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 (Me(2)daf) 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 Me(2)daf as a ligand than those containing bpy. New complexes Mn(CO)(3)Br(daf) (2), Mn(CO)(3)Br(Me(2)daf) (3), and [Ru(Me(2)daf)(3)](PF6)(2)(5) have been prepared and fully characterized to understand the influence of the Me(2)daf framework on their chemical and electrochemical properties. Structural data for2,3, and5from single-crystal X-ray diffraction analysis reveal a distinctive widening of the daf and Me(2)daf chelate angles in comparison to the analogous Mn(CO)(3)(bpy)Br (1) and [Ru(bpy)(3)](2+)(4) complexes. Electronic absorption data for these complexes confirm the electronic similarity of daf, Me(2)daf, and bpy, as spectra are dominated in each case by metal-to-ligand charge transfer bands in the visible region. However, the electrochemical properties of2,3, and5reveal that the redox-active Me(2)daf framework in3and5undergoes reduction at a slightly more negative potential than that of bpy in1and4. Taken together, the results indicate that Me(2)daf 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.