Hindered Rotation in New Air-Stable Ruthenium Olefin Metathesis Catalysts with Chromanylmethylidene Ligands

2009 ◽  
Vol 62 (10) ◽  
pp. 1363 ◽  
Author(s):  
Agnieszka Hryniewicka ◽  
Jacek W. Morzycki ◽  
Leszek Siergiejczyk ◽  
Stanisław Witkowski ◽  
Jacek Wójcik ◽  
...  
Keyword(s):  
Olefin Metathesis ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Asymmetric Induction ◽  
Dynamic Nmr ◽  
Nmr Analysis ◽  
Ring Closing Metathesis ◽  
Hindered Rotation ◽  
Metathesis Catalysts ◽  
First Time

Three new ruthenium complexes with chromanylmethylidene ligands were synthesized and dynamic NMR analysis of these compounds was carried out. The activation energy for the C–Ru rotation was measured for the first time and found to be of ~60 kJ mol–1. The complexes may potentially serve as latent catalysts for olefin metathesis – they promote the simple ring-closing metathesis reactions very slowly at room temperature, but are much more active at slightly elevated temperatures. No asymmetric induction was observed when the chiral α-tocopherol-derived catalyst was used.

scholarly journals Preparation of Ruthenium Olefin Metathesis Catalysts Immobilized on MOF, SBA-15, and 13X for Probing Heterogeneous Boomerang Effect

Catalysts ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 438 ◽  
Author(s):  
Artur Chołuj ◽  
Wojciech Nogaś ◽  
Michał Patrzałek ◽  
Paweł Krzesiński ◽  
Michał J. Chmielewski ◽  
...  
Keyword(s):  
Olefin Metathesis ◽  
Metal Organic Framework ◽  
Chemical Production ◽  
Metathesis Reaction ◽  
Solid Supports ◽  
13X Zeolite ◽  
Boomerang Effect ◽  
Metal Organic ◽  
Metathesis Catalysts ◽  
First Time

Promoted by homogeneous Ru-benzylidene complexes, the olefin metathesis reaction is a powerful methodology for C-C double bonds formation that can find a number of applications in green chemical production. A set of heterogeneous olefin metathesis pre-catalysts composed of ammonium-tagged Ru-benzylidene complexes 4 (commercial FixCat™ catalyst) and 6 (in-house made) immobilized on solid supports such as 13X zeolite, metal-organic framework (MOF), and SBA-15 silica were obtained and tested in catalysis. These hybrid materials were doped with various amounts of ammonium-tagged styrene derivative 5—a precursor of a spare benzylidene ligand—in order to enhance pre-catalyst regeneration via the so-called release-return “boomerang effect”. Although this effect was for the first time observed inside the solid support, we discovered that non-doped systems gave better results in terms of the resulting turnover number (TON) values, and the most productive were hybrid catalysts composed of 4@MOF, 4@SBA-15, and 6@SBA-15.

scholarly journals High Temperature Hardness of Bulk Single Crystal GaN

2000 ◽  
Vol 5 (S1) ◽  
pp. 343-348
Author(s):  
I. Yonenaga ◽  
T. Hoshi ◽  
A. Usui
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Room Temperature ◽  
Applied Load ◽  
Elevated Temperatures ◽  
Mechanical Stability ◽  
Bulk Single Crystal ◽  
Indentation Method ◽  
First Time ◽  
High Mechanical Stability

The hardness of single crystal GaN (gallium nitride) at elevated temperature is measured for the first time and compared with other materials. A Vickers indentation method was used to determine the hardness of crack-free GaN samples under an applied load of 0.5N in the temperature range 20 - 1200°C. The hardness is 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures GaN shows higher hardness than Si and GaAs. A high mechanical stability for GaN at high temperature is deduced.

scholarly journals Stable CAAC-based Ruthenium Complexes for Dynamic Olefin Metathesis Under Mild Conditions

2021 ◽  
Author(s):  
Oleksandr Kravchenko ◽  
Brian J.J. Timmer ◽  
Maurice Biedermann ◽  
Andrew Kentaro Inge ◽  
Olof Ramstrom
Keyword(s):  
Olefin Metathesis ◽  
High Stability ◽  
Room Temperature ◽  
Functional Group ◽  
Biologically Active ◽  
Dynamic Covalent Chemistry ◽  
Mild Conditions ◽  
Cross Metathesis ◽  
Potential Applications ◽  
Metathesis Catalysts

<p>A series of olefin metathesis catalysts bearing cyclic (alkyl)(amino)carbene (CAAC) ligands of varying size and steric demand has been synthesized and evaluated in ring-closing-, self-, and cross-metathesis reactions at room temperature. The catalysts were also probed for potential applications in dynamic covalent chemistry. The majority of the catalysts showed high stability, and remained active in the reaction mixtures for several days, including in methanol-based solutions. Higher temperatures could be used to control the reactivity towards sterically challenging substrates, enabling formation of tetrasubstituted olefins. The CAAC complexes exhibited remarkable functional group tolerance towards heteroaromatic and nucleophilic additives, making them potentially useful in the screening of biologically active compounds.</p>

scholarly journals Profluorescent substrates for the screening of olefin metathesis catalysts

2015 ◽  
Vol 11 ◽  
pp. 1886-1892 ◽  
Author(s):  
Raphael Reuter ◽  
Thomas R Ward
Keyword(s):  
Olefin Metathesis ◽  
Fluorescent Assay ◽  
Ring Closing Metathesis ◽  
Plate Assay ◽  
Metathesis Catalysts

Herein we report on a 96-well plate assay based on the fluorescence resulting from the ring-closing metathesis of two profluorophoric substrates. To demonstrate the validity of the approach, four commercially available ruthenium-metathesis catalysts were evaluated in six different solvents. The results from the fluorescent assay agree well with HPLC conversions, validating the usefulness of the approach.

High Temperature Hardness of Bulk Single Crystal GaN

1999 ◽  
Vol 595 ◽  
Author(s):  
I. Yonenaga ◽  
T. Hoshi ◽  
A. Usui
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Room Temperature ◽  
Applied Load ◽  
Elevated Temperatures ◽  
Mechanical Stability ◽  
Bulk Single Crystal ◽  
Indentation Method ◽  
First Time ◽  
High Mechanical Stability

AbstractThe hardness of single crystal GaN (gallium nitride) at elevated temperature is measured for the first time and compared with other materials. A Vickers indentation method was used to determine the hardness of crack-free GaN samples under an applied load of 0.5N in the temperature range 20 - 1200°C. The hardness is 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures GaN shows higher hardness than Si and GaAs. A high mechanical stability for GaN at high temperature is deduced.

9 kV 4H-SiC IGBTs with 88 mΩ·cm2 of R diff, on

2007 ◽  
Vol 556-557 ◽  
pp. 771-774 ◽  
Author(s):  
Qing Chun Jon Zhang ◽  
Charlotte Jonas ◽  
Bradley Heath ◽  
Mrinal K. Das ◽  
Sei Hyung Ryu ◽  
...  
Keyword(s):  
High Temperature ◽  
Threshold Voltage ◽  
High Power ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Gate Bias ◽  
Channel Mobility ◽  
Fast Switching ◽  
Blocking Voltage ◽  
First Time

SiC IGBTs are suitable for high power, high temperature applications. For the first time, the design and fabrication of 9 kV planar p-IGBTs on 4H-SiC are reported in this paper. A differential on-resistance of ~ 88 m(cm2 at a gate bias of –20 V is achieved at 25°C, and decreases to ~24.8 m(cm2 at 200°C. The device exhibits a blocking voltage of 9 kV with a leakage current density of 0.1 mA/cm2. The hole channel mobility is 6.5 cm2/V-s at room temperature with a threshold voltage of –6.5 V resulting in enhanced conduction capability. Inductive switching tests have shown that IGBTs feature fast switching capability at both room and elevated temperatures.

scholarly journals Stable CAAC-based Ruthenium Complexes for Dynamic Olefin Metathesis Under Mild Conditions

2021 ◽  
Author(s):  
Oleksandr Kravchenko ◽  
Brian J.J. Timmer ◽  
Maurice Biedermann ◽  
Andrew Kentaro Inge ◽  
Olof Ramstrom
Keyword(s):  
Olefin Metathesis ◽  
High Stability ◽  
Room Temperature ◽  
Functional Group ◽  
Biologically Active ◽  
Dynamic Covalent Chemistry ◽  
Mild Conditions ◽  
Cross Metathesis ◽  
Potential Applications ◽  
Metathesis Catalysts

<p>A series of olefin metathesis catalysts bearing cyclic (alkyl)(amino)carbene (CAAC) ligands of varying size and steric demand has been synthesized and evaluated in ring-closing-, self-, and cross-metathesis reactions at room temperature. The catalysts were also probed for potential applications in dynamic covalent chemistry. The majority of the catalysts showed high stability, and remained active in the reaction mixtures for several days, including in methanol-based solutions. Higher temperatures could be used to control the reactivity towards sterically challenging substrates, enabling formation of tetrasubstituted olefins. The CAAC complexes exhibited remarkable functional group tolerance towards heteroaromatic and nucleophilic additives, making them potentially useful in the screening of biologically active compounds.</p>

scholarly journals Halide exchanged Hoveyda-type complexes in olefin metathesis

2010 ◽  
Vol 6 ◽  
pp. 1091-1098 ◽  
Author(s):  
Julia Wappel ◽  
César A Urbina-Blanco ◽  
Mudassar Abbas ◽  
Jörg H Albering ◽  
Robert Saf ◽  
...  
Keyword(s):  
Olefin Metathesis ◽  
Ring Opening ◽  
Catalytic Performance ◽  
Ring Closing Metathesis ◽  
Cross Metathesis ◽  
Metathesis Reactions ◽  
Metathesis Catalysts

The aims of this contribution are to present a straightforward synthesis of 2nd generation Hoveyda-type olefin metathesis catalysts bearing bromo and iodo ligands, and to disclose the subtle influence of the different anionic co-ligands on the catalytic performance of the complexes in ring opening metathesis polymerisation, ring closing metathesis, enyne cycloisomerisation and cross metathesis reactions.

Inside the black box — Perspectives on transformations in catalysis

2008 ◽  
Vol 86 (10) ◽  
pp. 931-941 ◽  
Author(s):  
Deryn E Fogg
Keyword(s):  
Green Chemistry ◽  
Olefin Metathesis ◽  
Catalyst Activity ◽  
Black Box ◽  
Tandem Catalysis ◽  
Ring Closing Metathesis ◽  
Metathesis Catalysts ◽  
Tandem Metathesis

Tandem catalysis and olefin metathesis are powerful tools in the development of sustainable synthetic practices. This Award Lecture describes our advances in designing new tandem metathesis-hydrogenation methodologies for the synthesis of “designer materials” and Ru-pseudohalide metathesis catalysts that amplify opportunities for tuning catalyst activity, selectivity, and lifetime. Also discussed is the operation of a previously unrecognized oligomerization-backbiting pathway in ring-closing metathesis of conformationally flexible α,ω-dienes, which has important implications for the sustainable synthesis of medium and large rings.Key words: tandem catalysis, green chemistry, olefin metathesis, ring-closing metathesis, mechanism.

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