title: Attachment of a hydrogen-bonding carboxylate side chain to an [FeFe]-hydrogenase model complex: influence on the catalytic mechanism.
abstract: Azapropanedithiolate (adt)-bridged model complexes of [FeFe]-hydrogenase bearing a carboxylic acid functionality have been designed with the aim of decreasing the potential for reduction of protons to hydrogen. Protonation of the bisphosphine complexes 4-6 has been studied by in situ IR and NMR spectroscopy, which revealed that protonation with triflic acid most likely takes place first at the N-bridge for complex 4 but at the Fe-Fe bond for complexes 5 and 6. Using an excess of acid, the diprotonated species could also be observed, but none of the protonated species was sufficiently stable to be isolated in a pure state. Electrochemical studies have provided an insight into the catalytic mechanisms under strongly acidic conditions, and have also shown that complexes 3 and 6 are electro-active in aqueous solution even in the absence of acid, presumably due to hydrogen bonding. Hydrogen evolution, driven by visible light, has been observed for three-component systems consisting of [Ru(bpy)(3)](2+), complex 1, 2, or 3, and ascorbic acid in CH(3)CN/D(2)O solution by on-line mass spectrometry.
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden.
authors.forename: Weiming
authors.initials: W
authors.lastname: Gao
authors.forename: Junliang
authors.initials: J
authors.lastname: Sun
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Akermark
authors.forename: Mingrun
authors.initials: M
authors.lastname: Li
authors.forename: Lars
authors.initials: L
authors.lastname: Eriksson
authors.forename: Licheng
authors.initials: L
authors.lastname: Sun
authors.forename: Björn
authors.initials: B
authors.lastname: Akermark
mesh_terms: D001665:Binding Sites; D002264:Carboxylic Acids / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006860:Hydrogen Bonding; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D013055:Spectrophotometry, Infrared
chemical_list: D002264:Carboxylic Acids; D007506:Iron-Sulfur Proteins; D009942:Organometallic Compounds; D007501:Iron; C118830:iron hydrogenase; D006864:Hydrogenase