Formation of Exceptionally Weak C–C Bonds by Metal-Templated Pinacol Coupling

The ability of the bis(imidazolyl)ketone ligand BMdiPhIK (bis(1-methyl-4,5-diphenylimidazolyl)ketone) to function as a redox active ligand has been investigated. The reduction of [M(BMdiPhIK)Cl2] (M = Fe and Zn) complexes resulted in a pinacol-type coupling to form dinuclear complexes featuring very weak and abnormally elongated C–C bonds (1.729(5) and 1.708(3) Å for Fe and Zn, respectively). Oxidation of these complexes using ferrocenium in the presence of Cl− ions regenerated the original [M(BMdiPhIK)Cl2] complexes, showing the reversibility of the coupling process. This makes it a potentially interesting approach for the storage of electrons and application of the BMdiPhIK ligand as a redox active ligand. Graphical abstract: Formation of exceptionally weak C–C bonds by metal-templated pinacol couplin

Evaluación estilos de aprendizaje en trabajo social

En el marco de las nuevas estrategias de aprendizaje que se desprenden de las directrices de Bolonia que persiguen una mejora del rendimiento, es clave y primordial poder evaluar todos los factores que favorecen el aprendizaje. En este trabajo presentamos una parte de la investigación realizada con alumnos de Grado de Trabajo Social centrada en el estudio de la relación entre el enfoque de aprendizaje, con la forma de regular su aprendizaje y el tipo de rendimiento. La primera parte del trabajo se ha realizado tomando como base el cuestionario CHAEA, de Alonso, Gallego y Honey (1994). Los resultados obtenidos nos permiten afirmar que existen diferencias estadísticas significativas en las puntuaciones de los cuatro estilos de aprendizaje entre los alumno

Synthesis of Cyclopentadienyl-based Tricarbonyl Rhenium Complexes and some Unusual Reactivities of Cp-substituents

Cyclopentadienyl-based (Cp-based) tricarbonyl rhenium complexes [Cp′Re(CO)3] are convenient precursors for the corresponding Cp-based trioxorhenium complexes (Cp′ReO3), which are potential catalysts for the deoxydehydration (DODH) of diols to olefins. To evaluate the influence of different Cp substituents in Cp′ReO3 complexes in DODH, a series of alkyl-substituted Cp′Re(CO)3 complexes (1a–8a) were synthesized. High yields (86–98 %) were obtained from the reactions of Re2(CO)10 with the corresponding Cp′H ligands (1–8). The C–O infrared absorptions of 1a–8a indicate that the electron-donating character of the Cp ligand increases with the number of substituents attached directly to the Cp ring. Analogous aryl-substituted complexes 10a–12a containing bulky phenyl groups were accessed through the salt metathesis of ReBr(CO)5 with the lithium salt of the deprotonated ligand (Cp′Li), and the aryl groups decreased the electron donation. Furthermore, an unusual [6+4] cycloaddition reaction of (CpMe4H)Re(CO)3 (8a) with excess ligand resulted in the highly asymmetric Cp′Re(CO)3 complex 9a. Finally, the reaction of the tetraphenylcyclopentadienone ligand with Re2(CO)10 was investigated and led to the isolation of two unusual compounds, namely, Re(CO)3 complexes of the Shvo-type hydroxytetraphenylcyclopentadienyl ligand, [Ph4Cp(OH)]Re(CO)3 (13a), and a benzofuran-fused cyclopentadienyl ligand, [Ph3Cp(C6H4O)]Re(CO)3 (14a). X-ray crystal structures were obtained for the new Cp′Re(CO)3 complexes (CptBu2H3)Re(CO)3 (2a), [1,2,3-Me3(tetrahydroindenyl)]Re(CO)3 (7a), 9a, 13a, and 14a, which all have the typical three-legged “piano-stool” configuration

Organocatalyzed ring opening polymerization of regio-isomeric lactones: reactivity and thermodynamics considerations

Organocatalysts are increasingly gaining attention for the ring opening polymerization (ROP) of lactones due to numerous advantages. In this work, the goal is to expand the scope of catalysts for the ROP of alkyl substituted caprolactones: a mixture of beta,delta-trimethyl-epsilon-caprolactones (TMCL). Several organocatalysts were evaluated, with a focus on bifunctional organophosphorus catalysts including two novel categories, namely phosphonic acids and phosphinic acids. The effects of initial monomer concentration, temperature, catalyst loading and catalyst type on the monomer conversion at equilibrium and the reaction kinetics were addressed. The ceiling temperature of TMCL is 302 degrees C in bulk and 34 degrees C at 1 M, as determined experimentally. During polymerization, higher conversion and reaction rates were observed for the most substituted lactone ( proximal lactone). This difference of reactivity between the two regio-isomeric lactones was greater for lower reaction temperatures. Density functional theory (DFT) calculations on the ring opening of the lactones demonstrated that the difference of reactivity can be attributed to a lower enthalpic contribution of the proximal lactone making the ring opening of this lactone more energetically favored. The difference in calculated Gibbs free energy was found to increase with lower temperature

Formation of Exceptionally Weak C–C Bonds by Metal-Templated Pinacol Coupling

The ability of the bis(imidazolyl)ketone ligand BMdiPhIK (bis(1-methyl-4,5-diphenylimidazolyl)ketone) to function as a redox active ligand has been investigated. The reduction of [M(BMdiPhIK)Cl2] (M = Fe and Zn) complexes resulted in a pinacol-type coupling to form dinuclear complexes featuring very weak and abnormally elongated C–C bonds (1.729(5) and 1.708(3) Å for Fe and Zn, respectively). Oxidation of these complexes using ferrocenium in the presence of Cl− ions regenerated the original [M(BMdiPhIK)Cl2] complexes, showing the reversibility of the coupling process. This makes it a potentially interesting approach for the storage of electrons and application of the BMdiPhIK ligand as a redox active ligand. Graphical abstract: Formation of exceptionally weak C–C bonds by metal-templated pinacol couplin

Organocatalyzed ring opening polymerization of regio-isomeric lactones:reactivity and thermodynamics considerations

Organocatalysts are increasingly gaining attention for the ring opening polymerization (ROP) of lactones due to numerous advantages. In this work, the goal is to expand the scope of catalysts for the ROP of alkyl substituted caprolactones: a mixture of beta,delta-trimethyl-epsilon-caprolactones (TMCL). Several organocatalysts were evaluated, with a focus on bifunctional organophosphorus catalysts including two novel categories, namely phosphonic acids and phosphinic acids. The effects of initial monomer concentration, temperature, catalyst loading and catalyst type on the monomer conversion at equilibrium and the reaction kinetics were addressed. The ceiling temperature of TMCL is 302 degrees C in bulk and 34 degrees C at 1 M, as determined experimentally. During polymerization, higher conversion and reaction rates were observed for the most substituted lactone ( proximal lactone). This difference of reactivity between the two regio-isomeric lactones was greater for lower reaction temperatures. Density functional theory (DFT) calculations on the ring opening of the lactones demonstrated that the difference of reactivity can be attributed to a lower enthalpic contribution of the proximal lactone making the ring opening of this lactone more energetically favored. The difference in calculated Gibbs free energy was found to increase with lower temperature

Synthesis of Cyclopentadienyl-Based Trioxo-rhenium Complexes and Their Use as Deoxydehydration Catalysts

The cyclopentadienyl-based trioxo-rhenium complexes CptttReO3 (Cpttt = 1,2,4-tritert-butylcyclopentadienyl) 1b and Cp*ReO3 (Cp* = pentamethylcyclopentadienyl) 4b) are known to be active catalysts for the deoxydehydration (DODH) of vicinal diols to olefins. Here, we report on the preparation of a series of complexes of the general formula Cp′ReO3 (Cp′ = 1,3-di-tert-butylcyclopentadienyl (Cptt, 2b, 18%), 1,2,3-triisopropylcyclopentadienyl (3b, 4%), 1,2,3-trimethyl-4,5,6,7-tetrahydroindenyl (6b, 36%), and tetramethylcyclopentadienyl (7b, 33%)) in which the electronic and steric properties of the Cp′ ligand are varied. These complexes were synthesized via oxidative decarbonylation from the corresponding Cp′Re(CO)3 complexes with either H2O2 or tBuOOH. An in situ NMR investigation revealed that complexes 2b, 3b, and 6b are unstable under the oxidizing reaction conditions. This information was used to determine the optimal reaction time to isolate the complexes 2b, 3b, and 6b. These “piano-stool” configurated Cp′ReO3 complexes were characterized spectroscopically and by single crystal X-ray diffraction. The new complexes 2b, 3b, 6b, and 7b were found to be generally less thermally stable than CptttReO3 (1b) or Cp*ReO3 (4b). It appeared that 2b and 6b were better catalysts for the DODH of 1,2-octanediol to octene with PPh3 as an oxygen-atom acceptor. Remarkably, the less substituted Cp′ReO3 complexes (1b, 2b, and 3b) afforded significantly less 2-octene (presumably from isomerization of the primary 1-octene product) in comparison to those containing per-alkylated Cp-moieties (4b and 6b)