Finding and Exploiting New Four-Electron Donor Ligands

本研究项目通过促进从eta-2配体到单个金属中心的不寻常的四电子捐赠来解决小分子的活化问题。目标是构建具有电子和空间特性的单体金属试剂，这些试剂有利于来自三键的pi轨道或来自醛、酮和亚胺的一个孤对和原始pi键的四电子捐赠，这是基于金属碎片可以被设计成促进与小分子的前所未有的键相互作用的假设。这些金属配体片段的结构变化将探讨促进简单配体给予四电子的要求。基于已知的4电子给体炔配体和eta-2腈配体之间的相似，通过pi系统探索腈的选择性结合，并将最初的重点放在设计一个片段上，该片段将在d4八面体中留下一个空位，以便需要四个电子来符合18电子规则。结合炔烃将为金属试剂提供初步筛选，而有前途的金属配体组合将用于追求π结合的腈配合物。除了三键外，其他潜在的四电子给体配体包括-2配位醛、酮、亚胺、酮烯和酮亚胺。如果金属部分从单个配体中寻找4个电子，是否有可能将原始双键的π电子和底物杂原子上的孤对电子都与单个金属中心形成成键关系？这将需要在配位时对醛、酮或亚胺的几何结构进行大量重组，但它有望显著改变这些有机官能团的反应性。这些金属配体的反应性可能与这些基团的简单路易斯酸加合物的反应性有很大的不同。通过这个奖项，无机、生物无机和有机金属化学项目支持了北卡罗来纳大学教堂山分校化学系的Maurice S. Brookhart教授的研究。布鲁克哈特教授和他的学生正在研究如何设计选定的有机分子和金属中心之间的特定相互作用，从而可能影响这些结合的有机分子的催化转化。除了提供有关金属-有机键合性质的基本信息外，这些研究还为开发有机分子催化转化为更复杂或增值产品的有效方法提供了希望。

This research project addresses the activation of small molecules by promoting unusual four-electron donation from eta-2 ligands to a single metal center. The goal is to build monomeric metal reagents with electronic and steric properties that favor four-electron donation from either both filled pi orbitals of triple bonds or from one lone pair and the original pi bond of aldehydes, ketones and imines, building from the hypothesis that metal fragments can be designed to promote unprecedented bonding interactions with small molecules. Architectural variations of these metal ligand fragments will probe the requirements for promoting four-electron donation from simple ligands. Selective binding of nitriles through the pi system will be explored, based on the known analogy between four-electron donor alkyne ligands and eta-2 nitrile ligands and focusing initially on the design of a fragment that will leave one vacant site in a d4 octahedron so that four electrons will be required to conform to the eighteen electron rule. Binding alkynes will provide a preliminary screen for metal reagents, and promising metal ligand combinations will be utilized to pursue pi-bound nitrile complexes. In addition to triple bonds, other potential four-electron donor ligands include eta-2-coordinated aldehydes, ketones, imines, ketenes and ketenimines. If the metal moiety seeks four electrons from a single ligand, is it possible to bring both the pi electrons of the original double bond and a lone pair on the heteroatom of the substrate into a bonding relationship with a single metal center? This will require substantial reorganization of the aldehye, ketone, or imine geometry upon coordination, but it promises to significantly alter the reactivity of these organic functional groups. The reactivity of these metal ligand moieties may differ dramatically from the reactivity displayed by simple Lewis acid adducts of these groups.With this award, the Inorganic, Bioinorganic, and Organometallic Chemistry Program is supporting the research of Professor Maurice S. Brookhart, of the Department of Chemistry at the University of North Carolina at Chapel Hill. Professor Brookhart and his students are studying ways to design specific interactions between chosen organic molecules and metal centers that may effect catalytic transformations of these bound organic molecules. In addition to providing fundamental information about the nature of metal-organic bonding, these studies offer promise for the development of efficient methods for the catalytic conversion of organic molecules into more complex or value-added products.