scholarly journals Chemoselective C–C σ-Bond Activation of Biphenylene

2020 ◽  
Author(s):  
Richard Y Kong ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Strain Analysis ◽  
Molecular Orbitals ◽  
Membered Ring ◽  
P System ◽  
Frontier Molecular Orbitals ◽  
Reaction Intermediate ◽  
Reaction Proceeds

The chemoselective cleavage of an arene ring in biphenylene is reported using an aluminium(I) complex. The reaction proceeds with complete integrity of the central 4-membered ring despite this ring containing the weakest C–C σ-bond in the hydrocarbon scaffold. A reaction intermediate derived from the (4+1) cycloaddition of the aluminium(I) complex to the p-system of biphenylene was isolated. Further experiments and DFT calculations suggest that this intermediate is involved in breaking of the C–C σ-bond. Activation strain analysis was used to understand the origins of the remarkable chemoselectivity of this system. Both the symmetry and diffuseness of the frontier molecular orbitals of the aluminium(I) fragment are implicated in its unusual reactivity with biphenylene.

scholarly journals The Chemoselective C–C σ-Bond Activation of the Arene Ring of Biphenylene

2020 ◽  
Author(s):  
Richard Y Kong ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Strain Analysis ◽  
Molecular Orbitals ◽  
Membered Ring ◽  
P System ◽  
Frontier Molecular Orbitals ◽  
Reaction Intermediate ◽  
Reaction Proceeds

The chemoselective cleavage of an arene ring in biphenylene is reported using an aluminium(I) complex. The reaction proceeds with complete integrity of the central 4-membered ring despite this ring containing the weakest C–C σ-bond in the hydrocarbon scaffold. A reaction intermediate derived from the (4+1) cycloaddition of the aluminium(I) complex to the p-system of biphenylene was isolated. Further experiments and DFT calculations suggest that this intermediate is involved in breaking of the C–C σ-bond. Activation strain analysis was used to understand the origins of the remarkable chemoselectivity of this system. Both the symmetry and diffuseness of the frontier molecular orbitals of the aluminium(I) fragment are implicated in its unusual reactivity with biphenylene.

scholarly journals Chemoselective C–C σ-Bond Activation of Biphenylene

2020 ◽  
Author(s):  
Richard Y Kong ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Strain Analysis ◽  
Molecular Orbitals ◽  
Membered Ring ◽  
P System ◽  
Frontier Molecular Orbitals ◽  
Reaction Intermediate ◽  
Reaction Proceeds

The chemoselective cleavage of an arene ring in biphenylene is reported using an aluminium(I) complex. The reaction proceeds with complete integrity of the central 4-membered ring despite this ring containing the weakest C–C σ-bond in the hydrocarbon scaffold. A reaction intermediate derived from the (4+1) cycloaddition of the aluminium(I) complex to the p-system of biphenylene was isolated. Further experiments and DFT calculations suggest that this intermediate is involved in breaking of the C–C σ-bond. Activation strain analysis was used to understand the origins of the remarkable chemoselectivity of this system. Both the symmetry and diffuseness of the frontier molecular orbitals of the aluminium(I) fragment are implicated in its unusual reactivity with biphenylene.

scholarly journals Palladium-Catalysed C–F Alumination of Fluorobenzenes: Mechanistic Diversity and Origin of Selectivity

2020 ◽  
Author(s):  
Feriel Rekhroukh ◽  
Wenyi Chen ◽  
Ryan Brown ◽  
Andrew J. P. White ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Oxidative Addition ◽  
Fluorine Content ◽  
Model Potential ◽  
Heterometallic Complex ◽  
Experimental Support ◽  
Highly Active ◽  
Reaction Proceeds ◽  
Directing Group

A palladium pre-catalyst, [Pd(PCy<sub>3</sub>)<sub>2</sub>] is reported for the efficient and selective C–F alumination of fluorobenzenes with the aluminium(I) reagent [{(ArNCMe)<sub>2</sub>CH}Al] (<b>1</b>, Ar = 2,6-di-iso-propylphenyl). The catalytic protocol results in the transformation of sp<sup>2</sup> C–F bonds to sp<sup>2</sup> C–Al bonds and provides a route into reactive organoaluminium complexes (<b>2a-h</b>) from fluorocarbons. The catalyst is highly active. Reactions proceed within 5 minutes at 25 ºC (and at appreciable rates at even –50 ºC) and the scope includes low-fluorine-content substrates such as fluorobenzene, difluorobenzenes and trifluorobenzenes. The reaction proceeds with complete chemoselectivity (C–F vs C–H) and high regioselectivities ( >90% for C–F bonds adjacent to the most acidic C–H sites). The heterometallic complex [Pd(PCy<sub>3</sub>)(<b>1</b>)<sub>2</sub>] was shown to be catalytically competent. Catalytic C–F alumination proceeds with a KIE of 1.1–1.3. DFT calculations have been used to model potential mechanisms for C–F bond activation. These calculations suggest that two competing mechanisms may be in operation. Pathway 1 involves a ligand-assisted oxidative addition to [Pd(<b>1</b>)<sub>2</sub>] and leads directly to the product. Pathway 2 involves a stepwise C–H to C–F functionalisation mechanism in which the C–H bond is broken and reformed along the reaction coordinate, allowing it to act as a directing group for the adjacent C–F site. This second mechanism explains the experimentally observed regioselectivity. Experimental support for this C–H activation playing a key role in C–F alumination was obtained by employing [{(MesNCMe)<sub>2</sub>CH}AlH<sub>2</sub>] (<b>3</b>, Mes = 2,4,6-trimethylphenyl) as a reagent in place of 1. In this instance, the kinetic C–H alumination intermediate could be isolated. Under catalytic conditions this intermediate converts to the thermodynamic C–F alumination product.

scholarly journals Palladium-Catalysed C–F Alumination of Fluorobenzenes: Mechanistic Diversity and Origin of Selectivity

2020 ◽  
Author(s):  
Feriel Rekhroukh ◽  
Wenyi Chen ◽  
Ryan Brown ◽  
Andrew J. P. White ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Oxidative Addition ◽  
Fluorine Content ◽  
Model Potential ◽  
Heterometallic Complex ◽  
Experimental Support ◽  
Highly Active ◽  
Reaction Proceeds ◽  
Directing Group

A palladium pre-catalyst, [Pd(PCy<sub>3</sub>)<sub>2</sub>] is reported for the efficient and selective C–F alumination of fluorobenzenes with the aluminium(I) reagent [{(ArNCMe)<sub>2</sub>CH}Al] (<b>1</b>, Ar = 2,6-di-iso-propylphenyl). The catalytic protocol results in the transformation of sp<sup>2</sup> C–F bonds to sp<sup>2</sup> C–Al bonds and provides a route into reactive organoaluminium complexes (<b>2a-h</b>) from fluorocarbons. The catalyst is highly active. Reactions proceed within 5 minutes at 25 ºC (and at appreciable rates at even –50 ºC) and the scope includes low-fluorine-content substrates such as fluorobenzene, difluorobenzenes and trifluorobenzenes. The reaction proceeds with complete chemoselectivity (C–F vs C–H) and high regioselectivities ( >90% for C–F bonds adjacent to the most acidic C–H sites). The heterometallic complex [Pd(PCy<sub>3</sub>)(<b>1</b>)<sub>2</sub>] was shown to be catalytically competent. Catalytic C–F alumination proceeds with a KIE of 1.1–1.3. DFT calculations have been used to model potential mechanisms for C–F bond activation. These calculations suggest that two competing mechanisms may be in operation. Pathway 1 involves a ligand-assisted oxidative addition to [Pd(<b>1</b>)<sub>2</sub>] and leads directly to the product. Pathway 2 involves a stepwise C–H to C–F functionalisation mechanism in which the C–H bond is broken and reformed along the reaction coordinate, allowing it to act as a directing group for the adjacent C–F site. This second mechanism explains the experimentally observed regioselectivity. Experimental support for this C–H activation playing a key role in C–F alumination was obtained by employing [{(MesNCMe)<sub>2</sub>CH}AlH<sub>2</sub>] (<b>3</b>, Mes = 2,4,6-trimethylphenyl) as a reagent in place of 1. In this instance, the kinetic C–H alumination intermediate could be isolated. Under catalytic conditions this intermediate converts to the thermodynamic C–F alumination product.

scholarly journals Synthesis, characterization and application of Ru(II) complexes containing pyridil ligands for dye-sensitized solar cells

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Osman Dayan ◽  
Namik Özdemir ◽  
Fahrettin Yakuphanoğlu ◽  
Zafer Şerbetci ◽  
Ali Bilici
Keyword(s):  
Solar Cells ◽  
Dft Calculations ◽  
Isonicotinic Acid ◽  
Dye Sensitized Solar Cells ◽  
Molecular Orbitals ◽  
Frontier Molecular Orbitals ◽  
Dye Sensitized ◽  
Current Voltage ◽  
Current Voltage Characteristics ◽  
Sensitized Solar Cells

AbstractIn this research, a series of Ru(II) complexes, ([Ru(1-7)(ina)(NCS)2] (1-7=5-[6-(5-mercapto-1,3,4-oxadiazol-2-yl)pyridin- 2-yl]-1,3,4-oxadiazole-2-thiol’s, ina=isonicotinic acid) were synthesized and characterized using different spectroscopic and analytic techniques, such as NMR, UV, IR, CV and CHN. Also, the new complexes were used in dye-sensitized solar cells (DSSC) as sensitizers. Current-voltage characteristics showed that the modifications of ligands clearly affected DSSC yield. Additionally, DFT calculations were performed and showed locations of frontier molecular orbitals of the complexes. While the locations of HOMO and HOMO – 1 orbitals are on Ru(II) metal center and SCN− ligands, the location of LUMO and LUMO + 1 orbitals are on the 1-7 ligands.

Pt-Pd Nanoalloy for the Unprecedented Activation of Carbon-Fluorine Bond at Low Temperature

2019 ◽  
Author(s):  
Raghu Nath Dhital ◽  
keigo nomura ◽  
Yoshinori Sato ◽  
Setsiri Haesuwannakij ◽  
Masahiro Ehara ◽  
...  
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Dft Calculations ◽  
Bond Activation ◽  
Mild Conditions ◽  
Selective Transformation ◽  
Rate Determining Step ◽  
Highly Active ◽  
Harsh Conditions ◽  
Reaction Profile

Carbon-Fluorine (C-F) bonds are considered the most inert organic functionality and their selective transformation under mild conditions remains challenging. Herein, we report a highly active Pt-Pd nanoalloy as a robust catalyst for the transformation of C-F bonds into C-H bonds at low temperature, a reaction that often required harsh conditions. The alloying of Pt with Pd is crucial to activate C-F bond. The reaction profile kinetics revealed that the major source of hydrogen in the defluorinated product is the alcoholic proton of 2-propanol, and the rate-determining step is the reduction of the metal upon transfer of the <i>beta</i>-H from 2-propanol. DFT calculations elucidated that the key step is the selective oxidative addition of the O-H bond of 2-propanol to a Pd center prior to C-F bond activation at a Pt site, which crucially reduces the activation energy of the C-F bond. Therefore, both Pt and Pd work independently but synergistically to promote the overall reaction

Prediction of Antiglycation Activity by Calculating the Energies of Frontier Molecular Orbitals for New 4-Hydroxy-1,4-Dihydroazolo[5,1-c]-1,2,4-Triazines Used as an Example

2020 ◽  
Vol 46 (6) ◽  
pp. 1278-1284
Author(s):  
R. A. Litvinov ◽  
R. A. Drokin ◽  
D. D. Shamshina ◽  
M. Yu. Kalenova ◽  
L. E. Usmianova ◽  
...  
Keyword(s):  
Molecular Orbitals ◽  
Frontier Molecular Orbitals

Polarized .pi.-frontier molecular orbitals. A method for predicting diastereofacial selectivities

1993 ◽  
Vol 115 (10) ◽  
pp. 4024-4030 ◽  
Author(s):  
Xiao Ling Huang ◽  
J. J. Dannenberg ◽  
Miquel Duran ◽  
Juan Bertran
Keyword(s):  
Molecular Orbitals ◽  
Frontier Molecular Orbitals
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