Rare-earth and alkaline-earth metal complexes with alkylidene and imido ligands: synthesis, derivatization, and reactivity

关于结构和键的基本问题（Fischer-与schrock -型卡宾），以及它们作为烯烃复分解、费托过程和许多有机官能团转化的反应中间体的相关性，是过渡金属卡宾/烷基烯配合物的关键属性。与此同时，金属-亚胺（M=NR）基团参与多种化学转化，并被用作过渡金属烷基烯配合物的助剂，以促进立体选择性烯烃的转化和聚合。金属-配体多键的稳定和分离是稀土（Ln）和碱土（Ae）金属化学中一直存在的挑战，长期难以捉摸的烷基或亚胺实体的存在也导致了4f元素-配体键的新范式。本项目旨在对这种Ln/Ae配体多键的形成有一个基本的认识。我们和其他人最近开始通过（多个）甲基去质子化，在有机铝的帮助下形成稀土金属甲基、甲基和亚胺。我们希望证明这种有机铝辅助的去质子化途径具有更广泛的适用性，例如，通过扩展烷基烯和亚胺配体的范围，而且还可以制定新的反应方案，例如去卤硅化。使用大体积的辅助配体应该抑制广泛和不可控的氢提取，从而抵消簇的形成，从而确保离散的可重复形成，理想的单金属配合物。通过利用（双）金属烷基配合物的热稳定性来评估Tebbe和petasis样试剂的可行性将是一个主要目标。以四价（Ce）和二价氧化态（Sm, Eu, Yb）为中心的稀土金属络合物的鉴定和分离可能是最大的挑战。整体机理研究将由同位素标记技术和DFT计算支持。所得配合物的反应性将通过与常规使用的d过渡金属试剂（例如羰基烯烃反应）进行比较来探讨。

Fundamental issues regarding structure and bonding (Fischer- versus Schrock-type carbenes) and, moreover, their relevance as reaction intermediates in olefin metathesis, Fischer-Tropsch processes, and numerous organic functional group transformations are pivotal attributs of transition metal carbene/alkylidene complexes. In the same breath, metal-imido (M=NR) moieties engage in a multitude of chemical transformations and are utilized as ancillaries in transition metal alkylidene complexes to promote stereoselective olefin metathesis and polymerization. The stabilization and isolation of metal-ligand multiple bonds poses an ever ongoing challenge in rare-earth (Ln) and alkaline-earth (Ae) metal chemistry and the existence of long-time elusive alkylidene or imido entities has led to new paradigms in 4f element-ligand bonding as well. This project aims at a fundamental understanding of the formation of such Ln/Ae ligand multiple bonds. We and others have recently embarked on the organoaluminum-assisted formation of rare-earth metal methylidene, methine, and imido species via (multiple) methyl group deprotonation. We wish to demonstrate that this organoaluminum-assisted deprotonation pathway has a more general applicability, e.g., by extending the scope of alkylidene and imido ligands, but also to elaborate new reaction protocols, such as the dehalosilylation. The utilization of bulky ancillary ligands is supposed to suppress extensive and uncontrollable hydrogen abstraction and hence counteract cluster formation, thus ensuring the reproducible formation of discrete, ideally monometallic complexes. Assessing the feasibility of Tebbe- and Petasis-like reagents will be a primary target by exploiting the thermal stability of (bi)metallic alkyl complexes. The identification and isolation of rare-earth metal alkylidene and imide complexes with the Ln metal centers in the tetravalent (Ce) and divalent oxidation states (Sm, Eu, Yb) represents maybe the biggest challenge. The overall mechanistic investigations will be supported by isotope labeling techniques and DFT calculations. The reactivity of the obtained complexes will be explored by comparison with routinely employed d-transition-metal reagents, e.g., for carbonyl olefination reactions.