This research program is based around the synthesis and applications of heteroatom-containing, convex polycycles. The principal goals of the project are to prepare azatriquinanes which are asymmetric at the nitrogen atom for applications to chiral H+ or X+ delivery, to produce a range of azatriquinane-based transition metal ligands and host-guest systems, to synthesize new series of hetero (O, S, P, and/or B) triquinanes, triquinacenes, and acepentalenes, to devise a new synthetic entry into the heterotriquinane ring system via cyclononatrione, and to approach heterododecahedranes both by heterotriquinacene dimerizations and by total synthesis. These investigations will provide the researchers with broad experience in organic synthesis, coordination chemistry, crystallography, and fundamental aspects of aromaticity, strain, electron delocalization, and molecular architecture.
With the support of this award from the Chemical Synthesis Program, Professor Mark Mascal of the Department of Chemistry at the University of California Davis will explore the nature of molecules with curved surfaces -- from concave, to hemispherical, to completely closed-shell, polyhedral bodies. The study of such molecules answers fundamental questions regarding the electronic structure of organic (carbon-based) materials, and also presents opportunities for practical applications, particularly in the area of nanotechnology. This project also serves as an excellent training ground for graduate and postdoctoral researchers in fundamental and applied chemical synthesis. The broader impacts of this program include K-12 outreach by sponsoring summer research projects via the American Chemical Society SEED and UC Davis Youth Scholar Programs, the development of innovative student learning and assessment practices, involvement in programs which promote the participation of underrepresented groups in the Pacific Rim, and enhancing the relevance of research chemistry in undergraduate laboratory courses. Finally, the visual impact and beautiful symmetry of the curved and spherical molecular bodies being studied lends itself to additional outreach opportunities through the popular press and public science venues, and thereby a greater appreciation of the art of technology.
Project outcomes that address the intellectual merit of the project The heterotriquinane ring system consists of three fused, five-membered rings with a heteroatom ("X", for example, nitrogen, oxygen, or sulfur) in the center. The molecular structure is as shown below left. The fusion of these rings results in a puckered, trefoil shape, as shown below right, looking at the molecule edge-on. The principal objectives of the research program, as identified in the proposal, were as given below. This Project Outcomes Report will describe highlights of the progress made individually under each of these objectives. 1) to synthesize a range of azatriquinane-based transition metal ligands and host-guest systems Azatriquinane (the heterotriquinane with X=N) was used as a platform for constructing a "host" molecule that would be able to trap metal ions. A picture of the concept is shown below. We were able to demonstrate the synthesis of this novel host molecule and test it by preparing its cobalt and zinc complexes. Work is continuing on molecular capsules based around the azatriquinane framework. 2) to synthesize new series of hetero (O, S, P, and/or B) triquinanes Some extraordinary results have sprung from activities under this objective, particularly in heterotriquinanes where X=O (oxatriquinane). Using this platform, we have demonstrated the existence of tetravalent oxadionium R4O2+ species, which have never been directly observed before. We have also performed bimolecular nucleophilic substitution (SN2) at a tertiary carbon, which is generally considered to be an impossible reaction. Finally, we have made substituted oxatriquinanes that have world record C-O bond lengths. A normal C-O bond is about 1.43 Å long. In the molecule shown below, we have observed C-O bonds (shown in red) in excess of 1.65 Å. Work continues now on the first example of an isolable oxonium ylide based on the oxatriquinane platform. 3) to devise a new synthetic entry into the heterotriquinane ring system via cyclononatrione We have developed a new and practical synthetic route to 1,4,7-cyclononatrione (below left), a pivotal intermediate in the pursuit of new heterotriquinanes based on nitrogen, oxygen, sulfur and phosphorus. 4) to approach heterododecahedranes by heterotriquinacene dimerizations and total synthesis Starting from triquinane derivatives generated from cyclononatrione, we are in the process of undertaking the total synthesis of heterododecahedranes, which are molecular spheres consisting of two fused triquinane rings as exemplified below (right). Project outcomes that address the broader impacts of the project The activities carried out in the course of this research program provided opportunities for research, teaching, and mentoring in science and engineering. As described above, the project provided abundant opportunities for research, the products of which have been disseminated in journals of international diffusion and at conferences. Educational materials generated by the project involved the incorporation of research themes (chemical synthesis) into the undergraduate organic chemistry teaching laboratory at UC Davis. The graduate and postdoctoral workers involved in this project gained experience in the mentoring of undergraduate researchers in the lab. Both of the undergraduates involved in this project came from underrepresented groups (one African-American and one mixed-race African-American/Caucasian), the former of which has now gone on to do a PhD in chemistry (on this same project) and the latter of which has just been accepted into medical school. The project also proposed to included high school outreach. Participation of the PI in the COSMOS program (California State Summer School for Mathematics and Science) has led to an intensification of activity under this objective. The past two summers, the PI was involved as a mentor in this program with two other UC Davis faculty members. The mission of COSMOS is to motivate the most creative minds of the new generation of prospective scientists, engineers and mathematicians who will become industry leaders in California and nationwide. It is an intensive, four week residential program for high school students involving lectures, laboratory work, academic field trips, projects, and student presentations.
