Mixed valence trinuclear cobalt (II/III) complexes: Synthesis, structural characterization and phenoxazinone synthase activity

Abstract Three new mixed valence trinuclear Co(II/III) compounds [Co 3 L 2 ( μ 2 -C 6 H 5 CO 2 − ) 2 (CH 3 CN) 2 ](ClO 4 − ) 2 ·(CH 3 CN) 3 ( 1 ) [Co 3 L R 2 ( μ 2 -C 6 H 5 CO 2 − ) 2 (C 6 H 5 CO 2 − ) 2 ]·(CH 3 CN) 2 ( 2 ) and [Co 3 L R 2 ( μ 2 -C 6 H 5 CH CH CO 2 − ) 2 (C 6 H 5 CH CH CO 2 − ) 2 ]·((CH 3 ) 2 CO) 2 ( 3 ) have been synthesized by reacting the di-Schiff base ligand [H 2 L] or its reduced analog [H 2 L R ] (where H 2 L =  N , N ′-bis(salicylidene)-1,3-propanediamine) and (H 2 L R  =  N , N ′-bis(2-hydroxybenzyl)-1,3-propanediamine) with cobalt perchlorate hexahydrate and sodium benzoate or sodium cinnamate. The complexes have been characterized by IR, UV–Vis and single crystal X-ray diffraction analyses. All the complexes are linear trinuclear species [Co III Co II Co III ] in which two terminal octahedral Co III N 2 O 2 cores coordinate to the central octahedral Co II ion through μ 2 -phenoxido oxygen atom and the bridging carboxylato ions. In addition, the complexes ( 2 and 3 ) derived from reduced Schiff base ligand have, rather unusually, a terminally coordinated carboxylato ion to Co III , which is acetonitrile molecule in case of complex ( 1 ) with unreduced ligand. Complex 2 has been found to be an excellent functional model for the phenoxazinone synthase activity, in the aerial oxidation of 2-aminophenol to the corresponding 2-aminophenoxazine-3-one chromophore in acetonitrile solvent medium. Detailed kinetic data analysis of this oxidation reaction reveals a fairly high phenoxazinone synthase activity of 2 with k cat  = 153.60 h −1 .