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

关于结构和键合的基本问题（Fischer型与Schrock型卡宾），而且，它们作为烯烃复分解、Fischer-Tropsch过程和许多有机官能团转化中的反应中间体的相关性是过渡金属卡宾/亚烷基络合物的关键属性。同时，金属-亚氨基（M=NR）部分参与多种化学转化，并用作过渡金属亚烷基络合物中的辅基以促进立体选择性烯烃复分解和聚合。金属-配体多重键的稳定和分离在稀土（Ln）和碱土（Ae）金属化学中提出了一个持续的挑战，并且长时间难以捉摸的亚烷基或亚氨基实体的存在也导致了4f元素-配体键合的新范例。该项目旨在从根本上了解这种Ln/Ae配体多重键的形成。我们和其他人最近开始了有机铝辅助形成的稀土金属亚甲基，次甲基，亚氨基物种通过（多）甲基基团去质子化。我们希望证明这种有机铝辅助的去质子化途径具有更普遍的适用性，例如，通过扩大亚烷基和亚氨基配体的范围，而且还精心设计了新的反应方案，如脱卤硅烷化。利用庞大的辅助配体应该抑制广泛的和不可控的氢提取，因此抵消簇的形成，从而确保离散的，理想的monoclonal复合物的可再现的形成。评估Tebbe和Petasis样试剂的可行性将是利用（双）金属烷基络合物的热稳定性的主要目标。稀土金属亚烷基和酰亚胺配合物的识别和分离与Ln金属中心的四价（Ce）和二价氧化态（Sm，Eu，Yb）可能是最大的挑战。同位素标记技术和密度泛函理论计算将支持整个机理研究。将通过与常规使用的d-过渡金属试剂（例如，用于羰基烯化反应。

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.