4,5-Diazafluorene and 9,9'-Dimethyl-4,5-Diazafluorene as Ligands Supporting Redox-Active Mn and Ru Complexes.

4,5-diazafluorene (daf) and 9,9'-dimethyl-4,5-diazafluorene (Medaf) are structurally similar to the important ligand 2,2'-bipyridine (bpy), but significantly less is known about the redox and spectroscopic properties of metal complexes containing Medaf as a ligand than those containing bpy. New complexes Mn(CO)Br(daf) (), Mn(CO)Br(Medaf) (), and Ru(Medaf) () have been prepared and fully characterized to understand the influence of the Medaf framework on their chemical and electrochemical properties. Structural data for , , and from single-crystal X-ray diffraction analysis reveal a distinctive widening of the daf and Medaf chelate angles in comparison to the analogous Mn(CO)(bpy)Br () and [Ru(bpy)] () complexes. Electronic absorption data for these complexes confirm the electronic similarity of daf, Medaf, and bpy, as spectra are dominated in each case by metal-to-ligand charge transfer bands in the visible region. However, the electrochemical properties of , , and reveal that the redox-active Medaf framework in and undergoes reduction at a slightly more negative potential than that of bpy in and . Taken together, the results indicate that Medaf could be useful for preparation of a variety of new redox-active compounds, as it retains the useful redox-active nature of bpy but lacks the acidic, benzylic C-H bonds that can induce secondary reactivity in complexes bearing daf.