Synthesis of σ-(o-carboran-9-yl)- and σ-(m-carboran-9-yl)-π-cyclopentadienyldicarbonyliron and their rearrangement in reactions with bromine to π-(o-carboran-9-yl)cyclopentadienyl- and π-(m-carboran-9-yl)cyclopentadienyl-dicarbonylironbromides,respectively

9-o- and 9-m-carboranylcarboxylic acids were used to synthesize σ-(o-carboran-9-yl)- and σ-(m-carboran-9-yl)-π-cyclopentadienyldicarbonyliron. The latter complexes, in reactions with bromine, undergo rearrangement with the cleavage of the BFe σ-bond, involving migration of the 9-o- and 9-m-carboranyl groups into the cyclopentadienyl ring, to give π-(o-carboran-9-yl)cyclopentadienyl- and π-(m-carboran-9-yl)cyclopentadienyl-dicarbonyliron bromides, respectively. A simple method to obtain these acids by the oxidation of 9-alkyl-o- and 9-alkyl-m-carboranes with CrO₃ in CH₃COOH has been found.