Synthesis, Structures, and Electronic Properties of [8Fe-7S] Cluster Complexes Modeling the Nitrogenase P-Cluster.
In: Journal of the American Chemical Society, Jg. 131 (2009-09-16), Heft 36, S. 13168-13178
academicJournal
Zugriff:
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 [BFe-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. [ABSTRACT FROM AUTHOR]
Titel: |
Synthesis, Structures, and Electronic Properties of [8Fe-7S] Cluster Complexes Modeling the Nitrogenase P-Cluster.
|
---|---|
Autor/in / Beteiligte Person: | Ohki, Yasuhiro ; Imada, Motosuke ; Murata, Ayuro ; Sunada, Yusuke ; Ohta, Shun ; Honda, Masaru ; Sasamori, Takahiro ; Tokitoh, Norihiro ; Katada, Motomi ; Tatsumi, Kazuyuki |
Link: | |
Zeitschrift: | Journal of the American Chemical Society, Jg. 131 (2009-09-16), Heft 36, S. 13168-13178 |
Veröffentlichung: | 2009 |
Medientyp: | academicJournal |
ISSN: | 0002-7863 (print) |
DOI: | 10.1021/ja9055036 |
Schlagwort: |
|
Sonstiges: |
|