Flexibly Tethered Dinuclear Zinc Complexes: A Solution to the Entropy Problem in CO₂/Epoxide Copolymerization Catalysis?

Copolymerization of CO2 and epoxides mediated by zinc organyls

“…[35][36][37][38] The group of Williams demonstrated a zinc-based macrocyclic bimetallic catalyst, which showed remarkable activity even at atmospheric pressure of carbon dioxide. [39][40][41] More recently, Rieger et al [42][43][44] reported dinuclear zinc-b-diiminate complexes and Dinjus and co-workers Notably, most of these systems require halogen containing compounds, such as ammonium and phosphonium salts which are commonly employed co-catalyst for the synthesis of cyclicas well as polycarbonates from epoxides and CO 2 . We are generally interested in the reaction between epoxides and CO 2 .…”

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

“…Due to ah igherb asicity of the carbonyl oxygen [20] [e] Homopolymerization of propylene oxide for 5h at catalyst loading of catalyst/epoxide of 1:1000 (entry 6) and 1:4000 (entry 7) in a1 :1 (v/v = 1:1) mixture of tolueneand propylene oxide.…”

“…The crystallographically determined ZnÀZn distance of 7.70 f its very welltot he computed distance of 7.77 . [20] Experimental study After ensuring the trivalent coordination sphereo fb oth zinc centers,c omplex 1 was tested in co-polymerization of propylene oxide and carbon dioxide under variousr eaction conditions (Table1,e ntries 1-5).…”

“…[20] Suitable single crystals for diffraction experiments were obtained by slow diffusion of ether into as aturated toluene solution of the complex (Figure 1). Both zinc atoms are surrounded by three nitrogen atoms in the solids tate, which results in ad istorted trigonal planar geometry.T he ZnÀNb onding distances of the symmetric b-diketiminato ligand are in as imilar range (Zn1ÀN1 1.952 a nd Zn1ÀN2 1.960 ).…”

“…This soluble catalysts ystem shows for the first time as hift of the rate-determining step from ring opening of the epoxide to carbon dioxide insertion in the co-polymerization of epoxides and CO 2 at technical CO 2 pressures, which is attributed to the existence of af lexible tether combining two b-diketiminato zinc units. [20] However,k inetic investigationsf or complex 1 (Scheme 1) in the co-polymerizationo fp ropylene oxide and carbon dioxide revealed extremely low conversions. Herein, the reasonsf or the activity difference compared with CHO/CO 2 co-polymerization are investigated.…”