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

High Resolution Image Download MS PowerPoint Slide Cobalt and ruthenium chelate complexes of 2-guanidinobenzimidazole (GBI), mer -[Co(GBI) 3 ](BAr f ) 3 ·14H 2 O ( 1 3+ 3BAr f –; BAr f = B(3,5-C 6 H 3 (CF 3 ) 2 ) 4 ), and [(η 5 -C 5 H 5 )Ru(CO)(GBI)](BAr f ) 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 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 1 H NMR or UV–visible experiments provide evidence for key hydrogen bonding interactions (InOH/PMP; 1 3+ 3BAr f – / dl -lactide).