Highly Active Chromium Complexes Supported by Constrained Schiff-Base Ligands for Cycloaddition of Carbon Dioxide to Epoxides

Abstract

Novel constrained Schiff-base ligands (inden) were developed based on the well-known salen ligands. Chromium complexes supported by the constrained inden ligands were successfully synthesized and used as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO 2 ). The catalyst having tert-butyl ( t Bu) groups as substituents in combination with tetrabutylammonium bromide (TBAB) as a cocatalyst exhibited very high catalytic activity with a turnover frequency of up to 14800 h −1 for the conversion of CO 2 and propylene oxide into propylene carbonate exclusively at 100 °C and 300 psi of CO 2 under solvent-free conditions. The catalyst was found to be highly active for various epoxide substrates to produce terminal cyclic carbonates in 100% selectivity.

Highly Active Homoleptic Zinc and Magnesium Complexes Supported by Constrained Reduced Schiff Base Ligands for the Ring-Opening Polymerization of Lactide

“…Dichloromethane (DCM), benzene, n -hexane, and tetrahydrofuran (THF) were dried with a solvent purification system (MB SPS-5, MBraun). Magnesium bis­[bis­(tri­methyl­silyl­amide)] (Mg­(N­(SiMe 3 ) 2 ) 2 ) and 4,6-di- tert -butyl-7-hydroxy-1-indanone were synthesized according to a literature procedure.…”

“…All air-sensitive compounds were handled in a glovebox or using standard Schlenk techniques under a nitrogen atmosphere. Dichloromethane (DCM), benzene, n-hexane, and tetrahydrofuran (THF) were dried with a solvent purification system (MB SPS-5, 64 and 4,6-di-tert-butyl-7-hydroxy-1-indanone 27 were synthesized according to a literature procedure.…”

“…Recently, a new modification of the Schiff base backbone was reported by introducing the constrained five-membered ring connected to the phenolic group based on 7-hydroxy-1-indanone. The chromium and aluminum complexes supported by these constrained Schiff base ligands were reported to have very high catalytic activities for epoxide/CO 2 coupling reactions, giving cyclic carbonates exclusively. Some constrained Schiff base nickel complexes were also applied in the vinyl polymerization of norbornene, giving high catalytic activity .…”

Recent Advancements in Metal‐catalysts Design for CO2/Epoxide Reactions

“…In 2021 Phomphrai and coworkers reported a new family of constrained geometry salen ligands (inden‐ligands) that forces the N and O coordinating atoms to be coplanar with the aromatic ring, resulting in a more rigid coordinating environment for the metal center [30] . In particular the Cr(III) complex 1 in the presence of TBAB catalyzes the cycloaddition of CO 2 to PO with higher TOF (1900 h −1 ) compared to a regular ethylene‐bridged salen Cr(III)complex 2 (1250 h −1 ) under the same reaction conditions (80 °C, 2.1 MPa of CO 2 , 1 h) (Figure 1).…”

The Al(iii)-based polydentate chelate complex catalyzed cycloaddition of carbon dioxide and epoxides: synthetic optimization and mechanistic study

“…29 The high activity of such catalysts lies in the flexibility of the amine group, thus further reducing the activation barrier in the reaction. 30,31 Furthermore, many transition metallic pyridyl complexes also showed excellent catalytic efficiency due to the abundant extranuclear electron distribution. Some catalysts showed excellent performance even at warm conditions.…”