Reported in this Article are the preparation and characterization of a series of new Ru<inf>2</inf>(II,III) compounds bearing one cross-conjugated σ-geminal-diethynylethene ligand (gem-DEE), namely, Ru<inf>2</inf>(Xap)<inf>4</inf>(Y-gem-DEE) (Xap = N,N′-anilinopyridinate (ap) or 2-(3,5-dimethoxy)anilinopyridinate (DiMeOap), and Y = Si<sup>i</sup>Pr<inf>3</inf> (1) or H (2)) and [Ru<inf>2</inf>(ap)<inf>4</inf>]<inf>2</inf>(μ-gem-DEE) (3). Compounds 1-3 were characterized by spectroscopic and voltammetric techniques as well as the single crystal X-ray diffraction study of 2a. The X-ray structural data of 2a and the spectroscopic/voltammetric data of compounds 1 and 2 indicate that the gem-DEE ligands are similar to simple alkynyls in their effects on the molecular and electronic structures of the Ru<inf>2</inf>(Xap)<inf>4</inf> moiety. Similar to the previously studied [Ru<inf>2</inf>(ap)<inf>4</inf>]<inf>2</inf>(μ-C<inf>2n</inf>) type compounds, dimer 3 exhibits pairwise 1e<sup>-</sup> oxidations and reductions, albeit the potential splits within the pair (ΔE<inf>1/2</inf>) are significantly smaller than those of [Ru<inf>2</inf>(ap)<inf>4</inf>]<inf>2</inf>(μ-C<inf>4</inf>). The electronic absorption spectra of the reduced and oxidized derivatives of 1a and 3 were determined using spectroelectrochemistry methods. No discernible intervalence charge transfer transition (IVCT) was detected in the near-IR spectrum for either 3<sup>-</sup> or 3<sup>+</sup>, suggesting that the Ru<inf>2</inf>-Ru<inf>2</inf> coupling in these mixed-valence states is weak. DFT calculations on a model compound of 3 yielded six singly occupied molecular orbitals (SOMOs), which have Ru<inf>2</inf> contributions similar to those previously calculated for the [Ru<inf>2</inf>(ap)<inf>4</inf>]<inf>2</inf>(μ-C<inf>2n</inf>) type compounds. Among six SOMOs, SOMO-2 is the only one containing substantial dπ-π(gem-DEE) character across the entire Ru<inf>2</inf>-μ-gem-DEE-Ru<inf>2</inf> linkage, which explains the weakened Ru<inf>2</inf>-Ru<inf>2</inf> coupling.

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Journal Inorganic Chemistry
Forrest, W.P. (William P.), Choudhuri, M.M.R. (Mohommad M. R.), Kilyanek, S.M. (Stefan M.), Natoli, S.N. (Sean N.), Prentice, B.M. (Boone M.), Fanwick, P.E. (Phillip E.), … Ren, T. (Tong). (2015). Synthesis and Electronic Structure of Ru2(X ap)4(Y- gem -DEE) Type Compounds: Effect of Cross- Conjugation. Inorganic Chemistry, 54(15), 7645–7652. doi:10.1021/acs.inorgchem.5b01315