The Cobalt Porphyrin−Lewis Base System:  A Highly Selective Catalyst for Alternating Copolymerization of CO₂ and Epoxide under Mild Conditions

Abstract

The use of a cobalt porphyrin ((TPP)CoCl, 1) in combination with dimethylaminopyridine (DMAP) for the alternating copolymerization of CO 2 and epoxide is described. The (TPP)CoCl (1)-DMAP system quantitatively produced the alternating copolymer from CO 2 and cyclohexene oxide (CHO) under optimized conditions (50 atm, 80°C). This calatyst system also worked satisfactorily for the alternating copolymerization of CO 2 and a terminal epoxide, e.g., propylene oxide (PO), without formation of cyclic carbonate to give the polycarbonate. The alternating copolymerization of CO 2 and epoxide (CHO, PO) was achieved under very mild conditions, such as at ambient temperature and under CO 2 at 1 atm, by using the 1-DMAP catalyst system.

Highly Active and Readily Accessible Proline‐Based Dizinc Catalyst for CO2/Epoxide Copolymerization

“…While some catalysts for CO 2 /epoxide copolymerization are active even at the most desirable pressure of 1 atm CO 2 , they usually suffer from a number of different limitations . These include low chemoselectivity for the target polycarbonate, especially at low pressures; the use of toxic metals and additives; low turnover number (TON) and turnover frequency (TOF) values, and low catalyst isolation yields .…”

“…obtained for similar polymerization conditions . Furthermore, 1 differs from the so far known catalysts in that no additional coligands (such as acetate, HMDS, or solvents) are present in the employed complex . In this case, an external nucleophile (e.g., water) or the zinc‐bound (non‐bridging) alkoxido groups may initiate the polymerization.…”

Concerning the Deactivation of Cobalt(III)‐Based Porphyrin and Salen Catalysts in Epoxide/CO2 Copolymerization

“…A highest reported TOF value of 26 000 h −1 was achieved for poly(propylene carbonate) (PPC) formation by using a cobalt(III)–salen catalyst bearing four onium‐salt arms on its periphery designed by Lee and co‐workers 5b. Cobalt(III) tetraphenylporphyrin complex (TPPCoCl) has also been proven active for poly(propylene carbonate) formation with either bis(triphenylphosphine)iminium chloride (PPNCl)4a or 4‐dimethylaminopyridine (DMAP)4b as a co‐catalyst. A phenomenon of the catalyst deactivation via reduction to cobalt(II) species, however, was briefly mentioned in earlier publications for both cobalt(III)–salen5a and –porphyrin4d, e catalysts.…”

Synthesis of cyclic carbonates from epoxides catalyzed by metal–BINOL complexes

“…[4,5] One of the most favorable methodologies is the cycloaddition of CO 2 and epoxides to form cyclic carbonates, which are widely used as organic synthetic intermediates, aprotic polar solvents and polymerization monomers. [6][7][8][9] Many efficient catalytic systems have been developed for the synthesis of cyclic carbonates from CO 2 and epoxides. Examples include metal complexes, [10][11][12][13][14] which are some of the most efficient catalysts due to tunable structure and Lewis acidity of catalytic center among metal salts, [15][16][17][18][19] ionic liquids, [20][21][22][23][24][25][26] metal-organic frameworks [27][28][29][30][31] and N-heterocyclic carbenes.…”