Influence of structural and thermal factors on phenoxazinone synthase activities catalysed by coordinatively saturated cobalt(III) octahedral complexes bearing diazene–disulfonamide N⌃N⌃N chelators

Abstract

There are increasing efforts towards the development of new synthetic models that can mimic phenoxazinone synthase activity due to the important applications of several biomolecules bearing the phenoxazinone chromophore. However, deliberate studies of systematically varied coordination species for the knowledge of underlying molecular determinants of catalytic outcomes using fully characterized mimicking models are scarce. In this report, two new dianionic and synthetically obtained diazene–disulfonamide N⌃N⌃N chelators of the form RSO2–NH–Ph–N=N–Ph–NHSO2R (R $_2$ methyl for 1 and tolyl for 2) are coordinatively self-assembled around cobalt(III) centres in the presence or absence of co-ligands (acetate, bipyridine, 4-dimethylaminopyridine and/or water) to obtain four new and structurally analysed complexes [Co12][Et3NH], Co1$_2$OAc$=$bpy, Co1$_{\mathbf{2}}$OAc${\cdot }$bpy and Co2${\cdot }$dmap${\cdot }$w, which are all found to be octahedral cobalt(III) polyhedra, distorted to varying extents, by using Continuous Shape Measurement calculations. Based on structural and thermal factors, it is observed that the trends of the phenoxazinone synthase mimicking activities by these complexes correlate with their inherent abilities to generate vacant coordination space for substrate–metal ion interactions. Finally, it is also observed that coordinative steric strains control catalytic trends among the complexes at low temperatures while susceptibility to thermal dissociations is the determinant at higher temperatures.

Keywords

• Novel <i>o</i>-sulfonamide ligands
• Cobalt(III)
• Structure–property correlations
• Mimicking phenoxazinone synthase
• Continuous shape measurement