Heteroatom-containing pentadienyl

Fig. 4.2 illustrates the first few members of the series of equilibria of conjugated ions. In cations, they are the equilibria between the allyl 4.11 and the cyclopropyl cation 4.12, the pentadienyl 4.13 and the cyclopentenyl cation 4.14, and the heptatrienyl 4.15 and cycloheptadienyl cation 4.16, In anions, they are between the allyl 4.17 and the cyclopropyl anion 4.18, the pentadienyl 4.19 and the cyclopentenyl anion 4.20, and the heptatrienyl 4.21 and cycloheptadienyl anion 4.22. There are heteroatom-containing analogues, with nitrogen and oxygen lone pairs rather than a carbanion centre, and the systems can again have substituents and fused rings. 

Compound 95 has been shown to be a useful precursor for the synthesis of a range of open and closed dienyl complexes, in particular, the preparation of open and closed ruthenocene. A series of 1,5-, 2,4- and 3-substituted pentadienyl complexes of ruthenium have been prepared and characterised. A series of heteroatom-containing diene complexes of type 96 have been synthesised. 1,2-Diketones were shown, however, not to coordinate in this fashion, rather to undergo a one-electron transfer reaction giving enediolato-containing complexes. Complexes of type 97 have been synthesised on treatment of the triple decker complex [ (CpR)Co 2(p-r r -C6F[5Me)] with acetone, cyclohexanone, and acetophenone. The mechanism of formation was said to proceed through a... 

Substitution of three carbon atoms with heteroatoms in the pentadienyl anion leads to the structures shown in Scheme 21 (only vicinal N-substitution is considered). The resulting heterocycle is a triazoline ring. Photochromic molecules 43 containing this structural element have been made (Scheme 21).51,52... 

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