Bi- and tridentate ligand designs incorporating N-heterocyclic carbenes

本申请旨在研究含有n -杂环碳（NHC）供体的新型配体的发展，并评估它们与过渡金属产生新化学物质的能力。该提案的目标是双重的：生成在配位化学中具有普遍适用性的新配体，并为HQP提供培训机会。该方案是为三个学生的培训而设计的，并且三个单独的子项目被清楚地描绘出来。第一个子项目的目标是合成可以与顺式和反式金属配合的螯合，立体阻碍的（NHC）s，以及它们的低氧化态镍和钴化学物质的发展。这些都是概念上非常简单的合成词，迄今为止很少受到关注。到目前为止，我们的研究已经表明，在镍配合物中，这些双（NHC）s的行为与它们被广泛研究的含有单齿配体（NHC）2Ni的对偶物有很大的不同，它们有能力产生令人兴奋的新化学物质。目标铋（NHC）s将进一步精炼以获得更强的配合物，镍的化学反应将扩展到钴。第二个子项目的目标是合成三叉戟、CSiC和CBC钳形配体，其中两个NHC给体通过柔性烷基垂臂连接到中央主基给体上。大多数常见的钳形配体依赖于包含芳香环的刚性骨架，但我们的研究表明，柔性的akyl骨架能够更好地适应金属的首选配位几何形状，并且可以通过agostic和anagostic相互作用提供额外的稳定性。在这条研究路线中所追求的配体是通过将BH、SiH和SiH2基团结合到它们的烷基骨架中而得到的上述螯合配体。根据初步研究，这些钳形配体应该是易于合成的靶标，并且它们的强硼和硅中心给体有望使它们成为研究氧化态镍和钴体系的绝佳选择。第三个子项目分别针对具有中心NHC基团的三叉戟、NCN和CCC配体以及亚胺或苯基悬吊臂。在钌配合物中通过双翻转环金属化得到了CCC配体，并显示出在溶液和固体状态下激活小分子的能力。我们的研究表明，提出的NCN配体促进了一种以前未在NHCs中观察到的行为，NHCs是典型的辅助配体：配体辅助反应性，涉及碳。亚胺类垂臂的配体支持N(CH)N结构，而吡啶类垂臂的类似物支持含nhc的NCN结构。将合成具有一个吡啶和一个亚胺垂臂的不对称NCN类似物，努力促进N(CH)N和NCN之间的容易相互转化。

This application proposes to investigate the development of novel ligands incorporating N-heterocyclic carbene (NHC) donors and to assess their ability to generate new chemistries with transition metals. The target of the proposal is twofold: to generate new ligands with general applicability in coordination chemistry, and to provide training opportunities for HQP. The proposal is designed for the training of three students, and the three individual subprojects are clearly delineated. The first subproject targets the synthesis of chelating, sterically encumbered bis(NHC)s that can coordinate to metals in both cis and trans fashion, and the development of their low oxidation state nickel and cobalt chemistries. These are conceptually remarkably simple synthons that have received so far surprisingly little attention. Our investigations so far have shown that in nickel complexes, these bis(NHC)s behave substantially differently than their much investigated counterparts incorporating monodentate ligands, (NHC)2Ni, havig the ability to generate exciting new chemistries. The targeted bis(NHC)s will be further refined to obtain more robust complexes, and the nickel chemistry will be expanded to cobalt. The second subproject targets the synthesis of tridentate, CSiC and CBC pincer ligands incorporating two NHC donors connected to the central main group donor by flexible alkyl pendant arms. Most common pincer ligands rely on rigid skeletons incorporating aromatic rings, yet our research showed that flexible akyl skeletons are better at accommodating the preferred coordination geometry at the metal and can provide additional stabilization via agostic and anagostic interactions. The ligands pursued within this line of investigation are derived from the chelating ligands described above through incorporation of BH, SiH and SiH2 moieties into their alkyl skeletons. According to preliminary investigations, these pincer ligands should be easy synthetic targets and their strong boron and silicon central donors is expected to render them excellent for the investigation of nickel and cobalt systems in oxidation state I. The third subproject targets tridentate, NCN and CCC ligands with central NHC moieties and imine or phenyl pendant arms, respectively. The CCC ligands have been obtained via double rollover cyclometalation in ruthenium complexes and showed the ability to activate small molecules in solution and the solid state. Our investigations have shown that the proposed NCN ligands promote a behavior previously not observed for NHCs, which are quintessential ancillary ligands: ligand-assisted reactivity involving the carbene carbon. It was observed that ligands with imine pendant arms support N(CH)N structures, while the analogs with pyridyl pendant arms support NHC-containing NCN structures. Asymmetric NCN analogs with one pyridine and one imine pendant arm will be synthesized, striving to promote facile interconversion between the N(CH)N and NCN species.