Organometallic iridium(III) and rhenium(I) complexes with lumazine, alloxazine and pterin derivatives

Abstract Two organometallic complex fragments with 5d 6 configurated metal centres of different character, electrophilic [Ir III Cp*Cl] + and π-donating [Re I (CO) 3 Cl], were used as probes in compounds containing 1,3-dimethyllumazine (DML), 1,3-dimethylalloxazine (DMA), 2-pivaloylpterin (PP) and 6-methyl-2-pivaloylpterin (MPP) as biochemically relevant ligands. Evidence from spectroscopy (NMR, IR, UV–vis) in aprotic solvents points in most cases to the O4 and N5 atoms as chelate donors for metal binding. For [(DMA)Ir III Cp*Cl](PF 6 ) this was substantiated by a crystal structure analysis. With PP, however, an iridium(III) compound with pivaloyl-coordinated metal was obtained. Whereas both the Ir III and Re I complexes of the good π acceptor ligand DMA can be reduced reversibly and thus studied by (spectro)electrochemistry (IR, UV–vis, EPR: ligand-centred one-electron reduction), the DML system exhibits such behaviour only for the Ir III species. The complexes of the 2-pivaloylpterins showed only irreversible reduction.