Unexpected side reaction is discovered from the N-H insertion of phenyl diazoacetates with arylamines in the presence of Rh2(OAc)4 catalyst. This side reaction is not evident with copper catalysts such as Cu(acac)2 or...Unexpected side reaction is discovered from the N-H insertion of phenyl diazoacetates with arylamines in the presence of Rh2(OAc)4 catalyst. This side reaction is not evident with copper catalysts such as Cu(acac)2 or Cu(OTf)2. Good yield of the N-H insertion was obtained by using 0.2% of copper catalyst.展开更多
Insertion loss （IL） is one of the important parameters of asymmetrical digital subscriber loop （ADSL） transformers. In different frequency bands, the factors that affect insertion loss are different. Windings main...Insertion loss （IL） is one of the important parameters of asymmetrical digital subscriber loop （ADSL） transformers. In different frequency bands, the factors that affect insertion loss are different. Windings mainly affect insertion loss in mid and high frequency bands. The effects of winding ways, winding wire diameter and winding turns on insertion loss were discussed. The presented experiment shows that the insertion loss of an ADSL transformer could be under 0.4 dB in mid frequency band when the winding is 30 turns, in which the ADSL transformer satisfies the requirement of total harmonic distortion （THD）. Our experiments also show that the sandwich winding structure is better than the side by side winding structure and the twisted-pair winding structure, and the increase of winding diameter is one means to reduce insertion losses of an ADSL transformer in mid frequency band.展开更多
Main observation and conclusion Transition-metal-catalyzed C-H insertion of metal-carbene represents an excellent and powerful approach for C-H functionalization.However,despite remarkable advances in metal-carbene ch...Main observation and conclusion Transition-metal-catalyzed C-H insertion of metal-carbene represents an excellent and powerful approach for C-H functionalization.However,despite remarkable advances in metal-carbene chemistry,transition metal catalysts that are capable of enantioselective intermolecular carbene C-H insertion are mainly constrained to dirhodium(Ⅱ)and iridium(Ⅲ)-based complexes.展开更多
In view of the exciting advancement on silicon–carbon bond-forming transformations achieved in the past decade,this review intends to show a unified illustration of the recent findings on enantioselective Si–H bond ...In view of the exciting advancement on silicon–carbon bond-forming transformations achieved in the past decade,this review intends to show a unified illustration of the recent findings on enantioselective Si–H bond functionalization aided by asymmetric catalysis.Accordingly,this review describes the enantioselective silicon–carbon bond-forming Si–H bond functionalization,focusing on the reactivity and stereoselectivity in catalytic asymmetric hydrosilylation,carbene Si–H insertion,C–H silylation,and Si–C bond-forming cross-coupling reactions that were achieved with high enantioselectivity in the presence of transitionmetal catalyst systems.This review highlights recent and representative examples of the enantioselective Si–H bond functionalization,discusses the origins of silicon-involving stereoselectivities,and evaluates the substrate scopes and limitations in these catalytic asymmetric Si–H bond functionalization reactions due to the special reactivity of different hydrosilanes.展开更多
The synthesis and characterization of chiral polymers with diverse structure remain a long-term challenging research topic.Herein,a copper-catalyzed enantioselective insertion of carbene into Si-H bond was applied to ...The synthesis and characterization of chiral polymers with diverse structure remain a long-term challenging research topic.Herein,a copper-catalyzed enantioselective insertion of carbene into Si-H bond was applied to polycondensation,giving a new type of optically active degradable polyesters containing Si-C bond in the main chain.The polymerization features mild condition,broad substrate scope,excellent yields and enantioselectivities.Chiral diols could be obtained via reduction of optically active polyesters.Thermogravimetric analysis indicated these chiral polyesters exhibit good thermal stability.展开更多
This paper presents a novel microstrip feedline structure to introduce an extra and controllable transmission zero（TZ）with high rejection for a narrowband filter. This structure loads a reconfigurable capacitor at t...This paper presents a novel microstrip feedline structure to introduce an extra and controllable transmission zero（TZ）with high rejection for a narrowband filter. This structure loads a reconfigurable capacitor at the end of the input feedline without changing the main structure of the filter. The capacitor is recognized by a 2-bit inter-digital capacitor array. The asymmetrical microstrip feedline structure is suitable for multiple-pole filter designs. A low-loss six-pole high-temperature superconducting bandpass filter with a reconfigurable TZ is designed and fabricated. The center frequency of the filter is 5.22 GHz with TZ at the lower stopband. The TZ can be tuned among four different states. The out-of-band rejection at the TZ frequency is higher than 90 d B, and the insertion loss is lower than 0.92 d B. The measured results are consistent with the simulations.展开更多
The asymmetric carbenoid C–H insertion of 3-diazooxindoles into 1,4-cyclohexadiene has been accomplished in the presence of chiral bis(imidazoline) NCN pincer iridium(Ⅲ) complexes as the catalysts. With a catalyst l...The asymmetric carbenoid C–H insertion of 3-diazooxindoles into 1,4-cyclohexadiene has been accomplished in the presence of chiral bis(imidazoline) NCN pincer iridium(Ⅲ) complexes as the catalysts. With a catalyst loading of 0.5 mol%, the reactions proceeded smoothly at 0℃ to afford a variety of chiral 3-substituted oxindoles in good yields with moderate to excellent enantioselectivities(up to 99% ee). The protocol exhibits good functional group tolerance with respect to 3-diazooxindoles and is readily scaled up to 2 mmol scale without any loss in activity and enantioselectivity. Density functional theory(DFT)calculations have been performed to better understand the reaction mechanism and to explain the stereochemical outcome of the reactions.展开更多
基金We are grateful for financial support from the Chinese Academy of Sciences and National Nature Science Foundation of China(20202011).
文摘Unexpected side reaction is discovered from the N-H insertion of phenyl diazoacetates with arylamines in the presence of Rh2(OAc)4 catalyst. This side reaction is not evident with copper catalysts such as Cu(acac)2 or Cu(OTf)2. Good yield of the N-H insertion was obtained by using 0.2% of copper catalyst.
文摘Insertion loss （IL） is one of the important parameters of asymmetrical digital subscriber loop （ADSL） transformers. In different frequency bands, the factors that affect insertion loss are different. Windings mainly affect insertion loss in mid and high frequency bands. The effects of winding ways, winding wire diameter and winding turns on insertion loss were discussed. The presented experiment shows that the insertion loss of an ADSL transformer could be under 0.4 dB in mid frequency band when the winding is 30 turns, in which the ADSL transformer satisfies the requirement of total harmonic distortion （THD）. Our experiments also show that the sandwich winding structure is better than the side by side winding structure and the twisted-pair winding structure, and the increase of winding diameter is one means to reduce insertion losses of an ADSL transformer in mid frequency band.
基金Financial support from the National Natural Science Foundation of China(Nos.21971103,21672229)the National Science&Technology Major Project"Key New Drug Creation and Manufacturing Pro-gram",China(No.2018ZX09711002-006)the Guangdong Provincial Key Laboratory of Catalysis(No.2020B121201002)is gratefully acknowledged.
文摘Main observation and conclusion Transition-metal-catalyzed C-H insertion of metal-carbene represents an excellent and powerful approach for C-H functionalization.However,despite remarkable advances in metal-carbene chemistry,transition metal catalysts that are capable of enantioselective intermolecular carbene C-H insertion are mainly constrained to dirhodium(Ⅱ)and iridium(Ⅲ)-based complexes.
基金supported by the National Natural Science Foundation of China(22072035)the Special Support Program for High-level Talents of Zhejiang Province(2021R51005)+2 种基金the“Ten-Thousand Talents Plan”of Hangzhou cityHangzhou Innovation Team(TD2020015)Zhejiang Provincial Natural Science Foundation of China(LY21B030007,LY22B020006)。
文摘In view of the exciting advancement on silicon–carbon bond-forming transformations achieved in the past decade,this review intends to show a unified illustration of the recent findings on enantioselective Si–H bond functionalization aided by asymmetric catalysis.Accordingly,this review describes the enantioselective silicon–carbon bond-forming Si–H bond functionalization,focusing on the reactivity and stereoselectivity in catalytic asymmetric hydrosilylation,carbene Si–H insertion,C–H silylation,and Si–C bond-forming cross-coupling reactions that were achieved with high enantioselectivity in the presence of transitionmetal catalyst systems.This review highlights recent and representative examples of the enantioselective Si–H bond functionalization,discusses the origins of silicon-involving stereoselectivities,and evaluates the substrate scopes and limitations in these catalytic asymmetric Si–H bond functionalization reactions due to the special reactivity of different hydrosilanes.
基金Financial support from the National Natural Science Founda-tion of China(21690074)Dalian Institute of Chemical Physics(UN201701)the Chinese Academy of Sciences(XDB17020300)。
文摘The synthesis and characterization of chiral polymers with diverse structure remain a long-term challenging research topic.Herein,a copper-catalyzed enantioselective insertion of carbene into Si-H bond was applied to polycondensation,giving a new type of optically active degradable polyesters containing Si-C bond in the main chain.The polymerization features mild condition,broad substrate scope,excellent yields and enantioselectivities.Chiral diols could be obtained via reduction of optically active polyesters.Thermogravimetric analysis indicated these chiral polyesters exhibit good thermal stability.
基金Project supported by the National Natural Science Foundation of China(Grant No.61371009)the Chinese Ministry of Science and Technology(Grant No.2014AA032703)
文摘This paper presents a novel microstrip feedline structure to introduce an extra and controllable transmission zero（TZ）with high rejection for a narrowband filter. This structure loads a reconfigurable capacitor at the end of the input feedline without changing the main structure of the filter. The capacitor is recognized by a 2-bit inter-digital capacitor array. The asymmetrical microstrip feedline structure is suitable for multiple-pole filter designs. A low-loss six-pole high-temperature superconducting bandpass filter with a reconfigurable TZ is designed and fabricated. The center frequency of the filter is 5.22 GHz with TZ at the lower stopband. The TZ can be tuned among four different states. The out-of-band rejection at the TZ frequency is higher than 90 d B, and the insertion loss is lower than 0.92 d B. The measured results are consistent with the simulations.
基金supported by a grant from the National Nat-ural Science Foundation of China(No.21472176).
文摘The asymmetric carbenoid C–H insertion of 3-diazooxindoles into 1,4-cyclohexadiene has been accomplished in the presence of chiral bis(imidazoline) NCN pincer iridium(Ⅲ) complexes as the catalysts. With a catalyst loading of 0.5 mol%, the reactions proceeded smoothly at 0℃ to afford a variety of chiral 3-substituted oxindoles in good yields with moderate to excellent enantioselectivities(up to 99% ee). The protocol exhibits good functional group tolerance with respect to 3-diazooxindoles and is readily scaled up to 2 mmol scale without any loss in activity and enantioselectivity. Density functional theory(DFT)calculations have been performed to better understand the reaction mechanism and to explain the stereochemical outcome of the reactions.
