Non-symmetrically substituted ruthenocenes: Synthesis, structures, and bond nature. Electronic effects of substituents in ruthenocene

Non-symmetrically substituted ruthenocenes CpRuCp´ (Cp´ = C5H4CHO (1a), C5H4COMe (1b), C5H4SiMe3 (1c), 1,3-C5H3(SiMe3)2 (1d), and Cp* (1e)) were synthesized in high yields by the reaction of [CpRu(MeCN)3]+ with cyclopentadienide anions. The structures of complexes 1a,b,d were determined by X-ray diffraction analysis. According to the energy partition analysis data, donor substituents strengthen the interaction between the [RuCp]+ and Cp´– fragments, whereas acceptor substituents weaken the interaction. This bond is predominantly electrostatic (56—59%). Based on the calculated electrostatic potentials at the ruthe-nium nucleus, it is shown that the donor ability of the substituents decreases in the following order: NMe2 > NH2 > OMe > Me ≈ OH > Rc > Fc ≈ Allyl ≈ H > SiMe3 > CH=CH2 ≈ Ph > PH2 > > SH ≈ F > SiH3 ≈ C≡CH > Cl > Br ≈ I ≈ COOMe > COOH > COMe > CF3 > CHO > CN > NO2.