Electronic structure of [M(eta-P3C2Bu2t)(CO)(3)] (M = Mn or Re): a study by photoelectron spectroscopy and density functional calculations

The compounds [M(eta (5)-P3C2Bu2t)(CO)(3)] (M = Mn 1 or Re 2) are reported and their He I and He II photoelectron spectra assigned. Their electronic s tructure has been investigated by means of density functional calculations and reasonable agreement between experimental and calculated ionisation ene rgies is achieved. The bonding between the metal and the ring is predominan tly donation from the ring to the metal. Back donation into the highest pi orbitals of the ring is minimal. The calculations suggest substantial mixin g between the ring sigma and pi orbitals on coordination to the metal. Calc ulations on [Mn(eta (5)-P3C2Bu2t)(2)] reproduce the unusual (2)A ground sta te and show that this results from stabilisation of the metal e(2) type orb itals by formation of a delta bond with the unoccupied pi orbitals of the r ings.