Cobaltocenium terminal

As an extension of this work,Kaifer et al. prepared a series of PPI dendrimers (G-l-G-4) functionalized with cobaltocenium at the periphery [48] and studied their electrochemical behavior and binding interactions with P-CD. While the positively charged cobaltocenium-terminated dendrimer 27G-1 is not com-plexed by P-CD in aqueous media, electrochemical reduction of the dendrimer in the presence of excess P-CD triggers the formation of a multisite inclusion complex with this host to provide pseudorotaxane-terminated dendrimer 28G-1 (Fig. 10). Similar electrochemical and binding behavior toward P-CD was observed for the G-2 and G-3 dendrimers. However, the resulting multisite inclu-... 

Dendrimers Terminated with Cobaltocenium and Ferrocene-Cobaltocenium Units Like ferrocene, cobaltocenium is an excellent organometallic moiety to incorporate in or functionalize dendritic systems. As already discussed, it is indeed isoelectronic with ferrocene, highly stable, positively charged complex, which undergoes a reversible monoelectronic reduction to yield the neutral cobaltocene. 

Fig. 4.4 Fourth-generation POPAM dendrimer with terminal cobaltocenium units...

The last three compounds (30-32) all comprise three macrocyclic rings with cobaltocenium units attached to a terminal ring and in one case (32) with ferrocene at the other end. 

Whereas the majority of dendrimer-based lipophilic-hydrophilic inclusion phenomena discussed thus far results in random guest positioning on a branched framework, ordered interactions in supramolecular assemblies are also of interest. For example, Gonzalez et al. reported the surface modification of poIy(propyl-eneimine)s with cobaltocenium groups that are easily reduced to Co(0). Reaction of the amine termini with I-chlorooarbonylcobaltocenium afforded the metal-terminated dendrimers. The lipophilic, charge-neutral poly-cobaltocenes were rendered H2O soluble via addition of /1-cyclodextrin (36, fi-CD) based on its cylindrical... 

Noticeably, all metallocene derivatives treated so far in this section were of peptide hormones. We have recently initiated a programme to use cellular signalling peptides for the directed delivery of organometaiiic moieties inside a cell. In this project, we have prepared metallocenoyl derivatives of a nuclear localization signal (NLS, Scheme 5.20) [99]. NLS conjugates with an N-terminal ferrocenoyl (36) or cobaltocenium carbonyl group (37) were prepared by appropriate SPPS techniques on the resin and comprehensively characterized. 

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