Enseñanza de las propiedades electrónicas y magnéticas de los compuestos de coordinación mediante fichas de actividad

En esta comunicación se describe el desarrollo de una metodología de enseñanza consistente en guiar a los estudiantes en su aprendizaje a través de la resolución de una serie de fichas proporcionadas por la profesora. En estas fichas se plantean diferentes actividades consistentes en lecturas y visualización de vídeos seguidos de cuestiones teóricas y ejercicios prácticos que los alumnos deben resolver en grupos de cuatro. Con este sistema, los alumnos pueden expresar sus opiniones y razonamientos en voz alta a la vez que escuchan lo que exponen sus compañeros. En todo momento el profesor se encuentra accesible para que ellos puedan consultar todas sus dudas ayudándoles, cuando es necesario, a reconducir sus razonamientos. En concreto se va a aplicar dicha metodología al estudio de las propiedades electrónicas y magnéticas de los compuestos de coordinación, un tema de gran complejidad para los estudiantes de grado en Química

Different coordination modes of an aryl-substituted hydrotris(pyrazolyl) borate ligand in rhodium and iridium complexes

Complexes TptolRh(C2H4)2 (1a) and TptolRh(CH2C(Me)C(Me)CH2) (1b) have been prepared by reaction of KTptol with the appropriate [RhCl(olefin)2]2 dimer (Tptol means hydrotris(3-p-tolylpyrazol-1-yl)borate). The two complexes show a dynamic behaviour that involves exchange between κ2 and κ3 coordination modes of the Tptol ligand. The iridium analogue, TptolIr(CH2C(Me)CHCH2) (2) has also been synthesized, and has been converted into the Ir(III) dinitrogen complex [(κ4-N,N',N'',C-Tptol)Ir(Ph)(N2) (3) by irradiation with UV light under a dinitrogen atmosphere. Compound 3 constitutes a rare example of Ir(III)-N2 complex structurally characterized by X-ray crystallography. Its N2 ligand can be easily substituted by acetonitrile or ethylene upon heating and denticity changes in the Tptol ligand, from κ4-N,N',N'',C (monometallated Tptol, from now on represented as Tptol′) to κ5-N,N′,N″,C,C″ (dimetallated Tp tol ligand, represented as Tptol″) have been observed. When complex 3 is heated in the presence of acetylene, dimerization of the alkyne takes place to yield the enyne complex [(κ5-N,N′,N′′,C,C′-Tp tol)Ir(CH2CHCCH), 7̧ in which the unsaturated organic moiety is bonded to iridium through the carbon-carbon double bond.Ministerio de Educación y Ciencia CTQ2007-62814Consolider-Ingenio 2010 CSD2007-00006Junta de Andalucía FQM-3151, FQM-672CONACYT 22934

Palladium-mediated Intramolecular Dearomatization of Ligated Dialkylterphenyl Phosphines

Aryl-Pd(ii) chlorides stabilized by dialkylterphenyl phosphine ligands undergo a thermal isomerization process, leading to the formation of allyl-Pd(ii)-chloride species. The transformation involves the intramolecular functionalization of a C-H bond of the terphenyl group mediated by the Pd(ii) center.Ministerio de Ciencia, Innovación y Universidades CTQ2017-82893-C2-2-

Aprendizaje basado en problemas para la enseñanza de la química en la universidad

El objetivo del trabajo es analizar la eficacia de la metodología del aprendizaje basado en problemas (ABP) en una titulación del grupo de las STEM, en concreto en tres asignaturas de 1º, 2º y 3º del Grado en Química de la Universidad de Sevilla. Las clases se convierten para los estudiantes en un lugar de trabajo en grupo en el que deben resolver una serie de cuestiones concatenadas entre sí y que van progresando de menor a mayor complejidad a lo largo de los temas. Para resolver dichas cuestiones deben antes comprender los nuevos conceptos teóricos empleando para ello la bibliografía recomendada por el profesor y las opciones disponibles en internet. Al final de cada tema los alumnos comparan sus resultados con los del profesor y tienen que realizar, de manera individual, una reflexión acerca de sus errores, aciertos, incomprensiones, etc. Los resultados obtenidos al finalizar el curso correspondiente ponen de manifiesto una mejora de los resultados académicos en todas esas asignaturas, una reducción del tiempo de trabajo y un incremento significativo en el grado de satisfacción del alumnado

Important Role of NH-Carbazole in Aryl Amination Reactions Catalyzed by 2‑Aminobiphenyl Palladacycles

2-Aminobiphenyl palladacycles are among the most successful precatalysts for Pd-catalyzed cross-coupling reactions, including aryl amination. However, the role of NH-carbazole, a byproduct of precatalyst activation, remains poorly understood. Herein, the mechanism of the aryl amination reactions catalyzed by a cationic 2-aminobiphenyl palladacycle supported by a terphenyl phosphine ligand, PCyp2ArXyl2 (Cyp = cyclopentyl; ArXyl2 = 2,6-bis(2,6-dimethylphenyl)phenyl), P1, has been thoroughly investigated. Combining computational and experimental studies, we found that the Pd(II) oxidative addition intermediate reacts with NH-carbazole in the presence of the base (NaOtBu) to yield a stable aryl carbazolyl Pd(II) complex. This species functions as the catalyst resting state, providing the amount of monoligated LPd(0) species required for catalysis and minimizing Pd decomposition. In the case of a reaction with aniline, an equilibrium between the carbazolyl complex and the on-cycle anilido analogue is established, which allows for a fast reaction at room temperature. In contrast, heating is required in a reaction with alkylamines, whose deprotonation involves coordination to the Pd center. A microkinetic model was built combining computational and experimental data to validate the mechanistic proposals. In conclusion, our study shows that despite the rate reduction observed in some reactions by the formation of the aryl carbazolyl Pd(II) complex, this species reduces catalyst decomposition and could be considered an alternative precatalyst in cross-coupling reactions.The authors thank MCIN/AEI/ 10.13039/501100011033 (Grant PID2020-113797R), US/JUNTA/FEDER, UE (Grant US-1262266), and FEDER/Junta de Andalucía-Consejería de Economía y Conocimiento (Grant P20_00624) for the financial support. R.J.R. and A.N. acknowledge the support from the Research Council of Norway through the Centre of Excellence (No. 262695) and A.N. for its FRINATEK program (314321). R.J.R. thanks the Universidad de Sevilla (V and VI Plan Propio de Investigación) for research fellowships. R.J.R. thanks the Norwegian Metacenter for Computational Science (NOTUR) for computational resources (No. nn4654k). Thanks are also due to Nazaret Santamaría for helping with kinetic experiments

Boryl-assisted hydrogenolysis of a nickel–methyl bond

A stable Nickel(II) methyl complex containing a diphosphinoboryl (PBP) pincer ligand is described. Mechanistic studies on the hydrogenolysis of the Ni-Me bond suggest a metal ligand cooperation mechanism that involves the intermediacy of a - B‒H Ni(0) species that further undergoes B‒H oxidative addition to form a Ni(II) hydride complex

Structural pathway of regulated substrate transfer and threading through an Hsp100 disaggregase

Refolding aggregated proteins is essential in combating cellular proteotoxic stress. Together with Hsp70, Hsp100 chaperones, including Escherichia coli ClpB, form a powerful disaggregation machine that threads aggregated polypeptides through the central pore of tandem adenosine triphosphatase (ATPase) rings. To visualize protein disaggregation, we determined cryo–electron microscopy structures of inactive and substrate-bound ClpB in the presence of adenosine 5′-O-(3-thiotriphosphate), revealing closed AAA+ rings with a pronounced seam. In the substrate-free state, a marked gradient of resolution, likely corresponding to mobility, spans across the AAA+ rings with a dynamic hotspot at the seam. On the seam side, the coiled-coil regulatory domains are locked in a horizontal, inactive orientation. On the opposite side, the regulatory domains are accessible for Hsp70 binding, substrate targeting, and activation. In the presence of the model substrate casein, the polypeptide threads through the entire pore channel and increased nucleotide occupancy correlates with higher ATPase activity. Substrate-induced domain displacements indicate a pathway of regulated substrate transfer from Hsp70 to the ClpB pore, inside which a spiral of loops contacts the substrate. The seam pore loops undergo marked displacements, along with ordering of the regulatory domains. These asymmetric movements suggest a mechanism for ATPase activation and substrate threading during disaggregation

Ni(II) Precatalysts Enable Thioetherification of (Hetero)Aryl Halides and Tosylates and Tandem C−S/C−N Couplings

Ni-catalyzed C−S cross-coupling reactions have received less attention compared with other C-heteroatom couplings. Most reported examples comprise the thioetherification of most reactive aryl iodides with aromatic thiols. The use of C−O electrophiles in this context is almost uncharted. Here, we describe that preformed Ni(II) precatalysts of the type NiCl(allyl)(PMe2Ar’) (Ar’=terphenyl group) efficiently couple a wide range of (hetero)aryl halides, including challenging aryl chlorides, with a variety of aromatic and aliphatic thiols. Aryl and alkenyl tosylates are also well tolerated, demonstrating, for the first time, to be competent electrophilic partners in Ni-catalyzed C−S bond formation. The chemoselective functionalization of the C−I bond in the presence of a C−Cl bond allows for designing site-selective tandem C−S/C−N couplings. The formation of the two C-heteroatom bonds takes place in a single operation and represents a rare example of dual electrophile/nucleophile chemoselective process.We thank FEDER/Ministerio de Ciencia, Innovación y Universi dades-Agencia Estatal de Investigación (Grant CTQ2017-82893-C2-2-R) and US/FEDER/JUNTA, UE (Grant, US126226) for finan cial suppor

Synthesis, properties, and some rhodium, iridium, and platinum complexes of a series of bulky m-terphenylphosphine ligands

A series of sterically demanding aryl phosphine ligands (L) bearing terphenyl substituents, PR2Ar′ (R = hydrocarbyl, Ar′ = 2,6-diarylphenyl radical) has been prepared and characterized. The stability of these ligands towards oxidation in the air has been tested, and theoretical and experimental studies aimed to provide information on their electronic and steric properties have been performed. Treatment of the metal dimers [MCl(COD)]2(M = Rh, Ir; COD = 1,5-cyclooctadiene) with ligands PMe2ArXyl2(L1) and PMe2ArDipp2(L5), in a 1:1 metal:ligand ratio, afforded the expected square-planar 16-electron complexes [MCl(COD)(PMe2ArXyl2)] and [MCl(COD)(PMe2ArDipp2)], respectively. These compounds were readily converted into the corresponding dicarbonyl derivatives, [MCl(CO)2(PMe2ArXyl2)] and [MCl(CO)2(PMe2ArDipp2)], respectively. While the expected κ1-P coordination mode of the PR2Ar′ ligands is found for these rhodium and iridium species, the mononuclear Pt(II) derivative obtained by reaction of PtCl2with PMe2ArDipp2has composition [PtCl2(PMe2ArDipp2)], and exhibits a bidentate κ1-P, η1-arene coordination mode involving one of the ipso carbon atoms of a flanking terphenyl aryl ring. The corresponding carbonyl compound [PtCl2(CO)(PMe2ArDipp2)], was generated under a CO atmosphere and exhibits κ1-P coordination mode.Ministerio de Ciencia CTQ2013-42501-P, CTQ2014-51912-REDC, CTQ-2014-52769-C3-3-RJunta de Andalucía FQM-119 P09-FQM-4832, FQM-2126European Union 26722

Formation of C−X Bonds Through Stable Low-Electron Count Cationic Pt(IV) Alkyl Complexes Stabilized by N-Heterocyclic Carbenes

Cationic five-coordinate Pt(IV) alkyl complexes stabilized by bulky N-heterocyclic carbenes have been isolated and fully characterized. Related species have been postulated as key intermediates in carbon–heteroatom coupling reactions and most particularly in Shilov-type chemistry. The alkyl groups exhibit a pronounced electrophilic character and can undergo nucleophilic addition of pyridine, bromide, or iodide to form new carbon–heteroatom bonds. Nevertheless, direct reductive coupling to form C–X bonds can be operative in the absence of an external nucleophile source.Ministerio de Ciencia, Innovación y Universidades CTQ2013-45011Junta de Andalucía FQM-212