Isolation and characterization of a covalent Ce(IV)-Aryl complex with an anomalous (13)C 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)(κ(2)-ortho-oxa)(MBP)(2)] (3-THF) and [Li(DME)(3)][Ce(IV)(κ(2)-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(ipso) (13)C{(1)H} 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 (13)C{(1)H} 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(ipso) (13)C{(1)H} resonances and not just for diamagnetic actinide compounds.