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

Cobalt and ruthenium chelate complexes of 2-guanidinobenzimidazole (GBI), mer-[Co(GBI)(3)](BArf)(3)center dot 14H(2)O (1(3+) 3BAr(f)(-); BArf = B(3,5-C6H3(CF3)(2))(4)), and [(eta(5)-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 M-n 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 H-1 NMR or UV-visible experiments provide evidence for key hydrogen bonding interactions (InOH/PMP; 1(3+) 3BAr(f)(-)/DL-lactide).