Ruthenium thioether chemistry: the synthesis and structure of a host–guest complex [Ru([9]aneS3)2][BPh4]2·2Me2SO, and of [Ru([9]aneS3)2][BPh4]2·2MeNO2 and [Ru([18]aneS6)][BPh4]2([9]aneS3=1,4,7-trithiacyclononane, [18]aneS6= 1,4,7,10,13,16-hexathiacyclo-octadecane)

Abstract

Reaction of [{RuCl₂(arene)}₂](arene = C₆H₆, C₆Me₆, or 4-MeC₆H₄Prⁱ) with four molar equivalents of 1,4,7-trithiacyclononane ([9]aneS₃) in MeOH at 293 K affords a colourless or pale yellow solution. Addition of NaBPh₄ gives [Ru([9]aneS₃)₂][BPh₄]₂ which can be recrystallised from Me₂SO, MeNO₂, or MeCN. The complex [Ru([9]aneS₃)₂][BPh₄]₂·2Me₂SO crystallises in the monoclinic space group P2₁/c with a= 14.134(3), b= 11.096 3(19), c= 19.743(4)Å, β= 94.497(16)°, and Z= 2. The single crystal X-ray structure of the complex shows a centrosymmetric cation with homoleptic thioether co-ordination to an octahedral Ru^II ion. Each macrocycle is bound facially to the metal centre, Ru–S(1) 2.327 2(14), Ru–S(4) 2.335 7(14), Ru–S(7) 2.333 1 (14)Å. Two molecules of Me₂SO are associated with each [Ru([9]aneS₃)₂]²⁺ cation; these interact with the rear cavities of the co-ordinated trithia macrocycles to form a host/guest-type interaction, with the oxygen atoms involved in hydrogen bonding with the methylene protons of [9]aneS₃, O ⋯ H 2.201(8), 2.419(8), 2.790(8), and 3.291(8)Å. The Me₂SO molecules in [Ru([9]aneS₃)₂][BPh₄]₂·2Me₂SO can be replaced by MeCN or MeNO₂ by recrystallisation of the complex from these solvents. The complex [Ru([9]aneS₃)₂][BPh₄]₂·2MeNO₂ crystallises in the monoclinic space group P2₁/n with a= 11.200(5), b= 18.247(13), c= 14.323(17)Å, β= 90.78(4)°, and Z= 2. The single crystal X-ray structure of this species, however, shows that there is no secondary interaction between the two MeNO₂ molecules and the complex cation, the closest contact between the methylene protons and the oxygen atoms of MeNO₂ being over 3.5 Å. The complex cation [Ru([9]aneS₃)₂]²⁺ shows a quasi-reversible oxidation at platinum electrodes in MeCN at E_½=+1.41 V vs. ferrocene–ferrocenium indicating that Ru^II is highly stabilised by RuS₆ co-ordination. Reaction of RuCl₃·3H₂O with one molar equivalent of 1,4,7,10,13,16-hexathiacyclo-octadecane ([18]aneS₆) in refluxing dimethylformamide (dmf)–methanol affords [Ru([18]aneS₆)]Cl₂as a white precipitate. Dissolution of this product in hot water followed by addition of an excess of NaBPh₄ yields [Ru([18]aneS₆)][BPh₄]₂ which crystallises in the monoclinic space group P2₁/c, with a= 12.801(4), b= 10.663(3), c= 20.036(9)Å, β= 109.09(3)°, and Z= 2. The single crystal X-ray structure of the complex shows a centrosymmetric cation with hexathia co-ordination of the macrocycle to Ru^II in a meso configuration, Ru–S(1) 2.322 2(23), Ru–S(4) 2.332 6(25), Ru–S(7) 2.337 2(23)Å, and confirms that [18]aneS₆ can readily fully encapsulate a relatively large cation such as Ru^II. The oxidative chemistry of [Ru([9]aneS₃)₂]²⁺ and [Ru([18]aneS₆)]²⁺ is discussed.