Aquo chemistry of monoarene complexes of osmium(II) and ruthenium(II)

Article abstract of DOI:10.1021/ic50216a028

A number of derivatives of η-C₆H₆Os^II (BzOs^II) were prepared, exploiting the three positions not preempted by the arene ring and emphasizing ligands which are saturated. The species synthesized include [BzOs(NH₃)₃]²⁺, [BzOs(NH₃)₂Cl]⁺, and [BzOs(en)Cl]⁺. It was shown that a 2+ ion, presumably [BzOs(H₂O)₃]²⁺, is produced in an acidic solution of BzOsCl₂ when Cl^- is removed by Ag⁺. The determination of the acidity of the coordinated water for the aquo species is complicated by the condensation of the hydroxo form. However, [BzOs(en)H₂O]²⁺ prepared from [BzOs(en)Cl]⁺ by adding Ag⁺ behaves normally, and the value of pK_a was found to be 6.3 at 20°C; for [BzOs(NH₃)₂H₂O]²⁺ it was found to be 6.4, and for [BzRu(en)H₂O]²⁺ it is 7.9. The quotient governing association of Cl^- with [BzOs(en)H₂O]²⁺ was measured as 1.1 × 10². The acidity of the aquo ion and the stability of the chloride complex testify to the electron-withdrawing ability of the arene ring.