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

Abstract

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 (TPMA3Cl ) were replaced in one step and high yield by electron-donating cyclic amines (pyrrolidine (TPMAPYR ), piperidine (TPMAPIP ), and morpholine (TPMAMOR )) by nucleophilic aromatic substitution. The [CuII (TPMANR2 )Br]+ complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than [CuII (TPMA)Br]+ , indicating >3 orders of magnitude higher ATRP activity. [CuI (TPMAPYR )]+ 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 [CuII (TPMANR2 )Br]+ exhibited excellent control.