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Highly Active Families of Catalysts for the Ring-Opening Polymerization of Lactide: Metal Templated Organic Hydrogen Bond Donors Derived from 2‑Guanidinobenzimidazole

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journal contribution
posted on 17.12.2015, 01:25 authored by Coralie Thomas, John A. Gladysz
Cobalt and ruthenium chelate complexes of 2-guanidinobenzimidazole (GBI), mer-[Co­(GBI)3]­(BArf)3·14H2O (13+ 3BArf; BArf = B­(3,5-C6H3(CF3)2)4), and [(η5-C5H5)­Ru­(CO)­(GBI)]­(BArf) can serve as hydrogen bond donor catalysts and, together with equimolar quantities of 1,2,2,6,6-pentamethylpiperidene (PMP; hydrogen bond acceptor) and 4-phenylbenzyl alcohol initiator (InOH), effect controlled ring-opening polymerizations of dl-lactide at low loadings (1–3 mol %). These inexpensive systems afford polylactide with narrow dispersities (<1.18) and Mn values of 4000–11 000 g/mol. MALDI-ToF mass spectra show a series of peaks separated by m/z values of 144 and an absence of transesterification side reactions between polymer chains. Runs with multiple charges of monomer establish the living nature of the polymerization, and 1H NMR or UV–visible experiments provide evidence for key hydrogen bonding interactions (InOH/PMP; 13+ 3BArf/dl-lactide).