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.