Kinetic H/D Exchange Study of Co(III) Coordination Compounds of Diazines Using NMR Spectroscopy

Abstract

The Co(III) diazines complexes having composition [(NH₃)₅CoPhtz)]- (ClO₄)₃ (1) (Phtz = phthalazine), [(NH₃)₅CoPydz)](ClO₄)₃ (2) (Pydz = pyradazine), [(NH₃)₅Co(3-Me-Pydz)](ClO₄)₃ (3) (3-Me-Pydz = 3-methyl pyradazine) and [(NH₃)₅Co(3-MePhtz)](ClO₄)₃ (4) (3-MePhtz = 3-methyl phthalazine), [(NH₃)₅Co(ImH)](ClO₄)₃ (5) (ImH = imidazole), [(NH₃)₅Co(NMeIm)]( ClO₄)₃ (6) (N-MeIm = N-methylimidazole) undergo OD–-catalyzed H/D exchange at the ortho position of the coordinated site. Rate constants for H/D exchange of these complexes at 25°C or 60°C were obtained in alkaline D₂O solution using NMR spectroscopy. Reaction rate for [(NH₃)₅CoPhtz)](ClO₄)₃, [(NH₃)₅CoPydz)](ClO₄)₃, [(NH₃)₅Co(3-Me- Pydz)](ClO₄)₃ and [(NH₃)₅Co(3-MePhtz)](ClO₄)₃ at 25°C are faster compared to [(NH₃)₅Co(ImH)](ClO₄)₃, [(NH₃)₅Co(N-MeIm)](ClO₄)₃ (7). However [(NH₃)₅CoImCo(NH₃)₅]Br5 complex does not H/D exchange at 60°C even in strong alkaline D₂O solution.