Lanthanide Heteroatom-Stabilised Alkylidenes: A New Approach to Multiply Bonded Lanthanide Chemistry

当代镧系化学（镧系元素是元素周期表底部的14个元素）中最令人兴奋和最具挑战性的领域之一是分离镧系烷基烯（碳原子与镧系元素双键的化合物，Ln=C），目前已知的数量非常有限。因此，关于镧系烷基烷的稳定性、结构、键和反应性的基本问题仍然存在。这类物质是稀缺的，因为它们缺乏足够好的轨道相互作用，无法像许多过渡金属那样稳定Ln=C双键。然而，如果杂原子（磷或硅）附着在烷基烯上，它们可以帮助稳定Ln=C双键中的电子。第一笔资助将建立在申请人已经获得的初步研究结果的基础上，该研究利用了烷基烯杂原子稳定性，并利用他在镧系化学方面的专业知识，对该领域进行了重大而快速的扩展，以解决镧系烷基烯的新化学问题。新的镧系烷基烷将进行详细的结构和光谱分析，并结合理论计算，全面建立其稳定性、结构和键合。这些配合物的反应模式将在与过渡金属烷基烯反应平行的反应中进行筛选（环加成，wittig型）。重要的是，申请人的初步结果包括一个不仅具有正式的Ln=C双键，而且具有反应性的Ln-C单键的体系。这将两个非常活跃的碎片放置在同一个金属中心，并提供了一个独特的机会来利用它们在一起产生的协同作用。我们将利用这种协同作用来尝试获得以前未知的结构基序，例如第一个末端镧系亚胺（Ln=N双键）和第一个镧系四烯（Ln=Si和Ln=Ge双键）。这些将是非常有趣的不饱和有机烯烃和烯的无机版本（C=C， C=C=C），并且考虑到过渡金属烷基烯和亚胺被学术界和工业界广泛用于合成精细化学品、药物和商品塑料聚合物，它们有望产生新的反应性。

One of the most exciting and challenging areas of contemporary lanthanide chemistry (lanthanides are the 14 elements at the bottom of the periodic table) is the isolation of lanthanide alkylidenes (compounds which feature a carbon atom doubly bonded to a lanthanide, Ln=C), and only a very limited number are known. Therefore, enduring fundamental questions regarding the stability, structure, bonding, and reactivity of lanthanide alkylidenes remain. Such species are scarce because they lack sufficiently good orbital interactions to stabilise the Ln=C double bond in the way numerous transition metals can. However, if heteroatoms (phosphorus or silicon) are appended to the alkylidene they can help stabilise the electrons in the Ln=C double bond. This First Grant will build on preliminary results the applicant has obtained, which exploits alkylidene heteroatom stabilisation, and utilises his expertise in lanthanide chemistry, to effect a significant and rapid expansion of this field to address the new chemistry of lanthanide alkylidenes. New lanthanide alkylidenes will be subjected to a detailed structural and spectroscopic interrogation, which will be combined with theoretical computational calculations to comprehensively establish their stability, structure and bonding. The reactivity patterns of these complexes will be screened in reactions which parallel transition metal alkylidene reactions (cycloadditions, Wittig-type). Importantly, the applicants preliminary results include a system which exhibits not only a formal Ln=C double bond, but also a reactive Ln-C single bond. This places two very reactive fragments in close proximity at the same metal centre, and presents a unique opportunity to exploit the synergy resulting from them being harnessed together. We will use this synergy to attempt access to previously unknown structural motifs, such as the first terminal lanthanide imides (Ln=N double bond) and the first lanthanide tetrylenes (Ln=Si and Ln=Ge double bonds). These will be highly interesting inorganic versions of unsaturated organic olefins and allenes (C=C, C=C=C), and given the extensive use of transition metal alkylidenes and imides by academia and industry for the synthesis of fine chemicals, pharmaceutical drugs, and commodity plastic polymers, they promise novel new reactivities.