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 tetrapho sphaferrocene [Fe(eta (5)-P2C3Bu3t)(2)] are presented and the photoelectron spectra are reported for [Fe(eta (5)-P3C2Bu2t)(2)] 1a, [Fe(eta (5)-P2C3Bu3 t)(2)] 2a, [Fe(eta (5)-P2C3Bu3t)(eta (5)-P3C2Bu2t)] 3a and [Ru(eta (5)-P3C2 Bu3t)(2)] 4a. Density functional calculations were used to optimise the geo metry and calculate the ionization energies of the parent analogues. Good a greement was obtained with the experimental results, giving support to the theoretical modelling of these sandwich compounds. Analysis of their electr onic structure showed that replacement of RC fragments by P atoms in the et a (5)-ligated cyclopentadienyl rings increases their acceptor properties. E xtensive sigma pi mixing makes the description of the orbitals complex. Som e higher lying P sigma levels are found to have similar ionization energies to the d electrons.