Search results for "Catalysis"

Strong N−X⋅⋅⋅O−N Halogen Bonds: A Comprehensive Study on N‐Halosaccharin Pyridine N ‐Oxide Complexes

2019

A study of the strong N-X⋅⋅⋅- O-N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N-halosaccharins and pyridine N-oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from -47.5 to -120.3 kJ mol-1 ; the strongest N-I⋅⋅⋅- O-N+ XBs approaching those of 3-center-4-electron [N-I-N]+ halogen-bonded systems (ca. 160 kJ mol-1 ). 1 H NMR association constants (KXB ) determined in CDCl3 and [D6 ]acetone vary from 2.0×100 to >108  m-1 and correlate well with the calculat…

2018

Tetrel bonding is the noncovalent interaction of group IV elements with electron donors. It is a weak, directional interaction that resembles hydrogen and halogen bonding yet remains barely explored. Herein, we present an experimental investigation of the carbon-centered, three-center, four-electron tetrel bond, [N–C–N]+, formed by capturing a carbenium ion with a bidentate Lewis base. NMR-spectroscopic, titration-calorimetric, and reaction-kinetic evidence for the existence and structure of this species is reported. The studied interaction is by far the strongest tetrel bond reported so far and is discussed in comparison with the analogous halogen bond. The necessity of the involvement of …

Supercritical Carbon Dioxide: A Promoter of Carbon-Halogen Bond Heterolysis

2013

as the leaving groupdeparts from the carbon atom prior to the entrance of thenucleophile. Polar protic solvents with high dielectric con-stants promote polar bond heterolysis by providing effectiveH-bonding and electron-pair donation interactions to theleaving group and the incipient carbocation, respectively.Then, the solvent captures the carbocation intermediate togive the corresponding S

Halogen bonding—a key step in charge recombination of the dye-sensitized solar cell

2011

The halogen bonding between [Ru(dcbpy)(2)(SCN)(2)] dye and I(2) molecule has been studied. The ruthenium complex forms a stable [Ru(dcbpy)(2)(SCN)(2)]···I(2)·4(CH(3)OH) adduct via S···I interaction between the thiocyanate ligand and the I(2) molecule. The adduct can be seen as a model for one of the key intermediates in the regeneration cycle of the oxidized dye by the I(-)/I(3)(-) electrolyte in dye sensitized solar cells.

Synthesis of iodobiaryls and dibenzofurans by direct coupling at BDD anodes.

2014

The first direct oxidative phenol-arene cross-coupling reactions of an iodine-containing guaiacol derivative and the possible over-oxidation products of electron-rich phenols are described. Hereby, a "green" and targeted synthesis for dibenzofurans was developed.

Stereoselective Access to Fluorinated and Non-fluorinated Quaternary Piperidines: Synthesis of Pipecolic Acid and Iminosugar Derivatives

2012

The preparation of optically pure quaternary piperidines, both fluorinated and non-fluorinated, has been achieved from a chiral imino lactone derived from (R)-phenylglycinol. In the case of the fluorinated derivatives, the addition of (trifluoromethyl)trimethylsilane (TMSCF(3)) followed by iodoamination and migration of the CF(3) group allowed access to four derivatives of α-(trifluoromethyl)pipecolic acid. A theoretical study of the CF(3)-group rearrangement has been carried out to help establish the reaction mechanism of this uncommon transformation. Moreover, a route to trifluoromethyl-substituted iminosugars was also developed through the diastereoselective dihydroxylation of suitable s…

A First-Principles Study of the Ag/a-Al2O3(0001) Interface

2001

Ab initio simulations of the Ag/a-Al2O3(0001) interface have been performed for periodic slab models. We have considered Al- and O-terminated corundum surfaces, low and high substrate coverages by silver, as well as the two preferred Ag adsorption sites. The two different terminations give rise to qualitatively different results: silver physisorption on the Al-terminated substrate and chemisorption on O-terminated one. The latter could be treated as a possible model for the defective Al-terminated substrate, where the outermost aluminium ions are removed (completely or partly). This makes O-terminated surface highly reactive towards a deposited metal, in order to restore initial corundum st…

New Dinuclear Catalysts Rh2(N−O)2[(C6H4)P(C6H5)2]2 with Imidate Ligands:  Synthesis and Isomerization from Head-to-Tail to Head-to-Head Configuration…

2001

Two new dirhodium(II) catalysts of general formula Rh(2)(N-O)(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (N-O = C(4)H(4)NO(2)) are prepared, starting from Rh(2)(O(2)CCH(3))(2)(PC)(2)L(2) [PC = (C(6)H(4))P(C(6)H(5))(2) (head-to-tail arrangement); L = HO(2)CCH(3)]. The thermal reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with the neutral succinimide stereoselectively gives one compound that according to the X-ray structure determination has the formula Rh(2)(C(4)H(4)NO(2))(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (1). It corresponds to the polar isomer with two bridging imidate ligands in a head-to-head configuration. However, stepwise reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with (CH(3))(3)SiCl and potassiu…

Androgen hydroxylation catalysed by a cell line (SD1) that stably expresses rat hepatic cytochrome P-450 PB-4 (IIB1).

1989

Androgen hydroxylation catalysed by Chinese hamster fibroblast SD1 cells, which stably express cytochrome P-450 form PB-4, the rat P450IIB1 gene product, was assessed and compared to that catalysed by purified cytochrome P-450 PB-4 isolated from rat liver. SD1 cell homogenates catalysed the NADPH-dependent hydroxylation of androstenedione and testosterone with a regioselectivity very similar to that purified by P-450 PB-4 (16 beta-hydroxylation/16 alpha-hydroxylation = 6.0-6.8 for androstenedione; 16 beta/16 alpha = 0.9 for testosterone). Homogenates prepared from the parental cell line V79, which does not express detectable levels of P-450 PB-4 or any other cytochrome P-450, exhibited no a…

Iron Porphyrins as Models of Cytochromec Oxidase

2001

A series of iron porphyrins has been synthesized as models of cytochrome c oxidase; their activity as 4 e− catalysts in the reduction of dioxygen has been studied at pH 7. These compounds have been obtained by grafting very different residues onto the same iron complex, namely tripodal tetraamines, pickets, and straps, in order to change the environment of the metal center. In the case of porphyrins bearing a tripodal cap, the secondary amines have been alkylated with different substituents so as to modify the electronic environment of the distal pocket. Surprisingly, when the iron porphyrin is functionalized with four identical acrylamido pickets, the resulting complex exhibits biomimetic …