Amine-functionalized titanium dioxide supported dioxidomolybdenum(VI) complexes as functional model for phenoxazinone synthase enzyme

Two dioxidomolybdenum(VI) complexes, [(MoO2)-O-VI{H(2)dfba(bhz)(2)}(H2O)] (1) and [(MoO2)-O-VI{H(2)dfba(fah)(2)}(H2O)] (2) of ligands H(4)dfba(bhz)(2) (I) and H(4)dfba(fah)(2) (II) (H(2)dfba = 3,5-diformyl-4-hydroxybenzoic acid, Hbhz = benzoylhydrazide and Hfah = 2-furanoylhydrazide), respectively and their corresponding heterogenized complexes [(MoO2)-O-VI{Hdfba(bhz)(2)}(H2O)]@APTMS-TiO2 (3) and [(MoO2)-O-VI{Hdfba(fah)(2)}(H2O)]@APTMS-TiO2 (4) supported on amine-functionalized titanium dioxide (APTMS-TiO2, III) have been isolated and characterized by various spectroscopic techniques (FT-IR, UV-vis, diffusion reflectance, H-1 and C-13 NMR), elemental analysis (C, H and N), thermal, TEM and powder-XRD studies. Single-crystal X-ray study of [(MoO2)-O-VI{H(2)dfba(bhz)(2)}(EtOH)]center dot EtOH (1a center dot EtOH) confirms the octahedral structure. Both homogeneous and heterogeneous complexes have been explored as phenoxazinone synthase mimicking catalysts in the oxidation of 2-aminophenol to 2-aminophenoxazine-3-one in acetonitrile in the presence of aq. H2O2. The k(cat) value for the phenoxazinone synthase-like activity was found to be 1.46 x 10(-3) and 3.26 x 10(-3) min(-1) for catalysts 1 and 2, respectively. Catalysts 1, 2, 3 and 4 also gave 91, 86, 94 and 88 % yield of 2-aminophenoxazine-3-one (APX), respectively, under the optimized reaction conditions.

Automated summary

Two dioxidomolybdenum(VI) complexes and their heterogenized complexes supported on amine-functionalized titanium dioxide have been synthesized and characterized. These complexes exhibit high activity and yield as phenoxazinone synthase mimicking catalysts in the oxidation reaction of 2-aminophenol.