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(mu-O) MoO(L - O)](PF6)(2). The crystal structures of [MoO2(L - O)] PF6 and the mu-oxo bridged dimer are presented.