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)(2)Yb(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 Yb-III complexes coordinated by radical-anionic diazabutadiene ligands: (C5MenH5-n)(2)Yb-III(DAD(center dot-)) (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 Yb-III complex containing a covalently bonded imino-amido fragment, (eta(5)-C5MeH4)(2)Yb(N(C6H5)C(H)(Me)C(Me)=NC6H5). All new complexes have been characterized by X-ray diffraction studies and magnetic and spectroscopic measurements.