| 19694466 |
Ohki Y, Imada M, Murata A, Sunada Y, Ohta S, Honda M, Sasamori T, Tokitoh N, Katada M, Tatsumi K: Synthesis, structures, and electronic properties of [8Fe-7S] cluster complexes modeling the nitrogenase P-cluster. J Am Chem Soc. 2009 Sep 16;131(36):13168-78.
High-yield synthesis of the iron-sulfur cluster [{N (SiMe (3))(2)}{SC (NMe (2))(2)}Fe (4) S (3)](2)(mu (6)-S) {mu-N (SiMe (3))(2)}(2) (1), which reproduces the [8Fe-7S] core structure of the nitrogenase P (N)-cluster, has been achieved via two pathways: (1) Fe{N (SiMe (3))(2)}(2) + HSTip (Tip = 2,4,6-(i) Pr (3) C (6) H (2)) + tetramethylthiourea (SC (NMe (2))(2)) + elemental sulfur (S (8)); and (2) Fe (3){N (SiMe (3))(2)}(2)(mu-STip)(4) (2) + HSTip + SC (NMe (2))(2) + S (8). 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 degrees 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 (P (N)) having 8Fe (II) centers, while their 6Fe (II)-2Fe (III) oxidation states correspond to the oxidized form of P-cluster (P (OX)). 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 P (N)-cluster, and the synthetic models demonstrate the redox behavior between the two major oxidation states of the native P-cluster. Replacement of the SC (NMe (2))(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, (NEt (4))(2)[{N (SiMe (3))(2)}(SC (6) H (4)-4-Me) Fe (4) S (3)](2)(mu (6)-S){mu-N (SiM e (3))(2)}(2) (3a), and [(SBtp){SC (NMe (2))(2)}Fe (4) S (3)](2)(mu (6)-S){mu-N (SiMe (3))(2)}(2) (5; Btp = 2,6-(SiMe (3))(2) C (6) H (3)) 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 (57) Fe Mossbauer 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. |
31(0,1,1,1) |