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1.
Dr. Zhishan Su Dr. Weiyi Li Dr. Jun Wang Prof. Changwei Hu Prof. Xiaoming Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(5):1637-1646
The mechanism and the origin of selectivity of the asymmetric Strecker reaction catalyzed by a TiIV‐complex catalyst generated from a cinchona alkaloid, achiral substituted 2,2′‐biphenol, and tetraisopropyl titanate have been investigated by DFT and ONIOM methods. The calculations indicate that the reaction proceeds through a dual activation mechanism, in which TiIV acts as Lewis acid to activate the electrophile aldimine substrate, whereas the tertiary amine in cinchona alkaloid works as Lewis base to promote the activation and isomerization of HCN. The C? C bond formation step is predicted to be the selectivity‐controlling step in the reaction with an energy barrier of 9.3 kcal mol?1. The “asymmetric activation” is achieved by the transfer of asymmetry from the chiral cinchonine ligand to the axially flexible achiral biphenol ligand through coordination interaction with the central metal TiIV. The large steric hindrance from the 3,3′‐position substitute of biphenol, combined with the quinoline fragment of cinchona alkaloid and the orientation of hydrogen bonding of iPrOH, play a key role in controlling the stereoselectivity, which is in good agreement with the experimental observations. 相似文献
2.
Yoko Sakata Shuichi Hiraoka Dr. Mitsuhiko Shionoya Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(11):3318-3325
A series of heteroleptic [Ti 1 2X]? complexes have been selectively constructed from a mixture of TiIV ions, a pyridyl catechol ligand (H2 1 ; H2 1 =4‐(3‐pyridyl)catechol), and various bidentate ligands (HX) in the presence of a weak base, in addition to a previously reported [Ti 1 2(acac)]? (acac=acetylacetonate) complex. Comparative studies of these TiIV complexes revealed that [Ti 1 2(trop)]? (trop=tropolonate) is much more stable than the [Ti 1 2(acac)]? complex, which allows the replacement of acac with trop on the [Ti 1 2(acac)]? complex. This TiIV‐centered site‐selective ligand exchange reaction also takes place on a heteronuclear PdII? TiIV ring complex with the preservation of the PdII‐centered coordination structures. Intra‐ and intermolecular linking between two TiIV centers with a flexible or a rigid bis‐tropolone bridging ligand provided a tetranuclear and an octanuclear PdII? TiIV complex, respectively. These higher‐order structures could be efficiently constructed only through a stepwise synthetic route. 相似文献
3.
Ziwei Gao Caiyun Zhang Mingyuan Dong Lingxiang Gao Guofang Zhang Zhaotie Liu Gaofeng Wang Denghui Wu 《应用有机金属化学》2006,20(2):117-124
Two 4‐coordinated titanocene complexes, [(η5‐C5H5)2Ti(O,O′)(5‐NO2‐OCC6H3)] (I) and [(η5‐C5H5)2Ti(2‐OH‐5‐NO2‐O2CC6H3)2] (II), have been synthesized by reaction of Cp2TiCl2 and 5‐nitrosalicylic acid in aqueous media. Single‐crystal X‐ray analyses of I and II display the mononuclear forms of TiIV, and geometries at titanium atoms are distorted tetrahedrons, while the coordination environment at TiIV in complex I is different from that in complex II. Crystallographic characterization revealed that each of the complexes exhibits a three‐dimensional framework constructed through weak interactions, which are H‐bonding, π–π stacking and C–H·π interactions, but they differ greatly when forming the three‐dimensional network structure in both complexes. The results show that the dramatic change of conditions has great effect on the molecular structure of 5‐nitrosalicylate titanocene, thereby significantly influencing the weak interactions and the specific framework structure. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
4.
Correlation of Insulin‐Enhancing Properties of Vanadium‐Dipicolinate Complexes in Model Membrane Systems: Phospholipid Langmuir Monolayers and AOT Reverse Micelles
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Dr. Audra G. Sostarecz Dr. Ernestas Gaidamauskas Steve Distin Prof. Sandra J. Bonetti Prof. Nancy E. Levinger Prof. Debbie C. Crans 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):5149-5159
We explore the interactions of VIII‐, VIV‐, and VV‐2,6‐pyridinedicarboxylic acid (dipic) complexes with model membrane systems and whether these interactions correlate with the blood‐glucose‐lowering effects of these compounds on STZ‐induced diabetic rats. Two model systems, dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers and AOT (sodium bis(2‐ethylhexyl)sulfosuccinate) reverse micelles present controlled environments for the systematic study of these vanadium complexes interacting with self‐assembled lipids. Results from the Langmuir monolayer studies show that vanadium complexes in all three oxidation states interact with the DPPC monolayer; the VIII–phospholipid interactions result in a slight decrease in DPPC molecular area, whereas VIV and VV–phospholipid interactions appear to increase the DPPC molecular area, an observation consistent with penetration into the interface of this complex. Investigations also examined the interactions of VIII‐ and VIV‐dipic complexes with polar interfaces in AOT reverse micelles. Electron paramagnetic resonance spectroscopic studies of VIV complexes in reverse micelles indicate that the neutral and smaller 1:1 VIV‐dipic complex penetrates the interface, whereas the larger 1:2 VIV complex does not. UV/Vis spectroscopy studies of the anionic VIII‐dipic complex show only minor interactions. These results are in contrast to behavior of the VV‐dipic complex, [VO2(dipic)]?, which penetrates the AOT/isooctane reverse micellar interface. These model membrane studies indicate that VIII‐, VIV‐, and VV‐dipic complexes interact with and penetrate the lipid interfaces differently, an effect that agrees with the compounds’ efficacy at lowering elevated blood glucose levels in diabetic rats. 相似文献
5.
A Dimeric η1,η5‐Germole Dianion Bridged Titanium(III) Complex with a Multicenter Ti−Ge−Ge−Ti Bond
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M. Sc. Zhaowen Dong Dr. Oliver Janka Dipl.‐Ing. Jutta Kösters Dr. Marc Schmidtmann Prof. Dr. Thomas Müller 《Angewandte Chemie (International ed. in English)》2018,57(28):8634-8638
Dimeric germole dianion bridged TiIII and ZrIV complexes have been synthesized. In these complexes, the germole dianion adopts a formal η1,η5 coordination to the two metal centers. The bonding situation in these bridged dimers is dominated by a covalent Ge?Ge interaction that results, for example, in a strong antiferromagnetic coupling of the d1 Ti centers. 相似文献
6.
Stereoselective β‐mannosylation has been recognized as one of the greatest challenges of carbohydrate chemistry. Herein, we described a practical method for stereoselective construction of β‐mannosides by using a 2,6‐lactone‐bridged thiomannosyl donor through the remote acyl‐group participation as well as the steric effect of O‐4 substituent. The two effects are enabled through the conversion of a regular mannopyranosyl 4C1 conformation into a 2,6‐lactone bridged conformation. The lactone donor could be readily prepared in three steps on a gram scale and the β‐mannosylation proceeded smoothly with high stereoselectivity for primary, secondary and tertiary alcohol acceptors. In addition, this strategy was successfully applied to the synthesis of a naturally occurring trisaccharide. 相似文献
7.
8.
Practical Synthesis of anti‐β‐Hydroxy‐α‐Amino Acids by PdII‐Catalyzed Sequential C(sp3)H Functionalization
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Kai Chen Shuo‐Qing Zhang Huai‐Zhi Jiang Jing‐Wen Xu Prof. Dr. Bing‐Feng Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3264-3270
An improved and practical procedure for the stereoselective synthesis of anti‐β‐hydroxy‐α‐amino acids (anti‐βhAAs), by palladium‐catalyzed sequential C(sp3)?H functionalization directed by 8‐aminoquinoline auxiliary, is described. followed by a previously established monoarylation and/or alkylation of the β‐methyl C(sp3)?H of alanine derivative, β‐acetoxylation of both alkylic and benzylic methylene C(sp3)?H bonds affords various anti‐β‐hydroxy‐α‐amino acid derivatives. As an example, the synthesis of β‐mercapto‐α‐amino acids, which are highly important to the extension of native chemical ligation chemistry beyond cysteine, is described. The synthetic potential of this protocol is further demonstrated by the synthesis of diverse β‐branched α‐amino acids. The observed diastereoselectivities are strongly influenced by electronic effects of aromatic AAs and steric effects of the linear side‐chain AAs, which could be explained by the competition of intramolecular C?OAc bond reductive elimination from PdIV intermediates vs. intermolecular attack by an external nucleophile (AcO?) in an SN2‐type process. 相似文献
9.
Igor E. Uflyand Vasily P. Kurbatov Anatoly D. Pomogailo 《Transition Metal Chemistry》1992,17(6):501-505
Heterometallic complexes have been synthesized by the interaction of TiIV and SnIV chlorides with NiII and CoII enaminoketonates and enaminoiminates. The complexes were characterized by elemental analyses, magnetic susceptibility and
i.r. spectroscopy. The catalytic properties of the complexes in the preparation of linear low density polyethylene have been
studied.
TMC 2192 相似文献
10.
Influence of Ligand Architecture on Oxidation Reactions by High‐Valent Nonheme Manganese Oxo Complexes Using Water as a Source of Oxygen
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Prasenjit Barman Dr. Anil Kumar Vardhaman Dr. Bodo Martin Svenja J. Wörner Dr. Chivukula V. Sastri Prof. Dr. Peter Comba 《Angewandte Chemie (International ed. in English)》2015,54(7):2095-2099
Mononuclear nonheme MnIV?O complexes with two isomers of a bispidine ligand have been synthesized and characterized by various spectroscopies and density functional theory (DFT). The MnIV?O complexes show reactivity in oxidation reactions (hydrogen‐atom abstraction and sulfoxidation). Interestingly, one of the isomers (L1) is significantly more reactive than the other (L2), while in the corresponding FeIV?O based oxidation reactions the L2‐based system was previously found to be more reactive than the L1‐based catalyst. This inversion of reactivities is discussed on the basis of DFT and molecular mechanics (MM) model calculations, which indicate that the order of reactivities are primarily due to a switch of reaction channels (σ versus π) and concomitant steric effects. 相似文献
11.
Dr. Ioannis Liratzis Dr. Stephan Walleck Dr. Jan Oldengott Anja Stammler Dr. Hartmut Bögge Dr. Eckhard Bill Prof. Dr. Thorsten Glaser 《欧洲无机化学杂志》2023,26(5):e202200650
The ligand H6ioan has been used to synthesize the three dinuclear complexes [(ioan)MnIITiIV], [(ioan)FeIITiIV], and [(ioan)FeIIITiIV]+. The face-sharing bridging mode of the three phenolates provides short M-TiIV distances of ≈3.0 Å. Mössbauer spectra of [(ioan)FeIIITiIV]+ show a magnetically split six-line spectrum at 3 K in zero magnetic field demonstrating a slow magnetic relaxation. Magnetic measurements provide a zero-field splitting of |D|=5 cm−1 in [(ioan)FeIITiIV]. EPR spectroscopy demonstrates sizable zero-field splittings of the S=5/2 spin systems of [(ioan)MnIITiIV] (D=0.246 cm−1) and [(ioan)FeIIITiIV]+ (D<−1 cm−1) that can be related to enforced covalency of the M-Oph bonds. [(ioan)FeIIITiIV]+ exhibits a reversible reduction at −0.26 V vs. Fc+/Fc demonstrating the facile accessibility of FeIII and FeII. In contrast to an irreversible oxidation in [(ioan)NiIITiIV] at 0.78 V vs. Fc+/Fc, the reversible oxidation at 0.25 V vs. Fc+/Fc in [(ioan)MnIITiIV] indicates even the access of MnIII. These results indicate that pentanuclear complexes [(ioan)FeM1M2M1Fe(ioan)]n+ are meaningful targets to access electron delocalization in mixed-valence systems over five ions due to the facile accessibility of both FeII and FeIII in the terminal positions. This study provides important local spin-Hamiltonian and Mössbauer parameters that will be essential for the understanding of the potentially complicated electronic structure in the anticipated pentanuclear complexes. 相似文献
12.
Simon Smolders Tom Willhammar Andra Krajnc Kadir Sentosun Michael T. Wharmby Kirill A. Lomachenko Sara Bals Gregor Mali Maarten B. J. Roeffaers Dirk E. DeVos Bart Bueken 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(27):9258-9263
While titanium‐based metal–organic frameworks (MOFs) have been widely studied for their (photo)catalytic potential, only a few TiIV MOFs have been reported owing to the high reactivity of the employed titanium precursors. The synthesis of COK‐47 is now presented, the first Ti carboxylate MOF based on sheets of TiIVO6 octahedra, which can be synthesized with a range of different linkers. COK‐47 can be synthesized as an inherently defective nanoparticulate material, rendering it a highly efficient catalyst for the oxidation of thiophenes. Its structure was determined by continuous rotation electron diffraction and studied in depth by X‐ray total scattering, EXAFS, and solid‐state NMR. Furthermore, its photoactivity was investigated by electron paramagnetic resonance and demonstrated by catalytic photodegradation of rhodamine 6G. 相似文献
13.
Xuechao Yan Haiying Wang Shuai Guo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(47):17063-17067
The study of palladium(IV) species has great implications for PdII/PdIV‐mediated catalysis. However, most of the PdIV complexes rapidly decompose under ambient conditions, which makes the isolation, characterization and further reactivity study very challenging. The reported ancillary ligand platforms to stabilize PdIV species are dominated by chelating N‐donors such as bipyridines. In this work, we present two PdIV complexes with scarcely used C‐donors as the supporting platform. The anionic aryl donor and MIC (MIC=mesoionic carbene) are combined in a [CC′C]‐type pincer framework to access a series of ambient‐stable PdIV tris(halido) complexes. Their synthesis, solid‐state structures, stability, and reactivity are presented. To the best of our knowledge, the work presented herein reports the first isolated PdIV–MIC as well as the first PdIV carbene‐based aryl pincer. 相似文献
14.
Synthesis of α‐Chiral Butyrolactones by Highly Stereoselective Radical Transfer or Sequential Asymmetric Alkylations: Concise Preparation of Leupyrrin Moieties
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Michael Schrempp Sebastian Thiede Daniel Herkommer Prof. Dr. Andreas Gansäuer Prof. Dr. Dirk Menche 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):16266-16271
Inspired by the bioactive natural metabolites leupyrrin A1 and B1, two novel stereoselective methods for the highly concise synthesis of densely substituted α‐chiral butyrolactones are reported. The first approach relies on an innovative three‐step TiIII‐catalyzed radical reaction that proceeds with excellent chemo‐, regio‐, and stereoselectivity. The alternative route utilizes sequential asymmetric alkylations and enables asymmetric synthesis of the authentic α‐tetrasubstituted butyrolactone motif of the leupyrrins in only four steps from commercially available substrates. 相似文献
15.
Dr. Todor Baramov Bianca Schmid Ho Ryu Jinhoon Jeong Dr. Karlijn Keijzer Dr. Leonard von Eckardstein Prof. Dr. Mu-Hyun Baik Prof. Dr. Roderich D. Süssmuth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(28):6955-6962
The E. coli siderophore enterobactin, the strongest FeIII chelator known to date, forms hexacoordinate complexes with SiIV, GeIV, and TiIV. Synthetic protocols have been developed to prepare non-symmetric enterobactin analogues with varying denticities. Various benzoic acid residues were coupled to the macrocyclic lactone to afford a diverse library of ligands. These enterobactin analogues were bound to SiIV, GeIV, and TiIV, and the complexes were investigated through experimental and computational techniques. The binding behavior of the synthesized chelators enabled assessment of the contribution of each of the phenolic hydroxy groups in enterobactin to metal-ion complexation. It was found that at least four O-donors are needed for enterobactin derivatives to act as metal binders. Density functional theory calculations indicate that the strong binding behavior of enterobactin can be ascribed to a diminished translational entropy penalty, a common feature of the chelate effect, coupled with the structural arrangement of the three catechol moieties, which allows the triseryl base to be installed without distorting the preferred local metal-binding geometry of the catecholate ligands. 相似文献
16.
The complex formation of acetylacetone with SiIV and TiIV and of pyrocatechol with SbIII, SiIV, TiIV and SnIV have been investigated by pH-measurements in absolute methanolic solutions containing (CH3)4NCl, LiCl of Litiumtosylate (μ = 1; 20,0°). 相似文献
17.
Dr. Aurore Thibon Véronique Jollet Dr. Caroline Ribal Dr. Katell Sénéchal‐David Laurianne Billon Dr. Alexander B. Sorokin Prof. Frédéric Banse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(9):2715-2724
Ferric–hydroperoxo complexes have been identified as intermediates in the catalytic cycle of biological oxidants, but their role as key oxidants is still a matter of debate. Among the numerous synthetic low‐spin FeIII(OOH) complexes characterized to date, [(L52)Fe(OOH)]2+ is the only one that has been isolated in the solid state at low temperature, which has provided a unique opportunity for inspecting its oxidizing properties under single‐turnover conditions. In this report we show that [(L52)Fe(OOH)]2+ decays in the presence of aromatic substrates, such as anisole and benzene in acetonitrile, with first‐order kinetics. In addition, the phenol products are formed from the aromatic substrates with similar first‐order rate constants. Combining the kinetic data obtained at different temperatures and under different single‐turnover experimental conditions with experiments performed under catalytic conditions by using the substrate [1,3,5‐D3]benzene, which showed normal kinetic isotope effects (KIE>1) and a notable hydride shift (NIH shift), has allowed us to clarify the role played by FeIII(OOH) in aromatic oxidation. Several lines of experimental evidence in support of the previously postulated mechanism for the formation of two caged FeIV(O) and OH . species from the FeIII(OOH) complex have been obtained for the first time. After homolytic O? O cleavage, a caged pair of oxidants [FeIVO+HO . ] is generated that act in unison to hydroxylate the aromatic ring: HO . attacks the ring to give a hydroxycyclohexadienyl radical, which is further oxidized by FeIVO to give a cationic intermediate that gives rise to a NIH shift upon ketonization before the final re‐aromatization step. Spin‐trapping experiments in the presence of 5,5‐dimethyl‐1‐pyrroline N‐oxide and GC‐MS analyses of the intermediate products further support the proposed mechanism. 相似文献
18.
Magnetic Ordering Phenomena in the Cluster Compounds Ti7Cl16 and Ti7Br16 The magnetic susceptibilities of Ti7Cl16 and Ti7Br16 have been measured between 3.8 and 295 K by the Faraday method. The compounds show magnetic ordering points at 15.9 and 13.5 K, respectively. The determination of the oxidation states of the titanium ions and the exchange interactions between them is complicated by the fact that at room temperature competing antiferro-magnetic intra- and intercluster exchange interactions are already present. Calculations with simple models agree with the assumption that the compounds consist of Ti3 clusters with TiII and isolated TiIV ions. 相似文献
19.
Ning Li Jiang Liu Jing‐Jing Liu Long‐Zhang Dong Shun‐Li Li Bao‐Xia Dong Yu‐He Kan Ya‐Qian Lan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17420-17424
Over the past 200 years, the most famous and important heteroatom Keggin architecture in polyoxometalates has only been synthesized with Mo, W, V, or Nb. Now, the self‐assembly of two phosphate (PO43?)‐centered polyoxo‐titanium clusters (PTCs) is presented, PTi16 and PTi12, which display classic heteroatom Keggin and its trivacant structures, respectively. Because TiIV has lower oxidate state and larger ionic radius than MoVI, WVI, VV, and NbV, additional TiIV centres in these PTCs are used to stabilize the resultant heteroatom Keggin structures, as demonstrated by the cooresponding theoretical calculation results. These photoactive PTCs can be utilized as efficient photocatalysts for highly selective CO2‐to‐HCOOH conversion. This new discovery indicates that the classic heteroatom Keggin family can be assembled with Ti, thus opening a research avenue for the development of PTC chemistry. 相似文献
20.
A. A. Shubin R. S. Mitchenko T. V. Bezbozhnaya A. N. Vdovichenko 《Russian Chemical Bulletin》2005,54(10):2456-2459
A procedure was developed for the synthesis of previously unknown β-chlorovinyl derivatives of PtIV chloride complexes by chloroplatination of terminal alkynes catalyzed by PtII chloride complexes. The reaction is highly stereoselective and gives only the products of trans-anti-addition of platinum and chlorine atoms. The regioselectivity of the catalytic reaction formally corresponds to Markovnikov’s
rule, e.g., in alkynes containing electron-donating substituents, platinum attacks the terminal carbon atom. The σ-vinyl derivatives
of PtIV chloride complexes were characterized by IR spectroscopy and 1H and 13C NMR spectroscopy.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2380–2384, October, 2005. 相似文献