Ultrahigh Loading Copper Single Atom Catalyst for Palladium-free Wacker Oxidation

Wacker oxidation is an industry-adopted process to transform olefins into value-added epoxides and carbonyls. However, traditional Wacker oxidation involves the use of homogeneous palladium and copper catalysts for the olefin addition and reductive elimination. Here, we demonstrated an ultrahigh loading Cu single atom catalyst(14% Cu, mass fraction) for the palladium-free Wacker oxidation of 4-vinylanisole into the corresponding ketone with N-methylhydroxylamine hydrochloride as an additive under mild conditions. Mechanistic studies by ¹⁸O and deuterium isotope labelling revealed a hydrogen shift mechanism in this palladium-free process using N-methylhydroxylamine hydrochloride as the oxygen source. The reaction scope can be further extended to Kucherov oxidation. Our study paves the way to replace noble metal catalysts in the traditional homogeneous processes with single atom catalysts.     

货运动车组装载门凹陷对隧道内会车压力波的影响

随着我国技术经济水平的提高，电子商务产业快速发展，货运动车组应运而生。采用有限体积方法和重叠网格方法，以及SST k-ω高雷诺数湍流模型，数值模拟研究时速350 km的货运动车组在隧道内交会的压力波，探究货运动车组车体结构即装载门凹陷对隧道内交会压力波的影响。实车试验结果验证了本文数值模拟方法的准确性。研究结果表明，凹陷的装载门使平直车身处的最大正压值增大约20%~30%，且有无凹陷的装载门中心最大正压值的差异百分比维持在35%~80%，最大负压值差异百分比在20%~25%。     

Synthesis of Cyclic Compounds via Photoinduced Radical Cyclization Cascade of C=C bonds

Cyclic compounds constitute a great important class of substances in the science of medicine and biology, which renders the research on facile and efficient construction of such complex scaffolds from simple starting materials to be hot and appealing. Recently, the radical cascade reaction involving multiple bond formation/cleavage has emerged as an ideal and powerful route to give high‐value cyclic products, along with diminished cost and waste. As a simple and benign methodology, photoredox catalysis offers a readily available access to the generation of radical species. Alkenes have been recognized as one of the most valuable building blocks for the reason they allow installation of different functional groups simultaneously through addition to the C=C bonds. This account summarizes the recent advances in photoinduced radical cascade cyclization to the synthesis of cyclic compounds with C=C bonds working as the initial radical acceptors, and emphasis is put on the related reaction mechanisms.     

Synthesis and Electronic Properties of Novel 5,7-Diazapentacene Derivatives

A route to the synthesis of novel 5,7-diazapentacenes and some preliminary studies on their properties is reported. A single crystal X-ray diffraction study of the dihexyl derivative showed it had formed a dimer during the analysis. The materials possess lower lying frontier orbitals than pentacene and may have potential applications in organic electronic devices. This synthetic method may be applicable to the synthesis of other azaacenes.     

Rate sensitivity and deformation mechanism of semi-crystalline polymers during instrumented indentation

Instrumented indentation tests using both constant loading rate (CLR) and continuous stiffness measurement (CSM) operation modes were performed to investigate the deformation mechanism and their sensitivity to the deformation rate in semi-crystalline polymers through the quantitative analysis of load-depth loading and unloading curves. The strain rate was constant during the CSM tests, while the strain rate decreased with the increasing of loading time in CLR tests. The mechanical response mechanism of the semi-crystalline polymers to these tests was very complicated because of the combined effects of strain-hardening in the crystal phase and strain-softening in the amorphous phase. Results show that the loading index m reflects the strain-hardening or strain-softening response during indentation. When m > 2, the mechanical response was due to the strain-hardening, and when m < 2, the response was due to strain-softening. A method based on the measured contact hardness was proposed to obtain the unloading stiffness, and the other mechanical parameters could then be determined according to the unloading stiffness.     

Synthesis,Structures, and Near‐IR Absorption of Heterole‐Fused Earring Porphyrins

A reaction sequence of regioselective peripheral bromination, Suzuki–Miyaura coupling with 2‐borylated thiophene or pyrrole, and oxidative ring‐closure with FeCl₃ allowed the synthesis of heterole‐fused earring porphyrins 4Pd and 9Pd from the parent earring porphyrin 1 . Differently pyrrole‐fused porphyrins 5H and 6H and their Pd^II complexes 5Pd and 6Pd were also synthesized. The structures of 4Pd , 5H, 6Pd , and 8Pd have been revealed by X‐ray analysis to be slightly twisted owing to constraints imposed by heterole‐fused structures. 5Pd exhibits an intensified band at 1505 nm, while 4Pd and 9Pd display small but remarkably red‐shifted absorption bands reaching around 2200 nm.     

Multifold factorizations of cyclic groups into subsets

Let $(G,+)$ be an abelian group. A finite multiset A over G is said to give a λ-fold factorization of G if there exists a multiset B over G such that each element of G occurs λ times in the multiset $A+B:=\{a+b:a\in A,b\in B\}$. In this article, restricting G to a cyclic group, we will provide sufficient conditions on a given multiset A under which the exact value or an upper bound of the minimum multiplicity λ of a factorization of G can be given by introducing a concept of ‘lcm-closure’. Furthermore, a couple of properties on a given factor A will be shown when A has a prime or prime power order (cardinality). A relation to multifold factorizations of the set of integers will be also glanced at a general perspective.     

Dimerisation of Dipiperidinoacetylene: Convenient Access to Tetraamino-1,3-Cyclobutadiene and Tetraamino-1,2-Cyclobutadiene Metal Complexes

The reaction of 1,2-dipiperidinoacetylene ( 1 ) with 0.5 equivalents of SnCl₂ or GeCl₂⋅dioxane afforded the 1,2,3,4-tetrapiperidino-1,3-cyclobutadiene tin and germanium dichloride complexes 2 a and 2 b , respectively. A competing redox reaction was observed with excess amounts of SnCl₂, which produced a tetrapiperidinocyclobutadiene dication with two trichlorostannate(II) counterions. Heating neat 1 to 110 °C for 16 h cleanly produced the dimer 1,3,4,4-tetrapiperidino-3-buten-1-yne ( 3 ); its reaction with stoichiometric amounts of SnCl₂ or GeCl₂⋅dioxane furnished the 1,3,4,4-tetrapiperidino-1,2-cyclobutadiene tin and germanium dichloride complexes 4 a and 4 b , respectively. Transition-metal complexes containing this novel four-membered cyclic bent allene (CBA) ligand were prepared by reaction of 3 with [(tht)AuCl], [RhCl(CO)₂]₂, and [(Me₃N)W(CO)₅] to form [(CBA)AuCl] ( 5 ), [(CBA)RhCl(CO)₂] ( 6 ), and [(CBA)W(CO)₅] ( 7 ). The molecular structures of all compounds 2 – 7 were determined by X-ray diffraction analyses, and density functional theory (DFT) calculations were carried out to rationalise the formation of 3 and 4 a .     

Rapid,Traceless, AgI‐Promoted Macrocyclization of Peptides Possessing an N‐Terminal Thioamide

Peptide macrocyclization is often a slow process, plagued by epimerization and cyclodimerization. Herein, we describe a new method for peptide macrocyclization employing the Ag^I‐promoted transformation of peptide thioamides. The Ag^I has a dual function: chemoselectively activating the thioamide and tethering the N‐terminal thioamide to the C‐terminal carboxylate. Extrusion of Ag₂S generates an isoimide intermediate, which undergoes acyl transfer to generate the native cyclic peptide, resulting in a rapid, traceless macrocylization process. Cyclic peptides are furnished in high yields within 1 hour, free of epimerization and cyclodimerization.