title: Series of mixed valent Fe(II)Fe(I) complexes that model the Hox state of [FeFe]hydrogenase: redox properties, density-functional theory investigation, and reactivities with extrinsic CO.
abstract: A series of asymmetrically disubstituted models of the active site of [FeFe]-hydrogenase, (mu-pdt)[Fe(CO) 2PMe 3][Fe(CO) 2NHC] (pdt = 1,3-propanedithiolate, NHC = IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene IMes ( 1), IMesMe, 1-methyl,3-(2,4,6-trimethylphenyl)imidazol-2-ylidene ( 2) or IMe, 1,3-bis(methyl)imidazol-2-ylidene ( 3)), have been synthesized and characterized. The one-electron oxidation of these complexes to generate mixed valent models of the H ox state of [FeFe]-hydrogenase, such as the previously reported (mu-pdt)(mu-CO)[Fe(CO) 2PMe 3][Fe(CO)IMes] (+) ( 1 ox ) (Liu, T.; Darensbourg, M. Y. J. Am. Chem. Soc. 2007, 129, 7008-7009) has been examined to explore the steric and electronic effects of different N-atom substituents on the stability and structure of the mixed valent cations. The differences in spectroscopic properties, structures, and relative stabilities of 1 ox , (mu-pdt)[Fe(CO) 2PMe 3][Fe(CO) 2IMesMe] (+) ( 2 ox ), and (mu-pdt)[Fe(CO) 2PMe 3]-[Fe(CO) 2IMe] (+) ( 3 ox ) are discussed in the context of both experimental and theoretical data. Of the three derivatives, only that with greatest steric bulk on the NHC ligand, 1 ox , shows a clear indication of a mu-CO by solution nu(CO) IR and yields to crystallization as a rotated form, commensurate with the two-Fe subsite of H ox. In addition, the reactivity of the complexes with extrinsic CO to form CO adducts and/or exchange with (13)CO is explored by experiment and by using density-functional theory calculations.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, Texas 77845, USA.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Thomas
authors.forename: Tianbiao
authors.initials: T
authors.lastname: Liu
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hall
authors.forename: Marcetta Y
authors.initials: MY
authors.lastname: Darensbourg
mesh_terms: D001665:Binding Sites; D002248:Carbon Monoxide / Q000737:chemistry*; D004563:Electrochemistry; D004583:Electrons; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism; D007501:Iron / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008697:Methane / Q000031:analogs & derivatives / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D007506:Iron-Sulfur Proteins; D008024:Ligands; D009942:Organometallic Compounds; C030011:carbene; D002248:Carbon Monoxide; D007501:Iron; C118830:iron hydrogenase; D006864:Hydrogenase; D008697:Methane