Synthesis and characterization of molybdenum oxo complexes of two tripodal ligands: reactivity studies of a functional model for molybdenum oxotransferases
Reaction of the tetradentate ligand N-(2-hydroxybenzyl)-N,N-bis(2-pyridylmethyl)amine (L–OH) with MoO2Cl2 in methanol in the presence of NaOMe and PF6− results in the formation of [MoO2(L–O)]PF6. Similarly, the reaction of N-(2-mercaptobenzyl)-N,N-bis(2-pyridylmethyl)amine (L–SH) with MoO2(acac)2 leads to the formation of [MoO2(L–S)]+. The dioxo-molybdenum complex [MoO2(L–O)]+ reacts with phosphines in methanol to afford phosphine oxides and an air-sensitive molybdenum complex, tentatively identified as [Mo(IV)O(L–O)(OCH3)]. The latter complex is capable of reducing biological oxygen donors such as DMSO or nitrate, thereby mimicking the activity of DMSO reductase and nitrate reductase. Reaction of [MoO2(L–O)]PF6 with PPh3 in other solvents than methanol leads to the formation of the Mo(V) dimer [(L–O)OMo(μ-O)MoO(L–O)](PF6)2. The crystal structures of [MoO2(L–O)]PF6 and the μ-oxo bridged dimer are presented.