Copper-catalyzed atom transfer radical polymerization (Cu-ATRP) is among most powerful controlled radical polymerization techniques that has been widely used in synthesis of various polymers with precisely-controlled architectures. Control over polymer structures via Cu-ATRP is largely attributed to the fast inner sphere electron transfer (ISET) process, which involves a reversible halogen (X) transfer between a propagating substrate chain end (Pn-X) and active catalyst (CuI/L), resulting in the formation of propagating substrate radicals (Pn) and inactive catalyst X-CuII/L. However, the detailed mechanism of ISET process has not been fully explored by experiments and computations, which hinders rational design of Cu-ATRP catalysts. In this study, we attempt to establish an accurate computational model for ISET transition state [L/Cu--X--Pn]‡, and to provide a predictive model for novel catalyst discovery in Cu-ATRP. First, we employ density functional theory (DFT) methods to investigate the geometries and energies of transition states for representative substrates with a given catalyst. The method wb97XD/def2TZVP in SMD solvation model, which gives the best correlation between calculated and experimental transition state energies, has been identified as the most accurate method. Next, we develop the catalyst-substrate interaction model to dissect the total transition state energy into through-bond and through-space interaction between catalyst and substrate. The latter is subsequently segmented into electrostatic interaction, steric repulsion, and dispersion via energy decomposition analysis (EDA). This model has successfully applied to study the origin of catalyst effect on reactivity. Finally, we build a virtual catalyst screening protocol that inherits two key components: automatic geometry generation of transition states for a catalyst library, and efficient scoring function to approximate transition states energies. The top ranked catalyst candidates are further validated using high-level DFT calculations and experimental tests.

Computational study of copper-catalyzed atom transfer radical polymerization (Cu-ATRP) and catalyst discovery via virtual screening

255th National Meeting (2018)

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