Zirconium and Hafnium Permethylpentalene Compounds

A selection of new η⁸-permethylpentalene zirconium and hafnium complexes are reported. The first d-block metal bis­(permethylpentalene) sandwich complexes, (Pn*₂M ; Pn* = C₈Me₆ ; M = Zr, Hf) have been synthesized and structurally characterized. The bis-allyl species Pn*M­(C₃H₅)₂ (M = Zr, Hf) have been synthesized; these complexes are fluxional in solution and react with CO₂ to give the double-insertion product Pn*M­(κ²-O₂CCH₂CHCH₂)₂ (M = Zr, Hf). We also report monometallic, bimetallic, and polymeric σ-bonded alkyl derivatives such as (Pn*Zr)₂(μ-CH₂)­(μ-Me)₂, [Pn*Hf­(CH₂Ph)₃]­[Li­(1,4-dioxane)₄], and [Pn*ZrPh­(μ-Ph)₂­Li­(μ-1,4-dioxane)]_<i>n</i>

Zirconium and Hafnium Permethylpentalene Compounds

A selection of new η⁸-permethylpentalene zirconium and hafnium complexes are reported. The first d-block metal bis­(permethylpentalene) sandwich complexes, (Pn*₂M ; Pn* = C₈Me₆ ; M = Zr, Hf) have been synthesized and structurally characterized. The bis-allyl species Pn*M­(C₃H₅)₂ (M = Zr, Hf) have been synthesized; these complexes are fluxional in solution and react with CO₂ to give the double-insertion product Pn*M­(κ²-O₂CCH₂CHCH₂)₂ (M = Zr, Hf). We also report monometallic, bimetallic, and polymeric σ-bonded alkyl derivatives such as (Pn*Zr)₂(μ-CH₂)­(μ-Me)₂, [Pn*Hf­(CH₂Ph)₃]­[Li­(1,4-dioxane)₄], and [Pn*ZrPh­(μ-Ph)₂­Li­(μ-1,4-dioxane)]_<i>n</i>

Del mito al olvido : el Conde de Villalobos y la gimnástica española (1841-1867)

En este trabajo se presenta la singular figura del Conde de Villalobos, Francisco Aguilera Becerril y su significativa aportación a la educación física española de mediados del siglo XIX. La contribución de este filantrópico gimnasiarca se desarrolla a partir del legado de sus actuaciones prácticas e intelectuales realizadas en Madrid. Asimismo tratamos de demostrar la trascendencia de su influencia en el desarrollo de la gimnástica civil, médica, higiénica, pedagógica y militar en España. La construcción del relato se sustenta por una metodología que elabora una exégesis de los textos de la época y el apoyo historiográfico de las últimas aportaciones en torno al período de estudio. Concluimos manifestando que la figura del Conde de Villalobos aporta una representación mitológica que ha servido para encarnar las reivindicaciones del apostolado de la educación física en EspañaThis article presents the unique figure of the Count of Villalobos, Francisco Aguilera Becerril and his significant contribution to Spanish physical education in the mid-nineteenth century. The contribution of this philanthropic gymnasiarch came from the legacy of his practical and intellectual activities in Madrid. The article also aims to show the transcendence of his influence in the development of civil, medical, hygienic, pedagogical and military gymnastics in Spain. The construction of the story is based on a methodology which produces an interpretation of the texts of the period and the historiographical support of the latest contributions dealing with the period of study. The conclusion shows that the figure of the Count of Villalobos has provided a mythological representation which has served to embody the demands of the physical education mission in Spai

Zirconium and Hafnium Permethylpentalene Compounds

A selection of new η⁸-permethylpentalene zirconium and hafnium complexes are reported. The first d-block metal bis­(permethylpentalene) sandwich complexes, (Pn*₂M ; Pn* = C₈Me₆ ; M = Zr, Hf) have been synthesized and structurally characterized. The bis-allyl species Pn*M­(C₃H₅)₂ (M = Zr, Hf) have been synthesized; these complexes are fluxional in solution and react with CO₂ to give the double-insertion product Pn*M­(κ²-O₂CCH₂CHCH₂)₂ (M = Zr, Hf). We also report monometallic, bimetallic, and polymeric σ-bonded alkyl derivatives such as (Pn*Zr)₂(μ-CH₂)­(μ-Me)₂, [Pn*Hf­(CH₂Ph)₃]­[Li­(1,4-dioxane)₄], and [Pn*ZrPh­(μ-Ph)₂­Li­(μ-1,4-dioxane)]_<i>n</i>

Time-Resolved in Situ Neutron Diffraction under Supercritical Hydrothermal Conditions: A Study of the Synthesis of KTiOPO₄

In the first in situ neutron powder diffraction study of a supercritical hydrothermal synthesis, the crystallization of KTiOPO₄ (KTP) at 450 °C and 380 bar has been investigated. The time-resolved diffraction data suggest that the crystallization of KTP occurs by the reaction between dissolved K⁺(aq), PO₄^3–(aq), and [Ti­(OH)_<i>x</i>]^{(4–<i>x</i>)+}(aq) species

Fabrication of Lithium Silicates As Highly Efficient High-Temperature CO₂ Sorbents from SBA-15 Precursor

A series of lithium silicates with improved CO₂ sorption capacity were successfully synthesized using SBA-15 as the silicon precursor. The influence of Li/Si ratio, calcination temperature, and calcination duration on the chemical composition and CO₂ capture capacity of obtained lithium silicates was systematically investigated. The correlation between CO₂ sorption performance and crystalline phase abundance was determined using X-ray diffraction and a normalized reference intensity ratio method. Under the optimized condition, Li-SBA15-4 prepared using Li/Si = 4 that contains mainly Li₄SiO₄ achieved an extremely high CO₂ capture capacity of 36.3 wt % (corresponding to 99% of the theoretical value of 36.7 wt % for Li₄SiO₄), which is much higher than the Li₄SiO₄ synthesized from conventional SiO₂ sources. It also showed very high cycling stability with only 1.0 wt % capacity loss after 15 cycles. Li-SBA15-10 (Li/Si = 10) that mainly contains Li₈SiO₆ displayed an extremely high CO₂ uptake of 62.0 wt %, but its regeneration capacity was poor, with only 10.5 wt % of reversible CO₂ capture capacity. The influence of CO₂ concentration on the CO₂ capture performance of Li-SBA15-4 and Li-SBA15-10 samples was also studied. With the decrease in CO₂ concentration, relatively lower temperatures are needed for its maximum CO₂ capture capacity. The CO₂ sorption kinetics and mechanism for Li-SBA15-4 and Li-SBA15-10 samples were explored. Overall, we have shown that the lithium silicates synthesized from SBA-15 possessed much improved CO₂ sorption performance than that attained from conventional SiO₂

Slurry-Phase Ethylene Polymerization Using Pentafluorophenyl- and Pentafluorophenoxy-Modified Solid Polymethylaluminoxanes

Postsynthesis modification of solid polymethylaluminoxane (sMAO) with tris­(pentafluorophenyl)­borane or pentafluorophenol produces highly active metallocene supports “sMMAOs” for use in slurry-phase ethylene polymerization. Characterization of the sMMAOs using elemental analysis, BET isotherm, SEM-EDX, diffuse FT-IR, and solid-state NMR spectroscopy reveals that the surface methyl groups are exchanged for C₆F₅ and C₆F₅O moieties respectively, giving a material with reduced aluminum content and a lower specific surface area than sMAO. <i>rac</i>-Ethylenebis­(1-indenyl) zirconium dichloride, {(EBI)­ZrCl₂} immobilized on B­(C₆F₅)₃- and C₆F₅OH-modified sMAO displayed activity increases of 66% and 71% respectively for ethylene polymerization compared to the same zirconocene catalyst precursor on unmodified sMAO. In the case of B­(C₆F₅)₃-modified sMAO, this enhanced polymerization activity is accompanied by excellent control of polymer particle size and morphology, and a small decrease in polymer molecular weight and polydispersities

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Synthesis of Flame-Retardant Polypropylene/LDH-Borate Nanocomposites

New nanocomposites have been prepared using unmodified polypropylene (PP) and a new type of highly dispersed [Zn₂Al­(OH₆)]­[B₄O₅(OH)₄]_0.5 (Zn₂Al-borate) and [Mg₃Al­(OH)₈]­[B₄O₅(OH)₄]_0.5 (Mg₃Al-borate) layered double hydroxides (LDHs). PP/LDHs nanocomposites with LDH loadings of 1, 3, 6, 9, 15, and 30 wt % have been prepared by a novel solvent mixing method. Scanning electron microscopy (SEM) analysis shows that the precipitated nanocomposites materials form spherical particles with an average size of ca. 10 μm and that the LDH nanoparticles were well dispersed within the PP matrix. XRD analysis of the nanocomposites indicates that the LDHs are completely exfoliated. The thermal stability and flame retardancy properties of these new materials have been evaluated as a function of the nature of LDH and the LDH loadings. Cone calorimetry analysis indicates that PP/Zn₂Al-borate nanocomposites exhibited superior performance than the equivalent PP/Mg₃Al-borate nanocomposites; a 15 wt % of the highly dispersed Zn₂Al-borate LDH in PP was found to be the optimal loading. The 15% Zn₂Al-borate LDH in pristine (unmodified) PP resulted in reduction of the PHRR (peak heat release rate) (Rdctn) by 63.7%. We also demonstrated that the solvent mixing is superior to a melt mixing method. With a 6 wt % LDH loading, the reduction in PHRR is 23.8% for the melt mixing sample, which is lower than that of solvent mixing sample (29.9%), this behaviour can be attributed to the severe aggregation and poor dispersion of LDH particles

Synthesis and Characterization of Solid Polymethylaluminoxane: A Bifunctional Activator and Support for Slurry-Phase Ethylene Polymerization

An insoluble form of methylaluminoxane, also known as solid polymethylaluminoxane (sMAO), has been synthesized by the controlled hydrolysis of trimethylaluminum (TMA) with benzoic acid, followed by thermolysis. Characterization of sMAO by multinuclear NMR spectroscopy in solution and the solid state reveals an aluminoxane structure that features “free” and bound TMA and incorporation of a benzoate residue. Total X-ray scattering (or pair distribution function, PDF) measurements on sMAO allow comparisons to be made with simulated data for density functional theory (DFT) modeled structures of methylaluminoxane (MAO). Several TMA-bound (AlOMe)_<i>n</i> cage and nanotubular structures with <i>n</i> > 10 are consistent with the experimental data. The measured Brunauer–Emmett–Teller (BET) surface area of sMAO ranges between 312 and 606 m² g^–1 and shows an N₂ adsorption/desorption isotherm consistent with a nonporous material. sMAO can be utilized to support metallocene precatalysts in slurry-phase ethylene polymerization reactions. Metallocene precatalyst <i>rac</i>-ethylenebis­(1-indenyl)-dichlorozirconium, <i>rac</i>-(EBI)­ZrCl₂, was immobilized on sMAO samples, to afford solids which showed very high polymerization activities in hexane, comparable to those of the respective homogeneous catalysts formed by treatment of the precatalysts with MAO. <i>rac</i>-(EBI)­ZrCl₂ immobilized on an sMAO containing an Al:O ratio of 1.2 gave the highest ethylene polymerization activity