Using London Dispersion Force Effects to Stabilize Inorganic and Organometallic Molecules

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With the support of the Chemical Synthesis (SYN) Program of the Chemistry Division, Professor Phillip Power, Chemistry Department, University of California–Davis is studying the role of London dispersion (LD) effects in determining the structures and reactivity of inorganic molecules. Chemical bonds often involve the sharing of electrons between two atoms. These are bonds are typically quite strong and are the principal forces that hold many chemical compounds together. However, there are other, usually weaker forces that can influence the behavior of compounds. One of these is called London Dispersion (LD) and results from instantaneously generated electric dipoles that form when non bonded atoms approach one another. While these interactions are weak, they can stabilize normally unstable classes of compounds. The research provides details of how the LD effects can influence molecules leading to structures and reactivity that are counterintuitive. Such interactions have not generally been considered during the preparation of chemicals, but this project seeks to provide the groundwork to utilize LD in the design of new molecules. The project will provide training in sophisticated chemical techniques to a variety of students, including ones from underrepresented groups. In addition, there is an outreach component to K-12 students and teachers that aim to increase the participation of underrepresented groups in science. The main theme of this proposal is the investigation of the effects of the London Dispersion (LD) energies on the structures, stability, and reactivity of sterically crowded inorganic molecules. Despite the weak nature of such interactions (ca. 1 kcal mol-1 /H---H interaction) these are nonetheless ubiquitous and, collectively, can strongly influence molecular properties. Recent LD results have been obtained using terphenyl ligands in which alkyl substituents on two ‘flanking’ aryl rings generate the close H---H approaches for the LD force stabilization. However, in the terphenyl ligands the number of H atoms is limited and they also can interact further via nucleophilic interactions of their flanking rings. To overcome these limitations, ligands that have either less reactive aliphatic rings or rigid hydrocarbon framework groups at the ‘flanking’ positions will be prepared. The ability of these ligands to form and stabilize presently unknown (a) organocopper(I) compounds, (b) compounds with transition metal - main group element bonds, (c) uncomplexed, free-standing dialuminenes and (d) new LDF donor organolithium reagents will be explored. In addition, the use of LD forces in organometallic synthesis, for example, assembling (e) dimetallenes vs. metalylenes and (f) metal-metal bonded complexes in the alkaline earth, and early transition metals will be evaluated. This knowledge is expected to provide useful information on how LD forces enable the assembly of new compound classes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.