Presence Of Trifluoroacetic Acid Research Articles

Catalytic reduction of oxygen to water by non-heme iron complexes: exploring the effect of the secondary coordination sphere proton exchanging site.

In this study, we prepared non-heme FeIII complexes (1, 2, and 3) of an N4 donor set of ligands (H2L, Me2L, and BPh2L). 1 is supported by a monoanionic bispyridine-dioxime ligand (HL). In 2 and 3, the primary coordination sphere of Fe remained similar to that in 1, except that the oxime protons of the ligand were replaced with two methyl groups and a bridging -BPh2 moiety, respectively. X-ray structures of the FeII complexes (1a and 3a) revealed similar Fe-N distances; however, they were slightly elongated in 2a. The FeIII/FeII potential of 1, 2, and 3 appeared at -0.31 V, -0.25 V, and 0.07 V vs. Fc+/Fc, respectively, implying that HL and Me2L have comparable donor properties. However, BPh2L is more electron deficient than HL or Me2L. 1 showed electrocatalytic oxygen reduction reaction (ORR) activity in acetonitrile in the presence of trifluoroacetic acid (TFAH) as the proton source at Ecat/2 = -0.45 V and revealed selective 4e-/4H+ reduction of O2 to H2O. 1 showed an effective overpotential (ηeff) of 0.98 V and turnover frequency (TOFmax) of 1.02 × 103 s-1. Kinetic studies revealed a kcat of 2.7 × 107 M-2 s-1. Strikingly, 2 and 3 remained inactive for electrocatalytic ORR, which established the essential role of the oxime scaffolds in the electrocatalytic ORR of 1. Furthermore, a chemical ORR of 1 has been investigated using decamethylferrocene as the electron source. For 1, a similar rate equation was noted to that of the electrocatalytic pathway. A kcat of 6.07 × 104 M-2 s-1 was found chemically. Complex 2, however, underwent a very slow chemical ORR. Complex 3 chemically enhances the 4e-/4H+ reduction of O2 and exhibits a TOF of 0.24 s-1 and a kcat value of 2.47 × 102 M-1 s-1. Based on the experimental observations, we demonstrate that the oxime backbone of the ligand in 1 works as a proton exchanging site in the 4e-/4H+ reduction of O2. The study describes how the ORR is affected by the tuning of the ligand scaffold in a family of non-heme Fe complexes.

Highly Stable Amide-Functionalized Zirconium-Organic Frameworks: Synthesis, Structure, and Methane Storage Capacity.

With the development of crystalline porous materials toward methane storage, the stability issue of metal-organic framework (MOF) materials has caused great concern despite high working capacity. Considering the high stability of zirconium-based MOFs and effective functions of amide groups toward gas adsorption, herein, a series of UiO-66 type of Zr-MOFs, namely, Zr-fcu-H/F/CH3/OH, were successfully designed and synthesized by virtue of amide-functionalized dicarboxylate ligands bearing distinct side groups (i.e., -H, -F, -CH3, and -OH) and ZrCl4 in the presence of trifluoroacetic acid as the modulator. Single-crystal X-ray diffraction and topology analyses reveal that these compounds are archetypal fcu MOFs encompassing octahedral and tetrahedral cages, respectively. The N2 sorption isotherms and acid-base stability tests demonstrate that the materials possess not only relatively high surface areas, pore volumes, and appropriate pore sizes but also great hydrolytic stabilities ranging pH = 3-11. Furthermore, the volumetric methane storage working capacities of Zr-fcu-H, Zr-fcu-F, Zr-fcu-CH3, and Zr-fcu-OH at 298/273 K and 80 bar are 187/217, 175/193, 167/187, and 154/171 cm3 (STP) cm-3, respectively, which indicate that the zirconium-based crystalline porous materials are capable of storing relatively high amounts of methane.

Palladium-Catalyzed Stereocontrolled Synthesis of Aryl-C-Glycosides from Arylboronic Acids and Glycal Enones Through 1,4-Conjugate Addition Reactions

Abstract1,4-Conjugate addition of arylboronic acids to the glycal enones delivered 2-deoxy-α-aryl-C-glycosides in good yields. The reaction was catalyzed by palladium acetate in the presence of trifluoroacetic acid and 1,10-phenanthroline. A wide range of glycal enones derived from d-glucal, d-galactal, and d-rhamnal participated in the coupling reaction with different arylboronic acids smoothly. Different protecting groups including benzyl, acetyl, pivaloyl, and benzoyl were compatible under optimized conditions.

Isolation and Purification of Harpagogenin as an Nrf2-ARE Activator from the Tubers of Chinese Artichoke (Stachys sieboldii).

Chinese artichoke tuber (Stachys sieboldii Miq.) is used as an herbal medicine as well as edible food. This study examined the effect of the Chinese artichoke extracts on the nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway that induces the expression of antioxidant enzymes to explore its novel characteristics. Hot water extracts exhibited relatively high ARE activity. ARE activity was observed in two fractions when the hot water extracts were separated in the presence of trifluoroacetic acid using HPLC. Conversely, the highly active fraction disappeared when the hot water extracts were separated in the absence of trifluoroacetic acid. These results indicate that acidic degradation produces active ingredients. The structural analysis of the two active fractions identified harpagide, which is an iridoid glucoside, and harpagogenin. In vitro experiments revealed that harpagide was converted into harpagogenin under acidic conditions and that harpagogenin, but not harpagide, had potent ARE activity. Therefore, this study identified harpagogenin, which is an acid hydrolysate of harpagide, as an ARE activator and suggests that Nrf2-ARE pathway activation by Chinese artichoke contributes to the antioxidative effect.

Excited-State Dynamics in 4-[4'(Dimethylamino)styryl]pyridine, a Photobase: Role of Photoinitiated Proton-Coupled Electron Transfer.

The photoinitiated proton-coupled electron transfer (PCET) process in photoacid-based adducts is predominantly governed by the evolution of the electron-proton transfer state. However, such a process is underexplored in the case of photobases as the excited states evolve through multiple competitive channels. Here, we elucidate the excited-state dynamics of a photobase, 4-[4'-(dimethylamino)styryl]pyridine (DMASP), in the presence of hexafluoroisopropanol (HFIP) that enables PCET. Transient absorption measurements show the evolution of a protonated species in the excited state with a time constant of ∼2.5 ps. Fluorescence upconversion measurements reveal the signatures of an emissive intramolecular charge transfer state and a protonated state. The role of such states is further confirmed by time-resolved measurements in the presence of trifluoroacetic acid and computational analysis. Furthermore, the proton-abstraction dynamics of DMASP is analyzed in bulk methanol and butanol solvents. The extent of proton abstraction by DMASP is found to be higher in the presence of HFIP when compared with the normal alcohols over a time period of a few picoseconds.

1-(((6-(Methoxycarbonyl)-5-oxononan-4-yl)oxy)carbonyl)cyclopropane-1-carboxylic Acid

Here, we first report the 2′-acyloxy-1,3-dicarbonyl compound construction in a three-component oxidative reaction of alkyl ketene dimer with cyclic diacyl peroxide and trimethyl orthoformate. The discovered synthesis allows us to form 2′-functionalized 1,3-dicarbonyl compounds instead of the common 2-functionalized moiety. The reaction between 4-butylidene-3-propyloxetan-2-one and cyclopropyl malonoyl peroxide proceeds in the presence of trifluoroacetic acid and trimethyl orthoformate at 120 °C for 1 h. The synthesized compound was characterized by NMR spectroscopy, mass spectrometry, and IR spectroscopy.

Biologically inspired 3Fe4S cluster as structural mimics of FeMoco M‐cluster

AbstractA 3Fe4S cluster related to M‐cluster of Mo‐nitrogenase is reported. [K(THF)5][Fe3(μ‐bdt)2(μ‐PPh2)(CO)5] (1) is synthesized from photo‐assisted structural rearrangement of [K(THF)2][(μ,κ2‐bdt)Fe2(μ‐PPh2)(CO)5] under visible light irradiation. The molecular structure of 1 consists of a Fe3 core bearing one dithiolate bridge and the second dithiolate group capping onto the metallic plane. The structural motif of 1 is analogous to that of Mo‐participated 3Fe4S unit in M‐cluster of Mo‐nitrogenase, with the similar Fe‐Fe and Fe‐S bond distances. Upon protonation in 193 K, a Fe‐hydride species (1H) is generated and characterized to possess the bridging hydride group (δ = −12.57 ppm) by 1H‐NMR spectroscopy and DFT calculation. In CH3CN solution, complex 1 exhibits a reversible reduction and oxidation process at = −1.94 V and = −0.18 V, respectively, at 273 K. The reduction behavior of 1 in CH2Cl2 solution at 243 K displays a slight modification in the presence of trifluoroacetic acid, revealing a moderate anodic potential shift (~50 mV). The current amplitude of the reduction wave is linearly increased with the increasement of acid added, indicative of the catalytic event.

Synthesis of novel tetrahydropyrimidines via the reaction of sodium [1-(3,3-diethoxypropyl)ureido]methansulfonates with <i>C</i>-nucleophiles

A series of new substituted tetrahydropyrimidines was obtained by the reaction of sodium [1-(3,3-diethoxypropyl)ureido]methansulfonates with various C -nucleophiles (4-chlororesorcinol, sesamol, 2,4-dihydroxybenzoic acid, 4-hydroxy-6-methyl-2 H -pyran-2-one) in chloroform in the presence of trifluoroacetic acid.

Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst

Significant progress has been made in the bioinorganic modeling of the paramagnetic states believed to be involved in the hydrogen redox chemistry catalyzed by [NiFe] hydrogenase. However, the characterization and isolation of intermediates involved in mononuclear Ni electrocatalysts which are reported to operate through a NiI/III cycle have largely remained elusive. Herein, we report a NiII complex (NCHS2)Ni(OTf)2, where NCHS2 is 3,7-dithia-1(2,6)-pyridina-5(1,3)-benzenacyclooctaphane, that is an efficient electrocatalyst for the hydrogen evolution reaction (HER) with turnover frequencies of ~3,000 s−1 and a overpotential of 670 mV in the presence of trifluoroacetic acid. This electrocatalyst follows a hitherto unobserved HER mechanism involving C-H activation, which manifests as an inverse kinetic isotope effect for the overall hydrogen evolution reaction, and NiI/NiIII intermediates, which have been characterized by EPR spectroscopy. We further validate the possibility of the involvement of NiIII intermediates by the independent synthesis and characterization of organometallic NiIII complexes.

Kinetic and mechanistic investigations of dioxygen reduction by a molecular Cu(II) catalyst bearing a pentadentate amidate ligand.

A pentadentate Cu(II) complex, [CuII(dpaq)](ClO4) (1), featuring a redox active ligand, H-dpaq (H-dpaq = 2-[bis(pyridine-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate), catalyses four-electron reduction of dioxygen by decamethylferrocene (Fc*) in the presence of trifluoroacetic acid (CF3COOH) in acetone at 298 K. No catalytic oxygen reduction was observed in the presence of stronger Brønsted acids than CF3COOH, such as perchloric acid (HClO4) or trifluoromethanesulphonic acid (HOTf). In contrast, facile catalytic reduction of O2 occurs by Fc* with 1 and HClO4 or HOTf in dimethylformamide (DMF). The use of CF3COOH as the proton source in DMF results in the suppression of O2 reduction under otherwise identical reaction conditions. While the O2 reduction reactions in DMF are linearly dependent on the pKa of Brønsted acids, the acid dependence on catalytic O2-reduction reactivity by 1 in acetone showed complete reversal. Cyclic voltammetry studies using p-chloranil as the probe substrates in the presence of acids in the solvents reveal that the strengths of the protonic acids increase significantly in acetone compared to that in DMF. The amidate-N in [CuII(dpaq)](ClO4) (1) undergoes protonation in the presence of HClO4 or HOTf in DMF to form [CuII(H-dpaq)]2+ (1-H+), but not in the presence of CF3COOH. Enhanced acid strength of CF3COOH in acetone, however, effectively protonates 1 and triggers O2 reduction. Protonation of 1 with HClO4 or HOTf in acetone results in the change of its coordination environment, and this protonated species does not trigger O2 reduction. Detailed kinetic studies indicate that 1-H+ undergoes reduction by two-electrons and the reduced species binds O2 to form a Cu(II)-superoxo intermediate. This is followed by a rate-determining proton-coupled electron-transfer (PCET) reduction to generate the Cu(II)-hydroperoxo intermediate. While catalytic O2 reduction in acetone occurs predominantly via a 4e-/4H+ pathway, product selectivity (H2O vs. H2O2) in DMF depends upon the concentration of the reductant (Fc*). While dioxygen reduction to H2O2 is favoured at low [Fc*], mechanistic studies suggest that O2 reduction with high [Fc*] proceeds via a [2e- + 2e-] mechanism, where the released H2O2 during catalysis is further reduced to water.

A safety-catch protecting group strategy compatible with Boc-chemistry for the synthesis of peptide nucleic acids (PNAs).

Peptide Nucleic Acids (PNAs) are an intriguing class of synthetic biomolecules with great potential in medicine. Although PNAs could be considered analogs of oligonucleotides, their synthesis is more like that of peptides. In both cases, a Solid-Phase Synthesis (SPS) approach is used. Herein, the advantage using Boc as a temporal protecting group has been demonstrated to be more favored than Fmoc. In this context, a new PNA SPS strategy has been developed based on a safety-catch protecting group scheme for the exocyclic nitrogen of the side-chain bases and the linker. Sulfinyl (sulfoxide)-containing moieties are fully stable to the trifluoroacetic acid (TFA) used to remove the Boc group, but they can be reduced to the corresponding sulfide derivatives, which are labile in the presence of TFA. The efficiency of this novel synthetic strategy has been demonstrated in the synthesis of the PNA pentamer H-PNA(TATCT)-βAla-OH.

An Inventory of Fluorspar Production, Industrial Use, and Emissions of Trifluoroacetic Acid (TFA) in the Period 1930 to 1999

There is a generally accepted conclusion that trifluoroacetic acid (TFA) does occur naturally, in part based on the large quantities of TFA in the oceans (61 - 205 million tonnes, measured in 1998-2002). However, the recent review paper “Insufficient evidence for the existence of natural trifluoroacetic acid” concludes that “the presence of TFA in the deep ocean and lack of closed TFA budget is not sufficient evidence that TFA occurs naturally, especially without a reasonable mechanism of formation”. Industrial sources of TFA can only result from the use of fluoride minerals in industrial processes. Major industrial uses of fluorspar started significant expansion from about the same time (1930s). Over 190 million tonnes of fluorspar have been mined in the period 1930 to 1999. An inventory has been developed (1930-1999), accounting for most of the fluorspar production (86%) and estimating emissions of TFA. Industrial emissions of TFA are estimated as 230,000 to 470,000 tonnes. Significant other industrial uses of fluorides have not been identified that could account for the large burden of TFA in the oceans. This inventory provides complementary evidence that the quantity of TFA in the oceans must include a large natural burden.

A self-complementary macrocycle by a dual interaction system.

Self-complementary assembly is one of the most promising phenomena for the formation of discrete assemblies, e.g., proteins and capsids. However, self-complementary assembly based on multiple host-guest systems has been scarcely reported due to the difficulty in controlling each assembly. Herein, we report a dual interaction system in which the key assembly direction is well regulated by both π-π stacking and hydrogen bonding to construct a self-complementary macrocycle. Continuous host-guest behavior of anthracene-based molecular tweezers during crystallization leads to successful construction of a cyclic hexamer, which is reminiscent of Kekulé’s monkey model. Furthermore, the cyclic hexamer in a tight and triple-layered fashion shows hierarchical assembly into cuboctahedron and rhombohedral assemblies in the presence of trifluoroacetic acid. Our findings would be potentially one of metal-free strategies for constructing anthracene-based supramolecular assemblies with higher-order structure.

Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: Ferrocene-bridged dithiolate complexes [Fe2(CO)6(μ-EC5H4FeC5H4E)] (E = S, Se)

Ferrocene-bridged dithiolate complexes [Fe2(CO)6(μ-EC5H4FeC5H4E)] (E = S, Se) (1-2) have been studied as biomimics of [FeFe]-hydrogenases, ferrocene taking the role of an Fe4S4 surrogate. Both show a quasi-reversible electron reduction at E1/2 = -1.81 V and -1.56 V respectively with IR SEC showing that it is Fe2-based (ca. 50 cm−1 hypsochromic shift) and leads to a significant structural rearrangement with formation of a bridging carbonyl being at ca. 1715 cm−1. They also show reversible one-electron oxidation with a small (ca. 15 cm−1) hypsochromic ν(CO) shift, showing it is ferrocene-based, while oxidation of the Fe2 centre occurs outside of the potential window. DFT calculations on 1 show that the HOMO is ferrocene-based, and the LUMO Fe2-based, both in accord with the IR SEC results. However, the radical anion [1]− is calculated to have an elongated metal-metal vector rather than a bridging carbonyl, although a complex with an open structure [1(μ-CO)]− in which one thiolate group moves from a bridging to a terminal position is energetically similar. For 2, DFT shows the HOMO is Fe2-based, which is not supported experimentally. Complexes 1-2 are proton-reduction catalysts at their first reduction potential in the presence of trifluoroacetic acid. DFT suggests two competing pathways for H2 generation catalysed by 1, occurring upon protonation of either [1]− or [1(μ-CO)]− to give bridging and terminal hydride complexes respectively. For 2, DFT suggests that [2(μ-CO)]− is only slightly higher in energy than [2]−, probably a result of the weaker Fe-Se vs Fe-S bond, and thus proton-reduction likely proceeds (primarily) through the open-structure isomer.

Bulky oxadithiolate-bridged [FeFe]‑hydrogenase mimics [Fe2(μ-R2odt)(CO)4(κ2-diphosphine)] (R = Ph and H) with chelating diphosphines

In order to develop an attractive generation of bulky oxadithiolate-bridged [FeFe]‑hydrogenase mimics with chelating diphosphines, two new series of asymmetrically diphosphine-substituted diiron model complexes [Fe2(μ-R2odt)(CO)4(κ2-diphosphine)] (3–5) with bulky Ph2odt bridge and their reference counterparts (6–8) with common odt bridge were obtained from the Me3NO-assisted substitutions of diiron hexacarbonyl precursors [Fe2(μ-R2odt)(CO)6] (R2odt = (SCHR)2O, R = Ph (1) and H (2)) with different diphosphines such as (Ph2P)2NBn (labelled PNBnP, Bn = benzyl), (Ph2PCH2)2NBn (PCNBnCP), and (Ph2PCH2)2CH2 (DPPP)), respectively. All the as-prepared complexes have been characterized by elemental analysis, IR plus NMR spectroscopies, and particularly by X-ray crystallography for 3–8. It is interesting to note that complexes 3 and 6 chelating by small bite-angle PNBnP diphosphine have the favorable dibasal isomer whereas analogues 4, 5 and 7, 8 chelating by flexible backbone PCNBnCP or DPPP ligands possess the main apical-basal isomer in solution or in the solid state. Further, the electrochemical properties of two pairs of representative complexes 3, 6 and 5, 8 are explored and compared by cyclic voltammetry (CV) in the absence and presence of trifluoroacetic acid (CF3CO2H) as proton source, indicating that the complete protonations of 3, 6 and 5, 8 with higher concentration of CF3CO2H lead to two new catalytic waves for the electrocatalytic proton reduction to hydrogen (H2).

Synthesis and reactivity of 10,15,20-triaryl-5-oxaporphyrin copper complexes

5-Oxaporphyrin copper complexes having phenyl, 4-methoxycarbonylphenyl, and 4-chlorophenyl in the meso positions were prepared by oxidation of copper bilatrienones with H2O2 or meta-chloroperoxybenzoic acid in the presence of trifluoroacetic acid. The yields were 78% (COOMe), 88% (H) and 43% (Cl). The 5-oxaporphyrin copper complex is a cationic species and exhibited a more positive (ca. 0.7 V) redox potential than copper tetraphenylporphyrin. Quantum mechanical calculations revealed that it has a low LUMO level of −3.2 eV. The meso-aryl-5-oxaporphyrin copper complex underwent alcoholysis to yield 19-alkoxybilinone. Nucleophilic ring-opening of the 5-oxaporphyrin copper complexes with OH−, CH3O−, and C2H5O− gave bilindione, 19-methoxybilinone, and 19-ethoxybilinone, respectively, indicating that they are valuable precursors of linear tetrapyrroles.

Ultrathin Two‐Dimensional Metal–Organic Framework Nanosheets Based on a Halogen‐Substituted Porphyrin Ligand: Synthesis and Catalytic Application in CO2 Reductive Amination

Ultrathin two-dimensional metal-organic framework nanosheets have emerged as a promising kind of heterogeneous catalysts. Herein, we report a series of 2D porphyrinic metal-organic framework nanosheets (X-PMOF, X=F, Cl, Br), which was prepared from the self-assembly of a halogen-based porphyrin ligand X-TCPP (X-TCPP=5-(4-halogenatedphenyl)-10,15,20-tris(4-carboxyphenyl)-porphyrin) and ZrCl4 in the presence of trifluoroacetic acid as the modulating reagent. The framework of X-PMOF possessed the ftw topology as in MOF-525. The lamellar X-PMOF nanosheets with the thickness of down to 4.5 nm were assembled and aggregated into a flower-like morphology. With the introduction of iridium(III) atoms into the porphyrin rings, the resultant X-PMOF(Ir) nanosheets were prepared by a similar method. Catalytic results show that Br-PMOF(Ir) nanosheets were efficient for CO2 reduction and aminolysis, giving rise to formamides in high yields under room temperature and atmospheric pressure, and can be recycled and reused for 3 runs. The total turnover number of Br-PMOF(Ir) after 3 runs was 1644 based on Ir. Mechanistic studies disclose that the high efficiency of Br-PMOF(Ir) nanosheets was ascribed to three factors, including the superior activation capability of iridium(III) porphyrin for Si-H bonds, more active sites on the external surfaces of Br-PMOF(Ir) nanosheets, and the defects caused by unsymmetrical porphyrin ligand that increased the framework's affinity towards CO2 .

Abnormal push-pull benzo[4,5]imidazo[1,2-a][1,2,3]triazolo[4,5-e]pyrimidine fluorophores in planarized intramolecular charge transfer (PLICT) state: Synthesis, photophysical studies and theoretical calculations

The combination of excellent luminescence with high solvent polarity effect and aggregation induced emission (AIE) is an ideal combination for creating fluorophores/probes with high microenvironmental sensitivity. However, many push-pull chromophores of the D−A type in common intramolecular charge transfer (ICT) state with a significant solvatochromic effect and AIE activity, have poor luminescent properties. Herein, to overcome this problem by using reactions of nucleophilic aromatic hydrogen substitution (SNH), we have designed a series of novel 4-heteroaryl-substituted 2-aryl-2H-benzo[4,5]imidazo[1,2-a][1,2,3]triazolo[4,5-e]pyrimidine fluorophores possessing a planarized intramolecular charge transfer (PLICT) state. All these fluorophores exhibited high luminescence quantum yields (up to 60%) and large Stokes shift values of up to 7459 cm−1. Among them, the fluorophore 4h was found to exhibit the most pronounced positive solvatochromic effect and the probe 4f exhibited the most pronounced aggregation induced emission characteristics. This AIE behavior was further confirmed by means of time-resolved fluorescence lifetime measurements as well as DFT-assisted geometry optimization studies. In the presence of trifluoroacetic acid (TFA) compound 4h exhibited a well-pronounced acidochromism via visible color change from yellow-green to orange which returned to the original yellow-green solution after the addition of triethylamine (TEA). The Stern-Volmer constant for the probe 4h towards TFA was 38 M−1. Finally, for the compounds 4f, g, h theoretical calculations in the ground and excited states in different solvents were carried out to confirm the PLICT process. Based on all above the herein reported PLICT fluorophores 4a-h can be successfully applied as biological probes and optical switches.

Synthesis, redox properties, and catalytic hydrogen gas generation of porphycene cobalt complexes

A new meso-tetrakis(3,5-di-tert-butylphenyl) substituted porphycene and its cobalt complex were synthesized and characterized. Several meso-tetraarylporphycene cobalt complexes having different substituents showed catalytic activity for the hydrogen gas evolution reaction (HER) in the presence of trifluoroacetic acid (TFA) under electrochemical reductive conditions. The electrochemical potential of the HER was -1.50V vs. Ag/AgCl in THF. The active species of this reaction were determined to be the ligand reduced species of Co(II) porphycenes. The catalytic efficiencies of the cobalt complexes of meso-aryl substituted porphycenes and meso-tetraphenylporphyrin were compared and meso-tetraphenyl porphycene cobalt complex exhibited the best current efficiency of 72%. Based on these experimental results and theoretical calculations, we proposed a possible HER mechanism of this system.

Features of -C-C- coupling of quinoxaline-2-one with ethyl acetoacetate under acid catalysis

Quinoxalin-2-one (1) reacts with ethyl acetoacetate in trifluoroacetic acid (TFA) to form 3-(2-oxopropylideno)-3,4-dihydroquinoxaline-2-one (2) and 3-(3-oxo-3,4- dihydroquinoxaline-2-(1H)-ylidene)methylquinoxaline-2-(1H)-one (3). The reaction product 3 was also obtained by heating the compound 1 with acetone in the presence of TFA.