Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co-polymerization of Epoxides and CO2

• Published in: Chemistry : a European journal Vol. 21; no. 22; pp. 8148 - 8157
• Main Authors: Kissling, Stefan, Altenbuchner, Peter T., Lehenmeier, Maximilian W., Herdtweck, Eberhardt, Deglmann, Peter, Seemann, Uwe B., Rieger, Bernhard
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 26-05-2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Carbon dioxide; Chemical industry; Chemistry; co-polymerization; density functional calculations; epoxides; Polymerization; Zinc; carbon dioxide; density functional calculations; epoxides; zinc; co-polymerization
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201406055

The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO2 revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO2 co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion.
Put to rest: The most active catalytic system for the co‐polymerization of cyclohexene oxide and CO2 was thoroughly investigated toward propylene oxide/CO2 co‐polymerization. Experimental results and DFT calculations revealed that the received low conversions are a consequence of the formation of an energetically highly stable resting state as soon as the catalyst is exposed to both propylene oxide and CO2. This enables neither further epoxide ring openings nor CO2 insertion reactions (see figure).