Synthesis and reduction of [(C 5 H 4 SiMe 3 ) 2 Ln(μ-OR)] 2 (Ln = La, Ce) complexes: structural effects of bridging alkoxides.

Alcoholysis of Cp' 3 Ln (Ln = La, Ce; Cp' = C 5 H 4 SiMe 3 ) generate high-yielding (72-97%) bimetallic Ln III complexes of [Cp' 2 Ln(μ-OR)] 2 [R = Et, i Pr, or C 6 H 4 -4- t Bu]. 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. 1 H NMR spectroscopy of [Cp' 2 Ce(μ-OEt)] 2 and [Cp' 2 Ce(μ-O i Pr)] 2 revealed significantly upfield resonances assigned as methylene and methine moieties of -43.74 and -70.85 ppm, respectively. 2D 1 H DOSY NMR experiments of [Cp' 2 Ce(μ-O i Pr)] 2 in C 6 D 6 supported a dimeric structure in solution, including in the presence of a Lewis base ( i.e. , THF). Reduction of [Cp' 2 La(μ-O i Pr)] 2 using KC 8 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.