Details

Autor(en) / Beteiligte

• Ohki, Yasuhiro
• Imada, Motosuke
• Murata, Ayuro
• Sunada, Yusuke
• Ohta, Shun
• Honda, Masaru
• Sasamori, Takahiro
• Tokitoh, Norihiro
• Katada, Motomi
• Tatsumi, Kazuyuki

Titel

Synthesis, Structures, and Electronic Properties of [8Fe-7S] Cluster Complexes Modeling the Nitrogenase P-Cluster

Ist Teil von

• Journal of the American Chemical Society, 2009-09, Vol.131 (36), p.13168-13178

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2009

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• High-yield synthesis of the iron−sulfur cluster [{N(SiMe3)2}{SC(NMe2)2}Fe4S3]2(μ6-S) {μ-N(SiMe3)2}2 (1), which reproduces the [8Fe-7S] core structure of the nitrogenase PN-cluster, has been achieved via two pathways: (1) Fe{N(SiMe3)2}2 + HSTip (Tip = 2,4,6-iPr3C6H2) + tetramethylthiourea (SC(NMe2)2) + elemental sulfur (S8); and (2) Fe3{N(SiMe3)2}2(μ-STip)4 (2) + HSTip + SC(NMe2)2 + S8. The thiourea and terminal amide ligands of 1 were found to be replaceable by thiolate ligands upon treatment with thiolate anions and thiols at −40 °C, respectively, and a series of [8Fe-7S] clusters bearing two to four thiolate ligands have been synthesized and their structures were determined by X-ray analysis. The structures of these model [8Fe-7S] clusters all closely resemble that of the reduced form of P-cluster (PN) having 8Fe(II) centers, while their 6Fe(II)−2Fe(III) oxidation states correspond to the oxidized form of P-cluster (POX). The cyclic voltammograms of the [8Fe-7S] clusters reveal two quasi-reversible one-electron reduction processes, leading to the 8Fe(II) state that is the same as the PN-cluster, and the synthetic models demonstrate the redox behavior between the two major oxidation states of the native P-cluster. Replacement of the SC(NMe2)2 ligands in 1 with thiolate anions led to more negative reduction potentials, while a slight positive shift occurred upon replacement of the terminal amide ligands with thiolates. The clusters 1, (NEt4)2[{N(SiMe3)2}(SC6H4-4-Me)Fe4S3]2(μ6-S){μ-N(SiMe3)2}2 (3a), and [(SBtp){SC(NMe2)2}Fe4S3]2(μ6-S){μ-N(SiMe3)2}2 (5; Btp = 2,6-(SiMe3)2C6H3) are EPR silent at 4−100 K, and their temperature-dependent magnetic moments indicate a singlet ground state with antiferromagnetic couplings among the iron centers. The 57Fe Mössbauer spectra of these clusters are consistent with the 6Fe(II)−2Fe(III) oxidation state, each exhibiting two doublets with an intensity ratio of ca. 1:3, which are assignable to Fe(III) and Fe(II), respectively. Comparison of the quadrupole splittings for 1, 3a, and 5 has led to the conclusion that two Fe(III) sites of the clusters are the peripheral iron atoms.