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《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(1):253-261
(R)‐[1‐(Dimethylamino)ethyl]benzene reacts with nBuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero‐aggregate ( 2 a ) containing the lithiated arene, unreacted nBuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li4(C6H4CH(Me)NMe2‐2)2(nBu)2] ( 2 b ) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C6H4CH(Me)NMe2‐2) with nBuLi in a 1:1 molar ratio. The mono‐Et2O adduct [Li4(C6H4CH(Me)NMe2‐2)2(nBu)2(OEt2)] ( 2 c ) and the bis‐Et2O adduct [Li4(C6H4CH(Me)NMe2‐2)2(nBu)2(OEt2)2] ( 2 d ) were obtained by re‐crystallization of 2 b from pentane/Et2O and pure Et2O, respectively. The single‐crystal X‐ray structure determinations of 2 b – d show that the overall structural motifs of all three derivatives are closely related. They are all tetranuclear Li aggregates in which the four Li atoms are arranged in an almost regular tetrahedron. These structures can be described as consisting of two linked dimeric units: one Li2Ar2 dimer and a hypothetical Li2nBu2 dimer. The stereochemical aspects of the chiral Li2Ar2 fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and 1H, 13C, and 6Li NMR spectroscopy. 相似文献
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Chiral Lithiated Allylic α‐Sulfonyl Carbanions: Experimental and Computational Study of Their Structure,Configurational Stability,and Enantioselective Synthesis 下载免费PDF全文
Dr. Frank Gerhards Dr. Nicole Griebel Prof. Dr. Gerhard Raabe Prof. Dr. Hans‐Joachim Gais 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17904-17920
X‐ray crystal structure analysis of the lithiated allylic α‐sulfonyl carbanions [CH2?CHC(Me)SO2Ph]Li ? diglyme, [cC6H8SO2tBu]Li ? PMDETA and [cC7H10SO2tBu]Li ? PMDETA showed dimeric and monomeric CIPs, having nearly planar anionic C atoms, only O?Li bonds, almost planar allylic units with strong C?C bond length alternation and the s‐trans conformation around C1?C2. They adopt a C1?S conformation, which is similar to the one generally found for alkyl and aryl substituted α‐sulfonyl carbanions. Cryoscopy of [EtCH?CHC(Et)SO2tBu]Li in THF at 164 K revealed an equilibrium between monomers and dimers in a ratio of 83:17, which is similar to the one found by low temperature NMR spectroscopy. According to NMR spectroscopy the lone‐pair orbital at C1 strongly interacts with the C?C double bond. Low temperature 6Li,1H NOE experiments of [EtCH?CHC(Et)SO2tBu]Li in THF point to an equilibrium between monomeric CIPs having only O?Li bonds and CIPs having both O?Li and C1?Li bonds. Ab initio calculation of [MeCH?CHC(Me)SO2Me]Li ? (Me2O)2 gave three isomeric CIPs having the s‐trans conformation and three isomeric CIPs having the s‐cis conformation around the C1?C2 bond. All s‐trans isomers are more stable than the s‐cis isomers. At all levels of theory the s‐trans isomer having O?Li and C1?Li bonds is the most stable one followed by the isomer which has two O?Li bonds. The allylic unit of the C,O,Li isomer shows strong bond length alternation and the C1 atom is in contrast to the O,Li isomer significantly pyramidalized. According to NBO analysis of the s‐trans and s‐cis isomers, the interaction of the lone pair at C1 with the π* orbital of the CC double bond is energetically much more favorable than that with the “empty” orbitals at the Li atom. The C1?S and C1?C2 conformations are determined by the stereoelectronic effects nC–σSR* interaction and allylic conjugation. 1H DNMR spectroscopy of racemic [EtCH?CHC(Et)SO2tBu]Li, [iPrCH?CHC(iPr)SO2tBu]Li and [EtCH?C(Me)C(Et)SO2tBu]Li in [D8]THF gave estimated barriers of enantiomerization of ΔG≠=13.2 kcal mol?1 (270 K), 14.2 kcal mol?1 (291 K) and 14.2 kcal mol?1 (295 K), respectively. Deprotonation of sulfone (R)‐EtCH?CHCH(Et)SO2tBu (94 % ee) with nBuLi in THF at ?105 °C occurred with a calculated enantioselectivity of 93 % ee and gave carbanion (M)‐[EtCH?CHC(Et)SO2tBu]Li, the deuteration and alkylation of which with CF3CO2D and MeOCH2I, respectively, proceeded with high enantioselectivities. Time‐dependent deuteration of the enantioenriched carbanion (M)‐[EtCH?CHC(Et)SO2tBu]Li in THF gave a racemization barrier of ΔG≠=12.5 kcal mol?1 (168 K), which translates to a calculated half‐time of racemization of t1/2=12 min at ?105 °C. 相似文献
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Self‐Assembly of Chiral Propeller‐like Supermolecules with Unusual “Sergeants‐and‐Soldiers” and “Majority‐Rules” Effects 下载免费PDF全文
Bo Nie Tian‐Guang Zhan Tian‐You Zhou Dr. Ze‐Yun Xiao Prof. Guo‐Fang Jiang Prof. Xin Zhao 《化学:亚洲杂志》2014,9(3):754-758
Chiral amplification is an interesting phenomenon in supramolecular chemistry mainly observed in complicated systems in which cooperative effect dominate. Herein, chiral, supramolecular, propeller‐like architectures have been constructed through coassembly of an achiral disk‐shaped molecule and chiral amino acid derivatives driven by intermolecular hydrogen bonding. Both the “sergeants‐and‐soldiers” principle and “majority‐rules” effect are applicable in these discrete four‐component supermolecules, which are the simplest supramolecular system ever reported that exhibit chiral amplification. 相似文献
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Masahiro Nagaoka Hiroyuki Tsuruda Dr. Masa‐aki Amako Prof. Dr. Hiroharu Suzuki Prof. Dr. Toshiro Takao 《Angewandte Chemie (International ed. in English)》2015,54(49):14871-14874
A μ3‐η2:η2:η2‐silane complex, [(Cp*Ru)3(μ3‐η2:η2:η2‐H3SitBu)(μ‐H)3] ( 2 a ; Cp*=η5‐C5Me5), was synthesized from the reaction of [{Cp*Ru(μ‐H)}3(μ3‐H)2] ( 1 ) with tBuSiH3. Complex 2 a is the first example of a silane ligand adopting a μ3‐η2:η2:η2 coordination mode. This unprecedented coordination mode was established by NMR and IR spectroscopy as well as X‐ray diffraction analysis and supported by a density functional study. Variable‐temperature NMR analysis implied that 2 a equilibrates with a tautomeric μ3‐silyl complex ( 3 a ). Although 3 a was not isolated, the corresponding μ3‐silyl complex, [(Cp*Ru)3(μ3‐η2:η2‐H2SiPh)(H)(μ‐H)3] ( 3 b ), was obtained from the reaction of 1 with PhSiH3. Treatment of 2 a with PhSiH3 resulted in a silane exchange reaction, leading to the formation of 3 b accompanied by the elimination of tBuSiH3. This result indicates that the μ3‐silane complex can be regarded as an “arrested” intermediate for the oxidative addition/reductive elimination of a primary silane to a trinuclear site. 相似文献
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Rungthip Kunthom Takuto Adachi Yujia Liu Nobuhiro Takeda Masafumi Unno Ryoji Tanaka 《化学:亚洲杂志》2019,14(23):4179-4182
Novel polyhedral structures were prepared with a butterfly‐shape composed of oligosiloxane wings and a double‐decker silsesquioxane (DDSQ) body. The compounds were synthesized in two steps from commercially available alkoxysilanes, and their structures were confirmed using spectroscopic methods and X‐ray crystallography. Not like other phenyl‐substituted cage silsesquioxanes, these butterfly cages show very good solubility in common organic solvents. The crystal structures clearly showed their unique features: a larger space with longer siloxane chains and a very flexible framework. Moreover, these compounds are thermally stable with a Td5 (5 % weight loss temperature) over 320 °C. 相似文献
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Nadia Kapernaum David M. Walba Prof. Dr. Eva Korblova Dr. Chenhui Zhu Chris Jones Yongqian Shen Noel A. Clark Prof. Frank Giesselmann Prof. Dr. 《Chemphyschem》2009,10(6):890-892
W415 is a chiral smectic compound with a remarkably weak temperature dependence of its giant electroclinic effect in the liquid crystalline smectic A* phase. Furthermore it possesses a high spontaneous polarization in the smectic C* phase. The origin of this striking electroclinic effect is the co‐occurrence of a de Vries‐type ordering with a weak first‐order tilting transition (see the synchroton X‐ray scattering profiles).
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Structure and Function of a “Head‐to‐Middle” Prenyltransferase: Lavandulyl Diphosphate Synthase 下载免费PDF全文
Meixia Liu Prof. Dr. Chun‐Chi Chen Lu Chen Xiansha Xiao Prof. Dr. Yingying Zheng Dr. Jian‐Wen Huang Prof. Dr. Weidong Liu Dr. Tzu‐Ping Ko Ya‐Shan Cheng Dr. Xinxin Feng Prof. Dr. Eric Oldfield Prof. Dr. Rey‐Ting Guo Prof. Dr. Yanhe Ma 《Angewandte Chemie (International ed. in English)》2016,55(15):4721-4724
We report the first X‐ray structure of the unique “head‐to‐middle” monoterpene synthase, lavandulyl diphosphate synthase (LPPS). LPPS catalyzes the condensation of two molecules of dimethylallyl diphosphate (DMAPP) to form lavandulyl diphosphate, a precursor to the fragrance lavandulol. The structure is similar to that of the bacterial cis‐prenyl synthase, undecaprenyl diphosphate synthase (UPPS), and contains an allylic site (S1) in which DMAPP ionizes and a second site (S2) which houses the DMAPP nucleophile. Both S‐thiolo‐dimethylallyl diphosphate and S‐thiolo‐isopentenyl diphosphate bind intact to S2, but are cleaved to (thio)diphosphate, in S1. His78 (Asn in UPPS) is essential for catalysis and is proposed to facilitate diphosphate release in S1, while the P1 phosphate in S2 abstracts a proton from the lavandulyl carbocation to form the LPP product. The results are of interest since they provide the first structure and structure‐based mechanism of this unusual prenyl synthase. 相似文献