Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 3. Carbon-13 nuclear magnetic resonance and iron-57 Mössbauer spectroscopic studies on [(η-cyclohexadienyl)(η-cyclopentadienyl)]iron(II) complexes

Abstract

A series of [Fe(η-C₅H₄X)(η-C₆H_7–nX_n)](X = H or Me, n= 0–6) complexes has been prepared. A detailed analysis of their ¹³C NMR spectra is presented, the assignments being confirmed using distortionless enhancement by polarisation transfer (DEPT) techniques. The co-ordination shift of the cyclohexadienyl ligand shifts are not uniform and these anomalies are discussed in terms of possible bonding schemes. The effect of substitution by chlorine and methyl groups is also included. For the case where X = Me, evidence is presented for the occurrence of conformational isomers due to restricted rotation of the ligands. The ⁵⁷Fe Mössbauer parameters are reported as well as a temperature-dependence study. The results are discussed in terms of the somewhat distorted nature of the cyclohexadienyl ligand in these complexes.