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排序方式: 共有105条查询结果,搜索用时 15 毫秒
21.
Summary The reactions of TiX4 (X=Cl or Br) with the bidentate ligands, L, (Figure 1), yield hexacoordinate complexes TiX4·L, whereas similar reactions with VOCl3 lead to reduction of vanadium and give rise to vanadium(IV) pentacoordinate complexes, VOCl2·L. All the compounds have been characterized by elemental analyses, i.r., visible and e.p.r. spectra. The occupation of the sixth coordination position in pentacoordinate complexes, VOCl4·L, by different donor solvents, has been studied by means of visible and e.p.r. spectra. 相似文献
22.
Summary Titanium(IV) hexacoordinate thiuram disulphide complexes of the type [TiX4R2NC(S)SSC(S)NR2}] (X=Cl or Br; R=Me, Et, piperidinyl or morpholinyl) have been prepared by reaction between TiX4 (X=Cl or Br) and the thiuram disulphide. Similar reactions with VOCl3 lead to reduction of vanadium(V) and give rise to the oxovanadium(IV) pentacoordinate complexes [VOCl2{R2NC(S)SSC(S)NR2}]. However, the reactions of these same thiuram disulphide ligands with [VCl2(THF)2] (THF=tetrahydrofuran) cause oxidation of vanadium and to the reduction of the disulphide to the corresponding dithiocarbamate [R2NCS2]–, resulting in new dichlorobis (dithiocarbamate)vanadium(IV) complexes [VCl2-(R2NCS2)2]. All the compounds have been characterized by elemental analyses, i.r., visible and e.p.r. spectra. Both thiuram disulphides and dithiocarbamate ligands exhibit bidentate 相似文献
23.
Barragán E Olivo HF Romero-Ortega M Sarduy S 《The Journal of organic chemistry》2005,70(10):4214-4217
[reaction: see text] Addition of the chlorotitanium enolate of N-acetyl 4-isopropyl-1,3-thiazolidine-2-thione to five-membered, N-substituted N-acyl iminium ions furnished the corresponding Mannich-type addition products with good diastereoselectivity and in good yields. The synthetic utility of the addition product 8 was demonstrated in a chemospecific anti-aldol reaction with cinnamaldehyde. By using this strategy, we constructed three contiguous chiral centers with high stereocontrol employing the same chiral auxiliary. X-Ray crystallographic analysis of addition product 2 and aldol product 14 revealed their absolute stereochemistry. 相似文献
24.
Moisés Morán 《Transition Metal Chemistry》1981,6(3):173-175
Summary -Cp2Cr reacts with PX3 (X = Cl, Br or I) to give monocyclopentadienylchromium(III) derivatives -CpCrX2 (X = Cl, Br or I), while oxidative additions of IBr and ICl to -Cp2Cr give the corresponding mixed halogenated derivatives, -Cp2CrIX (X = Cl or Br). All products have been characterized by elemental analyses, magnetic moment measurements and by i.r. and e.p.r. spectra. 相似文献
25.
Wendy Flores-Fuentes Oleg Sergiyenko Félix F. Gonzalez-Navarro Moisés Rivas-López Daniel Hernandez-Balbuena Julio C. Rodríguez-Quiñonez Vera Tyrsa Lars Lindner 《Optical Review》2016,23(6):891-896
3D measurement by a cyber-physical system based on optoelectronic scanning instrumentation has been enhanced by outliers and regression data mining feedback. The prototype has applications in (1) industrial manufacturing systems that include: robotic machinery, embedded vision, and motion control, (2) health care systems for measurement scanning, and (3) infrastructure by providing structural health monitoring. This paper presents new research performed in data processing of a 3D measurement vision sensing database. Outliers from multivariate data have been detected and removal to improve artificial intelligence regression algorithm results. Physical measurement error regression data has been used for 3D measurements error correction. Concluding, that the joint of physical phenomena, measurement and computation is an effectiveness action for feedback loops in the control of industrial, medical and civil tasks. 相似文献
26.
27.
Nonsymmetrical 3,4‐Dithienylmaleimides by Cross‐Coupling Reactions with Indium Organometallics: Synthesis and Photochemical Studies
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Dr. Ángeles Mosquera Dr. M. Isabel Férnandez Prof. Dr. Moisés Canle Lopez Prof. Dr. José Pérez Sestelo Prof. Dr. Luis A. Sarandeses 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14524-14530
The synthesis and photochemical study of novel nonsymmetrical 1,2‐dithienylethenes (DTEs) with a maleimide bridge have been carried out. The synthetic approach to the DTEs was based on successive selective palladium‐catalyzed cross‐coupling reactions of 5‐susbtituted‐2‐methyl‐3‐thiophenyl indium reagents with 3,4‐dichloromaleimides. The required organoindium reagents were prepared from 2‐methyl‐3,5‐dibromothiophene by a selective (C‐5) coupling reaction with triorganoindium compounds (R3In) and subsequent metal–halogen exchange. The coupling reactions usually gave good yields and have a high atom economy with substoichiometric amounts of R3In. The results of photochemical studies show that these novel dithienylmaleimides undergo a photocyclization reaction upon irradiation in the UV region and a photocycloreversion after excitation in the visible region, thus they can be used as photochemical switches. ON–OFF operations can be repeated in successive cycles without appreciable loss of effectiveness in the process. 相似文献
28.
Moisés Canle López M Isabel Fernández Santiago Rodríguez J Arturo Santaballa Steen Steenken Emmanuelle Vulliet 《Chemphyschem》2005,6(10):2064-2074
Phenylurea herbicides undergo low-yield (phi(PI) <15 %) monophotonic photoionisation upon 193-nm laser flash excitation. The so-formed radical cations (phenylurea.+) are highly acidic (-1.5 < pKa <0.5) and deprotonate readily to yield the corresponding neutral radical (phenylurea.). Pulse radiolysis experiments allowed limitation of the reduction potential of phenylurea.+ within 2.22 V versus the normal hydrogen electrode (NHE) < E degrees (phenylurea.+/phenylurea) < 2.43 V versus NHE. The main photoproducts of UVC (lambda=193 nm) photodegradation of phenylureas correspond to a photo-Fries rearrangement. One-electron reduction with e-(aq) yields the corresponding radical anions (phenylurea.-), for which 4.3< pKa < 5.33. The rate constants for reaction with e-(aq) show that in photocatalysis the generation of phenylurea.- and O2.- on the surface of the photocatalyst may be competitive. High reactivity toward e-(aq) is predicted from linear free-energy relationships (LFER) for phenylureas bearing electron-withdrawing groups. Reaction with HO. takes place mainly via addition to the aromatic ring and/or H. abstraction from a saturated carbon atom (98 %), rather than one-electron oxidation (2 %). High reactivity toward oxidation by HO. is predicted from LFER for phenylureas bearing electron-donating groups. Adsorption studies for TiO2 in its polymorphic forms of rutile and anatase, as well as with the commercial mixture Degussa P-25, show photocatalysis is independent of the specific area of the catalyst. A variety of compounds are generated during the photocatalytic degradation of Diuron, while only two hydroxychloro derivatives are observed upon prolonged direct 365 nm irradiation. The photocatalytic degradation proceeds mainly by oxidation of the Me group of the side chain, hydroxylation of the aromatic ring, and dechlorination. The photoproducts of photocatalytic degradation differ from one polymorphic form of TiO2 to another. 相似文献
29.
Concise,Enantioselective, and Versatile Synthesis of (−)‐Englerin A Based on a Platinum‐Catalyzed [4C+3C] Cycloaddition of Allenedienes
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Ronald Nelson Dr. Moisés Gulías Prof. José L. Mascareñas Dr. Fernando López 《Angewandte Chemie (International ed. in English)》2016,55(46):14359-14363
A practical synthesis of (?)‐englerin A was accomplished in 17 steps and 11 % global yield from commercially available achiral precursors. The key step consists of a platinum‐catalyzed [4C+3C] allenediene cycloaddition that directly delivers the trans‐fused guaiane skeleton with complete diastereoselectivity. The high enantioselectivity (99 % ee) stems from an asymmetric ruthenium‐catalyzed transfer hydrogenation of a readily assembled diene–ynone. The synthesis also features a highly stereoselective oxygenation, and a late‐stage cuprate alkylation that enables the preparation of previously inaccessible structural analogues. 相似文献
30.
García-Fandiño R Gulías M Castedo L Granja JR Mascareñas JL Cárdenas DJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):272-281
The mechanism of the palladium-catalysed [3+2] intramolecular cycloaddition of alkylidenecyclopropanes to alkynes has been computationally explored at DFT level. The energies of the reaction intermediates and transition states for different possible pathways have been calculated in a model system that involves the use of PH3 as a ligand. The results obtained suggest that the most favourable reaction pathway involves the initial C--C oxidative addition of the cyclopropane to a Pd0 complex to give an alkylidenepalladacyclobutane, which isomerises to a methylenepalladacyclobutane intermediate. Subsequent cyclisation by alkyne carbometallation, followed by reductive elimination affords the final product. An alternative mechanism consisting of a palladaene-type rearrangement is less probable in terms of Gibbs energy, but cannot be fully discarded because it is competitive if one considers electronic energies. For substrates that present an ester group at the terminal position of the triple bond we have found an alternative, more favourable mechanistic route that explains why the [3+2] cycloaddition of these types of systems does not lead to the expected cycloadducts. 相似文献