Mechanism of the fluxional behaviour in (1–5-η-cycloheptadienyl)-(1–5-η-cycloheptatrienyl)iron

Evidence for a 1.2-shift mechanism of the 1-5-η-cycloheptatrienyl moiety with respect to the central iron atom of the title compound is presented together with absolute assignments of the ^(13)C n.m.r. chemical shifts of the C_(7)H_(7) ring. A low-temperature rocking motion of both rings can be frozen out at -70 °C

[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki-Miyaura reaction

The complex [PdCl2(P-N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P-N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 C in toluene with K2CO3 as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h(-1) can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid: lower reaction rates are obtained with Substrates bearing EDG substituents on the aryl group. (C) 2009 Elsevier Ltd. All rights reserved

Synthesis of 4-Isobutylbenzaldehyde an Important Intermediate for the Fragrance (+)- and (-)-Silvial®

The synthesis of 4-isobutylbenzaldehyde, a valuable precursor for the fragrance Silvial® (3-(4-isobutylphenyl)-2-methylpropanal), is reported. Three different synthetic approaches are reported starting either from 4-isobutylbenzoic acid (via benzyl alcohol, or via acyl chloride), or by Suzuki-Miyaura cross-coupling reaction between 4-bromobenzaldehyde and 2-methylpropylboronic acid

Mechanistic understanding of chromium-based oligomerisation catalysts : an EPR and ENDOR investigation

Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) spectroscopies have been used to study the fundamental nature of chromium-based selective oligomerisation catalysts. A series of 'pre-catalyst' complexes were fully characterised CW-EPR revealed each complex to possess an axial g matrix (g > ge > g ) and superhyperfine coupling to two equivalent 31P nuclei, consistent with a low-spin cf species of approximate Cjv symmetry, where the metal contribution to the SOMO is primarily dxy. The isotropic component to the 31P coupling was of a larger magnitude in those Cr(I) complexes bearing PNP ligands than those bearing PCP, indicating that the phosphorus 3s character in the SOMO was higher for the former. CW-ENDOR demonstrated that subtle structural differences in the complexes, namely in the phenyl ring conformations, occurred as a function of ligand type. Pulsed experiments proved that the technique is valid and viable for further work on the activated system. Upon activation of the pre-catalyst with an alkylaluminium, four distinct paramagnetic centres were identified. A Cr(I) bis-arene complex was firstly detected it was found to form either via intramolecular co-ordination of the ligand phenyl groups, or preferentially via solvent-based arene co-ordination, if such groups were available. Two further species (I and III) were subsequently observed at low temperatures the spin Hamiltonian parameters extracted for both showed that a significant modification to the structure of the pre-catalyst had occurred. Half-field transitions indicated the possibility of a dimeric nature to Species III. ENDOR measurements detected an exceptionally large proton coupling in the activated system, possibly due to the co ordination of alkyl fragments to the metal centre. A final, fourth paramagnetic centre (Species IV), was detected and classed as an intermediate species, due to the greater similarity between its g and A matrices with those of the parent complex, than the other activated species. Finally, a preliminary investigation into analogous pre-catalyst complexes bearing N-heterocyclic carbene ligands was performed, due to their similar employment in oligomerisation catalysis CW-EPR spectra revealed information on both their electronic and structural natures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Flor de celular: desafíos de la enseñanza y el aprendizaje en pandemia

La pandemia trajo nuevos desafíos, particularmente para la enseñanza de asignaturas en laboratorio, donde el instrumental óptico y el material de consulta apoyan significativamente las tareas docentes. El desarrollo de clases de Diversidad Biológica III en 2020 tuvo que ser rápidamente modificado, apoyado ahora en tecnologías virtuales e ingenio de docentes y estudiantes. Las clases de TP se enfocan en desarrollar competencias como identificar, clasificar y reconocer materiales botánicos. En el nuevo escenario de enseñanza-aprendizaje virtual se debió pensar cómo cada participante prepararía sus elementos de trabajo, observación y documentación. Además de los elementos de disección, etc., el uso del teléfono celular para la observación de caracteres y su documentación resultó central para para posibilitar el cumplimiento de los objetivos. Al inicio del ciclo se les sugirió montar un espacio de trabajo para hacer disecciones, colocando su teléfono sobre un soporte de modo tal que permita enfocar con la cámara, tomar fotos o hacer aumentos, simulando las prestaciones de una lupa esteroscópica.publishedVersionFil: Romanutti, Alejandra A. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Escuela de Biología. Cátedra de Diversidad Biológica III; Argentina.Fil: Galetto, Leonardo. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Escuela de Biología. Cátedra de Diversidad Biológica III; Argentina.Fil: Robbiati, Federico O. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Escuela de Biología. Cátedra de Diversidad Biológica III; Argentina.Fil: Scrivanti, L. Raquel. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Escuela de Biología. Cátedra de Diversidad Biológica III; Argentina.Fil: Trillo, Cecilia. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Escuela de Biología. Cátedra de Diversidad Biológica III; Argentina.Fil: Amarilla, Leonardo. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Escuela de Biología. Cátedra de Diversidad Biológica III; Argentina.Fil: Torres Carolina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Escuela de Biología. Cátedra de Diversidad Biológica III; Argentina