scholarly journals First experimental evidence for a bis-ethene chromium(I) complex forming from an activated ethene oligomerization catalyst

2020 ◽  
Vol 6 (51) ◽  
pp. eabd7057
Author(s):  
S. Chabbra ◽  
D. M. Smith ◽  
N. L. Bell ◽  
A. J. B. Watson ◽  
M. Bühl ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Experimental Evidence ◽  
Catalytic System ◽  
Isotope Labeling ◽  
Catalytic Transformation ◽  
Mechanistic Studies ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic

A bis-ethene chromium(I) species, which is the postulated key intermediate in the widely accepted metallacyclic mechanism for ethene oligomerization, is experimentally observed. This catalytic transformation is an important commercial route to linear α-olefins (primarily, 1-hexene and 1-octene), which act as comonomers for the production of polyethene. Here, electron paramagnetic resonance studies of a catalytic system based on [Cr(CO)4(PNP)][Al(OC(CF3)3)4] [PNP = Ph2PN(iPr)PPh2] activated with Et6Al2 provide the first unequivocal evidence for a chromium(I) bis-ethene complex. The concentration of this species is enhanced under ethene and isotope labeling studies that confirm its composition as containing [Cr(C2H4)2(CO)2(PNP)]+. These observations open a new route to mechanistic studies of selective ethene oligomerization.

Solubility of carbon nanotubes

2000 ◽  
Vol 633 ◽  
Author(s):  
Marc In Het Panhuis ◽  
Jonathan N. Coleman ◽  
Werner J. Blau
Keyword(s):  
Carbon Nanotubes ◽  
Electron Paramagnetic Resonance ◽  
Experimental Evidence ◽  
Experimental Technique ◽  
Carbon Material ◽  
Conjugated Polymer ◽  
Paramagnetic Resonance ◽  
Sample Bottle ◽  
Carbon Soot ◽  
Electron Paramagnetic

AbstractWe have described a novel experimental technique to separate nanotubes from other unwanted carbon species in arc generated carbon soot. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble while extraneous carbon material formed a sediment at the bottom of the sample bottle. This process was monitored using electron paramagnetic resonance (EPR) which showed that 63% of nanotubes were kept in solution while 98.1% of impurities were rejected. Optimal polymer characteristics for nanotube solubility were identified using geometry optimisation and experimental evidence. It was calculated that a successful polymer has a flat shaped helical backbone with solvent solubilising groups projected outwards. This is achieved with the following polymer characteristics, two solvent solubilising groups on a twist allowing π-conjugated backbone.

Electron paramagnetic resonance study of non-exchangeable vanadium(IV) in rectorites

Clay Minerals ◽  
1990 ◽  
Vol 25 (3) ◽  
pp. 283-287 ◽  
Author(s):  
B. A. Goodman ◽  
P. H. Nadeau
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Experimental Evidence ◽  
Epr Spectroscopy ◽  
Electron Paramagnetic Resonance Study ◽  
Paramagnetic Resonance ◽  
Octahedral Sites ◽  
Two Samples ◽  
Electron Paramagnetic

AbstractEPR spectroscopy was used to provide evidence for the existence of vanadium(IV) in two samples of rectorite. Possible sites for the vanadium are the tetrahedral and octahedral sites in the 2:1 layers and the non-exchangeable interlayer sites in the paragonite part of the structure. Consideration is given to each of these possibilities but the experimental evidence is insufficient to identify conclusively the location of the vanadium. Since substantial amounts of vanadium(IV) were present in the only well-defined rectorite samples obtainable, it is possible that the formation of rectorite is facilitated by the presence of vanadium.

Metal-Free Generation of Phosphorus-Centered Radicals for the Synthesis of Phosphorus-Based Heterocycles: A Personal Account

Synthesis ◽  
2017 ◽  
Vol 49 (15) ◽  
pp. 3444-3452 ◽  
Author(s):  
Valentin Quint ◽  
Ludovik Noël-Duchesneau ◽  
Elodie Lagadic ◽  
Fabrice Morlet-Savary ◽  
Jacques Lalevée ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Short Review ◽  
Photoredox Catalysis ◽  
Mechanistic Studies ◽  
Personal Account ◽  
Paramagnetic Resonance ◽  
Metal Free ◽  
Donor Acceptor ◽  
Free Generation ◽  
Electron Paramagnetic

This short review describes our recent efforts to generate phosphorus-based radicals under metal-free conditions and their use as key intermediates for the synthesis of phosphorus-based heterocycles. In this regard, the synthesis of benzo[b]phosphole oxides and 6-phosphorylated phenanthridines will be reported. While the synthesis of the former lies in the use of photoredox catalysis, the latter have been obtained through the use of an electron donor–acceptor complex from the combination of diphenyliodonium ion with triethylamine. Mechanistic aspects of both reaction types are discussed based on detailed mechanistic studies including electron paramagnetic resonance, UV–vis spectroscopic, NMR and steady-state photolysis experiments.1 Introduction2 Photoredox Catalysis for the Generation of Phosphinoyl Radicals3 Generation of Phosphinoyl Radicals through the Formation of EDA Complexes4 Conclusions

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