Ligand Migration in the Reaction of Titanium Complexes with AlMe3

2007 ◽  
Vol 72 (4) ◽  
pp. 541-559 ◽  
Author(s):  
Michał J. Kobyłka ◽  
Lucjan B. Jerzykiewicz ◽  
Jasson T. Patton ◽  
Szymon Przybylak ◽  
Józef Utko ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Catalytic Performance ◽  
Active Species ◽  
Titanium Complexes ◽  
Propene Polymerization ◽  
Ligand Migration ◽  
High Yields ◽  
Titanium Compounds ◽  
Insight Into ◽  
Gaining Insight

Five different titanium compounds cis-[Ti(η2-hbo)2(OEt)2]·0.5toluene (1), cis-[TiCl2(η2-thp)2] (2), [TiCl2(edbp)2] (3), [Ti2(μ-OMe)2(edbp)2(Me)2] (6), [Ti2(μ-OMe)2(edbp)2(OMe)2] (7) (Hhbo = 2-(2-hydroxyfenyl)benzoxazole, Hthp = tetrahydropyran-2-methanol, H2edbp = 2,2'-ethylidenebis(4,6-di-tert-butylphenol)), have been prepared and tested in combination with MAO as catalysts for propene polymerization and ethene and oct-1-ene copolymerization with the aim of gaining insight into the structure of the active species. Investigation of the 1/AlMe3 or 2/AlMe3 systems resulted in isolation of [Al(η2-hbo)2(Me)] (4) and [Al2(μ2-η2-thp)2(Me)4] (5) in high yields. This indicates that the trimethylaluminum contained in MAO abstracts ligands from 1 or 2, affecting thus the catalytic performance of the 1,2/MAO catalysts. In contrast, compound 3 reacted with MAO affording methylated product 6. Accordingly, the 3/MAO catalyst differed from the above ones, furnishing at 70 °C e.g., narrow molecular weight polypropylene (Mn = 454 000; Mw/Mn = 2.49; Tm = 158.2 °C).

Altering molecular weight distributions: Benzyl–phosphinimide titanium complexes as ethylene polymerization catalysts

2004 ◽  
Vol 82 (8) ◽  
pp. 1304-1313 ◽  
Author(s):  
Emily Hollink ◽  
Pingrong Wei ◽  
Douglas W Stephan
Keyword(s):  
Molecular Weight ◽  
Ethylene Polymerization ◽  
Active Species ◽  
Polymerization Catalysts ◽  
Subsequent Reaction ◽  
X Ray ◽  
Molecular Weight Distributions ◽  
Polymerization Catalysis ◽  
Weight Distributions ◽  
High Yields

The phosphines and corresponding phosphinimines R2BnPNSiMe3 (R = t-Bu, Cy), p-C6H4(CH2PR2)2 (R = t-Bu (1), Cy (2)), and p-C6H4(CH2PR2NSiMe3)2 (R = t-Bu (3), Cy (4)) were prepared in high yields. Subsequent reaction with Ti precursors afforded (R2BnPN)TiCp*Cl2 (Cp* = η-C5Me5; R = t-Bu (5), Cy (6)), (R2BnPN)TiCpCl2 (Cp = η-C5H5; R = t-Bu (7), Cy (8)), p-C6H4(CH2PR2NTiCp*Cl2)2 (R = t-Bu (9), Cy (10)), and p-C6H4(CH2PR2NTiCpCl2)2 (R = t-Bu (11), Cy (12)). Methylation of the above complexes gave (R2BnPN)TiCp*Me2 (R = t-Bu (13), Cy (14)), (R2BnPN)TiCpMe2 (R = t-Bu (15), Cy (16)), p-C6H4(CH2PR2NTiCp*Me2)2 (R = t-Bu (17), Cy (18)), and p-C6H4(CH2PR2NTiCpMe2)2 (R = t-Bu (19), Cy (20)). The activity of these species as catalyst precursors in ethylene polymerization catalysis was evaluated using Schlenk line and Buchi reactor techniques using activation by methylaluminoxane (MAO) or [Ph3C][B(C6F5)4]. All these catalysts showed good activities and yield polymers with relatively broad molecular weight distributions. The bimodal polymers derived from catalysts generated using MAO are proposed to result from additional active species, possibly as a result of reaction of MAO with the benzylic fragments. X-ray data are reported for 1, 4–8, 10, 12–14, 16, and 18–20.Key words: phosphinimides, polymerization, catalysis, polyethylene, titanium, polymer molecular weight distributions.

Recent Progress in Synthesizing Polyethers via Organocatalysts

Synlett ◽  
2021 ◽  
Author(s):  
Yao-Yao Zhang ◽  
Guan-Wen Yang ◽  
Guang-Peng Wu
Keyword(s):  
Molecular Weight ◽  
Recent Progress ◽  
Raw Materials ◽  
Catalytic Efficiency ◽  
Cost Effective ◽  
Catalytic Performance ◽  
Excellent Performance ◽  
Metallic Compounds ◽  
High Yields ◽  
Performance And Mechanism

Aliphatic polyethers are one of the most widely used polymers, whose synthesis is largely dependent on metallic compounds. Recent development of organocatalysts may break the limits of this long-standing field and infuse vitality into polyether production. In this Synpacts article, the recent advances of organocatalysts for polyether production is introduced in aspects of catalytic performance and mechanism. Moreover, attentions are paid to the latest contributions of bifunctional organoboron catalysts which can be prepared with high yields from cost-effective raw materials in two facile reactions and show excellent performance in the polyether production with remarkable catalytic efficiency, controllability on molecular weight, and explicit polymerization mechanism. Based on these advances, it is envisioned that new discoveries using organocatalysts will continue in the previsible future.

Standing up to the Demos

2018 ◽  
Author(s):  
Andrew Erskine
Keyword(s):  
Athenian Democracy ◽  
Parallel Lives ◽  
Standing Up ◽  
A Minor ◽  
Insight Into ◽  
Gaining Insight ◽  
The Way

Plutarch wrote twenty-three Greek Lives in his series of Parallel Lives—of these, ten were devoted to Athenians. Since Plutarch shared the hostile view of democracy of Polybius and other Hellenistic Greeks, this Athenian preponderance could have been a problem for him. But Plutarch uses these men’s handling of the democracy and especially the demos as a way of gaining insight into the character and capability of his protagonists. This chapter reviews Plutarch’s attitude to Athenian democracy and examines the way a statesman’s character is illuminated by his interaction with the demos. It also considers what it was about Phocion that so appealed to Plutarch, first by looking at his relationship with the democracy and then at the way he evokes the memory of Socrates. For him this was not a minor figure, but a man whose life was representative of the problems of Athenian democracy.

scholarly journals Insight into Active Centers and Anti-Coke Behavior of Niobium-Containing SBA-15 for Glycerol Dehydration

Catalysts ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 488
Author(s):  
Katarzyna Stawicka ◽  
Maciej Trejda ◽  
Maria Ziolek
Keyword(s):  
Coke Formation ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Silica Matrix ◽  
High Concentration ◽  
Active Centers ◽  
Acidic Sites ◽  
Glycerol Dehydration ◽  
Adsorption Desorption ◽  
Insight Into

Niobium containing SBA-15 was prepared by two methods: impregnation with different amounts of ammonium niobate(V) oxalate (Nb-15/SBA-15 and Nb-25/SBA-15 containing 15 wt.% and 25 wt.% of Nb, respectively) and mixing of mesoporous silica with Nb2O5 followed by heating at 500 °C (Nb2O5/SBA-15). The use of these two procedures allowed obtaining materials with different textural/surface properties determined by N2 adsorption/desorption isotherms, XRD, UV-Vis, pyridine, and NO adsorption combined with FTIR spectroscopy. Nb2O5/SBA-15 contained exclusively crystalline Nb2O5 on the SBA-15 surface, whereas the materials prepared by impregnation had both metal oxide and niobium incorporated into the silica matrix. The niobium species localized in silica framework generated Brønsted (BAS) and Lewis (LAS) acid sites. The inclusion of niobium into SBA-15 skeleton was crucial for the achievement of high catalytic performance. The strongest BAS were on Nb-25/SBA-15, whereas the highest concentration of BAS and LAS was on Nb-15/SBA-15 surface. Nb2O5/SBA-15 material possessed only weak LAS and BAS. The presence of the strongest BAS (Nb-25/SBA-15) resulted in the highest dehydration activity, whereas a high concentration of BAS was unfavorable. Silylation of niobium catalysts prepared by impregnation reduced the number of acidic sites and significantly increased acrolein yield and selectivity (from ca. 43% selectivity for Nb-25/SBA-15 to ca. 61% for silylated sample). This was accompanied by a considerable decrease in coke formation (from 47% selectivity for Nb-25/SBA-15 to 27% for silylated material).

1,3-Butadiene production from aqueous ethanol over ZnO/MgO-SiO2 catalysts: Insight into H2O effect on catalytic performance

2021 ◽  
Vol 616 ◽  
pp. 118081
Author(s):  
Pavlo I. Kyriienko ◽  
Olga V. Larina ◽  
Dmytro Yu. Balakin ◽  
Anatolii O. Stetsuk ◽  
Yurii M. Nychiporuk ◽  
...  
Keyword(s):  
Aqueous Ethanol ◽  
Catalytic Performance ◽  
Insight Into

scholarly journals Gaining Insight into Vitiligo Genetics through the Lens of a Large Epidemiologic Study

2021 ◽  
Vol 141 (4) ◽  
pp. 718-721
Author(s):  
Ken Okamura ◽  
Manuel Garber ◽  
John E. Harris
Keyword(s):  
Epidemiologic Study ◽  
Insight Into ◽  
Gaining Insight

scholarly journals Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi2O3 semiconductor

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Paola Riente ◽  
Mauro Fianchini ◽  
Patricia Llanes ◽  
Miquel A. Pericàs ◽  
Timothy Noël
Keyword(s):  
Experimental Studies ◽  
Heterogeneous Photocatalysis ◽  
Active Species ◽  
Organic Transformations ◽  
Alkyl Bromides ◽  
Catalytically Active ◽  
Visible Light Driven ◽  
Photocatalytic Reactions ◽  
Insight Into ◽  
Photocatalytic Processes

AbstractThe importance of discovering the true catalytically active species involved in photocatalytic systems allows for a better and more general understanding of photocatalytic processes, which eventually may help to improve their efficiency. Bi2O3 has been used as a heterogeneous photocatalyst and is able to catalyze several synthetically important visible-light-driven organic transformations. However, insight into the operative catalyst involved in the photocatalytic process is hitherto missing. Herein, we show through a combination of theoretical and experimental studies that the perceived heterogeneous photocatalysis with Bi2O3 in the presence of alkyl bromides involves a homogeneous BinBrm species, which is the true photocatalyst operative in the reaction. Hence, Bi2O3 can be regarded as a precatalyst which is slowly converted in an active homogeneous photocatalyst. This work can also be of importance to mechanistic studies involving other semiconductor-based photocatalytic processes.

scholarly journals A nickel phosphide nanoalloy catalyst for the C-3 alkylation of oxindoles with alcohols

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shu Fujita ◽  
Kohei Imagawa ◽  
Sho Yamaguchi ◽  
Jun Yamasaki ◽  
Seiji Yamazoe ◽  
...  
Keyword(s):  
Precious Metal ◽  
Cerium Dioxide ◽  
Catalytic Performance ◽  
Significant Loss ◽  
Nickel Phosphide ◽  
Cooperative Catalysis ◽  
Metal Phosphides ◽  
Borrowing Hydrogen ◽  
High Yields ◽  
Transition Metal Phosphides

AbstractAlthough transition metal phosphides are well studied as electrocatalysts and hydrotreating catalysts, the application of metal phosphides in organic synthesis is rare, and cooperative catalysis between metal phosphides and supports remains unexplored. Herein, we report that a cerium dioxide-supported nickel phosphide nanoalloy (nano-Ni2P/CeO2) efficiently promoted the C-3 alkylation of oxindoles with alcohols without any additives through the borrowing hydrogen methodology. Oxindoles were alkylated with various alcohols to provide the corresponding C-3 alkylated oxindoles in high yields. This is the first catalytic system for the C-3 alkylation of oxindoles with alcohols using a non-precious metal-based heterogeneous catalyst. The catalytic activity of nano-Ni2P/CeO2 was comparable to that reported for precious metal-based catalysts. Moreover, nano-Ni2P/CeO2 was easily recoverable and reusable without any significant loss of activity. Control experiments revealed that the Ni2P nanoalloy and the CeO2 support functioned cooperatively, leading to a high catalytic performance.

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