Mechanistic Insights of the Ir‐bipyridonate Catalyzed Aqueous Methanol Dehydrogenation and Transfer Dehydrogenation to Acetophenone: Experimental and DFT Study

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Mechanistic Insights of the Ir-bipyridonate Catalyzed Aqueous Methanol Dehydrogenation and Transfer Dehydrogenation to Acetophenone: Experimental and DFT Study

The mechanism of aqueous methanol dehydrogenation to yield carbon dioxide, either producing H2 in the absence of acceptor or transferring hydrogen to acetophenone to yield 1-phenylethanol, has been elucidated by a combination of DFT calculations, which includes solvating MeOH molecules, and NMR/kinetics experimental investigations.


Abstract

The mechanisms of the Cp*IrIII(bpyOO)-catalyzed (bpyOO=bidentate (NN) doubly deprotonated 2,2′-bipyridine-6,6′-diol) acceptorless methanol dehydrogenation and acetophenone transfer hydrogenation by methanol under basic conditions have been explored by the combination of 1H NMR, kinetics, and DFT computational studies. During dehydrogenation of methanol and of its dehydrogenated derivatives, the presence of two iridium hydride species (anionic [Cp*Ir(bpyOO)H]−, C* and neutral [Cp*Ir(bpyOOH)H], D*), which interconvert depending on pH, was detected. The DFT studies on a Cp model system highlighted three interrelated catalytic cycles of methanol, formaldehyde and formic acid dehydrogenation, all leading to the same hydride intermediates C and D. The dehydrogenation of methanol prefers a direct β-hydride transfer pathway from the methoxide ion to Ir, rather than the classical β-hydride elimination pathway from a coordinated methoxide ligand, but an alternative bifunctional H+/H− transfer with involvement of a ligand O atom may become competitive at lower pH. The transfer hydrogenation of acetophenone using methanol as hydrogen source features species C* as resting state, with the acetophenone reduction being rate-determining and following the reverse pathway of methanol oxidation, with a first-order acetophenone decay and a kinetic isotope effect of 2.36±0.09.

Synthesis, Structural and Redox Properties of Vanadyl β‐Cyanoporphyrin and its Utilization as Efficient Catalyst for Epoxidation of Olefins and Oxidative Bromination of Phenols

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Synthesis, Structural and Redox Properties of Vanadyl β-Cyanoporphyrin and its Utilization as Efficient Catalyst for Epoxidation of Olefins and Oxidative Bromination of Phenols

The elegant synthesis of free base 2-cyano-meso-tetraphenylporphyrin (H2TPPCN) is reported. Its vanadyl complex, [VIVOTPPCN], has been utilized as efficient and green catalyst for the bromination of various phenols in water at room temperature and epoxidation of olefins. The catalyst is recyclable and reusable.


Abstract

2-Cyano-5,10,15,20-tetraphenylporphyrin [H2TPPCN] (1) having cyano group at one of β-pyrrolic positions using nucleophilic substitution reaction of tetrabutylammonium cyanide (TBACN) on free-base 2-nitro-5,10,15,20-tetraphenylporphyrin, and its oxidovanadium(IV) complex [VIVOTPPCN] (2) were synthesized in good yields. Both the porphyrins 1 and 2 have been characterized by UV-Vis spectroscopy, mass spectrometry, and cyclic voltammetric techniques. Single crystal X-Ray crystallography revealed quasi-planar geometry for 1. Compounds 1 and 2 exhibited a red shift (λmax=7–9 nm) in the Soret band relative to [MTPP], where M=2H, VIVO owing to the electron-withdrawing effect of the cyano group at the β-position. The first oxidation (ΔE1/2=110–140 mV) and reduction potentials (ΔE1/2=220–260 mV) of 1 and 2 are anodically shifted relative to [MTPP] where M=2H, VIVO. Porphyrin 2 has been utilized as a catalyst for two reactions: epoxidation of olefins and bromination of phenols. The bromination of phenol using KBr/H2O2/HClO4 in water resulted in 100 % conversion with a TOF value as high as 19.6 s−1 in 0.5 h. Using H2O2/NaHCO3 in a CH3CN/H2O solvent mixture at 60 °C, epoxidation was carried out, and the highest conversion rate with a turnover frequency of 1.9 s−1 was achieved in the case of cyclohexene. Catalyst 2 was recovered successfully at the end of the reaction up to 5 cycles and had good thermal stability, indicating its industrial viability and applicability. Moreover, these cyano-functionalized porphyrins could be further utilized for the generation of molecular self-assemblies, post-functionalization of porphyrin core and various applications. The current findings in this work present insights for a facile approach for the synthesis of β-cyano functionalized porphyrin 1 and further shed light on the utility of its vanadyl complex 2 as an efficient catalyst for olefin epoxidation and phenol bromination reactions.

Comprehensive Photophysical and Nonlinear Spectroscopic Study of Thioanisolyl‐Picolinate Triazacyclononane Lanthanide Complexes

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Comprehensive Photophysical and Nonlinear Spectroscopic Study of Thioanisolyl-Picolinate Triazacyclononane Lanthanide Complexes

Three thioanisolyl-picolinates were incorporated with tacn in a joint macrocyclic ligand sensitising visible Eu(III) emission with 44 % quantum yield, near-infrared Yb(III) and Nd(III), and dual vis-NIR Sm(III) luminescence. Eu(III) and Sm(III) emission was achieved via one- (1 P, at 330 nm) and two-photon (2 P, at 640–710 nm) excitation.


Abstract

Detailed photophysical studies of luminescent lanthanide complexes are presented and elaborated using a newly developed thioanisolyl-picolinate antenna and the related tacn macrocyclic ligand. The new ligand proved to sensitise Nd(III), Sm(III), Eu(III) and Yb(III) emission. Eu(III) complex showed complete energy transfer, yielding high quantum yield (44 %) and brightness, while the Tb(III) analogue underwent a thermally activated back-energy transfer, resulting in a strong oxygen quenching of the triplet excited state. Transient absorption spectroscopy measurements of Gd(III), Tb(III) and Eu(III) compounds confirmed the sensitization processes upon the charge-transfer antenna excitation. The triplet excited state lifetime of the Tb(III) complex was 5-times longer than that of the Gd(III) analogue. In contrast, the triplet state was totally quenched by the energy transfer to the 4f-metal ion in the Eu(III) species. Nonlinear two-photon absorption highlighted efficient biphotonic sensitization in Eu(III) and Sm(III) complexes. In case of the Nd(III) compound, one-photon absorption in 4f–4f transitions was predominant, despite the excitation at the antenna two-photon band. This phenomenon was due to the Nd(III) 4f–4f transitions overlapping with the wavelength-doubled absorption of the complex.

Closed‐loop of Catalyzed Lactate Oxidization Synergistically Sensitizes Apoptosis and Ferroptosis for Cancer Therapy

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Closed-loop of Catalyzed Lactate Oxidization Synergistically Sensitizes Apoptosis and Ferroptosis for Cancer Therapy

Liposomes incorporated with lactate oxidase-loaded MnO2 nanoparticles (Lip-LM) was prepared. Lip-LM achieved an effective cascade catalytic oxidation of lactate through the closed-loop of self-sufficient O2 supplying. Lactate oxidation further amplified the oxidative-stress in cancer cells by producing ⋅OH and consuming GSH at the same time, synergistically increased the sensitivity of cancer cells to apoptosis and ferroptosis.


Abstract

Lactate accumulated in Tumor is a key oncometabolite and associated with various oncogenic processes, including proliferation, invasion, angiogenesis, metastasis, immunosuppression and therapeutic resistance. Particularly, lactate contributes to the apoptosis and ferroptosis resistance in cancer cells. Consequently, blockade of lactate provides a promising opportunity for cancer therapy. However, due to abnormal tumor microenvironment (TME) and intracellular glutathione (GSH) mediated ferroptosis resistance, the current approaches for regulating lactate to sensitize cells to apoptosis and ferroptosis are still challenging. Herein, we developed a catalytic lactate oxidizing liposomes (Lip-LM) incorporated with lactate oxidase (LOX)-loaded MnO2 nanoparticles. O2 regenerated from H2O2 constitute closed-loop of lactate oxidation catalyzed by LOX, enhancing the lactate-consuming efficacy in TME. Besides, glutathione is consumed by MnO2 to amplify the ferroptosis susceptibility of cancer cells. The results showed that Lip-LM achieved synergistical apoptosis and ferroptosis to enhance the anti-tumor efficacy of amplified oxidative stress in cancer cells through the strategy of self-sufficient O2 supplying and GSH consumption. The results of transcriptomics and proteomics analyses also support the synergistical anti-tumor mechanisms of Lip-LM. Hence, it is a promising catalytic nanoplatform combined lactate regulation and oxidative stress amplification and have great potential to further enhance therapeutic outcomes based on synergistical apoptosis and ferroptosis.

Total Synthesis of Laurane and Guaiane Sesquiterpenoids via Oxidative Nazarov Reaction

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Total Synthesis of Laurane and Guaiane Sesquiterpenoids via Oxidative Nazarov Reaction

We report here the concise total syntheses of four laurane-type and guaiane-type sesquiterpenoids via oxidative Nazarov reaction, using unfunctionalized TDCs as the substrates.


Comprehensive Summary

As one of the most common structural motifs in natural products, cyclopentenones usually can be fabricated by Nazarov cyclization using divinyl ketones or functionalized tertiary divinyl carbinols (TDCs) as substrates. However, straightforward method for transforming unfunctionalized TDCs to their corresponding cyclopentenones is currently lacking. Herein, we wish to report the total syntheses of four structurally distinct terpenoids, namely laurane-type marine sesquiterpenoids isolaurene, debromoaplysin and aplysin, and guaiane sesquiterpenoid guaiadienone A, all using a novel synthetic method, named oxidative Nazarov cyclization, as the key step. This work demonstrated our robust method is suitable for synthesizing various highly substituted cyclopentenones.