Synthesis and Characterization of the Most Active Copper ATRP Catalyst Based on Tris[(4-dimethylaminopyridyl)methyl]amine

The tris[(4-dimethylaminopyridyl)methyl]amine (TPMANMe2) as a ligand for copper-catalyzed atom transfer radical polymerization (ATRP) is reported. In solution, the [CuI(TPMANMe2)Br] complex shows fluxionality by variable-temperature NMR, indicating rapid ligand exchange. In the solid state, the [CuII(TPMANMe2)Br][Br] complex exhibits a slightly distorted trigonal bipyramidal geometry (τ = 0.89). The UV-vis spectrum of [CuII(TPMANMe2)Br]+ salts is similar to those of other pyridine-based ATRP catalysts. Electrochemical studies of [Cu(TPMANMe2)]2+ and [Cu(TPMANMe2)Br]+ showed highly negative redox potentials (E1/2 = -302 and -554 mV vs SCE, respectively), suggesting unprecedented ATRP catalytic activity. Cyclic voltammetry (CV) in the presence of methyl 2-bromopropionate (MBrP; acrylate mimic) was used to determine activation rate constant ka = 1.1 × 106 M-1 s-1, confirming the extremely high catalyst reactivity. In the presence of the more active ethyl α-bromoisobutyrate (EBiB; methacrylate mimic), total catalysis was observed and an activation rate constant ka = 7.2 × 106 M-1 s-1 was calculated with values of KATRP ≈ 1. ATRP of methyl acrylate showed a well-controlled polymerization using as little as 10 ppm of catalyst relative to monomer, while side reactions such as CuI-catalyzed radical termination (CRT) could be suppressed due to the low concentration of L/CuI at a steady state.