- Reversible trans-cis photoisomerization of new pyrrolidene heterocyclic imines
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A series of novel pyrrolidene imines bearing functionalized aryl or naphthyl moieties was synthesized and their photochromic properties studied by UV spectroscopy. UV irradiation of these heterocyclic Schiff bases at room temperature promotes the trans-ci
- Coelho, Paulo J.,Castro, M. Cidália R.,Raposo, M. Manuela M.
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- N-(Aryl)pyrrole-2-aldimine complexes of ruthenium: Synthesis, characterization and catalytic transfer-hydrogenation
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Reaction of N-(4′-R-phenyl)pyrrole-2-aldimines (HL-R, where H represents the acidic N-H hydrogen and, R = OCH3, CH3, H and Cl) with [Ru(bpy)2(EtOH)2]2+, formed in situ via Ag+-assisted removal of the chlorides from [Ru(bpy)2Cl2] in ethanolic medium, affords a group of pinkish-brown complexes of type [Ru(bpy)2(L-R)]+ isolated as nitrate salts. Structure of [Ru(bpy)2(LOCH3)]NO3 and [Ru(bpy)2 (L-CH3)]NO3 have been determined by X-ray crystallography. The aldimine-ligand (L-R) is coordinated to the metal center as a mono-anionic bidentate N,N-donor. All the complexes are diamagnetic, and show characteristic 1H NMR signals and intense absorptions in the visible region. Cyclic voltammetry on the complexes shows two irreversible oxidations within 0.64 to 1.14 V vs SCE and two irreversible reductions within -1.00 to -1.58 V vs SCE. The [Ru(bpy)2(LR)]+ complexes are found to serve as efficient catalyst-precursor for the transfer-hydrogenation of aldehydes and ketones.
- Kumar, Rohit,Paul, Piyali,Bhattacharya, Samaresh
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p. 721 - 728
(2020/09/16)
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- Monomethylaluminum and dimethylaluminum pyrrolylaldiminates for the ring-opening polymerization of rac-lactide: Effects of ligand structure and coordination geometry
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Two series of aluminum alkyl complexes supported by pyrrolylaldiminate ligands, LAlMe2 (1a-7a) and L2AlMe (1b-7b), were successfully synthesized and characterized by NMR spectroscopy and elemental analysis. Reactions of trimethylaluminum with the corresponding pyrrolylaldiminate ligands in the molar ratios of 1:1 and 1:2 yielded dimethylaluminum pyrrolylaldiminates (1a-7a) and monomethylaluminum pyrrolylaldiminates (1b-7b), respectively, in good yields. The structure of 3b, determined by single-crystal X-ray diffraction, displayed a distorted trigonal bipyramidal geometry with the τ value of 0.65. Upon addition of 1 equivalent of benzyl alcohol, all complexes promoted the living ring-opening polymerization of rac-lactide with a good control over molecular weights and polydispersities. Complexes 6a and 7a were found to efficiently mediate the immortal polymerization in the presence of excess equivalents of benzyl alcohol (up to 5 equivalents), as evidenced by the narrow PDI values and the good agreement between the experimental Mn values and monomer/benzyl alcohol ratios. The steric and electronic effects of the imine nitrogen substituents had a strong influence on the polymerization activities both in catalytic activity and polymer microstructure. The catalytic activity decreased as follows: 4-Me-C6H4 (3) > C6H5 (1) ≈ 4-F-C6H4 (2) ≈ 2-Me-C6H4 (5) > 4-OMe-C6H4 (4) ? 2-tBu-C 6H4 (6) > adamantyl (7). In comparison, the catalytic activity of the monomethylaluminum complex is slightly higher than that of the dimethylaluminum counterpart. The polymerization of rac-lactide by 6b yielded heterotactically enriched polylactide (Pr = 0.60) whereas the isotactic-enriched polymer (Pm = 0.74) was obtained from 7b. The Royal Society of Chemistry 2014.
- Tabthong, Sittichoke,Nanok, Tanin,Kongsaeree, Palangpon,Prabpai, Samran,Hormnirun, Pimpa
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p. 1348 - 1359
(2014/01/06)
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- Hydrolysis kinetic studies of schiff bases derived from pyrrolic aldehydes in buffered aqueous ethanol and sulfuric acid solutions: Structural effects of substitutes
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Two series of substituted N-pyrrolyl-2-methylene-aniline were synthesized and characterized to study their stability in a large domain of pH (0-14) and especially in the H0 domain (-4 to 0). The hydrolysis kinetics of the azomethine group was established in homogeneous media using a thermostated UV-vis spectrophotometer. The hydrolysis mechanism was investigated, and the experimental kinetic constants were calculated. Then, the pH-rate diagram profile was determined and the structural effect of substitutes on the kinetic constants was clarified and discussed.
- Bengharez, Zohra,El Bahri, Zineb,Mesli, Abderrezzak
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p. 404 - 414
(2013/07/05)
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- Novel Hydrolytic Cleavage of 4-(Pyrol-2-yl)azetidin-2-ones
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Alkaline hydrolysis of 1-aryl-3,3-diphenyl-4-(pyrol-2-yl)azetidin-2-ones results in an unusual dualpath fragmentation of the β-lactam ring to give diphenylacetic acid, 2-iminomethylpyrroles, arylamines, and 1,1-diphenyl-2-(pyrrol-2-yl)ethylene.The product distribution is shown to be dependent on temperature.
- Upadhyaya, Anil K.,Mehrotra, Kailash N.
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p. 957 - 960
(2007/10/02)
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