Redox and photoactive metallyne sigma-alkynyl complexes with cross-conjugated ligands

With the goal of realizing novel organometallic molecular wires for molecular electronic devices, electron delocalization in transition-metal complexes containing linear σ-polyynyl ligands have received a great deal of attention over the last decade. Largely unexplored are metal compounds containing cross-conjugated polyynes, the simplest of which being iso-triacetylene (geminal-diethynylethene or gem-DEE). Recently, on the basis of theoretical modeling, it has been postulated that oligomers of gem-DEE have conductance attenuated by quantum interference effects. We hypothesized that the combination of gem-DEE ligands with both redox (Ru2) and photoactive (Cr) transition metals will help to unravel the cross-conjugation and quantum interference effects. However, the metallation chemistry of gem-DEE ligands is limited to Pt(II) compounds which limits the investigation of the pi-conjugation therein, due to the electronic saturation of a d8 configuration in a square planar environment. Presented herein are the syntheses and characterizations of the first transition-metal complexes containing cross-conjugated ligands beyond Pt(II). An investigation of the pi-conjugation within was performed on two classes of metal σ-gem-DEE complexes in hope of elucidating the cross-conjugation and quantum interference effects: bis-[M]-σ-gem-DEE (where [M] is Ru2(III,III) and Cr(III) which may be the starting point for oligomers; and dimeric [M]-μ- gem-DEE-[M] (where [M] is Ru2), which allows for the assessment of the electronic coupling of the two metal termini via the gem-DEE bridge