Copolymerization of Epoxides and CO₂ by Cobalt(II) Oxaporphyrins with Mechanistic Explorations on Poly(Propylene Carbonate) Formation

Abstract

Two cobalt(II) oxaporphyrins (OTPPCoCl and OTPPCoSbF6) are synthesized in this work and are characterized, including by X‐ray crystallography. Both complexes are tested as catalysts in the copolymerization of propylene oxide (PO)/cyclohexene oxide (CHO) and CO2. Polycarbonate is obtained in CHO/CO2 copolymerization with OTPPCoCl as a catalyst, whereas in the case of PO, cyclic carbonate (CC) is majorly formed. An anion exchange from Cl− to SbF6 − of the cobalt(II) oxaporphyrin leads to a drastic change in the product selectivity: sole polyether is afforded for both epoxides. The polyether formation by OTPPCoSbF6 is postulated to proceed via a cationic mechanism. Further, an equivalent admixture of OTPPCoCl and OTPPCoSbF6 allows the formation of poly(propylene carbonate). In this copolymerization, the latter catalyst acts as a PO activator, while OTPPCoCl functions as the initiator. In addition, density functional theory (DFT) calculations reveal a lower ring‐opening energy of PO by OTPPCoSbF6, compared with the usual propagating species, OTPPCo‐alkoxides and OTPPCo‐carbonates.

Non-covalent interactions in molecular architectures and solvent-free catalytic activity towards CO2 fixation of mononuclear Co(iii) complexes installed on modified Schiff base ligands

“…S61 †) and the data are interpreted with the values reported in the literature. 43 The carbon atom of the -CvO moiety in polymeric carbonates exhibits 13 C NMR signals at 154.0 ppm (syndiotactic) and 153.3 ppm (isotactic). 100a,b Our findings (Fig.…”

“…Among them, the most eminent and economically reliable method, especially in terms of maximum atom economy, is CO 2 fixation to epoxides. 24–27 A number of metal-complex catalysts such as zinc, 28–32 cobalt, 33–65 b chromium, 66–69 magnesium, 70–72 iron, 73–75 c nickel, 76–78 and rare-earth metal 79–81 based catalysts have been developed for CO 2 fixation. Among these, cobalt salen complexes are well known for their enhanced activity and selectivity towards CO 2 fixation.…”

Synthesis and Characterization of Cobalt(II/II) and Cobalt(II/III) Macrocyclic Complexes and Their Application in the Copolymerization of Epoxides and CO2

“…Utilization of CO 2 as the C1 source for the production of valuable chemicals is attracting increasing interest because CO 2 is inexpensive, nontoxic, and abundant. − One promising method is the copolymerization of CO 2 and epoxides, which produces polycarbonates that have found many applications in packaging, agricultural, and biomedical industries. − A number of catalysts have been developed for copolymerization, including complexes of zinc, − cobalt, − chromium, − magnesium, − iron, − nickel, − and rare-earth metals. − Among these examples, cobalt salen complexes have been reported to show good activity and selectivity (Scheme , left). Coates et al reported the first Co­(III) salen complex, which gave >99% selectivity to poly­(propylene carbonate) .…”

A Rational Investigation of the Lewis Acid-Promoted Coupling of Carbon Dioxide with Cyclohexene Oxide: Towards CO2-Sourced Polycyclohexene Carbonate under Solvent- and Cocatalyst-Free Conditions

“…Thus, for the selective and efficient synthesis of polycarbonates (PCs) from the copolymerization of CO 2 and epoxides, many Lewis acid catalysts such as organometallic complexes usually used in combination with a nucleophile have been developed. In particular, the important characteristics of metal-based catalysts (zinc [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], aluminum [38,39], chromium [40][41][42][43], cobalt [44][45][46][47], magnesium [48,49], iron [19,[50][51][52][53][54], titanium [55,56], copper [57], ytterbium [58], . .…”