Examinando por Autor "Sobrino, Sonia"

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Efficient CO2 Fixation into Cyclic Carbonates Catalyzed by NNOScorpionate Zinc Complexes
(Royal Society of Chemistry, 2019) Sobrino, Sonia; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Garcés, Andrés; Lara- Sánchez, Agustín; Castro-Osma, José A.
A series of new chiral zwitterionic NNO-scorpionate mononuclear zinc alkyls [Zn(R)(κ3-NNO)]Br was developed in very high yields via suitable quaternization in the scorpionate ligand. These zwitterionic complexes performed as bifunctional catalysts and exhibited improved catalytic activity for the fixation of CO2 into cyclic carbonates compared to the neutral analog mononuclear [Zn(R)(κ3-NNO)] and binuclear [Zn(R)(κ2-NNμ-O)Zn(R)2] compounds. The catalyst system showed a broad substrate scope and functional group tolerance under mild and solvent-free conditions.
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
Mono- and Binuclear Chiral N,N,O-Scorpionate Zinc Alkyls as Efficient Initiators for the ROP of rac- Lactide
(Royal Society of Chemistry, 2017) Otero, Antonio; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Sobrino, Sonia; Garcés, Andrés; Lara-Sánchez, Agustín; Rodríguez, Ana M.
The preparation of new chiral bis(pyrazol-1-yl)methane-based N,N,O-donor scorpionate ligands in the form of the alcohol compounds bpzampeH (1) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(dimethylamino)phenyl]ethanol}, bpzaepeH (2) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(diethylamino)phenyl]ethanol}, and bpzimeH (3) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[1-methyl-1H-imidazol-2-yl]ethanol} has been carried out by the 1,2-addition reactions of a series of aldehydes. These new chiral heteroscorpionate ligands reacted with [ZnR2] (R = Me, Et, CH2SiMe3) in a 1 : 1 molar ratio in toluene to give the mononuclear monoalkyl zinc complexes [Zn(R)(κ3-NNO)] (4–12). When these reactions were carried out in a 1 : 2 molar ratio the binuclear trisalkyls [Zn(R)(κ2-NNμ-O)Zn(R)2] (13–18) were obtained. The structures of these complexes were elucidated by 1H and 13C{1H} NMR spectroscopy and the X-ray crystal structures of 4 and 5 were also established. Interestingly, alkyl-containing zinc complexes 4–13, 15 and 17 act as efficient single-component initiators for the ring-opening polymerization of rac-lactide at 20 °C to afford PLA materials with low molecular weights in a few hours. The dinuclear trisalkyls showed higher activity in comparison with the mononuclear zinc counterparts, suggesting a cooperative effect of the two remote metals. The narrow dispersity ranges (Mw/Mn = 1.05) of the isolated polymers in conjunction with the linear nature of the number average molecular weight versus conversion plot provided evidence for living behavior. Inspection of the kinetic parameters showed that the propagations have the usual pseudo-first-order dependence on rac-lactide and catalyst concentration. End-group analysis and MALDI-TOF mass spectrometry confirmed that the initiation occurs through nucleophilic attack of the alkyl on the lactide monomer. Microstructural analysis of poly(rac-lactide)s revealed that the most sterically hindered ligand on the alkoxide fragment exerts a moderate influence on the degree of stereoselectivity, with heteroenriched-PLAs (Ps = 0.68) produced at room temperature.
New Racemic and Single Enantiopure Hybrid Scorpionate/Cyclopentadienyl Magnesium and Zinc Initiators for the Stereoselective ROP of Lactides
(ACS, 2015) Honrado, Manuel; Otero, Antonio; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Garcés, Andrés; Lara-Sánchez, Agustín; Martínez-Ferrer, Jaime; Sobrino, Sonia; Rodríguez, Ana M.
The preparation of the first racemic bis(pyrazol-1-yl)methane-based NNCp-donor hybrid scorpionate/cyclopentadienyl magnesium and zinc complexes [Mg(R)(κ2-η5-NNCp)] (1–6) [NNCp = bpztcp, R = Me (1), Et (2), CH2SiMe3 (3); bpzpcp, R = Me (4), Et (5), CH2SiMe3 (6)] and [Zn(R)(κ2-η1-NNCp)] (7–12) [NNCp = bpztcp, R = Me (7), Et (8), CH2SiMe3 (9); bpzpcp, R = Me (10), Et (11), CH2SiMe3 (12)] has been carried out by the reaction of the corresponding racemic NNCp-H-donor scorpionate pro-ligands with Grignard reagents RMgCl, after deprotonation with nBuLi, or directly with ZnR2. The resulting alkyl magnesium complexes (1–6) have been employed in a protonolysis reaction with 2,6-dimethylphenol to yield the aryloxide magnesium complexes [Mg(OAr)(κ2-η5-NNCp)] (13 and 14) [NNCp = bpztcp (13), bpzpcp (14)]. Subsequently, the enantiopure scorpionate pro-ligand (R,R)-bpmycpH (16a) {bpmycpH = 1-{2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-(2R)-2-[(1R)-6,6-[3.1.1]-2-hepten-2-yl]ethyl}cyclopentadiene} and (R,R)-bpmycp′H (16b) {bpmycp′H = 2-{2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-(2R)-2-[(1R)-6,6-[3.1.1]-2-hepten-2-yl]ethyl}cyclopentadiene} reacted with RMgCl (after addition of nBuLi) or with ZnR2 to give the single enantiopure complexes [Mg(R)(κ2-η5-R,S-bpmycp)] (17–19) (R = Me (17), Et (18), CH2SiMe3 (19)) {R,S-bpmycp = 2-{2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-(2S)-2-[(1R)-6,6-[3.1.1]-2-hepten-2-yl]ethyl}cyclopentadienyl} and [Zn(R)(κ2-η1-R,S-bpmycp)] (20–22) (R = Me (20), Et (21), CH2SiMe3 (22)). The structures of these complexes were elucidated by 1H and 13C{1H} NMR spectroscopy, and the X-ray crystal structures of 2, 3, 7 and 21 were also established. These racemic and single enantiopure complexes 1–3, 5–9, 11–14, 19, and 21 can act as single-component initiators for the ring-opening polymerization of rac-lactide under mild conditions. Microstructural analysis of poly(rac-lactide)s revealed that, whereas the myrtenal substituent on the single enantiomerically pure initiator 21 exerts an appreciable influence on the degree of stereoselectivity to produce isotactic-enriched poly(lactide)s with a Pi value up to 0.77, the racemic mixtures of initiators impart more discrete levels of heteroselectivity in the production of PLAs, with a Ps value of 0.72.
Synthesis of an Enantiopure Scorpionate Ligand by a Nucleophilic Addition to a Ketenimine and a Zinc Initiator for the Isoselective ROP of rac-Lactide
(Royal Society of Chemistry, 2019) Honrado, Manuel; Sobrino, Sonia; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Garcés, Andrés; Lara-Sánchez, Agustín; Rodríguez, Ana M.
A novel nucleophilic addition of an organolithium to a ketenimine to prepare an enantiopure NNN-heteroscorpionate ligand is described. We verified its potential utility as a valuable scaffold for chirality induction through the preparation of enantiopure zinc complexes, which behave as highly efficient initiators to produce highly-enriched isotactic poly(lactide)s (Pi up to 0.88).
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.