Synthesis of Allylnickel Aryloxides and Arenethiolates: Study of Their Dynamic Isomerization and 1,3-Diene Polymerization Activity

A new family of allylnickel(I1) complexes, [Ni(η^3-+allyl)(µ-X)]_2 (X = ArO, ArS), have been synthesized by anion metathesis of the sodium or lithium salts of aryloxides or arenethiolates with [Ni(η^3-allyl)(µ-Br)]_2. The complexes are proposed to be dimeric and to consist of a mixture of cis and trans isomers. A dynamic process rapidly equilibrates the cis and trans isomers of the pentafluorophenoxide, 2,6-difluorophenoxide, and 3,5-bis(trifluoromethyl)phenoxide complexes on the ^1H NMR time scale. The 2,6-dimethylphenoxide, 2,6-diisopropylphenoxide, 2,4,6- tris(trifluoromethyl)phenoxide, and pentafluorothiophenoxide complexes are static at room temperature. A variable-temperature NMR study of the 3,5-bis(trifluoromethyl)phenoxide complex provided activation enthalpy and entropy values of 12.9 kcal/mol and -6.6 cal/ (K mol), respectively. Allyl rotation or cleavage of one of the µ-X bridges is proposed as the mechanism for the isomerization. The pentafluorophenoxide, 3,5-bis(trifluoromethyl)phenoxide, and 2,4,6-tris(trifluoromethy1)phenoxide complexes initiate the rapid polymerization of 1,3-cyclohexadiene and 1,3-butadiene to form high-molecular weight, 1,4-linked polymers

A Simple Method for Forming Hybrid Core-Shell Nanoparticles Suspended in Water

Core-shell hybrid nanoparticles, where the core is an inorganic nanoparticle and the shell an organic polymer, are prepared by a two-step method. Inorganic nanoparticles are first dispersed in water using poly(acrylic acid) (PAA) prepared by reversible addition fragmentation chain transfer (RAFT) polymerization as dispersant. Then, the resulting dispersion is engaged in a radical emulsion polymerization process whereby a hydrophobic organic monomer (styrene and butyl acrylate) is polymerized to form the shell of the hybrid nanoparticle. This method is extremely versatile, allowing the preparation of a variety of nanocomposites with metal oxides (alumina, rutile, anatase, barium titanate, zirconia, copper oxide), metals (Mo, Zn), and even inorganic nitrides (Si3N4)

18-Electron Ruthenium Phosphine Sulfonate Catalysts for Olefin Metathesis

The first instances of ruthenium alkylidene complexes based on chelating phosphine sulfonates are presented. Although these complexes are formally 18-electron complexes bearing <i>cis</i> phosphines and <i>cis</i> one-electron donors (sulfonates and chlorides), they are surprisingly active for ring-closing metathesis, cross-metathesis, and ring-opening metathesis polymerization, thus highlighting the unique potential of the sulfonate ligand in the design of a ruthenium metathesis catalyst

Polydopamine-Supported Lipid Bilayers

We report the formation of lipid membranes supported by a soft polymeric cushion of polydopamine. First, 20 nm thick polydopamine films were formed on mica substrates. Atomic force microscopy imaging indicated that these films were also soft with a surface roughness of 2 nm under hydrated conditions. A zwitterionic phospholipid bilayer was then deposited on the polydopamine cushion by fusion of dimyristoylphosphatidylcholine (DMPC) and dioleoylphosphatidylcholine (DOPC) vesicles. Polydopamine films preserved the lateral mobility of the phospholipids as shown by fluorescence microscopy recovery after photobleaching (FRAP) experiments. Diffusion coefficients of ~5.9 and 7.2 µm2 s−1 were respectively determined for DMPC and DOPC at room temperature, values which are characteristic of lipids in a free standing bilayer system

18-Electron Ruthenium Phosphine Sulfonate Catalysts for Olefin Metathesis

The first instances of ruthenium alkylidene complexes based on chelating phosphine sulfonates are presented. Although these complexes are formally 18-electron complexes bearing <i>cis</i> phosphines and <i>cis</i> one-electron donors (sulfonates and chlorides), they are surprisingly active for ring-closing metathesis, cross-metathesis, and ring-opening metathesis polymerization, thus highlighting the unique potential of the sulfonate ligand in the design of a ruthenium metathesis catalyst

Thermal conductivity improvement of adipic acid by the addition of AlO(OH) and AlO(OH)@SiO2 core-shell nanoparticles

Phase change materials (PCMs) can store and release a high amount of thermal energy at various operating temperatures. They can be integrated in both thermal management and thermal storage systems. However, the low thermal conductivity of PCMs is a challenge to tackle since it adversely affects the charge and discharge times in (the aforementioned applications). The aim of this study is to improve the thermal conductivity of adipic acid, which is a non-hazardous widely-available organic PCM capable of storing ∼250 J/g of thermal energy at 150 °C. To achieve this goal, boehmite nanoparticles (AlO(OH)) and core@shell nanoparticles boehmite@silica (AlO(OH)@SiO2) are dispersed in molten adipic acid at low concentration (i.e., 0.05. 0.1, and 0.2 wt%). The thermal conductivity measured using modified transient plane source technique (MTPS) shows that the presence of AlO(OH) and AlO(OH)@SiO2 core-shell nanoparticles leads to an increase of the thermal conductivity of adipic acid by 20 % and 14 %, respectively. This enhancement of thermal conductivity is achieved without reducing the enthalpy of the phase transition based on calorimetric measurements. As shown by thermogravimetric analysis, the mass loss of adipic acid is shifted toward higher temperature upon the addition of nanoparticles. Furthermore, the subcooling in nano-PCMs is decreased by 1.3 K compared to the one in pure adipic acid. These promising results bode well for the utilization of enhanced adipic acid as a PCM in thermal energy storage application

Thermodynamic Control in the Catalytic Insertion Polymerization of Norbornenes as Rationale for the Lack of Reactivity of Endo-Substituted Norbornenes

The catalytic insertion polymerization of substituted norbornenes (NBEs) leads to the formation of a family of polymers which combine extreme thermomechanical properties as well as unique optical and electronic properties. However, this reaction is marred by the lack of reactivity of endo substituted monomers. It has long been assumed that these monomers chelate the metallic catalyst, leading to species which are inactive in polymerization. Here we examine the polymerization of <i>cis</i>-5-norbornene-2,3-dicarboxylic anhydride (so-called carbic anhydride, CA) with a naked cationic Pd catalyst. Although <i>exo</i>-CA can be polymerized, the polymerization of <i>endo</i>-CA stops after a single insertion. Surprisingly, no chelate is formed between the catalyst and <i>endo</i>-CA. Using DFT calculation, it is shown that while the insertion of <i>exo</i>-NBEs is exergonic, the insertion of two <i>endo</i>-CA in a row is endergonic. In this latter case, the enthalpy gain corresponding to the insertion of a double bond is not sufficient to overcome the entropic penalty associated with ligand binding. Thus, the different reactivity between endo and exo NBEs is thermodynamic in nature, and it is not controlled by kinetic factors. Interestingly, thermodynamics is also the main factor controlling the stereochemistry of the chain. For CA polymerization, and even for unsubstituted NBE polymerization, the formation of <i>r</i> and <i>m</i> dyads is, respectively, exergonic and endergonic, resulting in a polymer which is essentially disyndiotactic. Thus, this study demonstrates that thermodynamics can control the chemo- and stereoselectivity of a catalytic polymerization

Probing the Regiochemistry of Acrylate Catalytic Insertion Polymerization via Cyclocopolymerization of Allyl Acrylate and Ethylene

When palladium phosphine sulfonate catalysts were used, ethylene and allyl acrylate were copolymerized. The copolymer structure was analyzed by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) and was found to contain both δ-valerolactone and γ-butyrolactones inserted within the chain. These cyclic structures were determined to be the outcome of 1,2 allyl insertions and 2,1 acrylate insertions except when the acrylate was cyclopolymerized: in this case, regiochemistry of the insertion was 1,2. This first example of cyclopolymerization with Pd phosphine sulfonate catalysts outlines the extraordinary versatility of this family of compounds and paves the way to new polyolefins containing complex repeat units built in