title: Carbon monoxide induced reductive elimination of disulfide in an N-heterocyclic carbene (NHC)/thiolate dinitrosyl iron complex (DNIC).
abstract: 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; 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). The typical biological ligands cysteine and glutathione themselves are subject to thiolate-disulfide redox processes, which when coupled to DNICs may lead to intricate redox processes involving iron, NO, and RS(-)/RS•. 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. This mechanism is further defined by density functional theory computations. Computational results indicate a unique role for the delocalized frontier molecular orbitals of the Fe(NO)2 unit, permitting ligand exchange of RS• and CO through an initial side-on approach of CO to the electron-rich N-Fe-N site, ultimately resulting in a 5-coordinate, 19-electron intermediate with elongated Fe-SR bond and with the NO ligands accommodating the excess charge.
authors.affiliation: Department of Chemistry, Texas A & M University , College Station, Texas 77843, United States.
authors.forename: Randara
authors.initials: R
authors.lastname: Pulukkody
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Kyran
authors.forename: Ryan D
authors.initials: RD
authors.lastname: Bethel
authors.forename: Chung-Hung
authors.initials: CH
authors.lastname: Hsieh
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hall
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Darensbourg
authors.forename: Marcetta Y
authors.initials: MY
authors.lastname: Darensbourg
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D009589:Nitrogen Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D004220:Disulfides; D006571:Heterocyclic Compounds; D009589:Nitrogen Oxides; D013438:Sulfhydryl Compounds; C030011:carbene; C073661:dinitrosyl iron complex; D002248:Carbon Monoxide; D007501:Iron; D008697:Methane