Systematic study on the catalytic synthesis of unsaturated 2-ketocarboxamides: palladium-catalyzed double carbonylation of 1-iodocyclohexene

1-Iodocyclohexene, a benchmark substrate, has been double carbonylated in the presence of palladium-phosphite precatalysts. Triarylphosphites with OR substituents, able to act both as P-monodentate and hemilabile P,O-heterobidentate ligands were used in this reaction. Systematic investigations have revealed that the chemoselectivity towards cyclohexenylglyoxylamides, i.e., the products obtained in aminocarbonylation by the insertion of two carbon monoxide, is strongly influenced by the amine nucleophile, temperature and carbon monoxide pressure. The highest yields of 2-ketocarboxamides were obtained at low temperature (30 °C) and high carbon monoxide pressure (110 bar). However, the structure of the phosphite ligand has practically no effect either on catalytic activity or chemoselectivity. This fact refers to the P-monodentate coordination of the ligands in catalytic intermediates or that palladium nanoparticles are the catalytically active species.     

Photophysical properties of unsymmetric meso-substituted porphyrins synthesized via the Suzuki coupling reaction

A new family of porphyrins containing different groups in meso positions was synthesized by Suzuki coupling reaction of meso mono- and dibromo-diarylporphyrins with several boronate esters, catalyzed by palladium organometallic complexes. These procedures gave high yields of unsymmetric porphyrins bearing carboxylate anchoring groups, with enhanced absorptions in the red and showing no tendency for aggregation in toluene or THF solutions. Such properties are of interest for application in dye-sensitized solar cells.     

Catalytic oxidative degradation of s-triazine and phenoxyalkanoic acid based herbicides with metalloporphyrins and hydrogen peroxide: Identification of two distinct reaction schemes

Oxidative degradation of the herbicides atrazine (1), atraton (2), ametryn (3) and mecoprop (4), was carried out with hydrogen peroxide and metalloporphyrins as catalysts. Two different reaction conditions were studied, the first involving Mn(TDCPP)Cl in an aprotic solvent with buffer (S-I), and the second using Fe(TPFPP)Cl in a protic solvent (S-II). Reaction products were characterized, and based on these it is shown that there are two distinct reaction schemes.In the case of the S-I conditions, it is suggested that the s-triazines were oxidized through hydroxylation of the alkyl side chains followed by dealkylation, while S-II was ineffective for these reactions. In contrast, mecoprop, was oxidized with high efficiency by S-II, leading to decarboxylation and further oxidation, while in the presence of S-I, low substrate conversion was observed, and reaction resulted mainly from oxidation at the benzyl position. Sulfoxidation of ametryn was observed with both systems.The different reactivity shown by the two systems supports the involvement of different reactive species, which we assign to the oxo and hydroperoxy complexes. These routes show similarities with metabolic pathways, with the reactivity pattern of S-I analogous to the reported metabolism of these pollutants with cytochrome P450 enzymes, while S-II catalyses mecoprop decarboxylation via a similar pathway to that seen with peroxidase catalysed reactions.     

Exciton polaritons in quantum wells in a transverse magnetic field

Physics of the Solid State - This paper reports on a study of the exciton polariton region in reflection spectra of wide CdTe/CdZnTe quantum wells (with well width exceeding by far the exciton Bohr...     

Carrier-diffusion-limited remote optical addressing of single quantum dots

We present a scheme for remotely addressing single quantum dots (QDs) by means of near-field optical microscopy that simply makes use of the polarization of light. A structure containing self-assembled CdTe QDs is covered with a thin metal film presenting sub-wavelength holes. When the optical tip is positioned some distance away from a hole, surface plasmons in the metal coating are generated which, by turning the polarization plane of the excitation light, transfer the excitation towards a chosen hole and induce emission from the underlying dots. In addition, our procedure gives valuable insight into the diffusion of photo-excited carriers in the QD plane that can put limits to the addressing scheme.     

Conforming Delaunay triangulations in 3D

We describe an algorithm which, for any piecewise linear complex (PLC) in 3D, builds a Delaunay triangulation conforming to this PLC. The algorithm has been implemented, and yields in practice a relatively small number of Steiner points due to the fact that it adapts to the local geometry of the PLC. It is, to our knowledge, the first practical algorithm devoted to this problem.     

Synthesis of Computationally Designed 2,5(6)-Benzimidazole Derivatives via Pd-Catalyzed Reactions for Potential E. coli DNA Gyrase B Inhibition

A pharmacophore model for inhibitors of Escherichia coli’s DNA Gyrase B was developed, using computer-aided drug design. Subsequently, docking studies showed that 2,5(6)-substituted benzimidazole derivatives are promising molecules, as they possess key hydrogen bond donor/acceptor groups for an efficient interaction with this bacterial target. Furthermore, 5(6)-bromo-2-(2-nitrophenyl)-1H-benzimidazole, selected as a core molecule, was prepared on a multi-gram scale through condensation of 4-bromo-1,2-diaminobenzene with 2-nitrobenzaldehyde using a sustainable approach. The challenging functionalization of the 5(6)-position was carried out via palladium-catalyzed Suzuki–Miyaura and Buchwald-Hartwig amination cross-coupling reactions between N-protected-5-bromo-2-nitrophenyl-benzimidazole and aryl boronic acids or sulfonylanilines, with yields up to 81%. The final designed molecules (2-(aminophen-2-yl)-5(6)-substituted-1H-benzimidazoles), which encompass the appropriate functional groups in the 5(6)-position according to the pharmacophore model, were obtained in yields up to 91% after acid-mediated N-boc deprotection followed by Pd-catalyzed hydrogenation. These groups are predicted to favor interactions with DNA gyrase B residues Asn46, Asp73, and Asp173, aiming to promote an inhibitory effect.     

Synthesis of new bis-BINOL-2,2′-ethers and bis-H8BINOL-2,2′-ethers evaluation of their Titanium complexes in the asymmetric ethylation of benzaldehyde

The preparation by means of different synthetic paths of a series of bis-BINOL and bis-H₈BINOL ligands is described. The ligands consist of two BINOL or H₈BINOL fragments, joined by diverse linkages through the oxygen at the 2′-position of the arylic fragments. These ligands were applied to the Ti(OⁱPr)₄ catalyzed asymmetric alkylation of benzaldehyde with Et₂Zn. The performance of these catalysts is very sensitive to the nature of the ether linkage. The ligand with a propylene link shows better enantioselectivity (ca. 70%) than those with two or four carbon atoms joining the BINOL fragments. Furthermore, using the propylene link, but replacing (R)-BINOL by (R)-H₈BINOL, a significant improvement in the stereoselectivity of the catalysts was achieved (ca. 80% ee in (R)-1-phenylpropan-1-ol). A cooperative effect was observed between the chirality at the BINOL fragment and that of a (S,S)-4,5-bis(methylene)-2,2-dimethyl-1,3-dioxolane link, derived from tartaric acid. When this chiral link combines with two (S)-BINOL fragments, the alkylation of benzaldehyde in toluene produces 70% ee of (S)-1-phenylpropan-1-ol, while the (R)-BINOL derivative ligand with the same link, in identical conditions, yields only 40% ee of the (R)-alcohol.     

Optical spin orientation of a single manganese atom in a quantum dot

The magnetic state of a single magnetic atom (Mn) embedded in an individual semiconductor quantum dot is optically probed using micro-spectroscopy. A high degree of spin polarization can be achieved for an individual Mn atom localized in a quantum dot using quasi-resonant or fully-resonant optical excitation at zero magnetic field. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magnetic field dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. The Mn spin distribution prepared by optical pumping is fully conserved for a few microseconds. This opens the way to full optical control of the spin state of an individual magnetic atom in a solid state environment.