Search results for "Reactivity"
showing 10 items of 880 documents
Proline-Modified Porphyrin Catalysts for Enantioselective Epoxidations: Design, Synthesis, and Reactivity
2004
International audience; The syntheses of various strapped and −picket-fence× chiral porphyrins are described, and their reactivities towards the enantioselective epoxidation of alkenes are reported. Four L-proline residues provide the chiralityfor the various meso-substituted catalysts, which differ by either the spatial arrangement of the stereogenic centers or the nature and length of the straps. The resulting bridged structures possess four amide linkages ineach strap, leading to highly rigid molecules with well-defined geometries whereas the strapped Fe catalysts gave rise to only moderate enantioselectivities, the C2-symmetrical ones being superior to the D2-symmetrical compounds. The …
Electron-Sponge Behavior, Reactivity and Electronic Structures of Cobalt-Centered Cubic Co9Te6(CO)8 Clusters
2008
Extended investigations of the reaction sequence [Cp′2Nb(Te2)H]/CH3Li/[Co2(CO)8] (Cp′ = tBuC5H4) led to the identification of Lin[3] {3 = [Co9Te6(CO)8]; n = 1, 2} salts through their transformation with [PPN]Cl into [PPN]n[3] (PPN = Ph3PNPPh3). These compounds form in the solid state columnar ([PPN][3]) or undulated 2D ([PPN]2[3]) supramolecular networks. Electrochemical studies of [Cp*2Nb(CO)2][3] (Cp* = C5Me5) or [Na(THF)6][3] revealed the presence of the redox couples [3]–/[3]2–/[3]3–/[3]4–/[3]5– regardless of the nature of the cation, whereas in the anodic part oxidative degradation of the cluster takes place. This behavior is in agreement with the observation that [3]– containing salts…
Towards the synthesis of substituted porphyrins by a pyridyl group bearing a reactive functionality
2010
Pyridyl-substituted porphyrins bearing a reactive functionality were prepared via Suzuki cross-coupling reactions and resulted in very good yields. These compounds are precursors of new porphyrin architectures able to coordinate two metals: one in the porphyrin core and the second around the pyridyl moiety. During the coupling reactions, a higher reactivity of a chloro picolyl group was evidenced compared to a bromo function on the same reacting molecule.
Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of S N Ar Chemistry
2020
The reactivity of the electron-rich anionic Al(I) ('aluminyl') compound K 2 [(NON)Al] 2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di- tert -butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C-H activation chemistry with n -butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical S N Ar chemistry, which implies the destabilization of transition states featuring electron-donating groups in either the ortho or the para positions. In the cases of tolu…
Squaramide-Catalyzed Asymmetric aza-Friedel-Crafts/N,O-Acetalization Domino Reactions Between 2-Naphthols and Pyrazolinone Ketimines
2017
N-Boc ketimines derived from pyrazolin-5-ones were explored to develop an unprecedented domino aza-Friedel-Crafts/N,O-acetalization reaction with 2-naphthols. The novel method requires a catalyst loading of only 0.5 mol % of a bifunctional squaramide catalyst, is scalable to gram amounts, and provides a new series of furanonaphthopyrazolidinone derivatives bearing two vicinal tetra-substituted stereogenic centers in excellent yields (95-98 %) and stereoselectivity (>99:1 d.r. and 97-98 % ee). A different reactivity was observed in the case of 1-naphthols and other electron-rich phenols, which led to the aza-Friedel-Crafts adducts in 70-98 % yield and 47-98 % ee.
Isolating reactive metal-based species in Metal-Organic Frameworks - viable strategies and opportunities.
2021
Structural insight into reactive species can be achieved via strategies such as matrix isolation in frozen glasses, whereby species are kinetically trapped, or by confinement within the cavities of host molecules. More recently, Metal–Organic Frameworks (MOFs) have been used as molecular scaffolds to isolate reactive metal-based species within their ordered pore networks. These studies have uncovered new reactivity, allowed observation of novel metal-based complexes and clusters, and elucidated the nature of metal-centred reactions responsible for catalysis. This perspective considers strategies by which metal species can be introduced into MOFs and highlights some of the advantages and lim…
Vinyl sulfone building blocks in covalently reversible reactions with thiols
2015
In the present study we use quantum-chemical calculations to investigate how the reactivity of vinyl sulfone-based compounds can be modified from an irreversible to a reversible reaction with thiols. Based on the predictions from theory, an array of nine different vinyl sulfones with systematically varying substitution pattern was synthesized and their crystal structures were determined. Subsequent Hirshfeld surface analyses employing the principle of electrostatic complementarity aid the understanding of the crystal packing of the synthesized compounds. Reactivity studies against the nucleophile 2-phenylethanethiol mirror the properties predicted by the quantum-chemical computations in sol…
Synthesis, reactivity and structural studies of selenide bridged carboranyl compounds.
2006
Reaction of the lithium salt Li[1-R-1,2-closo-C(2)B(10)H(10)] with selenium under mild conditions, followed by hydrolysis gave the diselenide compound (1-Se-2-R-1,2-closo-C(2)B(10)H(10))(2) in contrast to the well-reported mercapto compounds 1-SH-2-R-1,2-closo-C(2)B(10)H(10) obtained using a similar synthetic procedure. Details for the preparation and X-ray structural characterisation of the new compounds (2-Me-1,2-closo-C(2)B(10)H(10))(2)Se, (1-Se-2-R-1,2-closo-C(2)B(10)H(10))(2) (R = Me, Ph, ) are specified. To further explore the mechanism of the dimerization reaction, the complex [Au(1-Se-2-Me-1,2-closo-C(2)B(10)H(10))(PPh(3))] was synthesized, confirming the existence of the intermedia…
N-Acyl-glutarimides: Effect of Glutarimide Ring on the Structures of Fully Perpendicular Twisted Amides and N–C Bond Cross-Coupling
2020
N-Acyl-glutarimides have emerged as the most reactive precursors for N-C(O) bond cross-coupling reactions to date, wherein the reactivity is driven by ground-state destabilization of the amide bond. Herein, we report a full study on the effect of a glutarimide ring on the structures, electronic properties, and reactivity of fully perpendicular N-acyl-glutarimide amides. Most notably, this report demonstrates the generality of deploying N-acyl-glutarimides to achieve full twist of the acyclic amide bond, and results in the discovery of N-acyl-glutarimide amide with an almost perfect twist value, τ = 89.1°. X-ray structures of five new N-acyl-glutarimides are reported. Reactivity studies in t…
A metal-free and regioselective approach to (Z)-β-fluorovinyl sulfones and their chemoselective hydrogenation to β-fluoroalkyl sulfones
2018
Abstract A highly regioselective, metal-free hydrofluorination reaction of alkynyl sulfones was developed using TBAF—one of the cheapest and most commonly available fluoride sources. In addition, the reactivity of the resulting β-fluorovinyl sulfones was studied, focusing on their selective hydrogenation reaction. Both β-fluorovinyl sulfones and their hydrogenation products β-fluoroalkyl sulfones may find applications in medicinal and agrochemical sciences.