This project involves the use of the cascade cyclization reactions of the highly unsaturated benzannulated enyne-allenes as a key step for the synthesis of bowl-shaped (buckybowls) and basket-like (buckybaskets) polycyclic aromatic compounds. The overall strategy involves first constructing precursors containing multiple tetrahedral sp3-hybridized carbons. The presence of these tetrahedral sp3-hybridized carbons causes several parts of the molecules to be in close proximity to one another, allowing further connections to form carbon-carbon bonds by mild solution-phase chemistry leading to buckybowls and buckybaskets. A success of the proposed synthetic schemes would provide easy access to a variety of such compounds not readily accessible by other methods. In addition, helical heteroaromatic compounds will also be synthesized for helical supramolecular assemblies and asymmetric catalysis.
With this award the Organic and Macromolecular Chemistry Program is supporting the research of Professor Kung K. Wang of the Department of Chemistry at West Virginia University. Professor Wang's research efforts have focused on the use of unsaturated systems for the construction of nonplanar organic molecules having unusual architectures. Many of these molecules could possess interesting material properties or biological activities. Successful development of the synthetic methodology will have an impact on the manufacturing processes of the chemical and pharmaceutical industries.
Development of new synthetic pathways for bowl-shaped and basket-shaped polycyclic aromatic hydrocarbons (buckybowls and buckybaskets) is a research area of intense current interest because these curved hydrocarbons could serve as building blocks for the construction of fullerenes (C60 and related compounds) and as templates for carbon nanotubes. The hoop-like molecules called [n]cycloparaphenylenes ([n]CPPs, carbon nanohoops) epresent the shortest segments of the repeating units of a special type of single-walled carbon nanotubes (SWNTs) called armchair SWNTs. Development of new synthetic methods for carbon nanohoops has been actively pursued because these hoop-like molecules could also serve as templates for the construction of armchair SWNTS with a uniform diameter. This synthetic approach offers the potential advantage over the existing methods in the ability to produce armchair carbon nanotubes of uniform diameter, which is of critical importance for applications in a variety of nanotechnology fields, including electronics, energy, and nanophotonic devices. New synthetic pathways to several buckybowls, buckybaskets, and carbon nanohoops were developed with financial support from this NSF-funded project. Mild thermal conditions were employed, allowing delicate structural features to survive the experimental procedures and providing new methods to attach reactive structural features to the molecules. Molecules bearing several reactive sites were produced, affording new opportunities to assemble larger fullerene fragments and to produce longer carbon nanotubes. Several organic molecules possessing a severe helical twist were prepared. These helical compounds also bore reactive sites that allowed interactions with transition metals to form a group of compounds called metal complexes. While many metal complexes having linear and planar structures had been reported, metal complexes possessing a helical twist were rare. Two new helical metal complexes involving ruthenium metal were prepared. These ruthenium complexes are of interest because they could serve as photosensitizers to harvest energy from sunlight and are excellent models for the investigation of energy- and electron-transfer processes. Because metal complexes are involved in many chemical processes, these new ruthenium complexes also provide ample opportunities for the discovery of important new chemical processes of interest to chemical and pharmaceutical industries. Nine graduate students and three undergraduate students have participated in this research project. The development of well-trained synthetic organic chemists through their involvements in this research project added to the human resources for chemical and pharmaceutical industries. The graduate students gained experience in designing new synthetic strategies and in conducting contemporary organic synthesis in the laboratory. The undergraduate students were teamed up to work with graduate students so that they learned from the more experienced graduate students important laboratory skills and general laboratory practices. This approach appeared to have worked out well with the undergraduate students learning to do research in synthetic organic chemistry and the graduate students learning the art of teaching.
