While hundreds trivalent rare-earth (RE) metal-carbon σ-bond complexes have been synthesized, only a handful of tetravalent RE metal-carbon σ-bond complexes are known. However, tetravalent RE metal-carbon σ-bond complexes without chelate-assisted stabilization have never been reported because of synthetic challenges. Herein, we report the first synthesis and structural characterization of a complete series of cerium(IV) alkyl, aryl and alkynyl complexes without chelate-assisted stabilization. The Ce^IV-C σ-bond complexes are synthesized from reactions of imidazolin-2-iminato cerium(IV) chlorides with lithium alkyl, aryl or alkynyl reagents, and are all characterized by single crystal X-ray diffraction. The investigation on the decomposition of cerium(IV) alkyl complexes shows the generation of alkyl radicals, indicating a homolytic cleavage mechanism of Ce^IV-C(sp³) σ-bond, which is significantly different from the decomposition mechanism of RE^III-C(sp³) σ-bond. Quantum theoretical studies are performed to provide insights in the Ce^IV-C(spⁿ) (n = 1, 2, 3) σ-bonding properties as well as the high ¹³C{¹H} NMR chemical shifts of Ce^IV-C signals. The electronic influence of the supporting ligands is also studied theoretically, which reveals the strong electron-donating imidazolin-2-iminato ligand enhances the energy-level match of the Ce(IV) 5d orbitals with the alkyl group. This energy-level match strategy provides insights for preparing RE complexes with unusual chemical bonds.

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中文翻译：

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通过能级匹配策略努力形成铈(IV)-烷基、-芳基和-炔基配合物

虽然已经合成了数百种三价稀土 (RE) 金属-碳 σ-键配合物，但只有少数四价稀土 (RE) 金属-碳 σ-键配合物是已知的。然而，由于合成方面的挑战，没有螯合物辅助稳定作用的四价稀土金属-碳σ键配合物从未被报道过。在此，我们报告了全系列不含螯合物辅助稳定的铈（IV）烷基、芳基和炔基配合物的首次合成和结构表征。 Ce ^IV -C σ-键配合物是由咪唑啉-2-亚胺氯化铈(IV)与烷基锂、芳基锂或炔基试剂反应合成的，并且均通过单晶X射线衍射进行了表征。对铈(IV)烷基配合物分解的研究表明烷基自由基的产生，表明Ce ^IV -C( sp ^{3 ) σ-键的均裂机制，与RE III} -C的分解机制显着不同( sp ³ ) σ-键。进行量子理论研究是为了深入了解 Ce ^IV -C( sp ⁿ ) ( n  = 1, 2, 3) σ 键合特性以及Ce ^IV - C的高¹³ C{ ¹ H} NMR 化学位移信号。理论上还研究了支撑配体的电子影响，揭示了强给电子咪唑啉-2-亚胺配体增强了Ce(IV) 5d轨道与烷基的能级匹配。这种能级匹配策略为制备具有不寻常化学键的稀土配合物提供了见解。

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