Synthesis of a Series of Ln(III) (Ln = La, Ce, Lu) Aryl Complexes and Analysis of Their Ln-L Bonding Using Multinuclear NMR Spectroscopy and DFT Calculations

The reaction of [LaI₃(THF)₄] or [Ce(NO₃)₃(THF)₄] with 4 equiv of in situ generated LiFmes (FmesH = 1,3,5-(CF₃)₃C₆H₃) resulted in the formation of the novel homoleptic lanthanide-aryl complexes [Li(THF)₂(Et₂O)₂][La(Fmes)₄] ([Li][1]) and [Li(THF)_3.5(Et₂O)_0.5][Ce(Fmes)₄] ([Li][2]), respectively. Likewise, the reaction of [Lu(NO₃)₃(THF)₃] with 4 equiv of in situ generated LiFmes resulted in the formation of [Li(THF)₃][LuF(Fmes)₃] ([Li][3]). Complexes [Li][2] and [Li][3] were obtained as mixtures with unreacted LiFmes. Additionally, the reaction of [Lu(NO₃)₃(THF)₃] with 4 equiv of in situ generated LiC₆Cl₅ and 3 equiv of DME resulted in the formation of the homoleptic lutetium-aryl complex, [Li(DME)₃][Lu(C₆Cl₅)₄] ([Li][4]). All four complexes were characterized by X-ray crystallography and multinuclear NMR spectroscopy. In the solid state, all four complexes exhibit weak F/Cl→Ln dative interactions; however, these interactions do not apparently offer much stability, since all four complexes are thermally sensitive. DFT calculations reveal that the Ln-C_ipso and Lu–F bonds are modestly covalent, although the Lu–F bond exhibits less covalency than the Ln-C_ipso bonds. The calculations also indicate that the La–C_ipso bonds exhibit a small amount of 4f orbital participation, whereas the Lu–C_ipso bonds have (as expected) no 4f character. Despite this difference, the spin–orbit deshielding effects on the C_ipso¹³C chemical shifts are comparable between complexes [1]⁻ and [3]⁻.