Bi- and tridentate ligand designs incorporating N-heterocyclic carbenes

本申请提出研究结合N-杂环卡宾（NHC）供体的新型配体的开发，并评估它们与过渡金属产生新化学的能力。该提案的目标是双重的：产生新的配体在配位化学中的普遍适用性，并提供培训机会HQP。本提案是为培训三名学生而设计的，并明确界定了三个单独的分项目。第一个子项目的目标是合成螯合，空间位阻的双（NHC），可以协调的顺式和反式的方式，金属，和他们的低氧化态镍和钴化学的发展。这些在概念上非常简单的子，到目前为止很少受到关注。到目前为止，我们的研究表明，在镍配合物中，这些双（NHC）的行为与其大量研究的对应物结合单齿配体（NHC）2Ni有很大的不同，从而产生令人兴奋的新化学的能力。目标双（NHC）将进一步细化，以获得更坚固的配合物，镍化学将扩展到钴。第二个子项目的目标是三齿，CSiC和CBC钳形配体的合成纳入两个NHC捐助者连接到中心的主基团捐助者的灵活的烷基侧臂。最常见的钳形配体依赖于刚性骨架结合芳环，但我们的研究表明，灵活的烷基骨架更好地适应在金属的优选的配位几何形状，并可以通过agostic和anagostic相互作用提供额外的稳定。在这一研究路线内所追求的配体通过将BH、SiH和SiH2部分并入其烷基骨架中而衍生自上述螯合配体。根据初步研究，这些钳形配体应该是容易合成的目标，并且它们的强硼和硅中心给体预计使它们非常适合于研究氧化态I的镍和钴体系。第三个子项目的目标三齿，NCN和CCC配体与中央NHC部分和亚胺或苯基侧臂，分别。CCC配体是通过钌配合物的双翻转环化反应得到的，并显示出在溶液和固体状态下活化小分子的能力。我们的研究表明，所提出的NCN配体促进了以前没有观察到的NHC的行为，这是典型的辅助配体：配体辅助的反应性，涉及卡宾碳。观察到具有亚胺侧臂的配体支持N（CH）N结构，而具有吡啶基侧臂的类似物支持含NHC的NCN结构。将合成具有一个吡啶和一个亚胺侧臂的不对称NCN类似物，努力促进N（CH）N和NCN物种之间的容易的相互转化。

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.