Systematic Investigation of Relationship between Strength of NH···S Hydrogen Bond and Reactivity of Molybdoenzyme Models

A series of monooxomolybdenum­(IV) and dioxomolybdenum­(VI)
complexes containing two intramolecular NH···S hydrogen
bonds were synthesized and characterized by 1H NMR, UV–visible,
IR, and Raman spectroscopies, and electrochemical measurements. Elimination
of the steric effects enabled the accurate and quantitative evaluation
of NH···S hydrogen bonds. Strong correlations among
the strength of the hydrogen bond, the strength of the MoVIO bond, and the redox potential were clearly shown. The hydrogen
bonds stabilize the intermediate in the reaction between the monooxomolybdenum­(IV)
and Me3NO, resulting in acceleration of the reaction or
retardation of trans–cis rearrangement. The
proposed intermediate and the reaction mechanism, discussed on the
basis of theoretical calculations, provided a unified explanation
of the reaction.