Search results for "steric"
showing 10 items of 476 documents
Formation of novel T-shaped NNN ligands via rare-earth metal-mediated Si-H activation.
2014
Reactions of silylamides [Ln{N(SiHMe2)2}3(thf)2] with sterically crowded terphenylamine DmpNH2 (Dmp = 2,6-Mes2C6H3 with Mes = 2,4,6-Me3C6H2) afforded via a template reaction the formation of a new tridentate ligand, and derived complexes of composition [LnN{SiMe2N(Dmp)}2] (Ln = Ce, Pr) were obtained. Usage of the even more bulky amine Ar*NH2 (Ar* = 2,6-Trip2C6H3 with Trip = 2,4,6-iPr3C6H2) yielded the free protonated ligand NH{SiMe2NH(Ar*)}2.
Palladium-Catalysed CH Bond Electrophilic Fluorination of Highly Substituted Arylpyrazoles: Experimental and DFT Mechanistic Insights
2015
A general protocol for palladium-catalysed CH mono- and di-fluorination of highly substituted arylpyrazoles is reported. Coupling pathways and substrate limitations are discussed in the light of complementary mechanistic experimental and density functional theory (DFT) studies. The mono- and di-ortho-fluorination of arylpyrazoles having substituted pyrazole groups and ortho-, meta-, or para-substituted arene moieties is achieved. Various pyrazole groups can efficiently promote the direct CH activation/fluorination of substrates bearing valuable reactive ester, cyano, halide and nitro functions. The presence of methoxy, methyl and trifluoromethyl is tolerated on the pyrazole directing groups…
Synthesis of a macrobicycle incorporating the tris(pyrazolyl)methane ligand.
2004
Steric crowding of the 3-position of tris(pyrazolyl)borate and -methane ligands has produced tetrahedral metal complexes with controlled reactivity. As an alternative, we propose to incorporate the tris(pyrazolyl)methane chelate in a macrobicyclic structure in order to create a cavity with well-defined dimensions and shape. Acid-catalyzed equilibration of excess of the new pyrazole 3-(1H-pyrazol-3-yl)benzenemethanethiol acetate with HC(3,5-Me(2)pz)(3) followed by hydrolysis affords a functionalized tris(pyrazolyl)methane, which reacts with 1,3,5-tris(bromomethyl)benzene in K(2)CO(3)/DMF to give the title compound. [structure: see text]
Architecture dependence on the steric constrains of the ligand in cyano-bridged copper(I) and copper(II)-copper(I) mixed-valence polymer compounds co…
2002
A family of cyano-bridged copper(II)-copper(I) mixed-valence polymers containing diamine ligands of formula [Cu(pn)(2)][Cu(2)(CN)(4)] (1, pn = 1,2-propanediamine), [Cu(2)(CN)(3)(dmen)] (2, dmen = N,N-dimethylethylenediamine), and [Cu(3)(CN)(4)(tmen)] (3, tmen = N,N,N',N'-tetramethylethylenediamine) have been prepared with the aim of analyzing how their architecture may be affected by steric constraints imposed by the diamine ligands. In the absence of diamine and with use of the voluminous NEt(4)(+) cation, the copper(I) polymer [NEt(4)][Cu(2)(CN)(3)] (4) forms. The structure of 1 consists of a three-dimensional diamond-related anionic framework host, [Cu(2)(CN)(4)](2-), and enclathrated [C…
Study of Confined 5-Aza[5]helicene in Ytterbium(III) Bis(2-ethylhexyl) Sulfosuccinate Reversed Micelles
2007
Some relevant physicochemical properties of 5-aza[5]helicene (H5) in solutions of ytterbium bis(2-ethylhexyl) sulfosuccinate (Yb(DEHSS)3) reversed micelles have been investigated by UV-vis-NIR, photoluminescence, and FT-IR techniques with the aim of emphasizing the role played by specific Yb(III)/H5 interactions and confinement effects as driving forces of its binding to reversed micelles, preferential solubilization site, and local photophysical properties. It has been found that the binding strength of 5-aza[5]helicene to reversed micelles, triggered by steric and orientational constrains as well as the water content, is mainly regulated by its interaction with the Yb(III) counterion. Mor…
Synthesis and structural characterisation of bulky heptaaromatic (hetero)aryl o-substituted s-aryltetrazines
2020
An expedient two-step synthesis produces in good yield polyaromatic heptacyclic (hetero)arylated o-substituted s-aryltetrazines (s-Tz) directly from diphenyl s-tetrazine. This methodology overcomes the steric limitations of classical Pinner-like syntheses encountered for o-functionalized s-Tz. A single step palladium-catalyzed N-directed C–H bond tetrahalogenation is followed by a Pd-catalyzed Suzuki (hetero)arylation that is achieved simultaneously on four sites. The single crystal X-ray diffraction structure of the resulting typical polyaromatic heptacyclic aromatic compound 3,6-bis(2,6-diphenyl)-1,2,4,5-tetrazine (3) is analyzed, together with R-functionalized peripheral phenyl derivativ…
The proton complex of a diaza-macropentacycle: structure, slow formation, and chirality induction by ion pairing with the optically active 1,1'-binap…
2008
The protonation of a sterically crowded [N2S6] macropentacycle (1) with 1 equiv of CF3SO3H in CDCl3 is slow and gives the singly (oo(+) [1 x H](+)) and doubly (o(+)o(+) [1 x 2H](2+)) protonated forms as kinetic products, the i(+)o form of [1 x H](+) being the thermodynamic product. i(+)o [1 x H](+) is C3 helically chiral in the solid state and in solution. The barrier to racemization (DeltaG(double dagger)) of the [1 x H](+) propeller is71 kJ mol(-1). The ammonium proton is encapsulated in the tetrahedral coordination sphere provided by the endo (i) nitrogen bridgehead atom and the three proximal thioether sulfurs, which makes [1 x H](+) a proton complex. Use of the optically active acid (R…
The in, out Asymmetric Pseudo-Triple Helical Form of a D3h Diaza-Macropentacycle
2007
A sterically encumbered [N(2)S(6)] macropentacycle (5) related to diazamacrobicycles and cryptands has been synthesized in 53% yield by the [1+1] condensation reaction between functionalized macrocyclic and macrotricyclic precursors. A macrononacycle (18) resulting from the corresponding [2+2] condensation was isolated in 7% yield from the reaction mixture. Both compounds showed broad features in their room-temperature (1)H NMR spectra, but their maximal average symmetry (D(3h) and D(2h), respectively) was achieved at high temperature (380 K). At low temperature (200 K, CD(2)Cl(2) solution), the macropentacycle is "frozen" to a single asymmetric (C1) conformation on the (1)H NMR time scale,…
Synthesis, microwave spectrum, quantum chemical calculations, and conformational composition of a novel primary phosphine, cyclopropylethynylphosphin…
2014
International audience; The microwave spectrum of cyclopropylethynylphosphine, C3H5C≡CPH2, has been investigated in the 26-120 GHz spectral region. The spectrum is dominated by very rich and complex a-type R-branch pile-ups. There must be insignificant steric interaction between the phosphino group and the cyclopropyl ring due to the long distance between these two groups. However, the phosphino group does not undergo free or nearly free internal rotation. Instead, the spectra of two distinct conformers were assigned. Both these two forms have CS symmetry. The symmetry plane bisects the cyclopropyl ring and the phosphino group in both conformers, and the lone electron pair of the phosphino …
Substrate-dependent fluorinations of highly functionalized cycloalkanes
2016
Abstract Substrate-dependent fluorinations of several highly functionalized cycloalkanes with multiple stereocentres were investigated. The synthetic transformations were based on selective functionalization of the ring C C bonds of the readily available bicyclic β-lactams by epoxidation and regioselective nucleophilic oxirane opening with azide or cyanide, followed by hydroxy–fluorine exchange with Deoxofluor. Depending on the substituents and their relative steric arrangement, the attempted fluorinations produced different types of substituted cycloalkanes. These selective, substrate-directed synthetic procedures and their presumed pathways towards interesting highly functionalized fluori…