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 conventi onal synthesis from ethanolic solutions of the appropriate hydrated me tal salt and Ph(3)EO. Their reactivity with sulfur dioxide has been ex amined in the solid state (anaerobic conditions) and for toluene slurr ies 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 add ucts 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. wh ich 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(OP Me(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 . H2 O in the presence of air, although I-2 and Ph(3)AsI(4) appear to be pr oduced even under anaerobic conditions. Aerobic reactivity was also ob served for [Co(OEPh(3))(2)(NCS)(2)] (E = P or As); CoSO4 . H2O and lig and derivatives of sulfuric acid were again isolated, however, the fat e of the thiocyanate anion remains unclear. The inactivity of [Co(OPPh (3))(2)(NCS)(2)] under anaerobic conditions contrasts with its subsequ ent aerobic reactivity and suggests that simple adduct formation and o xidation of SO2 to sulfuric acid are not closely linked processes.