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

Two organometallic complex fragments with 5d(6) configurated metal centres of different character, electrophilic [(IrCp)-Cp-III*Cl](+) and pi-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, W-vis) in aprotic solvents points in most cases to the O4 and N5 atoms as chelate donors for metal binding. For [(DMA)(IrCp)-Cp-III*Cl](PF6) 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 pi 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. (C) 1999 Elsevier Science S.A. All rights reserved.