Atsushi Yashiro's research while affiliated with Tokyo Institute of Technology and other places

Control of radical reactivity is regarded as an important concern in the fields of catalysis and materials sciences. Radical species generated from monoruthenium acetylide complexes are, in general, highly reactive, and therefore structural characterization of these species has remained elusive. In this paper, a spectroscopic and structural characterization of the cationic radical species of a monoruthenium diacetylide bearing a Ru tetraphosphine fragment, [trans-(Ar–SC≡C)2Ru(dppe)2]SbCl6 ([1]+SbCl6) [Ar: p-t-BuC6H4; dppe: 1,2-bis(diphenylphosphino)ethane], is presented. The formation of the radical species [1]+ is supported by the vis-NIR, IR, and ESR studies. Furthermore, the solid-state structure of [1]+ reveals a significant contribution of the cumulenic Ru=C=C=S resonance structure. Remarkably, the thermal stability of [1]+ results from the incorporation of the electron-donating (arylsulfanyl)ethynyl ligands and the highly sterically demanding dppe ligands as compared with a monoruthenium complex with less-bulky and less-electron-rich derivatives.

In this work, the design, synthesis, and single‐molecule conductance of ethynyl‐ and butadiynyl‐ruthenium molecular wires with thioether anchor groups [RS=n‐C6H13S, p‐tert‐Bu−C6H4S), trans‐{RS−(C≡C)n}2Ru(dppe)2 (n=1 (1R), 2 (2R); dppe: 1,2‐bis(diphenylphosphino)ethane) and trans‐(n‐C6H13S−C≡C)2Ru{P(OMe)3}4 3hex] are reported. Scanning tunneling microscope break‐junction study has revealed conductance of the organometallic molecular wires with the thioacetylene backbones higher than that of the related organometallic wires having arylethynylruthenium linkages with the sulfur anchor groups, trans‐{p‐MeS−C6H4‐(C≡C)n}2Ru(phosphine)4 4ⁿ (n=1, 2) and trans‐(Th−C≡C)2Ru(phosphine)4 5 (Th=3‐thienyl). It should be noted that the molecular junctions constructed from the butadiynyl wire 2R, trans‐{Au−RS−(C≡C)2}2Ru(dppe)2 (Au: gold metal electrode), show conductance comparable to that of the covalently linked polyynyl wire with the similar molecular length, trans‐{Au−(C≡C)3}2Ru(dppe)2 6³. The DFT non‐equilibrium Green's function (NEGF) study supports the highly conducting nature of the thioacetylene molecular wires through HOMO orbitals.