Electron-donating Methyl Substituents Research Articles

Dicarboxylate-containing and fully substituted ferrocene with rapid dissolvability, high solubility, good stability, and moderate formal potential for mediated electrochemical detection.

An electron mediator with rapid dissolvability and high solubility in aqueous electrolyte solutions is essential for point-of-care testing based on mediated electrochemical detection. However, most ferrocenyl (Fc) compounds have slow dissolvability and poor solubility owing to high hydrophobicity of the Fc backbone. Moreover, many Fc compounds have poor stability and nonoptimal formal potential (). Herein, we present an Fc compound, Fc8m2c, which exhibits rapid dissolvability, high solubility, good stability, and moderate along with its high electron-mediation rate. The of Fc8m2c (0.17 V vs. Ag/AgCl) is tuned by two electron-withdrawing acyl substituents and eight electron-donating methyl substituents. Two pendant carboxylate groups of Fc8m2c allow for rapid dissolvability and high solubility (0.63 M in water), whereas full substitution in its two cyclopentadienyl ligands facilitates good chemical stability against decomposition in the presence of dissolved O2 and ambient light. A moderate enables the application of a potential of 0.07 V at which electrochemical background currents are low and also contributes toward resisting the decomposition of both Fc8m2c and Fc8m2c+. Fc8m2c provides a high electron-mediation rate constant (2.4 × 106 M-1 s-1) in glucose detection using glucose dehydrogenase. When Fc8m2c is applied to a glucose sensor, the calculated detection limit is ∼0.1 mM with a measurement period of 5 s. Considering that the normal concentration of glucose in serum is between 3.9 and 6.6 mM, the detection limit is sufficiently low. These results show that Fc8m2c is an excellent electron-mediator candidate for sensitive and rapid glucose detection.

Comparative Study of 1,3,5-Trinitrobenzene and 2,4,6-Trinitrotoluene Hydrogenation over Copper-Aluminum Oxide Catalyst in a Flow Reactor

The catalytic properties of a copper-aluminum oxide catalyst obtained from double layered hydroxide have been studied in hydrogenation of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) in a flow reactor. The reaction was carried out at temperature of 120°C, total pressure of 30 bar and substrate concentration of 0.10–0.15 M, using methanol as a solvent. 1,3,5-Triaminobenzene (TAB) and 2,4,6-triaminotoluene (TAT) were isolated from the reaction mixture in the form of double salts with sulfuric acid TAB⋅2H2SO4 and TAT⋅2H2SO4, the yield of which was 92 and 98%, respectively. At an initial trinitroarene concentration of 0.10 M, the hydrolysis of triaminobenzene salts made it possible to synthesize phloroglucinol and methylphloroglucinol in 78 and 91% yields. Increasing the concentration to 0.15 M reduces the yield to 71 and 88%, respectively. According to thermal analysis data, the observed differences in the yields of triaminobenzene salts and polyphenols are explained by the formation of different amounts of resinous by-products on the catalyst surface during hydrogenation of trinitroarene. Hydrogenation of TNT produces less resin, resulting in higher yields of TAT⋅2H2SO4 and methyl phloroglucinol. This is probably due to the presence of an electron-donating methyl substituent, which slows down polycondensation of TAT molecules.

End-Group Modifications with Bromine and Methyl in Nonfullerene Acceptors: The Effect of Isomerism

The development of isomeric molecules has been widely exploited in molecular structures associated with organic solar cells (OSC) and is an effective pathway to finely tune the photoelectric properties and device performance. The molecular properties of nonfullerene acceptors and the morphology of blend films can be effectively controlled by manipulating isomeric substituent positions on benzene-fused end-capping groups (EG) in acceptors. Here, three isomeric EGs were designed and synthesized which simultaneously possess an electron-withdrawing bromine and an electron-donating methyl substituent. By linking three isomeric EGs, (Br,Me), (Br,Me)-1, and (Br,Me)-2 each with the BTP-CHO core, three isomeric small-molecule acceptors (SMA) were obtained. The power conversion efficiency (PCE) of PM6:BTP-(Br,Me)-1-based OSCs is 13.43%, is much higher than that of PM6:BTP-(Br,Me)- (11.92%) and PM6:BTP-(Br,Me)-2- (11.08%) based devices. Our results show that isomeric EGs can provide strategies to tune the absorption spectra of SMAs, intramolecular charge transfer (ICT) and electron mobility of organic semiconductor device, and ultimately increase the performance of nonfullerene acceptors.

Introducing electron-donating substituents on ligand backbone of α-diimine nickel complex and the effects on catalyst thermal stability in ethylene polymerization

A novel α-diimine nickel pre-catalyst Cat.1 with two electron-donating methyl substituents on the ligand backbone was synthesized and investigated for ethylene polymerization using methylaluminoxane as cocatalyst. Cat.1 exhibited higher polymerization activity and produced highly branched polyethylene with slightly higher molecular weight than that of the typical Brookhart catalyst (B-Cat) at elevated temperature. By tracing the changes of active center number in the polymerization process, Cat.1 was found to have higher ratio of activated nickel ([C∗]/[Ni]), longer catalyst lifetime and larger chain propagation rate constant (kp) as compared with B-Cat. The computational studies demonstrated the electron-donating methyl substituents can make a more electron-rich ligand to influence the catalytic properties of Cat.1. Stronger interactions between the electron-rich ligand and the nickel center should be the main reasons for longer catalyst lifetime and enhanced thermal stability of Cat.1. The production of polyethylene with higher molecular weight by Cat.1 can be explained by its larger kp value and more stable transition state for ethylene insertion than for chain transfer reaction due to the electron-donating ligand. Overall, the results of this work clearly support the importance of ligand electronic effects on the thermal stability and intrinsic reactivity of active centers in α-diimine Ni(II) catalysts.

Solvent-free cycloaddition of CO2 and propylene oxide to cyclic carbonates using different ligand metal complexes

ABSTRACTTetradentate ligand metal complexes salen-Co(III)OBzF5, salen-CH3Co(III)OBzF5, salen-CH3Co(III)Br, and salen-ClCo(III)Br were synthesized. These complexes were used as catalysts for the chemical fixation of CO2 and propylene oxide to cyclic carbonates. Tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, [PPN]+Cl− ([PPN]+ = bis(triphenylphosphine)iminium), and tetrabutyl ammonium bromide were used as co-catalysts in the reactions. Additionally, the catalytic activity of naphthen-CoSO4 and salen-CoSO4 was also explored using the above co-catalysts. The conversion of propylene oxide to cyclic carbonate was found to increase with increase in temperature and pressure of carbon dioxide. It was noted that cyclic carbonate product could be obtained at a temperature as low as 60°C and pressure of 20 bar in just 2 h. Further, it was observed that introduction of electron-donating methyl substituent increased the nucleophilic character of the catalyst and reaction conversion. On the contrary, electron-withdrawing substituents like chlorine decreased the cyclic carbonate conversion, thereby making it a weaker nucleophilic catalyst.

Effect of Substituents on the Water Oxidation Activity of [RuII(terpy)(phen)Cl]+Procatalysts

A series of [Ru(II)(terpy-R)(phen-X)Cl]PF6 complexes was designed where terpy-R is the tridentate 4'-(4-methylmercaptophenyl)-2,2':6'2″-terpyridine ligand MeMPTP and phen-X is a substituted phenanthroline with hydro (1), 5-nitro (2), 5,6-dimethyl (3), and 3,4,7,8-tetramethyl (4). This series allows us to compare the reactivity of phenanthroline-containing procatalysts with that of its well-established bipyridine counterparts as well as to study the effects of electron-withdrawing and -donating substituents on water oxidation. These species were thoroughly characterized by spectroscopic and spectrometric methods, and the structures of 1, 3, and 4 were determined by single-crystal X-ray diffraction. The procatalysts 1-4 show opposite trends compared to known terpyridine/bipyridine species; the unsubstituted procatalyst 1 yields a turnover number (TON) of 410 followed by 250 and 150 for complexes 3 and 4 with electron-donating substituents. Species 2, with electron-withdrawing properties, yields the lowest TON of 60. Although the TONs decrease upon substitution, the presence of electron-donating methyl substituents enhances the rate of O2 evolution during an early stage of catalysis. Interestingly, no evidence of conversion from chlorido-containing procatalysts into expected aqua-containing catalysts was observed for 1-4 by NMR and UV-visible spectroscopy during the induction period. This observation, along with reactivity toward (NH4)2[Ce(IV)(NO3)6], suggests that water nucleophilic attack happens to a high-valent ruthenium species rather than while at the Ru(II) oxidation state. Reactivity follows a trend similar to the rate of O2 evolution in all complexes. Furthermore, the electrospray ionization mass spectrometry and (1)H NMR analyses of 1, as recovered after catalysis, indicate the presence of a chlorido ligand.

Influence of the aryl substituent identity in 4-arylamino-3-nitrocoumarins on their thermal behavior

Thermal behavior of structurally similar 4-arylamino-3-nitrocoumarin derivatives substituted with different electron-donor and electron-acceptor substituents on the aryl side group was investigated. The thermal stability of these compounds was studied by non-isothermal thermo-gravimetric analysis, differential thermo-gravimetry, differential thermal analysis, and pyrolysis–gas chromatography–mass spectrometry. The thermal degradation of the three synthesized 4-arylamino-3-nitrocoumarins, possessing an iodine atom, a nitro or a methyl group, proceeds in three steps. The thermal stability of the coumarin derivative with the electron-donating methyl substituent is lower than that of the compounds with the electron-accepting nitro group or iodine atom. This least stable compound (4-[(4-methylphenyl)amino]-3-nitro-2H-chromen-2-one) was also characterized with the greatest loss in mass that accompanied the degradation, and all of the three degradation steps of this compound began at the lowest temperature in comparison to the other two.

Theoretical and Experimental Spectroscopic Analysis of Cyano-Substituted Styrylpyridine Compounds

A combined theoretical and experimental study on the structure, infrared, UV-Vis and 1H NMR data of trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)] pyridine and trans-4-(m-cyanostyryl)pyridine is presented. The synthesis was carried out with an efficient Knoevenagel condensation using green chemistry conditions. Theoretical geometry optimizations and their IR spectra were carried out using the Density Functional Theory (DFT) in both gas and solution phases. For theoretical UV-Vis and 1H NMR spectra, the Time-Dependent DFT (TD-DFT) and the Gauge-Including Atomic Orbital (GIAO) methods were used, respectively. The theoretical characterization matched the experimental measurements, showing a good correlation. The effect of cyano- and methyl-substituents, as well as of the N-atom position in the pyridine ring on the UV-Vis, IR and NMR spectra, was evaluated. The UV-Vis results showed no significant effect due to electron-withdrawing cyano- and electron-donating methyl-substituents. The N-atom position, however, caused a slight change in the maximum absorption wavelengths. The IR normal modes were assigned for the cyano- and methyl-groups. 1H NMR spectra showed the typical doublet signals due to protons in the trans position of a double bond. The theoretical characterization was visibly useful to assign accurately the signals in IR and 1H NMR spectra, as well as to identify the most probable conformation that could be present in the formation of the styrylpyridine-like compounds.

DFT and Experimental Exploration of the Mechanism of InCl3-Catalyzed Type II Cycloisomerization of 1,6-Enynes: Identifying InCl2+ as the Catalytic Species and Answering Why Nonconjugated Dienes Are Generated

InCl(3) and other In(III) species have been widely applied as catalysts in many reactions. However, what are the real catalytic species of these reactions? Through DFT calculations and experimental investigation of the mechanism and regioselectivity of InCl(3)-catalyzed cycloisomerization reactions of 1,6-enynes (here all discussed 1,6-enynes are ene-internal-alkyne molecules), we propose that the catalytic species of this reaction is the in situ generated InCl(2)(+). Further electrospray ionization high-resolution mass spectroscopy (ESI-HRMS) supported the existence of InCl(2)(+) in acetonitrile solution. This finding of InCl(2)(+) as the catalytic species suggests that other reactions catalyzed by In(III) species could also have cationic In(III) species as the real catalysts. DFT calculations revealed that the catalytic cycle of the cycloisomerization of 1,6-enynes catalyzed by InCl(3) starts from InCl(2)(+) coordination to the alkyne of the substrate, generating a vinyl cation. Then nonclassical cyclopropanation of the vinyl cation to the alkene part of the substrate gives a homoallylic cation, which undergoes a novel homoallylic cation rearrangement involving a [1,3]-carbon shift to give the more stable homoallylic cation 15. Finally InCl(2)(+) cation coordination assisted nonconjugated [1,2]-hydride shifts deliver the final nonconjugated diene products. The preference of generating nonconjugated dienes instead of conjugated dienes in the cycloisomerization reaction is mainly due to two reasons: coordination of the InCl(2)(+) to the alkene part in [1,2]-H shift transition states disfavors the conjugated [1,2]-H shifts that generate cations adjacent to the positively charged alkene, and coordination of InCl(2)(+) to the nonconjugated diene product is stronger than coordination to the conjugated diene, making nonconjugated [1,2]-H shift transition states lower in energy than conjugated [1,2]-H shift transition states, on the basis of the Hammond postulate. DFT calculations predicted that the conjugated [1,2]-H shifts could become favored if the electron-donating methyl substituent in the alkyne moiety of the 1,6-enyne is replaced by a H atom. This prediction of producing a conjugated diene has been verified experimentally. Rationalization about why type II rather than type I products were obtained using InCl(3) as the catalyst in the cycloisomerization of 1,6-enynes has also been investigated computationally.

Effects of substituents in cyclopentadienyltitanium trichlorides on electronic absorption and 47,49Ti NMR spectra and styrene polymerization activated by methylalumoxane

In the series of the methylated compounds (η 5-C 5H 5− n Me n )TiCl 3 ( n = 0–5) 1– 6, linear correlations of λ max of the absorption band and δ 49,47Ti chemical shift with the number of Me groups were found. It is due to the dependence of both the magnitudes on the HOMO–LUMO energy gap which is influenced by electron donating methyl substituents. The catalysts made by combining 1– 6 with MAO (molar ratio Al/Ti 500) showed only a gross dependence of decreasing activity with the number of methyl groups. For compounds (η 5-C 5Me 4R)TiCl 3 7– 14 and ( η 5-C 5H(1,2,3-)Me 3R)TiCl 3 15– 20 where R = alkyl, silyl or phenyl no correlation between λ max and δ was found. Limited DFT calculations were performed to assign HOMO/LUMO orbitals involved. Crystal structures of 16 and 20 were determined and some other inspected to prove the absence of steric hindrance. The poor correlation of the spectroscopic properties with the catalytic activity is not surprising because steric effects of cyclopentadienyl ligands at cationic polymerization centers are generally anticipated.

Photochemical synthesis and spectroscopic characteristic of the first vinylsilane carbonyl complexes of tungsten(0)

A series of new vinylsilane complexes of the type [W(CO) 5(η 2-H 2C CHSiR 3)] ( 1a– e) and trans-[W(CO) 4(η 2-H 2C CHSiR 3) 2] ( 2a– e) (R = Me, OMe, OCH 2CH 2OMe, and Cl) have been synthesized photochemically and characterized by IR and 1H, 13C and 29Si NMR spectroscopy. The values of the coordination shifts of the vinylic protons and carbons, Δ δ = δ (free vinylsilane) − δ (coordinated vinylsilane), strongly suggest that trimethylvinylsilane ( a) is coordinated more loosely to the tungsten atom in compounds of type 1 and 2 than other vinylsilanes ( b– e). The strongest dπ–π* interaction takes place between the carbonyltungsten moiety and trichlorovinylsilane. Analysis of 13C NMR data of vinylsilane compounds revealed that the electron-donating methyl substituents and the electron-withdrawing chlorine substituents at the silicon atom cause opposite deviations from the ideal symmetrical η 2-coordination of vinylsilane to the tungsten atom. The bis(vinylsilane) complexes 2a– e are shown to exist in several isomeric forms, whose solution dynamics were investigated by variable-temperature 1H NMR studies.

Substituent Effect on Fluorescence and Photoisomerization of 1-(9-Anthryl)-2-(4-Pyridyl)ethenes

The fluorescence and photoisomerization quantum yields of trans-1-(9-anthryl)-2-(4-pyridyl)ethene (t-4-APyE), 1-(10-methyl-9-anthryl)-2-(4-pyridyl)ethene (t-4-MeAPyE), and 1-(10-chloro-9-anthryl)-2-(4- pyridyl)ethene (t-4-ClAPyE) were measured in cyclohexane, acetonitrile, and methanol at room temperature.Polar solvents result in the drastic reduction of fluorescence quantum yield and increase of photoisomerization quantum yield for all three compounds. These results are probably due to the stabilization of intramolecular charge transfer (ICT) excited state in polar solvent. The higher contribution of ICT in the presence of more electron-donating methyl substituent, manifested by largest positive fluorescence solvatochromism, indicates that the pyridine ring acts as an electron acceptor. Protonation or methylation makes pyridine ring stronger electron acceptor and causes long-wavelength ground state charge transfer absorption band and complete quenching of fluorescence. The fluorescence from t-4-APyE derivatives can be switched off responding external stimuli viz. medium polarity, protonation, or methylation.

Kinetics and mechanism of the oxidation of several ketones by tris(1,10-phenanthroline)Fe(III) in aqueous acid medium

The kinetics of the oxidation of acetone, 2-butanone, 2,4-dimethyl-3-pentanone, 3-methyl-2-butanone, and 3-pentanone by tris(1,10-phenanthroline)Fe(III) (ferriin) were determined in aqueous solutions containing either sulphuric or perchloric acid in the presence or absence of air. The kinetics are consistent only with a mechanism involving oxidation of the enol tautomer by ferriin. The rate constants of enolization calculated from this kinetic analysis agree well with the literature values. Relative reactivity of the four enols from symmetrical ketones were found to be in the order: 2,4-dimethyl-3-pentanone > 3-pentanone > cyclohexanone > acetone. The rate of oxidation of the enol form of 2,4-dimethyl-3-pentanone is approximately 1000 fold larger than that of the enol form of acetone, indicating that electron-donating methyl substituents enhance the rate of electron transfer from the enol tautomer to ferriin.Kinetics of the oxidation carried out in air were generally the same as in its absence; the rates of oxidation were found to be slower by a factor of 2 in most cases. This suggests that the initially formed enol radical reacts with O2 rather than a second ferriin to give the oxidized product. At high [ferriin] in air, pseudo zero-order kinetics were observed initially as in its absence. However, above about 50% reduction of ferriin, the reaction appears to involve auto-catalysis and was not studied further.