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)(L-1)(2) ] (2) or binuclear [OsX2(NO)(L-2)](2) (3) nitrosyls depending on L. The com plexes are also obtained by reacting (1) with NaNO2 plus HCl. Molecular wei ght determinations are in agreement with mono- and binuclear formulations. The diamagnetic orange-red nitrosyls exhibit nu(NO) at ca. 1890 cm(-1) indi cating NO+ character of the bound nitrogen monoxide. In H-1-n.m.r. a single sharp L-2 methyl signal is in line with the centrosymmetric geometry (4) o f the binuclear nitrosyls. The complexes display both spin-allowed and -for bidden charge transfer transitions in the 1000-200 nm range. Both (2) and ( 3) are electroactive and reductions characteristic of mono- and binuclear c ompositions are observable on the negative side of s.c.e. They react smooth ly with acetylacetone (acacH) in the presence of K2CO3 yielding K[Os(acamo) (L-1)(2)] (5) and K[Os(acac)(acamo)(L-2)] (6) [acamo = deprotonated MeC(O)C (=NOH)C(O)Me] respectively.