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La presente revisión de literatura busca identificar el abordaje de las inequidades entre educación urbana y rural en Colombia, ubicando vacíos y proponiendo líneas de investigación y diseño de políticas públicas. Se adoptó una estrategia flexible de recuperación de materiales con artículos de cuatro bases de datos de libre acceso. Los hallazgos sugieren que la investigación en Colombia es incipiente si se compara con los avances latinoamericanos sobre este problema, pero se puede considerar que el posconflicto, y las brechas tecnológicas puestas de plano por la pandemia de Covid-19, animan a reconsiderar la educación y el desarrollo rural desde los conceptos de equidad e inclusión. Se encuentra una potencialidad teórica de trabajo a partir del concepto de lucha por el reconocimiento como una forma de promover la participación de las comunidades rurales por poner en juego sus reales necesidades en contexto de políticas educativas diseñadas a medida de las ciudades.

The production of water-soluble and stable metallic nanoparticles that can act as recoverable catalysts still remains a challenge. Herein we report the behavior of a series of water-soluble platinum nanoparticles containing different sulfonated NHC ligands as recoverable catalysts for the hydrogenation of aromatic compounds in pure water. The NHC-protected nanoparticles are found to be active and, in general, can be reutilized with no loss of activity or selectivity, although differences are observed depending on the substitution of the NHC ligand or on the substrate being hydrogenated. Pt leaching was determined to be only 0.03–0.29%. TEM images reveal that the shape of the nanoparticles remains unaltered after catalysis. However, the size of the particles increased, although with no influence on their catalytic properties in many instances.

The preparation of trans-[Pt(dmso)2ClMe] (2) and cis-[Pt(dmso)2Me2] (3) from cis-[Pt(dmso)2Cl2] (1) and SnMe4 has been reexamined (dmso = dimethyl sulfoxide). The information obtained from experimental and DFT studies has permitted the improvement of previously reported methods for the synthesis of both complexes in terms of reaction times, reaction yields, and atom economy. These studies show that complex 1 reacts with a first equiv of SnMe4 to form trans-[Pt(dmso)2ClMe] (2) as an intermediate that quickly reacts with a second equiv of SnMe4 to yield cis-[Pt(dmso)2Me2] (3). When only 1 equiv of the organostannane reagent is added, the comproportionation of 3 with the excess of unreacted 1 leads the reaction back to the formation of trans-[Pt(dmso)2ClMe] (2). The mechanism of this comproportionation has been studied using DFT calculations.

El presente trabajo se realizó en Panadería Sevilla, una PYME que se encuentra localizada en el barrio Güisquiliapa, Jinotepe. La investigación realiza una descripción de proceso de producción de la entidad y la manera de cómo poder mejorarlo. Los métodos de trabajo son un conjunto de pasos que llevan a cabo los trabajadores de manera secuencial con el propósito de producir un bien o servicio, la aplicación de todas las herramientas de análisis necesarias permitirá conocer a fondo la manera de trabajar de la PYME. Por esta razón se plasmó a través de diagramas y el análisis de las 5S para una mayor comprensión de la situación actual de la empresa. De igual forma se tiene en cuenta la distribución de planta; cuya distribución presente es de manera continua debido a la secuencia de sus operaciones, y debido a que el área de trabajo es pequeña y se observa una gran variedad de ocupaciones para cada uno de los operarios; a esto se le puede añadir el nivel de insatisfacción de los colaboradores aumente. Se realiza un estudio a fondo que abarca desde los tiempos que conlleva realizar cada una de las operaciones, así como los inconvenientes que pueden presentarse a lo largo del proceso productivo es por ello una importancia en la formulación de mejoras aplicables al proceso. En consecuencia, la propuesta resultante surgió de la necesidad de identificar y solucionar estas dificultades, para lo cual se debe implementar un modelo de mejoramiento continuo en el departamento de producción.

122 páginas El objetivo del Sistema General de Seguridad en Salud colombiano ha sido siempre lograr la cobertura de toda la población y su satisfacción. Esto a pesar de los cambios que tiene constantemente desde la puesta en marcha de la Ley 100 de 1993. Estos cambios y la población cubierta por el sistema aumentan al igual que las necesidades y expectativas de los usuarios, creciendo así mismo las inconformidades de los afiliados. Dos de las principales causas de insatisfacción de la población están marcadas por deficiente prestación de los servicios de salud y por la demora en la generación de las autorizaciones, llevando a los usuarios a interponer medidas legales para exigir los derechos adquiridos por la ley y ofrecidos por el sistema. El presente trabajo explica las dinámicas que influyen en el proceso de autorizaciones, de manera específica, las denominadas de alto costo en una Empresa Administradora de Planes de Beneficio del país y de cómo afectan las finanzas de la Organización. Inicialmente hace una revisión de la literatura y la normativa vigente en el país, en relación con el Sistema de Seguridad Social y Salud colombiano, con el objeto de conocer la percepción de sus actores y usuarios, sobre esta temática. Finalizada la investigación se realizó un diagnóstico de la situación de la empresa y su alineación entre los procesos y los objetivos estratégicos financieros analizando los datos de la empresa y la percepción de los usuarios. Estos resultados nos permitieron formular estrategias a través de la metodología de VSM (Value Stream Mapping), para mejorar los procesos de autorizaciones de alto costo y alinearlo al cumplimiento del objetivo de rentabilidad de la EAPB, y así mismo satisfacer las necesidades de los usuarios en términos de oportunidad en la autorización.

International audience; A strategy involving the decomposition of palladium(II) organometallic complexes with sulfonated N‐heterocyclic carbene ligands leads to the formation of stable and water‐soluble Pd nanoparticles. Three different methodologies (thermal decomposition, reduction under 13CO atmosphere, and reduction with H2) gave particles with different shapes and sizes, ranging from 1.5 to 7 nm. The structures of the organometallic intermediates and organic decomposition products were elucidated by NMR spectroscopy. To check the accessibility of the surface, the nanoparticles were tested as catalysts for the chemoselective hydrogenation of styrene in water. An effect of the particle size on the catalyst activity was observed. The aqueous phase was recycled up to ten times without any precipitation of metallic palladium.

The synthesis of palladium(II) complexes containing N-heterocyclic carbene chelate ligands is reported. These chelate ligands have methylene or ethylene ring bridges and sulfonate, carbonate or ammonium functionalities to render the complexes soluble in water. Bis- [(bis-NHC)PdX2] (X = Cl, Br or I) and tetra-carbene [(bis-NHC)2Pd] complexes have been prepared and the crystal structures of two of them have been determined. The NHC ligand is coordinated to the metal center in normal (C2-bound) or abnormal (C4-bound) mode. Processes involving the formation of NHC-Pd bonds or the transfer of NHC ligands have been explored in water. The behavior of the bis-carbene complexes as catalysts for the aerobic oxidation of 1-phenylethanol is also discussed.

Pre-synthesized mono- and bis(NHC) palladium complexes have been grafted onto magnetic core/shell γ-Fe2O3/silica particles and tested as catalysts in model Suzuki-Miyaura coupling reactions. The bis(NHC) immobilized complex was found to be a robust catalyst that can operate under mild conditions in aqueous media, even for the activation of chloroarene, whereas the mono(NHC) counterpart rapidly deactivates. Moreover, it can be readily recovered by magnetic separation and reused many times, providing very high productivities, and with so low leaching of palladium that the crude products obtained contain ≤10 ppm Pd.

International audience; The synthesis of metal nanoparticles (NPs) under controlled conditions in water remains a challenge in nanochemistry. Two different approaches to obtain platinum NPs, which involve the treatment of aqueous solutions of preformed sulfonated (NHC)Pt(II) dimethyl complexes with carbon monoxide, and of (NHC)Pt(0) diolefin complexes with dihydrogen (NHC = N-heterocyclic carbene), are disclosed here. The resulting NPs were found to be highly stable in water under air for an indefinite time period. Coordination of the NHC ligands to the platinum surface via the carbenic carbon was monitored by solid-state NMR spectroscopy, and the presence of a platinum–carbon bond was unambiguously evidenced by the determination of a 13C–195Pt coupling constant (1106 and 1050 Hz for NPs containing 13C labeled-NHC ligands and prepared under CO and H2, respectively). The coordination of CO to the (NHC)Pt(II) precursors prior to formation of the NPs was confirmed by NMR spectroscopy. When using a disulfonated NHC ligand, a second coordination sphere containing bis(NHC)Pt(II) complexes is described. Under CO, the formation of NPs was found to be slower than in a previously reported thermal method (Angew. Chem., Int. Ed., 2014, 53, 13220–13224), but led to NPs of similar sizes, whereas under H2, the synthesis of platinum NPs progressed even more slowly and produced larger NPs. In addition to the influence of the synthetic approach, the present study highlights the importance of ligand design for NP stabilization.

Water-soluble Pd(II) complexes of general formula Nax[(NHC)PdCl2L] (L = Cl– (1), PPh3 (2), PPh2(C6H4-m-SO3Na) (3), and 4-Mepy (4)), where NHC is a dianionic sulfonated and sterically hindered N-heterocyclic carbene, have been prepared. The new complexes are active catalysts for the Suzuki–Miyaura cross-coupling of aryl chlorides and boronic acids in mixtures of isopropyl alcohol/water or, in the case of water-soluble aryl chlorides, in pure water. The trichloride complex 1, the crystal structure of which is reported, catalyzes the coupling of inactivated and sterically hindered substrates under mild conditions (60 °C, 0.1 mol % Pd). The corresponding biphenyls are obtained in almost quantitative yields, except in the case of some of the most hindered aryl chlorides, for which small amounts of arene are also formed by a competitive hydrodehalogenation process.

In Mexico the federal program "Agenda desde lo Local" was implemented to certify the good practices of municipal governments in order to contribute to local development and institutional strengthening of municipalities. For the design of this program took up the "Agenda 21" which is based on the principle of sustainable development, for which one of the most important components is human development. So, in this paper we evaluate the correlation between the results of the "Agenda desde lo Local" of a sample of municipalities and their rates of human development, marginalization and municipal development. The results show that these rates do not correlate significantly with the results of the "Agenda desde lo Local", therefore we can question the way it is construed into public policies and government programs the concepts of human and municipal development., En México se implementó el programa federal "Agenda desde lo Local" para certificar las buenas prácticas de los gobiernos municipales con la finalidad de coadyuvar al desarrollo local y al fortalecimiento institucional de los Ayuntamientos. Para el diseño de este programa se retomó la "Agenda 21", que se fundamenta en el principio de desarrollo sostenible, donde uno de los elementos más importantes es el desarrollo humano. En este trabajo se valora la relación entre los resultados de la "Agenda desde lo Local", a partir de una muestra de municipios y sus índices de Desarrollo Humano, marginación y desarrollo municipal. Los resultados muestran que estos índices no se correlacionan significativamente con los resultados generales de la "Agenda desde lo Local", con lo cual se cuestiona la forma en que se traduce en políticas públicas y programas de gobierno los conceptos de desarrollo humano y municipal.

Oxidative addition of CH3I and alkynes to the platinum(0) complex [Pt(AE)NHC] (1), in which the NHC ligand is a sulfonated version of the IPr ligand (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and AE is diallyl ether, is reported. Reaction with the haloalkane affords the iodomethyl complex [PtI(Me)NHC] (2), whereas the addition of alkynes via C(sp)-H bond activation leads to the corresponding new water-soluble hydride (NHC)PtII complexes 3 and 4. Complexes 3 and 4 were found to be moderately stable in water, displaying an interesting behavior in this solvent. Thus, in the presence of the corresponding olefin, the reaction can be reversible under mild conditions, thus allowing the formation of diolefinic (NHC)Pt0 complexes 1, 5, and 6, with elimination of the alkyne. Fil: Baquero, Edwin A.. Universidad de Alcalá; España. Universidad Nacional de Colombia; Colombia Fil: Silbestri, Gustavo Fabián. Universidad de Alcalá; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Flores, Juan C.. Universidad de Alcalá; España Fil: De Jesús, Ernesto. Universidad de Alcalá; España

International audience; The coordination of N-heterocyclic carbene (NHC) ligands to the surface of 3.7 nm palladium nanoparticles (PdNPs) can be unambiguously established by observation of Knight shift (KS) in the C-13 resonance of the carbenic carbon. In order to validate this coordination, PdNPs with sizes ranging from 1.3 to 4.8 nm were prepared by thermal decomposition or reduction with CO of a dimethyl NHC PdII complex. NMR studies after (CO)-C-13 adsorption established that the KS shifts the C-13 resonances of the chemisorbed molecules several hundreds of ppm to high frequencies only when the particle exceeds a critical size of around 2 nm. Finally, the resonance of a carbenic carbon is reported to be Knight-shifted to 600 ppm for C-13-labelled NHCs bound to PdNPs of 3.7 nm. The observation of these very broad KS resonances was facilitated by using Car-Purcell-Meiboom-Gill (CPMG) echo train acquisition NMR experiments.

International audience; The synthesis of water-soluble η 3-allyl Pd(II) complexes containing sulfonated N-heterocyclic carbene (NHC) ligands of general formula [Pd(NHC) n (η 3-allyl)Cl 2−n ] is reported (n = 1 (1) or 2 (8)). Monocarbene complexes were obtained with the most sterically hindered NHC ligands, and biscarbenes with the less sterically hindered NHCs. The behavior of the isolated complexes in water under acidic, neutral, or alkaline conditions has been studied. The complexes are rather stable in water under neutral or alkaline conditions, although displacement of the chlorido ligand by water or hydroxide occurs under these conditions. In acidic media, Pd−NHC bonds are protolysed, and it is especially noteworthy that this protolysis occurs preferentially to that of the Pd−allyl bonds in the case of the complexes with the less-sterically hindered NHC ligands. This behavior contrasts with that observed in dimethyl sulfoxide (dmso), where the Pd− allyl bonds are selectively broken upon treatment with Brö nsted acids. In addition, Pd−NHC bond breaking was promoted by the addition of a strong σ-donor ligand such as cyanide. Complex 1a is an active catalyst for the Suzuki−Miyaura cross-coupling of water-soluble aryl chlorides in neat water under moderate conditions (typically, 0.5 mol % Pd and 60 °C).

International audience; Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N‐heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high‐resolution TEM, and spectroscopic techniques. Solid‐state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a 13C–195Pt coupling constant for the first time in a nanosystem (940 Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle.

A family of water-soluble dimethyl complexes of formula cis-[PtMe2(dmso)(NHC·Na)] (2), in which NHC is an anionic N-heterocyclic carbene bearing a sulfonatopropyl chain on one of the nitrogen atoms and a sulfonatopropyl (a), methyl (b), mesityl (c), or 2,6-diisopropylphenyl group (d) on the other, have been prepared. The hydrolytic stability of the Pt–C bonds in these complexes under different neutral, alkaline, and acidic aqueous conditions has also been studied. Complexes 2 were found to be quite stable at room temperature in water under neutral or alkaline conditions. Degradation occurred at higher temperatures but involved C sp3–H activation and C–C reductive elimination processes in addition to Pt–Me bond hydrolysis. Hydrolytic cleavage of the platinum–methyl bonds was favored by good nucleophiles. Thus, the addition of KCN to an aqueous solution of 2 resulted in formation of the monomethyl complexes K[PtMe(CN)2(NHC·Na)] (9), whereas the dimethyl complexes K[PtMe2(CNR)(NHC·Na)] (10) were formed with ...

The complex (NHC)AgBr, which bears G1 poly(benzyl ether) dendritic substituents in the NHC ligand, forms a 1D coordination polymer based on unusual zigzag −Ag–halide– chains. The asymmetric distribution of the volume buried by the NHC ligand in the Ag coordination sphere is important to explain the formation of this structure. A Vbur eccentricity parameter has been introduced and used in conjunction with the %Vbur descriptor to analyze the X-ray structures of 100 (NHC)AgX complexes.

Iminopyridine ligands of general formula G n-PBE- ONN (G n-PBE = Frechet-type dendritic wedges of generation G0 ( 1 ), G1 ( 2 ), G2 ( 3 ), and G3 ( 4 ); – ONN = -O-4-(2,5-Me 2 C 6 H 2 )-N CH-2-py) have been prepared starting from H- ONN . Reaction of these bidentate ligands with [NiBr 2 (DME)] results in the nickel(II) complexes [NiBr 2 (G n - PBE - ONN )] ( 5 – 8 ). The methylaluminoxane (MAO)-activated monometallic complexes have been studied in the transformation of ethylene into mixtures of polyethylene and oily oligomers, and their catalytic performance scrutinized as a function of dendritic size. A comparison with the behavior observed for related polymetallic dendrimers has enabled the dendritic features that affect various catalytic parameters to be determined. Thus, it has been possible to discern whether the dendritic effect detected in the catalysis should be ascribed to the metallic nuclearity rather than the bulkiness of the metallodendrimer.

The agroforestry systems consider the integrated management of all production within the production unit processes and conservation practices related to the use of natural resources. From this point of view, it should be approached as a system composed by subsystems and the interactions that occur among them, in order to provide a sustainable, social, economic and ecological alternative to the traditional extensive ranching. The project objective was to evaluate the fattening of goats under an agrosilvopastoril production system established in the 2013 summer-autumn cycle, at the Technological Institute of Oaxaca Valley (ITVO). Completely randomized design with factorial arrangement evaluating three factors (age, sex and supplement) and two levels were used. 16 goats feeding with nutritional ITVO block, native grasses and guaje (Leucaena esculenta) were used. The variance analysis was made by the statistical package SAS (Statistical Analysis System) version 9.4. For the comparison of measures with Tukey test (α = 0.05) and a proximal analysis by Van Soest to obtain the quality of the forages. Weight gain related to sex was differential, males and females presented a value of 63.5±18.2 and 54.25±17.3 g day/animal not significant (p>0.05), respectively. Creole goats grazing and supplemented with a nutritional block had a weight gain of 70.5±20.3 g day/animal without supplement 47.29±18.9 g day/animal not significant (p>0.05). The greater weight gained in nutritional supplement found with block showed that the use of the same influences fattening goats.

The coordination of N-heterocyclic carbene (NHC) ligands to the surface of 3.7 nm palladium nanoparticles (PdNPs) can be unambiguously established by observation of Knight shift (KS) in the

The synthesis of carbosilane dendrons with bidentate bis(diphenylphosphanomethyl)amino ligands at the focal point and terminal alkyl or dimethylamino end-groups, together with their palladium(II) complexes and a cationic ammonium-quaternized derivative, is described. All compounds were characterized by elemental analysis and NMR spectroscopy ( 1 H, 13 C, 31 P and 29 Si).

The synthesis and characterization of new water-soluble platinum(0) complexes bearing sulfonated N-heterocyclic carbene (NHC) and divinyltetramethylsiloxane (dvtms) ligands are described. These complexes, of the general formula (NHC)Pt(dvtms), are active and recyclable catalysts for the hydrosilylation of phenylacetylene and other alkynes at room temperature in water. Our findings indicate that the NHC-Pt(0) bonds are reasonably stable under these catalytic conditions, although hydrolysis is observed at temperatures above 80 °C in pure water. © 2012 American Chemical Society. Fil: Silbestri, Gustavo Fabián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Alcalá; España Fil: Flores, Juan Carlos. Universidad de Alcalá; España Fil: De Jesús, Ernesto. Universidad de Alcalá; España

The hydrosilylation of deuterated acetylene with triethoxysilane can be directed to the synthesis of either cis or trans triethoxy(vinyl-d2)silanes by an appropriate choice of metal catalyst. In addition, we have demonstrated the viability of designing hydrosilylation−arylation sequential processes in which acetylene can be converted into styrenes or stilbenes using the same Pd catalyst for both reactions.

The synthesis of PtRu nanoparticles has been accomplished by using the dendrimer-encapsulated nanoparticle (DEN) approach. We report that the surface distribution of the particles can be tuned by suitable control of the reaction pathway. The present study focuses on the synthesis and characterization of Pt and PtRu nanoparticles and the evaluation of their performance as COad electro-oxidation catalysts. Bimetallic Pt/Ru particles displaying Ru-core Pt-shell (Ru@Pt) and Pt-core Ru-shell (Pt@Ru) structures, in which Ru or Pt are preferentially located on the outermost layer of the nanoparticles, have been synthesized. Characterization data confirm the formation of the bimetallic particles with the desired atomic distribution. The importance of the actual nature of the bimetallic samples in the COad electro-oxidation reaction has been discussed.

Quantitative determination of Zr in the system constituted by quartz microspheres functionalized with two kinds of organometallic compounds has been studied due to the importance of the correct quantization of the Zr from a catalytic point of view. Two parallel approximations were done, i.e. acid leaching and direct solid quantization. To validate the acid leaching TXRF measures, ICP-MS analysis were carried out. The results obtained by means of the optimization of the quantitative direct solid procedure show that, with a previous particle size distribution modification, TXRF obtain the same analytical results as ICP-MS and TXRF by acid leaching way but without previous chemical acid manipulation. This fact implies an important improvement for the analysis time, reagents costs and analysis facility and it proves again the versatility of TXRF to solve analytical problems in an easy, quick and accurate way. Additionally and for the direct solid TXRF measurements, a deeper study was done to evaluate the intrinsic analytical parameters of the Zr TXRF analysis of this material. So, the influence of the particle size distributions (modified by means of a high power ultrasound probe) with respect to uncertainty and detection limits for Zr were developed. The main analytical conclusion was the strong correlation between the average particle sizes and the TXRF analytical parameters of Zr measurements, i.e. concentration, accuracy, uncertainty and detection limits.

A series of carbosilane dendritic ligands of general formula Gn-[CH(3,5-Me 2 pz) 2 ] m and their corresponding palladium(II) complexes Gn-[CH(3,5-Me 2 pz) 2 Pd(X)Cl] m (X = Cl or Me) containing four (m = 1) or eight (m = 2) terminal bis(pyrazolyl)methane moieties, along with their corresponding mono-metallic counterparts (m = 0), have been synthesized. An appropriate choice of poly(pyrazolyl)methane ligand has allowed us to overcome the steric and solubility issues that previously limited the synthesis of polymetallic dendrimers containing (scorpionato)palladium complexes. The evaluation of these complexes as catalyst precursors in the Heck reaction between p-iodotoluene and methyl acrylate is also reported.

Neutral and cationic {bis(3,5-dimethylpyrazol-1-yl)methane}-palladium(II) complexes of general formula [PdClX{RCH(3,5-Me 2 pz) 2 }] (X=ClorMe) or [PdMe(MeCN){RCH(3,5-Me 2 pz) 2 }]-[BAr f 4 ], where R is a benzyl or benzyloxycarbonyl group or a poly(aryl ether) Frechet-type dendron, have been synthesized and fully characterized, including by X-ray diffraction methods in some cases. These palladium complexes have been evaluated as catalyst precursors in the Heck reaction between para-iodotoluene and methyl acrylate. The active catalytic species formed from these precursors are apparently not coordinated to the bis(pyrazolyl)methane ligands.

This overview covers the most relevant results obtained by our group in the last few years concerning the synthesis and catalytic applications of metal complexes anchored to the surface of carbosilane dendrimers functionalized with iminopyridine ligands. Nickel dibromide complexes activated with methylaluminoxane (MAO) have been studied for the polymerization of ethylene, whereas cat-ionic palladium(ii) derivatives have been applied to the copolymerization of carbon monoxide and tert-butylstyrene. In addition, palladium dendrimers have been tested in the Heck reaction between methyl acrylate and iodotoluene. Correlations between the catalyst activities or reaction products (product distributions, polymer molecular weights, etc.) and the dendrimer generation are discussed and tentative explanations for these correlations provided.

We present here the first example of the telomerisation of isoprene with glycerol and polyethylene glycol (PEG-200), opening a facile route to new terpene structures, based on a combination of renewable and petroleum-based feedstocks. The reaction is catalysed by a palladium-carbene complex. Significantly, this system gives >99% of linear monotelomer products. The factors that govern substrate conversion, dimerisation/telomerisation selectivity, and catalyst activity are studied and discussed.

2-(N-aryliminomethyl)pyrrole precursors (2,6-R2-C6H3-N CH-2-C4H3NH) (R = Me, IH; R = iPr, IIH) were prepared and transformed into their corresponding sodium salts (Na+I− and Na+II−) by treatment with NaH. Both salts readily react with [NiBr2(DME)] (DME = 1,2-dimethoxyethane) to give the respective bis{2-(N-arylimino-κN-methyl)pyrrolide-κN}nickel(II) complexes (1, 2) in almost quantitative yields. The oxidative addition of IH to [Ni(COD)2] (COD = 1,5-cyclooctadiene) results in the formation of 3, which is a mono(iminomethylpyrrolide)-η3-(cyclic-allyl)-type organonickel(II) complex. The crystal structure of compound 1 has been established by X-ray diffraction studies.

Dendrimers provide new and practical solutions to the complex problem of catalyst separation from the product stream. Dendrimers functionalized with active metal complexes are themselves soluble, nanosized catalysts that are capable of combining the high activity and selectivity of classical homogeneous catalysts with the enhanced separation capabilities added by the macromolecule. This report reviews the recovery and recycling of metallodendrimer catalysts by different separation techniques, such as nanofiltration, precipitation, or catalyst immobilization on solid supports, or by the use of appropriate solvent media, as illustrated by representative examples.

Pyridylimine ligands of general formula CS-{O-4-(2,5-C6H2R2)-NCH-2-Py}n, where CS is a trimethylsilyl group (n = 1, R = H, Ia or Me, Ib) or a carbosilane dendritic framework (IIa,b, n = 4; IIIa, n = 8), have been coordinated to platinum(II) and molybdenum(0) centers to give the mononuclear [(Ia,b){PtCl2}], tetranuclear [(IIb){PtCl2}4] and [(IIa){Mo(CO)3(MeCN)}4], and octanuclear [(IIIa){Mo(CO)3(MeCN)}8] complexes. The poor solubility of the polymetallic platinum compounds impedes the preparation of higher-generation dendrimers, although such a limitation is not found in the case of the more soluble molybdenum dendrimers.

A series of water-soluble (NHC)Pt(0)(dvtms) and (NHC)Pt(0)(AE) complexes containing different sulfonated NHC ligands (dvtms = divinyltetramethyldisiloxane and AE = diallyl ether) are reported. The dvtms compounds have been found to be quite robust and to display some conformational rigidity, whereas their AE counterparts are less stable and more flexible. The catalytic evaluation of these complexes in the hydrosilylation of alkynes in water revealed no benefits in favor of the complexes containing the more labile spectator diene (AE), and a fairly regular catalytic behavior for all complexes that restricts the location of the sulfonate group to the proximity of the metal site. Fil: Ruiz Varilla, Andrea M.. Universidad de Alcala. Facultad de Ciencias; España Fil: Baquero, Edwin A.. Universidad de Alcala. Facultad de Ciencias; España Fil: Silbestri, Gustavo Fabián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina Fil: Gonzalez Arellano, Camino. Universidad de Alcala. Facultad de Ciencias; España Fil: de Jesús, Ernesto. Universidad de Alcala. Facultad de Ciencias; España Fil: Flores, Juan C.. Universidad de Alcala. Facultad de Ciencias; España

Palladium complexes of general formula [PdCl2(L)2], 3a−c, were synthesized by reaction of [PdCl2(COD)] (COD = 1,5-cyclooctadiene) with the appropriate functionalized phosphine L = [P(C6H5)n((C6H4CH2CH2Si(CH2CH2CH2SiEtMe2)3)3-n)] (n = 2, 2a; 1, 2b; 0, 2c, respectively), which integrated carbosilane dendritic wedges attached to the para-carbon atom of the phenyl group. As a result of the inclusion of the carbosilane dendrons, the solubility of the corresponding palladium complexes 3 in supercritical carbon dioxide (scCO2) was increased in comparison with the palladium complex containing a PPh3 ligand, which showed negligible solubility. The employment of these complexes as precatalysts in a selected Heck coupling reaction in scCO2 was investigated. Good activities were found for 3a−c in such a medium due to the acquired solubility, in contrast with the palladium complex containing PPh3, which showed no activity.

A series of carbosilane dendritic compounds Gn-ONNMem, containing one (n = 0), four (n = 1), eight (n = 2), or 16 (n = 3) terminal pyridylimine ligands, substituted with m methyl groups (m = 0, 2, ...

Series of neutral and cationic palladium carbosilane dendritic compounds of the general formula Gn-ONNMem[Pd(X)Y] (X, Y = Cl; X = Me, Y = Cl; X = Me, Y = MeCN), containing 4 (n = 1), 8 (n = 2) or 16 (n = 3) terminal pyridylimine complexes, substituted with m methyl groups (m = 0, 2, 3), along with the corresponding monometallic counterparts (n = 0), have been synthesized. Monometallic or dendritic chloro methyl or cationic methyl palladium compounds consist of a cis/trans mixture of diastereoisomers, with compositions according to their electronic and steric features. The cationic compounds Gn-ONNMem[PdMe(MeCN)]+ are found to be active catalysts for the alternating copolymerization of CO and 4-tert-butylstyrene, producing mainly syndiotactic polyketones due to a chain-end stereocontrolled mechanism. Modification of the pyridylimine ligand framework by methyl substituents has a decisive influence on the activities of the palladium compounds. Some of them are found to retain some activity after several days...

A synthetic strategy has been developed for the preparation of new peripheral amine- or ammonium-terminated carbosilane dendrimers of type nG-[Si(OCH2CH2NMe2)y]x or nG-[Si(OCH2CH2NMe3+I–)y]x, respectively. It consists of the alcoholysis of well-known chlorosilane-terminated dendrimers with N,N-dimethylethanolamine and the subsequent quaternization with MeI. All these systems are susceptible to hydrolysis, although the decomposition depends on concentration and dendrimer generation. Evaluation of dendrimer toxicities by phase-contrast light microscopy and MTT assay were carried out, and evidence of dendrimer/oligonucleotide complex formation was carried out by gel electrophoresis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Titanium-containing carbosilane dendrimers of type n G-Si[(CH 2 ) 3 [{C 6 H 4 − y (OMe) y }O]Ti(C 5 H 5 )Cl 2 ] x , in which phenoxy group is anchored to the dendritic skeleton in para position through eugenol or 2-allyl-2,6-dimethoxyphenol precursors, were used in ethylene polymerization. Fresh toluene solutions of these dendrimers in conjunction with MAO behaved as moderate active systems. However, their aged toluene solutions, when they were activated with MAO became highly active catalysts as result of dendrimer aggregation processes. However, when the peripheral unit are replaced by [Ti(C 5 Me 5 )Cl 2 ] or [M(C 5 H 5 ) 2 Cl] groups or 2-allyl-6-methylphenol are incorporated to the peryphery of a carbosilane dendrimer no aggregation was observed upon aging.

The Si–Ph bond of PhSi[(CH2)3SiMe2Bz]3 (5) is cleaved with triflic acid to give TfOSi[(CH2)3SiMe2Bz]3, which, in turn, reacts with triethylammonium chloride or potassium cyclopentadienide to give, respectively, ClSi[(CH2)3SiMe2Bz]3 (8) and (C5H5)Si[(CH2)3SiMe2Bz]3 (10). This strategy can be applied to the post-growth incorporation of nucleophiles to the focal point of carbosilane dendritic wedges. In this way, cyclopentadiene-functionalized dendritic wedges of second and third generation C5H5-Gn-[(CH2)3SiMe2Bz]x (n = 2, x = 9, 11; n = 3, x = 27, 12) have been obtained starting from Ph-Gn-[(CH2)3SiMe2Bz]x (6, 7). The metallocenes [{(BzMe2SiCH2CH2CH2)3SiC5H4}2MCl2] (M = Ti, 14; Zr, 15) have also been obtained from 10 and their catalytic behavior in ethylene and propylene polymerization, using MAO as a cocatalyst, has been studied and compared to that of related non-dendritic complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)