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)­{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-κ2-N′N-RuClCp)­(PPh3)2Cp] undergo two essentially
reversible oxidations, the first centered on the (C2bpy-κ2-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 heterometallic binuclear complexes
[Ru­(C2bpy-κ2-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 Re → Ru­(CCbpy)
charge transfer character. The heterometallic complexes also exhibit
irreversible reductions associated with the Re hetereocycle moiety.