Dienyl compounds

In a metallation reminiscent of those described in Section 9.18.4.2.3 (Equation 8), treatment of the biscyclopenta-dienyl compound 124 with (ClMe2Si)2 gives the trisilaheterocycle 125 in 69% yield <1997JOM(541)9>. The cobalt cyclobutadiene complexes 126 are formed via intramolecular cyclizations in 56-70% yield. This demonstrates that silaheterocycles can be formed at a metal center to form complexes as well as being preformed and then added to a suitable metal center to give metal derivatives (Scheme 35) <19970M646>. 

Higher Cyclic Alkenes. The effect on the reactivity of cyclo-octatetraene and of cycloheptatriene upon co-ordination to —Fe(CO)s has been investigated. Product analysis indicates that nucleophilic attack of penta-fluorothiophenoxide at Fe(dienyl)(CO)3 takes place at the dienyl ligand rather than at the iron atom, for the cyclohexa- and cyclohepta- as well as the cyclopenta-dienyl compounds. ... 

Nucleophiles attack many dienyl compounds to give diene derivatives. Most such reactions are known for iron compounds. Thus, the reaction of (l,3-cyclohexadiene)tri-carbonyliron(O) with trityl tetrafluoroborate affords (cyclohexadienyl)tricarbonyliron cation, which reacts with a nucleophile forming a diene complex [equation (8.24)]. The... 

Dienes may react with nucleophiles to give allyl complexes or they may react with electrophiles to afford dienyl compounds [equations (8.24) and (8.25)]. Some diene reactions were already discussed in Chapter 7. The nucleophiles which may attack the terminal carbon atom to give allyl compounds are H , Cl, RCO , RO , OAc, etc. In complexes, the diene molecules often undergo oxidative cycloaddition reaction, and allyl compounds are subsequently formed [equation (7.40), Table 1.4]. 

Cyclopentadienylcobalt compounds cyclize with two acetylenes, with acetylene and olefins, and with two olefins to form the five-membered ring compounds containing a cobalt atom. The cyclization mechanism with a cobalt cyclopenta-dienyl compound is shown in Scheme 17.2 [40-44]. The reaction selectively proceeds since the carbon of acetylene bonded with a bulky group bonds to the cobalt atom [45]. 

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