Cobalticenium cation

Rhodocene, [Rh()7 -C5H5)2], is also known but is unstable to oxidation and has a tendency to form dimeric species. Claims for the existence of iridocene probably refer to Ir " complexes. However, the yellow rhodicenium and iridice-nium cations are certainly known and are entirely analogous to the cobalticenium cation in their resistance to oxidation and susceptibility to nucleophilic attack. 

Fig. 1. Space-filling models of (A) Cp2Co+1- and (B) CpjCo+ CoiCO)t based on X-ray crystallography showing the location of the anionic donors in the equatorial plane of the cobalticenium cation (27).

Fig. 2 Plot of the average diffusion layer thickness versus ultrasound intensity calculated from the limiting currents observed for the reduction of cobalticenium cations in acetonitrile at various ultrasound intensities and in cells A and B .

However, a consideration of the chemistry of these cyclopentadiene complexes slightly confuses the issue since the unsubstituted cyclopentadiene and the cxo-phenylcyclopentadiene complexes are both prepared from the cobalticenium cation. Thus it is necessary to postulate either that the attack of the nucleophilic H and Ph ions proceeds by different mechanisms or that the anomalous C-hydrogen was originally in the exo-position (see Chapter 7), p. 216. 

Treatment of the cobalticenium cation with sodium cyclopentadienide affords a binuclear complex [57]. Detailed spectral studies suggest that the complex has a structure such as 3.18 [58]. With the rhodicenium cation,... 

Attempts to reduce the rhodicenium cation with conventional reducing agents invariably give the cyclopentadiene complex Tr-C HsRhCjHe, and both the rhodicenium and cobalticenium cations undergo nucleophilic attack, by R", for example, where R = H or Ph (see Figure 26). Some unusual reactions of cobaltocene are shown in Figure 26. 

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