Espacios, tiempos y saberes para una subjetividad reflexiva en la escuela primaria Bellaterra

Este artículo presenta los principales resultados de una investigación narrativa sobre la construcción de la subjetividad en la escuela primaria. Dado que en este tipo de investigación, el investigador es considerado un sujeto social en relación con otros, el proceso de escritura de los diarios durante el trabajo de campo etnográfico muestra las tentativas para incluir a los otros en la representación, los diversos momentos de duda, y hace visibles las interrupciones y giros en nuestras posiciones investigadoras. Además, hemos tratado de escapar de la objetivación y fijación del sujeto, planteando una visión relacional y procesual de la subjetividad, a veces incluso fragmentada. Para ello, hemos interpretado la representación de la infancia y del aprendizaje en la escuela, cómo las maestras y los maestros con quienes trabajamos comparten una visión reflexiva, integral, cooperativa y comunitaria del sujeto escolar. También hemos observado e interpretado cómo los niños y niñas desarrollan formas de posicionamiento, identificación y diferenciación desde la relación con los otros. Así, hemos reconstruido cómo se forma la subjetividad infantil a partir de narrar escenas observadas en las aulas de diferentes grupos de niños y niñas y en otros espacios de la escuela donde estos grupos desarrollan diferentes actividadesIn this article we present the results of a narrative inquiry into the construction of subjectivity in primary schools. In this study the researchers' own subjectivities came under the same scrutiny as those who were the focus of the research, and were placed in relation to them. We will discuss the doubts that arose as we carried out our research as well as how our positions as researchers changed over the course of the study. We will also describe our attempts to give voice to teachers and learners through our narratives. This goal led us to produce an account of subjectivity that was relational, process-based, and, sometimes, fragmented. Our interpretation of the representation of childhood/learners and learning in school is based upon how the teachers we have worked with shared a reflective, integral, cooperative, and community view of learning. We will also discuss how learners develop forms of positioning, identification, and differentiation depending on their relationships with others. In this way we have been able to reconstruct the way in which learners' subjectivities are formed by narrating scenes observed in classrooms with different groups of peers, and in other areas of the school where these groups carry out different activitie

Controlling the Ambiphilic Nature of σ‑Arylpalladium Intermediates in Intramolecular Cyclization Reactions

The reactivity of main group organometallics, such as organolithium compounds (RLi) and Grignard reagents (RMgX), is quite straightforward. In these species the R group usually exhibits nucleophilic reactivity without any possibility of inducing electrophilic character. In contrast, in organopalladium complexes, researchers can switch the reactivity from electrophilic to nucleophilic relatively simply. Although σ-aryl and σ-vinylpalladium complexes are commonly used as electrophiles in C–C bond-forming reactions, recent research has demonstrated that they can also react with carbon–heteroatom multiple bonds in a nucleophilic manner. Nevertheless, researchers have completely ignored the issue of controlling the ambiphilic nature of such species.This Account describes our efforts toward selectively promoting the same starting materials toward either electrophilic α-arylation or nucleophilic addition reactions to different carbonyl groups. We could tune the properties of the σ-arylpalladium intermediates derived from amino-tethered aryl halides and carbonyl compounds to achieve chemoselective transformations. Therefore, chemists can control the ambiphilic nature of such intermediates and, consequently, the competition between the alternative reaction pathways by the adequate selection of the reaction conditions and additives (base, presence/absence of phenol, bidentate phosphines). The nature of the carbonyl group (aldehydes, ketones, esters, and amides) and the length of the tether connecting it to the aniline moiety also play an important role in the outcome of these processes.Our joint computational and experimental efforts to elucidate the reaction mechanism of these palladium-catalyzed transformations suggest that beyond the formation of the four-membered azapalladacycle, two major factors help to control the dual character of the palladium(II) intermediates derived from 2-haloanilines. First, their high nucleophilicity strongly modifies the interaction of the metal center with the carbonyl group. Second, the additive phenol exchanges the iodide ligand to give an arylpalladium(II) phenoxide complex, which has a beneficial effect on the arylation. The formation of this transient intermediate not only stabilizes the arylpalladium moiety, thus preventing the nucleophilic attack at the carbonyl group, but also assists the enolization reaction, which takes place in a more favorable intramolecular manner.The azapalladacycle intermediate is, in the words of J. R. R. Tolkien, “the one ring to bring them all and in the darkness to bind them.” With this intermediate, we can easily achieve the synthesis of a variety of heterocyclic systems by selectively promoting electrophilic α-arylation or nucleophilic addition reactions from the same precursors

Factors Controlling the Reactivity and Selectivity of the Diels–Alder Reactions Involving 1,2-Azaborines

The factors controlling the reactivity and endo/exo selectivity of the Diels–Alder reactions involving 1,2-azaborines have been computationally explored within the density functional theory framework. It is found that the AlCl₃-catalyzed [4 + 2]-cycloaddition reaction between these dienes and <i>N</i>-methylmaleimide proceeds concertedly and leads almost exclusively to the corresponding endo cycloadduct, which is in good agreement with previous experimental observations. In addition, the effect of the substituent directly attached to the boron atom of the 1,2-azaborine on the process is also analyzed in detail. To this end, the combination of the activation strain model of reactivity and the energy decomposition analysis methods has been applied to gain a quantitative understanding into the origins of the endo selectivity of the process as well as the influence of the boron and nitrogen substituent on the barrier heights of the transformations

Factors Governing the Diels–Alder Reactivity of (2,7)Pyrenophanes

The physical factors governing the Diels–Alder reactivity of (2,7)­pyrenophanes have been computationally explored using state-of-the-art Density Functional Theory calculations. It is found that the [4 + 2]-cycloaddition reactions between these cyclophanes and tetra­cyano­ethylene, which occur concertedly through highly asynchronous transition states, proceed with lower activation barriers and are more exothermic than the analogous process involving the parent planar pyrene. The influence of the bent equilibrium geometry of the pyrenophane as a function of the length of the bridge as well as the nature of the tether on the transformation are analyzed in detail. By means of the Activation Strain Model of reactivity and the Energy Decomposition Analysis methods, a detailed quantitative understanding of the reactivity of this particular family of cyclophanes is presented

Effects of Attractive Through Space π–π* Interactions on the Structure, Reactivity, and Activity of Grubbs II Complexes

On the basis of theoretical calculations, the present work suggests that Grubbs II-type complexes are stabilized by a weak π–π* interaction involving an electronic donation from the aryl group of the NHC ligand to the π* (RuC) molecular orbital, which is mainly centered on the carbenic carbon center (p_<i>z</i> atomic orbital). This interaction, which could persist in the active catalytic species throughout a metathesis reaction, can be tuned by modulating the electron density in the aryl group

Predicting and Understanding the Reactivity of Aza[60]fullerenes

The Diels–Alder reactivity of C₅₉NH azafullerene has been explored computationally. The regioselectivity of the process and the factors controlling the reduced reactivity of this system with respect to the parent C₆₀ fullerene have been analyzed in detail by using the activation strain model of reactivity and the energy decomposition analysis method. It is found that the presence of the nitrogen atom and the CH fragment in the fullerene reduces the interaction between the deformed reactants along the entire reaction coordinate

Rationalizing the Regioselectivity of the Diels–Alder Biscycloaddition of Fullerenes

The physical factors governing the regioselectivity of the double functionalization of fullerenes have been explored by means of density functional theory calculations. To this end, the second Diels–Alder cycloaddition reactions involving 1,3-butadiene and the parent C₆₀ fullerene as well as the ion-encapsulated system Li⁺@C₆₀ have been selected. In agreement with previous experimental findings on related processes, it is found that the cycloaddition reaction, involving either C₆₀ or Li⁺@C₆₀, occurs selectively at specific [6,6]-bonds. The combination of the activation strain model of reactivity and the energy decomposition analysis methods has been applied to gain a quantitative understanding into the markedly different reactivity of the available [6,6]-bonds leading to the observed regioselectivity in the transformation

Rhodium Complexes with a Pyridine-2-yloxy-silyl-Based N,Si-Ligand: Bonding Situation and Activity as Alkene Hydrogenation Catalysts

Rh(III) complexes [Rh(H)(X)(κ2-NSitBu2OPy)(L)] (X = Cl, L = PCy3, 2a; PHtBu2, 2b; X = OTf, L = PCy3, 3a; PHtBu2, 3b) (NSitBu2OPy = 4-methylpyridin-2-yloxy-ditertbutylsilyl) have been prepared and characterized by means of elemental analysis and nuclear magnetic resonance (NMR) spectroscopy. The solid-state structures of complexes 2a, 2b, and 3a have been determined by X-ray diffraction studies. Computational analyses of the bonding situation of these species evidence the electron-sharing nature of the Rh–Si bond and the significant role of the electrostatic component in the interaction between the transition metal fragment [Rh(H)(PR3)(X)]• and the [NSitBu2OPy]• ligand. In addition, a comparative study of the activity of 2a, 2b, 3a, 3b, and related iridium species as catalysts for the hydrogenation of olefins has been performed. The best catalytic results have been obtained when using the Rh(III) species 3a, with triflate and PCy3 ligands, as catalyst. Computational density functional theory studies show that the formation of the alkane is thermodynamically favored and that the rate-limiting step corresponds to the hydrogen activation, which takes place via a σ-complex-assisted metathesis mechanism

Rhodium Complexes with a Pyridine-2-yloxy-silyl-Based N,Si-Ligand: Bonding Situation and Activity as Alkene Hydrogenation Catalysts

Rh(III) complexes [Rh(H)(X)(κ2-NSitBu2OPy)(L)] (X = Cl, L = PCy3, 2a; PHtBu2, 2b; X = OTf, L = PCy3, 3a; PHtBu2, 3b) (NSitBu2OPy = 4-methylpyridin-2-yloxy-ditertbutylsilyl) have been prepared and characterized by means of elemental analysis and nuclear magnetic resonance (NMR) spectroscopy. The solid-state structures of complexes 2a, 2b, and 3a have been determined by X-ray diffraction studies. Computational analyses of the bonding situation of these species evidence the electron-sharing nature of the Rh–Si bond and the significant role of the electrostatic component in the interaction between the transition metal fragment [Rh(H)(PR3)(X)]• and the [NSitBu2OPy]• ligand. In addition, a comparative study of the activity of 2a, 2b, 3a, 3b, and related iridium species as catalysts for the hydrogenation of olefins has been performed. The best catalytic results have been obtained when using the Rh(III) species 3a, with triflate and PCy3 ligands, as catalyst. Computational density functional theory studies show that the formation of the alkane is thermodynamically favored and that the rate-limiting step corresponds to the hydrogen activation, which takes place via a σ-complex-assisted metathesis mechanism