Hydrogenation alkenylbenzenes

Hydrogenation of the side chain double bond of an alkenylbenzene is much easier than hydrogenation of the aromatic ring and can be achieved with high selectivity leav mg the ring unaffected... 

Only a few examples of alkenylbenzene hydroformylation are available. Styrene and a-methylstyrene were reported to lead to hydrogenation as the main reaction when Co2(CO)8 was used. 

Hydrogen bromide (but not the chloride) has a catalytic effect on the cyclization of alkenylbenzenes with sulphur. Undo mildly basic conditions, cinnamonitriles on heating with disulphur dichloride give the synthetically useful chloronitriles... 

There is ample chemical evidence that the 1-alkenyl substituent on the arene plays a crucial role during the assembly of the metal cluster. For example, no arene cluster complexes are formed with alkyl substituted benzene derivatives. Such complexes, 14, are perfectly stable and could be obtained indirectly through hydrogenation of the corresponding /rs-alkenylbenzene precursors (Table... 

The side-chain double bond is more reactive than the aromatic ring toward most electrophilic reagents. Many of the reactions of alkenes that were discussed in Chapter 6 find a parallel in the reactions of alkenylbenzenes. Thus, hydrogenation and halogen addition to a side-chain double bond can be achieved while leaving the ring unchanged. 

The tricobalt clusters of the type (CpCo)3(/t3-arene), 435, could only be synthesized with alkenylbenzenes as the facial ligands (see the mechanism of synthesis above). The exocyclic C=C bond did however play no role in the stabilization of these complexes. Indeed, the catalytic hydrogenation of this C=C unit in the side chain was achieved and the corresponding reduced compounds were perfectly stable as was evidenced by their crystal structure analyses, which showed a very similar geometry for the new complexes. In solution, hindered rotation of the /t3-arene was observed. ... 

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