Complexes Cu(O2Ncat)(tbeda) (1) and Cu(O2Ncat)(tmeda) (2) (tbeda = N,N,N′,N′-tetrabenzylethylenediamine, tmeda = N,N,N′,N′-tetramethylethylenenediamine, O2NcatH 2 = 4-nitrocatechol) have been prepared by the reaction of copper(II) perchlorate with 4-nitrocatechol in the presence of triethylamine and the appropriate bidentate ligand. These compounds represent structural and functional model systems for the copper-containing catechol 1,2-dioxygenase. Both complexes have been structurally characterized by X-ray crystallography and by UV-vis, IR, and EPR spectroscopies. Upon protonation of 1 and 2 with perchloric acid, the bidentate coordination of O2-Ncat could be reversible converted to the monodentate coordination of O2NcatH. The equilibrium constants were found to be 4200 and 3500, respectively, by measuring the UV-vis spectra in DMF. Back-titration with morpholine proved the reversibility of both reactions. Kinetic data on the oxygenation of 1 and 2 revealed overall second-order rate equations with kinetic parameters: k tbeda = (4.63 ± 0.23) × 10-2 mol-1 dm3 s-1, ΔH≠ = 51 ± 6 kJ mol-1, ΔS≠ = -137 ± 16 J mol-1 K-1; ktmeda = (0.89 ± 0.23) mol-1 dm3 s-1, ΔH≠ = 85 ± 7 kJ mol-1, ΔS≠ = -57 ± 19 J mol-1 K-1 at 365.16 K. Oxygenation of 1, 2, and [Cu(O2NcatH)(L)] ClO4 (L = tbeda, tmeda) in DMF solution at ambient conditions gives the corresponding intradiol ring-cleaved (2-nitro-muconato)copper(II) complexes. These data support the assumption that the reaction of the differently coordinated catecholate ligand with dioxygen shows only 1,2-dioxygenase activity.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry