Stille Coupling Research Articles

Effect of nitrated benzothiazole units on electro-optic properties of donor-acceptor monomers and their polymers

Donor-acceptor (D-A) method is an effective strategy to synthesize high-performance conjugated polymers. In this work, a series of D-A pentameric hybrid monomers with EDOT as donor unit and nitrated benzothiazole as acceptor unit have been successfully synthesized by Stille coupling reaction (EDOT-Th-BT, EDOT-Th-NO2-BT and EDOT-Th-2NO2-BT). The effects of nitro groups on the electrochemical and electronic properties of the monomers and their corresponding polymers were systematically investigated by optical, CV, and spectroelectrochemistry techniques. As the number of nitro group increase, the electronic spectra were red-shifted for the mono-nitrated polymer but blue-shifted for the di-nitrated polymers, while the fluorescence quantum yield were stepwise reduced (from 0.64 to 0.02) and the oxidation peaks were positively shifted. The porous structure of the nitrated polymer film was very beneficial for their good redox behavior and favorable electrochemical stability. As a result, all of them exhibited favorable electrochromic properties, including fast switching time (0.74 s for oxidation and 0.4 s for reduction of P(EDOT-Th-2NO2-BT)), optical contrast up to 23.3 %, high coloration efficiency up to 129 C−1 cm2, and multi-color electrochromic property from brown to cyan, providing a new possibility for the preparation of nitrated polymers-based NIR electrochromic devices.

Meso carbazole linked Bis-BODIPYs: Design, synthesis, structures and properties

In the present study, BODIPY 4 bearing carbazole ring system at meso position was successfully synthesized as a key building block by the acid-catalyzed condensation reaction of 6-bromo-9-ethyl-9H-carbazole-3-carbaldehyde 3 with 2,4-dimethylpyrrole in one step. The Suzuki and Stille coupling synthetic strategies were subsequently applied to the compound 4 for the construction of a new class of bis-BODIPYs 5 and 6 with extended π-conjugation by introducing phenyl and bithiophene as linkers between two N-ethylcarbazole units. The structures of novel compounds 4–6 were identified by mass, 1H and 13C NMR spectroscopy along with single crystal X-ray diffraction techniques. The photo-physical features of the targeted BODIPYs were investigated via absorption and fluorescence spectroscopies in solvents with different polarity. Photophysical studies reveal important transitions between carbazole and BODIPYs in solution state, which could be controlled by solvent polarity. Crystal geometry of the molecules and the optical band gaps were supported by DFT calculations. Electrochemical and in situ spectroelectrochemical properties of the synthesized compounds were also investigated to reveal electropolymerizable properties and electrochromic potentials of the targeted materials. The results suggested that the compounds 5 and 6 can be potentially used as useful materials in a range of electrochemical research areas.

Rational Design of Novel Conjugated Terpolymers Based on Diketopyrrolopyrrole and Their Applications to Organic Thin-Film Transistors.

Organic polymer semiconductor materials, due to their good chemical modifiability, can be easily tuned by rational molecular structure design to modulate their material properties, which, in turn, affects the device performance. Here, we designed and synthesized a series of materials based on terpolymer structures and applied them to organic thin-film transistor (OTFT) device applications. The four polymers, obtained by polymerization of three monomers relying on the Stille coupling reaction, shared comparable molecular weights, with the main structural difference being the ratio of the thiazole component to the fluorinated thiophene (Tz/FS). The conjugated polymers exhibited similar energy levels and thermal stability; however, their photochemical and crystalline properties were distinctly different, leading to significantly varied mobility behavior. Materials with a Tz/FS ratio of 50:50 showed the highest electron mobility, up to 0.69 cm2 V-1 s-1. Our investigation reveals the fundamental relationship between the structure and properties of materials and provides a basis for the design of semiconductor materials with higher carrier mobility.

Donor-Acceptor-Based Organic Polymer Semiconductor Materials to Achieve High Hole Mobility in Organic Field-Effect Transistors.

Organic polymer semiconductor materials are conveniently tuned to energy levels because of their good chemically modifiable properties, thus enhancing their carrier transport capabilities. Here, we have designed and prepared a polymer with a donor-acceptor structure and tested its potential as a p-type material for organic field-effect transistor (OFET) applications using a solution-processing method. The conjugated polymers, obtained via the polymerization of the two monomers relying on the Stille coupling reaction, possess extremely high molecular weights and thermodynamic stability. Theoretical-based calculations show that PDPP-2S-Se has superior planarity, which is favorable for carrier transport within the main chain. Photophysical and electrochemical measurements systematically investigated the properties of the material and the energy levels with respect to the theoretical values. The maximum hole mobility of the PDPP-2S-Se-based OFET device is 0.59 cm2 V-1 s-1, which makes it a useful material for potential organic electronics applications.

Semi-Synthesis of (+)-Digitoxigenin from Androstenedione

AbstractAn efficient stereoselective semi-synthesis of (+)-digitoxigenin has been achieved by a nine-step sequence with a 20.4% overall yield. The key features of the synthesis include a Saegusa–Ito oxidation reaction, a direct C14β-hydroxylation, and a Stille cross-coupling.

Palladium Nanoparticles Supported on Porous Silica Materials as Heterogeneous Catalysts of C−C Coupling and Cross‐Coupling Reactions

AbstractNoble metal nanoparticles supported on porous silica materials represent an important class of heterogeneous catalysts. Recently, a remarkable progress has been made concerning the synthesis, characterization, and catalytic application of noble metal nanoparticles immobilized on zeolites and mesoporous silica‐based materials. Various synthesis strategies have been developed, including the application of ligand‐assisted metal precursors, multistep synthesis procedures, post‐synthetic modifications, and magnetic mesoporous silica particles. Emphasis has been laid on the introduction of green procedures, based on the utilization of environmentally friendly solvents, efficient stabilizing agents, non‐toxic reagents, and mild reaction conditions. Palladium nanoparticles have long been recognized as the most efficient catalysts in a wide range of organic transformations, including the Heck, Suzuki, Stille, and Sonogashira reactions. Although these transformations have been extensively investigated in homogeneous catalytic systems, the application of heterogeneous catalysts, including silica‐supported Pd0 nanoparticles, has gained in increasing importance. This may be due to the easy handling and recovery of the latter catalysts, which facilitates their repeated applications. The aim of this review is to provide an outlook on the current research progress achieved on the development of novel synthetic procedures, affording highly dispersed Pd0 nanoparticles immobilized on porous silica materials, which proved to be efficient and recyclable catalysts in C−C coupling and cross‐coupling reactions. The focus of this review is on results published in the last six years with a handful of examples in previous years.

Total Synthesis of UCS1025A via Tandem Carbonylative Stille Cross Coupling and Diels‐Alder Reaction†

Comprehensive SummaryWe report an efficient and convergent strategy for the total synthesis of UCS1025A and its diastereomer tetra‐epi‐UCS1025A. UCS1025A is a representative member of the naturally occurring pyrrolizidinone polyketides, from which members with potent antibacterial, antifungal, and anticancer activities have been identified. Our approach features a tandem carbonylative Stille cross coupling and Diels‐Alder reaction to forge a key C—C bond and build the trans‐decalin system. This tandem process utilizes carbon monoxide as a one‐carbon linchpin to stitch a vinyl triflate and a vinylstannane together and form the desired enone moiety for the subsequent intramolecular Diels‐Alder cyclization. Our synthesis also provides a versatile approach for the synthesis of other related pyrrolizidinone‐containing polyketides.

Facile, Versatile and Stepwise Synthesis of High‐Performance Oligomer Acceptors for Stable Organic Solar Cells

AbstractOligomer acceptors have recently emerged as promising photovoltaic materials for achieving high power conversion efficiency (PCE) and long‐term stability in organic solar cells (OSCs). However, the limited availability of diverse acceptors, resulting from the sole synthetic approach, has hindered their potential for future industrialization. In this study, we present a facile and effective stepwise approach that utilizes two consecutive Stille coupling reactions for the synthesis of oligomer acceptors. To demonstrate the feasibility of the novel approach, we successfully synthesize a trimer acceptor, Tri‐Y6‐OD, and further systematically investigate the impact of oligomerization on device performance and stability. The results reveal that this approach has significant advantages compared to the conventional method, including reduced formation of unwanted by‐products and lower difficulties in purification. Remarkably, the OSC based on PM6 : Tri‐Y6‐OD achieves an impressive PCE of 18.03 % and maintains 80 % of the initial PCE (T80) for 1523 h under illumination, surpassing the performance of the corresponding small molecule acceptor Y6‐OD‐based device. Furthermore, the versatility of the synthetic strategy in obtaining diverse acceptors is further demonstrated. Overall, our findings provide a facile, versatile and stepwise way for synthesizing oligomer acceptors, thereby facilitating the development of stable and efficient OSCs.

Facile, versatile and stepwise synthesis of high-performance oligomer acceptors for stable organic solar cells.

Oligomer acceptors haverecently emerged aspromising photovoltaic materialsfor achieving high power conversion efficiency (PCE) and long-term stability in organic solar cells (OSCs). However, the limited availability of diverse acceptors, resulting from the sole synthetic approach, has hindered their potential for future industrialization.In this study, we present a facile and effective stepwise approach that utilizes two consecutive Stille coupling reactions for the synthesis of oligomer acceptors. To demonstrate the feasibility of the novel approach, we successfully synthesize a trimer acceptor, Tri-Y6-OD, and further systematically investigate the impact of oligomerization on device performance and stability. The result reveals that this approach has significant advantages compared to the conventional method, such as reduced formation of unwanted by-products and lower difficulties in purification. Remarkably, the OSC based on PM6:Tri-Y6-OD achieves an impressive PCE of 18.03% and maintains 80% of the initial PCE (T80) for 1523h under illumination, surpassing the performance of the corresponding small molecule acceptor Y6-OD-based device. Furthermore, the versatility of the synthetic strategy in obtaining diverse acceptors is further demonstrated. Overall, our findings provide afacile, versatile and stepwisewayfor synthesizingoligomeric acceptors, thereby facilitating the development of stable and efficient OSCs.

Synergistic Use of All-Acceptor Strategies for the Preparation of an Organic Semiconductor and the Realization of High Electron Transport Properties in Organic Field-Effect Transistors.

The development of n-type organic semiconductor materials for transporting electrons as part of logic circuits is equally important to the development of p-type materials for transporting holes. Currently, progress in research on n-type materials is relatively backward, and the number of polymers with high electron mobility is limited. As the core component of the organic field-effect transistor (OFET), the rational design and judicious selection of the structure of organic semiconductor materials are crucial to enhance the performance of devices. A novel conjugated copolymer with an all-acceptor structure was synthesized based on an effective chemical structure modification and design strategy. PDPPTT-2Tz was obtained by the Stille coupling of the DPPTT monomer with 2Tz-SnMe3, which features high molecular weight and thermal stability. The low-lying lowest unoccupied molecular orbital (LUMO) energy level of the copolymer was attributed to the introduction of electron-deficient bithiazole. DFT calculations revealed that this material is highly planar. The effect of modulation from a donor-acceptor to acceptor-acceptor structure on the improvement of electron mobility was significant, which showed a maximum value of 1.29 cm2 V-1 s-1 and an average value of 0.81 cm2 V-1 s-1 for electron mobility in BGBC-based OFET devices. Our results demonstrate that DPP-based polymers can be used not only as excellent p-type materials but also as promising n-type materials.

The Total Synthesis of Mollanol A by a Convergent Strategy

AbstractHere, we briefly highlight our 15-step total synthesis of mollanol A, the first isolated member of the mollane-type grayanoids, which relied on a convergent strategy. A Stille coupling and a vinylogous aldol reaction/intramolecular oxa-Michael addition sequence were used to assemble the two fragments that featured most of the important chiral centers and nearly all the essential oxidation states of the natural product. The bicyclo[3.2.1]octane fragment was synthesized by using an InCl3-catalyzed Conia–ene cyclization reaction. The challenging tetrasubstituted alkene was constructed through a 1,4-reduction of the conjugated alkenes at a late stage.1 Introduction2 Total Synthesis of Mollanol A3 Conclusion

Modular-Approach Synthesis of Giant Molecule Acceptors via Lewis-Acid-Catalyzed Knoevenagel Condensation for Stable Polymer Solar Cells.

The operational stability of polymer solar cells is a critical concern with respect to the thermodynamic relaxation of acceptor-donor-acceptor (A-D-A) or A-DA'D-A structured small molecule acceptors (SMAs) within their blends with polymer donors. Giant molecule acceptors (GMAs) bearing SMAs as subunits offer a solution to this issue, while their classical synthesis via the Stille coupling suffers from low reaction efficiency and difficulty in obtaining mono-brominated SMA, rendering the approach impractical for their large-scale and low-cost preparation. In this study, we present a simple and cost-effective solution to this challenge through Lewis acid-catalyzed Knoevenagel condensation with boron trifluoride etherate (BF3∙OEt2) as catalyst. We demonstrated that the coupling of the monoaldehyde-terminated A-D-CHO unit and the methylene-based A-link-A (or its silyl enol ether counterpart) substrates can be quantitatively achieved within 30 minutes in the presence of acetic anhydride, affording a variety of GMAs connected via the flexible and conjugated linkers. The photophysical properties was fully studied, yielding a high device efficiency of over 18%. Our findings offer a promising alternative for the modular synthesis of GMAs with high yields, easier work up, and the widespread application of such methodology will undoubtedly accelerate the progress of stable polymer solar cells.

Modular‐Approach Synthesis of Giant Molecule Acceptors via Lewis‐Acid‐Catalyzed Knoevenagel Condensation for Stable Polymer Solar Cells

AbstractThe operational stability of polymer solar cells is a critical concern with respect to the thermodynamic relaxation of acceptor‐donor‐acceptor (A‐D‐A) or A‐DA'D‐A structured small‐molecule acceptors (SMAs) within their blends with polymer donors. Giant molecule acceptors (GMAs) bearing SMAs as subunits offer a solution to this issue, while their classical synthesis via the Stille coupling suffers from low reaction efficiency and difficulty in obtaining mono‐brominated SMA, rendering the approach impractical for their large‐scale and low‐cost preparation. In this study, we present a simple and cost‐effective solution to this challenge through Lewis acid‐catalyzed Knoevenagel condensation with boron trifluoride etherate (BF3 ⋅ OEt2) as catalyst. We demonstrated that the coupling of the monoaldehyde‐terminated A‐D‐CHO unit and the methylene‐based A‐link‐A (or its silyl enol ether counterpart) substrates can be quantitatively achieved within 30 minutes in the presence of acetic anhydride, affording a variety of GMAs connected via the flexible and conjugated linkers. The photophysical properties was fully studied, yielding a high device efficiency of over 18 %. Our findings offer a promising alternative for the modular synthesis of GMAs with high yields, easier work up, and the widespread application of such methodology will undoubtedly accelerate the progress of stable polymer solar cells.

Building Block Engineering toward Realizing High-Performance Electrochromic Materials and Glucose Biosensing Platform.

The molecular engineering of conjugated systems has proven to be an effective method for understanding structure-property relationships toward the advancement of optoelectronic properties and biosensing characteristics. Herein, a series of three thieno[3,4-c]pyrrole-4,6-dione (TPD)-based conjugated monomers, modified with electron-rich selenophene, 3,4-ethylenedioxythiophene (EDOT), or both building blocks (Se-TPD, EDOT-TPD, and EDOT-Se-TPD), were synthesized using Stille cross-coupling and electrochemically polymerized, and their electrochromic properties and applications in a glucose biosensing platform were explored. The influence of structural modification on electrochemical, electronic, optical, and biosensing properties was systematically investigated. The results showed that the cyclic voltammograms of EDOT-containing materials displayed a high charge capacity over a wide range of scan rates representing a quick charge propagation, making them appropriate materials for high-performance supercapacitor devices. UV-Vis studies revealed that EDOT-based materials presented wide-range absorptions, and thus low optical band gaps. These two EDOT-modified materials also exhibited superior optical contrasts and fast switching times, and further displayed multi-color properties in their neutral and fully oxidized states, enabling them to be promising materials for constructing advanced electrochromic devices. In the context of biosensing applications, a selenophene-containing polymer showed markedly lower performance, specifically in signal intensity and stability, which was attributed to the improper localization of biomolecules on the polymer surface. Overall, we demonstrated that relatively small changes in the structure had a significant impact on both optoelectronic and biosensing properties for TPD-based donor-acceptor polymers.

Synthesis of novel fluorobenzene-thiophene hybrid polymer for high-performance electrochromic devices

Electrochromic devices based on high-performance polymer materials with exceptional optical contrast, superior cycling stability, and large coloration efficiency are critical for the advancement of electrochromics, and have the potential to innovate a broad range of applications, including flexible displays and wearable electronics. Here, we design and synthesize three precursors of fluorobenzene-3-methylthiophene D-A-D type polymers through one-step Stille coupling, and then prepare the corresponding polymer films with good electrochemical and electrochromic properties via low-potential electropolymerization at 0.52 V vs Ag/AgCl. Interestingly, such polymers exhibit overall high electrochromic performances during the electrochemical reaction with inversible color changes between yellow and dark blue, including high optical contrast (83% at 1050 nm), fast response time (1.4 s / 0.8 s), and long-term stability (< 2% reduction after 250 cycles). As-fabricated electrochromic devices display excellent cycling stability (< 3% optical contrast degradation after 1,000 cycles) at a low drive voltage (0.8 V). Due to these excellent electrochromic properties, d-A-D type polymers based on fluorobenzene-3-methylthiophene can be further developed for practical applications such as near-infrared camouflage and E-displays.

Design of novel organoboron small-molecule dyes based on dipolar nitrogen-boron-nitrogen unit for solution-processed photovoltaic devices

The nitrogen-boron-nitrogen (N–B–N) structure combined with strong polar B–N and B←N bonds simultaneously, opens a new window for the development of organoboron photovoltaic materials with narrow band gap and low highest occupied molecular orbital (HOMO) energy level. In this paper, two N–B–N-embedded blocks including boron dipyrromethane (BODIPY) and double B–N bridged bipyridyl (BNBP), are exploited to rationally regulate the band gap and energy level of the resulting material by virtue of their strong electron affinities. Thus, the thiophene as a weak electron-donating part is directly attached to strong electron-withdrawing BODIPY and BNBP respectively, giving much improved photoelectric properties for such simple push-pull architectures. To further improve photoelectric and thermal properties of the material, two novel extended D-π-A-π-D-type organoboron molecules namely BDPTPA and BNBPTPA, in which BODIPY and BNBP as strong electron-deficient core (A) connect strong electron-rich triphenylamine (D) via thiophene π-spacer, are synthesized by Stille reaction between BODIPY/BNBP and “π-D” segment. Therefore, BDPTPA exhibits a preferable electrochemical band gap as small as 1.36 eV close to near-infrared (NIR) region, which is one of the lowest values among the BODIPY-based small-molecule donors (SMDs). Furthermore, BNBPTPA shows stronger light absorption of up to 1.16 × 105 M−1 cm−1, deeper HOMO energy level of −5.28 eV and very excellent thermal stability (Td = 428 °C). It is mentioning that, BNBPTPA is first used as SMD material, blending with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) for solution-processed organic solar cell. Consequently, a reasonable power conversion efficiency (PCE) of 6.78% has been achieved with a satisfactory short-circuit density (Jsc) of 17.27 mA cm−2 and open-circuit voltage (Voc) of 0.87 V, which is the highest efficiency for BNBP-based SMDs so far. Our work demonstrates that a proposed molecular design and synthesis with dipolar N–B–N-containing unit and “π-D” fragment, can greatly broaden the types of new photovoltaic donor materials.

Photocatalytic H2 O2 Production by Thiophene-Coupled Benzotriazole and Anthraquinone-Based D-A-Type Polymer Nanoparticles.

In this article, the photocatalytic generation of an important solar fuel-H2 O2 -by a thiophene-coupled anthraquinone (AQ) and benzotriazole-based donor (D)-acceptor (A) polymer (PAQBTz) nanoparticles is systematically reported. The visible-light active and redox-active D-A type polymer is synthesized employing the Stille coupling polycondensation, and the nanoparticles are obtained by dispersing the PAQBTz polymer and polyvinylpyrrolidone solution, prepared in tetrahydrofuran to water. The polymer nanoparticles (PNPs) produce 1.61 and 1.36mM mg-1 hydrogen peroxide (H2 O2 ) in the acidic and neutral media, respectively, under AM1.5G simulated sunlight irradiation (λ > 420nm) with ≈2% modified Solar to Chemical Conversion (SCC) efficiency after 1h of visible light illumination in acidic condition. The results of the various experiments lay bare the different aspects governing H2 O2 production and indicate the H2 O2 synthesis through the superoxide anion-mediated and anthraquinone-mediated routes.

Total Synthesis of (–)-Naphthospironone A

Key words (–)-naphthospironone - decarboxylative radical addition - Stille coupling - aldol addition - Mukaiyama hydration

D-A Structural Oligomers Containing Benzothiadiazole or Benzophenone as Novel Multifunctional Materials for Electrochromic and Photodetector Devices.

In this study, six conjugated oligomers containing D-A structures were synthesized using the Stille coupling reaction and named PHZ1-PHZ6. All the oligomers utilized demonstrated excellent solubilities in common solvents and notable color variations in the domain of electrochromic characteristics. By designing and synthesizing two electron-donating groups modified with alkyl side chains and a common aromatic electron-donating group, as well as cross-binding them with two electron-withdrawing groups with lower molecular weights, the six oligomers presented good color-rendering efficiencies, among which PHZ4 presented the best color-rendering efficiency (283 cm2·C-1). The products also demonstrated excellent electrochemical switching-response times. PHZ5 presented the fastest coloring time (0.7 s), PHZ3 and PHZ6 presented the fastest bleaching times (2.1 s). Following 400 s of cycling activity, all the oligomers under study showed good working stabilities. Moreover, three kinds of photodetectors based on conducting oligomers were prepared, and the experimental results show that the three photodetectors have better specific detection performances and gains. These characteristics indicate that oligomers containing D-A structures are suitable for use as electrochromic and photodetector materials in the research.

Total Synthesis of Pentamycin by a Conformationally Biased Double Stille Ring Closure with a Trienyl-bis-stannane

The total synthesis of the potent polyene macrolide antibiotic pentamycin was accomplished by an expedient strategy involving a highly stereoselective assembly of the polyol segment in combination with an adventurous double Stille cross-coupling with a trienyl-bis-stannane closing the macrolactone and installing the sensitive pentaene fragment. Presumably, this remarkable linchpin insertion is enhanced by the linear hydrogen bonding skeleton of the polyol substrate. Further key features include a tailored Rychnovsky alkylation of cyanohydrin acetonides and elaborate Krische couplings to set the characteristic hydroxyl and hydroxymethyl bearing centers with excellent selectivity and yield. The total synthesis unequivocally confirms the full relative and absolute stereochemistry of this polyketide, including a previously uncertain hydroxyl bearing center.