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

The tris[(4-dimethylaminopyridyl)methyl]amine (TPMA) as a ligand for copper-catalyzed atom transfer radical polymerization (ATRP) is reported. In solution, the [Cu(TPMA)Br] complex shows fluxionality by variable-temperature NMR, indicating rapid ligand exchange. In the solid state, the [Cu(TPMA)Br][Br] complex exhibits a slightly distorted trigonal bipyramidal geometry (τ = 0.89). The UV-vis spectrum of [Cu(TPMA)Br] salts is similar to those of other pyridine-based ATRP catalysts. Electrochemical studies of [Cu(TPMA)] and [Cu(TPMA)Br] showed highly negative redox potentials (E = -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 k = 1.1 × 10 M s, 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 k = 7.2 × 10 M s was calculated with values of K ≈ 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 Cu-catalyzed radical termination (CRT) could be suppressed due to the low concentration of L/Cu at a steady state.