Regioselective conversions of H4pdta (1,2-propanediaminetetraacetic acid) and H4eed3a to their triacetates on peroxotitanates†
1,2-Propanediaminetetraacetic acid (H4pdta = C11H18O8N2) is degraded selectively to 1-methyl-1,2-propanediaminetriacetic acid (H3pd3a = C9H16O6N2) with a yield of 75% at room temperature, while N-(2-hydroxyethyl) ethylenediaminetriacetic acid (H4eed3a = C10H18O7N2) is converted with difficulty to ethylenediaminetriacetic acid (H3ed3a = C8H14O6N2) on peroxotitanates(IV), showing the influence of the uncoordinated leaving group. Various species in the reaction sequence are isolated and fully characterized, including (NH4)[Ti(O2)(Hpdta)]·H2O (1), (NH4)3[Ti(O2)(pdta)H(pdta)(O2)Ti]·7H2O (2), (NH4)[Ti(O2)(pd3a)]·H2O (3) and (NH4)[Ti(O2)(Heed3a)]·H2O (5). Peroxo dimer 2 forms a strong intramolecular hydrogen bond [2.451(3) Å] as an intermediate in the peroxo Ti-pdta system, which results in the absence of a fully deprotonated species of peroxo pdta titanate. A catalytic reaction of the peroxo titanate (NH4)3[Ti(O2)(pdta)H(pdta)(O2)Ti]·7H2O (2) for the conversion of pyridine to pyridine N-oxide shows 94% conversion at 80 °C.