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Understanding the molecular mechanism of the [3 + 2] cycloaddition reaction of benzonitrile oxide toward electron-richN-vinylpyrrole: a DFT study
2016
The [3 + 2] cycloaddition (32CA) reaction of benzonitrile oxide, BNO 2, with an electron-rich N-vinylpyrrole derivative, NVP 3a, in the presence of dichloromethane, has been theoretically studied using density functional theory (DFT) methods at the B3LYP/6-31G(d) level. This 32CA reaction presents a relatively high activation Gibbs free energy as a result of the low polar character of this zwitterionic-type (zw-type) reaction. Analyses of the calculated relative Gibbs free energies and transition state geometries indicate that the studied 32CA reaction, in excellent agreement with experimental outcomes, takes place in a complete regioselective manner as a consequence of the steric repulsion…
Comparison of calculated DFT/B3LYP and experimental 13C and 17O NMR chemical shifts, ab initio HF/6-31G* optimised structures, and single crystal X-r…
2003
Abstract Single crystal X-ray structures (monoclinic space group P2 1 ) for methyl 3-oxo-5β-cholan-24-oate and methyl 3,12-dioxo-5β-cholan-24-oate have been solved and compared with HF/6-31G* optimised structures. In the crystalline packings the side chains are connected with weak OC(sp 3 ) H ⋯ O -type of interactions between C25– H and C24– O –C25 and the keto ends with weak C(sp 3 ) H ⋯ O C-type of interactions between C4– H and O C3. The orientations of the side chains, which steric configurations are of great importance to the biological activity of the molecules, are compared with the experimental structure of methyl 3α-hydroxy-5β-cholan-24-oate. Probable reasons for the observed dif…
DNA interaction of new copper(II) complexes with sulfonamides as ligands
2007
New copper(II) complexes with sulfonamide ligands have been prepared and characterized. Sulfonamide ligands were prepared through a reaction between 8-aminoquinoline and either 2-mesitylene (Hqmesa), 4-tert-butylbenzene (Hqtbsa), or alpha-toluene (Halphaqtsa) sulfonyl chlorides. The structural analysis carried out for complex [Cu(alphaqtsa)(2)] indicated that the local environment of the Cu(II) cation is between a square planar and a tetrahedral geometry, with stacking of the benzene rings of the sulfonyl ligands between neighbor molecules. Powder EPR spectra at room temperature gave rhombic spectra for the [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] complexes and an axial spectrum for the [Cu(qt…
Phosphane tuning in heteroleptic [Cu(N^N)(P^P)]+ complexes for light-emitting electrochemical cells
2019
The synthesis and characterization of five [Cu(P^P)(N^N)][PF 6 ] complexes in which P^P = 2,7-bis( tert -butyl)-4,5-bis(diphenylphosphino)-9,9-dimethylxanthene ( t Bu 2 xantphos) or the chiral 4,5-bis(mesitylphenylphosphino)-9,9-dimethylxanthene (xantphosMes 2 ) and N^N = 2,2'-bipyridine (bpy), 6-methyl-2,2'-bipyridine (6-Mebpy) or 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me 2 bpy) are reported. Single crystal structures of four of the compounds confirm that the copper(I) centre is in a distorted tetrahedral environment. In [Cu(xantphosMes 2 )(6-Mebpy)][PF 6 ], the 6-Mebpy unit is disordered over two equally populated orientations and this disorder parallels a combination of two dynamic processe…
Stereocontrolled synthesis of five diastereomers of trimethyl 3-aminocyclopentane-1,2,4-tricarboxylates
2013
Abstract The sterically controlled oxidative cleavage of N - protected di exo - and di endo -substituted norbornene β-amino acids/esters resulted in four trimethyl 3-aminocyclopentane-1,2,4-carboxylate diastereomers. The sodium methoxide mediated isomerization of the four diastereomers in all cases yielded the thermodynamically most stable all- trans stereoisomer as a single product.
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…
A Computational Study of Ethylene C−H Bond Activation by [Cp*Ir(PR3)]
2001
It has previously been demonstrated that both [(C5Me5)Ir(PMe3)(CH=CH2)H] and [(C5Me5)Ir(PMe3)(H2C=CH2)] are formed when [(C5Me5)Ir(PMe3)] is thermolytically generated in the presence of ethylene. At higher temperatures, the vinyl hydride is converted to the eta2-ethylene adduct. Density functional theory has now been used to investigate this reaction, using the B3LYP functional, two types of basis sets (LanL2DZ and TZV*), and two models of the [(C5R5)Ir(PR3)] species (R=H and CH3). The study consists of full optimizations of local minima, first-order saddle points, and minimum energy crossing points (MECP). The experimental results are best accounted for by considering both singlet and trip…
Understanding the selectivity in the formation of δ-lactams vs. β-lactams in the Staudinger reactions of chloro-cyan-ketene with unsaturated imines. …
2014
The reactions of chloro-cyan-ketene with two phenyl substituted unsaturated imines yielding β- or δ-lactams have been investigated using DFT methods at the MPWB1K/6-311G(d,p) level in diethyl ether. The reactions are initialised by the nucleophilic attack of the unsaturated imines on the ketene with formation of zwitterionic intermediates. The subsequent C–C single bond formation at the imine carbon or at the β-conjugated position enables the formation of β- or δ-lactams. Analysis of the energies involved in the two competitive channels explains the selectivity experimentally observed; in the absence of any steric hindrance, formation of δ-lactams is favoured over the formation of β-lactams…
Spectral and structural studies on Ni(II) dithiocarbamates: Nickel sulfide nanoparticles from a dithiocarbamate precursor
2015
Abstract Three new planar Ni(II) dithiocarbamate complexes; [Ni(4-dpmpzdtc)2] (1), [Ni(4-dpmpzdtc)(PPh3)(NCS)] (2) and [Ni(bupcbzdtc)(PPh3)(NCS)] (3) (where, 4-dpmpzdtc = 4-(diphenylmethyl)piperazinecarbodithioato anion, bupcbzdtc = N-butyl-N-(4-chlorobenzyl))dithiocarbamato anion and PPh3 = triphenylphosphine) with “NiS4” and “NiS2PN” chromophore units were synthesized and characterized by single crystal X-ray structural analysis as well as UV–Vis, IR and NMR (1H, 13C and 31P) spectroscopy. For 2, 1H–1H COSY spectrum was also recorded. Single crystal X-ray structural analysis of 1–3, reveals a slightly distorted square planar geometry in all three complexes wherein the steric and electroni…
Shape-persistent poly-porphyrins assembled by a central truxene: synthesis, structure, and singlet energy transfer behaviors
2013
Four dyad systems composed of a central truxene and either one or three β-substituted zinc(II) porphyrins (ZnP: TruZnP (7) and TruTriZnP (9)) or free-bases (H2P: TruP (6) and TruTriP (8)) have been prepared. The presence of β-methyl groups minimizes π-conjugation through the quasi right angle made by the porphyrin and the truxene planes, and renders these dyads relatively rigid. The position of the absorption and emission 0–0 peaks confirms the role of the truxene and porphyrin as the energy donor and acceptor, respectively. Selective excitation of the truxene results in an efficient singlet energy transfer (S1 ET) from the truxene to the porphyrin unit. The rates for S1 ET (k ET ) are ext…