Diruthenium(ii)-capped oligothienylethynyl bridged highly soluble organometallic wires exhibiting long-range electronic coupling

Abstract

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with –CC–H termini have been successfully synthesized through stepwise Pd(0)/Cu(I)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(II) diacetylide complexes (O1-Ru₂, O3-Ru₂, O5-Ru₂ and O7-Ru₂, respectively) have been prepared by the reaction of cis-Ru(dppe)₂Cl₂ and NaPF₆ in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(II)–Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(II)–CC–Ph]-capped diacetylide organometallic wires (O1-Ru₂-Ph, O3-Ru₂-Ph, O5-Ru₂-Ph and O7-Ru₂-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(II)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(II)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(II) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.