Reactivity of Fluorinated-Chalcone Phosphines, RPEWO-F4, Induced by C–F Activation upon Coordination to PdCl2

Producción CientíficaThe E phosphine ligands (R = Ph, o-Tol, Cy), abbreviated as RPEWO-F4, are stable in solution, but they develop a rich reactivity on coordination to PdCl2. The chelate P-olefin coordination to PdCl2 leads eventually to a Z conformation of the fluorinated-chalcone group o-C6F4CH═CHC(O)Ph. From there, a cyclization reaction occurs involving the C═O group and activation of a F atom, yielding a strongly chelated PdCl2(P-carbene) complex. The carbene carbon atom in the complex displays some electrophilicity, which is expressed in hydrolysis, ammonolysis, and oxidation (with peroxide) reactions, affording PdCl2 complexes with new P,C,O-pincer, P,C,N-pincer, or P,O-chelate fluorinated ligands. The C–F activation reactions are slow in comparison to the catalysis rates when the [PdCl2(RPEWO-F4)] complexes have been used in Negishi catalyses. Consequently, the reactivity discussed here is not expected to interfere with the interpretation of the data obtained in Pd-catalytic studies or processes, at least for fast transmetalating nucleophiles.Ministerio de Economía, Industria y Competitividad (projects CTQ2017-89217-P and CTQ2016-80913-P)Junta de Castilla y León (projects VA051P17 and VA062G18

E–Z Isomerization of Phosphine-Olefin (PEWO-F4) Ligands Revealed upon PdCl2 Capture: Facts and Mechanism

Producción CientíficaThe PEWO phosphines R2P(o-C6H4CH═CHC(O)Ph), R2P(o-C6H2F2CH═CHC(O)Ph), and R2P(o-C6F4CH═CHC(O)Ph) and their P-monodentate complexes trans-[PdCl2(P-monodentate)2] show, in solution and (when available) in the X-ray diffraction structures, an E configuration of the double bond. In contrast, the structures of [PdCl2(P-chelate)] display E and Z configurations. The E/Z isomerization of the latter requires first decoordination of the double bond, which then allows for easy rotation about the electron-deficient double bond. Thus, the E/Z equilibria exist for the free and the P-monodentate complexes as well but are not observed because they are extremely displaced toward the E isomer. Their capture in the form of [PdCl2(P-chelate)], with equilibrium constants on the order Keq ≈ 1–3, allows the two configurations to be observed and isolated. Evaluation of their ability to couple Pf–Pf from cis-[PdPf2(THF)2] (Pf = C6F5) affords values of their ΔG⧧(Pf–Pf)Pd parameters confirming that higher substitution of H by F produces lower coupling barriers and a double bond that is more electron deficient when it is free and more electron withdrawing when it is coordinated.Junta de Castilla y León (projects VA051P17 and VA062G18)Ministerio de Economía, Industria y Competitividad (projects CTQ2016-80913-P and CTQ2017-89217-P

Complejos de rodio e iridio con un ligando pinza POP: reacciones de borilación

Estos estudios revelan diferencias de comportamiento entre los fragmentos {xant(PiPr2)2}M de rodio e iridio, debido al mayor carácter reductor del iridio y su preferencia por formar compuestos saturados. Así, en el caso del iridio se aíslan complejos saturados d6 octaédricos, mientras que con rodio se obtienen los derivados insaturados d8 plano-cuadrados y d6 pentacoordinados. La rigidez y robustez proporcionada por la fosfina y la hemilabilidad del átomo de oxígeno permite estabilizar una gran variedad de compuestos insaturados con el fragmento {xant(PiPr2)2}Rh, siendo el complejo de rodio RhH{xant(PiPr3)2} el de mayor relevancia, ya que a partir de este derivado monohidruro hemos desarrollado un procedimiento sencillo para la síntesis de derivados plano-cuadrado insaturados de rodio(I) con ligandos sililo y borilo. Este complejo monohidruro promueve la activación C-H de arenos. Los productos de activación C-H dependen de los sustituyentes del areno. Los grupos metilo mantienen alejado al fragmento metálico, mientras que los sustituyentes flúor lo acercan. Por lo tanto, la selectividad observada sugiere que la activación C-H está controlada termodinámicamente. La activación B-H de boranos y C-H de arenos promovida por el complejo monohidruro hace posible la borilación estequiométrica y catalítica de arenos. El estudio etapa por etapa de la reacción, permite aislar y caracterizar los intermedios clave del proceso. El compuesto catiónico insaturado d6 pentacoordinado [RhH{Si(OH)Ph2}{xant(PiPr2)2}]+ se forma como resultado de la adición de un enlace O-H del agua al doble enlace Rh-Si de un intermedio silileno. De este modo, este derivado catiónico actúa como precursor de un catalizador muy eficiente para la monoalcohólisis selectiva de difenilsilano Durante el estudio experimental el mecanismo de la reacción de borilación por descianación mediada por rodio hemos aislado los intermedios implicados, siendo uno de ellos una especie plano-cuadrada ¿1-iminoacilo N-boril sustituida de rodio(I) sin precedentes en la bibliografía

Highly enantioselective addition of dimethylzinc to fluorinated alkyl ketones, and the mechanism behind it

Producción CientíficaChiral-diamine catalyzed addition of ZnMe2 to PhC(O)CF2X (in dichloromethane at −30 °C) affords fluorinated alkyl tertiary alcohols in high yield (quantitative for X = H, F, Cl; 84% for X = CF3) and up to 99% ee. These conditions are similarly very efficient for other various ArC(O)CF3 molecules. A fine analysis of the results can be performed based on a double-cycle mechanism.Ministerio de Economía, Industria y Competitividad (Projects CTQ-2016-80913-P and CTQ2014-52796)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA051P17

Solid state luminescence of phosphine-EWO ligands with fluorinated chalcone skeletons and their PdX2 complexes: metal-promoted phosphorescence enhancement

Producción CientíficaComplexes trans-[PdX2L2] (X = Cl and Br), where L is 1-(PR2),2-(CH[double bond, length as m-dash]CH–C(O)Ph)-C6F4 (R = Ph, Cy, and iPr), display phosphorescent emission in the solid state, whereas due to their substantially lower lifetimes, the free ligands exhibit fluorescent behaviour. Alternatively, structurally identical derivatives with halide replaced by CN− or Pd replaced by Pt are non-emissive. DFT calculations explain this diverse behaviour, showing that the hybridization of orbitals of the MX2 moiety with those of the chalcone fragment of ligands is significant only for the LUMO of the emissive compounds. In other words, in our complexes, only MLMCT processes (LM = Metal-perturbed Ligand-centered orbital) lead to observable luminescence.Ministerio de Ciencia e Innovación (Projects PID2020-118547GB-I00 and PGC 2018-093863-B-C21)Ministerio de Ciencia e Innovación (FPI studentship: BES-2017-080726)Universidad de Valladolid. Margarita Salas postdoctoral fellowship (ref. CONVREC-2021-221)