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991.
Weiqing Mao Yaya Wang Dr. Li Xiang Prof. Dr. Qian Peng Dr. Xuebing Leng Prof. Dr. Yaofeng Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(44):10304-10308
Reaction of a scandium phosphoniomethylidene with carbon monoxide provides the first scandium phosphonioketene ( 1 ). X-ray diffraction analysis shows that the complex has a very short Sc−C bond (2.138(2) Å), and DFT calculations indicate that this unusual short bond length is due to the significant contribution of ionic coulomb interaction between carbon and scandium and the η2-O,C coordination fashion. Complex 1 is thermally stable, albeit shows high reactivity towards a series of unsaturated substrates, including carbon dioxide, ketone, imine, nitrile and isocyanide. In the reaction with tert-butyl isocyanide, not only an insertion of tert-butyl isocyanide into the Sc−C bond occur, but also a C−H activation on the phenyl ring. DFT calculations show that the reactivity of 1 operated by nucleophilic properties, and therefore the reaction mechanism favors the nucleophilic attack to isocyanide as a rate-determining step, followed by the stepwise C−H activation through an interesting C−H deprotonation. 相似文献
992.
Dr. Ludovic Castro Dr. Yat-Ming So Chang-woo Cho Prof. Dr. Rolf Lortz Kai-Hong Wong Dr. Kai Wang Prof. Dr. Polly L. Arnold Dr. Ka-Chun Au-Yeung Dr. Herman H.-Y. Sung Prof. Dr. Ian D. Williams Prof. Dr. Wa-Hung Leung Prof. Dr. Laurent Maron 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(46):10834-10839
A combined experimental and theoretical investigation on the cerium(IV) oxo complex [(LOEt)2Ce(=O)(H2O)] ⋅ MeC(O)NH2 ( 1 ; LOEt−=[Co(η5-C5H5){P(O)(OEt)2}3]−) demonstrates that the intermediate spin-state nature of the ground state of the cerium complex is responsible for the versatility of its reactivity towards small molecules such as CO, CO2, SO2, and NO. CASSCF calculations together with magnetic susceptibility measurements indicate that the ground state of the cerium complex is of multiconfigurational character and comprised of 74 % of CeIV and 26 % of CeIII. The latter is found to be responsible for its reductive addition behavior towards CO, SO2, and NO. This is the first report to date on the influence of the multiconfigurational ground state on the reactivity of a metal–oxo complex. 相似文献
993.
Dr. Jingfeng Huo Kangbao Zhong Yazhen Xue MyeeMay Lyu Dr. Yifan Ping Wenbai Ouyang Dr. Zhenxing Liu Prof. Yu Lan Prof. Jianbo Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(27):e202200191
We report herein a highly efficient palladium-catalyzed carbene insertion into strained Si−C bonds of benzosilacyclobutanes, which provides an efficient method to access α-chiral silanes. With a sterically hindered ligand, carbene insertion into the C(sp3)−Si bond of benzosilacyclobutanes occurred in excellent site- and enantioselectivity, while C(sp2)−Si bond insertion occurred selectively with less sterically hindered ligands. Reaction mechanism, in particular the roles of the chiral ligands in controlling the site-selectivity of the insertion reactions, are elucidated by using hybrid density functional theory. 相似文献
994.
Zixuan Huang Nathaniel Corrigan Shiyang Lin Cyrille Boyer Jiangtao Xu 《Journal of polymer science. Part A, Polymer chemistry》2019,57(18):1947-1955
As one of the emerging techniques for preparing discrete oligomers, the photo‐RAFT single unit monomer insertion (SUMI) process has shown its uniqueness and superiority in the control of both monomer sequence and stereochemistry. However, current precision polymer synthesis techniques are still burdened by the scalability challenges, such as low reaction yields, small product quantities, and long production times. Herein, we successfully established a practical protocol to address scalability problems in the photo‐RAFT SUMI processes. A series of discrete oligomers containing up to five monomer units were synthesized in batch and flow reactors by sequential and alternating SUMI of two monomers into a trithiocarbonate RAFT agent under mild reaction conditions and purified by automated flash chromatography. This protocol offers the process with large quantity (grams scale), excellent isolated yields (82%–95% for each step and 59% for five iterations), and short production time (several days for a pentamer). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1947–1955 相似文献
995.
William T.M. Irvine 《Comptes Rendus Mecanique》2018,346(3):170-174
This contribution to an issue of Comptes rendus Mécanique, commemorating the scientific work of Jean-Jacques Moreau (1923–2014), is intended to give a brief overview of recent developments in the study of helicity dynamics in real fluids and an outlook on the growing legacy of Moreau's work. Moreau's discovery of the conservation of hydrodynamic helicity, presented in an article in the Comptes rendus de l'Académie des sciences in 1961, was not recognized until long after it was published. This seminal contribution is gaining a new life now that modern developments allow the study of helicity and topology in fields and is having a growing impact on diverse areas of physics. 相似文献
996.
Dr. Shingo Harada Koki Tanikawa Haruka Homma Chigaya Sakai Tsubasa Ito Prof. Dr. Tetsuhiro Nemoto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12058-12062
An enantioselective insertion reaction of silver carbenes generated from donor–acceptor-substituted diazo compounds into the O−H bond of phenols was developed. A homobinuclear silver complex with a chiral phosphorous ligand was created in situ from AgNTf2 and (S)-XylylBINAP (in a 2:1 mole ratio). Detailed mechanistic studies using combined experimental and computational techniques revealed that one silver atom center of the catalyst forms a silver carbene and another one works as a Lewis acid for the nucleophilic addition of a phenol. Two counter-anions, two water molecules, and two silver atoms cooperatively mediate the subsequent protonation event to lower the activation energy and control enantioselectivity, affording an array of valuable α-aryl-α-aryloxy esters. 相似文献
997.
The stereoselective synthesis of 5,5-spiroacetals by Rh(II)-catalysed double C–H insertion of methylene acetals bearing two diazo ester substituents is described. The diastereoselectivity of this bidirectional approach can be tuned through appropriate choice of catalyst, and chiral catalysts lead to products with up to 89% ee. The diastereoselectivity of the first cyclisation suggests that the second cyclisation proceeds via a non-concerted pathway. 相似文献
998.
《Expositiones Mathematicae》2020,38(1):131-137
We present two proofs that all closed, orientable 3-manifolds are parallelisable. Both are based on the Lickorish–Wallace surgery presentation; one proof uses a refinement of this presentation due to Kaplan and some basic contact geometry. This complements a recent paper by Benedetti–Lisca. 相似文献
999.
Branko S. Jursic 《Journal of Molecular Structure》1999,460(1-3):11-18
Ab initio and density functional theory (DFT) computational studies were performed in order to determine the potential energy profiles for the inter-conversions of the small silicon–nitrogen built chemical systems: HSiN, HNSi, HSiNH2, and HNSiH2. Three hybrid DFT methods demonstrated high reliability in computing structures and potential energy profiles for these chemical transformations. The stability of some of these molecular systems and their interconversions was discussed and computational results were compared with experimental observations when available. 相似文献
1000.
We suggest a method to detect that two periodic knots are not equivariantly concordant, using surgery on factor links. We construct examples which satisfy all known necessary conditions for equivariant slice knots- Naik's and Choi-Ko-Song's improvements of classical results on Seifert forms and Casson-Gordon invariants of slice knots - but are not equivariantly slice.