Monthly Archives: March 2024

Reactions of Heteroallenes with Salan‐based Ti(IV) Complexes: A Joint Experimental and Computational Study

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Reactions of Heteroallenes with Salan-based Ti(IV) Complexes: A Joint Experimental and Computational Study

Salan-based Ti(IV) complexes react with t BuNCO leading to the insertion of one or two isocyanate molecules into Ti-Nsalan bonds. Conversely, the reaction of [(L*)Ti(NHMe2)2] (L*=N2O2 4−) with CO2 reveals its insertion into Ti-NHMe2 bonds. The insertion of heteroallenes into Ti−N bonds offers the possibility to use them to functionalize salan ligands or as building blocks to prepare high-value-added compounds.


Abstract

The reaction of Ti(NMe2)4 with the salan ligand precursor H2N2O2H2 led to the formation of [(L*)Ti(NHMe2)2] (L*=N2O2 4−) that forms [(H2N2O2)TiCl2] upon reaction with two equiv. of Me3SiCl. [(L*)Ti(py)2] was obtained from the reaction of [Ti(N t Bu)Cl2(py)3] with the sodium salt H2N2O2Na2. Treatment of [(L*)Ti(NHMe2)2] with two equiv. of t BuNCO led to the insertion of the isocyanate molecules into the Ti−Nsalan bonds with the formation of [{L*(N(tBu)CO)2}Ti]. Conversely, the reaction of [(H2N2O2)Ti(OiPr)2] with two equiv. of t BuNCO led to the insertion of one isocyanate molecule into a Ti−Nsalan bond with the formation of [{(HN2O2)(N( t Bu)CO)}Ti(OiPr)]. Computational studies were performed to gain insight into the reactivity of isocyanates with salan-based Ti(IV) complexes.

Solid‐State Emissive Pillar[6]arene Derivative Having Alternate Methylene and Nitrogen Bridges

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Solid-State Emissive Pillar[6]arene Derivative Having Alternate Methylene and Nitrogen Bridges

Herein, we synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridges. Owing to the charge transfer emission, the solid-state photoluminescence quantum yield (ΦPL) was enhanced compared with that of the parent pillar[6]arene (ΦPL=0.063→ΦPL=0.36). Furthermore, it displayed a turn-off sensing toward nitrobenzene (NB) vapor; a fluorescence quenching was observed when exposed to the NB vapor.


Abstract

Macrocyclic arenes show conformational adaptability, which allows host–guest complexations with the size-matched guest molecules. However, their emission properties are often poor in the solid states due to the self-absorption. Herein, we newly synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridging structures. Solvatochromic study reveals that the nitrogen-embedding into the cyclic structures can strengthen the intramolecular charge transfer (CT) nature compared to that of the linear nitrogen-bridged precursor. Owing to the large Stokes shift in the solid state, one of the nitrogen-embedded pillar[6]arenes shows high absolute photoluminescence quantum yield (ΦPL=0.36). Furthermore, it displays a turn-off sensing ability toward nitrobenzene (NB) vapor; a fluorescence quenching is observed when exposed to the NB vapor. From the structural analysis before and after the exposure of NB vapor, the amorphous nitrogen-embedded pillar[6]arene efficiently co-crystallize with NB and formed non-emissive intermolecular CT complexes with NB.

Biocatalytic and Regioselective Exchange of 2‐O‐Benzoyl for 2‐O‐(m‐Substituted)Benzoyl Groups to Make Precursors of Next‐Generation Paclitaxel Drugs

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A taxane 2-O-benzoyltransferase (mTBT, derived fromAccession #: AF297618) biocatalyzed the de-aroylation and re-aroylation of next-generation taxane precursors of drugs effective against multidrug-resistant cancer cells. Various taxanes bearing an acyl, hydroxyl, or oxo group at C13 were screened to assess their turnover by mTBT catalysis. The 13-oxotaxanes were the most productive where 2-O-debenzoylation of 13-oxobaccatin III was turned over faster compared to 13-oxo-10-O-(n-propanoyl)-10-O-deacetylbaccatin III and 13-oxo-10-O-(cyclopropane carbonyl)-10-O-deacetylbaccatin III, yielding ~20 mg of each. mTBT catalysis was likely affected by an intramolecular hydrogen bond with the C13-hydroxyl; oxidation to the 13-oxo recovered catalysis. The experimental data for the debenzoylation reaction was supported by Gaussian-accelerated molecular dynamics simulations that evaluated the conformational changes caused by different functional groups at C13 of the substrate. These findings also helped postulate where the 2-O-benzoylation reaction occurs on the paclitaxel pathway in nature. mTBT rearoylated the debenzoylated 13-oxobaccatin III acceptors fastest with a non-natural 3-fluorobenzoyl CoA among the other aroyl CoA thioesters evaluated, yielding ~10 mg of each with excellent regioselectivity at laboratory scale. Reducing the 13-oxo group to a hydroxyl yielded key modified baccatin III precursors (~10 mg at laboratory scale) of new-generation taxoids.

NIR‐II Organic Photothermal Cocrystals with Strong Charge Transfer Interaction for Flexible Wearable Heaters

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NIR-II Organic Photothermal Cocrystals with Strong Charge Transfer Interaction for Flexible Wearable Heaters

In this paper, two novel organic photothermal cocrystals (MTC and MFC) were rapidly prepared by coprecipitation method. Compared with MTC, the introduction of highly electronegative fluorine in MFC results in a stronger charge transfer interaction and a tighter crystal packing structure between MeCz and F4TCNQ. Consequently, the absorption range of MFC is extended to the NIR-II region and has a high photothermal conversion efficiency of 54.6%. At the same time, we chose MFC and flexible substrate HPDMS to combine and prepare a flexible wearable heater, which exhibited potential application value in the field of light-driven local thermotherapy.


Comprehensive Summary

The organic cocrystal strategy has provided a convenient and efficient platform for preparing organic photothermal materials. However, the rapidly directional preparation of cocrystals with desirable photothermal properties remains challenging due to a lack of suitable design ideas. Here, two new photothermal cocrystals, MTC and MFC, based on acceptor molecules (TCNQ and F4TCNQ) with different electron-withdrawing capacities were quickly prepared by the coprecipitation method, aiming to explore the effect of charge transfer (CT) interaction on photothermal properties. Compared with MTC, the stronger intermolecular CT interaction in MFC facilitates extending the absorption range (from the NIR-I to the NIR-II region) and enhancing the non-radiative transition process. Under the 808 nm laser irradiation, the photothermal conversion efficiency (PCE) of MFC is 54.6%, whereas MTC displays a mere 36.8%. The MFC cocrystal was further combined with a flexible polymer substrate (HPDMS) to prepare a flexible wearable heater (HPDMS@MFC), which exhibits excellent NIR-II photothermal performance. This work points out a research direction for the rapid assembly of efficient photothermal cocrystals and additionally provides an extensive application prospect for organic photothermal cocrystals in the field of wearable devices.

An Assembly of Pyrano[3,2‐b]indol‐2‐ones via NHC‐Catalyzed [3 + 3] Annulation of Indolin‐3‐ones with Ynals

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An Assembly of Pyrano[3,2-b]indol-2-ones via NHC-Catalyzed [3 + 3] Annulation of Indolin-3-ones with Ynals†

N-Heterocyclic carbenes (NHCs) serve as organocatalysts for the [3 + 3] annulation of readily available N-Ts indolin-3-ones with ynals in the presence of oxidant condition via an intermediate alkynyl acylazolium. The method provides pyrano[3,2-b]indol-2-ones with moderate to high yields. Further transformations lead to diverse densely-functionalized carbazoles with potential electroluminescent materials and other bioactivities.


Comprehensive Summary

We report herein an unprecedented N-heterocyclic carbene-catalyzed formal [3 + 3] annulation of ynals with N-Ts indolin-3-ones under the oxidation condition affording the functionalized pyrano[3,2-b]indol-2-ones. The alkynyl acylazoliums via the combination of a carbene with ynals in the presence of oxidate proved to be the important intermediates for the success of this transformation. This method features a broad substrate scope and mild conditions, including axially chiral skeletons with suitable substitutions.

Assessing the Intrinsic Activity of Pt‐Group Electrocatalysts for Carbon Monoxide Oxidation: Best Practices and Benchmarking Parameters

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Pt-groups are the state-of-the-art electrocatalysts for various fuel cells. However, their CO-poising is a critical hitch for large-scale applications, so the researchers are exerting huge efforts to solve this issue. However, the exponentially increasing attention in this field pressures the researchers to publish their findings quickly, which somewhat leads to unavoidable flawed evaluation parameters to reflect the intrinsic activity of electrocatalysts. The CO oxidation (COOxid) is highly sensitive to various factors. Thus, it is urgent to afford a deeper understanding of the inherent COOxid activity of state-of-the-art electrocatalysts and adopt accurate guidelines for researchers to test, optimize, and compare their electrocatalysts. This review provides exactitude in the evaluation and precise assessment of the key descriptors related to electrocatalysts (i.e., effect of both size, shape, and support) and CO oxidation (i.e., effect of electrolyte, working electrode, and CO surface diffusion). This is besides the fundamental aspects (i.e., COOxid Process, mechanism, measurements, calculations, thermodynamics, and kinetics). Various experimental results from our group and others besides in-situ analysis were provided to support our deep discussion. Finally, we provide a brief synopsis of the relevant milestones of the up-to-date challenges and perspectives.

Ionic liquid‐supported copper‐catalyzed synthesis of 2H‐indazoles under microwave irradiation

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Ionic liquid-supported copper-catalyzed synthesis of 2H-indazoles under microwave irradiation

One-pot synthesis of 2H-indazoles under microwave irradiation using an ionic liquid-supported copper-catalyst.


Abstract

Five-membered indazoles are recognized as a special scaffold having a broad spectrum of pharmacological properties among other heterocyclic compounds. New methods must be developed for the effective synthesis of 2H-indazole because of the exceptionally high biological activity of compounds containing a 2H-indazole core. We present the ionic liquid-supported copper-catalyzed one-pot synthesis of 2H-indazoles under microwave irradiation, continuing our ongoing investigation of the potential uses of bioactive compounds produced in the lab. The use of microwave and ionic liquid-supported catalyst makes this process greener and more highly energy efficient than the conventional reported methods. Overall, by forming consecutive C-N and N-N bonds with the help of an ionic liquid-supported copper catalyst, we have developed a novel green one-pot technique for the synthesis of the 2H-indazole motifs in very high yield.