Redox chemistry of [CO4(CO)33-CO)33-C7H7)(η5-C7H9)] - Reversible carbon-carbon coupling versus metal cluster degradation

Hubert Wadepohl, Stefan Gebert, Hans Pritzkow, Domenico Osella, Carlo Nervi, Jan Fiedler

Risultato della ricerca: Contributo su rivistaArticolo in rivistapeer review

Abstract

Chemical reduction of the tetracobalt cluster complex [C04(CO)33- CO)33-C7H7)(η5-C7H9)] (3), followed by addition of [PPh4]Br, gives the complex [{C04(CO)33-CO)33-C7H7)}2{μ-η44- 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)33-CO)33-C7H7)(C7H10)]- [5]-. Addition of [(η- C6H6)Ru(NCMe)3][BF4]2 after the borohydride reduction gives [Ru(η- C6H6)Co3(CO)33-CO)33-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 K(DIM) (2[3]- →[4]2-) = 0.30 ± 0.05 mM-1S-1.

Lingua originaleInglese
pagine (da-a)1833-1843
Numero di pagine11
RivistaEuropean Journal of Inorganic Chemistry
Numero di pubblicazione8
DOI
Stato di pubblicazionePubblicato - 2000
Pubblicato esternamente

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