Electronic structure of ruthenium(II) polyynyl complexes

The electronic structure of the polyynyl complexes [Ru{(C≡C)_nR}(PH₃)₂Cp] (n = 1-6; R = H, CH₃, C₆H₅, C₆H₄NH_2-p, C₆H₄NO_2-p, CN), the diynyl compounds [Ru{(C≡C)₂R}(CO)₂Cp], and the oxidized species [Ru{(C≡C)_nC₆H₅} (PH₃)₂Cp]⁺ have been studied using DFT methods. The optimized geometries are in good agreement with the few experimental structures available. The electronic structures are best described in terms of a strong σ-bonding component and a weaker interaction between the filled metal d orbitals and filled polyyne π orbitals. The charge distribution in the molecules and the energies and localization of the frontier orbitals have been examined to help rationalize the reactivity patterns emerging for this important class of compounds.