Hexatriynediyl Chain Spanning Two Cp*(dppe)M Termini (M = Fe, Ru): Evidence for the Dependence of Electronic and Magnetic Couplings on the Relative Orientation of the Termini

The binuclear complexes Cp*(dppe)FeC≡CC≡CC≡CM(dppe)Cp* (6, M = Fe; 8, M = Ru) were obtained in good yield by treatment of the iron chloro complex Cp*(dppe)Fe–Cl (5) in the presence of KF with the bis(silylated) hexatriyne Me3SiC≡CC≡CC≡CSiMe3 and the ruthenium complex Cp*(dppe)RuC≡CC≡CC≡CSiMe3 (7), respectively. The oxidized species 6(PF6)n (n = 1, 2) and 8(PF6) were obtained in ca. 80% yield by treatment of the parent neutral compounds with 1 or 2 equiv of [Cp2Fe](PF6) in THF or dichloromethane at −78 °C. The CV of these compounds show three reversible waves with a separation larger than 0.5 V. The salts 6(PF6)n (n = 1, 2), and 8(PF6) were characterized by XRD. Quantum chemistry calculations performed at the DFT level on the oxidized species show a strong contribution of the −C6– spacer to the delocalization of the spin density. IR spectra analyzed with the support of TD-DFT calculations are consistent with the delocalization of the odd electron on the fast IR time scale for the two mixed-valence complexe...