ELECTROCARBOXYLATION OF ORGANIC COMPOUNDS WITH CARBON DIOXIDE CATALYZED BY METALLOPORPHYRINS(Ⅲ)——EFFECTS OF AXIAL LIGANDS ON CATALYTIC ACTIVITY OF CoTPP

The effects of peptides,amino acids and organic bases as an axial ligand on reaction ac- tivities in the electrocarboxylation of benzyl chloride with CO_2 catalyzed by CoTPP are reported. The imidazole organic base,peptide containing —SH and amino acid containing imidazolyl en- hance the catalytic activity.The effect of imidazole amounts on the catalytic activity of CoTPP is studied.

Amine axial ligand-coordinated cobalt phthalocyanine-based catalyst for flow-type membraneless hydrogen peroxide fuel cell or enzymatic biofuel cell

In this study,an amine-coordinated cobalt phthalocyanine(CoPc)-based anodic catalyst was fabricated by a facile process,to enhance the performance of hydrogen peroxide fuel cells(HPFCs) and enzymatic biofuel cells(EBCs).For this purpose,polyethyleneimine(PEI) was added onto the reduced graphene oxide and CoPc composite(RGO/CoPc) to create abundant NH2 axial ligand groups,for anchoring the Co core within the CoPc.Owing to the PEI addition,the onset potential of the hydrogen peroxide oxidation reaction was shifted by 0.13 V in the negative direction(0.02 V) and the current density was improved by 1.92 times(1.297 mA cm^(-2)),compared to those for RGO/CoPc(0.15 V and 0.676 mA cm^(-2),respectively),due to the formation of donor-acceptor dyads and the prevention of CoPc from leaching out.The biocatalyst using glucose oxidase(GOx)([RGO/CoPc]/PEI/GOx) showed a better onset potential and catalytic activity(0.15 V and 318.7 μA cm^(-2)) than comparable structures,as well as significantly improved operational durability and long-term stability.This is also attributed to PEI,which created a favorable microenvironment for the enzyme.The maximum power densities(MPDs) and open-circuit voltages(OCVs) obtained for HPFCs and EBCs using the suggested catalyst were 105.2±1.3 μW cm^(-2)(0.317±0.003 V) and 25.4±0.9 μW cm^(-2)(0.283±0.007 V),respectively.This shows that the amine axial ligand effectively improves the performance of the actual driving HPFCs and EBCs.

A cobalt(Ⅱ)porphyrin with a tethered imidazole for efficient oxygen reduction and evolution electrocatalysis

Electrocatalytic oxygen reduction and evolution reactions are involved in new energy conversion and storage technologies,such as various fuel cells and metal-air batteries and also water splitting devices[1,2].However,both reactions are very slow in kinetics,and thus catalysts are required[3,4].

P-functionalized carbon nanotubes promote highly stable electrocatalysts based on Fe-phthalocyanines for oxygen reduction: Experimental and computational studies

Iron(Ⅱ) phthalocyanines(FePc) supported on functionalized nanostructured carbon materials have been studied as electrocatalysts for the oxygen reduction reaction(ORR) in an alkaline medium. Herein, two types of carbon nanotubes(CNTs) have been explored as support, Single-Walled Carbon Nanotubes and Herringbone Carbon Nanotubes(SWCNTs and h CNTs, respectively), both electrochemically modified with ortho-aminophenylphosphonic acid(2APPA), which provides phosphate axial coordinating ligands for the immobilization of FePc molecules. All the catalysts were prepared via a facile incipient wetness impregnation method. Comprehensive experimental analysis together with density functional theory(DFT) calculations has demonstrated both the importance of the five-coordinated Fe macrocycles that favor the interaction between the FePc and the carbon support, as well as the effect of the CNT structure in the ORR. FePc axial coordination provides a better dispersion, leading to higher stability and a favorable electron redistribution that also tunes the ORR performance by lowering the stability of the reaction intermediates. Interestingly, such improvement occurs with a very low content of metal(~1 wt% Fe),which is especially remarkable when h CNT support is employed. This work provides a novel strategy for the development of Fe-containing complexes as precious metal-free catalysts towards the ORR.

Axially Dissymmetric Chiral (R)-N,N′-Bis(2-hydroxy-3,5-di-tert-butyl-arylmethyl)-1,1′-binaphthalene-2,2′-diamine as Chiral Ligands in the Reaction of Diethylzinc to Aldehydes

Chiral ligand (R)-N, N'-Bis(2-hydroxy-3,5-di- tert-butyl-aryl-methyl)-1, 1'-binaphthalene-2,2'-diamine derived from the reduction of Schiff base (R)-2,2'-bis (3,5-di-tert-butyl-2-hy-droxybenzylideneamino)-1, 1'-binaphthyl with LiAIH(4) is fairly effective in the asymmetric addition reaction of diethylzinc to aldehydes by which good yields (46%-94%) of the corresponding sec-alcohols can be obtained in moderate ee (51%-79%) with R configuration for a variety of aldehydes.

DFT Studies on Second-order Nonlinear Optical Properties of a Series of Axially Substituted Bis（salicylaldiminato） Zinc（II） Schiff-base Complexes

Coordination of an axial ligand to metal center to enhance the second-order nonlinear optical（NLO） re- sponse of a two-dimensional bis（salicylaldiminato） zinc（II） Schiff-base complex is an unprecedented model. The second-order NLO responses of a series of axially substituted bis（salicylaldiminato） zinc（II） Schiff-base complexes were explored according to the finite field（FF） method at CAM-B3LYP/6-31＋G（d） level（LANL2DZ basis set for metal atoms）. The results show that the second-order NLO properties can be effectively tuned by exchanging the do- nor and accepter of the axial ligand and extending the length of the conjugated bridge along the axial direction. A system involving the electron acceptor along the appropriate direction has a large three-dimensional second-order NLO response. Meanwhile, time dependent density functional theory（TD-DFT） method was employed to calculate the physical parameters of excited states. The results show that the Y- and Z-polarized transitions of the zinc（II） Schiff-base complex are the first and second excited states, respectively, and have a low-lying excited energy. Al- though the X-polarized transition has a high excited energy, the large oscillator strength indicates that it will signifi- cantly contribute to the second-order NLO response.

Effects of axial ligand replacement on the redox potentialof cytochrome c

In order to demonstrate the effect of the sixth axial ligand on the biological funtionof heme proteins, we have determined the formal potentials and electron transfer numbersof imidazole (Im), 1-methylimidazole (1-MeIm) and 1-ethylimidazole (1-EtIm) complexes ofcytochrome c(cyt c) with an optically transparent thin-layer electrode.

A Cobalt(Ⅲ)Corrole with a Tethered Imidazole for Boosted Electrocatalytic Oxygen Reduction Reaction

Developing electrocatalysts with high activity and selectivity for the oxygen reduction reaction(ORR)is vital to promote the performance of the next-generation energy technologies,which depend on the efficiency of the catalytic reduction of dioxygen.In the structure of cytochrome c oxidases(CcOs),a histidine imidazole residue binding to the axial position of Fe plays a crucial role in facilitating the selective reduction of O_(2)to water.Inspired by nature,we herein report on the synthesis of CoIII corrole 1 tethered with an imidazole ligand as well as its electrocatalytic ORR and O_(2)binding features.As compared to the imidazolium-free analogue,complex 1 displayed remarkably boosted activity for the selective four-electron/four-proton(4e-/4H+)ORR with a half-wave potential of E1/2=0.82 V versus reversible hydrogen electrode(RHE)in 0.1 mol/L KOH solutions.Importantly,we demonstrate that the tethered axial imidazole ligand improves the O_(2)binding ability of 1 thermodynamically and dynamically,which is crucial to boost electrocatalytic ORR performance.This work presents an example to improve electrocatalytic ORR activity and selectivity of Co corroles by introducing an axial imidazole ligand to enhance the O_(2)binding and activation.

Formation of heterocaryotic and homonuclear bridged–dimeric complexes on surface

The formation of coordinated dimeric complexes bridged by axial ligands on surface is observed with the help of a 1,3,5-tris（10-carboxydecyloxy）benzene（TCDB） template through scanning tunneling microscopy（STM）. STM images of molecular adlayers of zinc tetraphenylporphyrin（Zn TPP）, zinc phthalocyanine（Zn Pc）, and their mixture are reported. Zn TPP and Zn Pc can spontaneously form highly an ordered structure with a 1：1 molar ratio, which is different from that of individual Zn Pc. The coordinated bimolecular complexes bridged with axial ligands, simply as Zn Pc–DPP–Zn TPP and Zn Pc–DPE–Zn Pc, are presented and the corresponding surface structures are compared. Zn Pc and Zn TPP can be connected by an axial ligand DPP and formed assembled structures out of surface. Two types of arrays with entirely new structure are obtained for the Zn Pc–DPE–Zn Pc complex. These bridged hybrid complexes provide an example of design of self-organized crystals on the basis of coordination through non-covalent interactions.

Establishing a theoretical insight for penta-coordinated ironnitrogen-carbon catalysts toward oxygen reaction

Developing highly active iron-nitrogen-carbon catalysts for electrocatalytic oxygen reduction reactions(ORR)is pivotal to future energy technology.The penta-coordinated Fe-N-C with an augmented activity toward the oxygen reduction has been regarded as one of the promising candidates to replace platinum-based ORR catalysts.However,the lack of pertinent fundamental understanding hinders further optimizing the catalytic activity of such catalysts.Herein,through density functional theory(DFT)calculations,we systematically investigated the catalytic activity and ligand/metal coordination effects of 17 penta-coordinated FeN-C catalysts(labeled as FeNC-Xs,X denotes axial ligand).Our results not only show the theoretical overpotential of FeNC-Xs is lower than that of conventional tetra-coordinated Fe-N-C catalysts(labeled as FeNC),verifying the preeminent performance of FeNC-Xs,but also further indicate that the axial coordination effect of X ligands can decrease the orbital hybridization of Fe active center with ORR-relevant intermediates,sequentially accelerating the ORR.More importantly,we reveal that the catalytic activity of FeNC-Xs increases with a decreased electronegativity of X ligands,which can be utilized to describe the axial coordination effect for FeNC-Xs.These findings can deeply advance the understanding of penta-coordinated iron-nitrogencarbon catalysts,which provide timely guidelines for designing optimum Fe-N-C based catalysts.

Paddlewheel dirhodium(II)complexes with N-heterocyclic carbene or phosphine ligand:New reactivity and selectivity

The dirhodium(II)-catalyzed organic reactions,including asymmetric transformation,are significantly benefitted from the discovery of simple and efficient protocols to introduce various bridging ligands,e.g.carboxylic acids,amide and phosphoric acids.Ligands lying at axial position of dirhodium(II)complexes could strongly affect the activity and selectivity of these metal complexes involved reactions.This review summarizes the newly explored reactivity of dirhodium(II)complexes with N-heterocyclic carbenes or phosphines as the axial ligands.The asymmetric tries are also highlighted,where their stereo-induction were solely from the axial ligand of dirhodium(II)complexes.In the last part,the reactions catalyzed by inherent chiral ortho-metalated dirhodium(II)/phosphine complexes are also discussed.