Electron-rich Fe(ii) and Fe(iii) organoiron σ-alkynyl complexes bearing a functional aryl group. Vibrational spectroscopic investigations of the substituent effect on the CC triple bond

Solid state Raman and IR spectra of [(η2-dppe)(η5-C5Me5)Fe(CC–C6H4–X)n+][PF6−]n (n = 0, 1; dppe = 1,2-(diphenylphosphino)ethane; X = NO2, CN, CF3, F, Br, H, Me, tBu, OMe, NH2) complexes (1a–j/[1a–j+][PF6−]) were recorded. The Raman spectra are discussed in connection with the corresponding solid state IR spectra. In the present set of compounds, Raman allows a firm identification of νCC stretching modes and confirms the occurrence of Fermi coupling with some substituents in a given oxidation state. Linear correlations between the IR frequencies or between the square roots of the intensities of the alkynyl stretch and the electronic substituent parameters (ESPs) allow establishment of the electronic origin of the substituent influence on the strength and polarization of the triple bond.