Structural, Spectroscopic, and Bonding Analyses of La(III)/Ce(III)-Tetrel Ate-Complexes

In comparison with the research of transition-metal-tetrel complexes, the chemistry of lanthanide tetrel complexes, especially for these bearing heavier tetrel element ligands, is still relatively underexplored. In this research, K[Cp₃Ln(III)CH₂Ph], [(DME)₃Li][Cp₃Ln(III)GePh₃], and [(DME)₃Li][Cp₃Ln(III)SnPh₃] [Ln(III) = La(III), Ce(III)] have been synthesized by reacting [(DME)₃Na][Cp₃La(μ-Cl)LaCp₃] or Cp₃Ce(THF) with alkali metal alkyl, germyl, and stannyl reagents. Additionally, [(DME)₃Li][Cp₃Ce(III)SnPh₃] is the first example of Ce(III)-Sn bond containing complex. All the obtained early Ln(III) tetrel ate-complexes were structurally analyzed by single-crystal X-ray diffraction. The formal shortness ratios of the Ln(III)-C, Ln(III)-Ge, and Ln(III)-Sn bonds are in the range of 1.03-1.11. Together with the previously reported [(DME)₃Li][Cp₃Ln(III)SiPh₃], a group of tetrel (up to Sn) lanthanocene ate-complexes with an analogous coordination pattern are presented. Computational studies suggest the strongly polarized nature of the Ln(III)-E (E = C, Si, Ge, Sn) bonds in these complexes, with 77-85% atomic orbital contribution from tetrel elements and 15-23% atomic orbital contribution from Ln(III). The UV-vis measurements of this series of complexes show that the characteristic absorptions are hypsochromically shifted for Ln(III) heavier tetrel complexes in comparison to their lighter congeners. Moreover, the HOMOs, in which the Ln(III)-E σ-bonding orbitals are the dominant components, of these series complexes act as donor orbitals of the major electron transitions, as being disclosed by the time-dependent density functional theory analysis.