New Insights into Trifluoromethyl Gold Chemistry

Se ha realizado un estudio exhaustivo de la química de trifluorometil complejos de oroque contienen entre uno y tres grupos CF3. Con ese objetivo, se han preparado loscomplejos de oro(I) [PPh4][CF3AuX] (X = Cl, Br, I), que son oxidados fácilmente porhalógenos, X2, para dar lugar a los complejos [PPh4][CF3AuX3] correspondientes.Mediante espectrometría de masas en tándem, los primeros conducen a los anionesmixtos [F−Au−X]− a través de la extrusión de CF2 en fase gas, mientras que los aniones[AuIIX3]− (X = Cl, Br) se generan por homólisis del enlace Au−C en los complejos deAu(III). Por reacción de [PPh4][CF3AuCF3] con XeF2 se ha preparado y caracterizadototalmente el primer difluoruro organometálico de oro(III) con disposición trans,[PPh4][trans-(CF3)2AuF2]. El estudio de la descomposición unimolecular del anión[trans-(CF3)2AuF2]− ha permitido detectar las especies [CF3AuFx]– (x = 1, 2, 3) en fasegas, así como los aniones [AuIIF3]− y [AuIF2]− en etapas posteriores del experimento.Además, los ligandos fluoruro en el complejo [PPh4][trans-(CF3)2AuF2] son sustituidosfácilmente por los halogenuros más pesados y por cianuro, con retención de laestereoquímica. De hecho, por comparación de las estructuras cristalinas de las especiesisolépticas e isomorfas [PPh4][trans-(CF3)2M(CN)2] (M = Ag, Au), se pudo concluirque Au(III) y Ag(III) tienen radios covalentes similares en su geometría plano cuadrada.La obtención del complejo [PPh4][(CF3)3AuI] por fotoadición oxidante de CF3I sobre[PPh4][CF3AuCF3] constituye la ruta de acceso más apropiada al fragmento (CF3)3Au.Esta especie de Au(III) abre la puerta a la síntesis de diferentes derivados aniónicos,cuyos análogos [(CH3)3AuX]− no se conocen. Además, se ha preparado el análogofluorado del trimetil oro, (CF3)3Au·OEt2, que es un sintón adecuado de la especieinsaturada de 14 electrones (CF3)3Au. Este fragmento es el ácido de Lewis R3Au (R =grupo organilo) más fuerte descrito hasta la fecha. Esta unidad (CF3)3Au, que presentaforma de T, se caracteriza por una marcada estabilidad estereoquímica y una bajatendencia a la eliminación reductora de CF3–CF3, contrariamente al comportamientoobservado para el análogo no fluorado (CH3)3Au. También se han preparado ycaracterizado diversos complejos neutros con ligandos de diferente capacidad dadora ydistintos átomos dadores, que presentan una estabilidad muy superior a sus análogos nofluorados. Los complejos aniónicos de Au(III) descritos presentan vías dedescomposición distintas en fase gas, donde solo ocurren procesos unimoleculares, y enfase condensada, donde son posibles caminos intermoleculares de menor energía.<br /

Unravelling the Role of the Pentafluoroorthotellurate Group as a Ligand in Nickel Chemistry

The pentafluoroorthotellurate group (teflate, OTeF5) is able to form species, for which only the fluoride analogues are known. Despite nickel fluorides being widely investigated, nickel teflates have remained elusive for decades. By reaction of [NiCl4]2− and neat ClOTeF5, we have synthesized the homoleptic [Ni(OTeF5)4]2− anion, which presents a distorted tetrahedral structure, unlike the polymeric [NiF4]2−. This high‐spin complex has allowed the study of the electronic properties of the teflate group, which can be classified as a weak/medium‐field ligand, and therefore behaves as the fluoride analogue also in ligand‐field terms. The teflate ligands in [NEt4]2[Ni(OTeF5)4] are easily substituted, as shown by the formation of [Ni(NCMe)6][OTeF5]2 by dissolving it in acetonitrile. Nevertheless, careful reactions with other conventional ligands have enabled the crystallization of nickel teflate complexes with different coordination geometries, i.e. [NEt4]2[trans‐Ni(OEt2)2(OTeF5)4] or [NEt4][Ni(bpyMe2)(OTeF5)3].Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Terminal Au-N and Au-O Units in Organometallic Frames

Since gold is located well beyond the oxo wall, chemical species with terminal Au−N and Au−O units are extremely rare and limited to low coordination numbers. We report here that these unusual units can be trapped within a suitable organometallic frame. Thus, the terminal auronitrene and auroxyl derivatives [(CF3)3AuN]− and [(CF3)3AuO]− were identified as local minima by calculation. These open-shell, high-energy ions were experimentally detected by tandem mass spectrometry (MS2): They respectively arise by N2 or NO2 dissociation from the corresponding precursor species [(CF3)3Au(N3)]− and [(CF3)3Au(ONO2)]− in the gas phase. Together with the known fluoride derivative [(CF3)3AuF]−, they form an interesting series of isoleptic and alloelectronic complexes of the highly acidic organogold(iii) moiety (CF3)3Au with singly charged anions X− of the most electronegative elements (X=F, O, N). Ligand-field inversion in all these [(CF3)3AuX]− species results in the localization of unpaired electrons at the N and O atoms

Unravelling the Role of the Pentafluoroorthotellurate Group as a Ligand in Nickel Chemistry

The pentafluoroorthotellurate group (teflate, OTeF5) is able to form species, for which only the fluoride analogues are known. Despite nickel fluorides being widely investigated, nickel teflates have remained elusive for decades. By reaction of [NiCl4]2− and neat ClOTeF5, we have synthesized the homoleptic [Ni(OTeF5)4]2− anion, which presents a distorted tetrahedral structure, unlike the polymeric [NiF4]2−. This high‐spin complex has allowed the study of the electronic properties of the teflate group, which can be classified as a weak/medium‐field ligand, and therefore behaves as the fluoride analogue also in ligand‐field terms. The teflate ligands in [NEt4]2[Ni(OTeF5)4] are easily substituted, as shown by the formation of [Ni(NCMe)6][OTeF5]2 by dissolving it in acetonitrile. Nevertheless, careful reactions with other conventional ligands have enabled the crystallization of nickel teflate complexes with different coordination geometries, i.e. [NEt4]2[trans‐Ni(OEt2)2(OTeF5)4] or [NEt4][Ni(bpyMe2)(OTeF5)3]

Preparation and Characterization of [Au(CF3)xF3−x(SIMes)] (x=1–3) Complexes

Trifluoromethylation of [AuF3(SIMes)] with the Ruppert–Prakash reagent TMSCF3 in the presence of CsF yields the product series [Au(CF3)xF3−x(SIMes)] (x=1–3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the 19F NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of trans‐[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the 13C NMR spectrum reveals that trans‐[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the Au−Ccarbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13C NMR spectrum is presented

Gold Teflates Revisited: from the Lewis Superacid [Au(OTeF5)3] to the Anion [Au(OTeF5)4]−

A new synthetic access to the Lewis acid [Au(OTeF5)3] and the preparation of the related, unprecedented anion [Au(OTeF5)4]− with inorganic or organic cations starting from commercially available and easy-to-handle gold chlorides are presented. In this first extensive study of the Lewis acidity of a transition metal teflate complex using different experimental and quantum chemical methods, [Au(OTeF5)3] was classified as a Lewis superacid. The solid state structure of the triphenylphosphane adduct [Au(OPPh3)(OTeF5)3] was determined, representing the first structural characterization of an adduct of this highly reactive [Au(OTeF5)3]. Therein, the coordination environment around the gold center slightly deviates from the typical square planar geometry. The related, unprecedented anion [Au(OTeF5)4]− shows a similar coordination motif

Air-stable aryl derivatives of pentafluoroorthotellurate

We report on two different sets of air-stable derivatives of pentafluoroorthotellurate containing fluorinated and non-fluorinated aryl groups. The acid cis-PhTeF4OH was obtained in gram scale and further transformed to Ag[cis-PhTeF4O], which was used as a cis-PhTeF4O transfer reagent to obtain [PPh4][cis-PhTeF4O]. Furthermore, the synthesis of trans-(C6F5)2TeF3OH was achieved by a selective hydrolysis of trans-(C6F5)2TeF4 in the presence of KF and subsequent protonation by aHF. Quantum-chemical calculations show a higher acidity and robustness against fluoride abstraction for trans-(C6F5)2TeF3OH compared to cis-PhTeF4OH

Reactivity of [AuF3(SIMes)] – Pathway to Unprecedented Structural Motifs

We report on a comprehensive reactivity study starting from [AuF3(SIMes)] to synthesize different motifs of monomeric gold(III) fluorides. A plethora of different ligands has been introduced in a mono-substitution yielding trans-[AuF2X(SIMes)] including alkynido, cyanido, azido, and a set of perfluoroalkoxido complexes. The latter were better accomplished via use of perfluorinated carbonyl-bearing molecules, which is unprecedented in gold chemistry. In case of the cyanide and azide, triple substitution gave rise to the corresponding [AuX3(SIMes)] complexes. Comparison of the chemical shift of the carbene carbon atom in the 13C{1H} NMR spectrum, the calculated SIMes affinity and the Au–C bond length in the solid state with related literature-known complexes yields a classification of trans-influences for a variety of ligands attached to the gold center. Therein, the mixed fluorido perfluoroalkoxido complexes have a similar SIMes affinity to AuF3 with a very low Gibbs energy of formation when using the perfluoro carbonyl route

Diferente comportamiento del platino y el oro en la formación de enlaces de hidrógeno M···H

Máster Universitario en Química molecular y Catálisis Homogénea.Recientemente el modelo del enlace de hidrógeno se ha ampliado para incluir algunos centros metálicos como aceptores de protones. Se ha comprobado que el platino(II) puede actuar como aceptor de protones en las interacciones M···H-D, mientras que el oro(III), pese a ser isoelectrónico, presenta gran controversia como potencial aceptor de hidrógeno. Para clarificar este tema, se han preparado una serie de derivados de oro(III) y platino(II) análogos, con grupos trifluorometilo, y ligandos de tipo quinolina con grupos capaces de formar interacciones M···H-D. La especie planocuadrada de oro(III), [PPh4][Au(CF3)3I] (1), se ha preparado por adición oxidante de CF3I sobre [PPh4][Au(CF3)2] comprobando que esta reacción transcurre por un mecanismo radicalario y que la adición tiene lugar en trans, lo que se demuestra al utilizar n-C4F9I y obtener [PPh4][trans-Au(CF3)2(C4F9)I] (2). Por reacción de 1 con AgClO4 en Et2O, se obtiene una disolución del complejo [Au(CF3)3(OEt2)] (3) que, por adición del ligando correspondiente, conduce a los complejos [Au(CF3)3L] (L = 8-hidroxiquinolina (4), 8-metilquinolina (5), 2-metil-8-hidroxiquinolina (6)). Los espectros de 1H RMN de 4, 5 y 6 no indican que exista enlace de hidrógeno, y la estructura molecular del complejo 4·Et2O demuestra que el Et2O es mejor base de Lewis que el oro(III). Se ha sintetizado el complejo [NBu4][Pt(CF3)3(NCCH3)] (7) para acceder a los complejos [NBu4][Pt(CF3)3L] (L = 8-hidroxiquinolina (8), 8-metilquinolina (9), 2-metil-8-hidroxiquinolina (10)). El 1H RMN confirma que en los complejos 8 y 10 existe enlace de hidrógeno al centro de platino(II), pues la señal del OH aparece muy desplazada a bajo campo y presenta satélites de 195Pt con constantes muy elevadas. La estructura molecular de 10 demuestra la existencia de interacción M···H-D. Los cálculos teóricos están de acuerdo con los resultados experimentales, y demuestran que la interacción M···H-O es repulsiva con el oro(III) en 4 pero atractiva con el platino(II) en 8.Peer Reviewe

Motivational pathways towards academic achievement in physics & chemistry: A comparison between students who opt out and those who persist

The main goal of the present investigation was to analyze the effect of motivation towards physics & chemistry on achievement in secondary school students. We focused our interest on the comparison between students who chose the subject when becoming optional in the Spanish educational system and those who opted out. Our analyses uncovered the existence of three different motivational profiles towards achievement in physics & chemistry, depending on the students' decisions to persist or to leave. Regardless of their choice, self-efficacy played a key role, not only as a direct predictor of academic achievement but also as a facilitator of the indirect effects of other motivational variables on academic performance. However, our models showed that, for students who opt out physics and chemistry, grade motivation and self-determination are more important predictors of performance than for those who choose the subject. Gender effects and educational implications are also addressed.A. P.-B. thanks the Spanish Ministerio de Educación, Cultura y Deporte for a grant (FPU15/03940)