Title: Multifunctional Catalysts for Ring-Opening Copolymerizations
The ring-opening copolymerization (ROCOP) of epoxides with CO2 or cyclic anhydrides is a versatile route toward synthesizing a wide range of polycarbonate and polyester copolymers. ROCOP most commonly uses binary catalyst systems comprising separate Lewis acid and nucleophilic cocatalyst components. However, the dependence on two discrete catalyst components leads to low activities at low loadings, and binary catalyst systems are prone to numerous side reactions. It was therefore proposed that covalently tethering the Lewis acid catalyst and cocatalyst together would increase both catalyst activity and selectivity in epoxide ROCOP. Since these initial efforts, many multifunctional catalysts featuring covalently tethered cationic or Lewis base cocatalyst(s) have been developed for epoxide ROCOP. This review examines multifunctional catalysts that have been developed for copolymerization of epoxides with CO2, cyclic anhydrides, carbonyl sulfide (COS), and cyclic thioanhydrides. In particular, we will assess how multifunctional catalysts’ mechanisms of operations lead to improved activity and selectivity in ROCOP. more »« less
Popowski, Yanay; Moreno, Juan J.; Nichols, Asa W.; Hooe, Shelby L.; Bouchey, Caitlin J.; Rath, Nigam P.; Machan, Charles W.; Tolman, William B.
(, Chemical Communications)
null
(Ed.)
Pentacoordinate Al catalysts comprising bipyridine (bpy) and phenanthroline (phen) backbones were synthesized and their catalytic activity in epoxide/anhydride copolymerization was investigated and compared to ( t-Bu salph)AlCl. Stoichiometric reactions of tricyclic anhydrides with Al alkoxide complexes produced ring-opened products that were characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography, revealing key regio- and stereochemical aspects.
Seong, Wooyong; Hahm, Hyungwoo; Kim, Seyong; Park, Jongwoo; Abboud, Khalil A.; Hong, Sukwon
(, Molecules)
null
(Ed.)
Bimetallic bis-urea functionalized salen-aluminum catalysts have been developed for cyclic carbonate synthesis from epoxides and CO2. The urea moiety provides a bimetallic scaffold through hydrogen bonding, which expedites the cyclic carbonate formation reaction under mild reaction conditions. The turnover frequency (TOF) of the bis-urea salen Al catalyst is three times higher than that of a μ-oxo-bridged catalyst, and 13 times higher than that of a monomeric salen aluminum catalyst. The bimetallic reaction pathway is suggested based on urea additive studies and kinetic studies. Additionally, the X-ray crystal structure of a bis-urea salen Ni complex supports the self-assembly of the bis-urea salen metal complex through hydrogen bonding.
Synthesis of a new mononuclear magnesium complex with a bulky bis(alkoxide) ligand environment and its reactivity in ring-opening polymerization (ROP) and ring-opening copolymerization (ROCOP) are reported. Reaction of n -butyl- sec -butylmagnesium with two equivalents of HOR (HOR = di- tert -butylphenylmethanol, HOC t Bu 2 Ph) formed Mg(OR) 2 (THF) 2 . The reaction proceeded via the Mg(OR)( sec -Bu)(THF) 2 intermediate that was independently synthesized by treating n -butyl- sec -butylmagnesium with one equivalent of HOR. Mg(OR) 2 (THF) 2 led to active albeit not well-controlled ROP of rac -lactide. In contrast, well-controlled ROCOP of epoxides with cyclic anhydrides was observed, including efficient and alternating copolymerization of phthalic anhydride with cyclohexene oxide as well as rare copolymerization of phthalic anhydride with limonene oxide and terpolymerization of phthalic anhydride with both cyclohexene oxide and limonene oxide. In addition, novel copolymerization of dihydrocoumarin with limonene oxide is described.
Hilliard, Jordon S.; Wade, Casey R.
(, Dalton Transactions)
A palladium diphosphine pincer complex H3(PNNNP-PdI) has been encapsulated in the benzotriazolate metal-organic framework MFU-4l-OH ([Zn5(OH)4(btdd)3], btdd2− = bis(1,2,3-triazolo)dibenzodioxin), and the resulting materials were investigated as Lewis acid catalysts for cyclization of citronellal to isopulegol. Rapid catalyst immobilization is facilitated by a Brønsted acid–base reaction between the H3(PNNNP-PdI) benzoic acid substituents and Zn–OH groups at the framework nodes. Catalyst loading can be controlled up to a maximum of 0.5 pincer complexes per formula unit [PdI-x, Zn5(OH)4−nx(btdd)3(H3−nPNNNP-PdI)x x = 0.06–0.5, n ≈ 2.75]. Oxidative ligand exchange was used to replace I− with weakly coordinating BF4− anions at the Pd–I sites, generating the activated PdBF4-x catalysts (x = 0.06, 0.10, 0.18, 0.40). The Lewis acid catalytic activity of the PdBF4-x series decreases with increasing catalyst density as a result of the appearance of mass transport limitations. Initial catalytic rates show that the activity of PdBF4-0.06 approaches the intrinsic activity of a homogeneous PNNNP-PdBF4 catalyst analogue. In addition, PdBF4-0.06 exhibits better catalytic activity than the metallolinker-based MOF Zr-PdBF4 and was not subject to leaching or catalyst degradation processes observed for the homogeneous analogue.
Sharifi_Golru, Samaneh; May, Andrew S; Biddinger, Elizabeth J
(, ACS Catalysis)
CO2 electroreduction (CO2ER) by using renewable energy resources is a promising method to mitigate the CO2 level in the atmosphere as well as producing valuable chemicals. Local environment at the electrode-electrolyte interface plays a key role in CO2ER activity and selectivity along with its competing hydrogen evolution reaction (HER). In addition to the catalyst and reactor design, electrolyte has also a significant impact on the interface. Herein, electrolyte additives were used to modify the local environment around the Cu catalyst during CO2ER. To this purpose, 10mM of ionic additives with bis(trifluoromethylsulfonyl)imide ([NTF2]-) and dicyanamide ([DCA]-) as anions and 1-butyl-3-methylimidazolium ([BMIM]+), potassium (K+), or sodium (Na+) as cations have been added to an aqueous potassium bicarbonate solution (0.1 M KHCO3). COMSOL Multiphysics was also used to calculate the local pH and CO2 concentration at electrode-electrolyte interface in different electrolytes. Results showed that the local environment modifications by the electrolyte additives altered the activity and selectivity of Cu in CO2ER. It was found that the CO2ER activity at -0.92 V was enhanced when using anion with high CO2 affinity and high hydrophobicity such as [NTF2]–. Among [NTF2]–-based additives, [BMIM][NTF2] had a higher faradaic efficiency (FE) for formate (38.7%) compared to K[NTF2] (23.2%) and Na[NTF2] (18.5%) at -0.92 V likely due to the presence of imidazolium cation which can further stabilize the intermediates on the surface and enhance CO2ER. Electrolytes containing [DCA]–-based additives with high hydrophilicity and low CO2 affinity had a very high HER selectivity (>90% FEH2) and low CO2ER selectivity regardless of the cation nature. This observation is attributed to the presence of hydrophilic [BMIM][DCA] in the vicinity of the catalyst which impacts the microenvironment around the catalyst. We observed that [DCA]– anions have a high affinity to adsorb on Cu catalysts as soon as the catalyst is submerged in the electrolyte. Although FTIR showed that [DCA]– anions desorb from the surface at negative potentials, it is likely that [DCA]– anions still remain in the proximity of the electrode, next to the adsorbed cations, impacting the transport of H2O and CO2, and altering the product selectivity. COMSOL calculations showed that the local pH is directly proportional to the H2 evolution activity. Also, hydrophilic salts such as those with the [DCA]– anion had a more alkaline local pH which leads to a lower CO2 concentration in the vicinity of the catalyst.
Lidston, Claire A., Severson, Sarah M., Abel, Brooks A., and Coates, Geoffrey W. Multifunctional Catalysts for Ring-Opening Copolymerizations. Retrieved from https://par.nsf.gov/biblio/10353447. ACS catalysis . Web. doi:10.1021/acscatal.2c02524.
Lidston, Claire A., Severson, Sarah M., Abel, Brooks A., & Coates, Geoffrey W. Multifunctional Catalysts for Ring-Opening Copolymerizations. ACS catalysis, (). Retrieved from https://par.nsf.gov/biblio/10353447. https://doi.org/10.1021/acscatal.2c02524
@article{osti_10353447,
place = {Country unknown/Code not available},
title = {Multifunctional Catalysts for Ring-Opening Copolymerizations},
url = {https://par.nsf.gov/biblio/10353447},
DOI = {10.1021/acscatal.2c02524},
abstractNote = {The ring-opening copolymerization (ROCOP) of epoxides with CO2 or cyclic anhydrides is a versatile route toward synthesizing a wide range of polycarbonate and polyester copolymers. ROCOP most commonly uses binary catalyst systems comprising separate Lewis acid and nucleophilic cocatalyst components. However, the dependence on two discrete catalyst components leads to low activities at low loadings, and binary catalyst systems are prone to numerous side reactions. It was therefore proposed that covalently tethering the Lewis acid catalyst and cocatalyst together would increase both catalyst activity and selectivity in epoxide ROCOP. Since these initial efforts, many multifunctional catalysts featuring covalently tethered cationic or Lewis base cocatalyst(s) have been developed for epoxide ROCOP. This review examines multifunctional catalysts that have been developed for copolymerization of epoxides with CO2, cyclic anhydrides, carbonyl sulfide (COS), and cyclic thioanhydrides. In particular, we will assess how multifunctional catalysts’ mechanisms of operations lead to improved activity and selectivity in ROCOP.},
journal = {ACS catalysis},
author = {Lidston, Claire A. and Severson, Sarah M. and Abel, Brooks A. and Coates, Geoffrey W.},
}
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