Efficient Aluminum Catalysts for the Chemical Conversion of CO₂ into Cyclic Carbonates at Room Temperature and Atmospheric CO₂ Pressure

Abstract

A series of dimeric aluminum compounds [Al(OCMe2CH2N(R)CH2X)]2 [X=pyridin‐2‐yl, R=H (PyrH); X= pyridin‐2‐yl, R=Me (PyrMe); X=furan‐2‐yl, R=H (FurH); X= furan‐2‐yl, R=Me (FurMe); X=thiophen‐2‐yl, R=H (ThioH); X= thiophen‐2‐yl, R=Me (ThioMe)] containing heterocyclic pendant group attached to the nitrogen catalyze the coupling of CO2 with epoxides under ambient conditions. In a comparison of their catalytic activities with those of aluminum complexes without pendant groups at N [X=H, R=H (HH); X=H, R=Me (HMe)] or with non‐heterocyclic pendant groups [X=CH2CH2OMe, R=H (OMeH); X=CH2CH2NMe2, R=H (NMe2H); X=CH2CH2NMe2, R=Me (NMe2Me)], complexes containing heterocycles, in conjunction with (nBu)4NBr as a cocatalyst, show higher catalytic activities for the synthesis of cyclic carbonates under the same ambient conditions. The best catalyst system for this reaction is PyrH/(nBu)4NBr system, which gives a turnover number of 99 and a turnover frequency of 4.1 h−1, making it 14‐ and 20‐times more effective than HH/(nBu)4NBr and HMe/(nBu)4NBr, respectively. Although there are no direct interactions between the aluminum and the heteroatoms in the heterocyclic pendants, electronic effects combined with the increased local concentration of CO2 around the active centers influences the catalytic activity in the coupling of CO2 with epoxides. In addition, PyrH/(nBu)4NBr shows broad epoxide substrate scope and seven terminal epoxides and two internal epoxides undergo the designed reaction.

Conversion of CO2 into Cyclic Carbonates under Ambient Conditions Catalyzed by Rare-Earth Metal Complexes Bearing Poly(phenolato) Ligand

“…CO 2 is an ideal C1 resource as it is rich, renewable, and nontoxic. − However, its stable thermodynamic properties greatly limit its application. , Cycloaddition of CO 2 and epoxides is a 100% atom-economic reaction which forms cyclic carbonates that have found extensive application as battery electrolyte, pharmaceutical/fine chemical intermediates, polymer and engineering plastic syntheses, aprotic polar solvents, etc. − Reactions of CO 2 and epoxides may also produce polycarbonates, which may be used as food packagings, adhesives, and optical media . A number of catalysts have been developed to catalyze the cycloaddition reaction, including transition metal (e.g., Cr, , Mn, , Fe, − Co, − and Zn), − main group metal (e.g., Al, − Mg, − and Ca), − rare-earth (RE) metal, − and organocatalysts. − …”

“…Organocatalysts include pincer-type compounds and phosphorus ylide-CO 2 adducts, which catalyzed cycloaddition of 1,2-disubstituted epoxides at 80 and 100 °C, respectively, in the presence of 1 bar CO 2 . , Other examples include the Cr­(salophen) complex and RE–Zn heterobimetallic complexes, which required both high temperature and pressure for disubstituted epoxides. ,, Among all examples discussed above, reactions of disubstituted epoxides under 1 bar CO 2 are mainly limited to 1,1-disubstituted epoxides and CHO, ,, whereas other disubstituted epoxides required elevated pressure. The only exceptions include the carboxylic acid-functionalized benzimidazolium salt reported by Dai et al and aluminum complexes chelated by ethanolateamine reported by Kim et al, which catalyzed cycloaddition of up to eight 1,2-disubstituted epoxides with 1 bar CO 2 at 80 and 75 °C, respectively. Therefore, development of a catalyst efficient for transformation of disubstituted epoxides under ambient conditions is highly desirable.…”

Synthesis, characterization, antimicrobial, and docking study of novel 1‐(furanyl)‐3‐(pyrrolyl)propenone‐based ligand and its chelates of 3d‐transition metal ions

“…The bands occurring in the wavenumber range 400–415 cm −l are assigned due to stretching vibration of ν(M–O). [ 29–32 ]…”

“…The bands occurring in the wavenumber range 400-415 cm Àl are assigned due to stretching vibration of ν(M-O). [29][30][31][32] It is reasonable to assume that the prepared ligand considered as a neutral bidentate ligand coordinated through the two carbonyl and epoxy oxygen atoms to the transition metal cations.…”

Self-Assembled Bimetallic Aluminum-Salen Catalyst for the Cyclic Carbonates Synthesis

“…The conversion reaction of CO 2 and epoxides to cyclic organic carbonates has a 100% atom economy, and the cyclic carbonates are important intermediates for polymers [ 2 , 3 ], agrochemicals, pharmaceuticals [ 4 ], electrolytes in lithium-ion batteries [ 5 ], polar aprotic solvents [ 6 , 7 ], and temporal protecting groups for cis-diols [ 8 ]. Owing to the usefulness of cyclic carbonate compounds, various catalysts have been developed for the reaction between CO 2 and epoxides [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ].…”