Reactivity of co-ordinated ligands. Part XII. Some heptafulvene complexes of tricarbonyliron and their electrophilic reactions

Abstract

Tricarbonyliron complexes of some simple heptafulvenes, which are mono- or di-substituted at the 8-carbon atom are prepared in good yield from cycloheptatriene derivatives. Attempts to prepare the parent complex led to a dimer. The complexes of the unsymmetrical heptafulvenes were isolated as mixtures of cis- and trans-isomers. In contrast to the unco-ordinated systems the complexes undergo electrophilic attack on the ring. Thus protonation occurs to give stable dienyl salts; formylation of tricarbonyl-8-p-tolylheptafulveneiron gives tricarbonyl-1-formyl-8-p-tolylheptafulveneiron (1) which is not a mixture of isomers. A europium shift reagent was used to demonstrate that this was the trans-isomer. The aldehyde (1) may be reduced to the corresponding primary alcohol, which on treatment with hexafluorophosphoric acid gave a salt which contained two exocyclic double-bonds. Reaction of this salt with methoxide ion gave an ether which gave the expected adduct with tetracyanoethylene. Formylation of tricarbonyl-8-methyl-8-p-tolylheptafulveneiron afforded the uncomplexed aldehyde, 1-formyl-8-methyl-8-p-tolylheptafulvene in which the tolyl group is trans to the carbonyl function.