Atom transfer radical addition (ATRA) catalyzed by copper complexes with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) ligand

Article abstract of DOI:10.1016/j.polymer.2015.02.021

Synthesis, characterization, electrochemical studies and ATRA activity of copper complexes with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) ligand in the presence of ascorbic acid as a reducing agent were reported. [Cu^II(TPEN′)Br][Br] (TPEN′ denotes tetracoordinated ligand) catalyst showed a very low activity in ATRA of CBr₄ to 1-octene, methyl methacrylate, methyl acrylate and styrene in methanol, which is a typical solvent used for ATRA reactions employing ascorbic acid. On the contrary, the yields and stereoselectivity towards monoadduct formation were dramatically increased in slightly polar but aprotic acetone. Based on molecular structures of isolated [Cu^II(TPEN)][BPh₄] and [Cu^II(TPEN′)Br][Br] complexes, as well as UV-Vis and cyclic voltammetry studies, an equilibrium was proposed involving inactive [Cu^II(TPEN)]²⁺ and ATRP active [Cu^II(TPEN′)Br]⁺ cations The halidophilicity of the bromide-based deactivating complex ([Cu^II(TPEN′)Br][Br]) decreased approximately 750 times upon changing the solvent from acetone (K_Br = 3000 ± 230) to methanol (K_Br = 4.1 ± 0.1), explaining poor catalytic activity in methanol. In acetone, [Cu^II(TPEN′)Br][Br] complex was nearly as active in ATRA reactions employing ascorbic acid as previously reported [Cu^II(TPMA)Br][Br].