Homoleptic and heteroleptic diorganoselenides containing pyrazole functionalities. Synthesis, characterization, and antioxidant activity

The diorganoselenides [2-(R2NCH2)C6H4](pzCH2CH2)Se [R = Me (1), Et (2), R2 = O(CH2CH2)2 (3); pz = pyrazole] and [2-{(CH2O)2CH}C6H4](pzCH2CH2) Se (4) were prepared by reacting pzCH2CH2Br with the corresponding alkali metal organoselenolate. Compound [2-(O=CH)C6H4](pzCH2CH2)Se (5) was obtained by deprotection of compound 4 under acidic conditions, whereas compound (pzCH2CH2)2Se (6) was prepared by reacting pzCH2CH2Br with Na2Se. The antioxidant activity of compounds 1–3 and 6 in the catalytic reac- tion between H2O2 and PhSH was investigated by a combination of experimen- tal methods (multinuclear NMR, UV-vis spectroscopy, cyclic voltammetry) and theoretical calculations. The formation of the intermediate selenoxide species 1a–6a was evidenced by multinuclear NMR experiments (1H, 13C{1H}, 77Se {1H}) that revealed the existence of intramolecular N!Se interactions. Density functional theory (DFT) calculations showed that these interactions are mostly covalent in nature. For compound 1, an autocatalytic mechanism is proposed.