title: Terminal hydride in [FeFe]-hydrogenase model has lower potential for H2 production than the isomeric bridging hydride.
abstract: Protonation of the symmetrical tetraphosphine complexes Fe2(S2CnH2n)(CO)2(dppv)2 afforded the corresponding terminal hydrides, establishing that even symmetrical diiron(I) dithiolates undergo protonation at terminal sites. The terminal hydride [HFe2(S2C3H6)(CO)2(dppv)2](+) was found to catalyze proton reduction at potentials 200 mV milder than the isomeric bridging hydride, thereby establishing a thermodynamic advantage for catalysis operating via terminal hydride. The azadithiolate protonates to afford, [Fe2[(SCH2)2NH2](CO)2(dppv)2](+), [HFe2[(SCH2)2NH](CO)2(dppv)2](+), and [HFe2[(SCH2)2NH2](CO)2(dppv)2](2+), depending on conditions.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Bryan E
authors.initials: BE
authors.lastname: Barton
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Rauchfuss
mesh_terms: D006859:Hydrogen / Q000737:chemistry* / Q000378:metabolism*; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism*; D007536:Isomerism; D008954:Models, Biological; D008958:Models, Molecular
chemical_list: D007506:Iron-Sulfur Proteins; D006859:Hydrogen; C118830:iron hydrogenase; D006864:Hydrogenase