21388-97-6Relevant articles and documents
Conformational folding induced by π-π interaction in a series of flexible dyads consisting of isomeric mesoporphyrin nitrobenzyl esters
Colominas, Carles,Eixarch, Lisbeth,Fors, Pere,Lang, Kamil,Nonell, Santiago,Teixido, Jordi,Trull, Francesc R.
, p. 997 - 1004 (1996)
A series of isomeric (ortho, meta and para) nitrobenzyl mono- and di-esters of mesoporhyrin, in which the nitrobenzyl group(s) is (are) mono-linked through one or both propionate chains of the porphyrin, have been synthesized and their room-temperature conformations in a number of solvents have been investigated using 1H NMR spectroscopy and theoretical calculations. Folding of these flexible dyads is consistent with the following observations: (1) 1H NMR ring current upfield shift in all solvents assayed [i.e., CDCl3, CDCl3-CD3OD (10:1) and C 6D6] of 0.5-2.5 ppm for the aryl protons; (2) these shifts are independent of temperature over the range 25 to -55°C; (3) the 1H NMR resonance values of mesoporphyrin benzyl ester (lacking the nitro group) are not shifted, indicating a preferred, sterically less crowded, extended conformation. The presence of the nitro group on the phenyl ring(s) is responsible for the folding of these flexible dyads, and the results can be interpreted in terms of π-π interactions (C. A. Hunter and J. K. M. Sanders, J. Am. Chem. Soc., 1990, 112, 5525-5534) between the two halves. In the theoretically calculated (molecular mechanics and semiempirical calculations) minimum-energy folded conformations, each benzyl group lies approximately parallel to the porphyrin π-system with its centre slightly offset relative to the centre of the porphyrin; however, for each isomer, significant structural differences between the ortho isomer and its meta and para counterparts are found. The implications of these differences for the photoinduced electron transfer efficiencies in these dyads are discussed.
Cycloaddition of CO2 with epoxides and esterification reactions using the porous redox catalyst Co-POM@MIL-101(Cr)
Marandi, Afsaneh,Bahadori, Mehrnaz,Tangestaninejad, Shahram,Moghadam, Majid,Mirkhani, Valiollah,Mohammadpoor-Baltork, Iraj,Frohnhoven, Robert,Mathur, Sanjay,Sandleben, Aaron,Klein, Axel
, p. 15585 - 15595 (2019/10/19)
The catalytic activity of the recently reported Co-POM@MIL-101(Cr) composite, synthesized from K5[CoW12O40] (Co-POM) and chromium(iii) terephthalate (MIL-101), was studied in the solvent-free cycloaddition of CO2 with epoxides and esterification of acetic acid with various alcohols. The materials containing varying amounts of Co-POM were synthesized using a one-pot HF-free method in a "bottle around ship" strategy. The material was thoroughly characterized using several methods such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance spectroscopy (EPR). Temperature programmed desorption (TPD) of NH3 and CO2, and the CO2 adsorption capacity (adsorption isotherms) were used to study the acid-base properties of the materials. The combination of the electron-transfer character of Co(iii)-POM and ordered mesopores in MIL-101(Cr) creates an efficient catalytic system with mild conditions (90 °C and 20 bar CO2 pressure) for solvent-free cycloaddition of CO2 to various epoxides. Esterification of acetic acid with alcohols was also carried out using the Co-POM@MIL-101 catalysts and high yields were achieved for different alcohols. The catalysis experiments also clearly show that the active site in this heterogeneous catalyst is the Co(iii) center in the Keggin anion structure. It presumably conducts both the cycloaddition of CO2 to epoxides and the esterification reaction via an outer-sphere electron transfer mechanism using the Co(iii)/Co(ii) redox pair. The heterogeneous Co-POM@MIL-101 catalysts were separated by simple filtration and reused five times in the cycloaddition of CO2 with styrene epoxide and seven times for the esterification of acetic acid with benzyl alcohol with negligible leaching of Co-POM and no considerable loss of activity.
Preparation, characterization and application of RHA/TiO2 nanocomposites in the acetylation of alcohols, phenols and amines
Seddighi, Mohadeseh,Shirini, Farhad,Goli-Jolodar, Omid
, p. 1003 - 1010 (2016/08/08)
In this work, anatase-phase nano-titania was prepared by embedding in rice husk ash, and identified using a variety of techniques. The obtained nanocomposite (RHA/TiO2) was used as a green and inexpensive catalyst for the promotion of the acetylation of alcohols, phenols and amines with Ac2O at room temperature under solvent free conditions. The procedure gave the products in excellent yields during all reaction times. Also this catalyst can be reused for several times without loss of its catalytic activity.
