Conformational analysis for the ligands CH2OR (R = Me, CH2Ph, and menthyl) and CH2SR (R = Me, Et, CH2Ph, and Ph) attached to the iron chiral auxiliary [(C5H5)Fe(CO)(PPh3)]
A conformational analysis of iron alkyl complexes of the type [(C5H5)Fe(CO)(PPh3)CH2XR] that have an oxygen or sulphur substituent attached to C(α) has been conducted in order to investigate the dependence of conformation on solvent polarity. 1H n.m.r. analysis, including variable temperature and n.O.e. experiments, indicated that the primary factor controlling conformational preferences in these complexes is steric interaction. For the complexes that do not have a significant steric bias between alternative conformations, the preferred conformation is observed, to be dependent on solvent polarity. This phenomenon is due to a dipolar interaction between the polarised C(α)–heteroatom bond and the chiral auxiliary [(C5H5)Fe(CO)(PPh3)] metal fragment.