"Noninnate" Ring-Opening Polymerization: Palladium-Catalyzed Stereoselective 1,4-Polymerization of...

In ring-opening polymerization (ROP), main-chain connectivity is largely dictated by the inherent electronic and steric properties of the monomer. As a result, even when different polymerization mechanisms are employed, the same backbone structure is obtained. Here, we report catalyst-controlled, noninnate connectivity in the ROP of alkynylcyclopropane dicarboxylates (ACPs). Leveraging π-propargyl palladium intermediates, we redirect the reactivity from the electronically favored 1,5-addition to a noninnate 1,4-addition pathway, furnishing a conjugated diene-based backbone with high regio- and stereoselectivity. The polymerization exhibits controlled characteristics under optimized conditions. Combined experimental and computational studies reveal that a strategically positioned quaternary carbon center enforces high configurational rigidity in the organopalladium intermediate, thereby suppressing undesired cyclization and enabling rapid, stereospecific β-hydride elimination. This work demonstrates overriding the innate connectivity in ROP by precisely controlling the fate of organometallic intermediates.