solvent (ethanol/water), low palladium loads, and aerobic conditions. The findings showed excellent catalytic activity with quantitative product yields. Additionally, the recyclability of the catalysts, by simply washing it with ethanol, was excellent, with a sp²-sp² coupling yield higher than 95% after five cycles of use. Finally, the feasibility of these catalysts to be employed in tangible organic reactions was assessed. Thus, the synthesis of a bulky compound, 4,4'-dimethoxy-5'-tert-butyl-m-terphenylene, which is a precursor of a thermal rearrangement monomer, was scaled-up to 2 g, with high conversion and 96% yield of the pure product.

Polyvinylpyridine-Supported Palladium Nanoparticles: An Efficient Catalyst for Suzuki–Miyaura Coupling Reactions

Palladium nanoparticles (Pd NPs) synthesized by the metal vapor synthesis technique were supported on poly(4-vinylpyridine) 2% cross-linked with divinylbenzene (Pd/PVPy). Transmission electron microscopy revealed the presence of small metal nanoparticles (dm = 2.9 nm) highly dispersed on the PVPy. The Pd/PVPy system showed high catalytic efficiency in Suzuki-Miyaura carbon–carbon coupling reactions of both non-activated and deactivated aromatic iodides and bromides with aryl boronic acids, carried out under an air atmosphere. The high turnover of the catalyst and the ability of the PVPy resin to retain active Pd species are highlighted. By comparing the catalytic performances of Pd/PVPy with those observed by using commercially available Pd-based supported catalysts, the reported system showed higher selectivity and lower Pd leaching.

Pd Nanocatalyst Adorned on Magnetic Chitosan@N-Heterocyclic Carbene: Eco-Compatible Suzuki Cross-Coupling Reaction

A novel magnetic-functionalized-multi-walled carbon nanotubes@chitosan N-heterocyclic carbene-palladium (M-f-MWCNTs@chitosan-NHC-Pd) nanocatalyst is developed in two steps. The first step entails the fabrication of a three-component cross-linking of chitosan utilizing the Debus-Radziszewski imidazole approach. The second step comprised the covalent grafting of prepared cross-linked chitosan to the outer walls of magnetically functionalized MWCNTs (M-f-MWCNTs) followed by introducing PdCl₂ to generate the m-f-MWCNTs@cross-linked chitosan with a novel NHC ligand. The repeated units of the amino group in the chitosan polymer chain provide the synthesis of several imidazole units which also increase the number of Pd linkers thus leading to higher catalyst efficiency. The evaluation of catalytic activity was examined in the expeditious synthesis of biaryl compounds using the Suzuki cross-coupling reaction of various aryl halides and aryl boronic acids; ensuing results show the general applicability of nanocatalyst with superior conversion reaction yields, high turnover frequencies (TOFs) and turnover numbers (TON). Meanwhile, nanocatalyst showed admirable potential in reusability tests, being recycled for five runs without losing significant activities under optimum reaction conditions. The successfully synthesis of catalyst and its characterization was confirmed using the Fourier transform infrared spectrometer (FT-IR), spectrometer transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photo-electron spectroscopy (XPS) and thermogravimetric analysis (TGA).