Search results for "ta116"
showing 10 items of 942 documents
Synthesis of densely functionalized cispentacin derivatives through selective aziridination and aziridine opening reactions: Orthogonally protected d…
2014
A novel substrate-directed synthetic route to a series of highly functionalized, orthogonally protected di- or triaminocyclopentanecarboxylate derivatives with multiple chiral centres from an unsaturated bicyclic β-lactam has been accomplished by applying stereoselective ring C–C double bond aziridination with chloramine-T and phenyltrimethylammonium tribromide, followed by regioselective aziridine opening with different N,O nucleophiles and hydrides. The functionalization strategy was successfully extended for access to enantiomerically pure orthogonally protected triaminocarboxylates.
Direct observation of a borane-silane complex involved in frustrated Lewis-pair-mediated hydrosilylations.
2014
Perfluorarylborane Lewis acids catalyse the addition of silicon-hydrogen bonds across C=C, C=N and C=O double bonds. This 'metal-free' hydrosilylation has been proposed to occur via borane activation of the silane Si-H bond, rather than through classical Lewis acid/base adducts with the substrate. However, the key borane/silane adduct had not been observed experimentally. Here it is shown that the strongly Lewis acidic, antiaromatic 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene forms an observable, isolable adduct with triethylsilane. The equilibrium for adduct formation was studied quantitatively through variable-temperature NMR spectroscopic investigations. The interactio…
Synthesis of novel functionalized cispentacins through C–C oxidative cleavage of diendo-norbornene β-amino acid
2013
Difunctionalized cispentacin derivatives with two new stereogenic centres have been synthesized from a diendo-norbornene β-amino acid in a stereocontrolled route, involving C–C double bond functionalization by dihydroxylation, followed by oxidative ring cleavage and transformation of the dialdehyde intermediates through a Wittig reaction.
Encapsulation of secondary and tertiary ammonium salts by resorcinarenes and pyrogallarenes: the effect of size and charge concentration
2015
The binding of different categories of alkyl ammonium (secondary and tertiary mono- and di-ammonium) salts with resorcinarenes and a pyrogallarene through weak interactions was analysed in all phases. 1H NMR spectroscopy and electrospray ionisation mass spectrometry were utilized in analysing the complexes in solution and in the gas phase, respectively. The 1H NMR titration studies in methanol-d4 reveal that the association constants for the 1:1 complexes vary according to the electronic properties of the hosts as well as the size, geometric orientation and charge concentration of the guest cations with binding constants of up to 950 M−1 in some cases. Mass spectrometry reveals 1:1 monomeri…
Synthesis and photophysical properties of hyperbranhced polyfluorenes containing 2,4,6-tris(tiophen-2-yl)-1,3,5-triazine as the core
2011
A series of new hyperbranched polymers containing a 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine core unit and polyfluorene chain arms have been synthesized via Suzuki coupling, and characterized by NMR, IR and GPC. All the polymers exhibit good thermal stability with a high decomposition temperature. By changing the 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine/fluorene ratio the UV-vis absorption and emission spectra can be partially tuned. It has been found that the polymers containing a low ratio of 2,4,6-tris(thiophen-2-yl)-1,3,5-triazine units (P1-P3) have an absorption maximum around 385 nm, localized in the polyfluorene chain, and a shoulder around 425 nm ascribable to a charge transfer stat…
Complexation of enantiomerically pure tetraalkylammonium cations by ethyl resorcinarene
2013
Molecular recognition via weak interactions of three enantiopure tetraalkylammonium cations 2–4 by ethyl resorcinarene 1 was studied in the solid state using single-crystal X-ray diffraction, in solution by proton nuclear magnetic resonance spectroscopy (1H NMR) titration and in the gas phase using electrospray ionisation mass spectrometry. The 1H NMR titration studies reveal the association constants for the 1:1 complexes to vary according to the size and electronic properties of the alkyl groups of the guest cations. In the solid state, the resorcinarene is deprotonated and the X-ray structure confirms the 1:1 complex 2+@1− to be held together by multiple cation…π and C–H…π interactions.…
Counterion influence on the N–I–N halogen bond
2015
A detailed investigation of the influence of counterions on the [N–I–N]+ halogen bond in solution, in the solid state and in silico is presented. Translational diffusion coefficients indicate close attachment of counterions to the cationic, three-center halogen bond in dichloromethane solution. Isotopic perturbation of equilibrium NMR studies performed on isotopologue mixtures of regioselectively deuterated and nondeuterated analogues of the model system showed that the counterion is incapable of altering the symmetry of the [N–I–N]+ halogen bond. This symmetry remains even in the presence of an unfavorable geometric restraint. A high preference for the symmetric geometry was found also in …
Halonium ions as halogen bond donors in the solid state [xl2]y complexes
2015
The utilization of halogen bonding interactions is one of the most rapidly developing areas of supramolecular chemistry. While the other weak non-covalent interactions and their influence on the structure and chemistry of various molecules, complexes, and materials have been investigated extensively, the understanding, utilizations, and true nature of halogen bonding are still relatively unexplored. Thus its final impact in chemistry in general and in materials science has not yet been fully established. Because of the polarized nature of a Z–X bond (Z=electron-withdrawing atom or moiety and X=halogen atom), such a moiety can act as halogen bond donor when the halogen is polarized enough by…
Halogen-bonded photoresponsive materials
2015
The aim of the present review is to illustrate to the reader the state of the art on the construction of supramolecular azobenzene-containing materials formed by halogen bonding. These materials include several examples of polymeric, liquid crystalline or crystalline species whose performances are either superior to the corresponding performances of their hydrogen-bonded analogues or simply distinctive of the halogen-bonded species. submittedVersion Peer reviewed
Halogen Bonding Based “Catch and Release”: Reversible Solid State Entrapment of Elemental Iodine with Mono-Alkylated DABCO Salts
2012
The halogen bonding (XB) between elemental iodine (I2) and neutral 1,4-diazabicyclo[2.2.2]octane (DABCO) and its monoalkylated PF6– salts was studied by X-ray crystallographic, thermoanalytical, and computational methods. DABCO was found to form both 1:1 and 1:2 complexes with I2 showing an exceptionally strong halogen bond (ΔEcp = −73.0 kJ/mol) with extremely short N···I distance (2.37 A) in the 1:1 complex (1a). In the more favored 1:2 complex (1b), the XB interaction was found to be slightly weaker [ΔEcp = −64.4 kJ/mol and d(N···I) = 2.42 A] as compared to 1a. The monoalkylated DABCO salts (2PF6–7PF6) form corresponding 1:1 XB complexes with I2 {[2···I2]PF6–([7···I2]PF6} similarly to the…