A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2 0 -(OC 6 H 3 -5-t-Bu) 2 -NHRNH}Cl 2 ] (Lig 1 TiCl 2 : R 5 C 2 H 4 ; Lig 2 TiCl 2 : R 5 C 4 H 8 ; Lig 3-TiCl 2 : R5 C 6 H 12 ) and [Ti{2,2 0 -(OC 6 H 2 -3,5-di-t-Bu) 2 -NHC 6 H 12 NH} Cl 2 ] (Lig 4 TiCl 2 ) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [M{2,2 0 -(OC 6 H 3 -3,5-di-t-Bu) 2 -NHC 6 H 12 NH}Cl 2 ] (Lig 4 VCl 2 : M5 V; Lig 4 ZrCl 2 : M 5 Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1-octene polymerization after activation by MAO and/or Al(i-Bu) The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig 1 TiCl 2 << Lig 2 TiCl 2 < Lig 3 TiCl 2 ) and declines after adding additional tert-Bu group on the aromatic rings (Lig 3 TiCl 2 < Lig 4 TiCl 2 ). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et 2 AlCl-activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra-high molecular weight PE (up to 3588 kg mol 21 ) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg mol v 21 ), with high molecular weight (1986 kg mol 21 ) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1-octene copolymers, whereas vanadium catalysts produced product mixtures.
A phenoxy-imine proligand with the additional OH donor group, 4,6-tBu2-2-(2-CH2(OH)-C6H4N = CH)C6H3OH (LH2), was synthesized and used to prepare group 4 and 5 complexes by reacting with Ti(OiPr)4 (LTi) and VO(OiPr)3 (LV). All new compounds were characterized by the FTIR, 1H and 13C NMR spectroscopy and LTi by the single-crystal X-ray diffraction analysis. The complexes were used as catalysts in the ring opening polymerization of ε-caprolactone. The influence of monomer/transition metal molar ratio, reaction time, polymerization temperature as well as complex type was investigated in detail. The complexes showed high (LTi) and moderate (LV) activity in ε-caprolactone polymerization and the resultant polycaprolactones exhibited Mn and Mw/Mn values ranging from 4.0 · 103 to 18.7 · 103 g/mol and from 1.4 to 2.5, respectively.
The reduction of the phenoxyimine moiety in three individual speciesnamely free ligand, aluminum complex, and titanium complexwith aluminum alkyls and aluminum hydride has been studied by means of DFT. It was demonstrated that the free phenoxyimine ligand in an equimolar mixture with trimethylaluminum does not undergo reduction. Instead, experimentally observed formation of the six-membered cyclic aluminum−phenoxyimine complex, useful in the ring-opening polymerization of lactones, takes place as the kinetically and thermodynamically favored process. However, it is anticipated that a 2-fold excess of the aluminum compound, especially aluminum hydride, acting on the resulting cyclic complex can convert the imine to the aluminum-subsituted amine functionality easily with an energetic barrier of approximately 10 kcal/mol. Finally, the propensity of the imine moiety in the titanium-based precursor of the coordinative olefin polymerization toward reduction with organoaluminum compounds is revealed and the mechanism of this reaction is also suggested.
Contrary to other N-(pyridyl)nitramines, the title compound cannot be rearranged to 3-amino-2-nitropyridine or other isomers. Hypothetical products of its transformation under influence of concentrated sulphuric acid, viz. 3-hydroxypyridine, 3,3′-azoxypyridine and 3,3′-azopyridine, were obtained from 3-nitro- and 3-aminopyridine in oxidation and reduction reactions. N-(3-Pyridyl)nitramine was prepared and rearranged in concentrated sulphuric acid. 3-Hydroxypyridine and 3,3′-azoxypyridine were isolated from the reaction mixture, other products were identified by the HPLC and GCMS methods. The results indicate that N-(3-pyridyl)hydroxylamine is an intermediate formed from N-(3-pyridyl)nitramine under the influence of concentrated sulphuric acid. The reaction path, leading to the final products, is discussed in context of the mechanism of nitramine rearrangement.
Para‐substituted N‐phenylnitramines were prepared either by oxidation of diazonium salts or by nitration under alkaline or acidic conditions. Isotopic [15N‐NO2] labelling indicated that the bands characteristic of the N‐nitro group appear in the 1318–1323 and 1585–1607 cm−1 regions. In the nitrogen NMR spectra, the nitramino group gives two resonances at −193 ± 3 (NH) and −32 ± 3 ppm (NO2). The chemical shifts in proton and carbon NMR spectra are predictable, based on increments and the additivity rule. The spectral data indicate the lack of conjugation between the nitramino group and another substituent bound to the ring. It seems to contradict the well‐known fact that substituents strongly (ρ = 4) influence the rate of nitramine rearrangement. The acidities of primary N‐phenylnitramines (3.77 < pKA < 5.62) are similar to those of benzoic acids and weakly dependent (ρ = 1) on the electronic character of a substituent. Based on the analogy with benzoic acids, it has been calculated that basicities of nitramines (pKB ≈ 21) are extremely low. Consequently, addition of protons to an intact nitramine molecule, as the preliminary step of the rearrangement, seems to be improbable. Migration of the N‐nitro group precedes protonation; the latter process facilitates transformation of intermediates into stable final products. Copyright © 2001 John Wiley & Sons, Ltd.
The geometries of the thiazole ring and the nitramino groups in N-(3H-thiazol-2-ylidene)nitramine, C3H3N3O2S, (I), and N-methyl-N-(thiazol-2-yl)nitramine, C4H5N3O2S, (II), are very similar. The nitramine group in (II) is planar and twisted along the C-N bond with respect to the thiazole ring. In both structures, the asymmetric unit includes two practically equal molecules. In (I), the molecules are arranged in layers connected to each other by N-H...N and much weaker C-H...O hydrogen bonds. In the crystal structure of (II), the molecules are arranged in layers bound to each other by both weak C-H...O hydrogen bonds and S...O dipolar interactions.
Chelidonic acid (4-oxo-4H-pyran-2,6-dicarboxylic acid) is present in plants of Papaveraceae family, especially in Chelidonium majus. Due to its anticancer, antibacterial, hepatoprotective, and antioxidant properties, it has been used in medical treatments. In this work, the X-ray structure of methanol solvate of chelidonic acid was determined. Layers of chelidonic acid are held by hydrogen bonds via COOH and C = O fragments and additionally bridged by methanol. The formed H-bond network between two acid units is different from typical –COOH dimers observed, e.g., in crystals of isophtalic acid. The molecular structure of 2,6-dimethyl-γ-pyrone (2Me4PN) and chelidonic acid, a 2,6-dicarboxylic derivate of γ-pyrone (4PN), was verified in silico using density functional theory (DFT-B3LYP) combined with large correlation-consistent basis sets. The impact of –CH3 and –COOH substituents on 4PN ring structure, dipole moments, geometric/magnetic indexes of aromaticity, and NBO charges was assessed following unconstrained geometry optimization in the gas phase, chloroform, methanol, DMSO, and water with solvent effect introduced using the polarized continuous model (PCM). H-bond network formed in chelidonic acid–methanol complex was analyzed and their interaction energy estimated. Theoretical modeling enabled prediction of accurate structural parameters, dipole moments, and geometric/magnetic indexes of aromaticity of the studied 4PN, 2Me4PN, and chelidonic acid molecules.
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