Osmium thioether chemistry: synthesis and single-crystal X-ray structures of [Os([9]aneS3)2][PF6]2·2MeNO2, [Os(4-MeC6H4Pri)([9]aneS3)][BPh4]2·MeNO2 and [OsH(CO)(PPh3)([9]aneS3)]PF6·0.5CH2Cl2([9]aneS3= 1,4,7-trithiacyclononane)

Abstract

Treatment of [{OsCl₂(4-MeC₆H₄Prⁱ)}₂] with 4 molar equivalents of [9]aneS₃ in EtOH for 48 h followed by addition of NH₄PF₆ affords the bis(sandwich) complex [Os([9]aneS₃)₂][PF₆]₂ in 55% yield. An alternative and more direct route is by reaction of [NH₄]₂[OsCl₆] with 2 molar equivalents of [9]aneS₃ in refluxing water–dimethylformamide–MeOH (3 : 1 : 1 v/v/v) for 48 h followed by addition of NH₄PF₆. The complex [Os([9]aneS₃)₂][PF₆]₂·2MeNO₂ crystallises in the monoclinic space group P2₁/a(alt. P2₁/c, no. 14) with a= 9.6621(5), b= 15.1573(8), c= 10.6367(7)Å, β= 100.524(5)° and Z= 2. A single-crystal X-ray structure determination shows a centrosymmetric cation with homoleptic thioether co-ordination at Os^II, Os–S(1) 2.3313(18), Os–S(4) 2.3380(19) and Os–S(7) 2.3408(20)Å, consistent with a d⁶ metal centre. The ion [Os([9]aneS₃)₂]²⁺ shows a reversible oxidation at E_½=+1.16 V vs. ferrocene–ferrocenium. Coulometry confirms this oxidation to be a one-electron process. Electrochemical or chemical oxidation of [Os([9]aneS₃)₂]²⁺ gives [Os([9]aneS₃)₂]³⁺ which has been characterised by electronic and ESR spectroscopy. Reaction of [{OsCl₂(4-MeC₆H₄Prⁱ)}₂] with 2 molar equivalents of [9]aneS₃ in MeOH followed by addition of NaBPh₄ affords the mixed-sandwich complex [Os(4-MeC₆H₄Prⁱ)([9]aneS₃)][BPh₄]₂ in 65% yield. The complex [Os(4-MeC₆H₄Prⁱ)([9]aneS₃)][BPh₄]₂·MeNO₂ crystallises in the triclinic space group P, a= 11.5027(8), b= 13.8509(13), c= 18.3983(12)Å, α= 94.72(1), β= 105.01(3)γ= 91.28(1)° and Z= 2. The crystal structure shows facial co-ordination of both [9]aneS₃ and 4-MeC₆H₄Prⁱ at octahedral Os^II. Interestingly, there is an unusual disorder of the trithia macrocycle with two enantiomers of [9]aneS₃ being present in the crystal: the two forms of the macrocycle were successfully modelled. Reaction of [MH₂(CO)(PPh₃)₃] with 1 molar equivalent of [9]aneS₃ in the presence of NH₄PF₆ in refluxing acetone (M = Ru) or refluxing 2-methoxyethanol (M = Os) for 2 h under N₂ gives [MH(CO)(PPh₃)([9]aneS₃)]PF₆. The complex [OsH(CO)(PPh₃)([9]aneS₃)]PF₆·0.5CH₂Cl₂ crystallises in the monoclinic space group P2₁/n(alt. P2₁/c, no. 14) with a= 15.955(6), b= 21.929(9), c= 8.895(7)Å, β= 96.69(8)° and Z= 4. The structure shows octahedral Os^II with [9]aneS₃ bound facially, Os–S(1) 2.377(3)(trans to CO), Os–S(4) 2.369(3)(trans to PPh₃), Os–S(7) 2.402(3)(trans to H), Os–H 1.60(9), Os–P 2.3344(24) and Os–C 1.868(11)Å. The reactivity of [MH(CO)(PPh₃)([9]aneS₃)]⁺ with O₂ and chlorinated solvents is discussed.