Diiron Thiadithiolates as Active Site Models for the Iron-Only Hydrogenases:  Synthesis, Structures, and Catalytic H₂ Production

Abstract

The first diiron thiadithiolates as active site models for the Fe-only hydrogenases were prepared. Treatment of Fe 3 (CO) 12 with excess 1,2,4-trithiolane in THF at reflux afforded parent model Fe 2 (µ-SCH 2 ) 2 S(CO) 6 (1) in 42% yield. Further treatment of 1 with Cp(CO) 2 Fe(BF 4 ) prepared in situ from Cp(CO) 2 FeI and AgBF 4 in CH 2 Cl 2 gave cationic model [Fe 2 (µ-SCH 2 ) 2 S(CO) 6 ][Cp(CO) 2 Fe](BF 4 ) (2) in 81% yield, while treatment of 1 with 2 equiv of Et 4 NCN in MeCN or with t-BuNC in CH 2 Cl 2 produced models (Et 4 N) 2 [Fe 2 (µ-SCH 2 ) 2 S(CO) 4 (CN) 2 ] (3) and Fe 2 (µ-SCH 2 ) 2 S(CO) 4 (t-BuNC) 2 (4) in 93% and 51% yields, respectively. All the new models 1-4 were characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1, 2, and 4. Furthermore, model 1 has been proved to be a catalyst for proton reduction of a weak acid Et 3 NHCl to give hydrogen under electrochemical conditions.

Synthesis and Characterization of Diiron Thiadithiolate Complexes Related to the Active Site of [FeFe]‐Hydrogenases

“…In their IR spectra there are three to four absorption bands in the range of 2047-1934 cm -1 assigned to the terminal carbonyls, which are shifted towards lower frequencies relative to those (2075-1990 cm -1 ) of the parent complex A. [7] This is obviously due to the increased strength of the π back bonding between the iron atoms and the at-tached carbonyl groups by substitution of the CO group by the stronger electron-donating phosphane or isocyanide ligands. [11] In addition, the IR spectra of 3 and 4 show one absorption band at ca.…”

“…There have been two methods previously reported for the synthesis of complex A, which involve the oxidative addition reaction of 1,2,4-trithiolane with Fe 3 (CO) 12 [7] and Fe 2 (CO) 9 [8] in thf. Now, we report a new method for the synthesis of complex A, which involves two elementary steps in one pot (i) the initial reductive cleavage of the S-S bond of [(µ-S 2 )Fe 2 (CO) 6 ] with Et 3 BHLi and (ii) the subsequent condensation of the resulting intermediate [(µ-LiS) 2 Fe 2 (CO) 6 ] [10] with excess thioether S(CH 2 Br) 2 (Scheme 1).…”

“…To the best of our knowledge, this is the first crystal structure of the isocyanide-monosubsti- [14] whereas in the crystal structure of the model complex [Fe 2 (µ-SCH 2 ) 2 S(CO) 4 (tBuNC) 2 ], one isocyanide group resides in an apical position and the other in a basal position. [7] Synthesis Compounds 5-9 are air-stable dark-red solids, which were characterized by elemental analysis and NMR and IR spectroscopy, and for 8 by X-ray crystallography. For example, the IR spectra of 5-9 display three absorption bands in the range 2047-1932 cm -1 , which can be assigned to the terminal carbonyl groups, whereas complex 7 exhibits an additional absorption band at 2118 cm -1 for the bridged diisonitrile.…”

“…This is because the central N atom in the ADT cofactor was recently suggested to play an important role in the heterolytic cleavage of H 2 or H 2 evolution in natural enzymes. [9] In addition, the central S atom in the TDT cofactor has a strong coordination ability with transition metals, [7] which may provide an easy route to structural modification. On the basis of our previous study on central heteroatom-containing models, we now report the synthesis and structural characterization of a series of new single and double diiron TDT-type models prepared by CO substitution and by coordination at the central S atom of the parent complex [Fe 2 (µ-SCH 2 ) 2 S(CO) 6 ] (A).…”

Electrochemical Insights into the Mechanisms of Proton Reduction by [Fe2(CO)6{μ‐SCH2N(R)CH2S}] Complexes Related to the [2Fe]H Subsite of [FeFe]Hydrogenase

“…Diiron hexacarbonyls with a propanedithiolate (pdt, S-A C H T U N G T R E N N U N G (CH 2 ) 3 S) or a azadithiolate (adt, SCH 2 N(R)CH 2 S) bridge have similar redox potentials, [29,34] but the former do not undergo protonation, [35] while protonation of the latter at the nitrogen atom produces a cation that is reducible at a less negative potential than the parent. This may allow a gain of several hundreds of millivolts (E 2 ÀE 1 ; Scheme 2) in the potential for proton reduction, the mechanisms of which have been thoroughly investigated both experimentally and by theoretical methods in the case of [Fe 2 (CO) 6 A C H T U N G T R E N N U N G (m-pdt)] and [Fe 2 (CO) 6 A C H T U N G T R E N N U N G (m-edt)] (edt = ethanedithiolate, SA C H T U N G T R E N N U N G (CH 2 ) 2 S), as well as for diphosphido-bridged hexacarbonyl complexes.…”