Polyenes metal-bound—

Fig. 2. Example of an HBDC molecular rotor chemically bound to a polyene chain holding a metal cluster. As in Fig. 1, X-X is the rotation axis. This molecule must be prepared in a quasi-classical state to ensure lifting of the cluster load using the polymer chain as a string...

When the metal fragment is a poor ir base, the L model (5.4) applies and the vinylic carbons bound to the metal behave as masked, metal-stabilized carbonium ions. In such a case we often see nucleophilic attack (e.g., Eq. 5.10)." This is an example of a more general reaction type—nucleophilic attack on polyenes or polyenyls, and will be discussed in more detail in S tion 8.3. 

In the vast majority of cases, the nucleophile adds to the face of the polyene opposite to the metal. Since the metal is likely to have bound to the least hindered face of the free polyene, we may therefore see a selective attack of the nucleophile on what was the more hindered face in the free polyene this is often useful in organic synthetic applications. 

Hydrogen chloride is bound with metallic (Zn, Ca, Ba) organic acid salts with formation of the metal chloride and the corresponding free fatty acids. The formation of polyene sequences can be prevented by combination reactions with thiol or mal-eate derivatives. Although efficient in blocking the degradation, most of the inor-... 

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