Chiral ruthenium-catalyzed enantioselective hydrogenation of tetrapyridine-type N-heteroarenes was firstly developed.The partial reduction of adjacent tetraheteroaromatic substrates proceeded smoothly in the presence of phosphine-free chiral cationic ruthenium diamine complexes,affording unprecedented high reactivity,enantioselecitivity and diastereoselectivity(up to 93%yield,>99%ee and 92:8 dr).The potential application of chiral tetradentate pyridine-amine products as chiral ligands has been demonstrated in the Cu-catalyzed asymmetric Friedel–Crafts alkylation reaction between indoles and nitroalkenes.
Chenghao LiShu-Xin ZhangYu FengYan-Mei HeQing-Hua Fan
Acceptorless alcohol dehydrogenation stands out as one of the most promising strategies in hydrogen storage technologies.Among various catalytic systems for this reaction,cost-effective molecular catalysts using phosphine-free ligands have gained considerable attention.However,the central challenge for using non-precious metals is to overcome the propensity of reacting by oneelectron pathway.Herein,we synthesized a phosphine-freeη^(5)-C_(5)Me_(5)-Co complex by using the metal-ligand cooperative strategy and compared its activity with analogous catalysts toward acceptorless alcohol dehydrogenation.The catalyst showed excellent performance with a turnover number of 130.4 and a selectivity close to 100%.The improved performance among the class ofη^(5)-C_(5)Me_(5)-Co complexes could be attributed to the more accessible Co center and its cooperation with the redox-active ligand.To further study the systematic structure-activity relationship,we investigated the electronic structures ofη^(5)-C_(5)Me_(5)-Co complexes by a set of characterizations.The results showed that the redox-active ligand has a significant influence on theη^(5)-C_(5)Me_(5)-Co moiety.In the meantime,the proximal O−/OH group is beneficial for shuttling protons.For the catalytic cycle,two dehydrogenation scenarios were interrogated through density functional theory,and the result suggested that the outer-sphere pathway was preferred.The formation of a dihydrogen complex was the rate-determining step with aΔG value of 16.9 kcal∙mol‒1.The electron population demonstrated that theη^(5)-C_(5)Me_(5)ligand played a key role in stabilizing transition states during dehydrogenation steps.This work identified the roles of vital ligand components to boost catalytic performance and offered rationales for designing metal-ligand cooperative nonprecious metal complexes.
Manipulating the self-assembly of transition metal telluride nanocrystals(NCs) creates opportunities for exploring new properties and device applications. Iron ditelluride(FeTe2) has recently emerged as a new class of magnetic semiconductor with three-dimensional(3D) magnetic ordering and narrow band gap structure, yet the self-assembly of FeTe2 NCs has not been achieved. Herein, the tree-like FeTe2 nanoarchitectures with orthorhombic crystal structure have been successfully synthesized by hot-injection solvent thermal approach using phosphine-free Te precursor. The morphology, size, and crystal structure have been investigated using transmission electron microscopy(TEM), high-resolution TEM(HRTEM),and powder x-ray diffraction(XRD). We study the formation process of tree-like FeTe2 NCs according to trace the change of the sample morphology with the reaction time. It was found that the FeTe2 nanoparticles show oriented aggregation and self-assembly behavior with the increase of reaction time, which is attributed to size-dependent magnetism properties of the samples. The magnetic interaction is thought to be the driving force of nanoparticle self-organization.
Hongyu WangMin WuYixuan WangHao WangXiaoli HuangXinyi Yang
Background and Originality Content Reduction of esters to alcohols is a fundamental transformation in organic chemistry,and is important for the production of a wide range of bulk and fine chemicals.Compared with traditional approaches using stoichiometric amounts of metal hydride reagents,catalytic hydrogenation represents an environmentally benign and atom economic alternative.
Zhihui ShaoRui ZhongRaffaella FerraccioliYibiao LiQiang Liu
A unique Pd＆Cu@Al catalyst was easily fabricated just by immersing commercial aluminum foil in a mixed xylene solution of PdC12 and CuCl2. The catalyst fabrication process led to aluminum oxide coatings in situ, which supported the metal nanoparticles and enhanced their catalytic activities for the phosphine-free Heck reaction of awl halides and styrenes with high turnover number （TON） up to 3.9×10^5. The reaction can be scaled up to at least 100 mmol and has been applied in modification of drug Lapatinib＇s intermediate with low metal residue. This novel catalyst is of good application potential in industrial production because it was extremely easy to be recycled, in regardless of the generation of the insoluble impurities or tars during the reaction processes.
The coordination mode of IL-supported diols used as phosphine-free ligands for palladium catalyzed Heck reaction has been investigated by tuning their compositions. The difference in coordination of these IL-supported diols with metal Pd in Heck reaction was related to the changes of the cation rings, leading to the different activities of Pd catalyst in the reaction. The experimental results indicated that the activities of Pd catalyst were affected mainly by n-electron density of the cation rings. Compared to pyridinium and piperidinium cations, imidazolium cations showed the best coordination to metal Pd. In the meantime, C-2 hydrogen and the length of alkyl side chains had impacts on the coordination as well.
