Enzymes such as cysteine dioxygenase (CDO) and nitrile hydratase (NHase) utilize cysteine-ligated low-spin iron centers to facilitate catalytic reactions. Both the CDO and NHase mechanisms are proposed to involve an Fe-sulfenate species, Fe(III)-S(R)O, as a key participant in reactivity. Sulfenate species have short lifetimes that impede their isolation and characterization. In this talk, we will show that a sterically encumbered, synthetic thiolate-ligated complex Fe(III)(Pr,Pr-NMe)+ reacts with oxo-atom donors to form a rare example of a stable Fe(III)-S(R)O species. In order to determine the mechanism of this reaction, the kinetics of this reaction were investigated, using electronic absorption spectroscopy, and the entropy and enthalpy of activation for the rate-determining step have been obtained. The differences in the rate-determining step between previously reported Fe(III)(Pr,Pr-NH)+ and the sterically encumbered Fe(III)(Pr,Pr-NMe)+ will also be compared. These rare Fe(III)-S(R)O species offer unique opportunities to elucidate mechanistic details of enzymes such as CDO and NHase.

Investigating the mechanism of formation of a rare thiolate-ligated Fe(III)-sulfenate

2019 Fall National Meeting

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