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Nils Rotthowe, Jakob Zwicker, Rainer F. Winter

Organometallics, 2019, 38, 14, 2782-2799

We present four new divinylarylene-bridged diruthenium complexes of the type {Ru(CO)Cl(PⁱPr₃)₂}₂(μ-CH═CH–Ar–CH═CH) with naphthalene-1,4-diyl (Ru₂NA), 2,1,3-benzothiadiazole (Ru₂BTD), bis(benzothiadiazolyl)ethene (Ru₂^vBTD₂), or bis(benzothiadiazolyl)ethyne (Ru₂^eBTD₂) as the arylene units. The radical cations of the complexes with shorter arylene bridges are intrinsically valence-delocalized on the IR time scale. In contrast to phenylene-bridged [{Ru(CO)Cl(PⁱPr₃)₂}₂(μ-CH═CH–C₆H₄-1,4-CH═CH)]²⁺ (Ru₂-p-phen²⁺), the dioxidized forms of complexes Ru₂BTD and Ru₂NA are electron paramagnetic resonance (EPR) silent. Replacing the E-stilbenediyl linker of the complex {Ru(CO)Cl(PⁱPr₃)₂}₂(μ-CH═CH–C₆H₄–CH═CH–C₆H₄–CH═CH) (Ru₂^vp-phen₂) by ^vBTD₂ or ^eBTD₂ enhances electronic coupling and charge delocalization of their one-electron-oxidized mixed-valent forms. While the latter radical cations are still charge-localized species on the IR time scale, they are fully delocalized on the slower EPR time scale. As a token of a quinoidally distorted bridge, Ru₂^eBTD₂²⁺ features a characteristic IR stretch of a cumulenic C═C═C═C increment. For compound Ru₂^vBTD₂, rearrangement to a quinoidal structure is manifested through potential inversion (i.e., the half-wave potential of the second oxidation is lower than that of the 0/1+ redox couple) in the CH₂Cl₂/NBu₄BAr^F electrolyte. The BTD complexes are intensely colored in their neutral states and exhibit strong NIR absorptions of their radical cations as well as of their dioxidized forms.

https://pubs.acs.org/doi/10.1021/acs.organomet.9b00318