To make copper-mediated ATRA synthetically attractive for the addition of monohalogenated initiators, more active catalysts need to be developed. Currently, TPMA and Me6TREN are highly active and commonly used ligands for this process. Since the reducing power of copper complexes have been correlated to their activity as ATRA catalysts, T*2M1 and T*1M2, hybrid ligands of TPMA and Me6TREN functionalized with electron donating groups, were synthesized. Complexes of T*2M1 and T*1M2 (shown in Figure 1) with CuI/IIX (X=Br or Cl) have been prepared and characterized using UV-Vis spectroscopy, single crystal X-ray diffraction (SC-XRD), and cyclic voltammetry. Electrochemical studies determined reduction potentials of -845 mV and -807 mV for CuI(T*2M1)Br and CuI(T*1M2)Br, respectively, relative to ferrocene/ferrocenium (Fc/Fc+) couple. Compared to the reduction potential of CuI(TPMA)Br, (E1/2 = -720 mV vs Fc/Fc+), both CuI(T*2M1)Br and CuI(T*1M2)Br are more reducing and thus expected to be more active ATRA catalysts. According to SC-XRD studies [CuII(L)Br][Br] (L = T*2M1 or T*1M2) were determined to be pentacoordinated whereas CuI(L)Br (L = T*2M1 or T*1M2) were found to be tetracoordinated. ATRA reactions with less active alkyl halides such as bromoacetonitrile and methyl bromoisobutyrate were successful, but required catalyst loadings as high as 0.4 mol% relative to alkene to achieve high yields.

Modified tris(2-pyridylmethyl)amine (TPMA) and tris[2-(dimethylamino)ethyl]amine (Me6TREN) hybrid ligands for use in copper-mediated atom transfer radical addition (ATRA)

254th National Meeting (2017)

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