Two mononuclear cobalt(III) complexes exhibiting phenoxazinone synthase activity

Abstract

Two mononuclear cobalt(III) complexes, namely [LCo(tmtp)(H2O)]ClO4⋅MeOH (1) (tmtp = tri(m‐tolyl)phosphine) and [LCo(PPh3)(H2O)]PF6 (2), have been prepared from a polydentate ligand, N,N′‐bis(3‐methoxysalicylidehydene)cyclohexane‐1,2‐diamine (H2L). Standard analytical techniques such as elemental analysis and UV–visible and Fourier transform infrared spectroscopies were used to characterize both complexes. The solid‐state molecular structures of both complexes were confirmed from single‐crystal X‐ray diffraction analysis. Structural analyses show that the Co(III) ion occupies the centre of a distorted octahedron in a complex cation: [LCo(tmtp)(H2O)]+ and [LCo(PPh3)(H2O)]+ for 1 and 2, respectively. Phenoxazinone synthase activities of both complexes were screened. Kinetic studies and other experimental observations reveal that the reaction follows rate saturation kinetics and proceeds through the formation of a catalyst (complex)–substrate adduct. The turnover number (Kcat) of complex 2 is 54.07 h−1, exhibiting better catalytic activity compared to 1 (Kcat = 45.11 h−1).