Development of Highly Active and Regioselective Catalysts for the Copolymerization of Epoxides with Cyclic Anhydrides: An Unanticipated Effect of Electronic Variation

Abstract

Recent developments in polyester synthesis have established several systems based on zinc, chromium, cobalt, and aluminum catalysts for the ring-opening alternating copolymerization of epoxides with cyclic anhydrides. However, to date, regioselective processes for this copolymerization have remained relatively unexplored. Herein we report the development of a highly active, regioselective system for the copolymerization of a variety of terminal epoxides and cyclic anhydrides. Unexpectedly, electron withdrawing substituents on the salen framework resulted in a more redox stable Co(III) species and longer catalyst lifetime. Using enantiopure propylene oxide, we synthesized semicrystalline polyesters via the copolymerization of a range of epoxide/anhydride monomer pairs.

Multinuclear cobalt-salen complexes with phenylene linker for epoxide polymerizations

“…The epoxide/CA copolymerization has been considered to be a promising route to structurally diverse polyesters . Recently, a variety of well‐defined zinc, magnesium, aluminum, chromium, Co, manganese, and iron complexes have been reported as efficient catalysts. In addition, Lu and coworkers developed biarylene‐linked bimetallic catalysts to achieve high activity and enantioselectivity via proximity effect …”

“…NMR spectroscopic analysis of the obtained copolymer revealed the completely alternating structure. It is noteworthy that dinuclear complex ( R,R , S,S )‐ 1 demonstrated much higher catalytic activity than the mononuclear Co–salen complex which has been reported as a highly active catalyst . Thereby, proximity effect would also operate in this copolymerization.…”

Switchable Polymerization Triggered by Fast and Quantitative Insertion of Carbon Monoxide into Cobalt–Oxygen Bonds

“…Cobalt Salcy [bis(salicylaldimine)] complexes featuring nucleophilic axial groups [(Salcy)Co III X; X=halides, carboxyl, etc.] are among the most investigated catalysts for the copolymerization, wherein the alternative insertion of anhydrides and epoxides is directly correlated to the reversible formation and dissociation of the Co−O bonds (Scheme A) . Relative to the polar Co−O bonds, Co−C bonds tend to break homolytically to generate carbon‐based radicals as is known to occur, for instance, in the biological action of vitamin B12 .…”

Phthalic anhydride promoted ring‐opening polymerization of cyclohexene oxide catalyzed by dinuclear chromium complex supported by piperazine‐bridged [ONSO] ligand

“…As part of our ongoing research in this field, we developed mononuclear chromium complexes with such [ONSO] type ligands ([ONSO]CrX) and found that [ONSO]CrX complexes efficiently mediate the ring‐opening copolymerization (ROCOP) of epoxides with norbornene anhydride or carbon dioxide assisted by Lewis base or onium salts, giving the corresponding polyester and polycarbonate, respectively. Moreover, many reports have demonstrated that some dinuclear metal complexes show high catalytic activity in comparison with mononuclear analogues for the same polymerization . To our best knowledge, there are no reports on the synthesis and application of bimetallic complexes supported by [ONSO] type ligands in the catalytic copolymerization of epoxides with anhydrides.…”