Synthesis,characterization and reactivity of electrophilic mono- and binuclear nitrosyls of osmium(II)ketoximates

The reaction of [OsX₂(HL)(L)] (1) {X = Cl or Br; HL = PhC(O)C(=NOH)Ph (HL¹) or PhC(O)C(=NOH)Me (HL2)] with n-BuONO yields mononuclear [OsX(NO)(L¹)₂] (2) or binuclear [OsX₂(NO)(L²)]₂2 (3) nitrosyls depending on L. The complexes are also obtained by reacting (1) with NaNO₂ plus HCl. Molecular weight determinations are in agreement with mono- and binuclear formulations. The diamagnetic orange-red nitrosyls exhibit (NO) at ca. 1890 cm^–1 indicating NO⁺ character of the bound nitrogen monoxide. In ¹H-n.m.r. a single sharp L² methyl signal is in line with the centrosymmetric geometry (4) of the binuclear nitrosyls. The complexes display both spin-allowed and -forbidden charge transfer transitions in the 1000–200 nm range. Both (2) and (3) are electroactive and reductions characteristic of mono- and binuclear compositions are observable on the negative side of s.c.e. They react smoothly with acetylacetone (acacH) in the presence of K2CO3 yielding K[Os(acamo)(L1)2] (5) and K[Os(acac)(acamo)(L2)] (6) [acamo = deprotonated MeC(O)C(=NOH)C(O)Me] respectively.