Invoking Side-Chain Functionality for the Mediation of Regioselectivity during Ring-Opening Polymerization of Glucose Carbonates

Abstract

The extent of participation of side-chain functionalities during the 1,5,7-triazabicyclo[5.4.0]­dec-5-ene (TBD) organobase-catalyzed ring-opening polymerizations (ROP) of six-membered cyclic d-glucose-based carbonates was found to result in significantly different regiochemical outcomes. High regioselectivity was observed for naturally derived poly­(4,6-d-glucose carbonate)­s (PGCs) containing carbonate side chain substituents in the 2- and 3-positions, whereas regioirregularity was found for analogous PGCs with ether side-chain substituents. The backbone connectivities and structural details of these PGCs were examined through a combination of comprehensive 1D and 2D NMR studies on unimers and dimers, verifying the ring-opening preferences and indicating the contribution of side-chain functionalities in regioselective ROP processes. A molecular understanding of the curious role of side-chain functionalities was demonstrated via density functional theory calculations, revealing stabilization effects of intermolecular hydrogen bonding between the side-chain functionalities and TBD in the transition states. Overall, this work provides fundamental insights into the organocatalytic ROP of these specific six-membered asymmetric cyclic glucose carbonates. More importantly, these findings serve as a foundation for future design strategies that incorporate adjacent functionalities within monomers to act as directing groups and impart molecular interactions that define regiochemical ring-opening.

Complexities of Regioselective Ring-Opening vs Transcarbonylation-Driven Structural Metamorphosis during Organocatalytic Polymerizations of Five-Membered Cyclic Carbonate Glucose Monomers

“…Recently, we showed that the regiochemistry of TBD-catalyzed ROPs of d -glucose-based 4,6-cyclic carbonates could be tuned by varying the side-chain substituents on the 2- and 3-positions of the sugar ring. 18 Density functional theory (DFT) calculations revealed that the regioselectivity differences may have resulted from intermolecular hydrogen bonding between the carbonate side-chain functionalities and TBD in the transition states. Further investigations are needed to fully understand the mechanistic origins of regiochemical outcomes, and then to translate that information into meaningful adjustments to polymer properties.…”

From Impossible to Possible: Atom‐Economic Polymerization of Low Strain Five‐Membered Carbonates

“…Ring‐opening polymerization (ROP) of cyclic monomers has been demonstrated as a valid way to synthesize valuable polymer materials [1–21] . The five‐membered propylene carbonate (PC) would be a desirable candidate, benefited from its wide sources (renewable CO 2 ), easy accessibility, low toxicity and broad application [22, 23] .…”

Photocatalytic Synthesis of Substituted Cyclic Carbonate Monomers for Ring‐Opening Polymerization

“…[5] Unlike their five-membered analogues, the ROP of larger-ring carbonates has been reported as a viable strategy towards the preparation of polycarbonates. [6] In particular, the ROP of six-membered carbonates has been most frequently studied building on a more diverse set of available monomers, thereby creating polycarbonate variability (Scheme 1a). [7] However, the synthesis of six-membered cyclic carbonates (6MCCs) can be tedious and only a handful of effective methods have been reported so far.…”