trans-Chloridobis(4-methyl­pyridine-κN)(4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine-κ3 N,N′,N′′)ruthenium(II) hexa­fluoridophosphate acetone monosolvate

The title compound, [RuCl(C6H7N)2(C27H35N3)]PF6·C3H6O, was obtained unintentionally as the product of the reaction of 1,1′-methyl­enebis(4-methyl­pyridinium) hexa­fluoriso­phos­phate and RuCl3(tpy*) (tpy* is 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine) in the presence of triethyl­amine and LiCl. The mol­ecular structure of the complex displays an octa­hedral geometry around the RuII ion and the unit cell contains an acetone solvent mol­ecule and one orientationally disordered PF6 − anion (occupancy ratio 0.75:0.25) which is hydrogen bonded to two H atoms of the tpy* ligand of the nearest [RuCl(pic)2(tpy*)]+ cation (pic is 4-methyl­pyridine). One of the tert-butyl groups of the tpy* ligand is also disordered over two sets of sites in a 0.75:0.25 ratio

Magnetically-actuated mesoporous nanowires for enhanced heterogeneous catalysis

We study the optimization of the catalytic properties of entirely magnetic CoPt compact and mesoporous nanowires of different diameters (25 - 200 nm). The nanowires are a single-entity magnetic-catalyst with a huge catalytically-active surface area, making them robust and easy to fabricate. We show that apart from the size and morphology of the nanowires, other factors can be optimized to enhance the catalytic activity of the nanowires. In particular, given the magnetic character of the nanowires, rotating magnetic fields are a very powerful approach to improve the performance of the catalyst by acting as nano-stirrers, improving the local flow of material towards the active sites of the catalyst. We demonstrate the versatility of the procedure by optimizing (i) the degradation of different types of pollutants (4-nitrophenol and methylene blue) and (ii) hydrogen production. For example, by using 25 nm wide CoPt mesoporous nanowires as catalysts, kinetic normalized constants knor as high as 20667 and 21750 s-1g-1 for 4-nitrophenol and methylene blue reduction, respectively, are obtained, and activity values for hydrogen production from borohydride are as high as 25.0 L H2 g-1 min-1, even at room temperature. These values outperform any current state-of-the-art proposed catalysis strategies for water remediation reactions by at least 10-times and are superior to most advanced approaches to generate hydrogen from borohydride. The recyclability of the nanowires together with the simplicity of the synthetic method makes this approach (using not only CoPt but also other mesoporous magnetic catalysts) very appealing for very diverse types of catalytic applications

Interplay between β-Diimino and β-Diketiminato Ligands in Nickel Complexes Active in the Proton Reduction Reaction

Acord transformatiu CRUE-CSICTwo Ni complexes are reported with κ4-P2N2 β-diimino (BDI) ligands with the general formula [Ni(XBDI)](BF4)2, where BDI is N-(2-(diphenylphosphaneyl)ethyl)-4-((2-(diphenylphosphaneyl)ethyl)imino)pent-2-en-2-amine and X indicates the substituent in the α-carbon intradiimine position, X = H for 1(BF4)2 and X = Ph for 2(BF4)2. Electrochemical analysis together with UV-vis and NMR spectroscopy in acetonitrile and dimethylformamide (DMF) indicates the conversion of the β-diimino complexes 12+ and 22+ to the negatively charged β-diketiminato (BDK) analogues (1-H)+ and (2-H)+ via deprotonation in DMF. Moreover, further electrochemical and spectroscopy evidence indicates that the one-electron-reduced derivatives 1+ and 2+ can also rapidly evolve to the BDK (1-H)+ and (2-H)+, respectively, via hydrogen gas evolution through a bimolecular homolytic pathway. Finally, both complexes are demonstrated to be active for the proton reduction reaction in DMF at Eapp = -1.8 V vs Fc+/0, being the active species the one-electron-reduced derivative 1-H and 2-H

Redox Metal-Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes

Water oxidation catalysis stands out as one of the most important reactions to design practical devices for artificial photosynthesis. Use of late first-row transition metal (TM) complexes provides an excellent platform for the development of inexpensive catalysts with exquisite control on their electronic and structural features via ligand design. However, the difficult access to their high oxidation states and the general labile character of their metal–ligand bonds pose important challenges. Herein, we explore a copper complex (1²⁻) featuring an extended, π-delocalized, tetra-amidate macrocyclic ligand (TAML) as water oxidation catalyst and compare its activity to analogous systems with lower π-delocalization (2²⁻ and 3²⁻). Their characterization evidences a special metal–ligand cooperativity in accommodating the required oxidative equivalents using 1²⁻ that is absent in 2²⁻ and 3²⁻. This consists of charge delocalization promoted by easy access to different electronic states at a narrow energy range, corresponding to either metal-centered or ligand-centered oxidations, which we identify as an essential factor to stabilize the accumulated oxidative charges. This translates into a significant improvement in the catalytic performance of 1²⁻ compared to 2²⁻ and 3²⁻ and leads to one of the most active and robust molecular complexes for water oxidation at neutral pH with a k_(obs) of 140 s⁻¹ at an overpotential of only 200 mV. In contrast, 2²⁻ degrades under oxidative conditions, which we associate to the impossibility of efficiently stabilizing several oxidative equivalents via charge delocalization, resulting in a highly reactive oxidized ligand. Finally, the acyclic structure of 3²⁻ prevents its use at neutral pH due to acidic demetalation, highlighting the importance of the macrocyclic stabilization

Magnetically-actuated mesoporous nanowires for enhanced heterogeneous catalysis

We study the optimization of the catalytic properties of entirely magnetic Co-Pt compact and mesoporous nanowires of different diameters (25-200 nm) by using magnetic actuation. The nanowires are a single-entity, robust, magnetic-catalyst with a huge catalytically-active surface area. We show that apart from conventional parameters, like the size and morphology of the nanowires, other factors can be optimized to enhance their catalytic activity. In particular, given the magnetic character of the nanowires, rotating magnetic fields are a very powerful approach to boost the performance of the catalyst. In particular, the magnetic field induces them to act as nano-stirrers, improving the local flow of material towards the active sites of the catalyst. We demonstrate the versatility of the procedure by optimizing (i) the degradation of different types of pollutants (4-nitrophenol and methylene blue) and (ii) hydrogen production. For example, by using as little as 0.1 mg mL⁻¹ of 25 nm wide Co-Pt mesoporous nanowires (with ∼3 nm pore size) as catalysts, kinetic normalized constants knor as high as 20,667 and 21,750 s⁻¹ g⁻¹ for 4-nitrophenol and methylene blue reduction, respectively, are obtained. In addition, activity values for hydrogen production from borohydride are as high as 25.0 L H₂ g⁻¹ min⁻¹, even at room temperature. These values outperform any current state-of-the-art proposed catalysis strategies for water remediation reactions by at least 10-times and are superior to most advanced approaches to generate hydrogen from borohydride. The recyclability of the nanowires together with the simplicity of the synthetic method makes this approach (using not only Co-Pt, but also other mesoporous magnetic catalysts) very appealing for very diverse types of catalytic applications

Unravelling the Mechanistic Pathway of the Hydrogen Evolution Reaction Driven by a Cobalt Catalyst

Acord transformatiu CRUE-CSICA cobalt complex bearing a κ-NP ligand is presented (1 or Co(L), where L is (1E,1'E)-1,1'-(pyridine-2,6-diyl)bis(N-(3-(diphenylphosphanyl)propyl)ethan-1-imine). Complex 1 is stable under air at oxidation state Co thanks to the π-acceptor character of the phosphine groups. Electrochemical behavior of 1 reveals a two-electron Co/Co oxidation process and an additional one-electron reduction, which leads to an enhancement in the current due to hydrogen evolution reaction (HER) at E=−1.6 V vs Fc/Fc. In the presence of 1 equiv of bis(trifluoromethane)sulfonimide, 1 forms the cobalt hydride derivative Co(L)-H (2), which has been fully characterized. Further addition of 1 equiv of CoCp* (Cp* is pentamethylcyclopentadienyl) affords the reduced Co(L)-H (2) species, which rapidly forms hydrogen and regenerates the initial Co(L) (1). The spectroscopic characterization of catalytic intermediates together with DFT calculations support an unusual bimolecular homolytic mechanism in the catalytic HER with 1

Organocatàlisi d'addicions conjugades mitjançant fosfines : reciclatge i mecanisme: síntesi de benzotiazines / :

Consultable des del TDXTítol obtingut de la portada digitalitzadaLes fosfines són organocatalitzadors eficaços d'una gran varietat de reaccions, que han estat revisades en diverses ocasions. Entre elles es troben l'α-hidroxialquilació de Morita-Baylis-Hillman, la reacció de Rauhut-Currier, diverses cicloaddicions o les α i γ addicions a compostos insaturats activats. En la present Tesi Doctoral s'han estudiat les addicions conjugades, reaccions que també es poden catalitzar mitjançant fosfines però que no s'havien estudiat exhaustivament utilitzant aquests catalitzadors. Concretament s'ha treballat amb addicions de Michael i addicions conjugades de compostos N-nucleòfils. S'ha estudiat l'abast i les limitacions del mètode així com el mecanisme de la reacció. Com a substrats nucleòfils en les addicions de Michael s'han mostrat actius compostos β-dicarbonílics de tipus dicetona, diester, cetoester i cetoamida substituïts i no substituïts en posició α, així com compostos cíclics o de cadena oberta. És important destacar també la gran diversitat d'electròfils aptes per aquestes reaccions (esters, nitrils, cetones, fosfonats, piridines, azodicarboxilats). Respecte a les addicions conjugades de compostos N-nucleòfils pobres en electrons, han mostrat activitat amides, tioamides, anilines, sulfonamides, benzamides i fenilamines. S'ha observat que la reactivitat d'aquests compostos depèn del pKa del nucleòfil i s'ha establert un valor límit aproximat de pKa = 25 fins al qual el mètode funciona, tot i que per obtenir bons rendiments, es requereix un pKa < 20. En aquells casos que els substrats de la reacció són menys reactius, la reacció de Rauhut-Currier (dimerització de l'acceptor) competeix amb l'addició conjugada però aquesta reacció secundària es pot evitar emprant electròfils que no dimeritzin com el metacrilat d'etil o el fosfonat de dietil. En alguns casos s'ha observat la reacció de retroaddició, que és a causa de la inestabilitat del producte i de la presència de la fosfina. Una altra part del treball de la present Tesi Doctoral ha consistit en sintetitzar dues fosfines polifluorades que s'han emprat amb èxit com a organocatalitzadors de diverses reaccions d'addició de Michael amb l'objectiu de ser reciclades i reutilitzades mitjançant processos de catàlisi bifàsica orgànica-fluorada. Tot i que la seva activitat com a catalitzadors és excel·lent, la seva reciclabilitat és limitada. Aquest resultat s'ha atribuït al fet que l'estat residual del catalitzador en aquestes reaccions no és la fosfina esperada sinó una sal de fosfoni derivada de l'addició conjugada de la fosfina a l'acceptor de Michael. Aquest treball s'ha realitzat en col·laboració amb el Prof. J. A. Gladysz a la Friedrich-Alexander Universität d'Erlangen-Nürnberg. Dels estudis mecanístics sobre les d'addicions conjugades catalitzades per fosfines han aportat proves per corroborar que la reacció s'inicia per l'atac de la fosfina catalítica a l'electròfil, generant un zwitterió que activa el nucleòfil i acaba donant una sal de fosfoni que serà l'estat residual del catalitzador en el cas de les fosfines més nucleòfiles (tributilfosfina per exemple). En canvi per les fosfines menys nucleòfiles com la trifenilfosfina, l'estat residual seria la pròpia fosfina de partida. Els estudis també indueixen a descartar una possible SN2directa del nucleòfil activat a la sal de fosfoni anterior i recolzen la hipòtesi que la ruta més probable implica l'atac del nucleòfil activat a una nova molècula d'olefina. Finalment, s'ha dissenyat una estratègia per sintetitzar benzo[d][1,3]tiazines. La ruta té 3 passos des de compostos comercialment assequibles i l'etapa clau implica una S-addició conjugada intramolecular.Nucleophilic Phosphine Catalysis (NPC) has recently attracted the attention of many scientists since it has given very good results in many reactions. Some examples are the α -hydroxialkylation of Morita-Baylis-Hillman, Rauhut-Currier reaction, cycloadditions or α and γ additions to activated olefins. Conjugate additions are another kind of reaction that phosphines can catalyze but it had not been studied exhaustively. In the present Doctoral Thesis it has been demonstrated that these compounds can effectively catalyze Michael addition reactions of β-carbonyl compounds to a broad diversity of electron poor olefins. Then the same methodology has been applied to a new family of nucleophilic substrates such as non-nucleophilic N-containing compounds obtaining excellent results. Some trends can be described from the former study. First of all, aliphatic phosphines are better catalysts than aromatic ones because of their greater nucleophilicity. The scope of nucleophiles is broad and also many electrophiles are active as Michael acceptors. The yields are very good in reactions where the nucleophile has a pKa < 20 but the method is applicable to substrates with a pKa up to 25, although in these cases the yields are lower and mixtures of mono and bisadducts are obtained. In some cases, Rauhut-Currier reaction (dimerization of the Michael acceptor) competes with the conjugate addition reaction but these secondary reactions can be avoided using electrophiles that can not dimerize, such as ethyl methacrylate or vinyl phosphonate. Finally, some reactions give retroaddition, which is caused by the instability of the compound and not by the presence of the phosphine. Once the efficiency of the method had been proofed, a method to recover and reuse the catalyst was designed based on organic-fluorous biphasic catalysis. This study was carried out in collaboration with Prof. J. A. Gladysz research group in the Friedrich-Alexander Universität d'Erlangen-Nürnberg. Two different polyfluorinated phosphines were successfully synthesized through known routes and then tested as organocatalysts in several Michael addition reactions. Although the activity of these phosphines is good, the recyclability is limited due to the fact that the rest state of the catalyst is a phosphonium salt derived from the addition of the phosphine to the olefin. Some NMR experiments have been carried out in order to study the mechanism of conjugate additions catalyzed by phosphines. It has been corroborated that the reaction starts with the addition of the phosphine to the electron-poor olefin generating a phosphonium salt, which would be the rest state of the catalyst in reactions involving the most nucleophilic phosphines (tributylphosphine for example). However, when the catalyst is less nucleophilic (triphenylphosphine) the rest state is believed to be the phosphine itself. Also a direct SN2 reaction between the activated nucleophile and the phosphonium salt has been discarded for the step where the new C-C bond is generated. Finally, a new synthetic strategy to synthesize benzo[d][1,3]thiazines has been developed. The route has three steps from commercially available compounds and its key step involves an intramolecular conjugate S-addition

Electronic, mechanistic and structural factors that influence the performance of molecular water oxidation catalysts anchored on electrode surfaces

To harness solar energy to generate fuels powerful anodes for the water oxidation reaction need to be developed. During the last decade, an extensive number of molecular water oxidation catalysts based on transition metals have been reported, and in some cases, these molecular catalysts have been anchored on conductive surfaces generating molecular anodes. In this review, we analyze the factors that influence the performance of these molecular anodes, which are largely related to their mechanism of O–O bond formation and the nature of the anchoring functionality

Hydroxytrifluoroethylation and Trifluoroacetylation Reactions via SET Processes

Altres ajuts: acords transformatius de la UABHydroxytrifluoroethyl and trifluoroacetyl groups are of utmost importance in biologically active compounds, but methods to tether these motifs to organic architectures have been limited. Typically, the preparation of these compounds relied on the use of strong bases or multistep routes. The renaissance of radical chemistry in photocatalytic, transition metal mediated, and hydrogen atom transfer (HAT) processes have allowed the installation of these medicinally relevant fluorinated motifs. This review provides an overview of the methods available for the direct synthesis of hydroxytrifluoroethyl- and trifluoroacetyl-derived compounds governed by single-electron transfer processes