ACS Organic & Inorganic Au最新文献

In this study, the electrocatalytic reduction of carbon dioxide by Mn^I, Re^I, and Ru^II bipyridine complexes bearing pendant amines is evaluated by DFT methods. Prior experimental studies showed that introducing pendant amines in the secondary coordination sphere of the catalyst shifts product selectivity from CO to HCOO^– (in the presence of a proton source) in the case of Mn. In contrast, CO is the major product with Re and Ru. This work includes a comprehensive study of the pathways leading to CO, HCOO^–, and H₂ to elucidate the energetic preferences that underlie product selectivity. Our results show that switching the metal center leads to changes in the preferred mechanism. While with Mn, the reaction is preferred in an endo configuration, allowing the participation of amines in the hydride formation, reactivity on the exo configuration is preferred with Re. In addition, the distinct redox properties of Re allow for the formation of Re OCOCO₂-bridged adducts that lead to CO without a proton source. Further, the ability of Ru to exchange the two Cl^– anions changes the preferred coordination number of Ru compared to Mn and Re and, consequently, its reaction mechanism. Overall, this study provides the structure and reactivity insight needed for further catalyst design.

In this study, the electrocatalytic reduction of carbon dioxide by Mn^I, Re^I, and Ru^II bipyridine complexes bearing pendant amines is evaluated by DFT methods. Prior experimental studies showed that introducing pendant amines in the secondary coordination sphere of the catalyst shifts product selectivity from CO to HCOO^- (in the presence of a proton source) in the case of Mn. In contrast, CO is the major product with Re and Ru. This work includes a comprehensive study of the pathways leading to CO, HCOO^-, and H₂ to elucidate the energetic preferences that underlie product selectivity. Our results show that switching the metal center leads to changes in the preferred mechanism. While with Mn, the reaction is preferred in an endo configuration, allowing the participation of amines in the hydride formation, reactivity on the exo configuration is preferred with Re. In addition, the distinct redox properties of Re allow for the formation of Re OCOCO₂-bridged adducts that lead to CO without a proton source. Further, the ability of Ru to exchange the two Cl^- anions changes the preferred coordination number of Ru compared to Mn and Re and, consequently, its reaction mechanism. Overall, this study provides the structure and reactivity insight needed for further catalyst design.

It is well-known that addition of a cationic functional group to a molecule lowers the necessary applied potential for an electron transfer (ET) event. This report studies the effect of a proton (a cation) on the mechanism of electrochemically driven hydride transfer (HT) catalysis. Protonated, air-stable [HFe₄N(triethyl phosphine (PEt₃))₄(CO)₈] (H4) was synthesized by reaction of PEt₃ with [Fe₄N(CO)₁₂]⁻ (A^–) in tetrahydrofuran, with addition of benzoic acid to the reaction mixture. The reduction potential of H4 is −1.70 V vs SCE which is 350 mV anodic of the reduction potential for 4^–. Reactivity studies are consistent with HT to CO₂ or to H⁺ (carbonic acid), as the chemical event following ET, when the electrocatalysis is performed under 1 atm of CO₂ or N₂, respectively. Taken together, the chemical and electrochemical studies of mechanism suggest an ECEC mechanism for the reduction of CO₂ to formate or H⁺ to H₂, promoted by H4. This stands in contrast to an ET, two chemical steps, followed by an ET (ECCE) mechanism that is promoted by the less electron rich catalyst A^–, since A^– must be reduced to A^2– before HA^– can be accessed.

It is well-known that addition of a cationic functional group to a molecule lowers the necessary applied potential for an electron transfer (ET) event. This report studies the effect of a proton (a cation) on the mechanism of electrochemically driven hydride transfer (HT) catalysis. Protonated, air-stable [HFe₄N(triethyl phosphine (PEt₃))₄(CO)₈] (H4) was synthesized by reaction of PEt₃ with [Fe₄N(CO)₁₂]^- (A ^-) in tetrahydrofuran, with addition of benzoic acid to the reaction mixture. The reduction potential of H4 is -1.70 V vs SCE which is 350 mV anodic of the reduction potential for 4 ^-. Reactivity studies are consistent with HT to CO₂ or to H⁺ (carbonic acid), as the chemical event following ET, when the electrocatalysis is performed under 1 atm of CO₂ or N₂, respectively. Taken together, the chemical and electrochemical studies of mechanism suggest an ECEC mechanism for the reduction of CO₂ to formate or H⁺ to H₂, promoted by H4. This stands in contrast to an ET, two chemical steps, followed by an ET (ECCE) mechanism that is promoted by the less electron rich catalyst A ^-, since A ^- must be reduced to A ^2- before HA ^- can be accessed.

Organic electrosynthesis has gained much attention over the last few decades as a promising alternative to traditional synthesis methods. Electrochemical approaches offer numerous advantages over traditional organic synthesis procedures. One of the most interesting aspects of electroorganic synthesis is the ability to tune many parameters to affect the outcome of the reaction of interest. One such parameter is the composition of the working electrode. By changing the electrode material, one can influence the selectivity, product distribution, and rate of organic reactions. In this Review, we describe several electrode materials and modifications with applications in organic electrosynthetic transformations. Included in this discussion are modifications of electrodes with nanoparticles, composite materials, polymers, organic frameworks, and surface-bound mediators. We first discuss the important physicochemical and electrochemical properties of each material. Then, we briefly summarize several relevant examples of each class of electrodes, with the goal of providing readers with a catalog of electrode materials for a wide variety of organic syntheses.

Organic electrosynthesis has gained much attention over the last few decades as a promising alternative to traditional synthesis methods. Electrochemical approaches offer numerous advantages over traditional organic synthesis procedures. One of the most interesting aspects of electroorganic synthesis is the ability to tune many parameters to affect the outcome of the reaction of interest. One such parameter is the composition of the working electrode. By changing the electrode material, one can influence the selectivity, product distribution, and rate of organic reactions. In this Review, we describe several electrode materials and modifications with applications in organic electrosynthetic transformations. Included in this discussion are modifications of electrodes with nanoparticles, composite materials, polymers, organic frameworks, and surface-bound mediators. We first discuss the important physicochemical and electrochemical properties of each material. Then, we briefly summarize several relevant examples of each class of electrodes, with the goal of providing readers with a catalog of electrode materials for a wide variety of organic syntheses.

In this study, we synthesized two new 3-C-substituted pentafluorophenyl-N-confused porphyrins (PFNCPs), one with acetylacetonate (PFNCP-acac, 2a) and the other with ylidene-2-propanone (PFNCP-ac, 3a), through a one-pot reaction in the absence of a catalyst. Under mild acidic and heating conditions, the acac-substituted compound underwent acyl cleavage degradation, yielding ac-substituted product 3a. Subsequent chelation of the acac-substituted PFNCP with BF₂ resulted in a boron diketonate derivative, PFNCP-acacBF₂ (4). Additionally, an electrocyclic reaction of the ac-substituted PFNCP 3a, without a catalyst, produced a tricyclic fused [6,6,5]-TF-PFNCP (5). This tricyclic product could also be obtained directly from PFNCP-acac 2a under heating conditions. The absorption spectra revealed that acac- and ac-substituted macrocycles exhibit either a single or split Soret band, respectively, in the 400-550 nm range, along with multiple Q bands spanning the 580-690 nm region. While BF₂ derivatization caused a slight red shift in the absorption spectra, the [6,6,5]-tricyclic fused NCP demonstrated a significant red shift. All newly synthesized compounds were characterized by using single-crystal X-ray structures, ¹H NMR spectroscopy, and mass spectrometry. Density functional theory (DFT) studies were conducted to elucidate the photophysical properties of these macrocycles.

In the present work, the oxidation mechanism of di-t-butyl-hydroxytoluene (BHT) was studied in an aqueous medium through different approaches to have a thorough vision of the physical chemistry: experiments with cyclic voltammetry (CV), quantum chemical calculations, and simulations of CV. Calculations of thermodynamic parameters, such as pK _a and standard oxidation potential (E _ox°), were used to analyze and rationalize the CV experiments. Subsequently, different pathways of the mechanism were constructed, and the most thermodynamically favorable one was selected. Numerical simulations were then used to model this mechanism and compare it with the experimental data. The results show that the oxidation process is due to the coupled loss of an electron and a proton in the first instance, followed by an irreversible second electron-transfer process without loss of protons, mainly due to the adsorption of the products of the first oxidation on the electrode surface. The effect of different pH values on this oxidative mechanism was also analyzed, with alkaline pH of 12 as a medium where changes in reactivity were observed as the appearance of a new peak in the second voltammetric sweep, the interpretation of this peak is also provided.

In this study, we synthesized two new 3-C-substituted pentafluorophenyl-N-confused porphyrins (PFNCPs), one with acetylacetonate (PFNCP-acac, 2a) and the other with ylidene-2-propanone (PFNCP-ac, 3a), through a one-pot reaction in the absence of a catalyst. Under mild acidic and heating conditions, the acac-substituted compound underwent acyl cleavage degradation, yielding ac-substituted product 3a. Subsequent chelation of the acac-substituted PFNCP with BF₂ resulted in a boron diketonate derivative, PFNCP-acacBF₂ (4). Additionally, an electrocyclic reaction of the ac-substituted PFNCP 3a, without a catalyst, produced a tricyclic fused [6,6,5]-TF-PFNCP (5). This tricyclic product could also be obtained directly from PFNCP-acac 2a under heating conditions. The absorption spectra revealed that acac- and ac-substituted macrocycles exhibit either a single or split Soret band, respectively, in the 400–550 nm range, along with multiple Q bands spanning the 580–690 nm region. While BF₂ derivatization caused a slight red shift in the absorption spectra, the [6,6,5]-tricyclic fused NCP demonstrated a significant red shift. All newly synthesized compounds were characterized by using single-crystal X-ray structures, ¹H NMR spectroscopy, and mass spectrometry. Density functional theory (DFT) studies were conducted to elucidate the photophysical properties of these macrocycles.

In the present work, the oxidation mechanism of di-t-butyl-hydroxytoluene (BHT) was studied in an aqueous medium through different approaches to have a thorough vision of the physical chemistry: experiments with cyclic voltammetry (CV), quantum chemical calculations, and simulations of CV. Calculations of thermodynamic parameters, such as pK_a and standard oxidation potential (E_ox°), were used to analyze and rationalize the CV experiments. Subsequently, different pathways of the mechanism were constructed, and the most thermodynamically favorable one was selected. Numerical simulations were then used to model this mechanism and compare it with the experimental data. The results show that the oxidation process is due to the coupled loss of an electron and a proton in the first instance, followed by an irreversible second electron-transfer process without loss of protons, mainly due to the adsorption of the products of the first oxidation on the electrode surface. The effect of different pH values on this oxidative mechanism was also analyzed, with alkaline pH of 12 as a medium where changes in reactivity were observed as the appearance of a new peak in the second voltammetric sweep, the interpretation of this peak is also provided.