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.

Highlights

  • 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

  • With these considerations in mind, we aimed to prepare a CeIV − Caryl bond from the CeIV bis(methylene bisphenolate) complex Ce(THF)2(MBP)[2], that was previously synthesized by members of the Schelter laboratory (1, Fig. 2)[29]

  • Dark red X-ray quality crystals of 3-THF were grown over 3 days from a cooled (−25 °C) mixture of 3-THF in toluene and THF layered with pentane

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Summary

Introduction

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. The covalency in M − X interactions can result in anomalous and diagnostic nuclear magnetic resonance shifts, X = 13C, 15N, 19F, 77Se, 125Te, resulting from participation of f-element orbital angular momentum[7,8,9,10,11,12,13] Another important aspect of detailed f-element electronic structure is multiconfigurational character, as described in the model example of cerocene, Ce(COT)[2], COT = cyclooctatetraene ligand[14]. Complexes containing a CeIV − C σ-bond, are limited to either an N-heterocyclic carbene (NHC) complexes, e.g., Ce[L4] (Fig. 1a), or a bis(iminophosphorano)methandiide complex, e.g., [Ce(BIPMTMS)(ODipp)2] (Fig. 1a)[22,23] The latter examples are expected to have electronic structures that deviate significantly from typical organometallic alkyl, aryl, or alkynyl ligands due to the heteroatom αsubstitution[22,23,24,25]. Relativistic density functional calculations verify that the high NMR shifts are due to large SOC effects supported by the increased covalency of the CeIV − Caryl bond

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