Institut für Anorganische Chemie, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
Dalton Trans. 2018 Jul 31;47(30):10113-10123. doi: 10.1039/c8dt01878b.
The stabilizing effect of a tris(tert-butoxy)siloxy ligand on cerium(iv) is revealed by electrochemical and computation methods as well as by targeted redox chemistry. Ceric homoleptic complex Ce[OSi(OtBu)3]4 was obtained by the reaction of [Et4N]2[CeCl6] with NaOSi(OtBu)3 at ambient temperature in acetonitrile, while cerous ion-separated complex [Ce{OSi(OtBu)3}4][K(2.2.2-crypt)] was readily synthesized from [Ce{OSi(OtBu)3}4K] and cryptand. The solid-state structures of monocerium complexes Ce[OSi(OtBu)3]4 and Ce[OSi(OtBu)3]4(THF) show 5- and 6-coordinate CeIV centers (one κ2-bonded siloxy ligand), while complex [Ce{OSi(OtBu)3}4][K(2.2.2-crypt)] exhibits a 4-coordinate CeIII center (all-terminal siloxy coordination). A comparative electrochemical study of Ce[OSi(OtBu)3]4 and [Ce{OSi(OtBu)3}4][K(2.2.2-crypt)] suggests a redox-modulated molecular rearrangement process, featuring oxidation-state dependent formation and release of a CeOtBu coordination. While the overall stabilization of CeIV by the siloxy ligand is evident, significant extra stabilization is gained if the siloxy ligand coordinates in a chelating fashion, which is further supported by DFT calculations. Natural bond orbital (NBO) analysis indicates an enhanced donation of the siloxy ligand electron density into the unfilled CeIV 6s, 4f, and 5d orbitals. CeIV to CeIII reduction readily occurs when homoleptic complex Ce[OSi(OtBu)3]4 is treated with cobaltocene, affording the separated ion pair [Ce{OSi(OtBu)3}4][CoCp2], featuring exclusive terminal siloxy bonding in the solid-state, similar to that detected for [Ce{OSi(OtBu)3}4][K(2.2.2-crypt)].
电化学和计算方法以及靶向氧化还原化学揭示了三（叔丁氧基）硅氧基配体对铈（IV）的稳定作用。通过在室温下在乙腈中用[Et4N]2[CeCl6]与 NaOSi（OtBu）3反应，得到铈同多金属配合物 Ce[OSi（OtBu）3]4，而铈离子分离配合物[Ce{OSi（OtBu）3}4][K（2.2.2- 穴醚）]可由[Ce{OSi（OtBu）3}4K]和穴醚容易合成。单核铈配合物 Ce[OSi（OtBu）3]4和 Ce[OSi（OtBu）3]4（THF）的固态结构显示 5- 和 6 配位 CeIV 中心（一个κ2-键合的硅氧基配体），而配合物[Ce{OSi（OtBu）3}4][K（2.2.2- 穴醚）]则呈现 4 配位 CeIII 中心（所有末端硅氧基配位）。Ce[OSi（OtBu）3]4 和[Ce{OSi（OtBu）3}4][K（2.2.2- 穴醚）]的电化学比较研究表明存在一种氧化还原调制的分子重排过程，其特征在于氧化态依赖的 CeOtBu 配位的形成和释放。虽然硅氧基配体对 CeIV 的整体稳定作用显而易见，但如果硅氧基配体以螯合方式配位，则会获得更大的额外稳定作用，这进一步得到了 DFT 计算的支持。自然键轨道（NBO）分析表明，硅氧基配体的电子密度更有效地捐赠到未填充的 CeIV 6s、4f 和 5d 轨道中。当同多金属配合物 Ce[OSi（OtBu）3]4 用环戊二烯基钴处理时，很容易发生 CeIV 到 CeIII 的还原，得到分离的离子对[Ce{OSi（OtBu）3}4][CoCp2]，其在固态中具有独特的末端硅氧基键合，类似于检测到的[Ce{OSi（OtBu）3}4][K（2.2.2- 穴醚）]。
