A study of the molecular and electronic structure of iron(II) and ruthenium(II) 1,3-di- and 1,2,4-tri-phospholyl sandwich compounds by photoelectron spectroscopy and density functional theory

The synthesis and variable temperature H-1 NMR spectrum of the new tetraphosphaferrocene [Fe(eta (5)-P2C3Bu3t)(2)] are presented and the photoelectron spectra are reported for [Fe(eta (5)-P3C2Bu2t)(2)] 1a, [Fe(eta (5)-P2C3Bu3t)(2)] 2a, [Fe(eta (5)-P2C3Bu3t)(eta (5)-P3C2Bu2t)] 3a and [Ru(eta (5)-P3C2Bu3t)(2)] 4a. Density functional calculations were used to optimise the geometry and calculate the ionization energies of the parent analogues. Good agreement was obtained with the experimental results, giving support to the theoretical modelling of these sandwich compounds. Analysis of their electronic structure showed that replacement of RC fragments by P atoms in the eta (5)-ligated cyclopentadienyl rings increases their acceptor properties. Extensive sigma pi mixing makes the description of the orbitals complex. Some higher lying P sigma levels are found to have similar ionization energies to the d electrons.