Diatomic ligands such as CO and CN have been stalwart and innocent supporters in the development of mechanistic organometallic chemistry. In contrast the non-innocent nitrosyl ligand has found more applications in bioinorganic chemistry, particularly as attached to iron in mono- and dinitrosyl iron complexes. The latter, DNICs, are analogues of the Fe(CO)3 unit, with a notable difference in their redox activity. DNICs readily convert, in the presence of suitable stabilizing ligands, between one-electron redox states of different magnetism: paramagnetic {Fe(NO)2}9, diamagnetic dimerized forms of {Fe(NO)2}9 and diamagnetic {Fe(NO)2}10 DNICs (Enemark-Feltham notation). Making use of an N-heterocyclic carbene-stabilized DNIC, (NHC)(RS)Fe(NO)2 we have explored the DNIC-promoted RS-/RS� oxidation in the presence of added CO wherein oxidized {Fe(NO)2}9 is reduced to {Fe(NO)2}10 through carbon monoxide (CO)/RS� ligand substitution. Kinetic studies indicate a bimolecular process, rate = k [Fe(NO)2]1[CO]1, and activation parameters derived from kobs dependence on temperature similarly indicate an associative mechanism. Computational investigations suggest a unique role for the delocalized frontier molecular orbitals of the Fe(NO)2 unit, permitting ligand exchange of �SR and CO through an initial side-on approach of CO to the electron-rich N-Fe-N site, resulting in a 5-coordinate, 19-electron intermediate with the NO ligands accommodating the excess charge. To provide further evidence for the computationally proposed mechanism, (NHC)(RS)Fe(NO)2 derivatives with varying para-substituents at the phenyl thiolate have been synthesized and characterized.  In accordance with the computational mechanistic proposal, a Hammett analysis found rate enhancement to correlate with electron donating substituents, while rates were seen to decrease with electron withdrawing substituents.

Carbon monoxide induced elimination of disulfide from dinitrosyl iron complexes: Hammett correlations of para-substituted [(NHC)Fe(NO)<sub>2</sub>S(p-PhX)] compounds

248th National Meeting (2014)

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Carbon monoxide induced elimination of disulfide from dinitrosyl iron complexes: Hammett correlations of para-substituted [(NHC)Fe(NO)2S(p-PhX)] compounds

Carbon monoxide induced elimination of disulfide from dinitrosyl iron complexes: Hammett correlations of para-substituted [(NHC)Fe(NO)₂S(p-PhX)] compounds