Oxygen atom transfer catalysis by dioxidomolybdenum(VI) complexes of pyridyl aminophenolate ligands

A series of new cationic dioxidomolybdenum(VI) complexes [MoO2(Ln)]PF6 (2–5) with the tripodal tetradentate pyridyl aminophenolate ligands HL2-HL5 have been synthesized and characterized. Ligands HL2-HL4 carry substituents in 4-position phenolate ring, viz. Cl, Br NO2, respectively, whereas ligand HL5, N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N-bis(2-pyridylmethyl)amine, is a derivative 3,5-di-tert-butylsalicylaldehyde. X-ray crystal structures 2, 3 5 reveal that they distorted octahedral geometry bonding parameters around metal centres being practically similar. Stoichiometric oxygen atom transfer (OAT) properties PPh3 were investigated using UV–Vis, 31P NMR mass spectrometry. In CH2Cl2 solution, dimeric Mo(V) complex [(µ-O){MoO(L5)}2](PF6)2 6 was formed while methanol solution an air-sensitive Mo(IV) [MoO(OCH3)(L5)] 7 obtained. The solid-state structure µ-oxo bridged dimer determined by diffraction. Complex unstable under ambient conditions capable reducing DMSO, thus showing reactivity analogous to DMSO reductases. Similarly, OAT reactions 2–4 also resulted formation unsaturated monomeric are 7. Catalytic at 25 °C could be observed, 1–5 as catalysts for oxidation deuterated dimethylsulfoxide (DMSO?d6), which functioned both solvent oxidant. All tested sulfoxidation methyl-p-tolylsulfide epoxidation various alkene substrates tert-butyl hydroperoxide (TBHP) 1 did not exhibit any activity used, 2–5 catalyzed methyl-p-tolylsulfide. Only 2 3, containing halide substituents, exhibited good moderate all studied, and, general, molybdenum(VI) only when cis-cyclooctene used substrate. No catalysed aqueous H2O2 potential