Examinando por Autor "Fajardo, Mariano"

Mostrando 1 - 7 de 7

Design of Novel Group 4 ansa-Metallocene Compounds and their Role as Catalysts in the Polymerization of Olefins
(2014-01-28) Prashar, Sanjiv; Gómez-Ruiz, Santiago; Fajardo, Mariano; Antiñolo, Antonio; Fernández-Galán, Rafael; Otero, Antonio; Rivilla, Iván
Since the discovery by Sinn and Kaminsky that zirconocene complexes in the presence of MAO were able to polymerize olefins there has been a dramatic expansion in this field. One of the main focuses of this research is centred on the tailoring of metallocene complexes that can direct the catalytic reaction in producing polymers with desired physical properties. Ligand design is therefore of utmost importance in the development of "made to measure" single-site olefin polymerization catalysts. In addition the introduction of functional groups in the ligand system can be later exploited in immobilizing the catalyst on different substrates. In this communication we describe the synthetic strategies used in the design of group four ansa-metallocene complexes and the application of these compounds as catalysts in the polymerization of ethylene and propylene. The principal design aims addressed include: 1. Variable substitution at the ansa-carbon bridging atom of the metallocene catalysts 2. Synthesis of hydride silylene ansa-bridged complexes that act as hydrosilylation reagents. 3. Functionalization of ansa-metallocene complexes 4. Synthesis of C1 symmetric ansa-metallocene catalysts which are isospecfic in the polymerization of propylene
Heterogeneous oxidative desulfurization catalysed by titanium grafted mesoporous silica nanoparticles containing tethered hydrophobic ionic liquid: A dual activation mechanism
(Elsevier, 2019-10-25) Cruz, Paula; Granados, Elizabeth-Adriana; Fajardo, Mariano; del Hierro, Isabel; Pérez, Yolanda
In this study, heterogeneous catalysts containing ionic liquid and/or titanium have been prepared and used for oxidative desulfurization. For the synthesis of hybrid mesoporous silica nanoparticles (ILBF4-MSN), a grafting method has been employed with the ionic liquid 1-octyl-3-(3-(triethoxysilyl)propyl)-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (ILBF4) which contains a long alkyl chain. Titanium hybrid mesoporous silica nanoparticles (ILBF4-x%TiCp2-MSN) and mesoporous silica nanoparticles containing titanium (TiCp2-MSN) have also been prepared using titanocene dichloride. The catalyst containing ionic liquid and titanium, ILBF4-3%TiCp2-MSN exhibited the highest desulfurization efficiency (99.1%) in model oil with high concentration of DBT and using H2O2 as oxidant. In addition, the effect of immobilization of the ionic liquid on titanium materials has been investigated by solid-state 13C, 47/49Ti and 19F NMR spectroscopy and solid state electrochemical techniques. The titanium species and ionic liquid play an important role in the oxidative desulfurization reaction since they might activate synergistically sulfur derivatives and enhance the process
Hydrosilylation in the Design and Functionalization of ansa-Metallocene Olefin Polymerization Catalysts
(2014-01-29) Gómez-Ruiz, Santiago; Prashar, Sanjiv; Fajardo, Mariano; Antiñolo, Antonio; Otero, Antonio
The group 4 ansa-metallocene complexes [M{Me(H)Si(¿5-C5Me4)(¿5-C5H4)}Cl2] (M = Ti, Zr, Hf),that contain a Si-H bond, have been used as hydrosilylation reagents with the silane substrates, Si(CH=CH2)4 and Me2Si(CH=CH2)2. Our results show that the hydrosilylation reaction takes place at only one of the vinyl groups to give [M{(CH2=CH)3SiCH2CH2(Me)Si(¿5-C5Me4)(¿5-C5H4)}Cl2] (M = Ti, Zr, Hf) and [M{(CH2=CH)Me2SiCH2CH2(Me)Si(¿5-C5Me4)(¿5-C5H4)}Cl2] (M = Ti, Zr, Hf). Hydrosilylation of the remaining vinyl groups can be achieved by using simple silane reagents, for example, HSiEt3 to give [M{(Et3SiCH2CH2)3SiCH2CH2(Me)Si(¿5-C5Me4)(¿5-C5H4)}Cl2] (M = Ti, Zr) and [M{(Et3SiCH2CH2)Me2SiCH2CH2(Me)Si(¿5-C5Me4)(¿5-C5H4)}Cl2] (M = Ti, Zr). All the compounds have been tested as homogeneous catalysts in the polymerization of ethylene and propylene
Mesoporous SBA-15 Modified with Titanocene Complexes and Ionic liquids: Interactions with DNA and other Molecules of Biological Interest Studied by Solid State Electrochemical Techniques.
(Royal Society of Chemistry, 2018) del Hierro, Isabel; Gómez-Ruiz, Santiago; Pérez, Yolanda; Cruz, Paula; Prashar, Sanjiv; Fajardo, Mariano
The immobilization of two titanocene complexes on SBA-15 has been accomplished following post-synthetic procedures. The ionic liquid, 1-methyl-3-[(triethoxysilyl)propyl]imidazolium chloride, has also been incorporated into the titanium containing materials to determine its influence on the interaction with molecules of biological interest. Cyclic voltammetry has been used to study the influence of the ionic liquid on the mechanism of reduction of titanocene derivatives. The interaction of titanocene and titanocene/ ionic liquid-containing mesoporous silica SBA-15 materials, with molecules of biological interest associated with important processes of metallodrug action against cancer cells, has been studied. Thus, we have carried out hydrolysis experiments on the materials functionalized with titanocene derivatives in physiological media to determine their stability and the interaction with serum/transport proteins such as transferrin and BSA and with target molecules such as guanosine, single-stranded DNA and double-stranded DNA by means of solid state voltammetry techniques. A qualitative analysis of the data based on peak current and reduction potential value changes of the couple Ti(IV)/Ti(III) in the presence of biomolecules at physiological pH, has revealed that grafted titanocene complexes show higher affinity for serum/transport proteins than for nucleic acids, indicating that the transport steps to the cells may be easier than the subsequent attack on DNA.
Supported Choline Hydroxide (Ionic Liquid) on Mesoporous Silica as Heterogeneous Catalyst for Knoevenagel Condensation Reactions
(Elsevier, 2018) del Hierro, Isabel; Pérez, Yolanda; Fajardo, Mariano
In this work hybrid mesoporous SBA-15 and mesoporous silica microspheres functionalized with choline hydroxide ionic liquid have been prepared. A two-step process inspired by the industrial production of choline hydroxide has been developed to synthesize the hybrid SBA-15 material with choline hydroxide ionic liquid (Chol-SBA-15) and the hybrid SBA-15 material with choline hydroxide ionic liquid and hexamethyldisilizane as capping agent (Chol-HMDS-SBA-15). For the preparation of hybrid mesoporous silica microspheres (Chol- MSMs), a co-condensation method has been employed with an ionic liquid prepared by reaction of 3-(glycidyloxypropyl) trimethoxysilane and trimethylamine in aqueous media. The synthesized materials have been fully characterized by elemental analysis, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N2 adsorption-desorption, transmission electron microscopy (TEM) and 13C CP/MAS NMR spectroscopy. These materials have been tested successfully as catalysts in Knoevenagel condensation of benzaldehyde with RCH2C≡N (R=CN (malononitrile), CO2Et (ethyl cyanoacetate)). The catalyst Chol-MSMs showed high catalytic activity, 99% of conversion and 99% of selectivity towards ethyl 2-cyano-3-phenylacrylate in 2 h of reaction and using ethanol as solvent. In addition, their reusability without loss of activity has been demonstrated
Synthesis of cationic niobocene imido derivatives
(2014-01-29) Hierro, Isabel del; Fajardo, Mariano; Garcés, Andrés; Gómez-Ruiz, Santiago; Pérez, Yolanda; Prashar, Sanjiv; Antiñolo, Antonio; Otero, Antonio; López-Mardomingo, Carmen
Following from our previous work in the synthesis and reactivity of niobium imido complexes,1 we have studied the preparation of cationic derivatives. The reduction of [Nb(=NPh)(eta5-C5H4SiMe3)2Cl] gives the short-lived niobocene(IV) radical [Nb(=NPh)(eta5-C5H4SiMe3)2. which was rapidly oxidized to the niobocene(V) cationic species [Nb(=NPh)(eta5-C5H4SiMe3)2(L)]+ (L = CO, ButNC) by the reaction with [Fe(eta5-C5H5)2][BPh4]. In a similar manner, the ansa-niobocene compound [Nb(=NBut){Me2Si(eta5-C5Me4)(eta5-C5H4)}(ButNC)][BPh4] was synthesized. However, in the attempted reduction of [Nb(=NBut){Me2Si(eta5-C5H4)2}Cl], the expected radical species was not observed. Instead the niobocene (V) imido dimer product was identified. The reaction with H2 and I2 gave [Nb(=NBut){Me2Si(eta5-C5H4)2}H] and [Nb(=NBut){Me2Si(eta5-C5H4)2}I], respectively.
Versatile titanium dioxide nanoparticles prepared by surface-grown polymerization of polyethylenimine for photodegradation and catalytic CeC bond forming reactions
(Elsevier, 2019-07-11) Ortiz-Bustos, Josefa; Fajardo, Mariano; del Hierro, Isabel; Pérez, Yolanda
Crystalline TiO2 anatase nanoparticles have been synthesized by a sol-gel procedure with a certain ratio of brookite phase due to low calcination temperature. TiO2 NPs have been successfully functionalized with hyperbranched polyethylenimine polymer (PEI) by the surface polymerization of aziridine or with N1-(3-trimethoxysilylpropyl)-diethylenetriamine (DT) by surface silanization to form catalyst with notable basic and photocatalytic properties. The TiO2 NPs have been characterized by X-ray diffraction (XRD), adsorption-desorption isotherms, fourier-transform infrared spectroscopy (FT-IR), diffuse reflectance UV–vis spectroscopy (DRUV-vis), elemental analysis, thermogravimetric analysis, transmission electron microscopy (TEM), photoluminiscence spectroscopy (PL) and solid-state voltammetry. Functionalized TiO2 NPs have revealed to be efficient in the photodegradation of methylene blue in water and as basic heterogeneous catalysts carbon-carbon forming reactions as Knoevenagel condensation, multicomponent reactions and Biginelli reaction. PEI-TiO2 with mesoporous structure and narrow size pore distribution, fulfill the requirements imposed to an eco-friendly and cost-effective catalyst since it is easily synthesized and recyclable.