Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers

Abstract

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Zwitterionic Iron(II) Compounds: Synthesis, Reactivity, and Catalytic Carbonylative Polymerization of Cyclic Ethers

“…Iron is among the first transition metals investigated for stoichiometric and catalytic carbonylation reactions. − The earth abundance and relatively low toxicity of iron have stimulated renewed interest in Fe-based catalysis. − We recently demonstrated a zwitterionic design strategy that enabled Ni­(II) complexes to catalyze the carbonylative polymerization of cyclic ethers . The zwitterionic design is formulated on the basis of the following mechanistic hypothesis.…”

“…As in the cases with the Ni catalysts, the presence of both THF and EO is required for either of them to substantially polymerize. THF, as a better nucleophile than EO, promotes the nucleophilic attack of EO on the Fe-acyl group to afford EO-acylium, which ring-opens much more readily than THF-acylium and in turn gives rise to cationic THF enchainment . Both carbonylative and simple ring-opening enchainments took place to afford the ester and ether units in the polymer chain, respectively (Figure ).…”

“…4−6 We recently demonstrated a zwitterionic design strategy that enabled Ni(II) complexes to catalyze the carbonylative polymerization of cyclic ethers. 7 The zwitterionic design is formulated on the basis of the following mechanistic hypothesis. The cationic charge at the Ni center of the zwitterion renders the Ni-acyl group electrophilic enough to react with a cyclic ether (Scheme 1), and ion-pairing between the resultant Ni(0) anion and cyclic ether−acylium promotes nucleophilic addition within the ion pair.…”

“…THF, as a better nucleophile than EO, promotes the nucleophilic attack of EO on the Fe-acyl group to afford EO-acylium, which ring-opens much more readily than THF-acylium and in turn gives rise to cationic THF enchainment. 7 Both carbonylative and simple ringopening enchainments took place to afford the ester and ether units in the polymer chain, respectively (Figure 2). Most of the ester units arose from EO carbonylative enchainment (peaks a and f), and only a small fraction was due to THF carbonylative enchainment (peak h).…”