Modifying commodity-relevant unsaturated polymers via Co-catalyzed MHAT

The past 2 decades have witnessed the rapid development of CoSalen-catalyzed hydrofunctionalization reactions, mostly on terminal and conjugation-activated olefins. However, the use of 1,2-dialkyl-substituted alkenes continues to pose challenges. In this study, we revisit this substrate class in the context of Carreira-type hydrofunctionalization reactions and introduce a simple yet effective modification (over a 250-fold-increase in turnover number [TON]). Near-quantitative yields can be achieved at a low catalyst loading, typically 0.05 mol %. The key lies in inhibiting the degradation of the salen backbone using molecular sieves. This protocol facilitates a study on the metal hydride hydrogen atom transfer (MHAT) regioselectivity of this type of alkene. We found that allylic electron-negative groups and hyperconjugation have profound effects, yielding regioisomeric ratios ranging from 6.5:1 to < 1:20. The high TONs, mild conditions, and versatility of this method further enable its application in the post-polymerization modification of several olefin-rich, commodity-relevant polymers, demonstrating the rich potential of MHAT hydrofunctionalization in macromolecular settings.