Mechanism of Reduction of 2,2-Dibromomethyl-1,3-propanediol by Ni ^I-Tetraazamacrocyclic Complexes in Aqueous Solution - A Pulse Radiolysis and Electrochemical Study

The reduction, catalytic reduction and the electrocatalytic reduction of halo-organic compounds are of major interest due to their role as pollutants. The mechanism and kinetics of reduction of 2,2-dibromomethyl-1,3-propanediol by several Ni^I tetraazamacrocyclic complexes, (Ni^IL ⁱ)⁺ (i = 1-4), in aqueous solutions to yield Br ^- and the non-halogenated compound was studied using the pulse radiolysis technique. The rate constants k = 5.3 × 10⁸, 1.6 × 10⁷, 6.0 × 10⁵ and 3.5 × 10 ⁴ M^-1S^-1 for L¹, L², L³ and L⁴ respectively, of the reactions (Ni ^ILⁱ)⁺ RBr → (Ni^IIL ⁱ)²⁺ + Br^- + R^. increase with the free-energy gain in the reaction. All these complexes are good electrocatalysts for the reduction of this substrate. The mechanisms of the reductions is are discussed.