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)(Pi
Pr3)2}2(μ-CHCHC6H4 -CHCH-1,3 and -1,4) (6 and 7), the bis-
(ethynylphenylene)-bridged complex trans-[AcS-p-C6H4-CCRu(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)(Pi
Pr3)2}2] (8), and the monometallic congeners Ru(CHCH-p-C6H4SAc)(CO)(η2
-O2C-pC6H4SAc)(Pi
Pr3)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.