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.