Photoinduced Ligand Exchange and Covalent DNA Binding by Two New Dirhodium Bis-Amidato Complexes

Two new dirhodium complexes, the head-to-tail (H,T) and head-to-head (H,H) isomers of cis-[Rh2(HNOCCH3)2(CH3CN)6]2+, were synthesized, separated, and characterized following the reaction of Rh2(HNOCCH3)4 with trimethyloxonium tetrafluoroborate in CH3CN. The products were characterized by 1H NMR spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray diffraction. Each bis-amidato isomer has a total of six CH3CN ligands, two along the internuclear Rh–Rh axis, CH3CNax, two in equatorial positions trans to the oxygen atoms of the bridging amidato groups, CH3CNeqO, and two in equatorial positions trans to the amidato nitrogen atoms, CH3CNeqN. When aqueous solutions of the complexes are irradiated with low energy light (λirr ≥ 495 nm, 60 min), both types of CH3CNeq ligands undergo efficient ligand exchange with solvent H2O molecules to form monoaqua, followed by bis-aqua, adducts, releasing two CH3CNeq ligands in the process. The quantum yields, Φ400nm, for the H,T and H,H isomers to form ...