To celebrate the 15th anniversary of Chemical Science, we invited authors who published with the journal in its early years and contributed seminal papers since then to revisit their original work and reflect on how their field has evolved. In their Reflection article, Koji Nakano and Kyoko Nozaki look back on their 2010 study of bimetallic cobalt(salen) complexes, which revealed a cooperative bimetallic mechanism for the alternating copolymerisation of epoxides with carbon dioxide.
Read the Reflection, for free, here: https://doi.org/10.1039/D5SC90244D
Their original work showed that placing two cobalt centres in close proximity allows one to activate the epoxide while the other delivers the propagating carbonate species, affording an elegant intramolecular division of labour that enhanced catalytic activity. In their Reflection, Nakano and Nozaki outline how this discovery helped motivate subsequent developments in both homobimetallic and heterobimetallic catalysts for epoxide/CO₂ copolymerisation.
Bimetallic Catalysts Beyond Polymerisation
The mechanistic principles highlighted in the Reflection, that proximity, complementarity and cooperative activation are all essential, now underpin advances across a wide range of bimetallic catalytic systems.
Yue, Yang, Tang et al. recently achieved atomic‑level spatial precision of cobalt and nickel sites within a covalent organic framework, creating a highly active bimetallic catalyst for CO₂ photoreduction in which the two metals influence each other electronically (https://doi.org/10.1039/D5SC08435K).
Römelt, Apfel et al. show that a CuICoII cryptate complex exhibits strong synergistic behaviour in visible‑light CO₂ reduction, outperforming its mononuclear analogues (https://doi.org/10.1039/D3SC02679E). These examples underscore how strategically combining metals can unlock reactivity that neither metal achieves alone.
Broader Advances in Polymerisation Chemistry
Other recent studies in Chemical Science reflect that the same emphasis on mechanistic clarity and controlled monomer insertion noted in the Reflection article is essential beyond bimetallic systems.
Seidel and Sumerlin et al. present a practical strategy for accessing alternating styrene–propylene and styrene–ethylene copolymers by coupling RAFT polymerisation with mild photocatalytic decarboxylation, sidestepping long‑standing reactivity‑ratio limitations (https://doi.org/10.1039/D3SC03827K).
Meanwhile, Plajer et al. offer monomer‑centred guidelines for selectivity in sulfurated ring‑opening copolymerisation, showing how an understanding of backbiting, chain‑end stability and ring strain can deliver perfectly alternating poly(esters‑alt‑thioesters) (https://doi.org/10.1039/D4SC05858E).
Though distinct from bimetallic approaches, both studies reinforce that precise control of fundamental steps in chain growth, as showcased in the Reflection and original Chemical Science paper, enables new polymer structures and reactivities.
Looking Ahead
Nakano and Nozaki’s Reflection highlights how the principles of cooperative catalysis have shaped fifteen years of progress in epoxide/CO₂ copolymerisation. Recent advances in both bimetallic activation strategies and mechanistically informed polymerisation methods show that these ideas continue to influence catalyst and polymer design across the field.
