scholarly journals Iminopyridine Ni(II) Catalysts Affording Oily Hyperbranched Oligoethylenes and/or Crystalline Polyethylenes Depending on the Reaction Conditions: Possible Role of In Situ Catalyst Structure Modifications

Author(s):  
Ilaria D'Auria ◽  
Zeinab Saki ◽  
Claudio Pellecchia

Nickel-based ethylene polymerization catalysts have unique features, being able to produce macromolecules with a variable content of branches, resulting in polymers ranging from semicrystalline plastics to elastomers to hyperbranched amorphous waxes and oils. In addition to Brookhart's α-diimine catalysts, iminopyridine Ni(II) complexes are among the most investigated systems. We report that Ni(II) complexes bearing aryliminopyridine ligands with bulky substituents both at the imino moiety and in the 6-position of pyridine afford either hyperbranched low molecular weight polyethylene oils or prevailingly linear crystalline polyethylenes or both depending on the ligand structure and the reaction conditions. The formation of multiple active species in situ is suggested by analysis of the post-polymerization catalyst residues, showing the partial reduction of the imino function. Some related arylaminopyridine Ni(II) complexes were also synthesized and tested, showing a peculiar behavior, i.e. the number of branches of the produced polyethylenes increases while ethylene pressure increases.

Macromol ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 121-129
Author(s):  
Ilaria D’Auria ◽  
Zeinab Saki ◽  
Claudio Pellecchia

Nickel-based ethylene polymerization catalysts have unique features, being able to produce macromolecules with a variable content of branches, resulting in polymers ranging from semicrystalline plastics to elastomers to hyperbranched amorphous waxes and oils. In addition to Brookhart’s α-diimine catalysts, iminopyridine Ni(II) complexes are among the most investigated systems. We report that Ni(II) complexes bearing aryliminopyridine ligands with bulky substituents both at the imino moiety and in the 6-position of pyridine afford either hyperbranched low molecular weight polyethylene oils or prevailingly linear crystalline polyethylenes or both, depending on the ligand structure and the reaction conditions. The formation of multiple active species in situ is suggested by analysis of the post-polymerization catalyst residues, showing the partial reduction of the imino function. Some related arylaminopyridine Ni(II) complexes were also synthesized and tested, showing a peculiar behavior, i.e., the number of branches of the produced polyethylenes increases while ethylene pressure increases.


2013 ◽  
Vol 2 (5) ◽  
pp. 547-576 ◽  
Author(s):  
Peng Zhai ◽  
Geng Sun ◽  
Qingjun Zhu ◽  
Ding Ma

AbstractOne key goal of heterogeneous catalysis study is to understand the correlation between the catalyst structure and its corresponding catalytic activity. In this review, we focus on recent strategies to synthesize well-defined Fischer-Tropsch synthesis (FTS) nanostructured catalysts and their catalytic performance in FTS. The development of those promising catalysts highlights the potentials of nanostructured materials to unravel the complex and dynamic reaction mechanism, particularly under the in situ reaction conditions. The crucial factors associated with the catalyst compositions and structures and their effects on the FTS activities are discussed with an emphasis on the role of theoretical modeling and experimental results.


2016 ◽  
Vol 12 ◽  
pp. 2588-2601 ◽  
Author(s):  
Vladimir A Stepchenko ◽  
Anatoly I Miroshnikov ◽  
Frank Seela ◽  
Igor A Mikhailopulo

The trans-2-deoxyribosylation of 4-thiouracil (4SUra) and 2-thiouracil (2SUra), as well as 6-azauracil, 6-azathymine and 6-aza-2-thiothymine was studied using dG and E. coli purine nucleoside phosphorylase (PNP) for the in situ generation of 2-deoxy-α-D-ribofuranose-1-phosphate (dRib-1P) followed by its coupling with the bases catalyzed by either E. coli thymidine (TP) or uridine (UP) phosphorylases. 4SUra revealed satisfactory substrate activity for UP and, unexpectedly, complete inertness for TP; no formation of 2’-deoxy-2-thiouridine (2SUd) was observed under analogous reaction conditions in the presence of UP and TP. On the contrary, 2SU, 2SUd, 4STd and 2STd are good substrates for both UP and TP; moreover, 2SU, 4STd and 2’-deoxy-5-azacytidine (Decitabine) are substrates for PNP and the phosphorolysis of the latter is reversible. Condensation of 2SUra and 5-azacytosine with dRib-1P (Ba salt) catalyzed by the accordant UP and PNP in Tris∙HCl buffer gave 2SUd and 2’-deoxy-5-azacytidine in 27% and 15% yields, respectively. 6-Azauracil and 6-azathymine showed good substrate properties for both TP and UP, whereas only TP recognizes 2-thio-6-azathymine as a substrate. 5-Phenyl and 5-tert-butyl derivatives of 6-azauracil and its 2-thioxo derivative were tested as substrates for UP and TP, and only 5-phenyl- and 5-tert-butyl-6-azauracils displayed very low substrate activity. The role of structural peculiarities and electronic properties in the substrate recognition by E. coli nucleoside phosphorylases is discussed.


2020 ◽  
Vol 13 (05) ◽  
pp. 2051031
Author(s):  
Abulikemu Abulizi ◽  
Hujiabudula Maimaitizi ◽  
Dilinuer Talifu ◽  
Yalkunjan Tursun

A photocatalyst of high-performance hierarchical nitrogen-doped MoS2 (N-MoS2) microsphere was fabricated by an in situ hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB). The as-prepared N-MoS2 microsphere was self-assembled by extremely thin interleaving petals, where CTAB acts as a nucleation site for the formation of the interleaving petals due to the strong interaction between CTA+ and [Formula: see text]. N-MoS2 showed higher N2 fixation ability (101.2 [Formula: see text] mol/g(cat)h) than the non-doped MoS2 under the visible light irradiation, and the improved photocatalytic activity could be ascribed to that the doped N narrows the band gap, and the surface reflecting and scattering effect caused by the hierarchical structure enhance the light adsorption. The trapping experiment of active species was also investigated to evaluate the role of photogenerated electrons in the photocatalytic reaction process. Meanwhile, the possible mechanism for the formation and excellent photocatalytic performance of N-MoS2 microsphere were also presented.


2016 ◽  
Vol 3 (1) ◽  
Author(s):  
I.E. Soshnikov ◽  
N.V. Semikolenova ◽  
A.A. Antonov ◽  
K.P. Bryliakov ◽  
V.A. Zakharov ◽  
...  

AbstractIn this work, previously undetected intermediates of several practically promising catalyst systems for ethylene polymerization and trimerization are discussed. In particular, the activation of ethylene polymerization catalysts (1) LNiCl2 (L = 2,4,6-trimethyl- (N-5,6,7-trihydroquinolin-8-ylidene)phenylamine) with AlEt2Cl and AlMe2Cl, (2) activation of bis(imino)pyridine vanadium(III) chloride L1VIIICl3 (L1 = 2,6-(ArN=CMe)2C5H3N, Ar = 2,6-iPr2C6H3; 2,6-Me2C6H3; 2,4,6-Me3C6H2; 3,5- F2C6H3) with AlMe3/[Ph3C]+[B(C6F5)]4¯ and MAO, and (3) selective ethylene trimerization catalyst (FI)TiCl3 (FI = phenoxyimine ligand with an additional aryl-OCH3 donor) with MAO have been assessed by NMR and EPR spectroscopy. The nature of ion-pair intermediates – the closest precursors of the propagating species – has been established, and the major catalyst deactivation pathways are discussed.


2006 ◽  
Vol 84 (5) ◽  
pp. 755-761 ◽  
Author(s):  
Chad Beddie ◽  
Pingrong Wei ◽  
Douglas W Stephan

A series of Ti–pyridyl-phosphinimide complexes of the form Cp′TiX2[NPR2(2-CH2Py)] (Cp′ = Cp, Cp*, R = i-Pr, t-Bu, X = Cl, Me) have been prepared and characterized. These complexes generate ethylene polymerization catalysts upon activation with MAO or B(C6F5)3. The resulting polymers exhibit broad molecular weight distributions. The role of the pyridyl group is discussed in light of stoichiometric reactions of CpTiCl2[NPR2(2-CH2Py)] with B(C6F5)3.Key words: phosphinimide complexes, pyridyl-phosphinimides, olefin polymerization.


2009 ◽  
Vol 28 (20) ◽  
pp. 6003-6013 ◽  
Author(s):  
Igor E. Soshnikov ◽  
Nina V. Semikolenova ◽  
Alexey N. Bushmelev ◽  
Konstantin P. Bryliakov ◽  
Oleg Y. Lyakin ◽  
...  

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