Oxidation of Nitrite by a <i>trans</i>-Dioxoruthenium(VI) Complex: Direct Evidence for Reversible Oxygen Atom Transfer

Reaction of trans-[RuVI(L)(O)2]2+ (1, L = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, a tetradentate macrocyclic ligand with N2O2 donor atoms) with nitrite in aqueous solution or in H2O/CH3CN produces the corresponding (nitrato)oxoruthenium(IV) species, trans-[RuIV(L)(O)(ONO2)]+ (2), which then undergoes relatively slow aquation to give trans-[RuIV(L)(O)(OH2)]2+. These processes have been monitored by both ESI/MS and UV/vis spectrophotometry. The structure of trans-[RuIV(L)(O)(ONO2)]+ (2) has been determined by X-ray crystallography. The ruthenium center adopts a distorted octahedral geometry with the oxo and the nitrato ligands trans to each other. The RuO distance is 1.735(3) Å, the Ru−ONO2 distance is 2.163(4) Å, and the Ru−O−NO2 angle is 138.46(35)°. Reaction of trans-[RuVI(L)(18O)2]2+ (1-18O2) with N16O2- in H2O/CH3CN produces the 18O-enriched (nitrato)oxoruthenium(IV) species 2-18O2. Analysis of the ESI/MS spectrum of 2-18O2 suggests that scrambling of the 18O atoms has occurred. A mechanism that involves linkage isomerization of the nitrato ligand and reversible oxygen atom transfer is proposed.