CAREER: Functionalized Bent para-Phenylenes: New Strategies and Tools for the Synthesis of Carbon Nanotubes

有了这个职业奖，化学系的化学合成项目支持了奥本大学布拉德利·L·默纳教授的研究。默纳教授研究的主要目标是开发控制合成碳纳米管的新策略。目前，阻碍碳纳米管合成的主要问题之一是我们无法以统一的方式制备它们。现代碳纳米管的合成导致混合物的出现，使纳米管结构和物理性能之间的关系复杂化。为了解决这一差距，Merner团队正在开发所需的合成工具，以制造碳纳米管的较小部分，然后可以系统地组装成较大的纳米管。通过控制较小片段的大小，可以有意控制较大纳米管的大小。由于碳纳米管是由一系列缝合在一起的苯环制成的，因此合成最初的目标是更大的环系统，这些系统既包含多个苯环，也包含将它们结合在一起并构建目标纳米管所需的功能。这种方法的关键是在建造更大的环的过程中使用无张力的苯替代品。一旦这些环被组装起来，然后被拉紧，弯曲的苯环就会释放出来，这样它们就会被困在更大的环结构中。这条路线提供了许多机会，可以获得以前无法获得的碳纳米管构建块。该计划的教育部分包括开发化学合成教学模块，作为奥本大学暑期科学学院的一部分，向东南部地区的初高中新生提供这些模块。希望在STEM相关领域进行研究生水平培训的人数不足的本科生参加化学合成暑期研究计划。此外，为了让更多的本科生接触研究生水平的研究经验，奥本大学注册的荣誉有机化学学生在默纳教授的实验室里合成重要的起始材料，供研究生在未来的合成方法开发中使用。碳纳米管在材料科学、工程和生物传感领域引起了人们的极大兴趣。然而，由于无法获得具有明确、均一结构的碳纳米管，它们在这些领域的使用受到阻碍。在这项研究项目中，默纳教授和他的团队正在通过新的合成策略来应对这一挑战，这种策略将非平面苯环嵌入到功能化的多环构建块中，这些苯环构成了碳纳米管。这是构建均匀碳纳米管的重要一步，因为如果积木的大小和形状可以控制，那么由积木组装的纳米管的大小和形状就可以控制。在这个项目中，系统地增加了构建块的分子复杂性，以便它们可以更好地了解应变分子的反应性、可能释放的应变能量以提供不希望看到的副产品，以及这些过程发生的反应机理。这些信息指导了更复杂系统的合成，最终导致了碳纳米管本身的构建。最初的策略使用基于非交叉耦合的方法来制备大环、功能化的碳纳米管亚结构。这些功能化系统被用于程序化的、后期的碳-碳键形成反应，以建立更大的结构。研究了几种连接相邻芳烃的环化策略，这些反应得到了代表碳纳米管侧壁结构的pi-扩展的大环链段。目标结构不仅导致开发新的化学工具来访问这些复杂的有机分子，而且还为本科生和研究生提供一流的化学合成培训，并加深对应变复杂碳氢化合物中化学反应的理解。

With this CAREER Award, the Chemical Synthesis Program of the Chemistry Division supports the research of Professor Bradley L. Merner at Auburn University. The main objective of Professor Merner's research is to develop new strategies for the controlled synthesis of carbon nanotubes. At the present, one of the chief problems interfering with the synthesis of carbon nanotubes is our inability to make them in a uniform manner. Modern carbon nanotube syntheses lead to mixtures that complicate correlations between nanotube structure and physical properties. To address this gap, the Merner group is developing the synthetic tools needed to build smaller sections of a carbon nanotube that can then be assembled into larger nanotubes in a systematic way. By controlling the size of the smaller pieces, the size of the larger nanotube can be intentionally controlled. Since carbon nanotubes are made of a series of benzene rings that are stitched together, the synthesis initially targets larger cyclic systems that contain both multiple benzene rings and the functionality needed to bind the them together and build the targeted nanotubes. The lynchpin of this approach is the use of an unstrained benzene surrogate during the construction of the larger rings. Once those rings are assembled, then strained, bent benzene rings are released so they are trapped with in the larger ring structure. The route offers many opportunities to access carbon nanotube building blocks that were previously unavailable. The educational component of the program involves the development of chemical synthesis-teaching modules that are offered to rising junior and senior-level high school students in the Southeast region as part of the Auburn University Summer Science Institute. Underrepresented undergraduate students wishing to pursue graduate-level training in STEM-related fields participate in a chemical synthesis summer research program. Furthermore, in order to expose more undergraduate students to graduate-level research experiences, students enrolled in honors organic chemistry at Auburn University synthesize important starting materials that are used in future synthetic method development by graduate students in Professor Merner's laboratory. Carbon nanotubes are of great interest in the fields of materials science, engineering and biological sensing. However their use in these areas is hampered by the inability to access carbon nanotubes that are of a defined, homogenous structure. In this research project, Professor Merner and his group are tackling this challenge with new synthetic strategies that imbed the nonplanar benzene rings that comprise carbon nanotubes within functionalized polycyclic building blocks. This is an important step in the construction of uniform carbon nanotubes because if the size and shape of the building blocks can be controlled, then the size and shape of the nanotube assembled from the building blocks can be controlled. In this project, the molecular complexity of the building blocks are increased systematically so that they can better understand the reactivity of strained molecules, possible releases of this strain energy to afford undesired by-products, and the reaction mechanisms by which these processes occur. This information guides the synthesis of the more complex systems eventually culminating in the construction of the carbon nanotubes themselves. The initial strategy being pursued uses a non-cross-coupling-based approach to prepare macrocyclic, functionalized carbon nanotube substructures. These functionalized systems are employed in programmed, late-stage carbon-carbon bond forming reactions to build larger structures. Several annulation strategies to join adjacent arenes are investigated and the reactions afford pi-extended macrocyclic segments that are representative of carbon nanotube sidewall structures. The target structures not only lead to development of new chemical tools for accessing these complex organic molecules, but also provide first-rate training in chemical synthesis to undergraduate and graduate students, and deepen the understanding of chemical reactivity in strained, complex hydrocarbons.