| Autor: |
Bott, S. G., Yang, K., Talafuse, K. A., Richmond, M. G. |
| Zdroj: |
Organometallics; March 2003, Vol. 22 Issue: 7 p1383-1390, 8p |
| Abstrakt: |
Thermolysis of the hydrogen-capped cluster HCCo2NiCp(CO)6 (1) with the redox-active diphosphine 2,3-bis(diphenylphosphino)maleic anhydride (bma) in DCE at ca. 80 °C affords the zwitterionic cluster Co2NiCp(CO)4(μ-CO)[μ2,η2,η1-C(H)PPh2C&dbd;C(PPh2)C(O)OC(O)] (2) as the first observable product. Cluster 2 is not stable and transforms into the phosphido-bridged cluster Co2NiCp(CO)4[μ2,η2,σ-C(H)PPh2C&dbd;CC(O)OC(O)](μ2-PPh2) (3). Both clusters 2 and 3 have been isolated and characterized in solution by IR and 31P NMR spectroscopies, and the solid-state structures of both 2 and 3 have been determined by X-ray crystallography. Cluster 2 exhibits an open Co2Ni core having one Co−Co and Co−Ni bond. The bma ligand is attached to the hydrocarbyl and CpNi moieties via the PPh2 groups, and one of the Co centers is tethered to the π bond of the bma ligand. The opened Co2Ni core of cluster 3 is structurally similar to 2 and consists of a μ2-PPh2 ligand that spans the Co−Co bond and a Ni−C σ bond resulting from the formal coupling of the maleic anhydride residue with the CpNi moiety. The reaction involving the conversion of 2 to 3 was examined by UV−vis spectroscopy and found to obey first-order kinetics. A rate-limiting step involving dissociative CO loss is supported by the rate retardation in the presence of added CO and the activation parameters (ΔH&thermod; = 31.4 ± 1.2 kcal/mol and ΔS&thermod; = 21 ± 4 eu). Our studies provide the first structural evidence for the attack of a phosphine ligand on the μ3-hydrocarbyl ligand in this genre of tetrahedral cluster and suggest that the nature of the capping CR group and the electrophilicity of the CpNi center play a role in determining the course of ligand substitution. Reactivity comparisons with the related bma-substituted clusters RCCo3(CO)7(bma) are discussed. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
|
