Examinando por Autor "Honrado, Manuel"

Mostrando 1 - 6 de 6

Copolymerization of Cyclic Esters Controlled by Chiral NNO-Scorpionate Zinc Initiators
(ACS Publications, 2016) Otero, Antonio; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Honrado, Manuel; Garcés, Andrés; Lara-Sánchez, Agustín; Rodríguez, Ana M.
Reaction of chiral alcohol-scorpionate compoundbpzteH [bpzteH = 2,2-bis(3,5-dimethylpyrazol- 1-yl)-1-para-tolylethanol] with [ZnR2] (R = Me, CH2SiMe3) in a 1:2 molar ratio afforded the dinuclear chiral alkyl zinc complexes [Zn(R)(k2-NN μ-O)Zn(R)2] (1–2) [k2-NN μ-O= bpzte, R = Me 1, CH2SiMe32]. Using these trialkyl complexes in an alcoholysis reaction with ArOH (1 equiv; Ar = 2,6-C6H3Me2) yielded the chiral dinuclear zinc complexes [(ZnR)2(kN:kN- μ-O)( μ-EAr)] (3– 4) [kN:kN- μ-O= bpzte, R = Me 3, CH2SiMe34]. The structures of the different compounds were determined by spectroscopic methods and, in addition, the X-ray crystal structures of 1 and 3 confirmed a dinuclear structure in all complexes, with the alkoxide of the heteroscorpionate ligands in a μ-bridging mode between the two Zn(II) centers. Trisalkyl and alkyl-aryloxide-containing zinc complexes 1–4 can act as single-component initiators for the ring-opening homopolymerization of e-caprolactone and L-/rac-lactide, affording materials with low molecular weights and narrow monomodal molecular weight distributions under mild conditions in only a few hours. Microstructural analysis of poly(rac-lactide) revealed that the alkyl-aryloxide 3 exerts a moderate level of heteroselectivity (Ps= 0.68). More interestingly, this initiators 3 and 4 also allowed the well-controlled random copolymerization of ε-CL and LLA as indicated by both the values of the reactivity ratios of the two comonomers (rCL = 1.15 and 0.92, and rLA = 1.37 and 1.05, for 3 and 4, respectively), and the average lengths of the caproyl and lactidyl sequences (LCL ~ 2.0; LLA ~ 2.5, for both initiators). The copolymers also showed to possess monomer contents in close agreement with their composition in the initial monomer feed. Inspection by differential scanning calorimetry on the thermal properties such as Tg of various copolymers produced by 3 revealed a strong dependence on monomer content, as these values vary linearly with the molar percentage of L-lactide unit in the copolymer over a temperature range of -30 to 42 ºC.
Enantiopure N,N,O-Scorpionate Zinc Amide and Chloride Complexes as Efficient Initiators for the Heteroselective ROP of Cyclic Esters
(Royal Society of Chemistry, 2014) Honrado, Manuel; Otero, Antonio; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Garcés, Andrés; Lara-Sánchez, Agustín; Rodríguez, Ana M.
The reaction of bpzbeH, bpzteH (racemic mixture) or (R,R)-bpzmmH (enantiopure) with the amide complexes Zn{N(SiMe3)2}2 or Zn{N(SiHMe2)2}2 in 1 : 1 molar ratio in toluene afforded the mononuclear amide zinc complexes [Zn(NR2)(κ3-NNO)] (1–6) [κ3-NNO = bpzbe, R = SiMe31, SiHMe22; bpzte, R = SiMe33, SiHMe24; (R,R)-bpzmm, SiMe35, SiHMe26]. These complexes were employed in a protonolysis reaction with HCl–Et2O in 2 : 1 molar ratio to yield the dinuclear amide/chloride zinc complexes [Zn(κ2-NN-μ-O)2{ZnCl(NR2)}] (7–12) [κ2-NN-μ-O = bpzbe, R = SiMe37, SiHMe28; bpzte, R = SiMe39, SiHMe210; (R,R)-bpzmm, SiMe311, SiHMe212]. The mononuclear complexes 5 and 6 and dinuclear complexes 11 and 12 are the first enantiopure-scorpionate zinc amide complexes to be synthesized. The single-crystal X-ray structure analysis of derivatives 1 and 3 confirmed a monomeric 4-coordinative structure in which the heteroscorpionate ligands are in a κ3 coordination mode, while 8 had a dimeric molecular disposition with two μ-bridging alkoxides of the heteroscorpionate ligands between the two six- and four-coordinate Zn(II) centers. Interestingly, the chiral amide-containing zinc complexes 1–5 and 11 can act as single-component initiators for the ring-opening polymerization of ε-caprolactone and lactides under mild conditions, affording, in a few hours, medium/low molecular weight polymers with low polydispersity indices. MALDI-ToF mass spectra confirmed that the initiation occurred through a nucleophilic attack by the amide on the lactide monomer, and inspection of the kinetic parameters showed that propagations present the usual pseudo-first order dependence on monomer and catalyst concentrations. In addition, microstructural analysis of poly(rac-lactide)s revealed that the myrtenal substituent on the alkoxide fragment has a significant influence on the degree of stereoselectivity, producing enriched-heterotactic PLAs with a Ps value of up to 0.79 under mild conditions.
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.
Stereoselective ROP of rac-Lactide Mediated by Enantiopure NNO-Scorpionate Zinc Initiators
(American Chemical Society, 2014) Honrado, Manuel; Otero, Antonio; Fernández-Baeza, Juan; Sánchez-Barba, Luis F.; Garcés, Andrés; Lara-Sánchez, Agustín; Rodríguez, Ana M.
The reaction of the enantiopure NNO-scorpionate ligand (R,R)-bpzmmH with [ZnR2] (R = Me, Et, CH2SiMe3) in a 1:2 molar ratio afforded the dinuclear tris-alkyls [Zn(R)(κ2-NNμ-O)Zn(R)2] (R = Me (1), Et (2), CH2SiMe3 (3)). The reaction of the bimetallic tris-alkyls 1–3 with an aromatic alcohol and thioalcohol yielded the dinuclear zinc complexes containing aryloxide/arylthioxide ligands [(ZnR)2(κN:κN-μ-O)(μ-EAr)] (Ar = 2,6-C6H3Me2; E = O, R = Me (4), Et (5), CH2SiMe3 (6); E = S, R = Me (7), Et (8), CH2SiMe3 (9)) by an alcoholysis or thioalcoholysis reaction. The structures of the different compounds were determined by spectroscopic methods and, in addition, the X-ray crystal structures of 2 and 5 were also unambiguously established. Alkyl- and aryloxide/thioaryloxide-containing enantiopure zinc complexes 3–6 and 9 can act as single-component living initiators for the ring-opening polymerization of lactides, affording materials with low molecular weights under mild conditions in only a few hours. Interestingly, microstructural analysis of poly(rac-lactide) by 1H NMR spectroscopy revealed that the most sterically hindered initiator, [(ZnCH2SiMe3)2(R,R-bpzmm)(μ-OAr)] (6), is one of the first examples of a zinc complex capable of exerting a significant influence on the degree of enantioselectivity, with enriched-isotactic PLAs (Pi = 0.74) produced through an enantiomorphic site control mechanism.
Studies on Multinuclear Magnesium tert-Butyl Heteroscorpionates: Synthesis, Coordination Ability and Heteroselective ROP of rac-Lactide
(American Chemical Society, 2017) Garcés, Andrés; Sánchez-Barba, Luis F.; Fernández-Baeza, Juan; Otero, Antonio; Honrado, Manuel; Lara-Sánchez, Agustín; Rodríguez, Ana M.
The reaction of the low sterically hindered heteroscorpionate lithium acetamidinates [Li(κ3-NNN)(thf)] {NNN = pbpamd (1) [pbpamd = N,N′-diisopropylbis(3,5-dimethylpyrazol-1-yl)acetamidinate], tbpamd (2) [tbpamd = N-ethyl-N′-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidinate], ttbpamd (3) [ttbpamd = N,N′-di-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidinate], phbpamd (4) [phbpamd = N,N′-di-p-tolylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] and the highly sterically demanding [Li(κ3-phbptamd)(thf)] (5) [phbptamd = N,N′-di-p-tolylbis(3,5-di-tert-butylpyrazol-1-yl)acetamidinate] with the commercially available Grignard reagent tBuMgCl in an equimolecular ratio yielded the magnesium tert-butyl heteroscorpionates [Mg(tBu)(κ3-NNN)] [NNN = pbpamd (6), tbpamd (7), ttbpamd (8), and phbptamd (9)]. In addition, subsequent reaction of monoalkyls 6–8 with two additional equivalents of tBuMgCl gave rise to two different classes of chiral tetraalkyls, which contain apical methine C–H activated heteroscorpionates that show two possible coordination modes, namely, the tetranuclear complexes [{(tBu)Mg(κ3-N,N,N;κ2-C,N)Mg(tBu)}2{μ-O,O-(OC4H8O)}] (κ3-N,N,N;κ2-C,N = pbpamd–10, tbpamd–11a) and [(tBu)Mg(κ2-N,N;κ2-N,N)Mg(tBu){μ-O,O-(OC4H8O)}]2 (κ2-N,N;κ2-N,N = tbpamd–11b). This reaction for 8 was unsuccessful, but an analog such as dinuclear complex [(thf)(tBu)Mg(κ2-N,N;κ2-N,N)Mg(tBu)(thf)] (κ2-N,N;κ2-N,N = phbpamd–12) could be obtained from its lithium salt. Contrary to complexes 10–12, the C–H activation process was not observed for complex 9, but interestingly, the coordination of one additional equivalent of MgtBu2 afforded dinuclear complex [Mg(tBu)(κ3-phbptamd){Mg(tBu)2}] (13). Similarly, coordination of MgtBu2 to 10 produces chiral trinuclear [{(tBu)Mg(pbpamd–)Mg(tBu)}{μ-O,O-(OC4H8O)}{Mg(tBu)2(thf)}] (14). The X-ray crystal structures of complexes 4, 6, 8, 9, 11b, 12, 13, and 14 confirm the nuclearity of each family, and the existence of apical σ-C(sp3)–Mg (14) and extended π-C2N2(sp2)–Mg2 (11b and 12) covalent bonds have unambiguously been also confirmed. Furthermore, mononuclear compounds 8 and 9, tetranuclear compound 10, and dinuclear compounds 12 and 13 can act as highly efficient single-component living initiators for the ring-opening polymerization of rac-lactide. More interestingly, the most sterically hindered initiators exhibit enhanced levels of heteroselectivity on the PLAs, with 9 reaching Ps values up to 0.85.
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).