Oxo−Molybdenum(VI,V,IV) Complexes of the Facially Coordinating Tris(mercaptoimidazolyl)borate Ligand:  Synthesis, Characterization, and Oxygen Atom Transfer Reactivity

A series of monooxo−Mo(IV,V) and dioxo−Mo(VI) complexes of the “soft” tripodal ligand, sodium tris(mercaptoimidazolyl)borate (NaTm^Me), have been synthesized as potential oxygen atom transfer (OAT) models for sulfite oxidase. Complexes have been characterized by X-ray crystallography, cyclic voltammetry, and EPR, where appropriate. Oxygen atom transfer kinetics of Tm^MeMoO₂Cl, both stoichiometric and catalytic, have been studied by a combination of UV−vis and ³¹P NMR spectroscopies under a variety of conditions. OAT rates are consistent with previously established relationships between redox potential/reactivity and mechanistic studies. The analysis of these complexes as potential structural and functional analogues of relevance to molybdoenzymes is further discussed.