Synthesis and characterization of molybdenum oxo complexes of two tripodal ligands: reactivity studies of a functional model for molybdenum oxotransferases

Abstract

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.