Rhodium-Catalyzed Trans-Bis-Silylation Reactions of 2-Ethynyl-3-pentamethyldisilanylpyridines

Rhodium-catalyzed reactions of 2-ethynyl-3-pentamethyldisilanylpyridine derivatives (1 and 2) are reported. The reactions of compounds 1 and 2 in the presence of catalytic amounts of rhodium complexes at 110 °C gave the corresponding pyridine-fused siloles (3) and (4) through intramolecular trans-bis-silylation cyclization. The reaction of 2-bromo-3-(1,1,2,2,2-pentamethyldisilanyl)pyridine with 3-phenyl-1-propyne in the presence of PdCl₂(PPh₃)₂-CuI catalysts afforded 1:2 bis-silylation adduct 6. DFT calculations were also performed to understand the reaction mechanism for the production of compound 3 from compound 1.

A Mini Review on the Development of Conjugated Polymers: Steps towards the Commercialization of Organic Solar Cells

This review article covers the synthesis and design of conjugated polymers for carefully adjusting energy levels and energy band gap (EBG) to achieve the desired photovoltaic performance. The formation of bonds and the delocalization of electrons over conjugated chains are both explained by the molecular orbital theory (MOT). The intrinsic characteristics that classify conjugated polymers as semiconducting materials come from the EBG of organic molecules. A quinoid mesomeric structure (D-A ↔ D⁺ = A^-) forms across the major backbones of the polymer as a result of alternating donor-acceptor segments contributing to the pull-push driving force between neighboring units, resulting in a smaller optical EBG. Furthermore, one of the most crucial factors in achieving excellent performance of the polymer is improving the morphology of the active layer. In order to improve exciton diffusion, dissociation, and charge transport, the nanoscale morphology ensures nanometer phase separation between donor and acceptor components in the active layer. It was demonstrated that because of the exciton's short lifetime, only small diffusion distances (10-20 nm) are needed for all photo-generated excitons to reach the interfacial region where they can separate into free charge carriers. There is a comprehensive explanation of the architecture of organic solar cells using single layer, bilayer, and bulk heterojunction (BHJ) devices. The short circuit current density (J_sc), open circuit voltage (V_oc), and fill factor (FF) all have a significant impact on the performance of organic solar cells (OSCs). Since the BHJ concept was first proposed, significant advancement and quick configuration development of these devices have been accomplished. Due to their ability to combine great optical and electronic properties with strong thermal and chemical stability, conjugated polymers are unique semiconducting materials that are used in a wide range of applications. According to the fundamental operating theories of OSCs, unlike inorganic semiconductors such as silicon solar cells, organic photovoltaic devices are unable to produce free carrier charges (holes and electrons). To overcome the Coulombic attraction and separate the excitons into free charges in the interfacial region, organic semiconductors require an additional thermodynamic driving force. From the molecular engineering of conjugated polymers, it was discovered that the most crucial obstacles to achieving the most desirable properties are the design and synthesis of conjugated polymers toward optimal p-type materials. Along with plastic solar cells (PSCs), these materials have extended to a number of different applications such as light-emitting diodes (LEDs) and field-effect transistors (FETs). Additionally, the topics of fluorene and carbazole as donor units in conjugated polymers are covered. The Stille, Suzuki, and Sonogashira coupling reactions widely used to synthesize alternating D-A copolymers are also presented. Moreover, conjugated polymers based on anthracene that can be used in solar cells are covered.

Development of a selective fluorescence derivatization strategy for thyroid hormones based on the Sonogashira coupling reaction

A new fluorescence derivatization technique for the determination of the thyroid hormones, 3,3',5-triiodo-L-thyronine (T₃, triiodothyronine) and 3,3',5,5'-tetraiodo-L-thyronine (T₄, L-thyroxine), in human serum was developed based on the Sonogashira coupling reaction. This derivatization reaction was recently utilized by our research group as a promising solution for the derivatization of ortho-substituted aryl halides that suffer from steric hindrance. T₃ and T₄ possess amino groups that could be derivatized by many reagents; however, these reagents are not useful in the case of biological analysis as they could non-selectively react with many biogenic amines and amino acids. Thus, herein we aimed at labeling the iodo-phenyl group of T₃ and T₄ as a selective fluorescence labeling approach suitable for biological analysis. The fluorescent alkyne, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET), can label the ortho-substituted aryl halides T₃ and T₄ in the presence of palladium and copper as catalysts, overcoming the steric hindrance of ortho-substitution. Furthermore, the application of the proposed method for the selective analysis of T₃ and T₄ in biological samples was successfully performed even in the presence of numerous biological components. The formed fluorescent derivatives produced from the reaction of DIB-ET and T₃ and T₄ could be determined by an HPLC system with fluorescence detection. The proposed method was successfully applied for the selective and sensitive determination of T₃ and T₄ in human serum with detection limits (S/N = 3) of 4.0 and 6.1 ng/mL and the recovery rate in the ranges of 84.3-92.1% and 81.3-84.9%, respectively. Therefore, the proposed method could be used as a new simple tool for the simultaneous determination of T₃ and T₄ in biological samples.

Pd nanoparticles loaded on modified chitosan-Unye bentonite microcapsules: A reusable nanocatalyst for Sonogashira coupling reaction

This work investigates the preparation of a catalytic complex of palladium nanoparticles supported on novel Schiff base modified chitosan-Unye bentonite microcapsules (Pd NPs@CS-UN). The complex has been characterized by FT-IR, EDS, XRD, TEM, HRTEM, Raman, ICP-OES and elemental mapping analyses. Pd NPs@CS-UN was used as a catalyst for Sonogashira coupling reactions between aryl halides and acetylenes, employing K₂CO₃ as the base and EtOH as a green solvent under aerobic conditions in which it showed high efficacy. Pd NPs@CS-UN was regenerated by filtration after the completion of the reaction. This catalytic process has many advantages including simple methodology, high yields, and easy work-up. The catalytic performance does not notably change even after five consecutive runs.

Aggregation-induced fluorescent response of urea-bearing polyphenyleneethynylenes toward anion sensing

A π-conjugated urea-bearing phenyleneethynylene polymer (Poly-2) was rationally designed by the Sonogashira coupling condensation reaction and had been demonstrated to have a unique fluorescent quenching effect for the optical detection of all determined anions, especially for CN^-. The fluorescent emission of Poly-2 was significantly quenched upon adding CN^-, together accompanied with a continuous red shift of the emission peak from 442 to 464 nm with the cyanide concentration increased from 0 to 1.0 mM. On the contrary, its precursor polymer, Poly-1, itself also displayed fluorescent responsibility with all selected anions but had no obvious selectivity and tendency. For instance, the addition of highly basic CN^-, N₃ ^-, AcO^-, or F^- to Poly-1 solution in DMF/H₂O (v/v = 1:1) led to the photoluminescence amplification, while the addition of weakly basic anions like Cl^-, I^-, and Br^- showed a fluorescence quenching effect. Both polymers were in a seriously self-aggregated state in solution no matter in the absence or presence of an anion. Interestingly, it was found that Poly-2 exhibited an aggregation-induced emission behavior, while Poly-1 had an aggregation-caused quenching effect, based on the relationship between photoluminescence and polymer aggregation state. The structural characterizations were carried out by NMR spectroscopy and size exclusion chromatography measurements; the photoluminescence properties of Poly-1 and Poly-2 together with anion sensing properties were followed by fluorescence spectroscopy, and the relationship between photoluminescence and aggregation behavior of both polymers in solution was investigated by dynamic light scattering measurements.

The Utility of Sonogashira Coupling Reaction for the Derivatization of Aryl Halides with Fluorescent Alkyne

Aryl halides are a very important category of compounds that include many vital drugs and key industrial additives, such as clofibrate and bromobenzene, respectively. Due to their importance, our research group previously developed a novel fluorescence labeling approach for their analysis using a fluorescent aryl boronic acid as a reagent, based on the Suzuki coupling reaction. This coupling reaction was successfully applied for the determination of aryl halides in biological fluids; however, there was a limitation of low reactivity towards ortho-substituted aryl halides. In the present study, a novel fluorescence derivatization approach for aryl halides was developed using, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET) as a fluorescent alkyne reagent, based on the Sonogashira coupling reaction. DIB-ET reacted with aryl bromides in the presence of palladium and copper as catalysts, yielding fluorescent derivatives that could be subsequently determined by an HPLC system with fluorescence detection. The detection limits (S/N = 3) for aryl bromides were in the range of 14 - 23 nM, which is 3.5 - 18-times more sensitive than our previously developed approach, Suzuki coupling derivatization. Moreover, in contrast to the previous technique, the reactivity of DIB-ET to ortho-substituted aryl bromides was almost equivalent to that of the para-substituted aryl bromides. Hence, by using this newly developed approach we could label the aryl halides with more sensitivity and reactivity. Finally, the proposed method was successfully applied for the selective determination of aryl bromides in human serum with good recovery (84.6 - 107%), which proves the ability of the developed method to determine occupational exposure to aryl halides.

An easy microwave-assisted synthesis of C8-alkynyl adenine pyranonucleosides as novel cytotoxic antitumor agents

We describe the synthesis of C8-alkynyl adenine pyranonucleosides 4, 5, and 8-phenylethynyl-adenine (II), via Sonogashira cross-coupling reaction under microwave irradiation. Compounds 4e and II were less cytostatic than 5-fluorouracil (almost an order of magnitude) against murine leukemia (L1210) and human cervix carcinoma (HeLa) cells, while the same compounds proved to be more active than 5-fluorouracil against human lymphocyte (CEM) cells.