Synthesis, characterisation, and solution behaviour of two dioxomolybdenum(VI) complexes of a bis(catecholamide) siderophore analogue

The bis(catecholamide) alpha,alpha'-bis(2,3-dihydroxybenzdylamino)-m-xylene (H(4)L(3)) has been synthesized and characterised. It is an analogue of the naturally occurring siderophore azotochelin and structurally related to an approved enterobactin model. Two dioxomolybdenum(VI) complexes of it have been synthesized, namely a di- and a mono-nuclear one. Variable-temperature proton NMR studies of the initially obtained dinuclear compound revealed that three kinetic processes are operative in Me(2)SO solution: geometrical isomerisation at lower temperatures, and inversion of configuration concomitant with dissociation into the monomer at higher temperatures. In contrast, the mononuclear complex obtained in this way isomerises and inverts almost simultaneously at 343-353 K. The crystal structure of Na-2[MoO(2)L(3)] confirmed the mononuclear nature of the complex and revealed that the cis, cis, cis geometrical isomer is adopted in the solid state.