REACTIVITY OF COBALT(II) COMPLEXES [CO(OEPH(3))(2)X(2)] (E=P OR AS, X=CL, BR, I OR NCS) WITH SO2 UNDER AEROBIC AND ANAEROBIC CONDITIONS - CRYSTAL-STRUCTURE OF COCRYSTALLISED [CO(OPME(3))(3)(OH2)(2)]I-2 AND [CO(OPME(3))(3)(OH2)(3)]I-2

Pseudo-tetrahedral complexes [Co(OEPh(3))(2)X(2)] (E = P or As; X = CI, Br, I or NCS) and [Co(OPMe(3))(2)I-2] have been isolated by conventional synthesis from ethanolic solutions of the appropriate hydrated metal salt and Ph(3)EO. Their reactivity with sulfur dioxide has been examined in the solid state (anaerobic conditions) and for toluene slurries or solutions (aerobic and anaerobic conditions). The [Co(OEPh(3))(2)X(2)] (X = CI or Br) complexes show no reactivity and are recovered unchanged from all forms of exposure to SO2. However, [Co(OEPh(3))(2)X(2)] (E = P or As, X = I or NCS) reacted slowly with SO2 in the solid state to form 1:1 adducts, as evidenced by elemental analyses and mass changes. The visible spectra of the precursor complexes and their adducts are similar, suggesting that SO2 is ligand-bound. On exposure to air. SO2-saturated toluene slurries and solutions of [Co(OPPh(3))(2)I-2] underwent a complex oxidation process resulting in the quantitative isolation of CoSO4 . H2O, (Ph(3)PO)(Ph(3)POH)(HSO4) and I-2. Visible spectroscopy indicates at least one iodine-containing intermediate. which may be analogous to the cocrystallised [Co(OPMe(3))(3)(OH2)(2)]I-2 and [Co(OPMe(3))(3)(OH2)(3)]I-2 recovered from the reaction of [Co(OPMe(3))(2)I-2] with SO2 and air. SO2-Saturated solutions of [Co(OAsPh(3))(2)I-2] afforded (Ph(3)As-OH)(HSO4), I-2, Ph(3)AsI(4) and CoSO4 . H2O in the presence of air, although I-2 and Ph(3)AsI(4) appear to be produced even under anaerobic conditions. Aerobic reactivity was also observed for [Co(OEPh(3))(2)(NCS)(2)] (E = P or As); CoSO4 . H2O and ligand derivatives of sulfuric acid were again isolated, however, the fate of the thiocyanate anion remains unclear. The inactivity of [Co(OPPh(3))(2)(NCS)(2)] under anaerobic conditions contrasts with its subsequent aerobic reactivity and suggests that simple adduct formation and oxidation of SO2 to sulfuric acid are not closely linked processes.