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991.
Phil Liebing Jorna Kalim Natalia Arefyeva Florian Oehler Mathias Wickleder Antonio Togni 《Angewandte Chemie (International ed. in English)》2019,58(25):8585-8588
Four complexes of MCl4 (M=Ti, Zr, Hf) with the hypervalent trifluoromethyl iodine reagent trifluoromethyl‐1,3‐dihydro‐3,3‐dimethyl‐1,2‐benziodoxole ( 1 ,=L) are described. With TiCl4, an I?O bond cleavage occurs, leading to the formation of the trifluoromethyliodonium alcoholate complexes [Ti2Cl6(L)4]Cl2 ( 2 a ) and Ti2Cl8(L) ( 2 b ). Reactions with ZrCl4 and HfCl4 form the complexes ZrCl4(L)2 ( 3 ) and HfCl4(L)2 ( 4 ), respectively, wherein the original I?O bond is retained and elongated compared to that in free 1 . Therefore, the reactivity of 1 can be easily and practically fine‐tuned by addition of different metal chlorides, following the order ZrCl4/HfCl4<TiCl4<2 TiCl4. Complexes 2 a , 3 , and 4 are remarkably bench‐stable forms of activated reagent 1 , while 2 b is readily accessible in situ. 2 a and 2 b represent the first “real” trifluoromethyliodonium reagents derived from iodanes, that is, with the I?O bond being completely cleaved. The new complexes were shown to be useful for the trifluoromethylation of para‐toluenesulfonate under aprotic conditions. 相似文献
992.
Marc Eric Vogt Fabian Duddeck Helmut Harbrecht Florian Stutz Martin Wahle Markus Zimmermann 《PAMM》2018,18(1)
In complex system design, design variables can be divided into two groups, early‐ and late‐decision variables. Early‐decision variables are equipped with tolerance regions which are specified during the early stages of the development process. Tolerance is necessary to account for changes of design variable values due to later and therefore unknown, design restrictions. In this sense, early‐decision variables are subject to lack‐of‐knowledge uncertainty. Tolerance regions for early‐decision variables can be significantly increased by the use of late‐decision variables. The latter are not equipped with tolerance regions and, by contrast, have to be arbitrarily well adjustable within their design intervals. The values of late‐decision variables are chosen in a later development phase when further design restrictions are known. Late‐decision variables then may compensate for the choice of early‐decision variables. Solution‐compensation spaces are regions of early‐ and late‐decision variables where for all values of early‐decision variables values for late‐decision variables from their associated intervals exist such that all design requirements are satisfied. A new approach to compute solution‐compensation spaces for linear systems is introduced. It is based on an enhanced Fourier‐Motzkin‐Elimination algorithm which uses H‐redundancy removal. The new algorithm is applied to a design problem from vehicle dynamics and we show that it outperforms the so‐called basic projection algorithm presented in [7]. 相似文献
993.
Film flow over surfaces containing topography is a key feature of a number of coating technologies. To date, detailed theoretical investigations of the same, underpinned by the long‐wave approximation, have been used to study the nature of the associated free‐surface disturbance formed; the internal flow structure being more‐or‐less of secondary importance. In the work reported here, a recently developed approach is used to explore the internal flow, embodying unsteady effects, for a related model problem in which the free‐surface is replaced by a moving upper boundary with its own topographical profile. 相似文献
994.
Priv.‐Doz. Dr. Florian Beuerle Dr. Bappaditya Gole 《Angewandte Chemie (International ed. in English)》2018,57(18):4850-4878
Porous organic materials are an emerging class of functional nanostructures with unprecedented properties. Dynamic covalent assembly of small organic building blocks under thermodynamic control is utilized for the intriguingly simple formation of complex molecular architectures in one‐pot procedures. In this Review, we aim to analyze the basic design principles that govern the formation of either covalent organic frameworks as crystalline porous polymers or covalent organic cage compounds as shape‐persistent molecular objects. Common synthetic procedures and characterization techniques will be discussed as well as more advanced strategies such as postsynthetic modification or self‐sorting. When appropriate, comparisons are drawn between polymeric frameworks and discrete organic cages in terms of their underlying properties. Furthermore, we highlight the potential of these materials for applications ranging from gas storage to catalysis and organic electronics. 相似文献
995.
Robert Naumann Florian Lehmann Prof. Dr. Martin Goez 《Angewandte Chemie (International ed. in English)》2018,57(4):1078-1081
We present the first working system for accessing and utilizing laboratory‐scale concentrations of hydrated electrons by photoredox catalysis with a green light‐emitting diode (LED). Decisive are micellar compartmentalization and photon pooling in an intermediate that decays with second‐order kinetics. The only consumable is the nontoxic and bioavailable vitamin C. A turnover number of 1380 shows the LED method to be on par with electron generation by high‐power pulsed lasers, but at a fraction of the cost. The extreme reducing power of the electron and its long unquenched life as a ground‐state species are synergistic. We demonstrate the applicability to the dechlorination, defluorination, and hydrogenation of compounds that are inert towards all other visible‐light photoredox catalysts known to date. A comprehensive mechanistic investigation from microseconds to hours yields results of general validity for photoredox catalysis with photon pooling, allowing optimization and upscaling. 相似文献
996.
Ronan Rocaboy Dr. David Dailler Florian Zellweger Dr. Markus Neuburger Dr. Christophe Salomé Dr. Eric Clot Prof. Dr. Olivier Baudoin 《Angewandte Chemie (International ed. in English)》2018,57(37):12131-12135
The Pd0‐catalyzed C(sp3)‐H arylation of 2‐bromo‐N‐methylanilides leads to unstable benzazetidine intermediates that rearrange to benzoxazines through 4π electrocyclic ring‐opening and 6π electrocyclization. The introduction of a bulky, non‐activatable amide group on the nitrogen atom was key to favor the challenging reductive elimination step and disfavor undesired reaction pathways. 相似文献
997.
Benjamin Hupp Dr. Jörn Nitsch Tanja Schmitt Dr. Rüdiger Bertermann Dr. Katharina Edkins Florian Hirsch Prof. Dr. Ingo Fischer Michael Auth Dr. Andreas Sperlich Priv.‐Doz. Dr. Andreas Steffen 《Angewandte Chemie (International ed. in English)》2018,57(41):13671-13675
The investigation of the mechanisms of mechanochromic luminescence is of fundamental importance for the development of materials for photonic sensors, data storage, and luminescence switches. The structural origin of this phenomenon in phosphorescent molecular systems is rarely known and thus the formulation of structure–property relationships remains challenging. Changes in the M–M interactions have been proposed as the main mechanism with d10 coinage metal compounds. Herein, we describe a new mechanism—a mechanically induced reversible formation of a cation–anion exciplex based on Cu–F interactions—that leads to highly efficient mechanochromic phosphorescence and unusual large emission shifts from UV‐blue to yellow for CuI complexes. The low‐energy luminescence is thermo‐ and vaporesponsive, thus allowing the generation of white light as well as for recovering the original UV‐blue emission. 相似文献
998.
999.
Large eddy simulations of turbulent flow between shrouded co-rotating disks, representing a simplified model of a hard disk drive, are performed. The computation domain surrounds a complete disk and is bounded at top and bottom by half a disk. Therefore, it is possible to compute the fluctuating pressure field surrounding the middle disk. Also, the influence of the shroud geometry is taken into account by comparing a flat shroud wall and a wall with rib chambers. In the flat shroud case, the fluctuating pressure on the upper- and lower-surface of a disk indicates a strong correlation with fluid motion travelling across the disk-tip clearance region. However, in the ribbed shroud case the organized flow structure that is observed in the flat shroud case disappears and the fluctuating pressure acting on the surface of the disk is remarkably diminished. 相似文献
1000.
Florian Luca 《Monatshefte für Mathematik》2003,138(3):209-223
In this paper, we show that if (u
n
)
n ≥ 0
is a Lucas sequence of integers whose roots are real quadratic units (like the Fibonacci sequence, for example), then for
every integer b > 1 the density of the set of positive integers n such that |u
n
| is a base b palindrome (i.e., the string of its base b digits reads the same from the left and from the right) is zero.
Received October 30, 2001; in revised form March 4, 2002 相似文献