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by ZFreixa in publications, Quimica 0 comments

Hydrogen tunneling. Giant KIE!

Hudrogen tunneling in the iridium-catalyzed hydrolysis/alcoholysis of hydrosilanes

Jun 27

by ZFreixa in publications, Quimica 0 comments

Fluorescent bicolour sensor for low-background neutrinoless double β decay experiments.

An interdisciplinary collaboration reached Nature! Abstract. Observation of the neutrinoless double β decay is the only practical way to establish that neutrinos are their own antiparticles1. Because of the small masses of neutrinos, the lifetime of neutrinoless double β decay is expected to be at least ten orders of magnitude greater than the typical lifetimes of natural radioactive chains, which can mimic the experimental signature of neutrinoless double β decay2. The most robust identification of neutrinoless double β decay requires the definition of a signature signal—such as the observation of the daughter atom in the decay—that cannot be generated by radioactive backgrounds, as well as excellent energy resolution. In particular, the neutrinoless double β decay of 136Xe could be established by detecting the daughter atom, 136Ba2+, in its doubly ionized state3–8. Here we demonstrate an important step towards a ‘barium-tagging’ experiment, which identifies double β decay through the detection of a single Ba2+ ion. We propose a fluorescent bicolour indicator as the core of a sensor that can detect single Ba2+ ions in a high-pressure xenon gas detector. In a sensor made of a monolayer of such indicators, the Ba2+ dication would be captured by one of the molecules and generate […]

Jun 27

by Zoraida Freixa in publications, Quimica 0 comments

Secondary Phosphine Oxides: Bifunctional Ligands inCatalysis

Minireview on the role of SPOs in catalysis. Abstract. Metal complexes of secondary phosphine oxides (SPOs) were introduced as homogeneous catalysts in the 1980s for hydroformylation and hydrogenation with platinum as the metal. As neutral species, the ligand properties resemble those of the corresponding tertiary phosphines as was shown in the coordination chemistry developed in the 1970s, but the participation of the OH in bonding and reaction mechanisms provides them with a peculiar additional function. While this was already proposed and recognized in the first publications, it took a while before this found wider appreciation. Meanwhile, SPOs have become popular ligands for homogeneous catalysts, and more recently also for catalysis based on metal nanoparticles. Here we review the relatively small number of publications that pay attention to SPOs as bifunctional ligands. Metal complexes of secondary phosphine oxides (SPOs) were introduced as homogeneous catalysts in the 1980s for hydroformylation and hydrogenation with platinum as the metal. As neutral species, the ligand properties resemble those of the corresponding tertiary phosphines as was shown in the coordination chemistry developed in the 1970s, but the participation of the OH in bonding and reaction mechanisms provides them with a peculiar additional function. While this was […]

May 21

by ZFreixa in publications, Quimica, Sin categoría 0 comments

Photoswitchable catalysis using organometallic complexes

A mini-review on Photoswitchable catalysis with organometallic compounds. This review describes the state of the art in photoswitchable organometallic catalysis, underlining the importance of ligand design. The implementation of spatio-temporal control on known catalytic processes has been appealing to several researchers for a long time. Even though the area is still in its infancy, the diversity of the existing examples shows that there are plenty possibilities in terms of the photochromic actuator of choice, and on the expected effect of the photochemical transformation on the catalytic process. The pioneering examples discussed here are, in many cases, just basic models far from efficient. However, they suffice to envisage the magnitude of the space that remains unexplored, letting us foresee that exciting innovations are awaiting. To access publication click here.

May 21

by ZFreixa in publications, Quimica, Sin categoría 0 comments

Proton-responsive Ruthenium(II) Catalysts for the Solvolysis of Ammonia-Borane

Our work on a proton-responsive hydrogen generation catalyst reached the cover in Organometallics! Two water-soluble ruthenium(II) complexes (1 and 2) containing the proton-responsive 6,6′-dihydroxy-2,2′-bipyridine (dhbp) ligand were studied as precatalysts for the solvolysis of ammonia-borane (AB) in water and/or alcohols. Both precursors generate in situ the same catalytic system. In spite of the excellent initial activities observed, it suffered a sudden deactivation at extended conversions. Detailed experimental studies combined with theoretical (density functional theory) calculations permitted us to describe the reaction mechanism as two interrelated pH-dependent catalytic cycles operating within a single run. According to this hypothesis, the deactivation observed occurred as a consequence of the increase in NH3 concentration and pH along the reaction progress. It was attributed to deprotonation of the dhbp ligand and amination or hydroxylation of the resulting compound. Accordingly, reactions performed in buffered solutions at neutral pH retarded this process, and up to 2.5 equiv of H2 per mole of AB were liberated in less than 1 min (TOF50% up to 33 113 h–1 (TOF = turnover frequency)). When the reaction was run in alcohols (MeOH, EtOH, or iPrOH) it proceeded at faster rates than in water, the one discussed here being the first homogeneous catalytic system active […]

Oct 07

by ZFreixa in publications 0 comments

Revisiting the iridacycle-catalyzed hydrosilylation of enolizable imines… cover!

Our work on the mechanism of hydrosilylation of enolizable imines catalyzed by Ir(III) metalacycles reached the cover in Catalysis Science & Technology! The hydrosilylation of enolizable imines using iridacycle catalysts has been investigated using a family of half-sandwich iridium(III) complexes. Several pitfalls had been detected when using standard procedures, and the use of in situ NMR spectroscopy appeared decisive to assess the actual reaction pathway. The results obtained clearly demonstrate that iridacycle-catalyzed hydrosilylation of enolizable imines with monohydrosilanes should be described as a domino reaction sequence, analogous to the one described by Oestreich et al. for boron-based Lewis acid catalysts. Equimolecular quantities of amine (b) and N-silylated enamine (c) were formed in the first stage, consuming 0.5 eq. of hydrosilane, which were subsequently converted into N-silylated amine (d) through a consecutive catalytic cycle using an additional 0.5 eq. of hydrosilane. However, when polyhydrosilanes were used as hydrosilylating agents, N-silylated amine (d) was directly obtained as the reaction product, but after a fast initial conversion, the reaction suffered from product inhibition. Additionally, iridacycles were also found to be active in the dehydrocoupling of Et3SiH and amines and in the hydrolysis of hydrosilanes, which can be competitive processes. These findings lead to an intricate mechanistic […]

Oct 07

by ZFreixa in publications 0 comments

Light-driven water oxidation using hybrid photosensitizer-decorated Co3O4 nanoparticles

A collaboration that originated as a CTP-network gave us this nice paper. Congratullations Jonathan! Abstract Cobalt nanoparticles (NPs) have been prepared by hydrogenation of the organometallic complex [Co(eta(3)-C8H13)(eta(4)-C8H12)] in 1-heptanol in the absence of any other stabilizer and then transformed into Co3O4 NPs using mild oxidative reaction conditions. After deposition onto glassy carbon rotating disk electrodes, the electrocatalytic performance of the Co3O4 NPs in water oxidation has been tested in 1M NaOH. The activity has been benchmarked with that of state-of-the-art Co3O4 NPs through electrochemically-active surface area (ECSA) and specific current density measurements. Furthermore, the covalent grafting of photosensitive polypyridyl-based RuII complexes onto the surface of Co3O4 NPs afforded hybrid nanostructured materials able to photo-oxidize water into O-2, while steady-state and time-resolved spectroscopic measurements gave some further insight into kinetics and pertinent reaction steps following excitation. These first-row transition metal oxide hybrid nanocatalysts display better catalytic performance than simple mixtures of non-grafted photosensitizers and Co3O4 NPs, thus evidencing the advantage of the direct coupling between the two entities for the photo-induced water oxidation reaction. (c) 2018 Elsevier Ltd. All rights reserved. Access full text here.