Multiferrocenyl Cobalt-Based Sandwich Compounds

The reaction of FcC=C-C=CFc [Fc = Fe(eta(5)-C5H4)(eta(5)-C5H5)] (1) with Co(eta(5)-C5H5)(CO)(2) (2) afforded ferrocenyl-functionalized cyclobutadiene and cyclopentadienone cobalt(I) compounds as well as multiferrocenyl benzene derivatives. The synthesis procedures are described. Eleven products could be separated by column chromatography and were characterized by NMR, UV/Vis, and IR spectroscopy, high-resolution ESI-TOF mass spectrometry and elemental analysis. For five representatives, the structure in the solid state was determined by single X-ray structure analysis. The electronic properties of the appropriate compounds were studied by using cyclic and square-wave voltammetry. Further investigation of the interaction between Fe-II/Fe-III centers in the mixed-valent species was achieved by in situ UV/Vis/NIR spectroelectrochemistry. These measurements demonstrated that weak electronic metal-metal interactions through the cobalt-coordinated cyclobutadiene building block occur (weakly coupled class II systems according to the classification of Robin and Day), whereas the cyclopentadienone core acts as an insulator (class I), and hence only electrostatic interactions are characteristic.