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 [formula omitted] complex (Cp′ = η⁵-Me₅C₅) has been investigated by a combination of ab initio relativistic effective core potential calculations for geometry optimization, DV-Xα 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-Xα calculations, as well as PE data on the closely related [formula omitted] 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 [formula omitted] complex. According with NMR data, a single energy minimum has been found for the conformation with smaller intraligand repulsive interactions involving the P_3p lone pair.