Ni/Photoredox-Catalyzed Enantioselective Cross-Electrophile Coupling of Styrene Oxides with Aryl Iodides.

A Ni/photoredox-catalyzed enantioselective reductive coupling of styrene oxides and aryl iodides is reported. This reaction affords access to enantioenriched 2,2-diarylalcohols from racemic epoxides via a stereoconvergent mechanism. Multivariate linear regression (MVLR) analysis with 29 bioxazoline (BiOx) and biimidazoline (BiIm) ligands revealed that enantioselectivity correlates with electronic properties of the ligands, with more electron-donating ligands affording higher ee's. Experimental and computational mechanistic studies were conducted, lending support to the hypothesis that reductive elimination is enantiodetermining and the electronic character of the ligands influences the enantioselectivity by altering the position of the transition state structure along the reaction coordinate. This study demonstrates the benefits of utilizing statistical modeling as a platform for mechanistic understanding and provides new insight into an emerging class of chiral ligands for stereoconvergent Ni and Ni/photoredox cross-coupling.

Continuous Polymer Synthesis and Manufacturing of Polyurethane Elastomers Enabled by Automation.

Connecting polymer synthesis and processing is an important challenge for streamlining the manufacturing of polymeric materials. In this work, the automated synthesis of acrylate-capped polyurethane oligomers is integrated with vat photopolymerization 3D printing. This strategy enabled the rapid manufacturing of a library of polyurethane-based elastomeric materials with differentiated thermal and mechanical properties. The automated semicontinuous batch synthesis approach proved enabling for resins with otherwise short shelf lives because of the intimate connection between synthesis, formulation, and processing. Structure-property studies demonstrated the ability to tune properties through systematic alteration of cross-link density and chemical composition.

Modifying Poly(caprolactone) Degradation through C-H Functionalization.

There is a growing need for degradable polymers for applications in sustainable plastics and medical implants. To enhance the utility of degradable polymers, both better understanding of the factors that influence their degradation and new tools to modulate degradation are needed. We report the C-H xanthylation of poly(caprolactone), a biodegradable polyester, which results in changes in materials properties even at small incorporations. Despite the functionalized materials exhibiting a decrease in crystallinity and hydrophobicity, xanthylated poly(caprolactone) degrades more slowly than its unfunctionalized counterpart. To understand this rate difference, kinetic studies with a small-molecule surrogate were performed and demonstrated that functionalization adjacent to the hydrolyzable ester functional group led to slower degradation. This study illustrates how the interplay between molecular and materials characteristics can impact degradation.