Bis-adducts of substituted phenylethynyl on a Ru₂(DMBA)₄ core: Effect of donor/acceptor modifications

The reactions between arylethynes (either BuLi activated or Et₃N assisted) and Ru₂-(RDMBA)₄X₂, where RDMBA is either N,N′-dimethylbenzamidinate (R = H) or N,N′-dimethyl-m-methoxybenzamidinate (R = m-MeO) and X is either Cl^- or NO₃^-, resulted in the compounds Ru₂(RDMBA)₄(C≡CC₆H₄ Y)₂ (Y = H (1a,b), 4-NO₂ (2a,b), 4-CN (3a,b), 3-CN (4a,b), 4-NMe₂ (5a,b); R = H (a), m-MeO (b)). The single-crystal X-ray diffraction study of 1b and 2a revealed the linear alignment of the arylethynyl ligands along the Ru-Ru vector. All of the compounds display two Ru-based one-electron processes, an oxidation and a reduction, and their electrode potentials correlate linearly with the Hammett constants of substituent Y. Compounds 5a,b display an additional pair of one-electron processes attributed to the oxidation of 4-NMe₂ groups, on the basis of which an extensive electron delocalization along the metallayne backbone was inferred.