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
Résumé
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 Fe chloro complex Cp*(dppe)Fe-Cl (5) in the presence of KF with the bis(silylated) hexatriyne Me3SiC≡CC≡CC≡CSiMe3 and the Ru complex Cp*(dppe)RuC≡CC≡CC≡CSiMe3 (7), resp. The oxidized species 6(PF6)n (n = 1, 2) and 8(PF6) were obtained in ∼80% yield by treatment of the parent neutral compds. with 1 or 2 equiv of [Cp2Fe](PF6) in THF or CH2Cl2 at -78°. The CV of these compds. show three reversible waves with a sepn. larger than 0.5 V. The salts 6(PF6)n (n = 1, 2), and 8(PF6) were characterized by XRD. Quantum chem. calcns. performed at the DFT level on the oxidized species show a strong contribution of the -C6- spacer to the delocalization of the spin d. IR spectra analyzed with the support of TD-DFT calcns. are consistent with the delocalization of the odd electron on the fast IR time scale for the two mixed-valence complexes 6(PF6) and 8(PF6). Combined ESR measurements on rigid glass and on single crystal samples clearly establish that the electronic properties of MV species and particularly their magnetic anisotropies depend on the conformation of the mols. In the case of the doubly oxidized species 6(PF6)2, which carries two unpaired electrons, the singlet vs. triplet ground states can be inverted by the rotation of one metal end with respect to the other around the all-C chain axis. Very strong NIR bands are found for the sym. 6(PF6) and nonsym. 8(PF6) MV (mixed-valence) derivs. allowing the detn. of very large electronic couplings (Hab = 3070 and 4025 cm-1, resp.).