The aerobic oxidation and oxidative esterification of 5-hydroxymethylfurfural (HMF) catalyzed by gold nanoparticles (AuNPs) supported on a semicrystalline nanoporous multiblock copolymer matrix consisting of syndiotactic poly(styrene)-cis-1,4-poly(butadiene) (sPSB) have been investigated. Depending on the reaction parameters (support nanoporosity, presence of water, solvent, temperature, cocatalyst, oxygen pressure), the conversion of HMF can be finely addressed to the formation of the desired oxidation product, such as 2,5-diformylfuran (DFF), 5-formylfuran-2-carboxylic acid (FFCA), methyl 5-(hydroxymethyl)furan-2-carboxylate (MHMFC), dimethyl furan-2,5-dicarboxylate (DMFC), and furan-2,5-dicarboxylic acid (FDCA), under optimized reaction conditions. The AuNP-sPSB catalyst is highly effective and selective because the polymer support acts as a conveyor and concentrator of the reactants toward the catalytic sites.
The efficient formationo fc yclic polyesters from the ring-opening polymerization of lactide, e-caprolactone, and b-butyrolactone catalyzed by a1 ,4-dithiabutanedyl-2,2'-bis (4,6-dicumylphenol) [OSSO]-FeCl complex activated with cyclohexene oxide was achieved. The catalystw as very active (initialt urnover frequencyu pt o2 718 h À1 ), robust,a nd workedw ith am onomer/ Fe ratio up to 10 000. The formationo fc yclic polymers was supported by using high-resolution matrix-assisted laser desorptioni onization (MALDI) MS, and the averager ing size ( % 5kDa for cyclic polylactide) independent of the reaction conditions. Am onometallic ring-opening polymerization/cyclization mechanism was proposed from the resultso fakinetic investigation.In the search of viable alternatives to fossil-based plastic materials, one of the most promising classes of sustainable (bio)polymers is aliphatic polyesters (APEs). [1] Indeed, several examples of APEs have been proposed as possible substitutes of well-establishedp olymeric commodities( e.g.,p olystyrene,p olyethylene, andp olypropylene). [2] Amongo thers, poly(lactic acid) (PLA), poly(e-caprolactone) (PCL), and poly(hydroxyb utyrate) (PHB) are the most investigated materials and already on the market. [3] The metal-mediated ring-opening polymerization (ROP) of lactides and lactonesi s, nowadays, the most efficient catalytic process for APEs production. [4] Indeed, av ery high degree of control over the polymerization process has been achieved, which offerst he possibility to obtain polymers with predictable molecular weights, compositions,a nd microstructures. [5] Amongo thers, polymers with ac yclic topologya re an intriguing synthetic target because the lack of chain-ends and the high conformational constraintl ead to materialp roperties that are different from their linear analogues. [6] Different approaches have been proposed for the production of cyclic polymers, [7] andnotable examples have been reported in literature. [8] However,t he formation of cyclic polyesters remains a challenge. [9] Such materials are highly attractive foru se in spe-cialized fields such as biomedicine. Indeed,t he biodistribution of cyclic aliphatic polyesters (cAPEs)i sd ifferent from that of linear APEs, [10] which offers an opportunity to develop new drug deliverys ystems. In this regard, the use of ac atalytic system based on ab iocompatiblem etal such as Fe would be of great interest because it would reduce hazards derived from metal residues in the final product. Fe complexes activei nt he ROP of cyclic esters are limited, [11][12][13][14][15][16][17][18][19][20][21][22][23] and no examples have been reported that produce cAPEs. Actually, the number of reports in which the production of cAPEs by means of aw ell-defined metal complex is described is limited, [24] and mosti nvolve the use of Al- [25][26][27] and Zn-based catalysts. [28] In recent years,wehave developed anumber of Fe catalystsf or the activation of CO 2 and oxiranes for the production of carbonates [29][30][31] anda chieved the...
A new class of zirconium and hafnium complexes coordinated by linear dianonic tetradentate NSSN ligands is reported. The ligands feature two amide functions coupled with two thioether groups linked by a central flexible ethane bridge and two lateral rigid phenylene bridges and differ for the substituents on the aniline nitrogen atoms, i.e., isopropyl, cyclohexyl, or mesityl substituents: NSSN-iPr, NSSN-Cy, or NSSN-Mes. They were prepared by reacting 2-aminothiophenol with dibromoethane to afford the NSSN ligands without substituents on the aniline nitrogen atoms, which were subsequently alkylated through a reductive amination of acetone or cyclohexanone or palladium-catalyzed cross-coupling reaction with mesityl bromide. The corresponding zirconium and hafnium complexes 1−5 were obtained through a transamination reaction between the neutral ligands and Zr(NMe 2 ) 4 or Hf(NMe 2 ) 4 [(NSSN-iPr)Zr(NMe 2 ) 2 ( 1), (NSSN-Cy)Zr(NMe 2 ) 2 ( 2), (NSSN-Mes)-Zr(NMe 2 ) 2 ( 3), (NSSN-iPr)Hf(NMe 2 ) 2 (4), and (NSSN-Cy)Hf(NMe 2 ) 2 ( 5)]. They were characterized in solution by NMR spectroscopy and in solid state by X-ray diffraction analysis (except for 3). All complexes present an octahedral coordination geometry with a fac−fac ligand wrapping and a cis relationship between the other two monodentate ligands. The catalytic performances of 1−5 in the ring-opening polymerization of cyclic esters were investigated. Complex 1 was the most active: its polymerization activity was superior to those generally displayed by zirconium complexes featuring OSSO ligands and compared well with those of the most active group 4 complexes operating in a toluene solution.
In this work the mechanism of L‐lactide polymerization promoted by NSSN zirconium complexes was investigated through DFT methods with the aim to understand as the electronic and steric features of the ligand affect the energy reaction. It was observed that the rate determining step of the process is the opening of the L‐lactide ring and that by increasing the steric hindrance, evaluated by changing geometric parameters and topographic steric maps, or the electron‐withdrawing properties of the ligand, the corresponding energy barrier increases. On the other hand, calculations foresee that a small and electron‐releasing substituent on the nitrogen atom of the ligand, such as the methyl group, is desirable in order to obtain NSSN zirconium based catalysts with improved activity in the ROP of the L‐lactide.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.