Chemical reduction of the tetracobalt cluster complex [CO4(CO)(3)(mu(3)-CO)(3)(mu(3)-C7H7) (eta(5)-C7H9)] (3), followed by addition of [PPh4]Br, gives the complex [(Co-4(CO)(3)(mu(3)-CO)(3)(mu(3)-C7H7))(2)(mu-eta(4):eta(4)-(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). 1.5C(7)H(8) has been determined and confirms the reductive coupling of two C04 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 [NnBu(4)]Cl results in the formation of [Co-4(CO)(3)(mu(3)-CO)(3)(mu(3)-C7H7) (C7H10)](-) [5](-). Addition of [(eta-C6H6)Ru(NCMe)(3)] [BF4](2) after the borohydride reduction gives [Ru(eta-C6H6)Co-3(Co)(3)(mu(3)-CO)(3)(mu(3)-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 nM(-1) s(-1).
Redox chemistry of [Co-4(CO)(3)(mu(3)-CO)(3)(mu(3)-C7H7)(eta(5)-C7H9)] - Reversible carbon-carbon coupling versus metal cluster degradation
NERVI, Carlo;
2000-01-01
Abstract
Chemical reduction of the tetracobalt cluster complex [CO4(CO)(3)(mu(3)-CO)(3)(mu(3)-C7H7) (eta(5)-C7H9)] (3), followed by addition of [PPh4]Br, gives the complex [(Co-4(CO)(3)(mu(3)-CO)(3)(mu(3)-C7H7))(2)(mu-eta(4):eta(4)-(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). 1.5C(7)H(8) has been determined and confirms the reductive coupling of two C04 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 [NnBu(4)]Cl results in the formation of [Co-4(CO)(3)(mu(3)-CO)(3)(mu(3)-C7H7) (C7H10)](-) [5](-). Addition of [(eta-C6H6)Ru(NCMe)(3)] [BF4](2) after the borohydride reduction gives [Ru(eta-C6H6)Co-3(Co)(3)(mu(3)-CO)(3)(mu(3)-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 nM(-1) s(-1).
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
