- Stereoselective protonation of 2-methyl-1-tetralone lithium enolate catalyzed by salan-type diamines
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Asymmetric protonation of ketone enolates is a convenient alternative to asymmetric alkylation of enolates that allows to convert racemic ketones into their optically active form. Here, we have reported an efficient enantioselective protonation of 2-methyl-1-tetralone lithium enolate catalyzed by salan-type diamines. A broad series of salan-type catalysts were synthesized, including several previously unknown, and subsequently tested in the title reaction. For the first time, a chiral amine used as organocatalyst has shown better results than as stoichiometric protonating agent. Application of only 10 mol% of salan allows to obtain the title ketone with high yield and enantiomeric excess up to 75%. The DFT calculations of the structure of the catalyst and its complex with lithium enolate were conducted, which makes it possible to propose a likely reaction mechanism.
- ?owicki, Daniel,Watral, Justyna,Jelecki, Maciej,Bohusz, Wiktor,Kwit, Marcin
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- Synthesis, Characterization, and in Vitro Cytotoxicity of Platinum(II) Complexes Bearing Chiral Tetradentate Salicylaldimine Ligands
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A series of platinum(II) complexes with chiral Schiff base ligands derived from various salicylaldehydes with (R,R′)- and (S,S′)-cyclohexanediamine were synthesized and characterized by ESI-MS, IR, and NMR. Obtained spectra with typical signals were in agreement with suggested molecular formulae of the complexes. Their photophysical properties were studied by UV-visible and emission spectroscopies. The UV-Vis showed the typical band with low energy at visible range 400-500 nm for MLCT, and this band can emit the luminescent band with emission maximum wavelengths at 529-595 nm. The in vitro cytotoxicity of obtained platinum(II) complexes was screened for KB and MCF-7 human cancer cell lines. The results showed that (S)-enantiomers were more active than (R)-enantiomers and the different positions of methoxy group in salicyl ring gave different cytotoxicities.
- Nguyen, Quang Trung,Nguyen, Van Tuyen,Pham Thi, Phuong Nam
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- Polymerization of Ethylene in the Presence of Titanium(IV), Zirconium(IV), and Vanadium(V) Coordination Compounds with Salen Ligands
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Abstract: Coordination compounds of titanium(IV), zirconium(IV), and vanadium(V) with chiral salen ligands have been obtained and characterized, and their catalytic activity in the polymerization reaction of ethylene has been studied. It has been shown that in the presence of polymethylaluminoxane as a cocatalyst, the activity of the titanium-containing catalyst system reaches 944 kgPE mol(Ti)?1 h?1 and leads to the preparation of ultrahigh-molecular-weight polyethylene.
- Bulychev, B. M.,Gagieva, S. Ch.,Lyadov, A. S.,Takazova, R. U.,Tuskaev, V. A.
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p. 291 - 297
(2020/05/25)
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- Efficient conversion of CO2into cyclic carbonates at room temperature catalyzed by Al-salen and imidazolium hydrogen carbonate ionic liquids
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A novel process for the efficient synthesis of cyclic carbonates from CO2 and epoxides at room temperature in the absence of a solvent has been achieved by using Al-salen complexes as catalysts and imidazolium hydrogen carbonate ionic liquids ([CnCmIm][HCO3]) as cocatalysts. As a halide ion-free cocatalyst, [CnCmIm][HCO3] showed higher catalytic reactivity compared to traditional halogen-containing quaternary ammonium salts (such as (nBu)4NBr) and organic bases. The catalytic system can be used for the cycloaddition of a series of substrates with good to excellent yields at room temperature in the absence of a solvent. Besides, the catalytic system can be easily recycled at least four times without significant loss of catalytic activity. A possible mechanism was proposed, in which Al-salen and carbene activate the epoxides and CO2 respectively.
- Hu, Xingbang,Liu, Jia,Liu, Ying,Yang, Guoqiang,Zhang, Dejin,Zhang, Zhibing
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supporting information
p. 4509 - 4515
(2020/08/10)
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- Stabilized Ru[(H2O)6]3+ in Confined Spaces (MOFs and Zeolites) Catalyzes the Imination of Primary Alcohols under Atmospheric Conditions with Wide Scope
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Imines are ubiquitous intermediates in organic synthesis, and the metal-mediated imination of alcohols is one of the most direct and simple methods for their synthesis. However, reported protocols lack compatibility with many other functional groups since basic supports/media, pure oxygen atmospheres, and/or released hydrogen gas are required during reaction. Here we show that, in contrast to previous metal-catalyzed methods, hexa-aqueous Ru(III) catalyzes the imination of primary alcohols with very wide functional group tolerance, at slightly acid pH and under low oxygen atmospheres. The inorganic metal complex can be supported and stabilized, integrally, within either faujasite-type zeolites (Y and X) or a metal organic framework (MOF), to give a reusable heterogeneous catalyst which provides an industrially viable process well below the flammability limit of alcohols and amines.
- Mon, Marta,Adam, Rosa,Ferrando-Soria, Jesús,Corma, Avelino,Armentano, Donatella,Pardo, Emilio,Leyva-Pérez, Antonio
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p. 10401 - 10406
(2018/10/24)
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- Solvent-Free Synthesis of Salen Ligands and Pd(II)- and Cu(II)-Salen Complexes: Their Use in the Oxidation of α-Tetralones to α-Naphthols
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Racemic trans -cyclohexane-1,2-diamine was allowed to react with eleven aldehydes with different patterns of substitution at the aromatic ring, in the absence of solvent, by manually milling the reagents. The corresponding imines were obtained in moderated to high chemical yields, in only 10 minutes of reaction. A one-pot, two-step preparation of stable complexes of selected imines with Pd(OAc) 2 and Cu(OAc) 2 and the use of these complexes as catalysts in the aromatization of methyl 1-oxo-1,2,3,4-tetrahydronaphthalene-2-carboxylate to the corresponding methyl 1-hydroxynaphthalene-2-carboxylates, is also reported.
- Cívicos, José F.,Coimbra, Juliana S. M.,Costa, Paulo R. R.
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p. 3998 - 4006
(2017/08/29)
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- Chiral and non-conjugated fluorescent salen ligands: AIE, anion probes, chiral recognition of unprotected amino acids, and cell imaging applications
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Natural products are usually non-conjugated and chiral, but organic luminescent materials are commonly polycyclic aromatic molecules with extended π-conjugation. In the present work, we combine with the advantages of non-conjugation and chirality to prepare a series of novel and simple salen ligands (41 samples), which have a non-conjugated and chiral (S,S) and (R,R) cyclohexane or 1,2-diphenylethane bridge but display strong blue, green, and red aggregation-induced emission (AIE) with large Stokes shifts (up to 186 nm) and high fluorescence quantum yields (up to 0.35). Through hydrogen and halogen bonds, these flexible salen ligands can be used as universal anion probes and chiral receptors of unprotected amino acids (enantiomeric selectivity up to 0.11) with fluorescence quantum yields up to 0.29 and 0.27, respectively. Moreover, the effects of different chiral bridges on the molecule arrangement, AIE, and anion and chiral recognition properties are also explored, which provide unequivocal insights for the design of non-conjugated chiral and soft fluorescent materials.
- Shen, Guangyu,Gou, Fei,Cheng, Jinghui,Zhang, Xiaohong,Zhou, Xiangge,Xiang, Haifeng
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p. 40640 - 40649
(2017/08/29)
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- Synthesis of N,N′-Dialkylated Cyclohexane-1,2-diamines and Their Application as Asymmetric Ligands and Organocatalysts for the Synthesis of Alcohols
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A series of N,N′-dialkylated derivatives of (1R,2R)-cyclohexane-1,2-diamine were synthesized, and a new approach to the one-pot preparation of this type of amine was demonstrated. The prepared diamines were used as organocatalysts for the two-step synthesis of α-hydroxy γ-keto esters from arenes, chlorooxoacetates, and ketones; they were also used as chiral ligands for Meervein-Ponndorf-Verley reductions and Henry reactions.
- Tsygankov, Alexey A.,Chun, Man-Seog,Samoylova, Alexandra D.,Kwon, Seongyeon,Kreschenova, Yuliya M.,Kim, Suhyeon,Shin, Euijin,Oh, Jinho,Strelkova, Tatyana V.,Kolesov, Valerii S.,Zubkov, Fedor I.,Semenov, Sergei E.,Fedyanin, Ivan V.,Chusov, Denis
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p. 615 - 619
(2017/03/11)
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- Efficient and diastereoselective synthesis of bis-quinazolinedione derivatives via low-valent titanium reagent
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An efficient and simple method for the synthesis of chiral benzo[5,6][1,3]oxazino[4,3-c]quinoxalinedione and octahydroquinoxalino-[1,2-c:4,3-c′]diquinazolinedione derivatives using 2-hydroxybenzaldehydes (or 2-nitrobenzaldehydes) and chiral cyclohexane-1,2-diamine as the starting materials promoted by low-valent titanium reagent has been described. The structures of all synthesized products were identified by their IR, 1H NMR, 13C NMR and HRMS analysis, and the structure of compound 8b was confirmed by X-ray diffraction analysis.
- Lin, Wei,Wang, Yazhen,Zheng, Yongxiang,Shi, Daqing
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- Salen(Co(III)) imprisoned within pores of a metal-organic framework by post-synthetic modification and its asymmetric catalysis for CO2 fixation at room temperature
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Herein, a new preparation strategy of chiral metal-organic frameworks (CMOFs) has been demonstrated. By adsorption and then post-synthetically modified (PSM) procedures, chiral salen(Co(iii)) could be imprisoned within the cages of an MOF and remained in its free form. This is the first report on the successful application of CMOFs in heterogeneous asymmetric catalysis for coupling CO2 with epoxides to obtain optically active cyclic carbonates at room temperature.
- Chen, Danping,Luo, Ran,Li, Meiyan,Wen, Mengqi,Li, Yan,Chen, Chao,Zhang, Ning
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supporting information
p. 10930 - 10933
(2017/10/11)
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- Substitutional group dependent colori/fluorimetric sensing of Mn2+, Fe3+ and Zn2+ ions by simple Schiff base chemosensor
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Schiff base is one of the easiest synthesizable chemosensor and exhibit strong coordination with metal ions; the property that has been vastly exploited for metal ions sensing. Simple Schiff base chemosensors (1a-d and 2a-d) were synthesized and demonstrated substitutional group dependent colorimetric sensing of metal ions. Chemosensor without (1a, 2a) and OCH3 substitution (1b, 2b) did not show any significant colour change for metal ions. However, a highly selective colorimetric change (colourless to pink) for Mn2+ ions (10-6 M) was observed with diethylamine substituted 1c, 2c. Hydroxyl substitution (1d, 2d) leads to selective colorimetric sensing (colourless to orange) of Fe3+ ions (10-6 M). PVA thin films of 2c/2d were fabricated and demonstrated selective colorimetric sensing of Mn2+ and Fe3+ ions. The practical applicability of the synthesized chemosensors were also demonstrated by performing selective colorimetric sensing of Mn2+ and Fe3+ ions in real samples such as tap, ground, pond and river water. Effect of substitution on the fluorescence selectivity of Zn2+ has also been investigated.
- Hariharan,Anthony, Savarimuthu Philip
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p. 1658 - 1665
(2015/03/30)
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- Fluorescence characteristics of Schiff base-N,N/-bis(salicylidene) trans 1,2-diaminocyclohexane in the presence of bile acid host
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Understanding the formation of bile acid micellar aggregates is of great importance due to its wide biological and pharmacological applications. In this paper, we study the fluorescence properties of Schiff base-N,N/-bis(salicylidene) trans 1,2-diaminocyclohexane (H2L) to understand micelle formation by aggregation of different important bile acids - cholic acid, deoxycholic acid, chenodeoxycholic acid and glycocholic acid by steady state and picosecond time-resolved fluorescence spectroscopy. The fluorescence band intensity was found to increase with concomitant blue shift with gradual addition of different bile acids. Several mean microscopic properties such as critical micelle concentration, polarity parameters and binding constant were estimated in the presence of bile acids. The increase in fluorescence quantum yields, fluorescence decay times and substantial decrease in nonradiative decay rate constants in bile acid micellar environment points to the restricted motion of the fluorophore inside the micellar subdomains.
- Roy, Nayan,Paul, Pradip C.,Sanjoy Singh
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p. 1052 - 1059
(2015/09/07)
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- Reductive and oxidative electrochemical study and spectroscopic properties of nickel(II) complexes with N2O2 Schiff bases derived from (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediamine
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Cyclic voltammetry, chronopotentiometry, chronocoulometry, controlled potential electrolysis and UV VIS were used in investigation of ligands and Ni(II) complexes with (±)-trans-N,N′-bis(salicylidene)-1,2- cyclohexanediamine substituted in orto- and/or para- positions of phenolate anions with tert-butyl and/or methoxy groups. Irreversible reduction and oxidation of ligands were shown. No influence of solvent on reduction of complexes, which results in Ni(I) complexes, was observed, however, an effect of solvent and substituents of phenolate anions on oxidation processes was proved. Anodic process in (CH3)2SO always results in appropriate Ni(III)-phenolate complex. Oxidation of orto- and para- substituted complexes in CH2Cl2 results in Ni(II)-mono-phenoxyl radicals, which undergo delocalisation and subsequently are oxidised to Ni(II)-bis-phenoxyl radicals. Last oxidation step of radicals produce long-lived Ni(II)-bis-phenoxonium cations. Complexes without substituents in para-and/or orto- position having formed Ni(II)-mono-phenoxyl radicals undergo dimerization. Mechanisms of electrode processes were studied and D and Ef values for processes of reduction and Ist step of oxidation of complexes were calculated.
- Tomczyk,Nowak,Bukowski,Bester,Urbaniak,Andrijewski,Olejniczak
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- A sensitive schiff-base fluorescent chemosensor for the selective detection of Zn2+
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A Schiff-base fluorescent probe - N, N/-bis(salicylidene) trans 1, 2 - diaminocyclohexane (H 2 L) was synthesized and evaluated as a chemoselective Zn2+ sensor. Upon treatment with Zn2+, the complexation of H 2 L with Zn2+ resulted in a bathochromic shift with a pronounced enhancement in the fluorescence intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Notably, this chemosensor could distinguish clearly Zn2+ from Cd2+. The stoichiometric ratio and association constant were evaluated using Benesi - Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job's plot analyses.
- Roy, Nayan,Pramanik, Harun A. R.,Paul, Pradip C.,Singh, Sanjoy T.
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p. 1099 - 1106
(2014/07/22)
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- CuII-salan compounds: Synthesis, characterization and evaluation of their potential as oxidation catalysts
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We report the synthesis and characterization of several salan-type Cu II complexes. Suitable crystals suitable for X-ray diffraction were obtained for several of the CuII complexes, including a half-salen compound, revealing square-planar coordination environments common to d9 species. The CuII-salan complexes are tested as catalysts in sulfoxidation, alkene oxidation, and oxidative naphthol coupling. At room temperature the compounds exhibit low to moderate catalytic activity in sulfoxidations and alkene oxidations, but no activity in oxidative naphthol coupling. The saturated coordination environments around the Cu centers probably are the main reason for the lower catalytic activities compared to the Ti- and V-salan analogs. Spectroscopic and mass spectrometry studies revealed that the CuII-salan complexes decompose, in the presence of H2O2, significantly faster at 40 °C than at room temperature. The catalytic activity observed is probably due to the CuII-salan degradation products, observed in the mass spectrometry studies, and not to the original CuII-salan precursors.
- Ad?o, Pedro,Barroso, Sónia,Avecilla, Fernando,Oliveira, M. Concei??o,Pessoa, Jo?o Costa
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p. 212 - 223
(2014/05/06)
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- Enantioselective epoxidation of styrene by manganese chiral schiff base complexes immobilized on MCM-41
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Two chiral MnIII complexes synthesized and characterized by single-crystal X-ray diffraction were grafted onto mesoporous silica MCM-41. The MCM-41-immobilized solid chiral catalysts were characterized by various spectrochemical and physicochemical methods (XRD, FTIR, 29Si NMR, TGA, UV/Vis/DRS, EPR, cyclic voltammetry, SEM, BET). Both the homogeneous and heterogeneous MnIII chiral complexes are found to be effective catalysts for epoxidation of styrene. MCM-41-supported chiral catalysts are found to retain their catalytic activity up to five cycles. When an ionic liquid was implemented to enhance the catalytic recyclability of the homogeneous catalysts, they can be recycled up to three times. However, after the third cycle the catalytic activities of the complexes were found to decrease due to rupturing of the chiral catalyst.
- Mandal, Moon,Nagaraju, Vemu,Sarma, Bipul,Karunakar,Bania, Kusum K.
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p. 749 - 761
(2015/04/14)
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- Dual catalyst system for asymmetric alternating copolymerization of carbon dioxide and cyclohexene oxide with chiral aluminum complexes: Lewis base as catalyst activator and lewis acid as monomer activator
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Optically active aluminum complexes such as Schiff base, binuclear β-ketoiminate, and bisprolinol complexes were found to promote asymmetric alternating copolymerizations of carbon dioxide and cyclohexene oxide. The aluminum Schiff base complexes-tetraethylammonium acetate afforded isotactic poly(cyclohexene carbonate)s with low enantioselectivities. Lewis bases having two coordinating sites were utilized to enhance activity and selectivity based on the binuclear structure of the aluminum β-ketoiminate clarified by X-ray crystallography. [2gAlMe]2-bulky bisimidazole produced the alternating copolymer with high enantioselectivity (62% ee). The polymerization is considered to preferentially proceed at more crowded, enantioselective site owing to coordination of bulky Lewis bases to aluminums in less enantioselective sites. 32AlMe-2-picoline also exhibited a high enantioselectivity (67% ee). Methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) was applied to perform faster and more enantioselective copolymerizations at low temperature (82% ee). The asymmetric copolymerizations were found to be significantly dependent on size of epoxide, temperature, and kind/amount of activators.
- Nishioka, Kiyoshi,Goto, Hidetoshi,Sugimoto, Hiroshi
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p. 8172 - 8192
(2013/01/15)
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- A novel type of catalysts for the asymmetric C-C bond formation based on chiral stereochemically inert cationic Co iii complexes
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Schiff bases derived from (1R,2R)-1,2-diaminocyclohexane and 1 eq. of salycylic (or substituted salycylic) aldehyde form stereochemically inert positively charged chiral octahedral Co iii complexes of Δ-configuration with the stereoselectivity approaching 100%. To evaluate the calatylic activity and stereoinduction of the resulting complexes with various counteranions in the outer sphere, a model reaction of trimethylsilyl cyanide addition to benzaldehyde was used. O-trimethylsilylmandelonitrile formed in the process had an enantiomeric purity up to 27%. Complexes with F - counterion showed high catalytic activity.
- Belokon,Larionov,Mkrtchyan,Khrustalev,Nijland,Saghyan,Godovikov,Peregudov,Babievsky,Ikonnikov,Maleev
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p. 2252 - 2260
(2013/10/01)
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- Synthesis and characterization of cobalt(iii) cyanide complexes: Cobalt participation in the decomposition of radical anion of TCNQ
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Reaction of Co(CH3COO)2·4H2O, KTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) with the racemic or chiral H 2salency (N,N′-bis(salicylidene)-1,2-cyclohexanediamine) ligand afforded three Co(iii) complexes K[Co(salency)(CN)2]·CH 3OH (1), K[Co(S,S-salency)(CN)2]·H2O (1S) and K[Co(R,R-salency)(CN)2]·CH3OH (1R), which have been fully characterized. The cyanide groups in these three complexes are generated from the in situ decomposition of the radical anion of TCNQ with the participation of cobalt(ii). Single-crystal X-ray diffraction analysis reveals that complex 1 exhibits an infinite double stair-like chain structure. However, the chiral complexes 1S and 1R show chain structures consisting of two independent sub-chains. All of these chains are bridged by the K+ ions, with the cyanides interacting with K+ in the end-on and unusual side-on π-type mode. Second-order nonlinear optical effect studies in the solid state revealed that 1S and 1R are SHG active. The Royal Society of Chemistry.
- Tan, Chun-Hong,Ma, Xiao,Zhu, Qi-Long,Huang, Yi-Hui,Wen, Yue-Hong,Hu, Sheng-Min,Sheng, Tian-Lu,Wu, Xin-Tao
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p. 8708 - 8713
(2013/02/23)
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- Large stokes shift chiral polymers containing (R,R)-salen-based binuclear boron complex: Synthesis, characterization, and fluorescence properties
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Two novel chiral fluorescence polymers P-1 and P-2 incorporating (R,R)-salen-based binuclear boron complex in the main chain backbone were synthesized by (R,R)-salen-based boron complex (M-1) with 9,9-dibutyl-2,7- diethynyl-9H-fluorene (M-2) and 1,4-dibutoxy-2,5-diethynylbenzene (M-3) via Pd-catalyzed Sonogashira coupling reaction, respectively. The chiral polymers were characterized by 1H NMR, UV-vis spectroscopy, photoluminescence (PL), gel permeation chromatography (GPC), TGA, DSC, cyclic voltammetry (CV), and theoretical calculation using density-functional theory (DFT) method. P-1 and P-2 show anisotropic fluorescence property with emission spectral maxima at 474 nm and 514 nm, respectively. Both two chiral polymers can exhibit high fluorescence quantum yields (up to 44% and 52%) with large Stokes shifts over 90 nm. The DFT theoretical calculation of the polymer repeating units indicates that the optical band gaps of P-1 is higher than that of P-2, which was consistent with the CV determination results.
- Ma, Xiao,Jiao, Jiemin,Yang, Jing,Huang, Xiaobo,Cheng, Yixiang,Zhu, Chengjian
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scheme or table
p. 3894 - 3899
(2012/10/18)
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- Peroxidative bromination and oxygenation of organic compounds: Synthesis, X-ray crystal structure and catalytic implications of mononuclear and binuclear oxovanadium(V) complexes containing Schiffbase ligands
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Treatment of of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H 2L1) in methanol with aqueous NH4VO3 solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex [VOL1(MeOH)]·ClO4 (1) as deep blue solid while the treatment of same solution of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H2L1) with aqueous solution of VOSO 4 leads to the formation of di-(μ-oxo) bridged vanadium(V) complex [VO2L2]2 (2) as green solid where HL 2 = (R,R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL 2 is generated in situ by the hydrolysis of one of the imine bonds of HL1 ligand during the course of formation of complex [VO 2L2]2 (2). Both the compounds have been characterized by single crystal X-ray diffraction as well as spectroscopic methods. Compounds 1 and 2 are to act as catalyst for the catalytic bromide oxidation and C-H bond oxidation in presence of hydrogen peroxide. The representative substrates 2,4-dimethoxy benzoic acid and para-hydroxy benzoic acids are brominated in presence of H2O2 and KBr in acid medium using the above compounds as catalyst. The complexes are also used as catalyst for C-H bond activation of the representative hydrocarbons toluene, ethylbenzene and cyclohexane where hydrogen peroxide acts as terminal oxidant. The yield percentage and turnover number are also quite good for the above catalytic reaction. The oxidized products of hydrocarbons have been characterized by GC Analysis while the brominated products have been characterized by 1H NMR spectroscopic studies.
- Si, Tapan Kumar,Drew, Michael G.B.,Mukherjea, Kalyan Kumar
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experimental part
p. 2286 - 2293
(2011/10/11)
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- Relationship between anticancer activity and stereochemistry of saldach ligands and their iron(III) complexes
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(R,R)-, (S,S)- and (R,S)-N,N′-bis(salicylidene)-1,2- diaminocyclohexane (saldach) and their iron(III) complexes were screened for anticancer activity against MCF-7 and MDA-MB 231 breast cancer as well as HT-29 colon carcinoma cells. Antiproliferative effects depended on the presence of the central atom iron but were independent on the configuration at the saldach ligand. While the free ligands were inactive, the iron(III) derivatives displayed anticancer activity within a concentration range of 1 to 5 μM irrespective of the used cell line. At 5 μM they were even more active than cis-platin. A mode of action comparable to cis-platin can be excluded because it is very likely that the DNA is not the primary target of [FeIII (saldach)] complexes.
- Hille, Annegret,Gust, Ronald
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experimental part
p. 625 - 631
(2010/05/18)
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- Chiral salan aluminium ethyl complexes and their application in lactide polymerization
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Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC6H 2(R-O-R4)CH2)2{CH3N(C 6H10)NCH3}-C2H5] (4, 7: R = H; 5, 8: R = Cl; 6, 9: R = CH3) are reported. Enantiomerically pure salan ligands 1-3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variabletemperature (VT) 1H NMR in the tern-perature range of 220-335 K, 1H- 1H NOESY at 220K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core. The geometry is intermediate between square pyramidal with a cis-(O,O), trans-(Me,Me) ligand disposition and trigonal bipyramidal with a rrans-(O,O) and trans(Me,Me) disposition. A slow exchange between these two geometries at 220 K was indicated by 1H-1H NOESY NMR. In the presence of propan-2-ol as an initiator, enantiomerically pure (R,R) complexes 4-6 and their racemic mixtures 7-9 were efficient catalysts in the ring-opening polymerization of lactide (LA). Polylactide materials ranging from isotactically biased (Pm up to 0.66) to medium heterotactic (P r up to 0.73) were obtained from rac-lactide, and syndiotactically biased polylactide (Pr up to 0.70) from wicso-lactide. Kinetic studies revealed that the polymerization of (S,S)-LA in the presence of 4/propan-2-ol had a much higher polymerization rate than (R,R)-LA polymerization (kss/kRR = 10.1).
- Du, Hongzhi,Velders, Aldrik H.,Dijkstra, Pieter J.,Sun, Jingru,Zhong, Zhiyuan,Chen, Xuesi,Feijen, Jan
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supporting information; experimental part
p. 9836 - 9845
(2010/04/05)
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- Synthesis of chlorinated biphenyls by Suzuki cross-coupling using diamine or diimine-palladium complexes
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Several novel diimines (Salen-type ligands) 2a-2i and their reduced diamine counterparts 3b,3d-3g and 3i form complexes 4a-4i, 5b,5d-5g, and 5i with PdCl2 in DMF or methanol. Using 1 mol-% of the isolated complexes 4e and 5f many polychlorinated biphenyls (PCBs) can be prepared in moderate to excellent yields according to the Suzuki cross-coupling protocol with contact to air. Several 4-acetylbiphenyls prepared by this method can be converted in moderate yields into the corresponding biphenylcarboxylic acids (BCAs) by alkaline cleavage. An X-ray crystal structure determination confirms the structure of complex 5f. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Kylmaelae, Tuula,Kuuloja, Noora,Xu, Youjun,Rissanen, Kari,Franzen, Robert
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supporting information; experimental part
p. 4019 - 4024
(2009/04/11)
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- Titanium-salan-catalyzed asymmetric oxidation of sulfides and kinetic resolution of sulfoxides with H2O2 as the oxidant
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Asymmetric oxidation of sufides to sulfoxides by aqueous hydrogen peroxide with catalysis by titanium-salan complexes is presented. Optically active sulfoxides have been obtained with good to high enantioselectivities (up to 97% ee) by a tandem enantioselective oxidation and kinetic resolution procedure, the catalyst performing over 500 turnovers with no loss of enantioselectivity. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Bryliakov, Konstantin P.,Talsi, Evgenii P.
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experimental part
p. 3369 - 3376
(2009/04/07)
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- Practical by ligand design: A new class of monodentate phosphoramidite ligands for rhodium-catalyzed enantioselective hydrogenations
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A new class of low-cost and easy-to-prepare monodentate phosphoramidite ligands (Cydam-Phos) has been developed from readily accessible and cheap trans-1,2-diaminocyclohexane as starting material through a three-step transformation. This type of ligands exhibited excellent enantioseletivities and high activities in rhodium(I)-catalyzed asymmetric hydrogenations of dehydro-α-amino acid methyl esters 9 (ee: 96.2-99.8%) and acetylenamides 11 (91.8-98.8%). The remarkable substituent effects exhibited by the ligands on the enantioselective control of the catalysis are rationalized on the basis of molecular structure of the catalyst precursor.
- Zhao, Baoguo,Wang, Zheng,Ding, Kuiling
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p. 1049 - 1057
(2007/10/03)
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- Molybdenum(VI) cis-dioxo complexes with chiral schiff base ligands: Synthesis, characterization, and catalytic applications
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Three optically active Molybdenum (VI) dioxo complexes with tetrahydro salen and substituted tetrahydro salen derivatives as ligands were synthesized and examined as catalysts for asymmetric epoxidation. Complexes of the type MoO2(L)(Solv) and WO2(L) (L = tridentate, trans-2-aminocyclohexanol derived chiral Schiff base, Solv = alcohol) were prepared and characterized by elemental analysis, NMR and IR spectroscopy. These complexes are applicable as catalysts for olefin epoxidation reactions with tert-butyl hydroperoxide (TBHP) being the oxidizing agent. In case of cis-β-methylstyrene moderate enantiomeric excesses of up to 26% can be reached when the reaction is carried out at 0°C.
- Zhou, Xiangge,Zhao, Jin,Santos, Ana M.,Kühn, Fritz E.
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p. 1223 - 1228
(2007/10/03)
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- Conformations of Pyridoxal Schiff Bases of Amino Acids. A Circular Dichroism Study
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The conformations of a series of peridoxal-L-amino acid Schiff bases in methanol solution were deduced from their circular dichroism spectra.The N-salicylidene analogues of the pyridoxal Schiff bases were used as appropriate reference compounds.The predominant conformation of the Cα-N bond was found to be approximately the same for all the Schiff bases and involves a pseudoequatorial disposition of the Cα-H bond with respect to the plane of the extended ? system.The sign of the Cotton effects near 420 and 340 nm varies with the nature (polar, nonpolar, aromatic) of the amino acid side chain, according to the chirality of the dominant interaction of the amino acid residue with the pyridoxylideneamino chromophore.The circular dichroism spectra of zinc(II) complexes of N-pyridoxylidene-L-amino acids were also discussed in relation to the metal-free systems.
- Casella, Luigi,Gullotti, Michele
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p. 803 - 809
(2007/10/02)
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