Photoelectron Spectroscopy of f-Element Organometallic Complexes. 10. Investigation of the Electronic Structure and Geometry of Bis(η5-pentamethylcyclopentadienyl)phosphathoracyclobutane by Relativistic ab Initio, Multipolar DV-Xα Calculations and Gas-Phase UV Photoelectron Spectroscopy

The electronic structure of the phosphathoracyclobutane CP'2Th(CH2PMeCH2) complex (Cp' = eta5-Me5C5) has been investigated by a combination of ab initio relativistic effective core potential calculations for geometry optimization, DV-Xalpha calculations, and UV photoelectron spectroscopy. The formation of the four-membered ring involves bonding interactions analogous to those found in cyclobutane. Metal-ligand bonding involves both 5f and 6d metal atomic orbitals with a major role of the latter. The gas-phase UV photoelectron spectrum has been assigned using both comparative arguments and TSIE values obtained from DV-Xalpha calculations, as well as PE data on the closely related CP'2+Th(CH2SiMe2CH2) complex. The optimized structure is indicative of a slightly puckered four-membered metallacyclic ring having the P-CH3 vector in an endocyclic axial orientation. The structure shows close analogies with diffraction data for the related CP'2+Th(CH2SiMe2CH2) complex. According with NMR data, a single energy minimum has been found for the conformation with smaller intraligand repulsive interactions involving the P3p lone pair.