A new diruthenium(II,III) compound, Ru₂(CCPh)(PhNpy)₄·2CH₂Cl₂, with an axial η¹-acetylide ligand

Abstract

The compound Ru₂(CCPh)(PhNpy)₄ was prepared by reacting Ru₂Cl(PhNpy)₄ and Li(CCPh) in a toluene-tetrahydrofuran mixture. The product, which was purified by column chromatography on a neutral alumina column using benzene as an eluting agent, was obtained in ca. 70% yield. Crystals of composition Ru₂(CCPh)(PhNpy)₄·2CH₂Cl₂ (1), obtained from a CH₂Cl₂-hexane mixture (1:1 V/V) at -20 °C, belong to the triclinic system, space group P 1, with unit cell dimensions of a = 13.857(6), b = 19.338(9), c = 10.463(4) Å, α = 104.03(4)°, β = 108.25(4)°, γ = 93.55(4)°, V = 2554(2) ų, Z = 2. The structure was refined to R = 0.064 (R_w = 0.073). The complex has a diruthenium(II,III) unit bridged by four PhNpy- ligands, all oriented in the same direction. The axial ligand on the ruthenium is an η¹acetylide, CCPh. The Ru(1)-Ru(2) distance in 1 is 2.319(2) Å. The Ru(1)-C(1) and average Ru---N distances are 2.08(3) and 2.07[2] Å, respectively. The C(1)-C(2) distance is 1.14(3) A and the Ru(2)- Ru(1)-C(1) group is essentially linear. The Ru(1)- C(1)-C(2) and C(1)-C(2)-C(3) angles are 172(3) and 173(3)°, respectively. The complex is paramagnetic, exhibiting a moment of 3.92 μ_B (308 K). The Ru---Ru bond order is 2,5 with a σ²∏⁴δ²- (δ∏)³ ground electronic configuration. The electronic spectrum of the compound in CH₂ Cl₂ displays two absorption bands in the visible region, viz., at 735 nm (ε = 1050 M^-1 cm^-1) and at 480 nm (ε = 1630 M^-1 cm^-1). Cyclic voltammetry in CH₂Cl₂ in the presence of 0.1 M (TBA)PF₆ at 100 mV s^-1 shows nearly reversible metal-centered one-electron oxidation and reduction processes at +0.235 V (δE_p = 70 mV) and -0.985 V (δE_p = 70 mV), respectively, vs. an Ag---AgCl reference electróde. A quasireversible oxidation at +1.050 V is also observed.