Theoretical and Spectroscopic Studies of (µ-Butatriene)hexacarbonyldiiron Compounds

The bonding scheme in (µ-butatriene)hexacarbonyldiiron complexes is discussed on the basis of their ¹³C NMR and He I excited-gas-phase photoelectron spectra. ¹³C butatriene resonances have been assigned by using the proton-coupled NMR spectra. At room temperature a single resonance is seen in the carbonyl region, which splits into three resonances at lower temperatures. PE data are analyzed by comparison arguments with related M₂(CO)₆L systems and qualitative quantum-mechanical considerations. CNDO type calculations, which are in qualitative agreement with the proposed assignments, outline the presence of two strong Fe-C bonds accounting for the major Fe₂(CO)₆-butatriene interaction.