title: Sulfur oxygenates of biomimetics of the diiron subsite of the [FeFe]-hydrogenase active site: properties and oxygen damage repair possibilities.
abstract: This study explores the site specificity (sulfur vs the Fe-Fe bond) of oxygenation of diiron (Fe(I)Fe(I) and Fe(II)Fe(II)) organometallics that model the 2-iron subsite in the active site of [FeFe]-hydrogenase: (mu-pdt)[Fe(CO)(2)L][Fe(CO)(2)L'] (L = L' = CO (1); L = PPh(3), L' = CO (2); L = L' = PMe(3) (4)) and (mu-pdt)(mu-H)[Fe(CO)(2)PMe(3)](2) (5). DFT computations find that the Fe-Fe bond in the Fe(I)Fe(I) diiron models is thermodynamically favored to produce the mu-oxo or oxidative addition product, Fe(II)-O-Fe(II); nevertheless, the sulfur-based HOMO-1 accounts for the experimentally observed mono- and bis-O-atom adducts at sulfur, i.e., (mu-pst)[Fe(CO)(2)L][Fe(CO)(2)L'] (pst = -S(CH(2))(3)S(O)-, 1,3-propanesulfenatothiolate; L = L' = CO (1-O); L = PPh(3), L' = CO (2-O); L = L' = PMe(3) (4-O)) and (mu-pds)[Fe(CO)(2)L][Fe(CO)(2)L'] (pds = -(O)S(CH(2))(3)S(O)-, 1,3-propanedisulfenato; L = PPh(3), L' = CO (2-O(2))). The Fe(II)(mu-H)Fe(II) diiron model (5), for which the HOMO is largely of sulfur character, exclusively yields S-oxygenation. The depressing effect of such bridging ligand modification on the dynamic NMR properties arising from rotation of the Fe(CO)(3) correlates with higher barriers to the CO/PMe(3) exchange of (mu-pst)[Fe(CO)(3)](2) as compared to (mu-pdt)[Fe(CO)(3)](2). Five molecular structures are confirmed by X-ray diffraction: 1-O, 2-O, 2-O(2), 4-O, and 6. Deoxygenation with reclamation of the mu-pdt parent complex occurs in a proton/electron-coupled process. The possible biological relevance of oxygenation and deoxygenation studies is discussed.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Tianbiao
authors.initials: T
authors.lastname: Liu
authors.forename: Bin
authors.initials: B
authors.lastname: Li
authors.forename: Michael L
authors.initials: ML
authors.lastname: Singleton
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hall
authors.forename: Marcetta Y
authors.initials: MY
authors.lastname: Darensbourg
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry*; D020134:Catalytic Domain; D006864:Hydrogenase / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*
chemical_list: D007506:Iron-Sulfur Proteins; D013455:Sulfur; D007501:Iron; D006864:Hydrogenase; D010100:Oxygen