Three chiral aminopyridine ligands derived from L-proline were prepared. Careful evaluation of the corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed a broad substrate scope ...Three chiral aminopyridine ligands derived from L-proline were prepared. Careful evaluation of the corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed a broad substrate scope in the presence of 0.2 mol% manganese complex and 0.5 equiv. 2,2-dimethylbutyric acid, with aqueous hydrogen peroxide as an oxidant. A variety of olefins including styrenes, chromenes, and cinnamamides were transformed successfully into the target epoxides with moderate to excellent enantioselectivity（yield up to 95%, ee up to 99%）.展开更多
Although the oxygen reduction process to hydrogen peroxide(H_(2)O_(2))is a green option for H_(2)O_(2)generation,the low activity and selectivity hindered the industry's process.In recent years,the electrochemical...Although the oxygen reduction process to hydrogen peroxide(H_(2)O_(2))is a green option for H_(2)O_(2)generation,the low activity and selectivity hindered the industry's process.In recent years,the electrochemical synthesis of H_(2)O_(2)through a 2e-transfer method of oxygen reduction reaction(ORR)has piqued the interest of both academics and industry.Metal oxide catalysts have emerged as a novel family of electrochemical catalysts due to their unusual physical,chemical,and electrical characteristics.In this work,we first developed a Ruddlesden-Popper perovskite oxide(Pr_(2)NiO_(4+δ))as a highly selective and active catalyst for 2e-ORR to produce H_(2)O_(2).Molybdenum was introduced here to adjust the oxidation states of these transition metals with successful substitution into Ni-site to prepare Pr_(2)Ni1-xMoxO_(4+δ),and the molybdenum substitution improves the H_(2)O_(2)selectivity during the ORR process,in 0.1 M KOH,from 60%of Pr_(2)NiO_(4+δ)to 79%of Pr_(2)Ni_(0.8)Mo_(0.2)O_(4+δ)at 0.55 V versus RHE.A limiting H_(2)O_(2)concentration of_0.24 mM for Pr_(2)NiO_(4+δ)and 0.42 mM for Pr_(2)Ni_(0.8)Mo_(0.2)O_(4+δ)was obtained at a constant current of 10 mA/cm2 using a flow-cell reactor using a gas-diffusion electrode.展开更多
基金supported by the National Natural Science Foundation of China(21473226,21773273)Key Research Program of Frontier Sciences,CAS(QYZDJ-SSW-SLH051)Natural Science Foundation of Jiangsu Province(BK20170420)~~
文摘Three chiral aminopyridine ligands derived from L-proline were prepared. Careful evaluation of the corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed a broad substrate scope in the presence of 0.2 mol% manganese complex and 0.5 equiv. 2,2-dimethylbutyric acid, with aqueous hydrogen peroxide as an oxidant. A variety of olefins including styrenes, chromenes, and cinnamamides were transformed successfully into the target epoxides with moderate to excellent enantioselectivity（yield up to 95%, ee up to 99%）.
基金The authors are grateful for the FWO(12ZV320N)and NNSF(22005250).O.M.M.thanks CONACYT-Mexico.K.W.is grateful to Guangzhou Elite Project.W.Z.,W.G,S.X.,and Q.L.are grateful to CSC.
文摘Although the oxygen reduction process to hydrogen peroxide(H_(2)O_(2))is a green option for H_(2)O_(2)generation,the low activity and selectivity hindered the industry's process.In recent years,the electrochemical synthesis of H_(2)O_(2)through a 2e-transfer method of oxygen reduction reaction(ORR)has piqued the interest of both academics and industry.Metal oxide catalysts have emerged as a novel family of electrochemical catalysts due to their unusual physical,chemical,and electrical characteristics.In this work,we first developed a Ruddlesden-Popper perovskite oxide(Pr_(2)NiO_(4+δ))as a highly selective and active catalyst for 2e-ORR to produce H_(2)O_(2).Molybdenum was introduced here to adjust the oxidation states of these transition metals with successful substitution into Ni-site to prepare Pr_(2)Ni1-xMoxO_(4+δ),and the molybdenum substitution improves the H_(2)O_(2)selectivity during the ORR process,in 0.1 M KOH,from 60%of Pr_(2)NiO_(4+δ)to 79%of Pr_(2)Ni_(0.8)Mo_(0.2)O_(4+δ)at 0.55 V versus RHE.A limiting H_(2)O_(2)concentration of_0.24 mM for Pr_(2)NiO_(4+δ)and 0.42 mM for Pr_(2)Ni_(0.8)Mo_(0.2)O_(4+δ)was obtained at a constant current of 10 mA/cm2 using a flow-cell reactor using a gas-diffusion electrode.
