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 homometallic ruthenium and heterometallic ruthenium–rhenium complexes. The two metal centers are only weakly coupled, as evinced by IR and UV–vis–near NIR spectroelectrochemical experiments and supported by quantum chemical calculations. The alkynyl complexes of the type [Ru­(CCbpy)­{L_n}] ({L_n} = {(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-κ²-<i>N</i>′<i>N</i>-RuClCp)­(PPh₃)₂Cp] undergo two essentially reversible oxidations, the first centered on the (C₂bpy-κ²-<i>N</i>′<i>N</i>-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 heterometallic binuclear complexes [Ru­(C₂bpy-κ²-<i>N</i>′<i>N</i>-ReCl­(CO)₃)­{L_n}] display similar behavior, with initial oxidation on the ruthenium fragment giving rise to a new optical absorption band with Re → Ru­(CCbpy) charge transfer character. The heterometallic complexes also exhibit irreversible reductions associated with the Re hetereocycle moiety