Divinylphenylene- and Ethynylvinylphenylene-Bridged Mono‑, Di‑, and Triruthenium Complexes for Covalent Binding to Gold Electrodes

In
this work, we describe the preparation and the properties of
the novel bis­(vinylphenylene)-bridged diruthenium complexes {Ru­(CO)­(η2-O2C-p-C6H4SAc)­(PiPr3)2}2(μ-CHCH-C6H4-CHCH-1,3
and -1,4) (6 and 7), the bis­(ethynylphenylene)-bridged
complex trans-[AcS-p-C6H4-CC-Ru­(dppe)2-CC-p-C6H4-CC-Ru­(dppe)2-CC-p-C6H4-SAc] (11), the bis­(1-ethynyl-4-vinylphenylene)-bridged triruthenium complex trans-[{Ru­(dppe)2}­{−CC-p-C6H4-CHCH-Ru­(CO)­(η2-O2C-p-C6H4SAc)­(PiPr3)2}2]
(8), and the monometallic congeners Ru­(CHCH-p-C6H4SAc)­(CO)­(η2-O2C-p-C6H4SAc)­(PiPr3)2 (4) and trans-[Ru­(dppe)2(−CC-p-C6H4-SAc)2] (10). These mono-, bi-, and trimetallic complexes feature terminal acetyl-protected
thiol functions for covalent binding to gold surfaces or for bridging
the gaps of gold nanoelectrodes. All complexes display low oxidation
potentials, and IR studies of the neutral complex 8 and
of its various oxidized forms 8n+ indicate the high vinyl/ethynyl bridging ligand contribution
to the oxidation processes and complete charge delocalization in all
available oxidation states (n = 1–3). Strong
delocalization of the relevant occupied frontier MOs over the entire
π-conjugated {Ru}–bridge–{Ru′}–bridge–{Ru}
backbone is also supported by DFT calculations on the parent complexes V8 and V8OMe. The benzoate
ligand bearing the functional group for gold binding is outside the
conjugation path and insulates the wirelike central portion of these
molecules from their periphery. Upon insertion into molecular junctions,
these molecules are expected to enhance sequential tunneling and to
facilitate Coulomb blockade behavior. They will thus contribute to
our understanding of structure–property relationships for metal-containing
molecular wires.