Multiple-bond metathesis mediated by sterically pressured uranium complexes
Multiple-bond metathesis mediated by sterically pressured uranium complexes
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DOI：
10.1002/anie.200501667
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Meyer, K
中科院分区：
文献类型：
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作者：
Castro-Rodríguez, I;Nakai, H;Meyer, K
近年来，空间位阻配体被越来越多地用于合成配位不饱和、高反应活性的金属配合物。[1]旁观者配体和螯合剂所施加的空间限制通常转化为分子和电子结构的变化，因为它们直接影响配位模式和金属-配体轨道相互作用;后者在原子转移化学中特别重要。相对于具有较少定制配体的络合物，具有分子工程化配体环境的不饱和金属离子通常由于空间压力的增加而显示出改变和增加的反应性。空间剪裁，高活性过渡金属配合物实现了各种各样的小分子活化和原子转移化学非常成功。[2-6]然而，施加空间压力的策略并不总是足以实现某些期望的反应性。例如，最近一类基于过渡金属的氮转移试剂（氮丙啶化催化剂）利用高价过渡金属氮化物络合物，其在用三氟乙酸酐（TFAA）活化时容易将亚氨基酰基实体转移到烯烃。[7-9]由于高度共价的dπ-pπ相互作用，用TFAA活化MN是必不可少的，从而产生非常强的金属-氮化物三键。[10-12]然而，在铀化学中，价f轨道不像金属d轨道那样参与成键。因此，铀的亚氨基和难以捉摸的氮化物中的UN形式三键在本质上是离子性的，可以描述为U（δ+）-N（δ +）。因此，我们预期空间加压的铀亚氨基和/或氮化配合物与定制设计的螯合剂，以表现出增加的亲核性对有机基板。因此，我们的目标是合成不同空间需求的高价铀亚氨基和氮化配合物，以探索氮转移和基团转移化学的可能应用。（1，（tBuArOH）3 tacn = 1，4，7-三（3，5-二叔丁基-2-羟基苄基）-1，4，7-三氮杂环壬烷）[13]与三甲基甲硅烷基叠氮化物（Me 3SiN 3），得到了叠氮和亚胺铀配合物[（（tBuArO）3 tacn）U（L）]（L= NH3
In recent years, sterically encumbering ligands have been used increasingly to synthesize coordinatively unsaturated, highly reactive metal complexes.[1] The steric constraints imposed by spectator ligands and chelators often translate into molecular and electronic structural changes as they directly impact the coordination mode and metal–ligand orbital interactions; the latter being particularly important in atom-transfer chemistry. Relative to complexes with less customized ligands, unsaturated metal ions with molecularly engineered ligand environments often show altered and increased reactivity as a result of the increased steric pressure. Sterically tailored, highly reactive transition-metal complexes achieve a wide variety of small-molecule activation and atom-transfer chemistry very successfully.[2–6] The strategy of applying steric pressure, however, is not always sufficient to achieve certain desired reactivities. The most recent class of transition-metal-based nitrogen-transfer reagents (aziridination catalysts), for example, takes advantage of high-valent transition-metal nitrido complexes that readily transfer the imidoacyl entity to olefins upon activation with trifluoroacetic acid anhydride (TFAA).[7–9] The MN activation with TFAA is indispensable due to the highly covalent dπ–pπ interaction, thus resulting in very strong metal–nitrido triple bonds.[10–12] In uranium chemistry, however, the valence f orbitals do not participate in bonding to the same extent as metal d orbitals. As a result, the UN formal triple bond in the uranium imido and the elusive nitrido species is considerably more ionic in nature and can be described as U (δ+)–N (δÀ). Accordingly, we expected sterically pressured uranium imido and/or nitrido complexes with custom-designed chelators to exhibit increased nucleophilicity toward organic substrates. We therefore aimed to synthesize high-valent uranium imido and nitrido complexes of varying steric demand to explore possible applications for nitrogen-and group-transfer chemistry.We recently reported the reaction of the trivalent precursor complex [((tBuArO) 3tacn) U](1,(tBuArOH) 3tacn= 1, 4, 7-tris (3, 5-di-tert-butyl-2-hydroxybenzyl)-1, 4, 7-triazacyclononane)[13] with trimethylsilyl azide (Me3SiN3), which yielded the azido and imido uranium complexes [((tBuArO) 3tacn) U (L)](L= NÀ