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

摘要

The tris[(4-dimethylaminopyridyl)methyl]amine (TPMA~(NMe2)) as a ligand for copper-catalyzed atom transfer radical polymerization (ATRP) is reported. In solution, the [Cu~(I)(TPMA~(NMe2))Br] complex shows fluxionality by variable-temperature NMR, indicating rapid ligand exchange. In the solid state, the [Cu~(II)(TPMA~(NMe2))Br][Br] complex exhibits a slightly distorted trigonal bipyramidal geometry (τ = 0.89). The UV–vis spectrum of [Cu~(II)(TPMA~(NMe2))Br]~(+) salts is similar to those of other pyridine-based ATRP catalysts. Electrochemical studies of [Cu(TPMA~(NMe2))]~(2+) and [Cu(TPMA~(NMe2))Br]~(+) showed highly negative redox potentials ( E _(1/2) = −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 k _(a) = 1.1 × 10~(6) 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 k _(a) = 7.2 × 10~(6) M~(–1) s~(–1) was calculated with values of K _(ATRP) ≈ 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~(I)-catalyzed radical termination (CRT) could be suppressed due to the low concentration of L/Cu~(I) at a steady state.