Examinando por Autor "Navarro, Marta"

Mostrando 1 - 6 de 6

Bimetallic Scorpionate-based Helical Organoaluminums for the Efficient Carbon Dioxide Fixation into a Variety of Cyclic Carbonates
(Royal Society of Chemistry, 2020) Navarro, Marta; Sánchez-Barba, Luis F.; Garcés, Andrés; Fernández-Baeza, Juan; Fernández, Israel; Lara-Sánchez, Agustín; Rodríguez, Ana M.
A new family of bimetallic helical aluminum complexes can be obtained via warming up the preliminary dinuclear adduct complexes, or alternatively, by direct heating of the protioligands with 2 equiv of AlR3. X-ray diffraction analysis corroborated both high coordination versatility in the ligands and the existence of helical chirality in the complexes. DFT calculations confirmed the preferential arrangement of the ancillary scorpionates in the bimetallic complexes and rationalized a proposed reaction mechanism. Bimetallic complexes were investigated as catalysts in combination with halides for the cycloaddition reaction of CO2 with a wide range of epoxides for cyclic carbonate formation. These studies led to the development of a sustainable, inexpensive, efficient and selective bicomponent system with very broad substrate scope, including internal and challenging bio-based trisubstituted terpene derived substrates, reaching high conversions for translimonene oxide at mild conditions (79% conv., 70 ºC, 10 bar CO2, 1 mol%, 66 h).
Development of Heterobimetallic Al/Mg Complexes for the Very Rapid Ring-Opening Polymerization of Lactides
(ACS, 2023) Navarro, Marta; González-Lizana, David; Sánchez-Barba, Luis F.; Garcés, Andrés; Fernández, Israel; Lara-Sánchez, Agustín; Rodríguez, Ana M.
The successful architecture of active catalytic species with enhanced efficiencies is critical for the optimal exploitation of sustainable resources in industrially demanded processes. In this work, we describe the preparation of novel helical heterobimetallic Al/Mg-based complexes of the type [AlMe2(pbpamd–)MgR{κ1-O-(OC4H8O)}] [R = Et (1a), tBu (2a)] as potential catalysts. The design was performed through the sequential addition of the Al fragment to the ligand, followed by the Mg platform, resulting in a planar π-C2N2(sp2)–Al/Mg bridging core between metals. The new heterobimetallic species have been unambiguously characterized by single-crystal X-ray analysis. NOESY, DOSY, and EXSY NMR studies as well as density functional theory calculations corroborate both a rearrangement in solution to scorpionate complexes containing an unprecedented apical carbanion with a direct σ-C(sp3)–Al covalent bond named [{Mg(R)(pbpamd–) Al(Me)2}] [R = Et (1b), tBu (2b)] and an interconversion equilibrium between both isomers. We verified their utility and high efficiency as catalysts in the well-controlled ring-opening polymerization of the biorenewable l- and rac-lactide (LA) at 23 °C, reaching a remarkable turnover frequency value close to 25000 h–1 for rac-LA at this temperature and exerting a significant level of heteroselectivity (Pr = 0.80). Very interestingly, the kinetics demonstrate apparent first-order with respect to the catalyst and LA, which supports a synergic intramolecular cooperation between centers with electronic modulation among them.
Efficient Bulky Organo-Zinc Scorpionates for the Stereoselective Production of Poly(rac-lactide)s
(MDPI, 2021-07-19) Navarro, Marta; Garcés, Andrés; Sánchez-Barba, Luis Fernando; de la Cruz-Martínez, Felipe; Fernández-Baeza, Juan; Lara-Sánchez, Agustín
The direct reaction of the highly sterically demanding acetamidinate-based NNN-scorpionate protioligand Hphbptamd [Hphbptamd = N,N0-di-p-tolylbis(3,5-di-tertbutylpyrazole-1-yl)acetamidine] with one equiv. of ZnMe2 proceeds in high yield to the mononuclear alkyl zinc complex [ZnMe(k3-phbptamd)] (1). Alternatively, the treatment of the corresponding lithium precursor [Li(phbptamd) (THF)] with ZnCl2 yielded the halide complex [ZnCl(k3-phbptamd)] (2). The X-ray crystal structure of 1 confirmed unambiguously a mononuclear entity in these complexes, with the zinc centre arranged with a pseudotetrahedral environment and the scorpionate ligand in a k3-coordination mode. Interestingly, the inexpensive, low-toxic and easily prepared complexes 1 and 2 resulted in highly efficient catalysts for the ring-opening polymerisation of lactides, a sustainable bio-resourced process industrially demanded. Thus, complex 1 behaved as a single-component robust initiator for the living and immortal ROP of rac-lactide under very mild conditions after a few hours, reaching a TOF value up to 5520 h􀀀1 under bulk conditions. Preliminary kinetic studies revealed apparent zero-order dependence on monomer concentration in the absence of a cocatalyst. The PLA materials produced exhibited narrow dispersity values, good agreement between the experimental Mn values and monomer/benzyl alcohol ratios, as well as enhanced levels of heteroselectivity, reaching Ps values up to 0.74.
Efficient Production of Poly(Cyclohexene Carbonate) via ROCOP of Cyclohexene Oxide and CO2 Mediated by NNO-Scorpionate Zinc Complexes
(MDPI journals, 2020) Sobrino, Sonia; Navarro, Marta; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Lara-Sánchez, Agustín; Garcés, Andrés; Castro-Osma, José A.; Rodríguez, Ana M.
New mono- and dinuclear chiral alkoxide/thioalkoxide NNO-scorpinate zinc complexes were easily synthesized in very high yields, and characterized by spectroscopic methods. X-ray diffraction analysis unambiguously confirmed the different nuclearity of the new complexes as well as the variety of coordination modes of the scorpionate ligands. Scorpionate zinc complexes 2, 4 and 6 were assessed as catalysts for polycarbonate production from epoxide and carbon dioxide with no need for a co-catalyst or activator under mild conditions. Interestingly, at 70 °C, 10 bar of CO2 pressure and 1 mol % of loading, the dinuclear thioaryloxide [Zn(bpzaepe)2{Zn(SAr)2}] (4) behaves as an efficient and selective one-component initiator for the synthesis of poly(cyclohexene carbonate) via ring-opening copolymerization of cyclohexene oxide (CHO) and CO2, affording polycarbonate materials with narrow dispersity values
Unprecedented NNC-Scorpionate Zirconium-based Bicomponent System for the Very Efficient CO2 Fixation into a Variety of Cyclic Carbonates
(American Chemical Society, 2020) Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Lara-Sánchez, Agustín; Sobrino, Sonia; Martínez-Ferrer, Jaime; Garcés, Andrés; Navarro, Marta; Rodríguez, Ana M.
Two new derivatives of the bis(3,5-dimethylpyrazol-1-yl)methane modified by introduction of organosilyl groups on the central carbon atom, one of which bearing a chiral fragment, have been easily prepared. We verified the potential utility of these compounds through the reaction with [Zr(NMe2)4] for the preparation of novel zirconium complexes in which an ancillary bis(pyrazol-1-yl)methanide acts as a robust monoanionic tridentate scorpionate in a κ3-NNC chelating mode, forming strained four-membered heterometallacycles. These κ3-NNC-scorpionate zirconium amides were investigated as catalysts in combination with tetra-n-butylammonium bromide as cocatalyst for CO2 fixation into five-membered cyclic carbonate products. The study has led to the development of an efficient zirconium-based bicomponent system for the selective cycloaddition reaction of CO2 with epoxides. Kinetics investigations confirmed apparent first-order dependence on the catalyst and cocatalyst concentrations. In addition, this system displays very broad substrate scope, including mono- and disubstituted substrates, as well as the challenging biorenewable terpene derived limonene oxide, under mild and solvent-free conditions.
Very efficient organo-zinc scorpionates for CO2 fixation into a variety of cyclic carbonates: synthesis, coordination ability and catalytic studies
(Royal Society of Chemistry, 2023-03-29) Navarro, Marta; Garcés, Andrés; Sánchez-Barba, Luis Fernando; González-Lizana, David; Lara-Sánchez, Agustín
The fixation of CO2 mediated by metal-based catalysts for the production of organic molecules of industrial interest such as cyclic carbonates is urgently required under green and eco-friendly conditions. Herein, we describe the easy preparation of sterically demanding scorpionate ligands bearing different electron-withdrawing groups, and their coordination ability for the preparation of robust zinc-based mononuclear complexes of the type [ZnMe(κ3-NNN′)] (4–6). These complexes, in combination with co-catalysts comprising larger ionic radius-based halides such as tetra-n-butylammonium, functioned as very active and selective catalysts for CO2 fixation into five-membered cyclic carbonates. These studies have led to the development of sustainable, inexpensive, and low-toxicity systems formed by 4–5 and Bu4NBr for the cycloaddition of CO2 into epoxides under very mild and solvent-free conditions, reaching very good to excellent conversions (TOF = 260 h−1). Moreover, these bicomponent systems show a broad substrate scope and functional group tolerance, including mono- and di-substituted epoxides, as well as bio-renewable diepoxides. Very interestingly, these are the first zinc-based systems reported to date for the successful transformation of the very challenging tri-substituted terpene-derived cis/trans-limonene oxide, whose reaction proceeds with high stereoselectivity to the formation of the bicyclic trans-limonene carbonate. Additionally, these bicomponents can be efficiently used up to six times without significant loss of activity. Kinetic investigations confirmed that the reaction shows an apparent first-order dependence on the catalyst and co-catalyst concentrations, which indicates an intramolecular monometallic mechanism.