title: A functional [NiFe]-hydrogenase model compound that undergoes biologically relevant reversible thiolate protonation.
abstract: Two model compounds of the active site of [NiFe]-hydrogenases with an unusual {S(2)Ni(μ-S)(μ-CO)Fe(CO)(2)S}-coordination environment around the metals are reported. The neutral compound [Ni(xbsms)(μ-CO)(μ-S)Fe(CO)(2)('S')], (1) (H(2)xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) is converted to [1H][BF(4)] by reversible protonation using HBF(4)·Et(2)O. The protonation takes place at the terminal thiolate sulfur atom that is coordinated to nickel. Catalytic intermediates with a protonated terminal cysteinate were suggested for the native protein but have not yet been confirmed experimentally. [1H][BF(4)] is the first dinuclear [NiFe] model compound for such a species. Both complexes have been synthesized and characterized by X-ray crystallography, NMR-, FTIR-, and (57)Fe-Mössbauer spectroscopy as well as by electronic absorption and resonance Raman spectroscopy. The experimental results clearly show that the protonation has a significant impact on the electronic structure of the iron center, although it takes place at the nickel site. DFT calculations support the interpretation of the spectroscopic data and indicate the presence of a bonding interaction between the metal ions, which is relevant for the enzyme as well. Electrochemical experiments show that both 1 and [1H][BF(4)] are active for electrocatalytic proton reduction in aprotic solvents.
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Weber
authors.forename: Tobias
authors.initials: T
authors.lastname: Krämer
authors.forename: Hannah S
authors.initials: HS
authors.lastname: Shafaat
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyhermüller
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Maurice
authors.initials: M
authors.lastname: van Gastel
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lubitz
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011522:Protons; D017550:Spectroscopy, Fourier Transform Infrared; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D011522:Protons; D013438:Sulfhydryl Compounds; C043296:nickel-iron hydrogenase; D006864:Hydrogenase