Organometallic complexes in synthesis. Part V. Some tricarbonyliron derivatives of cyclohexadienecarboxylic acids

Abstract

Reactions of iron pentacarbonyl with several methyl cyclohexadienecarboxylates lead to tricarbonyliron complexes. The most stable of these is the ‘conjugated’ isomer (2; R = Me), which can be obtained from the others by treatment with methanolic acid or in some cases with methanolic methoxide. The latter method is the first observed example of base-catalysed isomerisation in tricarbonylcyclohexadieneiron complexes. When deuteriated reagents are used the acidic procedure leads to incorporation of one deuterium atom only, in the 6-position. irrespective of the starting material. Reactions of the acids with diborane yield the carbinols, one of which [tricarbonyl-1 -(hydroxymethyl)cyclohexa-1,3-dieneiron (8)], on treatment with acid, produces the rearranged carbonium salt (9). Hydride abstraction from the isomeric esters gives a series of carbonium salts, which react with water at various rates to produce hydroxy-complexes and dimeric ethers. Complexing of some methyl methylcyclohexa-1,4-dienecarboxylates is reported. Aspects of theory connected with hydrogen migration and hydride abstraction are discussed.