Improved Syntheses of 1,2-Disubstituted Ferrocenes

Abstract

1,2-Disubstituted ferrocenes, in particular 1,2-dihaloferrocenes, are important starting materials. Herein, we describe significantly improved high-yielding syntheses of 1,2-disubstituted ferrocenes such as 1,2-dibromo- and 1,2-diiodoferrocene as well as 1-bromo-2-iodoferrocene, and 1-bromo-2-fluoroferrocene. DFT calculations show that 1,2-dihaloferrocenes do not differ much in their highest occupied molecular orbital (HOMO) energies; however, their lowest unoccupied molecular orbital (LUMO) energies – and thus the HOMO/LUMO gaps – correlate with the sum of the halogen electronegativities. In addition, a synthesis of the rather sensitive 2-aminoferrocenecarboxylic acid, the ferrocene analogue of anthranilic acid, is presented, which starts from ferrocene-1,2-dicarboxylic acid. However, 2-aminoferrocenecarboxylic acid rapidly decomposed and thus could not be properly characterized. Ferrocene-1,2-dicarboxylic anhydride serves as the starting material for preliminary photochemical decarbonylation/decarboxylation experiments resulting in 1,2-dideuterioferrocene when carried out in [D8]toluene.