Synthesis and reduction of [(C5H4SiMe3)2Ln(μ-OR)]2 (Ln = La, Ce) complexes: structural effects of bridging alkoxides

Abstract

Alcoholysis of Cp′₃Ln (Ln = La, Ce; Cp′ = C₅H₄SiMe₃) generate high-yielding (72–97%) bimetallic Ln^III complexes of [Cp′₂Ln(μ-OR)]₂ [R = Et, ⁱPr, or C₆H₄-4-^tBu]. Single-crystal X-ray diffraction of these complexes reveal unexpected decreases in Ln⋯Ln distances, increasing Cp_cent–Ln–Cp_cent angles, and increasing intermolecular C⋯C contacts with bulkier bridging alkoxides, in line with structural control driven by significant dispersion forces. ¹H NMR spectroscopy of [Cp′₂Ce(μ-OEt)]₂ and [Cp′₂Ce(μ-OⁱPr)]₂ revealed significantly upfield resonances assigned as methylene and methine moieties of −43.74 and −70.85 ppm, respectively. 2D ¹H DOSY NMR experiments of [Cp′₂Ce(μ-OⁱPr)]₂ in C₆D₆ supported a dimeric structure in solution, including in the presence of a Lewis base (i.e., THF). Reduction of [Cp′₂La(μ-OⁱPr)]₂ using KC₈ in the presence of 2.2.2-cryptand at −78 °C generated a purple solution and X-band EPR spectroscopy revealed an eight-line hyperfine pattern indicative of a La^II species.