scholarly journals Phosphorous(v) Lewis acids: water/base tolerant P3-trimethylated trications

2018 ◽  
Vol 54 (88) ◽  
pp. 12467-12470 ◽  
Author(s):  
J. M. Bayne ◽  
V. Fasano ◽  
K. M. Szkop ◽  
M. J. Ingleson ◽  
D. W. Stephan
Keyword(s):  
Lewis Acids ◽  
Methyl Groups ◽  
Water Base ◽  
Phosphonium Cations

The water/base intolerance of the previously reported electrophilic phosphonium cations has been overcome by replacing the labile electron-withdrawing groups generally attached to phosphorus (e.g. –F, –OAr, –CF3) with methyl groups.

Air- and water-stable Lewis acids: synthesis and reactivity of P-trifluoromethyl electrophilic phosphonium cations

2018 ◽  
Vol 54 (6) ◽  
pp. 662-665 ◽  
Author(s):  
V. Fasano ◽  
J. H. W. LaFortune ◽  
J. M. Bayne ◽  
M. J. Ingleson ◽  
D. W. Stephan
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Acid Catalysts ◽  
Bronsted Acid ◽  
Lewis Acid Catalysts ◽  
Reaction Conditions ◽  
Brönsted Acid ◽  
And Function ◽  
Water Alcohol ◽  
Phosphonium Cations

Electrophilic phosphonium cations (EPCs) containing a –CF3 group are stable to air, water, alcohol and strong Brønsted acid and function as Lewis acid catalysts without requiring anhydrous reaction conditions.

scholarly journals Crystal structures of titanium–aluminium and –gallium complexes bearing twoμ2-CH3units

2017 ◽  
Vol 73 (5) ◽  
pp. 691-693 ◽  
Author(s):  
Tim Oswald ◽  
Mira Diekmann ◽  
Annika Frey ◽  
Marc Schmidtmann ◽  
Rüdiger Beckhaus
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
Lewis Acids ◽  
Methyl Groups ◽  
X Ray Diffraction ◽  
X Ray ◽  
Methyl Methyl ◽  
Low Valent ◽  
Titanium Aluminium ◽  
Gallium Complexes

The isotypic crystal structures of two titanocene complexes containing anEMe3unit (E =Al, Ga; Me = methyl) with twoμ2-coordinating methyl groups, namely [μ-1(η5)-(adamantan-1-yl-2κC1)cycylopentadienyl]di-μ2-methyl-methyl-2κC-[1(η5)-pentamethylcyclopentadienyl]aluminiumtitanium(III), [AlTi(CH3)3(C10H15)(C15H18)], and [μ-1(η5)-(adamantan-1-yl-2κC1)cycylopentadienyl]di-μ2-methyl-methyl-2κC-[1(η5)-pentamethylcyclopentadienyl]galliumtitanium(III), [GaTi(CH3)3(C10H15)(C15H18)], are reported. Reacting a dinuclear nitrogen-bridged low-valent titanium(III) complex with the Lewis acids AlMe3or GaMe3results in the loss of molecular dinitrogen and the formation of two monomeric titanocene(III) fragments bearing twoμ2-bridging methyl groups. Single crystal X-ray diffraction reveals the formation of a newE—C bond involving the pentafulvene ligand while the bridging and terminal methyl groups remain intact.

The use of homogeneous and heterogeneous Lewis acids to catalyse the photoisomerizations of phenols

1985 ◽  
Vol 63 (12) ◽  
pp. 3449-3455 ◽  
Author(s):  
Satish K. Chadda ◽  
Ronald F. Childs
Keyword(s):  
Oxygen Atom ◽  
Lewis Acid ◽  
Equilibrium Position ◽  
Lewis Acids ◽  
Methyl Groups ◽  
Substituted Phenols ◽  
Keto Form ◽  
Ring Carbon ◽  
Bicyclic Ketones

The reaction of methyl substituted phenols with CH2Cl2 solutions of Al2Br6, leads to the formation of two types of complexes. In both of these the aluminum is bound to the oxygen atom of the phenol but they differ in that the OH proton can either remain on oxygen, oxonium complex, or migrate to one, usually the para, ring carbon, keto complex. The equilibrium position between the two types of complex depends on the position of the methyl groups. Irradiation of a complex of the keto type leads initially to the formation of a complexed bicyclo[3.1.0]hexenone and subsequently to the formation of an isomeric complexed phenol. Only in the case of the tetramethylphenols is the yield of the bicyclic ketone high enough to warrant the use of this photoisomerization as a preparative procedure, although the technique can be used to isomerize a range of phenols to their 4-substituted isomers. The photoisomerizations are not restricted to the use of a homogeneous Lewis acid such as Al2Br6 but heterogeneous aluminosilicates can also be used. The adsorption of 2,3,5,6-tetramethylphenol,1h, on an aluminosilicate was monitored quantitatively and it was shown that a monolayer was formed in which the phenol was at least partially present in the keto form. Irradiation of 1h in the presence of stirred slurries of the aluminosilicate led to the formation of 2,3,4,6-tetramethylphenol. No bicyclic ketones were present in the contacting solution but traces were detected on the catalyst when the irradiations were carried out on adsorbed material in the absence of a solvent. In the case of heterogeneous acids, the selectivity in the adsorption of the starting phenol and the photoproducts is important in determining the composition of the final mixture

scholarly journals Methyl groups as widespread Lewis bases in noncovalent interactions

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Oliver Loveday ◽  
Jorge Echeverría
Keyword(s):  
Electron Density ◽  
Lewis Acids ◽  
Alkaline Earth ◽  
Noncovalent Interactions ◽  
Theoretical Calculations ◽  
Methyl Groups ◽  
Halogen Bonds ◽  
Common Pattern ◽  
Lewis Bases ◽  
Significant Strength

AbstractIt is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding. Here, we show that methyl groups, when bound to atoms less electronegative than carbon, can counterintuitively participate in noncovalent interactions as electron density donors. Thousands of experimental structures are found in which methyl groups behave as Lewis bases to establish alkaline, alkaline earth, triel, tetrel, pnictogen, chalcogen and halogen bonds. Theoretical calculations confirm the high directionality and significant strength of the interactions that arise from a common pattern based on the electron density holes model. Moreover, despite the absence of lone pairs, methyl groups are able to transfer charge from σ bonding orbitals into empty orbitals of the electrophile to reinforce the attractive interaction.

Cyclisation intramoléculaire des acides benzyl-2 pentène-4 oïques. Préparation de quelques tétraméthylnaphtalènes

1967 ◽  
Vol 45 (11) ◽  
pp. 1267-1274 ◽  
Author(s):  
P. Canonne ◽  
A. Regnault
Keyword(s):  
Lewis Acids ◽  
Aluminium Chloride ◽  
Methyl Groups ◽  
Secondary Reactions

The cyclization of 2-benzyl-4-pentenoic acids, catalyzed by protonic and Lewis acids, resulted in the formation of variable quantities of α-benzyl-γ-valerolactones and tetrahydronaphthalenecarboxylic acids (65 – 85%) which, after reduction and dehydrogenation, yielded tetramethylnaphthalenes substituted in the 1,3-positions. 1,3,5,7-Tetramethylnaphthalene, in particular, had not as yet been described. Aluminium chloride favors cyclization and does not give rise to lactonization, but it induces secondary reactions such as the migration of methyl groups.

Reduction of carbon impurities in aluminium nitride from time-resolved chemical vapour deposition using trimethylaluminum

2020 ◽  
Author(s):  
Polla Rouf ◽  
Pitsiri Sukkaew ◽  
Lars Ojamäe ◽  
Henrik Pedersen
Keyword(s):  
Chemical Vapour Deposition ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Aluminium Nitride ◽  
Methyl Groups ◽  
Time Resolved ◽  
Thermally Induced ◽  
Light Emitting ◽  
Carbon Impurities ◽  
Wide Range

<p>Aluminium nitride (AlN) is a semiconductor with a wide range of applications from light emitting diodes to high frequency transistors. Electronic grade AlN is routinely deposited at 1000 °C by chemical vapour deposition (CVD) using trimethylaluminium (TMA) and NH<sub>3</sub> while low temperature CVD routes to high quality AlN are scarce and suffer from high levels of carbon impurities in the film. We report on an ALD-like CVD approach with time-resolved precursor supply where thermally induced desorption of methyl groups from the AlN surface is enhanced by the addition of an extra pulse, H<sub>2</sub>, N<sub>2</sub> or Ar between the TMA and NH<sub>3</sub> pulses. The enhanced desorption allowed deposition of AlN films with carbon content of 1 at. % at 480 °C. Kinetic- and quantum chemical modelling suggest that the extra pulse between TMA and NH<sub>3</sub> prevents re-adsorption of desorbing methyl groups terminating the AlN surface after the TMA pulse. </p>

Detection of Chemical Exchange in Methyl Groups of Macromolecules

2019 ◽  
Author(s):  
Michelle Gill ◽  
Andrew Hsu ◽  
Arthur G. Palmer, III
Keyword(s):  
Relaxation Rate ◽  
Chemical Exchange ◽  
Double Quantum ◽  
Methyl Groups ◽  
Multiple Quantum ◽  
Relaxation Data ◽  
E Coli ◽  
Methyl Trosy ◽  
Dynamics Simulations ◽  
Exchange Broadening

<div> <div> <div> <p>The zero- and double-quantum methyl TROSY Hahn-echo and the methyl <sup>1</sup>H-<sup>1</sup>H dipole- dipole cross-correlation nuclear magnetic resonance experiments enable estimation of multiple quantum chemical exchange broadening in methyl groups in proteins. The two relaxation rate constants are established to be linearly dependent using molecular dynamics simulations and empirical analysis of experimental data. This relationship allows chemical exchange broadening to be recognized as an increase in the Hahn-echo relaxation rate constant. The approach is illustrated by analyzing relaxation data collected at three temperatures for <i>E. coli </i>ribonuclease HI and by analyzing relaxation data collected for different cofactor and substrate complexes of <i>E. coli </i>AlkB. </p> </div> </div> </div>

The synthesis and stereochemistry of the ternary cobalt(III) complex with a stereospecific ligand derived from (S)-leucine

1986 ◽  
Vol 51 (2) ◽  
pp. 318-326 ◽  
Author(s):  
Milan Strašák ◽  
Pavol Novomeský
Keyword(s):  
Ir Spectroscopy ◽  
Aqueous Medium ◽  
Absorption Spectroscopy ◽  
Absolute Configuration ◽  
Nmr Spectra ◽  
Methyl Groups ◽  
Electron Absorption Spectroscopy ◽  
Electron Absorption ◽  
C Nmr

A new stereospecific ligand, ethylenediamine-N,N'-di(S)-α-isocapronic acid, was synthesized by condensation of (S)-leucine with 1,2-dibromoethane in alkaline aqueous medium. It follows from the 1H and 13C NMR spectra that the terminal methyl groups are chemically and magnetically nonequivalent. Of the four theoretically possible isomers of the ternary cobalt (III) complex with ethylenediamine, separation on catex yielded only one, whose absolute configuration was determined by a combination of 1H and 13C NMR, electron absorption spectroscopy and CD and IR spectroscopy.

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