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

Abstract

The synthesis of bona fide organometallic CeIV complexes is a formidable challenge given the typically oxidizing properties of the CeIV cation and reducing tendencies of carbanions. Herein, we report a pair of compounds comprising a CeIV − Caryl bond [Li(THF)4][CeIV(κ2-ortho-oxa)(MBP)2] (3-THF) and [Li(DME)3][CeIV(κ2-ortho-oxa)(MBP)2] (3-DME), ortho-oxa = dihydro-dimethyl-2-[4-(trifluoromethyl)phenyl]-oxazolide, MBP2– = 2,2′-methylenebis(6-tert-butyl-4-methylphenolate), which exhibit CeIV − Caryl bond lengths of 2.571(7) – 2.5806(19) Å and strongly-deshielded, CeIV − Cipso13C{1H} NMR resonances at 255.6 ppm. Computational analyses reveal the Ce contribution to the CeIV − Caryl 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 CeIV − Cipso13C{1H} resonances and not just for diamagnetic actinide compounds.

X-ray absorption spectra of f-element complexes: insight from relativistic multiconfigurational wavefunction theory

“…Covalent bonding involving the Ln 4f orbitals has long been considered to be of minor importance, but there are notable exceptions. The 4f orbitals contribute to covalent bonding, e.g., in CeO 2 , Ce(C 8 H 8 ) 2 , and other Ce(IV) systems, [16][17][18][19][20][21][22][23] NPrO, 24 PrO 2 + , 25 TbO 2 and PrO 2 , 26 and (C 5 Me 5 ) 2 Yb. 27 5f-shell bonding can be pronounced, especially for elements up to Cm.…”

Covalency of Trivalent Actinide Ions with Different Donor Ligands: Do Density Functional and Multiconfigurational Wavefunction Calculations Corroborate the Observed “Breaks”?

“…Complementary to orbital-based approaches, the electron density-based quantum theory of atoms-in-molecules (QTAIM) provides an alternative path to quantify different types of bonding interactions. Successful applications have been reported for a wide range of weak to strong interactions in chemical systems with main-group elements, lanthanides, as well as actinides. ,− QTAIM descriptors for chemical bonding (vide infra) generally show good correlation with experimental observations, ,,,− albeit not without exceptions when dealing with actinide complexes …”

Synthesis of Parent Acetylide and Dicarbide Complexes of Thorium and Uranium and an Examination of Their Electronic Structures

“…Indeed, the use of NMR spectroscopy to study covalency is emerging as a valuable technique for probing the electronic structure of f-element–ligand bonds. A variety of nuclei have been employed for this purpose, including 77 Se, 125 Te, and 15 N. − This analysis has also been applied to a variety of organometallic actinide and lanthanide complexes, including those containing alkyl, aryl, and carbene ligands. − …”