Synthesis and characterization of the most active copper ATRP catalyst based on tris[(4-dimethylaminopyridyl)methyl]amine
Résumé
The tris[(4-dimethylaminopyridyl)methyl]amine (TPMANMe2) as a ligand for copper-catalyzed atom transfer radical polymn. (ATRP) is reported. In soln., the [CuI(TPMANMe2)Br] complex shows fluxionality by variable-temp. 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. Electrochem. studies of [Cu(TPMANMe2)]2+ and [Cu(TPMANMe2)Br]+ showed highly neg. redox potentials (E1/2 = -302 and -554 mV vs. SCE, resp.), suggesting unprecedented ATRP catalytic activity. Cyclic voltammetry (CV) in the presence of Me 2-bromopropionate (MBrP; acrylate mimic) was used to det. activation rate const. ka = 1.1 × 106 M-1 s-1, confirming the extremely high catalyst reactivity. In the presence of the more active Et α-bromoisobutyrate (EBiB; methacrylate mimic), total catalysis was obsd. and an activation rate const. ka = 7.2 × 106 M-1 s-1 was calcd. with values of KATRP ≈ 1. ATRP of Me acrylate showed a well-controlled polymn. 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 concn. of L/CuI at a steady state.
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