Electrochemical reduction of bis(β-diketones): 1,10-di(α-cyclohexanone)decane-1,10-dione and 3,14-diacetylhexadecane-2,15-dione. Characterization and electron paramagnetic resonance properties of their electrogenerated mononuclear copper(II) complexes
Abstract
The preparation and characterization of the bis(β-diketone) 1,10-di(α-cyclohexanone)decane-1,10-dione (H2L11) and 3,14-diacetylhexadecane-2,15-dione (H2L2
2) ligands, are reported. A direct electrochemical generation of CuIIL complexes is achieved. The electrochemical reductions of 1 and 2 have been investigated in tetrahydrofuran at a dropping mercury electrode. Voltammetric, coulometric and UV–visible results indicate that their two-electron reduced form ultimately generates the corresponding anions (L1)2– and (L2)2–. The reaction of (L1)2– and (L2)2– with CuII trifluoromethanesulfonate gives the corresponding 1 : 1 complexes (CuIIL1
1′) and (CuIIL2
2′). In frozen-chloroform solutions, the latter complexes show well resolved electron paramagnetic resonance (EPR) spectra. The observed hyperfine splittings due to the nuclear spin I= 3/2 of the copper ion allow the determination of the following magnetic parameters: g∥= 2.304, g⊥= 2.062, a∥= 142 × 10–4 cm–1, a⊥= 25.2 × 10–4 cm–1 for 1′, and g∥= 2.277, g⊥= 2.048, a∥= 160 × 10–4 cm–1, a⊥= 22.4 × 10–4 cm–1 for 2′. The UV–VIS absorption spectra and the results obtained from the experimental and simulated EPR spectra indicate that the complex 1′ has a square-planar geometry whereas 2′ is a square-planar distorted complex.