My students have worked on a variety of projects at CCSU. The majority of the focus has been on the photoelectron spectra of vanadyl complexes. That particular project depends on collaboration with the Center for Gas Phase Electron Spectroscopy at the University of Arizona. While continuing that work, I will focus on other projects which can be done entirely at CCSU.

The ligand di-2-pyridyl ketone (dpk) displays an unusual hydration reaction in the presence of a transition metal ion. In aqueous solution, the ligand forms a geminal diol (dpkoh) at the sp² bridging carbon atom. This ligand has been explored as a bridging ligand for use in building crystalline, metal-containing polymers, and as an indicator for identifying metal ions in aqueous solution. I wish to better understand the nature of the reactivity of this ligand while providing a research opportunity for undergraduates.

Previous studies have focused on the isolation and structural characterization of complexes of the form M(dpkoh)₂ (M = Cr, Co, Ni, Cu, Ru) and M(dpkoh) (M = Pd, Au). These compounds are formed by reacting the dpk ligand with the metal ion in the appropriate molar ratio. Additionally, two silver analogs have been isolated. In these cases, however, hydration did not occur at the ketone. Instead, the ligand bridged metal centers to form a crystalline polymer.

Students synthesize and structurally characterize additional complexes using different transition metal ions, with a focus on the 3d block. Analogues of dpk, such as the oxime derivative (dpko) and the thio analog (dpt)will also be studied. Since dpko and dpt are not expected to undergo any reaction with the solvent, a different coordination mode should be seen with metal ions.

The mechanism of formation of these complexes has not been fully elucidated. There are two possible pathways. First, the dpkoh is formed simply by the reaction of dpk with water, then the resulting diol binds in a tridentate fashion to the metal center. This seems unlikely based on the instability of geminal diols. A second mechanism entails bidentate coordination of the ligand to the metal through the two pyridyl nitrogen atoms, then hydration at the ketone site. This mechanism seems more viable since electron donation to the metal center would make the carbonyl carbon atom a stronger Lewis acid. Subsequent attack by a water molecule leads to the observed geminal diol. Because of the orientation of the OH group with respect to the metal center, coordination is then likely.

We use UV-visible spectroscopy to monitor the reaction progress and determine the order of the reaction for various metal centers. Furthermore, students will study the effect that other ligands (such as halides) have on the reaction rate. Based on this information we will derive the formation constants for the transition ions and determine the selectivity of this ligand.

This investigation is ideal for undergraduate participation. The synthesis, characterization, and kinetic analyses will provide valuable research experience to undergraduates who may in the future opt for research careers in industry, academia, or government labs. Students will present the results of their work at local, regional, and national American Chemical Society meetings, and any publications evolving from this project will include students as co-authors.