A reduced 2Fe2S cluster probe of sulfur-hydrogen versus sulfur-gold interactions.

The Ph3 PAu(+) cation, renowned as an isolobal analogue of H(+) , was found to serve as a proton surrogate and form a stable Au2 Fe2 complex, [(μ-SAuPPh3 )2 {Fe(CO)3 }2 ], analogous to the highly reactive dihydrosulfide [(μ-SH)2 {Fe(CO)3 }2 ]. Solid-state X-ray diffraction analysis found the two SAuPPh3 and SH bridges in anti configurations. VT NMR studies, supported by DFT computations, confirmed substantial barriers of approximately 25 kcal mol(-1) to intramolecular interconversion between the three stereoisomers of [(μ-SH)2 {Fe(CO)3 }2 ].

Regioselectivity in ligand substitution reactions on diiron complexes governed by nucleophilic and electrophilic ligand properties.

The discovery of a diiron organometallic site in nature within the diiron hydrogenase, [FeFe]-H2ase, active site has prompted revisits of the classic organometallic chemistry involving the Fe-Fe bond and bridging ligands, particularly of the (μ-SCH2XCH2S)[Fe(CO)3]2 and (μ-SCH2XCH2S)[Fe(CO)2L]2 (X = CH2, NH; L = PMe3, CN(-), and NHC's (NHC = N-heterocyclic carbene)), derived from CO/L exchange reactions. Through the synergy of synthetic chemistry and density functional theory computations, the regioselectivity of nucleophilic (PMe3 or CN(-)) and electrophilic (nitrosonium, NO(+)) ligand substitution on the diiron dithiolate framework of the (μ-pdt)[Fe(CO)2NHC][Fe(CO)3] complex (pdt = propanedithiolate) reveals the electron density shifts in the diiron core of such complexes that mimic the [FeFe]-H2ase active site. While CO substitution by PMe3, followed by reaction with NO(+), produces (μ-pdt)(μ-CO)[Fe(NHC)(NO)][Fe(CO)2PMe3](+), the alternate order of reagent addition produces the structural isomer (μ-pdt)[Fe(NHC)(NO)PMe3][Fe(CO)3](+), illustrating how the nucleophile and electrophile choose the electron-poor metal and the electron-rich metal, respectively.

Electrocatalytic O₂ reduction by [Fe-Fe]-hydrogenase active site models.

The instability of [Fe-Fe]-hydrogenase and its synthetic models under aerobic conditions is an inherent challenge in their development as practical H2 producing electrodes. The electrochemical oxygen reduction reaction of a series of synthetic model complexes of the [Fe-Fe] hydrogenase is investigated, and a dominant role of the bridgehead nitrogen in reducing the amount of partially reduced oxygen species (PROS), which is detrimental to the stability of these complexes, is discovered.

Redox active iron nitrosyl units in proton reduction electrocatalysis.

Base metal, molecular catalysts for the fundamental process of conversion of protons and electrons to dihydrogen, remain a substantial synthetic goal related to a sustainable energy future. Here we report a diiron complex with bridging thiolates in the butterfly shape of the 2Fe2S core of the [FeFe]-hydrogenase active site but with nitrosyl rather than carbonyl or cyanide ligands. This binuclear [(NO)Fe(N2S2)Fe(NO)2](+) complex maintains structural integrity in two redox levels; it consists of a (N2S2)Fe(NO) complex (N2S2=N,N'-bis(2-mercaptoethyl)-1,4-diazacycloheptane) that serves as redox active metallodithiolato bidentate ligand to a redox active dinitrosyl iron unit, Fe(NO)2.

Sulfonated diiron complexes as water-soluble models of the [Fe-Fe]-hydrogenase enzyme active site.

A series of diiron complexes developed as fundamental models of the two-iron subsite in the [FeFe]-hydrogenase enzyme active site show water-solubility by virtue of a sulfonate group incorporated into the -SCH(2)NRCH(2)S- dithiolate unit that bridges two Fe(I)(CO)(2)L moieties. The sulfanilic acid group imparts even greater water solubility in the presence of β-cyclodextrin, β-CyD, for which NMR studies suggest aryl-sulfonate inclusion into the cyclodextrin cavity as earlier demonstrated in the X-ray crystal structure of 1Na·2 β-CyD clathrate, where 1Na = Na(+)(μ-SCH(2)N(C(6)H(4)SO(3)(-))CH(2)S-)[Fe(CO)(3)](2), (Singleton et al., J.