Bi- and tridentate ligand designs incorporating N-heterocyclic carbenes

这项应用建议研究含有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作用的能力。该提议的目标有两个：产生在配位化学中具有普遍适用性的新配体，以及为HQP提供培训机会。该提案是为培训三名学生而设计的，并明确划定了三个单独的分项目。 第一个子项目的目标是合成能够以顺式和反式方式与金属配位的螯合、空间位阻的双(Nhc)S，并开发它们的低氧化态镍和钴化学。这些合成子在概念上非常简单，但到目前为止，人们对它们的关注出奇地少。到目前为止，我们的研究表明，在镍配合物中，这些双(Nhc)S的行为与那些被广泛研究的含有单齿配体(Nhc)2Ni的化合物有本质的不同，具有产生令人兴奋的新化学反应的能力。靶向的双(NHC)S将被进一步精制，以获得更健壮的络合物，镍的化学成分将扩展到钴。 第二个分项目的目标是合成三齿酸、CSIC和CBC钳形配体，其中包括两个NHC给体，它们通过灵活的烷基垂臂与中央主族给体相连。大多数常见的钳形配体依赖于含有芳环的刚性骨架，但我们的研究表明，柔性的烷基骨架更容易适应金属上的首选配位几何构型，并可以通过配位和配位相互作用提供额外的稳定。通过将BH、SiH和SiH2部分掺入到它们的烷基骨架中，在这一研究范围内进行的配体是从上述螯合配体衍生而来的。根据初步研究，这些钳形配体应该是容易合成的靶标，它们强大的硼和硅中心施主有望使它们成为研究氧化态I中镍和钴体系的极佳材料。 第三个分项目的目标分别是具有中心NHC基团的三齿、NCN和CCC配体以及亚胺或苯基悬挂臂。通过双滚转环金属化合成了CCC配体，并在溶液和固体中表现出活化小分子的能力。我们的研究表明，建议的NCN配体促进了一种以前没有在NHC中观察到的行为，这是典型的辅助配体：涉及卡宾碳的配体辅助反应。结果表明，具有亚胺悬挂臂的配体支持N(CH)N结构，而具有吡啶悬挂臂的类似物支持含NHC的NCN结构。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物种之间的简单相互转化。

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.