scholarly journals Low-Valent Tungsten Redox Catalysis Enables Controlled Isomerization and Carbonylative Functionalization of Alkenes

2021 ◽  
Author(s):  
Tanner Jankins ◽  
William Bell ◽  
Yu Zhang ◽  
Zi-Yang Qin ◽  
Milan Gembicky ◽  
...  
Keyword(s):  
Redox Cycle ◽  
Redox Catalysis ◽  
Model Complexes ◽  
History Of ◽  
Internal Site ◽  
Directing Group ◽  
Coordinate Geometry ◽  
Instrumental Role

Tungsten catalysis has played an instrumental role in the history of organometallic chemistry, with electrophilic, fully oxidized W(VI) catalysts featuring prominently in olefin polymerization and metathesis reactions. Here, we report that the simple W(0) precatalyst, W(CO)<sub>6</sub>, catalyzes the isomerization and hydrocarbonylation of alkenes via a W(0)/W(II) redox couple. The 6- to 7-coordinate geometry changes associated with this redox process are key in allowing isomerization to take place over multiple positions and stop at a defined unactivated internal site that is primed for <i>in situ</i> functionalization. DFT studies and crystallographic characterization of multiple directing-group-bound W(II) model complexes illuminate potential intermediates of this redox cycle and showcase the capabilities of the 7-coordinate W(II) geometry to facilitate challenging alkene functionalizations.

Low-Valent Tungsten Redox Catalysis Enables Controlled Isomerization and Carbonylative Functionalization of Alkenes

2021 ◽  
Author(s):  
Tanner Jankins ◽  
William Bell ◽  
Yu Zhang ◽  
Zi-Yang Qin ◽  
Milan Gembicky ◽  
...  
Keyword(s):  
Redox Cycle ◽  
Redox Catalysis ◽  
Model Complexes ◽  
History Of ◽  
Internal Site ◽  
Directing Group ◽  
Coordinate Geometry ◽  
Instrumental Role

Tungsten catalysis has played an instrumental role in the history of organometallic chemistry, with electrophilic, fully oxidized W(VI) catalysts featuring prominently in olefin polymerization and metathesis reactions. Here, we report that the simple W(0) precatalyst, W(CO)<sub>6</sub>, catalyzes the isomerization and hydrocarbonylation of alkenes via a W(0)/W(II) redox couple. The 6- to 7-coordinate geometry changes associated with this redox process are key in allowing isomerization to take place over multiple positions and stop at a defined unactivated internal site that is primed for <i>in situ</i> functionalization. DFT studies and crystallographic characterization of multiple directing-group-bound W(II) model complexes illuminate potential intermediates of this redox cycle and showcase the capabilities of the 7-coordinate W(II) geometry to facilitate challenging alkene functionalizations.

A Novel Technique for “In-Situ” Characterization of Devolatilization Rate of Solid Fuels in Fluidized Beds

2005 ◽  
Author(s):  
R. Solimene ◽  
R. Chirone ◽  
A. Marzocchella ◽  
P. Salatino
Keyword(s):  
Fluidized Bed ◽  
Fluidized Beds ◽  
Volatile Matter ◽  
Solid Fuels ◽  
In Situ Characterization ◽  
Flow Restriction ◽  
History Of ◽  
Fuel Particles

The characterization of volatile matter (VM) emission from solid fuel particles during fluidized bed combustion/gasification is relevant to reactor performance influencing the fate of VM as it results from competing phenomena of release, mixing/segregation and burn-out. The rate and the time-history of volatile matter release strongly affect axial segregation of fuel particles in the bed, favoring the establishment of the stratified combustion regime. On the other hand, the comparison between the devolatilization and radial solids mixing time scales affects the radial distribution of volatile matter across the reactor. Short devolatilization times determine VM release localized near feeding point. The knowledge of devolatilization kinetics, as determined by thermogravimetric analysis, does not take into account key process phenomena such as the effective time-temperature history of the devolatilizing particle. A novel and easy-to-use diagnostic technique for “in-situ” characterization of the devolatilization rate of fuel particles in gas fluidized beds is proposed in the present paper. It is based on the time-resolved measurement of pressure in a bench scale fluidized bed reactor equipped with a calibrated flow restriction at the exhaust. The procedure consists of the injection of a single fuel particle (or small batches of multiple particles) and continuous monitoring of the pressure in the reactor. The bed was kept at a constant temperature by external heating and fluidized with nitrogen. Gas pressure inside the reactor increases during devolatilization as a consequence of the increased flow rate, due to the emission of volatile matter, across the calibrated flow restriction at the exhaust. Experimental data are analyzed in the light of a model of the experiment based on the transient mass balance on the reactor volume referred to the fluidizing gas and to the volatile matter. The comparison between experimental pressure time series and model computations enables the characterization of the kinetic parameters of devolatilization rate for samples of different coals as well as of non-fossil solid fuels.

scholarly journals Neuronal migration genes and a familial translocation t(3;17): which genes are implicated in the phenotype?

2019 ◽  
Author(s):  
Meriam HADJ AMOR ◽  
Sarra Dimassi ◽  
Hanen Hannachi ◽  
Amel Taj ◽  
Adnene Mlika ◽  
...  
Keyword(s):  
Neuronal Migration ◽  
Critical Region ◽  
Fluorescent In Situ Hybridization ◽  
Array Comparative Genomic Hybridization ◽  
Gene Dosage ◽  
Comparative Genomic ◽  
History Of ◽  
Cytogenetic Characterization

Abstract Background: While Miller-Dieker syndrome critical region deletions are well known delineated anomalies, submicroscopic duplications in this region have recently emerged as a new distinctive syndrome. So far, only few cases have been described overlapping 17p13.3 duplications. Methods: In this study, we report on clinical and cytogenetic characterization of two new cases involving 17p13.3 and 3p26 chromosomal regions in two sisters with familial history of lissencephaly. Fluorescent In Situ Hybridization and array Comparative Genomic Hybridization were performed. Results: A deletion including the critical region of the Miller-Dieker syndrome of at least 2,9 Mb and a duplication of at least 3,6 Mb on the short arm of chromosome 3 were highlighted in one case. The opposite rearrangements, duplication 17p13.3 and deletion 3p were seen in the second case. This double chromosome aberration is the result of an adjacent 1:1 meiotic segregation of a maternal reciprocal translocation t(3;17)(p26.2;p13.3). Conclusions: 17p13.3 and 3p26 deletions have a clear range of phenotypic features while duplications still have uncertain clinical significance. However, we could suggest that regardless of the type of the rearrangement, the gene dosage and interactions of CNTN4, CNTN6 and CHL1 in the 3p26 and PAFAH1B1, YWHAE in 17p13.3 could result in different clinical spectrums.

scholarly journals Neuronal migration genes and a familial translocation t(3;17): Candidate genes implicated in the phenotype

2019 ◽  
Author(s):  
Meriam HADJ AMOR ◽  
Sarra Dimassi ◽  
Hanen Hannachi ◽  
Amel Taj ◽  
Adnene Mlika ◽  
...  
Keyword(s):  
Neuronal Migration ◽  
Critical Region ◽  
Fluorescent In Situ Hybridization ◽  
Array Comparative Genomic Hybridization ◽  
Gene Dosage ◽  
Comparative Genomic ◽  
History Of ◽  
Cytogenetic Characterization

Abstract Background: While Miller-Dieker syndrome critical region deletions are well known delineated anomalies, submicroscopic duplications in this region have recently emerged as a new distinctive syndrome. So far, only few cases have been described overlapping 17p13.3 duplications. Methods: In this study, we report on clinical and cytogenetic characterization of two new cases involving 17p13.3 and 3p26 chromosomal regions in two sisters with familial history of lissencephaly. Fluorescent In Situ Hybridization and array Comparative Genomic Hybridization were performed. Results: A deletion including the critical region of the Miller-Dieker syndrome of at least 2,9 Mb and a duplication of at least 3,6 Mb on the short arm of chromosome 3 were highlighted in one case. The opposite rearrangements, 17p13.3 duplication and 3p deletion were observed in the second case. This double chromosomal aberration is the result of an adjacent 1:1 meiotic segregation of a maternal reciprocal translocation t(3;17)(p26.2;p13.3). Conclusions: 17p13.3 and 3p26 deletions have a clear range of phenotypic features while duplications still have an uncertain clinical significance. However, we could suggest that regardless of the type of the rearrangement, the gene dosage and interactions of CNTN4, CNTN6 and CHL1 in the 3p26 and PAFAH1B1, YWHAE in 17p13.3 could result in different clinical spectrums.

scholarly journals Neuronal migration genes and a familial translocation t(3;17): Candidate genes implicated in the phenotype

2019 ◽  
Author(s):  
Meriam HADJ AMOR ◽  
Sarra Dimassi ◽  
Hanen Hannachi ◽  
Amel Taj ◽  
Adnene Mlika ◽  
...  
Keyword(s):  
Neuronal Migration ◽  
Critical Region ◽  
Fluorescent In Situ Hybridization ◽  
Array Comparative Genomic Hybridization ◽  
Gene Dosage ◽  
Comparative Genomic ◽  
History Of ◽  
Cytogenetic Characterization

Abstract Background: While Miller-Dieker syndrome critical region deletions are well known delineated anomalies, submicroscopic duplications in this region have recently emerged as a new distinctive syndrome. So far, only few cases have been described overlapping 17p13.3 duplications. Methods: In this study, we report on clinical and cytogenetic characterization of two new cases involving 17p13.3 and 3p26 chromosomal regions in two sisters with familial history of lissencephaly. Fluorescent In Situ Hybridization and array Comparative Genomic Hybridization were performed. Results: A deletion including the critical region of the Miller-Dieker syndrome of at least 2,9 Mb and a duplication of at least 3,6 Mb on the short arm of chromosome 3 were highlighted in one case. The opposite rearrangements, 17p13.3 duplication and 3p deletion were observed in the second case. This double chromosomal aberration is the result of an adjacent 1:1 meiotic segregation of a maternal reciprocal translocation t(3;17)(p26.2;p13.3). Conclusions: 17p13.3 and 3p26 deletions have a clear range of phenotypic features while duplications still have an uncertain clinical significance. However, we could suggest that regardless of the type of the rearrangement, the gene dosage and interactions of CNTN4, CNTN6 and CHL1 in the 3p26 and PAFAH1B1, YWHAE in 17p13.3 could result in different clinical spectrums.

scholarly journals Fluorination of arylboronic esters enabled by bismuth redox catalysis

Science ◽  
2020 ◽  
Vol 367 (6475) ◽  
pp. 313-317 ◽  
Author(s):  
Oriol Planas ◽  
Feng Wang ◽  
Markus Leutzsch ◽  
Josep Cornella
Keyword(s):  
Transition Metals ◽  
Active Catalyst ◽  
Reductive Elimination ◽  
Redox Cycle ◽  
Redox Catalysis ◽  
Acidic Properties ◽  
Bond Forming ◽  
Mechanistic Investigation ◽  
Boronic Esters

Bismuth catalysis has traditionally relied on the Lewis acidic properties of the element in a fixed oxidation state. In this paper, we report a series of bismuth complexes that can undergo oxidative addition, reductive elimination, and transmetallation in a manner akin to transition metals. Rational ligand optimization featuring a sulfoximine moiety produced an active catalyst for the fluorination of aryl boronic esters through a bismuth (III)/bismuth (V) redox cycle. Crystallographic characterization of the different bismuth species involved, together with a mechanistic investigation of the carbon-fluorine bond-forming event, identified the crucial features that were combined to implement the full catalytic cycle.

Fabrication and characterization of poly(3,4-ethylenedioxythiophene)/gold nanocomposite via in-situ redox cycle system

2005 ◽  
Vol 153 (1-3) ◽  
pp. 149-152 ◽  
Author(s):  
B.Y. Kim ◽  
M.S. Cho ◽  
Y.S. Kim ◽  
Y. Son ◽  
Y. Lee
Keyword(s):  
Redox Cycle ◽  
Cycle System ◽  
Fabrication And Characterization

The Use of Advanced Analytical Techniques for Characterization of the Chemical, Physical, and Crystallographic Nature of a Surface

1973 ◽  
Vol 31 ◽  
pp. 132-133 ◽  
Author(s):  
R. E. Herfert
Keyword(s):  
Surface Characterization ◽  
Analytical Techniques ◽  
X Ray Diffraction ◽  
Depth Of Penetration ◽  
X Ray ◽  
The Past ◽  
Transmission Electron ◽  
Scanning Electron

Studies of the nature of a surface, either metallic or nonmetallic, in the past, have been limited to the instrumentation available for these measurements. In the past, optical microscopy, replica transmission electron microscopy, electron or X-ray diffraction and optical or X-ray spectroscopy have provided the means of surface characterization. Actually, some of these techniques are not purely surface; the depth of penetration may be a few thousands of an inch. Within the last five years, instrumentation has been made available which now makes it practical for use to study the outer few 100A of layers and characterize it completely from a chemical, physical, and crystallographic standpoint. The scanning electron microscope (SEM) provides a means of viewing the surface of a material in situ to magnifications as high as 250,000X.

A very rapid in situ Kikuchi technique to determine relative crystal misorientation

1988 ◽  
Vol 46 ◽  
pp. 830-831
Author(s):  
J. I. Bennetch
Keyword(s):  
Electron Beam ◽  
Analytical Techniques ◽  
Superplastic Forming ◽  
The Other ◽  
Kikuchi Pattern ◽  
Kikuchi Line ◽  
Line Analysis

In a recent study of the superplastic forming (SPF) behavior of certain Al-Li-X alloys, the relative misorientation between adjacent (sub)grains proved to be an important parameter. It is well established that the most accurate way to determine misorientation across boundaries is by Kikuchi line analysis. However, the SPF study required the characterization of a large number of (sub)grains in each sample to be statistically meaningful, a very time-consuming task even for comparatively rapid Kikuchi analytical techniques.In order to circumvent this problem, an alternate, even more rapid in-situ Kikuchi technique was devised, eliminating the need for the developing of negatives and any subsequent measurements on photographic plates. All that is required is a double tilt low backlash goniometer capable of tilting ± 45° in one axis and ± 30° in the other axis. The procedure is as follows. While viewing the microscope screen, one merely tilts the specimen until a standard recognizable reference Kikuchi pattern is centered, making sure, at the same time, that the focused electron beam remains on the (sub)grain in question.

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