Diruthenium(III,III) Bis(alkynyl) Compounds with Donor/Acceptor-Substituted geminal-Diethynylethene Ligands

Reported in this contribution are the preparation and characterization of a series of Ru-2(DMBA)(4) (DMBA = N,N'-dimethylbenzamidinate) bis(alkynyl) compounds, trans-Ru-2(DMBA)(4)(X-gem-DEE)(2) [gem-DEE = sigma-geminal-diethynylethene; X = H (1), (SiPr3)-Pr-i (2), Fc (3); 4-C6H4NO2 (4), and 4-C6H4NMe2 (5)]. Compounds 1-5 were characterized by spectroscopic and voltammetric techniques as well as the single-crystal X-ray diffraction studies of 2 and 3. Both the single-crystal structural data of compounds 2 and 3 and the spectroscopic/voltammetric data indicate that the gem-DEE ligands are similar to simple acetylides in their impact on the molecular and electronic structures of the Ru-2(DMBA)(4) core. Furthermore, density functional theory calculations revealed more extensive pi delocalization in aryl-donor-substituted gem-DEEs and that the hole-transfer mechanism will likely dominate the charge delocalization in Ru-2-gem-DEE-based wires.