Roles of chloro compound in homogeneous [Cr(2-ethylhexanoate)3/2,5-dimethylpyrrole/triethylaluminum/chloro compound] catalyst system for ethylene trimerization

In the present work, effect of basic components on the energy pathway of ethylene oligomerization by landmark Chevron-Phillips catalyst has been explored in detail using density functional theory (DFT). Studied factors were chosen considering the main components of Chevron-Phillips catalyst, i.e. ligand, cocatalyst and halocarbon compounds, comprising i) the type of alkyl substituents in pyrrole ligand as methyl, iso-propyl, tert-butyl, and phenyl, as well as the simple hydrogen, and the electronwithdrawing fluoro and trifluoromethyl; ii) the number of Cl atoms in Al-compound (as AlMe2Cl, AlMeCl2 and AlCl3) which indicates halocarbon amount and iii) cocatalyst type as alkylboron, alkylaluminium, or alkylgallium. Besides main ingredients, solvent effect, from toluene or methylcyclohexane, on oligomerization pathway was explored as well. In this regard, the full catalytic cycles for the main product (1-hexene) formation as well as side reactions, i.e. 1-butene release and chromacyclononane formation, were calculated on the basis of the metallacycle based mechanism. Based on results, a modification on the Chevron-Phillips catalyst system, to reach higher 1-hexene selectivity and activity, is suggested.

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Direct Observation of Chain Lengths and Conformations in Oligofluorene Distributions from Controlled Polymerization by Double Electron-Electron Resonance

10.26434/chemrxiv.10002785 ◽

2019 ◽

Author(s):

Dennis Bücker ◽

Annika Sickinger ◽

Julian D. Ruiz Perez ◽

Manuel Oestringer ◽

Stefan Mecking ◽

...

Keyword(s):

Chain Length ◽

Length Distribution ◽

Catalyst System ◽

Chain Conformation ◽

Controlled Polymerization ◽

Chain Length Distribution ◽

Electron Resonance ◽

Double Electron ◽

The Individual ◽

Double Electron Electron Resonance

Synthetic polymers are mixtures of different length chains, and their chain length and chain conformation is often experimentally characterized by ensemble averages. We demonstrate that Double-Electron-Electron-Resonance (DEER) spectroscopy can reveal the chain length distribution, and chain conformation and flexibility of the individual n-mers in oligo-(9,9-dioctylfluorene) from controlled Suzuki-Miyaura Coupling Polymerization (cSMCP). The required spin-labeled chain ends were introduced efficiently via a TEMPO-substituted initiator and chain terminating agent, respectively, with an in situ catalyst system. Individual precise chain length oligomers as reference materials were obtained by a stepwise approach. Chain length distribution, chain conformation and flexibility can also be accessed within poly(fluorene) nanoparticles.

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Mechanistic Insights into Fe Catalyzed α-C-H Oxidations of Tertiary Amines

10.26434/chemrxiv.9101405 ◽

2019 ◽

Author(s):

Christopher J. Legacy ◽

Frederick T. Greenaway ◽

Marion Emmert

Keyword(s):

Free Radical ◽

Catalytic Mechanism ◽

Catalyst System ◽

Oxidation Products ◽

Tertiary Amines ◽

Catalyst Activation ◽

Rate Determining Step ◽

Fe Catalyst ◽

Ligand Coordination ◽

Rate Kinetics

We report detailed mechanistic investigations of an iron-based catalyst system, which allows the α-C-H oxidation of a wide variety of amines, including acyclic tertiary aliphatic amines, to afford dealkylated or amide products. In contrast to other catalysts that affect α-C-H oxidations of tertiary amines, the system under investigation employs exclusively peroxy esters as oxidants. More common oxidants (e.g. tBuOOH) previously reported to affect amine oxidations via free radical pathways do not provide amine α-C-H oxidation products in combination with the herein described catalyst system. Motivated by this difference in reactivity to more common free radical systems, the investigations described herein employ initial rate kinetics, kinetic profiling, Eyring studies, kinetic isotope effect studies, Hammett studies, ligand coordination studies, and EPR studies to shed light on the Fe catalyst system. The obtained data suggest that the catalytic mechanism proceeds through C-H abstraction at a coordinated substrate molecule. This rate-determining step occurs either at an Fe(IV) oxo pathway or a 2-electron pathway at a Fe(II) intermediate with bound oxidant. We further show via kinetic profiling and EPR studies that catalyst activation follows a radical pathway, which is initiated by hydrolysis of PhCO3 tBu to tBuOOH in the reaction mixture. Overall, the obtained mechanistic data support a non-classical, Fe catalyzed pathway that requires substrate binding, thus inducing selectivity for α-C-H functionalization.<br>

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