η⁴-Bonding in (Arene)ruthenium Complexes of Octamethylnaphthalene

The reaction of [RuCl₂(arene)]₂ (arene = p-cymene, benzene, mesitylene, prehnitene, hexamethylbenzene, 1,3,5-triethylbenzene, and 1,3,5-triisopropylbenzene) with octamethylnaphthalene (OMN) under three sets of conditions leads to the bis(arene) complexes [Ru(OMN)(arene)]²⁺. These 18-electron cations containing two η⁶-rings can be easily reduced with sodium amalgam to complexes with the formula Ru(OMN)(arene). The neutral complexes contain a η⁶-arene and a η⁴-OMN ring as shown by a single-crystal X-ray crystallographic analysis of Ru(OMN)(C6Me6) [P2_l/n space group, Z = 8, a = 19.768 (6) Å, b = 14.524 (3) Å, c = 19.676 (6) Å, β = 117.13 (2)°]. Protonation of the complexed OMN ring in Ru(OMN)(C₆H₆) yields an isolable cyclohexadienyl species, [Ru(C₁₀Me₈H)(C₆H₆)]⁺, while reaction of Ru(OMN)(C₆H₆) with Cr-(CO)₃(CH₃CN)₃ produces the binuclear compound (C₆H₆)Ru(μ-OMN)Cr(CO)₃. The reactivity of the neutral complexes with hydrogen is discussed.