饱和的碳氢键氧化是合成化学和化学工业中一类重要的化学反应.然而,饱和C(sp^(3))−H键离解能(BDEs)较高、极性较弱,导致了底物难以活化和催化转化效率较低等问题.在过去的几十年,C(sp^(3))−H键的定向活化转化取得了重要的进展.其中,关于...饱和的碳氢键氧化是合成化学和化学工业中一类重要的化学反应.然而,饱和C(sp^(3))−H键离解能(BDEs)较高、极性较弱,导致了底物难以活化和催化转化效率较低等问题.在过去的几十年,C(sp^(3))−H键的定向活化转化取得了重要的进展.其中,关于C(sp^(3))−H键催化氧化的研究主要涉及一些键能低的、预活化的C−H键,包括苄基型、亚甲基型、脂肪族X−CH_(2)(X=O,N)和甲苯等,含有未活化C(sp^(3))−H键的复杂化合物的选择性氧化仍具有挑战性.例如,芳基醚C(sp^(3))−H键功能化通常采用计量的过氧化物氧化剂,或者通过单电子氧化和碱促进的去质子化进一步构建C−C/C−N键,产物选择性较低,也带来了一些不利的环境影响.因此,有必要开发高效、温和的芳基醚C(sp^(3))−H键选择氧化方法,并将其应用于有机合成和药物开发.近年来,光催化C(sp^(3))−H键氧化因其操作简便、氧化还原中性等优点,已发展成为一种有用且多样的催化研究工具.本文发展了一种利用氧气作为氧化剂,在可见光驱动下选择性地将芳基醚C(sp^(3))−H键氧化成为甲酸苯酯类产物的新方法.使用Mes-10-phenyl-Acr^(+)−BF_(4)^(-)光催化剂,高效活化多种氯源(如盐酸、无机氯盐和有机氯化物)得到氯自由基,由于其具有较高的氧化能力(+2.03 V vs.SCE)和对氢原子的亲和力,能够通过氢原子转移过程活化芳基醚C(sp^(3))−键,攫取氢自由基得到相应的烷基碳自由基(•CH_(2)OPh)中间体,进一步被分子氧选择氧化得到酯类目标产物.研究结果表明,多种链状芳基醚和不同取代(如给电子基和吸电子基)芳基醚均可发生氧化反应,高收率地合成了一系列官能团丰富的甲酸苯酯类化合物.本文方法具有反应条件温和、操作简单、官能团耐受性好以及可规模化放大等优点,并且少量的水对反应没有明显影响.机理实验研究结果表明,芳基醚C(sp^(3))−H键的断裂是反应过程的决速步骤.紫外可见吸收光谱结果表明,氯离子与催化剂之间的相互作用强于底物,并且自由基捕获实验证实反应体系中存在氯自由基和烷基碳自由基物种,表明反应经历自由基路径.此外,电子顺磁共振测试结果表明,反应过程中存在单线态氧物种,可能是激发态的光催化剂直接与氧气发生能量转移得到;同位素实验(18O)揭示了甲酸苯酯类化合物氧的来源.综上,本文实现了温和条件下光催化芳基醚C(sp^(3))−H键选择氧化反应,高收率合成了一系列甲酸苯酯类化合物.该方法避免了化学计量的过氧化物和碱等添加剂的使用以及底物的过度氧化,阐明了催化反应机制,为其他醚类化合物的C(sp^(3))−H键氧化功能化提供了新思路,为后续化学合成和药物开发提供了参考和启示.展开更多
Propane dehydrogenation(PDH)on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production,while the detail mechanism remains debatable.Ga_(2)O_(2)^(2+) stabilized by framework Al pairs have been identified ...Propane dehydrogenation(PDH)on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production,while the detail mechanism remains debatable.Ga_(2)O_(2)^(2+) stabilized by framework Al pairs have been identified as the most active species in Ga/H-ZSM-5 for PDH in our recent work.Here we demonstrate a strong correlation between the PDH activity and a fraction of Ga_(2)O_(2)^(2+) species corresponding to the infrared GaH band of higher wavenumber(GaHHW)in reduced Ga/H-ZSM-5,instead of the overall Ga_(2)O_(2)^(2+) species,by employing five H-ZSM-5 supports sourced differently with comparable Si/Al ratio.This disparity in Ga_(2)O_(2)^(2+) species stems from their differing capacity in completing the catalytic cycle.Spectroscopic results suggest that PDH proceeds via a two-step mechanism:(1)C-H bond activation of propane on H-Ga_(2)O_(2)^(2+) species(rate determining step);(2)β-hydride elimination of adsorbed propyl group,which only occurs on active Ga_(2)O_(2)^(2+) species corresponding to GaHHW.展开更多
Selective oxidation of saturated C(sp^(3))-H bonds in hydrocarbon to target chemicals under mild conditions remains a signifi-cant but challenging task because of the chemical inertness and high dissociation energy of...Selective oxidation of saturated C(sp^(3))-H bonds in hydrocarbon to target chemicals under mild conditions remains a signifi-cant but challenging task because of the chemical inertness and high dissociation energy of C(sp^(3))-H bonds.Semiconductor photocatalysis can induce the generation of holes and oxidative radicals,off ering an alternative way toward selective oxidation of hydrocarbons under ambient conditions.Herein,we constructed N-doped TiO_(2) nanotubes(N-TNTs)that exhibited remark-able activity and selectivity for toluene oxidation under visible light,delivering the conversion of toluene and selectivity of benzaldehyde of 32% and>99%,respectively.Further mechanistic studies demonstrated that the incorporation of nitrogen induced the generation of N-doping level above the O 2p valance band,directly contributing to the visible-light response of TiO_(2).Furthermore,hydroxyl radicals generated by photogenerated holes at the orbit of O 2p were found to be unselective for the oxidation of toluene,aff ording both benzaldehyde and benzoic acid.The incorporation of nitrogen was able to inhibit the generation of hydroxyl radicals,terminating the formation of benzoic acid.展开更多
The title compound (C14H12N2O2, Mr = 240.26) crystallizes in the monoclinic system, space group P21/a with a = 7.394(1), b = 21.334(3), c = 7.423(1) ? b = 89.82(1)? V = 1170.8(3) ?, Z = 4, Dc = 1.363 g/cm3, m(MoKa) = ...The title compound (C14H12N2O2, Mr = 240.26) crystallizes in the monoclinic system, space group P21/a with a = 7.394(1), b = 21.334(3), c = 7.423(1) ? b = 89.82(1)? V = 1170.8(3) ?, Z = 4, Dc = 1.363 g/cm3, m(MoKa) = 0.93 cm-1 and F(000) = 504.00. The final R and wR are 0.0440 and 0.1370 for 2153 observed reflections (I > 2s(I)), respectively. The dihedral angle between the two phenyl rings is 52.9 and that between the NO2 group and its attached ring is 3.0. In the crystal, molecules are stacked along [100] through p…p interactions. The CH…O hydrogen bond (3.403 ? 120.4? laterally connects the stacks along [010] to form networks (001) which are further anti- parallelly connected by CH…O (3.382 ? 142.9) and p…p interactions extending along [001]. Also presented here is a brief study on the CH…O hydrogen bonds in nitro-substituted benzyl-ideneanilines which can be classified into five types, namely, )5(12R, )4(21R, )8(22R, )6(12R and )7(22R, with the first three occurring more often.展开更多
Previous carbene insertion to C–H bonds of 1,3-azoles relied on metal carbene species. Herein, we report a metal-free C(sp^(2))–H bond functionalization of 1,3-azoles with trifluoroacetylsilanes. The reaction featur...Previous carbene insertion to C–H bonds of 1,3-azoles relied on metal carbene species. Herein, we report a metal-free C(sp^(2))–H bond functionalization of 1,3-azoles with trifluoroacetylsilanes. The reaction features mild conditions, broad substrate scope and wide functional group tolerance. The mechanistic study supports that the success of the reaction is probably attributed to the dual roles of trifluoroacetylsilanes under the photocatalyzed conditions: generating carbenes which undergo cyclopropanation and generating biradicals which promote ring-opening aromatization of the in situ generated fused cyclopropanes.展开更多
文摘饱和的碳氢键氧化是合成化学和化学工业中一类重要的化学反应.然而,饱和C(sp^(3))−H键离解能(BDEs)较高、极性较弱,导致了底物难以活化和催化转化效率较低等问题.在过去的几十年,C(sp^(3))−H键的定向活化转化取得了重要的进展.其中,关于C(sp^(3))−H键催化氧化的研究主要涉及一些键能低的、预活化的C−H键,包括苄基型、亚甲基型、脂肪族X−CH_(2)(X=O,N)和甲苯等,含有未活化C(sp^(3))−H键的复杂化合物的选择性氧化仍具有挑战性.例如,芳基醚C(sp^(3))−H键功能化通常采用计量的过氧化物氧化剂,或者通过单电子氧化和碱促进的去质子化进一步构建C−C/C−N键,产物选择性较低,也带来了一些不利的环境影响.因此,有必要开发高效、温和的芳基醚C(sp^(3))−H键选择氧化方法,并将其应用于有机合成和药物开发.近年来,光催化C(sp^(3))−H键氧化因其操作简便、氧化还原中性等优点,已发展成为一种有用且多样的催化研究工具.本文发展了一种利用氧气作为氧化剂,在可见光驱动下选择性地将芳基醚C(sp^(3))−H键氧化成为甲酸苯酯类产物的新方法.使用Mes-10-phenyl-Acr^(+)−BF_(4)^(-)光催化剂,高效活化多种氯源(如盐酸、无机氯盐和有机氯化物)得到氯自由基,由于其具有较高的氧化能力(+2.03 V vs.SCE)和对氢原子的亲和力,能够通过氢原子转移过程活化芳基醚C(sp^(3))−键,攫取氢自由基得到相应的烷基碳自由基(•CH_(2)OPh)中间体,进一步被分子氧选择氧化得到酯类目标产物.研究结果表明,多种链状芳基醚和不同取代(如给电子基和吸电子基)芳基醚均可发生氧化反应,高收率地合成了一系列官能团丰富的甲酸苯酯类化合物.本文方法具有反应条件温和、操作简单、官能团耐受性好以及可规模化放大等优点,并且少量的水对反应没有明显影响.机理实验研究结果表明,芳基醚C(sp^(3))−H键的断裂是反应过程的决速步骤.紫外可见吸收光谱结果表明,氯离子与催化剂之间的相互作用强于底物,并且自由基捕获实验证实反应体系中存在氯自由基和烷基碳自由基物种,表明反应经历自由基路径.此外,电子顺磁共振测试结果表明,反应过程中存在单线态氧物种,可能是激发态的光催化剂直接与氧气发生能量转移得到;同位素实验(18O)揭示了甲酸苯酯类化合物氧的来源.综上,本文实现了温和条件下光催化芳基醚C(sp^(3))−H键选择氧化反应,高收率合成了一系列甲酸苯酯类化合物.该方法避免了化学计量的过氧化物和碱等添加剂的使用以及底物的过度氧化,阐明了催化反应机制,为其他醚类化合物的C(sp^(3))−H键氧化功能化提供了新思路,为后续化学合成和药物开发提供了参考和启示.
文摘Propane dehydrogenation(PDH)on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production,while the detail mechanism remains debatable.Ga_(2)O_(2)^(2+) stabilized by framework Al pairs have been identified as the most active species in Ga/H-ZSM-5 for PDH in our recent work.Here we demonstrate a strong correlation between the PDH activity and a fraction of Ga_(2)O_(2)^(2+) species corresponding to the infrared GaH band of higher wavenumber(GaHHW)in reduced Ga/H-ZSM-5,instead of the overall Ga_(2)O_(2)^(2+) species,by employing five H-ZSM-5 supports sourced differently with comparable Si/Al ratio.This disparity in Ga_(2)O_(2)^(2+) species stems from their differing capacity in completing the catalytic cycle.Spectroscopic results suggest that PDH proceeds via a two-step mechanism:(1)C-H bond activation of propane on H-Ga_(2)O_(2)^(2+) species(rate determining step);(2)β-hydride elimination of adsorbed propyl group,which only occurs on active Ga_(2)O_(2)^(2+) species corresponding to GaHHW.
基金the National Natural Science Foundation of China(Nos.22025206,21991094)supported by the Ministry of ScienceTechnology of the People’s Republic of China(No.2018YFE0118100)+1 种基金the CAS-NSTDA Joint Research Project(No.GJHZ2075)Dalian Science and Technology Innovation Fund(No.2019J11CY009).
文摘Selective oxidation of saturated C(sp^(3))-H bonds in hydrocarbon to target chemicals under mild conditions remains a signifi-cant but challenging task because of the chemical inertness and high dissociation energy of C(sp^(3))-H bonds.Semiconductor photocatalysis can induce the generation of holes and oxidative radicals,off ering an alternative way toward selective oxidation of hydrocarbons under ambient conditions.Herein,we constructed N-doped TiO_(2) nanotubes(N-TNTs)that exhibited remark-able activity and selectivity for toluene oxidation under visible light,delivering the conversion of toluene and selectivity of benzaldehyde of 32% and>99%,respectively.Further mechanistic studies demonstrated that the incorporation of nitrogen induced the generation of N-doping level above the O 2p valance band,directly contributing to the visible-light response of TiO_(2).Furthermore,hydroxyl radicals generated by photogenerated holes at the orbit of O 2p were found to be unselective for the oxidation of toluene,aff ording both benzaldehyde and benzoic acid.The incorporation of nitrogen was able to inhibit the generation of hydroxyl radicals,terminating the formation of benzoic acid.
文摘The title compound (C14H12N2O2, Mr = 240.26) crystallizes in the monoclinic system, space group P21/a with a = 7.394(1), b = 21.334(3), c = 7.423(1) ? b = 89.82(1)? V = 1170.8(3) ?, Z = 4, Dc = 1.363 g/cm3, m(MoKa) = 0.93 cm-1 and F(000) = 504.00. The final R and wR are 0.0440 and 0.1370 for 2153 observed reflections (I > 2s(I)), respectively. The dihedral angle between the two phenyl rings is 52.9 and that between the NO2 group and its attached ring is 3.0. In the crystal, molecules are stacked along [100] through p…p interactions. The CH…O hydrogen bond (3.403 ? 120.4? laterally connects the stacks along [010] to form networks (001) which are further anti- parallelly connected by CH…O (3.382 ? 142.9) and p…p interactions extending along [001]. Also presented here is a brief study on the CH…O hydrogen bonds in nitro-substituted benzyl-ideneanilines which can be classified into five types, namely, )5(12R, )4(21R, )8(22R, )6(12R and )7(22R, with the first three occurring more often.
基金supported by the National Key R&D Program of China (2022YFA1506100)the National Natural Science Foundation of China (21901191)+1 种基金the Fundamental Research Funds for the Central Universities (2042023kf0202)the China Postdoctoral Science Foundation (2023TQ0250)。
文摘Previous carbene insertion to C–H bonds of 1,3-azoles relied on metal carbene species. Herein, we report a metal-free C(sp^(2))–H bond functionalization of 1,3-azoles with trifluoroacetylsilanes. The reaction features mild conditions, broad substrate scope and wide functional group tolerance. The mechanistic study supports that the success of the reaction is probably attributed to the dual roles of trifluoroacetylsilanes under the photocatalyzed conditions: generating carbenes which undergo cyclopropanation and generating biradicals which promote ring-opening aromatization of the in situ generated fused cyclopropanes.
