Search Results (5)

The dinuclear aluminum salt {[iBu₂(DMA)Al]₂(μ-H)}⁺[B(C₆F₅)₄]⁻ (AlHAl; DMA = N,N-dimethylaniline) is the prototype of a new class of molecular cocatalysts for catalytic olefin polymerization, its modular nature offering easy avenues for tailoring the activator to specific needs. We report here, as proof of concept, a first variant (s-AlHAl) bearing p-hexadecyl-N,N-dimethylaniline (DMA_C16) units, which enhances solubility in aliphatic hydrocarbons. The novel s-AlHAl was used successfully as an activator/scavenger in ethylene/1-hexene copolymerization in a high-temperature solution process. Full article

Homogeneous olefin polymerization catalysts are activated in situ with a co-catalyst ([PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ or [Ph₃C]⁺[B(C₆F₅)₄]⁻) in bulk polymerization media. These co-catalysts are insoluble in hydrocarbon solvents, requiring excess co-catalyst (>3 eq.). Feeding the activated species as a solution in an aliphatic hydrocarbon solvent may be advantageous over the in situ activation method. In this study, highly pure and soluble ammonium tetrakis(pentafluorophenyl)borates ([Me(C₁₈H₃₇)₂N-H]⁺[B(C₆F₅)₄]⁻ and [(C₁₈H₃₇)₂NH₂]⁺[B(C₆F₅)₄]⁻) containing neither water nor Cl⁻ salt impurities were prepared easily via the acid–base reaction of [PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ and the corresponding amine. Using the prepared ammonium salts, the activation reactions of commercial-process-relevant metallocene (rac-[ethylenebis(tetrahydroindenyl)]Zr(Me)₂ (1-ZrMe₂), [Ph₂C(Cp)(3,6-^tBu₂Flu)]Hf(Me)₂ (3-HfMe₂), [Ph₂C(Cp)(2,7-^tBu₂Flu)]Hf(Me)₂ (4-HfMe₂)) and half-metallocene complexes ([(η⁵-Me₄C₅)Si(Me)₂(κ-N^tBu)]Ti(Me)₂ (5-TiMe₂), [(η⁵-Me₄C₅)(C₉H₉(κ-N))]Ti(Me)₂ (6-TiMe₂), and [(η⁵-Me₃C₇H₁S)(C₁₀H₁₁(κ-N))]Ti(Me)₂ (7-TiMe₂)) were monitored in C₆D₁₂ with ¹H NMR spectroscopy. Stable [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻ species were cleanly generated from 1-ZrMe₂, 3-HfMe₂, and 4-HfMe₂, while the species types generated from 5-TiMe₂, 6-TiMe₂, and 7-TiMe₂ were unstable for subsequent transformation to other species (presumably, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species). [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species were also prepared from 5-TiCl(Me) and 6-TiCl(Me), which were newly prepared in this study. The prepared [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, and [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species, which are soluble and stable in aliphatic hydrocarbon solvents, were highly active in ethylene/1-octene copolymerization performed in aliphatic hydrocarbon solvents. Full article

Crude oil and refinery products are transported worldwide to meet human energy needs. During transportation via pipeline, huge pumping power is required to overcome the frictional pressure drop and the associated drag along the pipeline. The reduction of both is of great interest to industry and academia. Highly expensive ultrahigh molecular weight (UHMW, MW a million Dalton) drag reducing polymers (DRPs) are currently used to address this problem. The present paper, therefore, emphasizes particularly the development of a high-performance catalyst system that synthesizes DRPs (using higher alpha-olefins)—a highly promising cost reduction alternative. This homogeneous catalyst system features a new concept that uses a cost-effective titanium-based Ziegler–Natta precatalyst and a cocatalystLewis base complex having both steric hindrance (around N heteroatom) and electronic effect. This novel work, which involves precatalyst–cocatalyst molecular separation and cocatalystmonophenyl amine association-dissociation phenomena, already generated several US patents. The subject catalyst prepares UHMW DRPs at room temperature, avoiding the use of zero and sub-zero temperatures. The resulting product almost tripled the rate of transportation of a selected grade of refinery product and saved about 50% pumping energy at ppm level pipeline concentration. It is also very easily soluble. Hence, massive modification of existing pipeline will be unnecessary. This will save additional infrastructure cost. This paper also summarizes challenges facing the development of improved heterogeneous catalysts, dispersed polymerization process, molecular simulation-based DRP product formulation, and model/theory of turbulent mixing and dispersion in the transportation pipeline setting. Full article

Metal complexes of meso-arylporphyrins (Cr(III), Fe(III), and Zn(II)) were evaluated in the coupling reaction of cyclohexene oxide (CHO) with CO₂ in compressed medium, where the Cr complexes were demonstrated to be the most active systems, leading predominantly to copolymerisation products. It is noteworthy that no addition of solvent was required. To improve the catalytic activity, and to simultaneously increase the solubility in compressed CO₂, a new fluorinated catalyst, tetrakis(4-trifluoromethylphenyl)porphyrinatochromium(III) chloride (CrCl-pCF₃TPP), was applied to this reaction. The alternating copolymerisation of CHO with CO₂, using the Cr(III) fluorinated porphyrin catalyst, required the use of a co-catalyst, bis(triphenylphosphine)iminium chloride (PPNCl), with the best yields of copolymers being obtained at 80 °C, and CO₂ pressures in the range of 50–110 bar, over a period of 24 h, with a low catalyst/substrate molar ratio (0.07%). The polycarbonate’s structure was analysed by ¹H NMR, ¹³C NMR, and MALDI-TOF spectroscopy, which demonstrated high carbonate incorporations (98–99%). Gel permeation chromatography revealed number-average molecular weights (M_n) in the range of 4800–12,800 and narrow molecular weight distributions (M_w/M_n ≤ 1.63). Full article

This review describes new reactions catalyzed by recently discovered types of metal complexes and catalytic systems (catalyst + co-catalyst). Works of recent years (mainly 2010–2016) devoted to the oxygenations of saturated, aromatic hydrocarbons and other carbon–hydrogen compounds are surveyed. Both soluble metal complexes and solid metal compounds catalyze such transformations. Molecular oxygen, hydrogen peroxide, alkyl peroxides, and peroxy acids were used in these reactions as oxidants. Full article