Newer manifestations of reactivity of coordinated peroxide at metal and non-metal centres

Abstract

Newer reactions of coordinated peroxide at metal and non-metal centres are described. Reactions of peroxo-metal complexes with SO₂(g), NO₂(g), and CO₂(g) have been carried out in aqueous medium. Typically, reactions of a highly peroxygenated metal complex, A[V(O₂)₃].3H₂O (A=Na,K), follow an unprecedented sequence. The deep blue ESR-silent solution of A[V(O₂)₃].3H₂O reacts to produce a yellow, ESR-inactive solution that on further reaction with the chosen substrate affords a green-blue ESR-active (cf. VO²⁺) solution. The reaction proceeds through distinct steps such that, first, one of the coordinated peroxides undergoes a two-electron irreversible cleavage of the O-O bond leading to a diperoxy-mono(sulphato)vanadate(V) intermediate, [(O₂)₂V-O-SO₃]^-, that readily undergoes hydrolysis to produce H₂SO₄ and an aquaoxo-diperoxovanadate(V) complex, [VO(O₂)₂H₂O]^-. The latter complex reacts with more SO₂(g) causing reduction of vanadium (V) to vanadium (IV) and conversion of coordinated peroxide to coordinated sulphate producing the bis(sulphato)vanadyl complex, [VO(SO₂)₂(H₂O)₂]^2-. Further, the reaction of A[V(O₂)₃].3H₂O with SO₂(g) in the presence of AF, yielding a ternary fluoro(sulphato)oxovanadate (IV) complex A₄[VO(SO₄)₂F₂(H₂O)].2H₂O, serves as a paradigm for the synthesis of ternary complexes of vanadyl, VO2+. It is also evidentinteralia that the [V(O₂)₃]- species offers potential as a novel synthon. Some recent developments in the peroxo-chemistry of B, C, P and As are highlighted. Heretofore unreported salts of peroxo phosphoric acid, viz. (NH₄)₃[PO₃(O₂)].3H₂O and Na₃[PO₃(O₂)].3H₂O, have been synthesized and their potential as oxidants explored. Their role in oxidising organic substances is highlighted, especially as a substitute for the alkaline-H₂O₂ reagent.