Novel alkyl zinc complexes supported by acetamidate/thioacetamidate heteroscorpionate ligands have been successfully synthesized and characterized. These complexes exhibited different coordination ...modes depending on the electronic and steric effects of the acetamidate/thioacetamidate moiety. Their catalytic activity has been tested toward the hydroelementation reactions of alkynyl alcohol/acid substrates, affording the corresponding enol ether/unsaturated lactone products under mild reaction conditions. Kinetic studies have been performed and confirmed that reactions are first-order in catalyst and zero-order in alkynyl substrate. DFT calculations supported a reaction mechanism through the formation of the catalytically active species, an alkoxide-zinc intermediate, by a protonolysis reaction of the Zn–alkyl bond with the alcohol group of the substrate. Based on the experimental and theoretical results, a catalytic cycle has been proposed.
The reaction between bis(1,2,3‐triazol‐1‐yl)methane derivatives and nBuLi and various aldehydes, yielded novel neutral ligand precursors incorporating alcohol functional groups. The resulting ...compounds exhibited distinct characteristics depending on the steric hindrance of the aldehyde employed. In instances where aromatic aldehydes were utilized, functionalization occurred at the methine group bridging both triazole rings. Conversely, the use of pivalic aldehyde prompted functionalization at the C5 position of the triazole ring. These compounds were subsequently employed as ligand precursors in the synthesis of organometallic aluminum and zinc complexes, yielding dinuclear complexes with high efficiency. The structural elucidation of all compounds was accomplished through spectroscopic methods and validated by X‐ray crystallography. Preliminary catalytic investigations into the coupling reaction of cyclohexene oxide and CO2 revealed that aluminum and zinc complexes catalyzed the selective formation of polyether and polycarbonate materials, respectively.
The synthesis of new alcohol neutral ligand precursors based on bis(1,2,3‐triazol‐1‐yl)methane moieties is reported. A substrate‐dependent functionalization is observed allowing access to a variety of ligand precursors. The coordination chemistry of some of them against aluminum and zinc have also been investigated.
The coupling reaction of carbon dioxide and terminal, internal, and highly substituted epoxides derived from renewable resources such as furfural, limonene, carvone, carvyl acetate, terpinen-4-ol, or ...ionone leads to the synthesis of new bioderived cyclic carbonates using an efficient aluminum catalyst under mild and solvent-free reaction conditions. Interestingly, the synthesis of highly substituted bioderived cyclic carbonates can occur with excellent diastereoselectivity, obtaining in some cases one diastereoisomer as the major product. The X-ray crystal structures of two enantiomerically pure carvone-based cyclic carbonates are reported.
Ring-opening copolymerization reactions of epoxides, carbon dioxide and cyclic esters to produce copolymers is a promising strategy to prepare CO2-based polymeric materials. In this contribution, ...bimetallic chloride indium complexes have been developed as catalysts for the copolymerization processes of cyclohexene oxide, carbon dioxide and l-lactide under mild reaction conditions. The catalysts displayed good catalytic activity and excellent selectivity towards the preparation of poly(cyclohexene carbonate) (PCHC) at one bar CO2 pressure in the absence of a co-catalyst. Additionally, polyester-polycarbonate copolymers poly(lactide-co-cyclohexene carbonate) (PLA-co-PCHC) were obtained via an one-pot one-step route without the use of a co-catalyst. The degree of incorporation of carbon dioxide can be easily modulated by changing the CO2 pressure and the monomer feed, resulting in copolymers with different thermal properties.
Despite the great interest in zinc catalysis for hydroelementation reactions, the use of zinc complexes as catalysts for the hydroalkoxylation of alkynyl alcohols has not been reported to date. ...Scorpionate zinc complexes have been successfully designed as precatalysts for the hydroalkoxylation reaction of alkynyl alcohols under mild reaction conditions. Zinc amide complex 8 has been shown to be an excellent precatalyst for the highly selective intramolecular hydroalkoxylation process to yield the corresponding exocyclic enol ethers. Kinetic studies have been performed and confirmed that reactions are first-order in catalyst and zero-order in alkynyl alcohol. NMR spectroscopy and X-ray diffraction analysis provided evidence for the formation of an alkynyl zinc compound which has been shown to be a key intermediate in the hydroalkoxylation process. On the basis of the experimental results, a catalytic cycle is proposed.
The catalytic activity and high selectivity reported by bimetallic heteroscorpionate acetate zinc complexes in ring-opening copolymerization (ROCOP) reactions involving CO2 as substrate encouraged us ...to expand their use as catalysts for ROCOP of cyclohexene oxide (CHO) and cyclic anhydrides. Among the catalysts tested for the ROCOP of CHO and phthalic anhydride at different reaction conditions, the most active catalytic system was the combination of complex 3 with bis(triphenylphosphine)iminium as cocatalyst in toluene at 80 °C. Once the optimal catalytic system was determined, the scope in terms of other cyclic anhydrides was broadened. The catalytic system was capable of copolymerizing selectively and efficiently CHO with phthalic, maleic, succinic and naphthalic anhydrides to afford the corresponding polyester materials. The polyesters obtained were characterized by spectroscopic, spectrometric, and calorimetric techniques. Finally, the reaction mechanism of the catalytic system was proposed based on stoichiometric reactions.
Novel bimetallic zinc acetate complexes supported by heteroscorpionate ligands have been developed for the ring-opening copolymerization of cyclohexene oxide and CO
and the terpolymerization of ...cyclohexene oxide, phthalic anhydride, and CO
. Heteroscorpionate ligands precursors
-
were reacted with two equivalents of zinc acetate to afford the dinuclear zinc complexes {Zn(κ
-bpzappe)}(μ-O
CCH
)
-{Zn(HO
CCH
)} (
), {Zn(κ
-bpzbdmape)}(μ-O
CCH
)
-{Zn(HO
CCH
)} (
), and {Zn(κ
-bpzbdeape)}(μ-O
CCH
)
{Zn(HO
CCH
)} (
) in excellent yields. The molecular structure of these compounds was determined spectroscopically and confirmed by X-ray diffraction analysis. Zinc acetate complexes
-
were screened as catalysts for the copolymerization of cyclohexene oxide and CO
to produce poly(cyclohexene)carbonate, and complex
was found to be the most active catalyst for this process in the absence of a cocatalyst. Furthermore, the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO
was studied using the combination of complex
and 4-dimethylaminopyridine as catalyst system yielding the corresponding polyester-polycarbonate materials.
Novel dinuclear calcium complexes have been employed as bifunctional catalysts for the ring-opening copolymerisation reaction of epoxides and cyclic anhydrides. The catalysts exhibited good ...performance and quantitative formation of ester linkages for the poly(CHO- alt -PA) production under mild reaction conditions and in the absence of a cocatalyst. Furthermore, these catalysts demonstrated tolerance to a variety of bio-sourced epoxides/phthalic anhydrides, providing access to a range of potentially functionalisable polyesters. On the other, polymerisation kinetic analyses revealed a half-order dependence on catalyst concentration and first-order dependence on cyclic anhydride concentration, whilst MALDI-ToF analyses supported an initiation step involving the ring-opening of the epoxide. Taken together, these findings underpin a mononuclear pathway, with the ring-opening of the cyclic anhydride identified as the rate-limiting step in the process.
Novel heteroscorpionate rare-earth-metal complexes (Y, La, and Lu) have been developed for the coupling reaction of CO2 and cyclohexene oxide under mild conditions. The reaction of an alcohol ...heteroscorpionate ligand precursor (bpzbdmapeH) with 1 equiv of the tris(silylamide) and tris(alkyl) precursors M{N(SiHMe2)2}3(thf)2 (M = Y, La, Lu) and M(CH2SiMe3)3(thf)2 (M = Y, Lu) proceed to give good yields of the neutral heteroscorpionate mononuclear bis(dimethylsilyl)amide complexes M{N(SiHMe2}2(κ3-bpzbdmape)(thf) (M = Y (1), La (2), Lu (3)) and the alkyl complexes M(CH2SiMe3)2(κ3-bpzbdmape)(thf) (M = Y (4), Lu (5)). These compounds were isolated with a distorted-octahedral geometry due to the coordination of a THF molecule. The molecular structures of these compounds were determined by spectroscopic methods, and the X-ray crystal structure of 1 was also established. Complexes 1–5 were efficient catalysts for the coupling reaction of CO2 and cyclohexene oxide, and complex 4 was found to be the most active and selective catalyst to produce poly(cyclohexene carbonate) in the absence of a cocatalyst. Furthermore, in combination with the appropriate amounts of cocatalytic additives, complex 4 allowed the highly selective synthesis of cyclic carbonate or polycarbonate at only 1 bar of CO2 pressure. Under these conditions, poly(cyclohexene carbonate) was obtained when PPNCl was used as the nucleophilic cocatalyst, while the use of Bu4NBr led to the selective production of cis-cyclohexene carbonate.
Bio‐derived furan‐ and diacid‐derived cyclic carbonates have been synthesized in high yields from terminal epoxides and CO2. Furthermore, four highly substituted terpene‐derived cyclic carbonates ...were isolated in good yields with excellent diastereoselectivity in some cases. Eleven new cyclic carbonates derived from 10‐undecenoic acid under mild reaction conditions were prepared, providing the corresponding carbonate products in excellent yields. The catalyst system also performed the conversion of an epoxidized fatty acid n‐pentyl ester into a cyclic carbonate under relatively mild reaction conditions (80 °C, 20 bar, 24 h). This bis(cyclic carbonate) was obtained in high yields and with different cis/trans ratios depending on the co‐catalyst used. An allyl alcohol by‐product was only observed as a minor product when bis(triphenylphosphine)iminium chloride was used as co‐catalyst. Finally, two cyclic carbonates were used as building blocks for the preparation of non‐isocyanate poly(hydroxy)urethanes by reaction with 1,4‐diaminobutane.
Waste not, want not: Efficient preparation of a wide variety of cyclic carbonates from epoxides derived from unsaturated acids and CO2 has been carried out using a lanthanum catalyst. Moreover, the versatility of this catalyst has been confirmed by the synthesis of eleven monosubstituted cyclic carbonates and a bis(cyclic carbonate) derived from a waste epoxidized fatty acid. Finally, some of the previously synthesized bis(cyclic carbonates) have been used as starting materials to prepare polyhydroxyurethanes by reaction with 1,4‐diaminobutane.
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