Reaction of Cu(ClO4)2⋅6 H2O with a tripodal 2N2O ligand, H2Me2NL, having a p-(dimethylamino)phenol moiety, in CH2Cl2/MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me2NL)(H2O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me2NL)(MeOH)]ClO4 (2), which could be obtained also from the isolated complex 1 by reaction with O2 in CH2Cl2/MeOH. The X-ray crystal structures of 1 and 2 revealed similar square-pyramidal structures, but 2 showed the (dimethylamino)phenoxyl radical features. Complex 1 exhibits characteristic CuII EPR signals of the d x2-y2 ground state in CH2Cl2/MeOH at 77 K, whereas 2 is EPR-silent. The EPR and X-ray absorption fine structure (XAFS) results suggest that 2 is assigned to the CuII–(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH2Cl2 solution of 1 exhibits distortion from the dx2-y2 ground state and a temperature-dependent equilibrium between the CuII–(dimethylamino)phenolate and the CuI–(dimethylamino)phenoxyl radical. From these results, CuII–phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O2 via the CuI–phenoxyl radical species.
All Science Journal Classification (ASJC) codes
- Organic Chemistry