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 [LaI 3 (THF) 4 ] or [Ce(NO 3 ) 3 (THF) 4 ] with 4 equiv of in situ generated LiFmes (FmesH = 1,3,5-(CF 3 ) 3 C 6 H 3 ) resulted in the formation of the novel homoleptic lanthanide-aryl complexes [Li(THF) 2 (Et 2 O) 2 ][La(Fmes) 4 ] ([Li][ 1 ]) and [Li(THF) 3.5 (Et 2 O) 0.5 ][Ce(Fmes) 4 ] ([Li][ 2 ]), respectively. Likewise, the reaction of [Lu(NO 3 ) 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(NO 3 ) 3 (THF) 3 ] with 4 equiv of in situ generated LiC 6 Cl 5 and 3 equiv of DME resulted in the formation of the homoleptic lutetium-aryl complex, [Li(DME) 3 ][Lu(C 6 Cl 5 ) 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 ipso 13 C chemical shifts are comparable between complexes [ 1 ] − and [ 3 ] − .