Diseño de Plataformas Moleculares Multifuncionales

El boro es un elemento que forma compuestos químicos que presentan enlaces de tres centros y dos electrones, de tipo B-H-B o B-B-B como, por ejemplo, el anión octahidrotriborato, B3H8-.El anión octahidrotriborato es un compuesto muy importante en la química del boro, ya que es un intermedio de reacción en la síntesis de boranos superiores y de diversos complejos de metales de transición. También cabe destacar que este anión, en disolución, es fluxional, ya que todos los átomos de hidrógeno, presentes en la molécula, se intercambian en el tiempo de escala de los experimentos de Resonancia Magnética Nuclear (RMN) de 1H; el mecanismo de intercambio que se ha propuesto en la bibliografía consiste en una pseudorrotación del grupo BH2.Una de las formas más estables en las que se puede encontrar el anión es como CsB3H8 o ((n-С4H9)4N)[B3H8]. Estas sales se pueden utilizar para sintetizar metalaboranos de B3H8-, que son complejos de metal en donde el anión triborato funciona como ligando. Una síntesis interesante de este tipo es la que ha permitido obtener la molécula de rodatetraborano, [Rh(η2-B3H8)(H)2(PPh3)2].El rodatetraborano es un complejo de Rh(III) en donde el B3H8-, actúa como un ligando quelato bidentado. Este metalaborano, en disolución, también presenta comportamientos fluxionales, que han sido estudiados y caracterizados por RMN. A temperaturas superiores a los 290 K, se produce la apertura de los enlaces B-H-B y la migración de los átomos de H terminales de manera sincronizada.<br /

Tuning PCP-Ir complexes: the impact of an N-heterocyclic olefin

A new PCP-type ligand based on an N-heterocyclic olefin (NHO) scaffold has been prepared. The flexibility of this ligand, which is able to adopt facial coordination modes in Ir(I) or meridional in Ir(III) complexes, can be attributed to the dual nature (ylide–olefin) of the NHO scaffold. This results in a rare case of olefin “slippage” that is supported by X-ray crystallography and DFT calculations.This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) (CONSOLIDER INGENIO CSD2009-0050, CTQ2011-27593 and CTQ2012-35665 projects) and the DGA/FSE-E07. The support from KFUPM-University of Zaragoza research agreement and the Centre of Research Excellence in Petroleum Refining & KFUPM is gratefully acknowledged.Peer Reviewe

An alternative mechanistic paradigm for the β-Z hydrosilylation of terminal alkynes: The role of acetone as a silane shuttle

The β-Z selectivity in the hydrosilylation of terminal alkynes has been hitherto explained by introduction of isomerisation steps in classical mechanisms. DFT calculations and experimental observations on the system [M(I)2{κ-C,C,O,O-(bis-NHC)}]BF4 (M=Ir (3 a), Rh (3 b); bis-NHC=methylenebis(N-2-methoxyethyl)imidazole-2-ylidene) support a new mechanism, alternative to classical postulations, based on an outer-sphere model. Heterolytic splitting of the silane molecule by the metal centre and acetone (solvent) affords a metal hydride and the oxocarbenium ion [R 3Si - O(CH3)2]+, which reacts with the corresponding alkyne in solution to give the silylation product [R 3Si - CHï£C - R]+. Thus, acetone acts as a silane shuttle by transferring the silyl moiety from the silane to the alkyne. Finally, nucleophilic attack of the hydrido ligand over [R3Si - CHï£C - R]+ affords selectively the β-(Z)- vinylsilane. The β-Z selectivity is explained on the grounds of the steric interaction between the silyl moiety and the ligand system resulting from the geometry of the approach that leads to β-(E)-vinylsilanes. Silanes catch the shuttle: An outer-sphere mechanism that explains the β-Z hydrosilylation of terminal alkynes based on the role of acetone as a silane shuttle is disclosed. Heterolytic splitting of the silane molecule by the metal centre and acetone affords a metal hydride and the oxocarbenium ion [R 3Si - O(CH3)2]+, which reacts with the alkyne in solution to give the silylation product [R3Si - CHï£C - R]+ (see figure). © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) (CONSOLIDER INGENIO-2010, CTQ2011-27593 projects, and “Ramón y Cajal” (P.J.S.M.) and “Juan de la Cierva” (M.I.) programmes) and the DGA/FSE (E07).Peer Reviewe

Reactividad del decaborano con bases de Brønsted y compuestos de plata: Estudios estructurales y espectroscópicos

En este TFG se ha sintetizado la sal de Proton Sponge, [PSH][B10H13]. Los reactivos empleados, decaborano y Proton Sponge, son solubles en hexano y se disolvieron individualmente, y tras verter la base sobre el decaborano, B10H14, se observó la precipitación instantánea de la sal. Así, este procedimiento de síntesis es una forma nueva y conveniente de preparar una sal de decaborano, que es estable al aire, y fácil de pesar y manipular. Se ha observado por primera vez en el sistema nido-decaborano, el movimiento tautomérico de los átomos de hidrógeno puente de su estructura. El clúster aniónico, [B10H13]-, presenta procesos fluxionales en los que intervienen los átomos de hidrógeno puente, y se ha podido caracterizar con detalle que los tres átomos de hidrógeno puente de su estructura participan en un intercambio de posición continuo con movimiento constante alrededor de la cara hexagonal del clúster. La obtención de la sal se debe a la abstracción de un átomo de hidrógeno puente del decaborano por la base Proton Sponge. Cabría esperar que la base atacara acercándose por la parte de arriba de la cara hexagonal del B10H14, donde se encuentran los átomos de hidrógeno ácidos; pero los cálculos DFT indican que las configuraciones de menor energía son aquellas en las que el catión interacciona con la periferia del clúster. Este hecho nos hace sugerir que la base, PS, podría capturar el protón también en la periferia del clíster, cerca de los átomos terminales, disminuyendo así las repulsiones estéricas entre el clúster poliédrico y la base orgánica. La sal de decaborano es un producto de partida útil para el estudio de su reactividad con moléculas orgánicas, complejos metálicos, etc

An insight into transfer hydrogenation reactions catalysed by iridium(III) bis-N-heterocyclic carbenes

A variety of [M(L)2(L′)2{κC,C′-bis(NHC)}]BF4 complexes (M = Rh or Ir; L = CH3CN or wingtip group; L′ = I– or CF3COO–; NHC=N-heterocyclic carbene) have been tested as pre-catalysts for the transfer hydrogenation of ketones and imines. The conversions and TOF's obtained are closely related to the nature of the ligand system and metal centre, more strongly coordinating wingtip groups yielding more active and recyclable catalysts. Theoretical calculations at the DFT level support a classic stepwise metal-hydride pathway against the concerted Meerwein–Ponndorf–Verley (MPV) mechanism. The calculated catalytic cycle involves a series of ligand rearrangements due to the high trans effect of the carbene and hydrido ligands, which are more stable when situated in mutual cis positions. The reaction profiles obtained for the complexes featuring an iodide or a trifluoroacetate in one of the apical positions agree well with the relative activity observed for both catalysts.The authors would like to acknowledge the support by the Ministry of Higher Education, Saudi Arabia, in establishment of the Centre of Research Excellence in Petroleum Refining & Petrochemicals at KFUPM (KACST-funded project ART-32-68). The support under the KFUPM–University of Zaragoza research agreement is also highly appreciated. This work was further supported by the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) (CONSOLIDER INGENIO CSD2009-0050, CTQ2011-27593 and CTQ2012-35665 projects) and the Diputación General de Aragón (DGA/FSE-E07).Peer Reviewe

Surface characterization of alkane viral anchoring films prepared by titanate-assisted organosilanization

Studies of virus adsorption on surfaces with optimized properties have attracted a lot of interest, mainly due to the influence of the surface in the retention, orientation and stability of the viral capsids. Besides, viruses in whole or in parts can be used as cages or vectors in different areas, such as biomedicine and materials science. A key requirement for virus nanocage application is their physical properties, i.e. their mechanical response and the distribution of surface charge, which determine virus-substrate interactions and stability. In the present work we show two examples of viruses exhibiting strong surface interactions on homogeneous hydrophobic surfaces. The surfaces were prepared by titanate assisted organosilanization, a sol-gel spin coating process, followed by a mild annealing step. We show by surface and interface spectroscopies that the process allows trapping triethoxy-octylsilane (OCTS) molecules, exhibiting a hydrophobic alkane rich surface finishing. Furthermore, the surfaces remain flat and behave as more efficient sorptive surfaces for virus particles than mica or graphite (HOPG). Also, we determine by atomic force microscopy (AFM) the mechanical properties of two types of viruses (human adenovirus and reovirus) and compare the results obtained on the OCTS functionalized surfaces with those obtained on mica and HOPG. Finally, the TIPT+OCTS surfaces were validated as platforms for the morphological and mechanical characterization of virus particles by using adenovirus as initial model and using HOPG and mica as standard control surfaces. Then, the same characteristics were determined on reovirus using TIPT+OCTS and HOPG, as an original contribution to the catalogue of physical properties of viral particlesThis work was supported by the grant Ayudas a Proyectos de I+D para Jovenes Doctores de la Universidad Autonoma de Madrid 2021 (SI3/PJI/2021–00216) supported by Comunidad de Madrid and Universidad Autonoma de Madrid to M.H-P. Also, M.H-P acknowledges funding from the Spanish Ministry of Science and Innovation (TED2021–129937B-I00). Grant PID2019–104098GB-I00/AEI/ 10.13039/501100011033, co-funded by the Spanish State Research Agency and the European Regional Development Fund to C.S.M. The CNB-CSIC was further supported by a Spanish State Research Agency Severo Ochoa Excellence grant (SEV 2017–0712). C.S.M is a member of the CSIC funded consortium LifeHub (CSIC grant number: 202120E47). REACT-EU funding by Comunidad Autonoma de Madrid is also acknowledged. M.M.S acknowledges funding from MCIN/AEI /10.13039/501100011033 (PID2020–112770RB-C22). P.J.P acknowledges projects FIS2017–89549-R; and FIS2017–90701-REDT. P.J.P also acknowledges the Human Frontiers Science Program (HFSPO RGP0012/2018

A neutral Pt3 stack unsupported by any bridging ligand

Pt⋯Pt⋯Pt interactions via their d8 orbitals, combined with π–π stacking of deprotonated, chelating 2-(3′-pyrazolyl)pyridine (pyzpy) ligands, are responsible for trans-Pt(pyzpy)2 (2) crystallization in a stack of three molecules unsupported by any bridging ligand

Hydrolysis and methanolysis of silanes catalyzed by iridium(III) bis-N-heterocyclic carbene complexes: Influence of the wingtip groups

New [Ir(CH3CN)2(I)2{κC,C′-bis(NHC)}]BF4 complexes featuring bis-NHC ligands with a methylene bridge and different N substitution (−CH2CH2CH2CH3 and −CH2CH2OPh) were synthesized. NMR studies and X-ray diffraction structures evidenced that the wingtip group −CH2CH2OPh presents a hemilabile behavior in solution, with the oxygen atom coordinating and dissociating at room temperature, which contrasts with the strong coordination of the ether functions in the complex [Ir(I)2{κC,C′,O,O′-bis(NHCOMe)}]BF4 (bis(NHCOMe) = methylenebis(N,N′-bis(2-methoxyethyl)imidazol-2-ylidene)), previously reported by us. These complexes proved to be efficient catalysts for the hydrolysis and methanolysis of silanes, affording molecular hydrogen and silyl alcohols or silyl ethers as the main reaction products in excellent yields. The hydrogen generation rates were very much dependent on the nature of the hydrosilane and the coordination ability of the wingtip group. The latter also played a key role in the recyclability of the catalytic system.This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) (CONSOLIDER INGENIO CSD2009-0050, CTQ2011-27593 projects, and “Juan de la Cierva” (M.I.) and Ramón y Cajal (P.J.S.M.) programs) and the DGA/FSE-E07. The authors express their appreciation to the support from the Ministry of Higher Education, Saudi Arabia, in establishment of the Center of Research Excellence in Petroleum Refining & Petrochemicals at King Fahd University of Petroleum & Minerals (KFUPM) and the support from KFUPM-University of Zaragoza research agreement.Peer Reviewe

Novel homogeneous Ir-catalysts: Ligand design, applications and mechanisms

Resumen del trabajo presentado a la 2nd World Chemistry Conference and Exhibition (WCCE), celebrada en Valencia (España) del 9 al 11 de julio de 2018.This presentation will deal with two main subjects: (i) the preparation ofthe frrst PCP-type ligand based on an N-heterocyclic olefm (NHO) scaffold, accompanied by an evaluation of the impact of this type of ligand in the activity of iridium complexes in several relevant catalytic processes; and (ii) the development of well- defined Ir-NHC complexes as catalysts for the dehydrogenative silylation of aromatic C-H bonds. (i) A great variety of pincer complexes has been reported in the literature. In particular, transition metal complexes containing PCP pincer ligands have shown remarkable activities in relevant catalytic processes. Recent work by us on this subject has resulted in the preparation of an ewPCP-type ligand based on an N- heterocyclic olefin (NHO) scaffold. The flexibille coordination of this NHO-based PCP-ligand can be attributed to the dual nature (ylide-olefm) oftbe NHO. Iridium(I) complexes featuring this ligand show excellent activities in transfer hydrogenation reactions. The active species ([Ir(KP,C,P'-NHO-PPh2)(iPrO)]), formed via COD dissociation and subsequent isopropoxide coordination, features an NHO moiety that behaves as a hemilabile ligand, which allows the catalyst to adopt stabJe square planar geometries in the transition states, thus reducing the energetic barrier of the process. More recently, we have tested the activity ofthese complexes in the dehydrogenation of formic acid, showing outstanding activities in water and in neat formicacid. (ii) The preparation of fine chernicals by the catalytic functionalization of C-H bonds has seen an outstanding development in recent years, with borylation and silylation reactions being prominent examples of this chemistry. In this regard, the versatility of oganosilicon compounds can be attributed to the low cost and non-toxic nature of silicon reagents, together with their straight forward functionalization by various reactions. Moreover, conjugated organosilicon materials are attractive targets per se owing to their unique properties, which permit a widespread applicability in the field of organic electronics and photonics. Most of the catalysts employed so far for this reaction are generated >in situ> from commercial metal precursors and ligands. Hence, we have focused on the development of well-defined organometallic catalysts bearing appropriate ligands in order to improve the efficiency of current silylation catalysts. In particular, the use of NHC-Ir (III) complex [Ir(H)2(IPr)(py)3][BF4] (IPr = 1 ,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) as a catalyst has allowed for the preparation of a wide range of aryl- and heteroarylsilanes. The directed and non-directed functionalization of C-H bonds has been accomplisbed successfully using the areneas tbe limiting reagent and a variety of hydrosilanes, including Et3SiH, Ph2MeSiH, PhMe2SiH, Ph3SiH and(Et0)3SiH.Peer Reviewe

Relevance of motion-related assessment metrics in laparoscopic surgery

INTRODUCTION: Motion metrics have become an important source of information when addressing the assessment of surgical expertise. However, their direct relationship with the different surgical skills has not been fully explored. The purpose of this study is to investigate the relevance of motion-related metrics in the evaluation processes of basic psychomotor laparoscopic skills, as well as their correlation with the different abilities sought to measure. METHODS: A framework for task definition and metric analysis is proposed. An explorative survey was first conducted with a board of experts to identify metrics to assess basic psychomotor skills. Based on the output of that survey, three novel tasks for surgical assessment were designed. Face and construct validation study was performed, with focus on motion-related metrics. Tasks were performed by 42 participants (16 novices, 22 residents and 4 experts). Movements of the laparoscopic instruments were registered with the TrEndo tracking system and analyzed. RESULTS: Time, path length and depth showed construct validity for all three tasks. Motion smoothness and idle time also showed validity for tasks involving bi-manual coordination and tasks requiring a more tactical approach respectively. Additionally, motion smoothness and average speed showed a high internal consistency, proving them to be the most task-independent of all the metrics analyzed. CONCLUSION: Motion metrics are complementary and valid for assessing basic psychomotor skills, and their relevance depends on the skill being evaluated. A larger clinical implementation, combined with quality performance information, will give more insight on the relevance of the results shown in this study