Assessing the 4f Orbital Participation in the Ln-C Bonds of [Li(THF) 4 ][Ln(C 6 Cl 5 ) 4 ] (Ln = La, Ce).

The reaction of [Ln(NO 3 ) 3 (THF) 4 ] (Ln = La, Ce) with 4 equiv of LiC 6 Cl 5 in Et 2 O resulted in the formation of the homoleptic lanthanide-aryl "ate" complexes [Li(THF) 4 ][La(C 6 Cl 5 ) 4 ] ([Li][ 1 ]) and [Li(THF) 4 ][Ce(C 6 Cl 5 ) 4 ] ([Li][ 2 ]). These complexes represent the first isolated homoleptic perchlorophenyl complexes for the lanthanides. In the solid state, both [Li][ 1 ] and [Li][ 2 ] exhibit octa-coordinate lanthanide centers, with four Ln-C σ-bonds and four Cl → Ln dative interactions involving the ortho -Cl atoms of the C 6 Cl 5 ligands. Despite this apparent steric saturation, both [Li][ 1 ] and [Li][ 2 ] are highly temperature sensitive and quickly decompose in solution at room temperature. Density functional calculations show that the Ln-C ipso donation bonds feature only weak 4f participation (e.g., ∼1% 4f weight for [ 1 ] - ). Nonetheless, the 13 C chemical shift of the C ipso nuclei of [ 1 ] - includes ca. 8 ppm of deshielding from the spin-orbit interaction due to the participation of the 4f (and 5d) orbitals in the La-C bonds.