The carbon–carbon couplings of 4,4＇＇-dibromo-p-terphenyl（DBTP） on Cu（110） surface have been investigated at a single molecular level by scanning tunneling microscopy. After annealing at 353 K, a mixture of para...The carbon–carbon couplings of 4,4＇＇-dibromo-p-terphenyl（DBTP） on Cu（110） surface have been investigated at a single molecular level by scanning tunneling microscopy. After annealing at 353 K, a mixture of parallel non-organometallic and organometallic intermediates of DBTP molecules along the[1–10] direction of the surface has been observed. Further annealing at 393 K causes one group of molecules to form oligomers with para-para and para-meta motifs via Ullmann reaction and the other group of molecules to synthesize oligomers with meta-meta motifs via direct carbon–carbon coupling reaction. Statistical results directly reveal that the occurrence of reaction type is strongly related to the initial binding configuration of DBTP molecules.展开更多
Owing to serious poison of downstream olefin polymerization catalysts from acetylene impurities,selective reduction of acetylene to ethylene is a pivotal process in petrochemical industry.However,during thermocatalyti...Owing to serious poison of downstream olefin polymerization catalysts from acetylene impurities,selective reduction of acetylene to ethylene is a pivotal process in petrochemical industry.However,during thermocatalytic and electrocatalytic acetylene semihydrogenation,acetylene C-C coupling inevitably occurs on current catalysts.The resultant oligomeric species(particularly long-chain hydrocarbons)block active sites and mass transportation,and eventually decrease catalytic activity and stability.In this work,we report Ag nanowires(NWs)as high-performance electrocatalysts for acetylene semihydrogenation,where the C-C coupling is unprecedentedly suppressed by weakening acetylene adsorption.In pure acetylene,1,3-butadiene Faradaic efficiency(FE)of Ag NWs is only 2.1%,which is far lower than 41.2%for Cu nanoparticles at−0.2 V versus reversible hydrsogen electrode.Ethylene partial current density of Ag NWs reaches 217 mA/cm^(2)at 0.85 V,which is considerably higher than those for state-of-the-art Cu-based electrocatalysts.Markedly,no 1,3-butadiene is produced on Ag NWs in a large two-electrode flow cell fed with crude ethylene containing 1 vol%acetylene,presenting thorough termination of acetylene C-C coupling.In situ electrochemical Raman spectroscopy and theoretical investigations reveal that weak acetylene adsorption on Ag surfaces is intrinsically responsible for prohibiting their oligomerization.This work will spark the rapid development of high-performance and stable electrocatalysts for reducing alkynes to olefins.展开更多
Palladium(Pd)-catalyzed cross-coupling reaction is a widely studied process with significant economic interest and represents one of the most successful nanocatalytic examples.Owing to the observed leaching of Pd ions...Palladium(Pd)-catalyzed cross-coupling reaction is a widely studied process with significant economic interest and represents one of the most successful nanocatalytic examples.Owing to the observed leaching of Pd ions from both monometallic and short-range-ordered Pd bimetallic nanocatalysts,there is ambiguity regarding whether the coupling reaction has a heterogeneous component.Herein,facilitated by theoretical calculations,we discovered that the Pd ion leaching-free Pd_(3)Cu intermetallic compound was able to catalyze the cross-coupling reaction heterogeneously with activity comparable with that of Pd ions leached from monometallic Pd.The observation that Pd_(3)Cu acted as a heterogeneous catalyst was further confirmed by the reaction-promoting effect of hot electrons generated by the Ag core in Ag@Pd_(3)Cu nanoplates upon photon adsorption and could only participate in the reaction on the surface of the nanocatalyst.Additionally,it demonstrated experimentally the effectiveness of the heterogeneous route in the coupling reaction.This study shows that the combination of plasmonic catalysis and intermetallic compounds is a promising strategy for designing robust nanocatalysts to synthesize value-added chemicals.展开更多
Unnatural a-amino acids have been extensively used in the modern drug discovery and protein engineering studies. They have also found applications in the development of chiral molecular catalysts and the total synthes...Unnatural a-amino acids have been extensively used in the modern drug discovery and protein engineering studies. They have also found applications in the development of chiral molecular catalysts and the total synthesis of diverse natural products. Accordingly the development of cost-effective approaches for the preparation of unnatural a-amino acids has received increasing attentions. Among all the available methods for this purpose, direct C–H functionalization of simple amino acids represents one of the most attractive approaches because it exhibits good atom-economy and step-efficiency. In particular, selective functionalization of either the primary or secondary C（sp^3）–H bonds in the amino acids has been explored to make versatile C–C, C–N, C–O, C–B and C–F bonds to modify the side chain of amino acids and even peptides. The present review surveys the recent advances of synthesis of chiral unnatural a-amino acids and peptides through palladium-catalyzed functionalization of un-activated C（sp^3）–H bonds.展开更多
The preparation of supported Pd nanoparticles on Tris(tris(hydroxymethyl)aminomethane)‐ modi‐fied Si O2 gel and their catalytic application in Heck coupling are investigated. The catalyst was char‐acterized using a...The preparation of supported Pd nanoparticles on Tris(tris(hydroxymethyl)aminomethane)‐ modi‐fied Si O2 gel and their catalytic application in Heck coupling are investigated. The catalyst was char‐acterized using a combination of X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy, and scanning electron microscopy/energy‐dispersive X‐ray spec‐troscopy. The supported Pd nanoparticles were found to be a highly active and reusable catalyst for the Heck reaction at a low Pd loading(0.02 mol%) because of stabilization by the Tris moieties. Several reaction parameters, including the type and amount of solvent, base, and temperature, were evaluated. The heterogeneity of the catalytic system was investigated using different approaches, and showed that slight Pd leaching into the reaction solution occurred under the reaction condi‐tions. Despite this metal leaching, the catalyst can be reused seven times without significant loss of its activity.展开更多
基金financially supported by Natural Science Foundation of China (Nos. 61474059, U1432129 and 11504158)National Key Basic Research Program of China (No. 2013CB934200)
文摘The carbon–carbon couplings of 4,4＇＇-dibromo-p-terphenyl（DBTP） on Cu（110） surface have been investigated at a single molecular level by scanning tunneling microscopy. After annealing at 353 K, a mixture of parallel non-organometallic and organometallic intermediates of DBTP molecules along the[1–10] direction of the surface has been observed. Further annealing at 393 K causes one group of molecules to form oligomers with para-para and para-meta motifs via Ullmann reaction and the other group of molecules to synthesize oligomers with meta-meta motifs via direct carbon–carbon coupling reaction. Statistical results directly reveal that the occurrence of reaction type is strongly related to the initial binding configuration of DBTP molecules.
基金This work was supported by the Fundamental Research Funds for the Natural Science Foundation of Shaanxi Province(nos.2020JQ-141 and 2021JQ-094)the National Natural Science Foundation of China(nos.22005245 and 52101271)+1 种基金the National Key Research and Development Program of China(no.SQ2021YFE010191)the Startup Fund(no.D5000210090)of Northwestern Polytechnical University.
文摘Owing to serious poison of downstream olefin polymerization catalysts from acetylene impurities,selective reduction of acetylene to ethylene is a pivotal process in petrochemical industry.However,during thermocatalytic and electrocatalytic acetylene semihydrogenation,acetylene C-C coupling inevitably occurs on current catalysts.The resultant oligomeric species(particularly long-chain hydrocarbons)block active sites and mass transportation,and eventually decrease catalytic activity and stability.In this work,we report Ag nanowires(NWs)as high-performance electrocatalysts for acetylene semihydrogenation,where the C-C coupling is unprecedentedly suppressed by weakening acetylene adsorption.In pure acetylene,1,3-butadiene Faradaic efficiency(FE)of Ag NWs is only 2.1%,which is far lower than 41.2%for Cu nanoparticles at−0.2 V versus reversible hydrsogen electrode.Ethylene partial current density of Ag NWs reaches 217 mA/cm^(2)at 0.85 V,which is considerably higher than those for state-of-the-art Cu-based electrocatalysts.Markedly,no 1,3-butadiene is produced on Ag NWs in a large two-electrode flow cell fed with crude ethylene containing 1 vol%acetylene,presenting thorough termination of acetylene C-C coupling.In situ electrochemical Raman spectroscopy and theoretical investigations reveal that weak acetylene adsorption on Ag surfaces is intrinsically responsible for prohibiting their oligomerization.This work will spark the rapid development of high-performance and stable electrocatalysts for reducing alkynes to olefins.
基金the National Key R&D Program of China(no.2016YFA0203102)the National Natural Science Foundation of China(nos.21577157,21777177,and 21822608)。
文摘Palladium(Pd)-catalyzed cross-coupling reaction is a widely studied process with significant economic interest and represents one of the most successful nanocatalytic examples.Owing to the observed leaching of Pd ions from both monometallic and short-range-ordered Pd bimetallic nanocatalysts,there is ambiguity regarding whether the coupling reaction has a heterogeneous component.Herein,facilitated by theoretical calculations,we discovered that the Pd ion leaching-free Pd_(3)Cu intermetallic compound was able to catalyze the cross-coupling reaction heterogeneously with activity comparable with that of Pd ions leached from monometallic Pd.The observation that Pd_(3)Cu acted as a heterogeneous catalyst was further confirmed by the reaction-promoting effect of hot electrons generated by the Ag core in Ag@Pd_(3)Cu nanoplates upon photon adsorption and could only participate in the reaction on the surface of the nanocatalyst.Additionally,it demonstrated experimentally the effectiveness of the heterogeneous route in the coupling reaction.This study shows that the combination of plasmonic catalysis and intermetallic compounds is a promising strategy for designing robust nanocatalysts to synthesize value-added chemicals.
文摘Unnatural a-amino acids have been extensively used in the modern drug discovery and protein engineering studies. They have also found applications in the development of chiral molecular catalysts and the total synthesis of diverse natural products. Accordingly the development of cost-effective approaches for the preparation of unnatural a-amino acids has received increasing attentions. Among all the available methods for this purpose, direct C–H functionalization of simple amino acids represents one of the most attractive approaches because it exhibits good atom-economy and step-efficiency. In particular, selective functionalization of either the primary or secondary C（sp^3）–H bonds in the amino acids has been explored to make versatile C–C, C–N, C–O, C–B and C–F bonds to modify the side chain of amino acids and even peptides. The present review surveys the recent advances of synthesis of chiral unnatural a-amino acids and peptides through palladium-catalyzed functionalization of un-activated C（sp^3）–H bonds.
基金We gratefully acknowledge the funding support for this project from the Isfahan University of Technology, I. R. Iran. Further financial support from the Center of Excellence in Sensor and Green Chemistry Research, Isfahan University of Technology, is gratefully acknowledged.
文摘The preparation of supported Pd nanoparticles on Tris(tris(hydroxymethyl)aminomethane)‐ modi‐fied Si O2 gel and their catalytic application in Heck coupling are investigated. The catalyst was char‐acterized using a combination of X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy, and scanning electron microscopy/energy‐dispersive X‐ray spec‐troscopy. The supported Pd nanoparticles were found to be a highly active and reusable catalyst for the Heck reaction at a low Pd loading(0.02 mol%) because of stabilization by the Tris moieties. Several reaction parameters, including the type and amount of solvent, base, and temperature, were evaluated. The heterogeneity of the catalytic system was investigated using different approaches, and showed that slight Pd leaching into the reaction solution occurred under the reaction condi‐tions. Despite this metal leaching, the catalyst can be reused seven times without significant loss of its activity.
