Diiron thiadithiolates as active site models for the iron-only hydrogenases:: Synthesis, structures, and catalytic H2 production

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 (mu-SCH2)(2)S(CO)(6) (1) in 42% yield. Further treatment of 1 with Cp(CO)(2)Fe(BF4) prepared in situ from Cp(CO)(2)FeI and AgBF4 in CH2Cl2 gave cationic model [Fe-2(mu-SCH2)(2)S(CO)(6)][Cp(CO)(2)Fe](BF4) (2) in 81% yield, while treatment of 1 with 2 equiv of Et4NCN in MeCN or with t-BuNC in CH2Cl2 produced models (Et4N)(2)[Fe-2(mu-SCH2)(2)S(CO)(4)(CN)(2)] (3) and Fe-2(mu-SCH2)(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 Et3NHCl to give hydrogen under electrochemical conditions.