Two-dimensional (2D) layered double metal cyanides as alternative catalysts for CO2/propylene oxide copolymerization

Although zinc-cobalt double metal cyanide (DMC) complex is a popular catalyst for the copolymerization of CO2 and epoxides, it faces important challenges, such as poor CO2 uptake, high cyclic carbonate formation, low ability to produce high-molecular-weight polymers, and an induction period. Therefore, the pursuit of alternative DMC complexes that can overcome these limitations has been a recurring research strategy in recent years. In this work, four novel 2D layered tetracyanonickelate complexes (M & PRIME;[Ni(CN)(4)]; M & PRIME; = Ni2+, Co2+, Fe2+, Mn2+) were prepared, thoroughly characterized, and tested as catalysts for CO2 and propylene oxide copolymerization. These complexes yielded random polyethercarbonates (R-PEC = 51-94%) with medium-to-low CO2 content (F-CU = 13.1-42.4 mol%), moderate molecular weight (M-n = 11 000-36 500 g mol(-1)), and broad dispersity (D = 2.5-5.0). The Co-Ni DMC catalyst led to a 100% conversion of PO after 24 h, thus revealing itself as a possible alternative to the classic Zn-Co DMC compound. The catalytic performance of these compounds was compared in detail and their kinetics were assessed by in situ IR spectroscopy. While the Co-Ni DMC complex demonstrated remarkable selectivity, it requires further improvements in terms of activity and CO2 uptake to surpass its counterpart. Future research efforts should focus on driving these critical aspects.