Pentamethyldiethylenetriamine Research Articles

Photo-Accelerated Synthesis of Oligo(triazole amide)s.

A photo-assisted process is explored for improving the synthesis of oligo(triazole amide)s, which are prepared by solid phase synthesis using a repeated cycle of two reactions: amine-carboxylic acid coupling and copper-catalyzed azide-alkyne cycloaddition (CuAAC). The improvement of the second reaction is investigated herein. A catalytic system involving Cu(II)Cl2, N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDETA)and a titanocene photoinitiator is explored for reducing the reaction time of CuAAC. This catalyst is first tested on a model reaction involving phenylacetylene and ethyl azidoacetate in DMSO. The kinetics of these model experiments are monitored by 1H NMR in the presence of different concentrations of the photoinitiator. It is found that 30 mol% of photoinitiator leads to quantitative reactions in only 8 min. These conditions are then applied to the solid phase synthesis of oligo(triazole amide)s, performed on a glycine-loaded Wang resin. The backbone of the oligomers is constructed using 6-heptynoic acid and 1-amino-11-azido-3,6,9-trioxaundecane as submonomers. Due to slow reagent diffusion, the CuAAC step required more time in the solid phase than in solution. Yet, one hour only is necessary to achieve quantitative CuAAC on the resin, which is twice as fast as previously-reported conditions. Using these optimized conditions, oligo(triazole amide)s of different length are prepared.

Sodium Alkyl(trimethylsilyl)amides: Substituent- and Solvent-dependent Solution Structures and Reactivities.

The preparation of sodium isopropyl(trimethylsilyl)amide (NaPTA), sodium (1-phenylethyl)(trimethylsilyl)amide (NaPETA), sodium tert-butyl(trimethylsilyl)amide (NaBTA), and isotopologues [15N]NaPTA and [15N]NaBTA are described. Solution structural studies using a combination of 29Si NMR spectroscopy, the Method of Continuous Variations, and density functional theory computations provided insights into aggregation and solvation in a range of solvents including toluene, N,N-dimethylethylamine, triethylamine, MTBE, THF, 1,2-dimethoxyethane (DME), diglyme, N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA). 12-crown-4, 15-crown-5, and 18-crown-6 revealed solvent- and substituent-dependent dimer-monomer mixtures with affiliated solvation numbers. Complexation of the three crown ethers documented both crown and substituent dependencies. Qualitative studies of reactivity showed a variety of reactions of NaPETA. Aminolysis of methyl benzoate with dialkylamines mediated by NaPTA afforded high yields of benzamides. Quantitative rate studies of aminolysis of methyl benzoate by NaPTA revealed a 47,000-fold range of rates. Detailed rate studies in toluene and THF showed dimer-based mechanisms. The role of primary- and secondary-shell solvation by THF is discussed, including nuances of methods used to separate the two contributions. PMDTA-solvated NaPTA monomer reacts as a monomer whereas bis-diglyme solvated monomer reacts as a dimer. Rate studies exploring the structure-reactivity correlations of the three crown ethers show mono- and bis-crown-based pathways in which 15-crown-5─the crown ether often said to be of choice for sodium─was decidedly inferior as an accelerant.

Practical cuprous catalyzed anti-Markovnikov difluoroacetamidation of α-(trifluoromethyl)styrenes

An anti-Markovnikov difluoroacetamidation of α-(trifluoromethyl)styrenes was successfully performed, yielding 2,2,5,5,5-pentafluoropentanamides in good yields. This reaction was catalyzed by CuBr in the presence of pentamethyldiethylenetriamine (PMDETA) in MeCN, conducted under a nitrogen atmosphere. To assess the influence of substituent groups on the aromatic ring, two series of substrates were tested within the developed catalytic system. Additionally, scale-up applications and mechanistic studies were carried out.

Copper and ZnO Dual-Catalyzed Photo-Assisted Depolymerization of Poly(Methyl Methacrylate) without Deoxygenation

Despite significant advancements in thermal and photothermal depolymerizations, the success of these techniques relies on tedious deoxygenation procedures. Herein, we report the development of the depolymerization technique efficient without prior deoxygenation, which was enabled by copper/ligand complexes and the inclusion (0.25 wt% relative to solvent) of zinc oxide (ZnO) nanocrystals activated by UV light. This approach was tested for poly(methyl methacrylate) (PMMA) prepared by atom transfer radical polymerization (ATRP); the effects of solvent polarity and the activity of ligands were investigated. Unexpectedly, a low-activity Cu-complex with 2,2‘-bipyridine ligand, in combination with a low-polarity solvent, 1,2,4-trichlorobenzene, enabled relatively high depolymerization yields in less than 1 h at 150 °C. Higher activity ATRP complexes with tris(2-pyridylmethyl)amine (TPMA) and N,N,N‘,N‘‘,N‘‘-pentamethyldiethylenetriamine (PMDETA) ligands, were less efficient, which was associated with their thermal decomposition and/or the excessive formation of radicals and premature termination of the chain ends. The presented facile approach was designed to be used even in partially aerated reactors, opening new avenues for efficient depolymerization.

Design of blend-amine solid adsorbents for CO2 capture: Enhances adsorption- equilibrium cycle strategies and mechanism

Blend amine-functionalized absorbents show great potential in the field of amine scrubbing for CO2, as they harness the absorption benefits of various monomer amines in combination. However, there is a lack of research on the application of the emerging concept of blend amines to solid amine adsorbents. Building upon this foundation, this study firstly incorporated Aminoethylethanolamine (AEEA) into Polyethyleneimine (PEI) of varying molecular weights to create a range of new binary solid amine adsorbents. The research then compared the adsorption performance differences between these binary adsorbents and pure PEI adsorbents. The enhanced dispersion of PEI by AEEA results in an increase in the effective active sites available. The amine efficiency and CO2 adsorption capacity of the AEEA-PEI blend amine system were maximally increased by 92.0% and 84.6%, respectively, compared to the pure PEI system. Furthermore, through DFT calculations, it is clear that the presence of AEEA lowers the overall activation energy of the reaction due to its superior proton acceptance compared to PEI. However, the AEEA-PEI system exhibits weak cycling stability attributed to the limited regeneration capacity of AEEA. Fortunately, this issue can be successfully addressed by introducing a strong base, N,N,N',N'',N''-pentamethyl diethylenetriamine (PMDETA). The CO2 adsorption cycling stability for AEEA-PEI-PMDETA system maximally improved by up to 17.1% compared to the AEEA-PEI system. The mechanism behind the effectively suppression of cycling losses by PMDETA was further elucidated through DFT calculations. Consequently, the novel ternary amine solid adsorbent introduced in this study, aimed at enhancing the CO2 adsorption performance of monomer amine solid adsorbents, offers a fresh strategy for fundamental theoretical investigations into CO2 adsorption.

Computational study on CO2 absorption mechanism and structure–activity relationship of biphasic solvent

The biphasic solvents are conducive to improving the efficiency of CO2 capture and reducing the energy consumption caused by regeneration. This study explored their reaction process at the molecular level based on density functional theory (DFT): selection of diamines such as active amines with distinct amino groups, 1,4-butanediamine (BDA) and N-(2-aminoethyl)ethanolamine (AEEA), and with typical phase separation promoters, 2-(diethylamino)ethanolamine (DEEA), and N,N,N′,N′,N′′-pentamethyldiethylenetriamine (PMDETA). This study systematically explores the potential reaction paths in CO2 capture to quantitatively assesse the structure–activity relationships among different amines in different stages of absorption, the influence of reaction sequence on reaction rates, and further elucidates the characteristics of product formation and its impact on the phase separation process. The results indicated that the zwitterion mechanism is widely applicable and remains the dominant explanation for the biphasic solvent CO2 capture mechanism. The intramolecular proton transfer reaction is the key to influencing the absorption rate of CO2, but in the case of interproton transfer, the rate-determining step needs to be judged in conjunction with the type of amino groups on it. And the amine groups on AEEA react with CO2 in different orders, forming distinct zwitterions that have similar activity in later intramolecular proton transfers. Under the zwitterion mechanism, primary amino groups exhibit stronger proton affinity than secondary ones. In solvents approaching saturation stage, DEEA reacts with AEEA and CO2 earlier than PMDETA. This study reveals the reaction mechanism of biphasic solvents and the key paths in different phases, providing insights for developing new solvents.

Effects of Structurally Different Tertiary Amines on the Properties of Quaternized Anionic Exchange Membranes Potentially Applicable for Water Electrolysis.

In this work, two structurally different monoamines (trimethylamine [TMA] and N-methylpiperidine [N-MPip]) are used for the amination of a g-VBC-15 graft copolymer, obtained by the functionalization of a mechanically robust, commercially available styrene-butadiene block copolymer (SB) with vinylbenzyl chloride (VBC) via solution free-radical polymerization. Results demonstrate that g-VBC-15-based membranes quaternized with TMA have superior electrochemical performance than N-MPip counterparts; while, the mechanical properties are good and only slightly inferior to those of N-MPip. Therefore, TMA is the selected monoamine to be alternatively mixed with two polyamines (tetramethyl-1,3-propanediamine [TMPDA] and N,N,N',N'',N''-pentamethyldiethylenetriamine [PMDETA]) into different proportions, in order to modulate the average functionality of the amination mixture in terms of number of amine functional groups available for the quaternization reaction of the membranes. g-VBC-15-based membranes derived therefrom are extensively characterized to assess their thermal, mechanical, and ex situ electrochemical properties. Results indicate that membranes quaternized with a TMA/PMDETA mixture (90:10 in mole) display the highest conductivity among all the investigated membranes aminated with polyamine-based mixtures. Moreover, they have comparable mechanical and electrochemical properties to those quaternized with TMA, while exhibiting a reduced water uptake.

Solubilizer reconstructs the influences of the hydrogen-bond network of nonaqueous biphasic solvent on the absorption, phase splitting and desorption

Nonaqueous biphasic solvent has remarkable energy-saving potential. The weak force between N, N, N′, N″, N‴-pentamethyldiethylenetriamine (PMDETA) and Dimethyl sulfoxide (DMSO) contributes to facilitating the separation between DMSO and PMDETA, thereby enabling efficient liquid–liquid phase separation. Nevertheless, the weak interactions of PMDETA with other solvent molecules pose considerable challenges in the formulation of fresh homogeneous phase solutions. This study proposes a strategy to enhance PMDETA dissolution by introducing a solubilizer into a hybrid phase splitter, thereby increasing the concentration of PMDETA in the solvent. With the addition of a small quantity of solubilizer, the absorption, regeneration, and phase separation performance among the absorbents are comparable. The phase separation performance is influenced by the number of hydrogen bonds formed by the solubilizer, and the concentration of solubilizer in the lower phase is dependent on its hydrophobicity. Characterization using 13C NMR and FT-IR indicates that CO2 products primarily exist in the form of MEACOO−/MEAH+. Through DFT and molecular dynamics simulations, the impact of the solvent environment surrounding Ethanolamine (MEA) on the MEA+COO− deprotonation reaction is analyzed. While PMDETA offers a more favorable proton acceptance energy compared to MEA, the limited opportunities for PMDETA to come into contact with MEA molecules may be the primary hindrance to its participation in the reaction. Significantly lower corrosivity and regeneration energy requirements for non-aqueous biphasic solvents compared to 30 wt% MEA make them ideal candidates for energy-efficient, low-corrosivity CO2 capture.

Effect of alcohols on CO2 absorption, phase splitting, and desorption behaviors of biphasic anhydrous system: The primary amine-tertiary amine of DGA-PMDETA

Chemical absorption with organic amine solution is the most mature technology for CO2 capture. Some biphasic anhydrous absorbents show potential in reducing regeneration energy consumption, but high viscosity of the CO2 rich phase hinders its practical application. Alcohols are commonly employed as dilutes to reduce viscosity reducers, while its effect on CO2 absorption and phase splitting behaviors are still unclear. In this study, the effects of alcohols on CO2 absorption and phase-splitting of biphasic anhydrous 2-(2-Aminoethoxy)ethanol (DGA) -N,N,N′,N″,N″-pentamethyl diethylenetriamine (PMDETA) -alcohol systems are investigates. Adding alcohol reduces the viscosity of the CO2-rich phase, enhances desorption rate, and decreases the phase splitting time. The rich phase entrainment stage and the rich phase thickening stage, can be distinguished along with during CO2 absorption. The majority DGA reacts with CO2 in the rich phase since the phase splitting begins. This work may provide some basis for further biphasic absorbent design and regulation.

Enhancing CO2 capture of an aminoethylethanolamine‐based non‐aqueous absorbent by using tertiary amine as a proton‐transfer mediator: From performance to mechanism

Non-aqueous absorbents (NAAs) have attracted increasing attention for CO2 capture because of their great energy-saving potential. Primary diamines which can provide high CO2 absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability. In this study, a promising strategy that using tertiary amines (TAs) as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine (AEEA, diamine)/dimethyl sulfoxide (DMSO) (A/D) NAA. Surprisingly, some employed TAs such as N,N-diethylaminoethanol (DEEA), N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA), 3-dimethylamino-1-propanol (3DMA1P), and N,N-dimethylethanolamine (DMEA) enhanced not only the regenerability of the A/D NAA but also the CO2 absorption performance. Specifically, the CO2 absorption loading and cyclic loading were increased by about 12.7% and 15.5%–22.7%, respectively. The TA-enhanced CO2 capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations. During CO2 absorption, the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species (AEEACOO−) to store CO2, thus enhancing CO2 absorption. For CO2 desorption, the TA first provided protons directly to AEEACOO− as a proton donor; moreover, it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO−. Consequently, the presence of TA made it easier for AEEACOO− to obtain protons to decompose, resulting in enhanced CO2 desorption. In a word, introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO2 absorption performance and the regenerability, which was an efficient way to “kill two birds with one stone”.

Exploration of Solid-State vs Solution-State Structure in Contact Ion Pair Systems: Synthesis, Characterization, and Solution-State Dynamics of Zinc Diphenyl Phosphate, [Zn{O2P(OPh)2}2], Donor-Base-Supported Complexes.

A family of zinc phosphate complexes supported by nitrogen donor-base ligands have been synthesized, and their molecular structures were identified in both the solid (X-ray crystallography) and solution state (DOSY NMR spectroscopy). [Zn{O2P(OPh)2}2]∞ (1), formed from the reaction of Zn[N(SiMe3)2]2 with HO(O)P(OPh)2 coordinates to donor-base ligands, i.e., pyridine (Py), 4-methylpyridine (4-MePy), 2,2-bipyridine (bipy), tetramethylethylenediamine (TMEDA), pentamethyldiethylenetriamine (PMDETA), and 1,3,5-trimethyl-1,3,5-triazacyclohexane (Me3-TAC), to produce polymeric 1D structures, [(Py)2Zn{O2P(OPh)2}2]∞ (2) and [(4-MePy)2Zn{O2P(OPh)2}2]∞ (3), the bimetalic systems, [(Bipy)Zn{O2P(OPh)2}2]2 (4), [(TMEDA)Zn{O2P(OPh)2}2]2 (5), and [(Me3-TAC)Zn{O2P(OPh)2}2]2 (7), as well as a mono-nuclear zinc bis-diphenylphosphate complex, [(PMDETA)Zn{O2P(OPh)2}2] (6). 1H NMR DOSY has been used to calculate averaged molecular weights of the species. Studies are consistent with the disassembly of polymeric 3 into the bimetallic species [(Me-Py)2·Zn2{O2P(OPh)2}4], where the Me-Py ligand is in rapid exchange with free Me-Py in solution. Further 1H DOSY NMR studies of 4 and 5 reveal that dissolution of the complex results in a monomer dimer equilibrium, i.e., [(Bipy)Zn{O2P(OPh)2}2]2 ⇆ 2[(Bipy)Zn{O2P(OPh)2}2] and [(TMEDA)Zn{O2P(OPh)2}2]2 ⇆ 2[(TMEDA)Zn{O2P(OPh)2}2], respectively, in which the equilibria lie toward formation of the monomer. As part of our studies, variable temperature 1H DOSY experiments (223 to 313 K) were performed upon 5 in d8-tol, which allowed us to approximate the enthalpy [ΔH = -43.2 kJ mol-1 (±3.79)], entropy [ΔS = 109 J mol-1 K-1 (±13.9)], and approximate Gibbs free energy [ΔG = 75.6 kJ mol-1 (±5.62) at 293 K)] of monomer-dimer equilibria. While complex 6 is shown to maintain its monomeric solid-state structure, 1H DOSY experiments of 7 at 298 K reveal two separate normalized diffusion coefficients consistent with the presence of the bimetallic species [(TAC)2-xZn2{O2P(OPh)2}4], (x = 1 or 0) and free TAC ligand.

Volumetric properties of ternary mixtures of N, N, N', N'-tetramethylethylenediamine/pentamethyldiethylene triamine + acetonitrile + H2O from (288.15 to 323.15) K

The densities of two ternary mixtures, N, N, N', N'-tetramethylethylenediamine (TMEDA) + acetonitrile (ACN) + H2O and pentamethyldiethylenetriamine (PMDETA) + ACN + H2O, and the corresponding binary mixtures TMEDA + ACN, PMDETA + ACN, TMEDA + H2O, PMDETA + H2O and ACN + H2O, were measured at different temperatures and 0.1 MPa. The studied temperatures are T = (288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K. From the experimental data, excess molar volume (VmE), apparent molar volume (Vφ), partial molar volume (V¯) and excess partial molar volume (V¯E), were calculated. Furthermore, the VmE values for the binary mixtures were fitted to the Redlich-Kister polynomial equation. For the ternary systems, the VmE values were fitted to Nagata-Tamura equation and the fitting results were compared with those by Cibulka, Singh and Redlich-Kister equations. All the results were analyzed from the intermolecular interactions and molecular structure.

Visible light‐induced metal‐free atom transfer radical (co)polymerization of maleimides using commercial organocatalysts

AbstractMetal‐free photocontrolled atom transfer radical polymerization (ATRP) has recently received increasing attention due to its ability to avoid heavy metal contamination. However, the polymerization of 1,2‐disubstituted olefin monomers by photocontrolled ATRP has rarely been reported. In this contribution, visible light‐induced metal free atom transfer radical (co)polymerization of maleimides (MI) by using several commercial organocatalysts was investigated in both batch and continuous flow processes. It was shown that the combination of the commercial dye eosin Y (EY) and cocatalyst N,N′,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) can mediate controlled and selective ATRP of various N‐alkyl substituted MI monomers. The effect of polymerization time, initiators and catalysts are discussed. The results revealed that molecular weight (Mn) of the obtained polymers was increased by increase in monomers conversion with their narrow polydispersities (PDI ≤1.2). MIs alternating copolymerization with styrenes (St) under irradiation of visible light was also done which generated the polymaleimide resins with ultrahigh glass transition temperatures (Tg up to 259°C). Moreover, continuous flow process was also used for the co‐polymerization of MI and St by using a tubular reactor to get polymaleimide resins. Thus, this work provides an effective strategy to obtain copolymers of MI monomers and styrenes via both batch and continuous flow processes, enabling technical advantages for potential large‐scale applications.

N-substituted methyl ethylenediamine derivatives as corrosion inhibitors for carbon steel in 1 M hydrochloride acid

Three N-substituted methyl ethylenediamine derivatives, tetramethylethylenediamine (TDA), pentamethyldiethylenetriamine (PTA), and hexamethyltriethylenetetramine (HTA) were prepared for the corrosion inhibition of 20# steel in 1 M HCl solution. Their corrosion inhibition properties were investigated using weight loss, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) measurements, and surface analysis techniques. Quantum chemical calculations and molecular dynamics (MD) simulations were applied to analyze the molecular structure-activity relationship of corrosion inhibitors. The results indicated that all three methyl ethylenediamine derivatives exhibited excellent inhibition properties. The order of inhibition efficiency of these inhibitors was TDA < PTA < HTA. Furthermore, all three inhibitors act as mixed-type inhibitors and mainly inhibited the cathodic reaction. The adsorption mechanism of corrosion inhibitors follows the Langmuir isotherm and proceeds by physisorption and chemisorption. The results of quantum chemical calculations and MD simulations effectively support the experimental results. The excellent corrosion inhibition property is attributed to the interaction between tertiary amine groups and Fe, which effectively inhibits corrosion.

Synthesis and Characterization of Novel Nano Six-arms of (polylactide-dipentaerythritol)-block-N-hydroxyethyl Acrylamide and N,N-dimethylamino Ethyl Methacrylate Biocopolymers by Atom Transfer Radical Polymerization

Novel block biocopolymers were made by copolymerizing the prepared polylactide-dipenta-erythritol macromonomer with two different monomers, N-hydroxyethyl acrylamide (HEAA) and N,N-dimethylamino ethyl methacrylate (DMAEMA), with an activator generated by atom transfer radical polymerization (ATRP), to have a different duplicating unit of 10, 25, 50, and 100. ATRP employs a copper(I) bromide (CuBr) catalyst system with N, N, N′, N′′, N′′-pentamethyl diethylenetriamine (PMDETA). Different spectroscopic and analytical methods used for characterization of the prepared biocopolymers, such as FT-IR, 1H NMR, 13C NMR, and GPC, showed that they had narrow dispersity with controllable molecular weight and were accompanied by nanostructures as examined by SEM technique on all biocopolymers, confirming the correctness of the expected structures of biocopolymers. The shape and size of the produced polymeric nanoparticles were determined using a scanning electron microscope (SEM), and they were developed using the Image-J application.

Energy-efficient carbon dioxide capture using a novel low-viscous secondary amine-based nonaqueous biphasic solvent: Performance, mechanism, and thermodynamics

Biphasic solvents have been widely studied for CO2 capture due to their remarkable energy-saving potentiality. However, most existing biphasic solvents suffer from the high viscosity of their CO2-rich phase. This study proposed a novel low-viscous secondary amine-based nonaqueous biphasic solvent for CO2 capture. With dimethyl sulfoxide (DMSO) as the organic diluent and pentamethyldiethylenetriamine (PMDETA) as the phase splitting agent, the secondary amine of 2-methyl-ethynolamine (MAE) was proved to be the optimal candidate for preparing the biphasic solvent. The MAE/DMSO/PMDETA (M/D/P) biphasic solvent could realize a high CO2 loading of 0.84 mol mol−1 and the viscosity of its CO2-rich phase was only 8.87 mPa s, which was significantly lower than that of most reported biphasic solvents. The reaction mechanism analysis revealed that M/D/P absorbed CO2 to form products of protonated amines, carbamate, and carbamic acid species. Since the products were polar and showed a stronger affinity to polar DMSO, while less polar PMDETA was isolated, thereby resulting in a phase change. Thermodynamics analysis showed that the M/D/P biphasic solvent could sharply cut down the sensible heat and latent heat during CO2 desorption. Eventually, the total regeneration energy penalty of M/D/P was significantly reduced by 46.3% compared with the benchmark aqueous MEA solution.

Structural, molecular and thermal properties of cardanol based monomers and polymers synthesized via atom transfer radical polymerization (ATRP)

Cardanol, a byproduct of the cashew processing industry, has been widely studied feeedstock for sustainable monomers and polymers. In this article, the Atom Transfer Radical Polymerization (ATRP) of three radically polymerizable monomers, namely, cardanyl acrylate (CA), hydrogenated cardanyl acrylate (PA) and hydrogenated cardanyl methacrylate (PMA), was studied. The monomers as well as the polymers were structurally characterized and studied by differential scanning calorimetry (DSC) to understad their thermal behavior. The PA monomer showed melting (Tm) at 35 °C and crsytallization (Tc) at −3.27 °C. The synthesized polymer shows Tm of 16.5 °C and the Tc increased to 7.2 °C. In PMA monomer, the Tm was observed at 15.21 °C and Tc at −11 °C and the correponding values for the polymer decreasing to 1 °C and −18 °C, respectively. The coressponding transitions of CA monomer and its polymer were broad and less defined. The homopoymerization of CA and PMA yielded good conversions but the PA polymer yield was low under identical conditions, probably due to the higher monomer crystallinity of PA. The effect of different ATRP ligands, viz, pentamethyldiethylenetriamine (PMDETA) and bipyridine (dNbpy), on the conversion, molecular weight and polydispersity was also investigated.

Polyethylene glycol-based RAFT agent cum ATRP macroinitiator initiated block copolymerization of methyl methacrylate

PMMA-b-PEG-b-PMMA block copolymer has been synthesized by the activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) of methyl methacrylate (MMA) using modified polyethylene glycol (PEG) as initiator. PEG is chemically modified by CS2 followed by an esterification to incorporate initiating sites for ATRP as well as for RAFT polymerization. The prepared macroinitiator has been characterized by FT-IR and NMR analyses for its structural validation. FT-IR and NMR analyses confirmed the successful synthesis of the macro initiator. This macro initiator has been used to prepare ABA type triblock copolymer with MMA via ARGET-ATRP. The polymerization reaction is carried out using cupric bromide (CuBr2) as catalyst in combination with N,N,N′,N″,N″-pentamethyl diethylenetriamine (PMDETA) as ligand in N, N dimethyl formamide (DMF) at 70C. Ascorbic acid is used as reducing agent. The conversion of the monomer was calculated gravimetrically. The successful preparation of the block copolymer is confirmed by FT-IR, 1H NMR and 13C NMR analyses. The MALDI-TOF mass analysis of the block copolymers also confirm the presence of monomer MMA, dithionate and PEG parts in the block copolymer. The purified block copolymer is analyzed by TGA, and SEM analyses. TGA analysis shows that the prepared block copolymer has better (Tmax = 366C) thermal stability than the PMMA (Tmax = 349C) homopolymer.

Ketone Enolization with Sodium Hexamethyldisilazide: Solvent- and Substrate-Dependent E-Z Selectivity and Affiliated Mechanisms.

Ketone enolization by sodium hexamethyldisilazide (NaHMDS) shows a marked solvent and substrate dependence. Enolization of 2-methyl-3-pentanone reveals E-Z selectivities in Et3N/toluene (20:1), methyl-t-butyl ether (MTBE, 10:1), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA)/toluene (8:1), TMEDA/toluene (4:1), diglyme (1:1), DME (1:22), and tetrahydrofuran (THF) (1:90). Control experiments show slow or nonexistent stereochemical equilibration in all solvents except THF. Enolate trapping with Me3SiCl/Et3N requires warming to -40 °C whereas Me3SiOTf reacts within seconds. In situ enolate trapping at -78 °C using preformed NaHMDS/Me3SiCl mixtures is effective in Et3N/toluene yet fails in THF by forming (Me3Si)3N. Rate studies show enolization via mono- and disolvated dimers in Et3N/toluene, disolvated dimers in TMEDA, trisolvated monomers in THF/toluene, and free ions with PMDTA. Density functional theory computations explore the selectivities via the E- and Z-based transition structures. Failures of theory-experiment correlations of ionic fragments were considerable even when isodesmic comparisons could have canceled electron correlation errors. Swapping 2-methyl-3-pentanone with a close isostere, 2-methylcyclohexanone, causes a fundamental change in the mechanism to a trisolvated-monomer-based enolization in THF.

Deaggregation of Zinc Dihydride by Lewis Acids Including Carbon Dioxide in the Presence of Nitrogen Donors.

Thermally sensitive polymeric zinc dihydride [ZnH2]n can conveniently be prepared by the reaction of ZnEt2 with [AlH3(NEt3)]. When reacted with CO2 (1 bar) in the presence of chelating N-donor ligands Ln = N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethyl-1,3-propanediamine (TMPDA), N,N,N',N″,N''-pentamethyldiethylenetriamine (PMDTA), and 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (Me4TACD), insertion into the Zn-H bond readily occurred. Depending on the denticity n, formates [(Ln)Zn(OCHO)2] were isolated and structurally characterized, either as a molecule (Ln = TMEDA, TMPDA, PMDTA) or a charge-separated ion pair [(Ln)Zn(OCHO)][OCHO] (Ln = Me4TACD). The reaction of [ZnH2]n with the mild Lewis acid BPh3 in the presence of chelating N-donor ligands Ln gave a series of hydridotriphenylborates, either as a contact ion pair [(L2)Zn(H)(HBPh3)] (L2 = TMEDA, TMPDA) or a separated ion pair [(Ln)Zn(H)][HBPh3] (Ln = PMDTA, Me4TACD). In the crystal, the contact ion pair [(TMEDA)Zn(H)(HBPh3)] showed a bent Zn-H-B bridge indicative of a delocalized Zn-H-B interaction. In contrast, a linear Zn-H-B bridge for [(TMPDA)Zn(H)(HBPh3)] was observed, suggesting a contact ion pair. In THF solution, both complexes show an exchange with free BPh3 as well as [HBPh3]-. DFT calculations suggest the presence of [HBPh3]- anion with a highly polarized B-H bond that interacts with the Lewis acidic zinc hydride cation [(L2)Zn(H)]+. The hydridotriphenylborates [(Ln)Zn(H)(HBPh3)] underwent CO2 insertion to give (formato)zinc (formoxy)triphenylborate complexes [(Ln)Zn(OCHO)][(OCHO)BPh3] (Ln = TMPDA, PMDTA, Me4TACD). For Ln = TMEDA, a dinuclear complex [(Ln)2Zn2(μ-OCHO)3][(OCHO)BPh3] was isolated. Hydridotriphenylborates [(Ln)Zn(H)(HBPh3)] catalyzed the hydrosilylation of CO2 (1 bar) by nBuMe2SiH in THF at 70 °C to give formoxysilane and (methoxy)silane.