A reactive hydroxoferric porphyrazine complex, [(PyPz)FeIII(OH) (OH2)]4+ (1, PyPz = tetramethyl-2,3-pyridino porphyrazine), has been prepared via one-electron oxidation of the corresponding ferrous species [(PyPz)FeII(OH2)2]4+ (2). Electrochemical analysis revealed a pH-dependent and remarkably high FeIII–OH/FeII–OH2 reduction potential of 680 mV vs Ag/AgCl at pH 5.2. Nernstian behavior from pH 2 to pH 8 indicates a one-proton, one-electron interconversion throughout that range. The O–H bond dissociation energy of the FeII–OH2 complex was estimated to be 84 kcal mol−1. Accordingly, 1 reacts rapidly with a panel of substrates via C–H hydrogen atom transfer (HAT), reducing 1 to [(PyPz)FeII(OH2)2]4+ (2). The second-order rate constant for the reaction of [(PyPz)FeIII(OH) (OH2)]4+ with xanthene was 2.22 × 103 M−1 s−1, 5–6 orders of magnitude faster than other reported FeIII–OH complexes and faster than many ferryl complexes.
Organic isocyanates are versatile intermediates that provide access to a wide range of functionalities. In this work, we have developed the first synthetic method for preparing aliphatic isocyanates via direct C-H activation. This method proceeds efficiently at room temperature and can be applied to functionalize secondary, tertiary, and benzylic C-H bonds with good yields and functional group compatibility. Moreover, the isocyanate products can be readily converted to substituted ureas without isolation, demonstrating the synthetic potential of the method. To study the reaction mechanism, we have synthesized and characterized a rare Mn-NCO intermediate and demonstrated its ability to transfer the isocyanate moiety to alkyl radicals. Using EPR spectroscopy, we have directly observed a Mn intermediate under catalytic conditions. Isocyanation of celestolide with a chiral manganese salen catalyst followed by trapping with aniline afforded the urea product in 51% enantiomeric excess. This represents the only example of an asymmetric synthesis of an organic urea via C-H activation. When combined with our DFT calculations, these results clearly demonstrate that the C-NCO bond was formed through capture of a substrate radical by a Mn-NCO intermediate.
Diaryl thioethers and S-cycles were obtained on the basis of the copper-catalyzed reaction of carbon disulfide and aryl iodides in the presence of DBU. This reaction enables the one-pot synthesis of diaryl thioethers by employing cheap, available, and easy-to-handle carbon disulfide with aryl iodides. The reaction was successfully employed in the construction of sulfur-containing cyclic molecules.
The conjugate of oleanlic acid with adenine was synthesized and it could be gelled in mixed solvents of THF and water, but no gel was formed in the single organic solvent. The self-aggregation behaviour and physical properties of the organogel were characterized by 1 H NMR, FT-IR, and scanning electron microscopy. The morphology and the stability of the gel were remarkably affected by the uracil derivative through destroying hydrogen-bonding.
In this work, poly(ethylene terephthalate)
(PET) chain-extending
products with different molecular weights were prepared by reactive
extrusion using isocyanate trimer (C-HK) as the trifunctional chain
extender. The effect of the chain extender C-HK on the intrinsic viscosity,
melt flow property, crystallization behavior, crystallization morphology,
and mechanical property of PET was investigated. The results showed
that when the content of the chain extender was increased from 0.6
to 1.4 wt%, the viscosity average molecular weight of PET was effectively
increased from 2.36 × 10
4
to 5.46 × 10
4
g·mol
–1
. After the chain extending, the crystallinity
and the time of semicrystallization of PET were significantly decreased.
After the isothermal crystallization at 220 °C for 5 min, the
spherulites formed by pure PET became larger. With the increase in
molecular weight of PET after chain extension, its spherulite size
was significantly decreased without changing the crystalline structure.
The chain-extended PET also exhibited more excellent bending-resistant
and impact-resistant properties. While the tensile strength of PET
after chain extension was slightly decreased, the bending strength
was increased by a maximum value of 56.8%, and the impact strength
was increased by a maximum value of five times.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.