Abstract

ϵ-Caprolactone (ϵ-CL) adducts of cationic, amine tris(phenolate)-supported niobium(V) and tantalum(V) ethoxides initiate the ring-opening polymerization of lactones. The Ta(V) species prepared and applied catalytically herein exhibits higher activity in the ring-opening polymerization (ROP) of ϵ-caprolactone than the previously reported, isostructural Nb(V) complex, contradicting literature comparisons of Nb(V)- and Ta(V)-based protocols. Both systems also initiate the ROP of δ-valerolactone and rac-β-butyrolactone, kinetic studies confirming retention of higher activity by the Nb congener. Polymerizations of rac-β-butyrolactone and δ-valerolactone were previously unrealized under Group V- or Ta-mediated conditions, respectively, although the former has afforded only low molecular weight, cyclic poly-3-hydroxybutyrate. Cationic ethoxo-Nb(V) and −Ta(V) δ-valerolactone adducts are also reported, demonstrating the facility of δ-valerolactone as a ligand and the generality of the synthetic method. Both δ-valerolactone-bearing complexes initiate the ROP of ϵ-caprolactone, δ-valerolactone, and rac-β-butyrolactone. Accordingly, we have elucidated trends in reactivity and investigated the initiation mechanism for such systems, the insertion event being predicated upon intramolecular nucleophilic attack on the coordinated lactone by the adjacent alkoxide moiety. This mechanism enables quantitative, stoichiometric installation of a single monomer residue distinct from the bulk of the polymer chain, and permits modification of polymer properties via both manipulation of the molecular architecture and tuning of the polymerization kinetics, and thus dispersity, through hitherto inaccessible independent control of the initiation event.

Original languageEnglish
Pages (from-to)27-38
Number of pages12
JournalInorganic Chemistry
Volume63
Issue number1
Early online date20 Dec 2023
DOIs
Publication statusPublished - 8 Jan 2024

Funding

We thank the University of Bath for a studentship to S.N.M. and the EPSRC (EP/L016354/1, Centre for Doctoral Training in Sustainable Chemical Technologies; EP/P016405/1, funded P.M. PDRA position) for funding this work. A.B. acknowledges the Royal Society (UF/160021 fellowship). Funding was provided by TotalEnergies Corbion PLA. Analytical facilities and expertise were provided through the Material and Chemical Characterization Facility (MC) at the University of Bath ( https://www.bath.ac.uk/research-facilities/material-and-chemical-characterisation-facility-mc2/ ). 2

FundersFunder number
Engineering and Physical Sciences Research CouncilEP/P016405/1, EP/L016354/1
Royal SocietyUF/160021
University of Bath

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