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)]

Abstract

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.