| Autor: |
Wadepohl, Hubert, Gebert, Stefan, Pritzkow, Hans, Osella, Domenico, Nervi, Carlo, Fiedler, Jan |
| Zdroj: |
European Journal of Inorganic Chemistry; August 2000, Vol. 2000 Issue: 8 p1833-1843, 11p |
| Abstrakt: |
Chemical reduction of the tetracobalt cluster complex [Co4(CO)3(μ3-CO)3(μ3-C7H7)(η5-C7H9)] (3), followed by addition of [PPh4]Br, gives the complex [{Co4(CO)3(μ3-CO)3(μ3-C7H7)}2{μ-η4:η4-(C7H9)2}]2− as a mixture of two diastereomers [4A]2− and [4B]2− in high yield. The crystal structure of [4A]2−[PPh4]2·1.5C7H8 has been determined and confirms the reductive coupling of two Co4 cluster coordinated apical cycloheptadienyl rings to form a bridging bicycloheptyl-3,5,3',5'-tetraene ligand. Reduction of 3 with Li[HBEt3] and subsequent treatment with aqueous [NnBu4]Cl results in the formation of [Co4(CO)3(μ3-CO)3(μ3-C7H7)(C7H10)]− [5]−. Addition of [(η-C6H6)Ru(NCMe)3][BF4]2 after the borohydride reduction gives [Ru(η-C6H6)Co3(CO)3(μ3-CO)3(μ3-C7H7)] (6), a product derived from reductive Co4 cluster degradation. A detailed electrochemical and spectro-electrochemical study of the redox behaviour of 3 and [4]2− has been carried out. The complex potential current response of 3 is rationalized in terms of the formation of the radical anion [3]− as the primary intermediate, which may be reversibly reduced further to give the much more stable [3]2− and then [3]3−. Dimerization of [3]− to give [4]2− occurs by formation of a new carbon−carbon bond between the apical C7H9 ligands. The two redox-active moieties in [4]2− behave as independent, non-interacting redox centres. The oxidized form 4 is unstable and dissociates back to 3 almost quantitatively, thus completing a redox cycle characteristic of a molecular battery. The homogeneous rate constant for dimerization has been evaluated as kDIM (2 [3]− → [4]2−) = 0.30 ± 0.05 mM−1 s−1. |
| Databáze: |
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