Electronic structure factors of Ge–H bond activation by transition metals. Photoelectron spectra of [Mn(η5-C5H5)(CO)2(HGePh3)], [Mn(η5-C5H4Me)(CO)2(HGePh3)], and [Mn(η5-C5Me5)(CO)2(HGePh3)]

Abstract

The He I photoelectron spectra of [Mn(η⁵-C₅H₅)(CO)₂(HGePh₃)], [Mn(η⁵-C₅H₄Me)(CO)₂-(HGePh₃)], and [Mn(η⁵-C₅Me₅)(CO)₂(HGePh₃)] have been obtained to measure the nature and extent of Ge–H bond interaction with the transition metal centre in these complexes. The principal electronic structure factors contributing to the addition of the Ge–H bond to the transition metal involve the interaction of the Ge–H σ and σ* orbitals with the metal. The shape and splitting pattern of the metal-based ionisation band indicates the extent of Ge–H σ* interaction. The electron distribution between the Ge–H bond and the metal is indicated by the relative stabilities of the metal- and ligand-based ionisations. The electron charge-density shift from the metal to the ligand is negligible in these three complexes and the metal ionisations reflect the formal d⁶ electron count at the metal centre. The electronic structure of the Ge–H interaction with the metal is in the initial stages of Ge–H bond addition to the metal, before oxidative addition has become prevalent. The mechanism of interaction of the Ge–H bond with the manganese centre is predominantly through interaction of the filled Ge–H σ-bonding orbital with the empty metal orbitals. It is concluded that the magnitude of Ge–H σ interaction with the metal centre is similar to that of the corresponding Si–H σ interaction.