Preliminary Kinetic Investigations Research Articles

Synthesis, characterization and base hydrolysis of cobalt(III) complexes coordinated by substituted phenylthioether ligands

A synthetic route to the preparation of cobalt(III) complexes coordinated by bidentate phenylthioether ligands is described. Complexes of the type ((2-(X-phenylthio)ethylamine)-N,S)bis(ethylenediamine)cobalt(III) perchlorate, [(en)2Co(S(X-phenyl)CH2CH2NH2)](ClO4)3, where X = 4-methoxy (2a), 4-methyl (2b), 3-methyl (2c), nothing (2d), 3-methoxy (2e), 4-bromo (2f) and 3-bromo (2g) were prepared. The synthetic route involves reaction of trans-dichloridobis(ethylenediamine)cobalt(III) chloride with NH2CH2CH2SC6H4X to produce cis-[(en)2CoCl(NH2CH2CH2SC6H4X)]Cl2 (1a–g). Formation of the Co–S bond, completing the ring closure, is then accomplished by removing the coordinated chlorido by addition of AgClO4 in sulfolane. Complexes were characterized by 1H and 13C NMR spectroscopy, UV-Vis spectroscopy and elemental analysis. In addition, the solid-state structure (X-ray) of the monohydrate of 2d confirms the coordination mode of the ligand. Preliminary kinetic investigations in basic solution show that the Co–S bond is broken resulting in the formation of [(en)2Co(OH)(NH2CH2CH2SC6H4X)]2+. At 15.0°C, a Hammett Plot is linear (r2 = 0.981) with ρ = 2.24 ± 0.13.

Cobalt-catalyzed conformationally restricted alkylarylation enables divergent access to Csp3-rich N-heterocycles.

Due to the intrinsic spatial orientation and structural novelty, Csp3-rich N-heterocycles have been recognized as increasingly sought-after scaffolds as compared to the aromatic ring-based moieties, which have generated considerable recent attention in drug discovery. Hence, we disclose a modular cobalt-catalyzed conformationally restricted alkylarylation strategy for the divergent access to Csp3-rich N-hetero(spiro)cycles. Herein, multiple effects, including radical rebound and conformational restriction, play critical roles in the stabilization of the stereospecific alkyl-cobalt-aryl intermediate. Under simple and mild reaction conditions, cobalt catalyst combines a range of polyfunctionalized cyclenyl bromides and organozinc pivalates to rapidly and reliably forge the architecturally complex Csp3-rich N-hetero(spiro)cycles (>70 examples, >20 : 1 dr), including but not limited to the [5,5]-, [5,6]-, [5,7]-, [5,12]-bicycles, tri- and tetracyclic N-heterocycles, as well as various novel N-heterospirocyclic scaffolds in one synthetic operation. Preliminary kinetic investigations suggested that the final reductive elimination might be the rate-determining step. Moreover, ample substrate scope, good functional group compatibility and facile derivatizations to the pharmaceutically active molecules show the potential applications of this technology to organic syntheses and drug discoveries in medicinal chemistry.

Boric acid as a hydrogen bond donor with TBAB catalyze the cycloaddition of CO2 to internal bio-epoxides under solvent-free conditions

The cycloaddition of CO2 with epoxides is regarded as one of the most efficient methods to synthesize cyclic carbonate because of the 100% atom utilization. Therefore, it is necessary to develop efficient catalysts for the synthesis of cyclic carbonates. Hydrogen bond donors (HBDs) have been widely investigated due to their ability to activate epoxides and dramatically enhance the cycloaddition process. In this study, boric acid as a cheap HBD combined with TBAB as an effective co-catalysis system for cyclic carbonates synthesis through cycloaddition of CO2 to epoxidized soybean biodiesel. 92.3% yield of cyclic carbonates product was achieved at 100 °C with 10 bar pressure of CO2 for 10 h under solvent-free conditions. To further evaluate the catalyst activity, preliminary kinetic investigations were conducted and the results showed that activation energies (Ea) of cyclic carbonate formation were different (58.5 kJ/mol for TBAB, 44.22 kJ/mol for TBAB-boric acid). The results show that boric acid as HBD can efficiently improve the yield of cyclic carbonates. Thus, the developed catalyst system provides an efficient and economical approach for the industrial production of bio-based cyclic carbonates.

Heterogeneous Photodegradation for the Abatement of Recalcitrant COD in Synthetic Tanning Wastewater

Tannery wastewater is considered one of the most contaminated and problematic wastes since it consists of considerable amounts of organic and inorganic compounds. These contaminants result in high chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS). In this work, the heterogeneous photodegradation of recalcitrant COD in wastewater from the tanning industry was investigated, in particular the recalcitrant COD due to the presence of vegetable tannins extracted from mimosa and chestnut and from synthetic tannins based on 4,4′ dihydroxy phenyl sulfone. TiO2 Aeroxide P-25 was employed to study the photodegradation of model molecules in batch conditions under different parameters, namely initial concentration of COD, temperature, and catalyst dose. The maximum COD abatement reached was 60%. Additionally, preliminary kinetic investigation was conducted to derive the main kinetic parameters that can be useful for process scale-up. It was found to be independent of the temperature value but linearly dependent on both catalyst loading and the initial COD value.

Cationic indium complexes for the copolymerization of functionalized epoxides with cyclic ethers and lactide.

We report the first example of discrete cationic indium complexes for the copolymerization of epoxides, cyclic ethers, and lactide. [SalenIn][SbF6] in particular proved to be a highly active catalyst for the homo-polymerization of functionalized epoxides and their copolymerization with other cyclic ethers THF, oxetane and oxepane. This catalyst also proved competent in the polymerization of epichlorohydrin and lactide, forming copolymers with good activity and control. Investigation of the role of counteranions and solvent donors on the kinetics of polymerization of epoxides revealed a subtle effect of solvents on initiation rates.

C2v-symmetric metalloporphyrin promoted cycloaddition of epoxides with CO2 under atmospheric pressure

A series of C2v-symmetric diphenylporphyrin complexes containing a metal ion (Mg, Al, Mn, Fe, Co, Zn) have been synthesized and applied as catalysts for the solvent-free cycloaddition of epoxides and carbon dioxide under atmospheric pressure and mild temperature, in concert with phenyltrimethylammonium tribromide (PTAT) as a co-catalyst. The activity of these catalysts deeply relies on their coordinated metal species. [5,15-Diphenylporphyrin]manganese(III) chloride (DPP-MnCl) has been found to be the most effective catalyst under optimal reaction conditions. It's worth mentioning that the cycloaddition of phenyl glycidyl ether (GPE) and CO2 proceeded successfully by DPP-MnCl/PTAT even at 25 °C and atmospheric pressure. Moreover, preliminary kinetic investigations of this cycloaddition were carried out by using catalysts DPP-MnCl, DPP-CoCl and DPP-Zn, revealing that the (phenoxymethyl)ethylene carbonate (PEC) formation with the lowest activation energy is catalyzed by DPP-MnCl. Furthermore, a Lewis acid-base dual cooperative catalytic mechanism has been carefully proposed in light of the catalyst systems and the experimental results.

Highly Active Chiral Oxazolinyl Aminophenolate Magnesium Initiators for Isoselective Ring-Opening Polymerization of rac-Lactide: Dinuclearity Induced Enantiomorphic Site Control

The most important challenge in ring-opening polymerization of rac-lactide today is to obtain isotactic PLAs with high molecular weights. The goal of our work is to address this important challenge by developing novel catalysts that enable precise control over stereoselectivity and produce high molecular weight PLAs at the same time. Here we report some rare examples of isoselective magnesium complexes toward the ROP of rac-LA, which are supported by chiral oxazolinyl aminophenolate ligands. Preliminary kinetic investigations confirmed that isotactic PLAs could be achieved via an enantiomorphic site control mechanism by using these chiral magnesium complexes. A pair of racemic magnesium initiators proved to integrate hyperactivity (TOF up to 54 000 h–1 at 25 °C) with sufficient isoselectivity (Pm = 0.80) toward the ROP of rac-LA, leading to the formation of isotactic stereoblock PLA with high molecular weight (Mn = 461 kg mol–1) and a semicrystalline property (Tm = 164 °C). Detailed structural investigati...

Highly efficient fixation of carbon dioxide to cyclic carbonates with new multi-hydroxyl bis-(quaternary ammonium) ionic liquids as metal-free catalysts under mild conditions

A series of multi-hydroxyl bis-(quaternary ammonium) ionic liquids were prepared by a simple method, and used as bifunctional catalysts for the fixation of CO2 through the cycloaddition with epoxides in the absence of co-catalyst and solvent. All these ionic liquid compounds were proved to be efficient catalysts for the synthesis of cyclic carbonates from CO2 and epoxides in excellent yield and selectivity. Thanks to synergistic effects of hydroxyl groups and halogen anion, the cycloaddition reaction proceeded smoothly even at atmospheric pressure. The influences of the type of catalyst, catalyst loading, CO2 pressure, reaction time and temperature on the yields have been investigated in detail and the optimal conditions were screened as (120 °C, 2 MPa, 3 h, IL loading 0.25 mol%). Meanwhile, preliminary kinetic investigations were in progress by using four typical catalysts and clarified the activation energies (Ea) of cyclic carbonate formation (37.2 kJ/mol for IL1, 38.1 kJ/mol for IL3, 39.1 kJ/mol for IL5, and 58.9 kJ/mol for IL6), which agrees well with the catalytic activity. The catalyst system could be reused at least five consecutive times successfully. Notably, a high turnover frequency (TOF) value of (33,300 h−1) for IL1 was achieved with a high yield of 83.2% within 1 h via adjusting reaction variables. Finally, an inferred mechanism was presented according to the kinetic studies and experimental results.

Synthesis of cyclic carbonates from epoxides over bifunctional salen aluminum oligomers as a CO2-philic catalyst: Catalytic and kinetic investigation

The solvent-free cycloaddition reaction of carbon dioxide (CO2) with epoxides has been efficiently achieved with the enhanced catalytic activity employing a series of polyether-based salen aluminum oligomers as excellent bifunctional catalysts. These CO2-philic Al(salen) derivatives could act as an easy-to-handle and homogenous catalyst and might present the enhanced recycling performance compared to the polyether-free catalysts. The promising catalysis data such as the reduced apparent activation energy suggested the synergistic effect of the metal center (Lewis acid) and the halide anion (nuclephile) had significant impact on the catalytic performance. Finally, the preliminary kinetic investigations further demonstrated that the reaction was apparent first order with respect to the concentration of epoxide and catalyst and thus followed a possible monometallic synergistic catalytic mechanism, whereas the binary catalytic system was connected with the non-first-order kinetics.

Exploring the application potential of incompletely soluble organosolv lignin as a macromonomer for polyurethane synthesis

A new type of organosolv wheat straw lignin, so-called Biolignin™, was studied. It is obtained according to the biomass processing in water diluted organic acid media and is not completely soluble in conventional organic solvents traditionally applied for polyurethanes (PU) synthesis. The fractionation of the lignin by sequential extraction with dichloromethane, methanol and a mixture of both solvents was performed. The total yield of the separated soluble fractions was 40%. The separated fractions were characterized, and preliminary kinetic investigations were used to reveal the reactivity of fractions obtained towards 4,4′-methylene diphenylene diisocyanate (MDI) in dioxane media. PU films were synthesized by casting the three component systems: lignin fraction – polyethylene glycol with a molecular weight of 400gmol−1 – polymeric methyl diisocyanate prepolymerized in tetrahydrofurane solution at a constant NCO/OH ratio of 1.05. The content of lignin in PU compositions was varied in a range of 5–40%. The PU films were characterized in terms of crosslink density, tensile properties, glass transition temperature and thermal stability. The obtained results show that the isolated fractions of Biolignin™ act as a crosslinking macromonomer in the PU network. Depending on the lignin fraction type and its content in the composition, the tensile properties of PU films with a high elastic state at room temperature or the tensile properties of glassy cross-linked films were obtained. Evidence for the activity of lignin fractions as antioxidants of PU compositions and charcoal formation promoters in the case of the high temperature treatment of PU in air was obtained.

Illuminating CO2 reduction on frustrated Lewis pair surfaces: investigating the role of surface hydroxides and oxygen vacancies on nanocrystalline In2O(3-x)(OH)y.

Designing catalytic nanostructures that can thermochemically or photochemically convert gaseous carbon dioxide into carbon based fuels is a significant challenge which requires a keen understanding of the chemistry of reactants, intermediates and products on surfaces. In this context, it has recently been reported that the reverse water gas shift reaction (RWGS), whereby carbon dioxide is reduced to carbon monoxide and water, CO2 + H2 → CO + H2O, can be catalysed by hydroxylated indium oxide nanocrystals, denoted In2O(3-x)(OH)y, more readily in the light than in the dark. The surface hydroxide groups and oxygen vacancies on In2O(3-x)(OH)y were both shown to assist this reaction. While this advance provides a first step toward the rational design and optimization of a single-component gas-phase CO2 reduction catalyst for solar fuels generation, the precise role of the hydroxide groups and oxygen vacancies in facilitating the reaction on In2O(3-x)(OH)y nanocrystals has not been resolved. In the work reported herein, for the first time we present in situ spectroscopic and kinetic observations, complemented by density functional theory analysis, that together provide mechanistic information into the surface reaction chemistry responsible for the thermochemical and photochemical RWGS reaction. Specifically, we demonstrate photochemical CO2 reduction at a rate of 150 μmol gcat(-1) hour(-1), which is four times better than the reduction rate in the dark, and propose a reaction mechanism whereby a surface active site of In2O(3-x)(OH)y, composed of a Lewis base hydroxide adjacent to a Lewis acid indium, together with an oxygen vacancy, assists the adsorption and heterolytic dissociation of H2 that enables the adsorption and reaction of CO2 to form CO and H2O as products. This mechanism, which has its analogue in molecular frustrated Lewis pair (FLP) chemistry and catalysis of CO2 and H2, is supported by preliminary kinetic investigations. The results of this study emphasize the importance of engineering the surfaces of nanostructures to facilitate gas-phase thermochemical and photochemical carbon dioxide reduction reactions to energy rich fuels at technologically significant rates.

ChemInform Abstract: Copper‐Catalyzed Trifluoromethylation‐Initiated Radical Oxidative Annulation Toward Oxindoles.

A copper-catalyzed radical oxidative trifluoromethylation and arylation of electron-withdrawing alkenes has been developed, in which economical sodium trifluoromethanesulfinate is used as the CF3 source. A preliminary kinetic investigation indicated that the generation of CF3 radicals under the mild conditions might be a facile process.

Alternating copolymerization of CO2 and propylene oxide catalyzed by C2v-porphyrin cobalt: Selectivity control and a kinetic study

Some C2v (Cs)-porphyrin cobalt complexes have been devised, synthesized and utilized as efficient catalysts in combination with dimethylaminopyridine for the alternating copolymerization of propylene oxide and carbon dioxide. The C2v-catalyst [5,15-diphenylporphyrin]cobalt(III) chloride (1d) has demonstrated excellent reactivity and selectivity under optimized conditions. The axial counterions and the substituents of these metalloporphyrins exhibited distinct infection on the catalytic activity and selectivity. Synchronously, preliminary kinetic investigations of this reaction were achieved by using two catalyst systems illustrating the activation energies of copolymerization and coupling reaction, respectively. A competition mechanism between the polymerization and cycloaddition of propylene oxide and CO2 has been carefully proposed according to our experimental results.

Copper‐Catalyzed Trifluoromethylation‐Initiated Radical Oxidative Annulation toward Oxindoles

AbstractA copper‐catalyzed radical oxidative trifluoromethylation and arylation of electron‐withdrawing alkenes has been developed, in which economical sodium trifluoromethanesulfinate is used as the CF3 source. A preliminary kinetic investigation indicated that the generation of CF3 radicals under the mild conditions might be a facile process.

A highly active and site selective indium catalyst for lactide polymerization

Chiral indium salen complexes are highly active, isoselective catalysts for the ring opening polymerization of racemic lactide. The polymerizations are well controlled and polymers with high molecular weights and low molecular weight distributions are obtained. Preliminary kinetic investigations with the enantiopure complex confirm enantiomorphic site control as the dominant contributor to selectivity and formation of block copolymers.

Palladium‐Catalyzed Transformation of Renewable Oils into Diesel Components

AbstractA size‐controlled palladium nanoparticle catalyst prepared by adsorption of colloidal palladium nanoparticles on barium sulfate is efficient and highly selective in transforming vegetable oils into diesel‐like fuel. Preliminary kinetic investigations using model compounds indicated that decarboxylation of aliphatic esters on palladium in a hydrogen‐rich atmosphere showed a zero‐order rate. Hydrogen temperature‐programmed desorption measurements revealed that the high‐temperature desorption of hydrogen species might be the rate‐determining step.

Low temperature catalytic steam reforming of ethanol. 2. Preliminary kinetic investigation of Pt/CeO2 catalysts

Catalytic activity, selectivity and stability of a Pt/CeO2 (5wt% Pt) catalyst were investigated in the low temperature ethanol steam reforming reaction for hydrogen production.Experimental results showed that the catalyst is very active and selective, with negligible CO production and complete ethanol conversion already at 300°C. The main promoted reactions are ethanol decomposition, ethanol steam reforming and CO water gas shift, and a preliminary kinetic investigation showed that the apparent reaction orders are 0.5 and 0 for ethanol and steam respectively, with an apparent activation energy of 18kJmol−1 evaluated in the range 300–450°C.Kinetic evaluations and temperature programmed desorption experiments suggest a surface reaction mechanism involving the following step: (i) ethanol dissociative adsorption on catalyst surface to form acetaldehyde intermediate, (ii) decarbonylation to produce mainly H2, CH4 and CO, and (iii) WGS reaction of CO adsorbed on Pt sites to produce H2 and CO2.

The Wall Teichoic Acid Polymerase TagF Is Non-processive in Vitro and Amenable to Study Using Steady State Kinetic Analysis

Wall teichoic acids are a chemically diverse group of anionic polymers that constitute up to 50% of the Gram-positive cell wall. These polymers play a pivotal role in virulence and have been implicated in a diverse range of physiological functions. The TagF-like family of enzymes has been shown to be responsible for wall teichoic acid priming and polymerization events. Although many such enzymes are well validated therapeutic targets, a mechanistic understanding of this enzyme family has remained elusive. TagF is the prototypical teichoic acid polymerase and uses CDP-glycerol to catalyze synthesis of the linear (1,3)-linked poly(glycerol phosphate) teichoic acid in Bacillus subtilis 168. Here we used a synthetic soluble analog of the natural substrate of the enzyme, Lipid , to conduct the first detailed mechanistic investigation of teichoic acid polymerization. Through the use of a new high pressure liquid chromatography-based assay to monitor single glycerol phosphate incorporations into the Lipid analog, we conducted a detailed analysis of reaction product formation patterns and unequivocally showed TagF to be non-processive in vitro. Furthermore by monitoring the kinetics of polymerization, we showed that Lipid analog species varying in size have the same K(m) value of 2.6 microm and validated use of Bi Bi velocity expressions to model the TagF enzyme system. Initial rate analysis showed that TagF catalyzes a sequential Bi Bi mechanism where both substrates are added to the enzyme prior to product release consistent with a single displacement chemical mechanism.

Reaction and subsequent transformation of anionic acetylide–carbene complexes using the Ph3PAu+ fragment

The metallated Fischer-type carbene complexes (CO)(5)M=C(NMe(2))C[triple bond]CLi (M = Cr, W) react with Ph(3)PAuNO(3) to form the beta-substituted products (CO)(5)M=C(NMe(2))C[triple bond]CAuPPh(3). In solution these products isomerise by formal metal fragment exchange to furnish Ph(3)PAuC(=NMe(2))C[triple bond]CM(CO)(5). A preliminary kinetic investigation by means of (1)H-NMR spectroscopy indicates an unusual and complicated reaction mechanism. Model DFT calculations predict small energy differences between the products before and after the metal fragment exchange.

Synthesis and structural characterisation of novel platinum-based drug candidates with extended functionality by incorporation of bis(diphenylphosphino)ferrocene units as metal chelators

Among the metal-based anticancer drugs, cisplatin ( cis-diaminedichloroplatinum(II)) is the most widely used species in therapy. Despite its clinical success, cisplatin still suffers in generating resistance, as well as being highly toxic due to poor selectivity between healthy and sick cells. By molecular design it ought to be possible to generate new cis-platinum compounds with increased selectivity and improved cellular behaviour. In this paper, we report a synthetic pathway for construction of derivatives of 1,1′-bis(diphenylphosphino)-ferrocene, together with their corresponding cis-platinum compounds with the aim testing them for their interaction capacity with respect to various DNA models. We also report a synthetic route for a nucleoside-based cis-platinum compound containing a bidentate ferrocenylphosphine derivative connected through a succinamic-based linker to the 5-position of the heterocyclic moiety of uridine. Our preliminary kinetic investigation of 5-{ N-[1-[1′,2-bis(diphenylphosphino)ferrocenyl]ethyl]- N′-[prop-2-yn-3-yl]succinamide} uridinedichloroplatinum(II) showed that this compound reacted faster with the phosphorothioate containing oligonucleotides d(T 6p(S)T 6), with an observed first-order rate constant k obs=(1.4±0.1)×10 −4 s −1, compared with the G-N7 target in d(T 7GGT 7), for which the observed first-order rate constant is k obs=(7.2±0.5)×10 −4 s −1.