Coordinating Tectons: Bimetallic Complexes from Bipyridyl Terminated Group 8 Alkynyl Complexes

Bipyridyl appended ruthenium alkynyl complexes have been used to prepare a range of binuclear homo-metallic ruthenium and hetero-metallic ruthenium-rhenium complexes. The two metal centers are only weakly coupled, as evinced by IR and UV-vis spectroelectrochemical experiments and supported by quantum chemical calculations. The alkynyl complexes of the type [Ru(C≡Cbpy){Ln}] ({Ln} = {(PPh3)2Cp}, {(dppe)Cp*}, {Cl(dppm)2} undergo reversible one electron oxidations centered largely on the alkynyl ligands as has been observed previously for closely related complexes. The homometallic binuclear complexes, exemplified by [Ru(C2bpy-κ-N’N-RuClCp)(PPh3)2Cp] undergo two essentially reversible oxidations, the first centered on the (C2bpy-κ-N’N-RuClCp) moiety and the second on the Ru(C≡Cbpy)(PPh3)2Cp fragment, leading to radical cations that can be described as Class II mixed-valence complexes. The hetero-metallic binuclear complexes [Ru(C2bpy-κ-N’N-ReCl(CO)3){Ln}] display similar behavior, with initial oxidation on the ruthenium fragment giving rise to a new optical absorption band with ReàRu(C≡Cbpy) charge transfer character. The heterometallic complexes also exhibit irreversible reductions associated with the Re hetereocycle moiety.