Dinitrosyliron complexes (DNICs) are organometallic-like compounds of biological significance in that they appear in vivo as products of NO-degradation of iron-sulfur clusters or derived from the cellular chelatable iron pool (CIP); synthetic analogues have potential as NO storage and releasing agents.  Their reactivity is expected to depend on ancillary ligands and the redox level of the distinctive Fe(NO)2 unit:  paramagnetic {Fe(NO)2}9, diamagnetic dimerized forms of {Fe(NO)2}9 and diamagnetic {Fe(NO)2}10 DNICs (Enemark-Feltham notation).  We reported (J.A.C.S, 2013) an interesting process of carbon monoxide (CO)/RS� ligand substitution from an N-Heterocyclic Carbene (NHC) stabilized DNIC. Kinetic studies indicated an associative mechanism and computational investigations indicated a unique role for the delocalized frontier molecular orbitals of the Fe(NO)2 unit, resulting in a 5-coordinate, 19-electron intermediate with the NO ligands accommodating the excess charge. To further test the computationally proposed mechanism, (NHC)(SPhX)Fe(NO)2 derivatives with varying para-substituents at the phenyl thiolate were synthesized and characterized. The series included p-OCH3, p-CH3, p-Cl, p-CF3 and p-NO2 derivatives. Hammett correlations were analyzed to study the effects of the electron density at the N-Fe-N site on the rate of reaction. In accordance with the computational mechanistic proposal, rate enhancement was observed with electron donating substituents, while rates were seen to decrease with electron withdrawing substituents.

Deciphering the mechanism of carbon monoxide induced elimination of disulfide from a dinitrosyl iron complex: Hammett correlations of a series of <i>para</i> substituted (NHC)( SPhX)Fe(NO)<sub>2</sub> compounds

247th National Meeting (2014)

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Deciphering the mechanism of carbon monoxide induced elimination of disulfide from a dinitrosyl iron complex: Hammett correlations of a series of para substituted (NHC)( SPhX)Fe(NO)2 compounds

Deciphering the mechanism of carbon monoxide induced elimination of disulfide from a dinitrosyl iron complex: Hammett correlations of a series of para substituted (NHC)( SPhX)Fe(NO)₂ compounds