Isolation and characterization of a covalent Ce^IV-Aryl complex with an anomalous ¹³C chemical shift

The synthesis of bona fide organometallic Ce^IV complexes is a formidable challenge given the typically oxidizing properties of the Ce^IV cation and reducing tendencies of carbanions. Herein, we report a pair of compounds comprising a Ce^IV − C_aryl bond [Li(THF)₄][Ce^IV(κ²-ortho-oxa)(MBP)₂] (3-THF) and [Li(DME)₃][Ce^IV(κ²-ortho-oxa)(MBP)₂] (3-DME), ortho-oxa = dihydro-dimethyl-2-[4-(trifluoromethyl)phenyl]-oxazolide, MBP^2– = 2,2′-methylenebis(6-tert-butyl-4-methylphenolate), which exhibit Ce^IV − C_aryl bond lengths of 2.571(7) – 2.5806(19) Å and strongly-deshielded, Ce^IV − C_ipso¹³C{¹H} NMR resonances at 255.6 ppm. Computational analyses reveal the Ce contribution to the Ce^IV − C_aryl bond of 3-THF is ~12%, indicating appreciable metal-ligand covalency. Computations also reproduce the characteristic ¹³C{¹H} resonance, and show a strong influence from spin-orbit coupling (SOC) effects on the chemical shift. The results demonstrate that SOC-driven deshielding is present for Ce^IV − C_ipso¹³C{¹H} resonances and not just for diamagnetic actinide compounds.