Early Lanthanide(III) Ate Complexes Featuring Ln–Si Bonds (Ln = La, Ce): Synthesis, Structural Characterization, and Bonding Analysis

While research on lanthanide (Ln) complexes with silyl ligands is receiving growing attention, significantly unbalanced efforts have been devoted to different Ln elements. In comparison with the intense investigations on Ln elements such as Sm and Yb, the chemistry of silyl lanthanum and cerium complexes is much slower to develop, and no solid-state structure of a silyl lanthanum complex has been reported so far. In this research, four types of ate complexes, including [(DME)3Li][Cp3LnSi(H)Mes2], [(18-crown-6)K][Cp3LnSi(CH3)Ph2], [(DME)3Li][Cp3LnSiPh3], and [(12-crown-4)2Na] [Cp3LnSi(Ph)2Si(H)Ph2] (Ln = La, Ce), were synthesized by reacting [(DME)3Na][Cp3La(μ-Cl)LaCp3] or Cp3Ce(THF) with alkali metal silanides. All of the synthesized silyl Ln ate complexes were structurally characterized. La-Si bond lengths are in a range of 3.1733(4)-3.1897(10) Å, and the calculated formal shortness ratios of the La-Si bonds (1.071.08) are comparable to those in the reported silyl complexes having other Ln metal centers. The Ce-Si bond lengths (3.1415(6)-3.1705(9) Å) are within the typical range of reported silyl cerium ate complexes. 29Si solid-state NMR measurements on the diamagnetic silyl lanthanum complexes were conducted, and large one-bond hyperfine splitting constants arising from = 7/2) were resolved. Computational studies on these silyl lanthanum and cerium complexes suggested the polarized covalent feature of the Ln-Si bonds, which is in line with the measured large 1J139La-Si splitting constants.