60th Annual Report on Research 2015

The goal of my research is to achieve inner-sphere, homogeneous gold(III) activation and functionalization of strong, sp³-hybridized C-H bonds, similar to the bonds found in alkanes. To this end, we synthesize novel gold(III) complexes containing ligands designed to direct strong, sp³-hybridized C-H bonds toward the gold(III) metal center through chelation. During the first year of this grant, my research group developed the synthesis shown in Fig. 1 of a novel gold(III) complex (1). Importantly, these conditions allowed us to obtain a seemingly monomeric complex. Our previous metallation attempts in the presence of Ag(I) salts had lead to oxo-bridged gold(III) dimers. Based on the high stability of the oxo-bridged dimers, monomeric gold(III) complexes will be more likely to facilitate C-H bond activation reactions.

Figure 1. The synthesis of novel gold(III) complex 1.

In attempting to synthesize a similar complex to 1 but with the t-butyl amide of 8-aminoquinoline shown in Fig. 2, preliminary evidence suggests that a metal complex (2) is generated, and ¹H NMR spectroscopy indicates that 2 contains an N-H bond. This implies that the 8-aminoquinoline-based ligand is only monodentate in 2. When the solvent was changed to methanol for the metallation, complex 3 was generated, and it lacked a visible N-H peak in its ¹H NMR spectrum. This could indicate bidentate coordination, as shown in Fig. 2. The yield and purity of 3 improved slightly when one equivalent of sodium bicarbonate was added to the reaction mixture. Further characterization of 2 and 3 is ongoing. Attempts were also made to synthesize complexes containing ligands 4 and 5 shown in Fig. 3. While all attempts with 4 were unsuccessful, we are beginning to see promising results with 5 when the metallations are performed at higher temperatures.

Figure 2. The synthesis of novel gold(III) complexes 2 and 3.

Figure 3.  Additional amides of 8-aminoquinoline that have been tested for metallation of gold(III).

Prior to the start of the funding period, my research group synthesized and fully characterized complex 6 (shown in Fig. 4), which contains a tert-butylphenanthroline ligand. This complex was previously synthesized by reacting the ligand with KAuCl₄ and just over one equivalent of AgBF₄. Based on our success synthesizing complexes 1, 2, and 3 in mixtures of organic solvents and water, we attempted to apply these conditions to the synthesis of 6. When the metallations were performed in mixtures either of acetonitrile and water or of tetrahydrofuran and water, 6 was generated. The yield and purity of 6 improved when one equivalent of sodium bicarbonate was added to the reaction mixture. While metallation to form 6 likely does not involve a proton transfer, it is possible that the sodium bicarbonate is preventing alternative reaction pathways or that sodium bicarbonate is affecting ligand substitution at the gold(III) metal center.

Figure 4. Gold(III) complex 6.

Attempts are underway to achieve C-H bond activation with the novel gold(III) complexes. These are focused on using silver(I) to abstract chloride and open up coordination sites at gold(III).

From May 1, 2014 to August 31, 2015, a total of twelve undergraduate students worked on this project. Ten of those students were paid out of this grant with two of the ten also earning upper division structured research course credit for hours worked on the project while not being paid. Two additional students were not paid but earned structured research course credit for their work on the project. Three of the students graduated in the spring of 2015. Two of these students went on to chemistry graduate school, and one of them went on to pharmacy school.

Overall, the students gained experience in ligand synthesis, metal complex synthesis, C-H bond activation reactions, and air-free chemical techniques, including the use of both a Schlenk line and an inert atmosphere glove box. The glove box was purchased as capital equipment through this PRF grant with matching funds provided by Colorado Mesa University.

The research and glove box funded through this grant have also been used to improve my capstone Advanced Laboratory course. One of the projects in this course involves synthesizing some of the ligands described above. This gives the students experience using the Schlenk line, column chromatography, and NMR spectroscopy. I have the students read the PRF grant proposal in order to introduce them to the project and to the format of grant proposals. I have also incorporated training on the glove box into this course.

The funding of this project has had an impact on the broader Grand Junction community through our work with the John McConnell Math & Science Center. My research group and I have given two presentations on energy to the middle school summer camp students. Using a variety of demonstrations, we taught the campers about energy sources and transfers of energy involved in chemical reactions. I am also in the process of working with Colorado Mesa University students to design one or two new displays for the center. One will be a hands-on display that helps children to see the diversity of products generated from oil and natural gas.

My research group and I are extraordinarily grateful for this grant. It has allowed us to develop syntheses of novel gold(III) complexes, and twelve undergraduate research students have been trained in a variety of synthetic inorganic chemistry techniques. Furthermore, it has helped me to improve my capstone Advanced Laboratory course, and it has helped to facilitate my research group's involvement in the education of local children.