Electrochemistry of Octamethyl[3]ruthenocenophane: Synthesis and Structure of the First Dicationic Derivative of Ruthenocene, [{η⁵:η⁵-C₅Me₄(CH₂)₃C₅Me₄}Ru(NCMe)](PF₆)₂

The octamethyl[3]ruthenocenophane {η⁵:η⁵-C₅Me₄(CH₂)₃C₅Me₄}Ru (1) was synthesized by the reaction of RuCl₃·3H₂O with HC₅Me₄(CH₂)₃C₅Me₄H in triethylene glycol at 200 °C. Other sterically congested ruthenocene derivatives, (η⁵-C₅Me₅)₂Ru (2) and (η⁵-C₅Me₄H)₂Ru (3), were also prepared in high yields by this simple method. The cyclic voltammogram of 1 in CH₂Cl₂ shows a reversible 1e oxidation wave at E_1/2 = +0.36 V vs SCE, while that in CH₃CN exhibits a 2e oxidation wave at +0.30 V vs SCE and a smaller 2e reduction wave at —0.04 V vs SCE. The bulk electrolysis of 1 at +0.30 V vs SCE in 0.1 M NH₄PF₆/CH₃CN gave the dication salt containing CH₃CN as an additional ligand, [{η⁵:η⁵-C₅Me₄(CH₂)₃C₅Me₄}Ru(NCMe)](PF₆)₂(4), almost quantitatively. The ECE mechanism including the CH₃CN coordination/dissociation process was suggested for the redox reaction between 1 and its dication [1·NCCH₃]²⁺ based on the cyclic voltammograms of 1–4 as well as the crystal structure analysis of 1 and 4. Crystal data for 1: C₂₁H₃₀Ru, space group P2₁/a, a = 15.272(2) Å, b = 11.090(1) Å, c = 10.991(2)Å, β = 101.07(2)°, V = 1826.8(4) ų, Z = 4, R = 0.052, and R_w= 0.084 based on 4435 reflections with [|F_o| > 3σ(F_o)]. Crystal data for 4: C₂₃H₃₃F₁₂NP₂Ru, space group Pmnm, a = 11.031(1) Å, b = 14.883(1) Å, c = 8.973(1) Å, V = 1473.1(2) ų, Z = 2, R = 0.059, and R_w= 0.085 based on 2528 reflections with [|F_o| > 3σ(Fo)].