A spectroscopic study of bis(η 6-arene)iron(II) salts

Abstract

A number of bis(η 6-arene)iron(II) salts have been synthesised from the following ligands: benzene, toluene, ethylbenzene, ortho, meta and para xylenes, mesitylene, 1,2,3,4-tetramethylbenzene, 1,2,3,5-tetramethylbenzen, 1,2,4,5-tetramethylbenzene, pentamethylbenzene, and hexamethylbenzene. The stabilities of these complexes in solution vary considerably both with solvent basicity and the degree of alkyl substitution. 1H and 13C NMR data are reported. The observed large upfield shifts of ligand 13C signals is discussed in terms of shielding by the d z 2 electrons of the central iron atom. 13C shifts correlate reasonably well with the total charge density at the relevant carbon atom for a variety of sandwich complexes, including those discussed in this work. 57Fe Mössbauer data are presented; quadrupole splittings increase systematically with the number of methyl substituents on the ligands. These changes are explained in terms of imbalances in the electronic population of metal-based e 2 and ligand-based e 1 orbitals.