p-Substituted Tris(2-pyridylmethyl)amines as Ligands for Highly Active ATRP Catalysts: Facile Synthesis and Characterization

A facile and efficient two-step synthesis of p-substituted tris(2-pyridylmethyl)amine (TPMA) ligands to form Cu complexes with the highest activity to date in atom transfer radical polymerization (ATRP) is presented. In the divergent synthesis, p-Cl substituents in tris(4-chloro-2-pyridylmethyl)amine (TPMA^3Cl) were replaced in one step and high yield by electron-donating cyclic amines (pyrrolidine (TPMA^PYR), piperidine (TPMA^PIP), and morpholine (TPMA^MOR)) by nucleophilic aromatic substitution. The Cu^II(TPMA^NR2)Br]⁺ complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than Cu^II(TPMA)Br]⁺, indicating >3 orders of magnitude higher ATRP activity. Cu^I(TPMA^PYR)]⁺ exhibited the highest reported activity for Br-capped acrylate chain ends in DMF, and moderate activity toward C?F bonds at room temperature. ATRP of n-butyl acrylate using only 10–25 part per million loadings of Cu^II(TPMA^NR2)Br]⁺ exhibited excellent control.