Chiral Cobalt(III) Complexes as Bifunctional Brønsted Acid–Lewis Base Catalysts for the Preparation of Cyclic Organic Carbonates

Abstract

Stereochemically inert cationic cobalt(III) complexes were shown to be one-component catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa carbon dioxide pressure. The optimal catalyst possessed an iodide counter anion and could be recycled. A catalytic cycle is proposed in which the ligand of the cobalt complexes acts as a hydrogen-bond donor, activating the epoxide towards ring opening by the halide anion and activating the carbon dioxide for subsequent reaction with the halo-alkoxide. No kinetic resolution was observed when terminal epoxides were used as substrates, but chalcone oxide underwent kinetic resolution.

Carbocation/Polyol Systems as Efficient Organic Catalysts for the Preparation of Cyclic Carbonates

“…We have previously developed several catalytic systems for the synthesis of cyclic carbonates by coupling of CO 2 and epoxides. These included highly efficient and robust aluminum (salen) complexes, and stereochemically inert Co III complexes that function as “Brønsted acids in disguise” with the central metal ion only serving as an activator of the catalytically active Brønsted acidic NH groups …”

“…These included highly efficient andr obust aluminum (salen) complexes, [19,20] ands tereochemically inert Co III complexes that function as "Brønsted acids in disguise" with the central metal ion only serving as an activator of the catalytically active Brønsteda cidic NH groups. [21] Herein, we describe the use of well-known, commercially available, and stable carbocations in the form of triarylmethane dyes (Figure 1) as catalysts for the synthesis of cyclic carbonates.W et ested the iodide salt form of malachite green (MGI), brilliant green (BGI), and crystal violet (CVI) as bifunctionalc atalysts,t he activitieso fw hich were augmented by the addition of Brønsted acids.…”

Synthesis and Investigations of Chiral NNO Type Copper(II) Coordination Polymers

“…In our earlier work we used the chiral NNO and ONO type ligands based on Schiff bases of chiral diamines (or amino acids) and salicylaldehydes to construct new type of chiral octahedral inert cobalt(III) complexes . These complexes were efficient catalysts for different asymmetric reactions …”

Self‐Assembly of Luminescent Lanthanide Mesocates as Efficient Catalysts for Transforming Carbon Dioxide into Cyclic Carbonates

“…In terms of catalysis, the cycloaddition of CO 2 with epoxides to synthesize useful chemicals under mild conditions is of industrial and economical importance, because it is a 100 % atom‐economical reaction and is recognized to be environmentally benign . Although main‐group and transition metals such as aluminum, calcium, magnesium, indium, cobalt, zinc,, iron, manganese, niobium, and vanadium in addition to complexes have been reported to catalyze the coupling of CO 2 with epoxides efficiently, most of them suffer from limitations such as high reaction pressure (>1.0 MPa), large catalyst loadings (>5 mol %), catalyst stability, or/and extra reaction conditions . Another problem preventing their further applications is that the many reported homogeneous catalysts are not recyclable.…”

“…To this end, four lanthanide mesocates were easily assembled from af lexible acylhydrazonel igand, and we would like to initiate ap rogram to study the catalytic properties of such achiral structures as an application trial with the aim to unify the best features.I nt erms of catalysis, the cycloaddition of CO 2 with epoxides to synthesize useful chemicals under mild conditions is of industrial and economical importance, because it is a1 00 %a tom-economical reaction and is recognized to be environmentally benign. [9] Although main-group [10] and transition metals [11] such as aluminum, [12] calcium, [13] magnesium, [14] indium, [15] cobalt, [16] zinc, [11e,17] iron, [18] manganese, [19] niobium, [20] and vanadium [21] in addition to complexesh ave been reported to catalyzet he couplingo fC O 2 with epoxides efficiently,m ost of them suffer from limitations such as high reactionp ressure (> 1.0 MPa), large catalyst loadings (> 5mol %), catalysts tability,o r/and extra reaction conditions. [11b, 22] Another problem preventingtheir furtherapplicationsi sthat the many reported homogeneous catalysts are not recyclable.…”