Isolation and characterization of a covalent Ce<sup>IV</sup>-Aryl complex with an anomalous <sup>13</sup>C chemical shift.
basic_science · Level V
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- Record sourced from PubMed, PMID 33731719.
- Also identified by DOI 10.1038/s41467-021-21766-4 and PMC identifier 7969749.
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Abstract
The synthesis of bona fide organometallic Ce<sup>IV</sup> complexes is a formidable challenge given the typically oxidizing properties of the Ce<sup>IV</sup> cation and reducing tendencies of carbanions. Herein, we report a pair of compounds comprising a Ce<sup>IV</sup> - C<sub>aryl</sub> bond [Li(THF)<sub>4</sub>][Ce<sup>IV</sup>(κ<sup>2</sup>-ortho-oxa)(MBP)<sub>2</sub>] (3-THF) and [Li(DME)<sub>3</sub>][Ce<sup>IV</sup>(κ<sup>2</sup>-ortho-oxa)(MBP)<sub>2</sub>] (3-DME), ortho-oxa = dihydro-dimethyl-2-[4-(trifluoromethyl)phenyl]-oxazolide, MBP<sup>2-</sup> = 2,2'-methylenebis(6-tert-butyl-4-methylphenolate), which exhibit Ce<sup>IV</sup> - C<sub>aryl</sub> bond lengths of 2.571(7) - 2.5806(19) Å and strongly-deshielded, Ce<sup>IV</sup> - C<sub>ipso</sub> <sup>13</sup>C{<sup>1</sup>H} NMR resonances at 255.6 ppm. Computational analyses reveal the Ce contribution to the Ce<sup>IV</sup> - C<sub>aryl</sub> bond of 3-THF is ~12%, indicating appreciable metal-ligand covalency. Computations also reproduce the characteristic <sup>13</sup>C{<sup>1</sup>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<sup>IV</sup> - C<sub>ipso</sub> <sup>13</sup>C{<sup>1</sup>H} resonances and not just for diamagnetic actinide compounds.