Synthesis,characterization and electrocatalytic performance of a dinuclear triazenidosilver(I) complex for hydrogen production

Our group has developed a series of molecular electrocatalysts for hydrogen generation based on triazenido–metal complexes (cobalt, copper, etc.). In this paper, we first present the electrocatalytic performance of a new dinuclear silver complex, [Ag₂(L)₂], formed by the reaction of the triazenido ligand 1‐[(2‐carboxymethyl)benzene]‐3‐[(2‐methoxy)benzene]triazene (HL) with AgNO₃. At room temperature, the silver complex shows photoluminescence at 653 nm. The electrocatalytic systems based on this silver complex can afford 106.57 and 1536.36 moles of hydrogen per mole of catalyst per hour from acetic acid at an overpotential (OP) of 991.6 mV and from a neutral aqueous buffer (pH = 7.0) at an OP of 837.6 mV, respectively. Electrochemical investigations show that both silver ion and triazenido ligand play a role in determining the catalytic activities of the electrocatalytic system.     

A convenient method to prepare random LA/CL copolymers from poly(L-lactide) and ε-caprolactone

Sequential addition of L-lactide(LA) followed by ε-caprolactone(CL), and simultaneous addition of both monomers, afforded random LA/CL copolymers in the presence of lanthanide aryloxides under mild conditions. Transesterification was proved to play a predominant role in random copolymer formation. Moreover, treatment of poly(L-lactide) with ε-CL led to random copolymer formation, which provides a new strategy not only to prepare random LA/CL copolymers, but also to directly modify PLLA.     

高分散Ru/FeOx催化剂在二氧化碳选择加氢反应中的应用及其催化活性的调控

由于化石能源的大量开采和利用造成CO2过度排放,从而导致严重的温室效应和气候环境问题,给人类生存带来极大威胁.CO2选择加氢反应可以将CO2催化加氢生成高附加值的CO产物.与其他的CO2转化反应策略相比,该过程中H2的消耗更少,成为可有效处理及转化CO2的手段之一.同时,应尽可能抑制CO2深度加氢以及甲烷的产生,研制及设计具有高CO选择性的新型高效催化剂及其构效关系的分析仍十分重要.据报道,负载型贵金属基催化剂的使用有利于H2分子的活化,具有优异的催化活性,因而广泛应用于多种催化反应中.然而,贵金属催化剂实现工业应用的最大挑战是资源的限制及其高额的成本.近年来,由贵金属制备的负载型亚纳米团簇受到广泛关注,主要包括如Au,Pt,Pd,Ru等贵金属,可有效应用于多相催化反应.人们还致力于提高负载型亚纳米团簇的分散度,促进催化剂活性位点的有效暴露,有利于大幅度提高催化剂的有效利用率.本文采用共沉淀法成功制备了超高分散的负载型Ru基催化剂,通过CO2选择加氢-程序升温表面反应(TPSR)和质谱联用技术测试了催化剂性能,发现CO2加氢反应生成CO选择性达100%.采用XRD,BET和TEM等方法对催化剂结构进行表征,并结合H2-TPR,H2-TPD和XPS等表征结果深入探讨了催化剂构效关系,并提出了针对该催化剂体系较为合理的反应模型.在CO2选择加氢反应的催化性能测试中,2.50%Ru/FeOx催化剂对目标产物CO选择性仅为41%; 随着Ru负载量降低至0.25%和0.1%时,CO选择性明显提高至80%; 当进一步降低Ru含量至0.01%时,CO选择性接近100%,且表现出优异的反应速率.在360 oC时,0.01%Ru/FeOx催化剂的相对反应速率为7.71 molCO2molRu-1 min-1,是2.50%Ru/FeOx催化剂相对反应速率的154倍.H2-TPR结果表明,贵金属Ru可以明显促进载体FeOx的还原,并产生丰富的氧空位,进而促进CO2的吸附、活化.而且CO2选择加氢TPSR结果显示,目标产物CO的起始生成温度总是滞后于原料H2的初始活化温度,与H2-TPR结果及文献报道的CO2选择加氢反应机理一致.通过H2-TPD深入理解H2在催化剂表面的活化和氢溢流现象,以及Hads与不同催化剂之间的相互作用力,0.01%Ru/FeOx催化剂相对较高的H2脱附峰温度表明,该样品中Ru与Hads具有极强的相互作用力,相对抑制了Hads与COads深入加氢生成CH4,从而提高了CO选择性,而2.50%Ru/FeOx催化剂的情况则与此相反.本文提出了从Hads吸附作用力强弱来考虑CO2选择加氢反应选择性的新思路,同时为设计CO2选择加氢制高附加值CO的高催化反应速率、高CO选择性的高分散Ru基催化剂提供了一种经济简易的催化剂设计思路.     

An efficient process for the synthesis of gem-dinitro compounds under high steric hindrance by nitrosation and oxidation of secondary nitroalkanes

A new nitrosation and oxidation process to synthesize gem-dinitro compounds was accomplished by using nitryl chloride as nitrosation reagent and ozone as oxidizing agent. The main features of the present protocol include the compatibility to substances with high steric hindrance, high yields and mild reaction conditions. A plausible mechanism involving the formation of an intermediate of gem-nitrosonitro compound by means of single electron transfer was also proposed.     

A high-efficiency and low-cost AEE polyurethane chemo-sensor for Fe3+ and explosives detection

An aggregation enhanced emission (AEE) polyurethane named STMPU-211 containing 0.13% mole concentration of 4,4′-((1Z,3Z)-1,4-diphenylbuta-1,3-diene-1,4-diyl) dibenzaldehyde (TABDAA) in the soft segments was synthesized and proved to be sensitive to Fe³⁺ and nitroaromatic explosives. The fluorescence of the AEE polyurethane was reduced in the presence of Fe³⁺, and almost quenched when 5000?μM Fe³⁺ was added. Meanwhile, the fluorescence intensity of STMPU-211 solution in DMF/water mixture was decreased when explosives like 2,4,6-trinitrophenol (PA) and 3-nitro-1,2,4-triazol-5-one (NTO) were applied. Especially, the quenching coefficient K_SV value of PA was 5.7?×?10⁶?M^?1, confirming that the polyurethane STMPU-211 could be a highly sensitive sensor for the detection of PA. Therefore, AEE polyurethanes with low concentration of TABDAA have promising applications in biological probe, environment monitoring and antiterrorism fields.     

Formal [4 + 1] cycloaddition strategy for the synthesis of dihydrobenzofurans via Michael addition of 2-(2-nitrovinyl)-phenols and malonate esters (C1 synthon) and subsequent iodine-catalyzed oxidative annulation

A novel [4 + 1] cycloaddition protocol for the synthesis of dihydrobenzo(naphtho)furan skeletons from readily available 2-(2-nitrovinyl)-phen(naphth)ols and malonate esters via a tandem Michael addition/iodine-catalyzed oxidative annulation has been developed. This method provides a new and facile application of malonate esters as 1,1-nucleophilic/electrophilic type C1 synthons without a pre-functionalization step and the plausible reaction mechanism is proposed.     

Dynamic Ultralong Organic Phosphorescence by Photoactivation

Smart materials with ultralong phosphorescence are rarely investigated and reported. Herein we report on a series of molecules with unique dynamic ultralong organic phosphorescence (UOP) features, enabled by manipulating intermolecular interactions through UV light irradiation. Our experimental data reveal that prolonged irradiation of single‐component organic phosphors of PCzT, BCzT, and FCzT under ambient conditions can activate UOP with emission lifetimes spanning from 1.8 to 1330 ms. These phosphors can also be deactivated back to their original states with short‐lived phosphorescence by UV irradiation for 3 h at room temperature or through thermal treatment. Additionally, the dynamic UOP was applied successfully for a visual anti‐counterfeiting application. These findings may provide unique insight into dynamic molecular motion for optical processing and expand the scope of smart‐response materials for broader applications.     

Enantioselective phospha-Michael reaction of diethyl phosphonate with exocyclic α,β-unsaturated benzocyclic ketones catalyzed by a dinuclear zinc−AzePhenol catalyst

The dinuclear zinc complexes as high performance catalysts were used to catalyze phospha-Michael reaction of exocyclic α,β-unsaturated benzocyclic ketones under mild conditions, and the desired products possessing 1-indanones or 1-tetralones skeleton were obtained with excellent enantioselectivities of up to 99%/99% ee and yields of up to 99%. The absolute stereochemistry of the major products catalyzed by (R,R)-L1 was determined to be the (R,R)-configuration by X-ray crystallographic analysis of 3d. A positive nonlinear effect was observed and the possible mechanism was proposed.     

Total syntheses of melinonine-E and strychnoxanthine: Evolution of the synthetic strategy enabled by novel method development

In this full account, the evolution of a synthetic strategy was detailed from a nitroso-ene cyclization to an aza-Wacker reaction for ring construction in the syntheses of melinonine-E and strychnoxanthine. The aza-Wacker cyclization to form the bridged ring was successfully developed and applied in the first asymmetric syntheses of melinonine-E and strychnoxanthine in 5–6 steps from a readily available chiral lactone. The proposed biogenesis of these two rare β-carbolinium alkaloids was revised based on their absolute configurations. Moreover, the substrate scope of the aza-Wacker cyclization demonstrated its potential for accessing various bridged ring skeletons. The mechanistic investigation established that the profound effect of the N-substituent on the amide was crucial to the success of the cyclization via the tunable amidopalladation pathway.