Heterolytic H2 activation on a carbene-ligated rhodathiaborane promoted by isonido-nido cage opening

A new mechanism of H2 activation is reported to occur on a carbene-ligated rhodathiaborane that features metal-thiaborane bifunctional synergistic effects. The key is the creation of vacant coordination sites by an isonido-nido structural transformation leading to the heterolytic H-H bond splitting. © 2013 The Royal Society of Chemistry.We gratefully acknowledge the Spanish Ministry of Science and Innovation (CTQ2009-10132, CSD2009-00050, and CSD2006-0015, CTQ2012-35665) for financial support. B.C. thanks the ‘‘Diputación General de Aragón’’ for a pre-doctoral scholarship.Peer Reviewe

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

Efficient Rhodium-catalyzed multicomponent reaction for the synthesis of novel propargylamines

[{Rh(μ-Cl)(H)2(IPr)}2] (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazole-2-ylidene) was found to be an efficient catalyst for the synthesis of novel propargylamines by a one-pot three-component reaction between primary arylamines, aliphatic aldehydes, and triisopropylsilylacetylene. This methodology offers an efficient synthetic pathway for the preparation of secondary propargylamines derived from aliphatic aldehydes. The reactivity of [{Rh(μ-Cl)(H)2(IPr)}2] with amines and aldehydes was studied, leading to the identification of complexes [RhCl(CO)IPr(MesNH2)] (MesNH2 = 2,4,6-trimethylaniline) and [RhCl(CO)2IPr]. The latter shows a very low catalytic activity while the former brought about reaction rates similar to those obtained with [{Rh(μ-Cl)(H)2(IPr)}2]. Besides, complex [RhCl(CO)IPr(MesNH2)] reacts with an excess of amine and aldehyde to give [RhCl(CO)IPr{MesN[DOUBLE BOND]CHCH2CH(CH3)2}], which was postulated as the active species. A mechanism that clarifies the scarcely studied catalytic cycle of A3-coupling reactions is proposed based on reactivity studies and DFT calculations.This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) (CONSOLIDER INGENIO CSD2009-0050, CTQ2011-27593, CTQ2012-35665 and CTQ2013-42532-P 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. V. P. thankfully acknowledges the resources from the supercomputer >Memento>, technical expertise and assistance provided by BIFI-ZCAM (Universidad de Zaragoza). L.R.-P thanks to CONACyT for a postdoctoral fellowship (204033).Peer Reviewe

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

Comunicación corta. Composición de ácidos grasos de los depósitos grasos de cordero como discriminador del origen

The development of quality labels for different lamb meats makes necessary to implement analytical methodologies to guarantee consumers the origin of the products. Eighty single birth male lambs from five Southern Spain sheep breeds (Grazalema Merino, Churra Lebrijana, Spanish Merino, Montesina and Segureña) were selected for the study and fed according to their traditional production system (with or without weaning). The fatty acid composition of five different depots (intramuscular, intermuscular, subcutaneous, omental and kidney knob) was analyzed by gas chromatography, showing a high variability among lamb types. The lipid profile of single fat depots was not able to assign 100% of the carcasses to their origin, but using the information from two depots (including intramuscular, or combining an external and an internal fat depot) led to a reliability of 100%. Any combination of 3, 4 or 5 depots also obtained 100% correct discrimination.La aparición de distintivos de calidad para carnes de cordero hace necesario el desarrollo de métodos analíticos que garanticen al consumidor el origen de dichos productos. Se seleccionaron para este estudio ochenta corderos machos, provenientes de un parto simple, de cinco razas andaluzas (Merino de Grazalema, Churra Lebrijana, Merino Español, Montesina y Segureña) y se alimentaron de acuerdo a su sistema tradicional (con o sin destete). Se analizó la composición de ácidos grasos de cinco depósitos grasos (intramuscular, intermuscular, subcutáneo, omental y perirenal) con cromatografía de gases. La grasa de estos depósitos presentó gran variabilidad. El perfil lipídico de un único depósito no fue suficiente para asignar correctamente el origen del 100% de las canales, pero usando la información de dos depósitos (incluyendo el intramuscular, o combinando un depósito externo y otro interno) se obtuvo una fiabilidad del 100%. Cualquier combinación de 3, 4 o 5 depósitos también obtuvo una fiabilidad del 100% respecto a la proveniencia de la canal.Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (España) RZ03-019Unión Europea. 5th Framework Programme of Research and Technological Developmen

Revisión sistemática sobre la eficacia y seguridad de los neuroestimuladores periféricos del ganglio esfenopalatino para el tratamiento de la cefalea crónica en racimos refractaria

[EN] Introduction: This study aimed to assess the safety and effectiveness of peripheral neurostimulation of the sphenopalatine ganglion (SPG) in the treatment of refractory chronic cluster headache. Development: Various medical databases were used to perform a systematic review of the scientific literature. The search for articles continued until 31 October 2016, and included clinical trials, systematic reviews and/or meta-analyses, health technology assessment reports, and clinical practice guidelines that included measurements of efficiency/effectiveness or adverse effects associated with the treatment. The review excluded cohort studies, case–control studies, case series, literature reviews, letters to the editor, opinion pieces, editorials, and studies that had been duplicated or outdated by later publications from the same institution. Regarding effectiveness, we found that SPG stimulation had positive results for pain relief, attack frequency, medication use, and patients’ quality of life. In the results regarding safety, we found a significant number of adverse events in the first 30 days following the intervention. Removal of the device was necessary in some patients. Little follow-up data, and no long-term data, is available. Conclusions: These results are promising, despite the limited evidence available. We consider it essential for research to continue into the safety and efficacy of SPG stimulation for patients with refractory chronic cluster headache. In cases where this intervention may be indicated, treatment should be closely monitored. [ES] Introducción: El objetivo es evaluar la eficacia y seguridad de los neuroestimuladores periféricos del ganglio esfenopalatino (GEP) para el tratamiento de la cefalea en racimos crónica refractaria al tratamiento. Desarrollo: Revisión sistemática de la literatura científica. Se identificaron estudios mediante una búsqueda en diferentes bases de datos. Las estrategias de búsqueda se realizaron hasta el 31 de octubre de 2016, incluyendo ensayos clínicos, revisiones sistemáticas o metaanálisis, informes de evaluación de tecnologías sanitarias y guías de práctica clínica que recogieran medidas de eficacia/efectividad o efectos adversos asociados al tratamiento. Se excluyeron estudios de cohortes, casos y controles, series de casos, revisiones narrativas, cartas al director, artículos de opinión, editoriales y estudios duplicados o desfasados por estudios posteriores de la misma institución. Respecto a la eficacia, los resultados son positivos tras la estimulación del GEP en relación con el alivio de dolor, el número de episodios, el uso de la medicación o la calidad de vida del paciente. En relación con la seguridad, hay un número importante de efectos adversos en los primeros 30 días de la intervención y en algunos pacientes fue necesaria la retirada del dispositivo. Los datos de seguimiento son a corto plazo y escasos. Conclusiones: Los resultados resultan prometedores a pesar de que la evidencia disponible es limitada. Consideramos fundamental continuar con la investigación sobre la seguridad y eficacia de los neuroestimuladores del GEP en la cefalea en racimos crónica. En aquellos casos en que pueda estar indicada la intervención, el tratamiento debería realizarse supervisado en un estudio de monitorización.S

Primeros resultados sobre la caracterización de la grasa de la raza bovina Pajuna

Con un censo muy reducido (550 hembras reproductoras en el año 2006) la raza bovina Pajuna Serrana se localiza muy irregularmente por las provincias de Córdoba, Granada, Cádiz y Jaén. Esta raza, caracterizada por su gran rusticidad, se ha venido explotando fundamentalmente de forma extensiva como animal de trabajo y, en menor medida, para la obtención de carne. Entre las estrategias para el desarrollo y la expansión de la raza, la Asociación de Criadores de Ganado Vacuno de Raza Pajuna está orientando sus esfuerzos hacia la caracterización de las particularidades organolépticas de su carne que actualmente se encuentra en amenaza de extinción (RD 1682/1997 de noviembre de 1977)

Ligand-controlled regioselectivity in the hydrothiolation of alkynes by rhodium N-heterocyclic carbene catalysts

Rh-N-heterocyclic carbene compounds [Rh(μ-Cl)(IPr)(ν 2- olefin)] 2 and RhCl(IPr)(py)(ν 2-olefin) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl(IPr)(py)(ν 2- olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electronic and steric effects exerted by IPr, pyridine, and hydride ligands accounts for the observed regioselectivity. Both IPr and pyridine ligands stabilize formation of square-pyramidal thiolate-hydride active species in which the encumbered and powerful electron-donor IPr ligand directs coordination of pyridine trans to it, consequently blocking access of the incoming alkyne in this position. Simultaneously, the higher trans director hydride ligand paves the way to a cis thiolate-alkyne disposition, favoring formation of 2,2-disubstituted metal-alkenyl species and subsequently the Markovnikov vinyl sulfides via alkenyl-hydride reductive elimination. DFT calculations support a plausible reaction pathway where migratory insertion of the alkyne into the rhodium-thiolate bond is the rate-determining step. © 2012 American Chemical Society.Financial support from the Ministerio de Ciencia e Innovación (MICINN/FEDER) of Spain (Project CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010, Projects MULTICAT (CSD2009-00050) and Factoría de Cristalización (CSD2006-0015) are gratefully acknowledged. R.C. thanks the CSIC and the European Social Fund for his Research Contract in the framework of the “Ramón y Cajal” Program.Peer Reviewe