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Dinuclear and Mononuclear Iron(II)−Thiolate Complexes with Mixed CO/CN - Ligands: Synthetic Advances for Iron Sites of [Fe]-Only Hydrogenases

2000; American Chemical Society; Volume: 122; Issue: 3 Linguagem: Inglês

10.1021/ja992300q

1943-2984

Wen‐Feng Liaw, Nan-Hung Lee, Chien‐Hong Chen, Chien‐Ming Lee, Gene‐Hsiang Lee, Shie‐Ming Peng,

Advanced battery technologies research

The pentacoordinate, 16-electron FeII complex [PPN][Fe(CO)2(CN)(S,NH-C6H4)] (1), stabilized by strong S, N π-donation of chelating [S,NH-C6H4]2- ligand, was prepared by the reaction of 2-aminophenyl disulfide and [PPN][Fe(CO)4(CN)]. Protonation of complex 1 by electrophiles (2-mercaptopyrimidine and 2-aminophenylthiol) yielded hexacoordinate iron(II)−thiolate cyanocarbonyl complexes [PPN][Fe(CO)(CN)(S-C4H3N2)2] (5) and [PPN][Fe(CO)2(CN)(S-C6H4NH2)(S,NH2-C6H4)] (3), respectively. The IR spectrum of complex 5 in the aprotic solvent CH3CN displayed a weak ν(CN) band at 2090 cm-1 and a strong ν(CO) band at 1945 cm-1. Chemical oxidation of complex 5 in CH3CN at − 20 °C with [Cp2Fe][PF6] displayed absorption bands at 2096 and 1962 cm-1 which were assigned to the ν(CN) and ν(CO) vibrational frequencies respectively of the thermally unstable neutral FeIII(CO)(CN)(S-C4H3N2)2. Complex 5 was reobtained upon addition of [PPN][BH4] to FeIII(CO)(CN)(S-C4H3N2)2 in CH3CN at −20 °C. The first dinuclear Fe(II)−thiolate cyanocarbonyl compound [PPN]2[(CN)(CO)2Fe(μ-S,S-C6H4)]2 (4), the promising structural and functional model compound of the dinuclear iron active sites of [Fe]-only hydrogenases isolated from D. desulfuricans and C. pasteurianum, was prepared by reacting 1,2-benzenedithiol with complex 1 in THF at −10 °C. The X-ray structural analysis shows that complex 4 possesses crystallographically imposed centrosymmetry. Two six-coordinate Fe(II) centers are connected via two thiolate bridges, and both CN- ligands point into the antiparallel direction. The IR spectrum of complex 4 in the aprotic solvent CH2Cl2 revealed a weak absorption band for the CN- ligands at 2101 cm-1, and two strong absorption bands for the CO groups at 2013 and 1960 cm-1. When the CH2Cl2 solution of complex 4 was exposed to 13CO at 0 °C, absorbances at 1968 and 1915 cm-1 appeared within 10 min. Reappearance of the 2013 and 1960 cm-1 bands on the removal of the 13CO and replacement with 12CO atmosphere demonstrated reversibility of the CO ligand lability of complex 4. The vibrational spectroscopies of the Fe(CO)2(CN) and Fe(CO)(CN) fragments (ν(CN) ranges from 2094 to 2105 cm-1, ν(CO) ranges from 1928 to 2013 cm-1) found in complexes 1, 3, 4, and 5 may be regarded as spectroscopic references of [Fe] hydrogenases in the various enzymatic states.