Bimetallic Nickel Complexes that Bear Diamine‐Bis(Benzotriazole Phenolate) Derivatives as Efficient Catalysts for the Copolymerization of Carbon Dioxide with Epoxides

Abstract

We report the facile synthesis and structural characterization of efficient bimetallic nickel catalysts that bear diamine‐bis(benzotriazole phenolate) derivatives for the copolymerization of CO2 and epoxides. Thermally robust di‐nickel 2 is an effective catalyst for the alternating copolymerization of cyclohexene oxide (CHO) with CO2 to give turnover numbers of up to >4000 and turnover frequencies of up to >400 h−1. Ni catalyst 2 leads to not only controlled CO2/CHO coupling, but it has also been applied to catalyze the copolymerization of 4‐vinyl‐1,2‐cyclohexene oxide (VCHO) and CO2 to obtain the corresponding polycarbonate with the vinyl functionality on the side chains. This is the first example of a dinuclear Ni complex that is efficient for both CO2/VCHO copolymerization and the formation of a high‐molecular‐weight copolymer with a large amount of carbonate linkages.

Metal Complexes as Catalysts/Moderators for Polymerization Reactions

“…In this regard, Ko and co-workers designed and synthesized a series of air-stable binuclear Ni II complexes of benzotriazole-modified salen and salan ligands, bridged through phenoxy and acetate co-ligands (5.232-5.244, Figure 5.21). [431][432][433][434] These catalysts were all found highly active and efficient, without additional co-catalysts, for the copolymerization of CHO and CO2, leading to a high selectivity in PCHC containing 99% of carbonate linkages. The highest catalytic performances were achieved by the di-nickel-salen catalyst containing electron-withdrawing carboxylate (5.234) 434 and the sterically less encumbered a dinickel-salan catalyst (5.244), 433 reaching TOFs of 432 and 328 h -1 , respectively, under optimal conditions (CHO:di-Ni = 3200, T = 130-140 °C, PCO2 ≈ 20 bar).…”

“…[431][432][433][434] These catalysts were all found highly active and efficient, without additional co-catalysts, for the copolymerization of CHO and CO2, leading to a high selectivity in PCHC containing 99% of carbonate linkages. The highest catalytic performances were achieved by the di-nickel-salen catalyst containing electron-withdrawing carboxylate (5.234) 434 and the sterically less encumbered a dinickel-salan catalyst (5.244), 433 reaching TOFs of 432 and 328 h -1 , respectively, under optimal conditions (CHO:di-Ni = 3200, T = 130-140 °C, PCO2 ≈ 20 bar). The di-nickel catalyst 5.234 also exhibited a relatively good selectivity when CPO was used as monomer toward the formation of completely alternated PCPC (71% together with 29% of cyclopentene carbonate), although the activities were very low (TOF < 7 h -1 ) at high temperature (T = 100 °C) under 20 bar of CO2 and producing only cyclic carbonate and homopolymer above 100 °C.…”

Update and Challenges in Carbon Dioxide‐Based Polycarbonate Synthesis

“…The imine‐chelated complex ( Ni‐I ; Figure ), in particular, proved remarkably active (in the absence of a cocatalyst) in the ROcP of CO 2 /CHO (turnover number (TON)=2484, TOF=38.7 h −1 , M n =47.7 kg mol −1 , Ð M =1.19) . By modifying the bonding environment of the nitrogen atoms (imine to amine), the resulting nickel catalyst ( Ni‐II ; Figure ) displayed increased stability and efficiency (TON>4000) under similar reaction conditions . The same catalyst ( Ni‐II ) also performed well if the alkene‐containing monomer VCHO was used; thus showing the potential to create a functional polycarbonate.…”

Recent Developments in Ring-Opening Copolymerization of Epoxides With CO2 and Cyclic Anhydrides for Biomedical Applications

“…The Ko group has proposed a series of multinuclear metal catalysts, for instance, di-nickel (Lin et al, 2016;Tsai et al, 2016;Huang et al, 2017;Li et al, 2019b;Su et al, 2020a,b), di-zinc (Chang et al, 2016), di-cobalt (Su et al, 2019b), and bi-yttrium (Su et al, 2019a), using amine bis(benzotriazole phenolate) and its derivatives as the ligand, for the ROCOP of epoxides with CO 2 or cyclic anhydrides (Su et al, 2014;Chuang and Ko, 2015;Yu et al, 2016;Li et al, 2017a;Chang et al, 2018). In 2016, the Ko group reported the heat-resistant metal catalysts, bearing multidentate diaminebis(benzotriazole phenolate) (DiBTP) derivatives (Figure 6, cat.…”

“…7-8), which remained active at a temperature of up to 140 • C. 8a showed a better catalytic activity than 7 due to the less sterically encumbered coordination sphere, which promotes the coordination of CHO monomers or the insertion of CO 2 during the copolymerization. 8a can also catalyze the copolymerization of VCHO with CO 2 to produce cross-linkable poly(vinyl cyclohexene carbonate) (Lin et al, 2016). Then this group also synthesized a series of cobalt, nickel, and zinc complexes based on bis(benzotriazolyliminophenolate) (BilBTP) derivatives (Figure 6, cat.…”