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Dinuclear Zirconium Complex Bearing 1,5-Bridged-Calix[8]arene Ligand as Effective Catalyst for the Synthesis of Macrolactones

Abstract

“Macrocyclizing Cycles with a Macrocycle.” The synthesis of a dinuclear zirconium complex bearing a 1,5-m-xylene-diyl-bridged calix[8]arene ligand and tert-butoxide groups, via protonolysis of the calix proligand with two equivalents of zirconium(IV) tert-butoxide, has been accomplished. 1H, 13C and two-dimensional NMR spectroscopy revealed for the complex a conformationallly locked solution structure with C2v symmetry, where the two zirconium atoms lie in close proximity. The elucitated structure has been validated through DFT calculations. The complex has been successful used as catalyst in the ring opening polymerization (ROP) of lactones such as rac-lactide (LA), ε-caprolactone (ε-CL) and β-butyrolactone (β-BL). The activities for the ROP of LA well compares with that for the so far reported most active group 4 complexes. Interestingly, the MALDI-TOF-MS investigations on the resulting polymer architecture revealed a highly selective formation of cyclic polymers (70-80 mol%). The cooperation of the intramolecular zirconium atoms has been proved comparing the polymerization results with those obtained using a mononuclear zirconium complex featuring a calix[4]arene ligand.

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Publication details

The article was received on 15 Dec 2017, accepted on 16 Apr 2018 and first published on 16 Apr 2018


Article type: Paper
DOI: 10.1039/C7CY02537H
Citation: Catal. Sci. Technol., 2018, Accepted Manuscript
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    Dinuclear Zirconium Complex Bearing 1,5-Bridged-Calix[8]arene Ligand as Effective Catalyst for the Synthesis of Macrolactones

    R. Lapenta, N. A. De Simone, A. Buonerba, C. Talotta, C. Gaeta, P. Neri, A. Grassi and S. Milione, Catal. Sci. Technol., 2018, Accepted Manuscript , DOI: 10.1039/C7CY02537H

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