Sterically Governed Redox Reactions. One-Electron Oxidation of Ytterbocenes by Diazabutadienes: Formation of Radical-Anionic Diazabutadiene vs Covalently Bonded Imino–Amido Ligand

The reactions of ytterbocenes (C5MenH5–n)2Yb(THF)x (n = 1, 4, 5; x = 1, 2) with 1,4-diazabutadienes (DAD) 2-RC6H4NC(Me)C(Me)NC6H4R-2 (R = H, Me) revealed a new example of steric control on redox processes. The steric saturation of the ytterbium coordination sphere proved to be a crucial factor which determines the outcome of the metal–ligand electron transfer reaction and the mode of transformation of the DAD ligand. The reactions of ytterbocenes containing bulky C5Me5 or C5Me4H ligands lead to the formation of YbIII complexes coordinated by radical-anionic diazabutadiene ligands: (C5MenH5–n)2YbIII(DAD•–) (n = 4, 5). In the case of the less sterically demanding C5MeH4 ligand and PhNC(Me)C(Me)NPh, oxidation of the ytterbium atom affords a metallocene-type YbIII complex containing a covalently bonded imino–amido fragment, (η5-C5MeH4)2Yb(N(C6H5)C(H)(Me)C(Me)NC6H5). All new complexes have been characterized by X-ray diffraction studies and magnetic and spectroscopic measurements.