A Reduced 2Fe2S Cluster Probe of Sulfur–Hydrogen versus Sulfur–Gold Interactions

Abstract

[1] These complexes could therefore be early abiotic analogues of the diiron hydrogenase ([FeFe]-H 2 ase) active site (Figure 1), to be later replaced by biosynthetic paths required for protection of the organism from the toxic diatomic ligands in the [FeFe]H 2 ase active site.I nf act, [(m-S 2 ){Fe(CO) 3 } 2 ]e njoys current fame as the synthetic precursor to ah ost of small molecules that are biomimetic analogues of the active site of [FeFe]H 2 ase,t hus connecting the inorganic to the biological world, through organometallic chemistry (Figure 1).Studies of SH À as al igand are of importance to the bioinorganic chemistry of iron;h owever,e xamples and studies of isolated Fe À SH units are sparse.[2] Discrete hydrosulfido complexes can be synthesized through protonation of sulfido ligands,anexample of which is the protonation of the reduced, anionic sulfido-bridged species [(m-S) 2 {Fe(CO) 3 } 2 ] 2À to form [(m-SH) 2 {Fe(CO) 3 } 2 ].[3] Although the spectroscopic signatures (n(CO) and NMR spectra) of [(m-SH) 2 {Fe(CO) 3 } 2 ] have been known for decades,i ts X-ray crystal structure has not been reported until now.Because of the well-known isolobal analogy between Ph 3 PAu + and H + ,the former may serve as asurrogate for the latter,t hus leading to experimental strategies particularly useful in the structural determination of many organometallic compounds containing transition-metal hydrides.[4] The Ph 3 PAu + unit has also been used to model the protonation of metal-bound thiolates,w ith the generation of thiolatebridged M(m-SR)Au I moieties.[5] Herein we report the isolation of [(m-SAuPPh 3 ) 2 {Fe(CO) 3 } 2 ]and [(m-SH) 2 {Fe(CO) 3 } 2 ], and their characterization by X-ray diffraction. Thes pectroscopic properties and chemical reactivity of these two complexes as well as the nickelated complex [(m 3 -S) 2 Ni-(dppe){Fe(CO) 3 } 2 ]( dppe = 1,2-bis(diphenylphosphanyl)-ethane) were compared.[6] Interestingly,the stable polymetallic complexes can be used as synthons for [(m-SCH 2 N-(R)CH 2 S){Fe(CO) 3 } 2 ]t hrough the intermediacyo ft he highly unstable HS analogue;the azadithiolate is anecessary cofactor for the 2Fesubsite of [FeFe]H 2 ase. [7] Reduction of the disulfide bond of [(m-S 2 ){Fe(CO) 3 } 2 ]b y LiEt 3 BH (2 equiv) in THF at À78 8 8Cp roduces the [(m-S) 2 {Fe(CO) 3 } 2 ]2À dianion, whose versatility has been amply demonstrated by the preparation of myriad diiron complexes containing features of the [FeFe]H 2 ase active site.[8] Protonation of the dianion with trifluoroacetic acid (2 equiv) by the method of Seyferth and co-workers yielded (m-SH) 2 [{Fe-(CO) 3 } 2 ]( 1)a nd shifted the n(CO) bands of the dianion by approximately + 50 cm À1 ,asexpected for the formation of the neutral SH derivative.[3] Theproduct 1 was an air-sensitive red solid with similar n(CO) values to those of its persulfide precursor,[(m-S 2 ){Fe(CO) 3 } 2 ](see Figure S1 in 2À .T he n(CO) values in the IR spectrum of 2 show ashift from those of the dianion by only about + 10 cm À1 (see Figure S1);t hat is,t here is an approxim...

A matrix of heterobimetallic complexes for interrogation of hydrogen evolution reaction electrocatalysts

“…In contrast, the binding between the sulfurs of the metallothiolate NiN 2 S 2 and an exogeneous metal are more geometrically flexible because of the multiple S lone pairs. From NBO bonding analysis, sulfur in the NiN 2 S 2 metalloligand is found to use mainly p orbitals for bonding to Ni and C. 43 , 44 For example, in a free NiN 2 S 2 , p character makes up 83% and 86% of the S contributions in the S–Ni bonds and S–C α bonds (C α and C β refer to the C 2 H 4 linker connecting S and N where C α is directly bound to S, Fig. 4A ), which leaves one lone pair in a p orbital and another in an s-dominated orbital on each S. Because a receiver group, a Fe(NO) 2 unit in our case, may bind to either lobe of the p lone pair(s), whose orientation is determined by the Ni–S–C α torsion angle, a diversity of structures results.…”