Different delocalization ranges of asymmetric isocyanidometal-bridged trinuclear compounds by regulating the metal center and the ligand electron-donating ability

A series of asymmetric isocyanidometal-bridged compounds <i>cis</i>-[Cp⁵(dppe)M(μ-CN)Ru(bpy)₂(μ-NC)Ru(dppe)Cp<i>^x</i>][PF₆]<i>₂</i> (<b><i>N²</i>⁺</b>[PF₆]<i>₂</i>: M = Fe and <i>x</i> = 0, <i>N</i> = 1; M = Fe and <i>x</i> = 1, <i>N</i> = 2; M = Ru and <i>x</i> = 0, <i>N</i> = 3; M = Ru and <i>x</i> = 1, <i>N</i> = 4. Cp⁰ = cyclopentadienly; Cp¹ = 1-methyl-cyclopentadienly; Cp⁵ = 1,2,3,4,5-pentamethylcyclopentadienly, dppe = 1,2-bis(diphenylphosphino)ethane, bpy = 2,2′-bipyridine) were fully characterized. For the one- and two-electron oxidized states of <b><i>N²</i>⁺</b>[PF₆]<i>₂</i>, <b><i>N³</i>⁺</b>[PF₆]<i>₃</i>, and <b><i>N⁴</i>⁺</b>[PF₆]<i>₄</i>, both their MMCT and electronic delocalization properties were investigated. The investigation results show that both the one-electron oxidized asymmetric Fe-Ru-Ru compounds <b>1³⁺</b> and <b>2³⁺</b> are localized, the charge being on the Fe centers. When the terminal Fe is substituted with Ru, the charge of <b>3³⁺</b> is mainly delocalized between the Ru(2) and Ru(3) centers, while upon an addition of a methyl group on the terminal 1,3-cyclopentadienly ligand, the charge of <b>4³⁺</b> is further delocalized into the Ru(1) center. Furthermore, for the two-electron oxidized asymmetric compounds <b>1⁴⁺</b>–<b>4⁴⁺</b>, both the Fe-Ru-Ru and Ru-Ru-Ru series are highly delocalized.