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43124-B3
Magnetic Studies and Room Temperature Carbon-Carbon Bond Cleavage in Ruthenium Carboxylate Clusters

Laura E. Pence, University of Hartford

Our investigations into the determination of a generalizable strategy for the synthesis and purification of oxo-bridged basic triruthenium carboxylate clusters have continued to establish that this deceptively simple system is actually exceedingly complex.  As noted in our previous report, the common synthetic strategy:

            Figure 1.  General strategy for the synthesis of basic ruthenium carboxylates

is actually very sensitive to acid strength, even when carried out in organic solvents.  Careful studies of the ubiquitous acetate system by Toma and co-workers¹ have elucidated that the redox and acid-base transformations in the cluster can occur simultaneously in proton-coupled electron transfer (PCET) processes.  These transformations, also seen in ruthenium polypyridyl systems studied by Meyer,² feature conversion of aqua ligands to hydroxo and oxo ligands during simultaneous electron transfer. 

Prior to the publication of Toma's results, we elected to focus on finalizing the preparation and characterization of the [Ru₃O(O₂CCH(CH₃)₂)₆(py)₃]PF₆ species.³  Unsurprisingly, the synthesis and isolation of the isobutyrate product displays the same PCET processes as the acetate species, thus making it critical to identify crucial details of the reaction to maximize the yield of the Ru₃(III,III,III) species.  Less than optimum reaction conditions lead to the isolation of green or black products which have yet to be definitively characterized, but ¹H NMR has been used to distinguish them from the desired blue cationic species.  Although large amounts of high-boiling carboxylic acids are difficult to remove from the initial reaction, they are required to produce the aqua species, [Ru₃O(O₂CCH(CH₃)₂)₆(H₂O)₃]⁺ as the primary product.  We are currently working to optimize the subsequent pyridine exchange step also to minimize the pH since the deprotonation of the aqua ligands to hydroxo groups blocks the axial ligand exchange. 

Our comprehensive characterization of the [Ru₃O(O₂CCH(CH₃)₂)₆(py)₃]PF₆ species has been assisted by our collaborators, Prof. John Turner and Prof. Ted Barnes, both at the University of Tennessee.  Undergraduate Brad O'Dell under the direction of Prof. Turner has examined the SQUID magnetic susceptibility as well as the ¹H NMR spectra of the complex, which displays pronounced temperature dependence as seen in the figure below.  Analysis of the magnetic data are ongoing , but thus far it has been established that the system is strongly correlated and is not a simple paramagnet.

            Figure 2.  Stack plot of variable temperature ¹H NMR spectra of             [Ru₃O(O₂CCH(CH₃)₂)₆(py)₃]PF₆

This grant award has had substantial impact on my student and I.  At the University of Hartford, promotion to Full Professor is based on sustained and distinguished performance in both teaching and scholarship as well as adequate performance in the area of service.  This grant award has not only contributed to demonstrating my sustained and distinguished performance in the traditional scholarship of discovery, it has also formed the foundation of my ability to carry out laboratory research involving undergraduates, which is an important focus for the faculty members in my department.  Jennifer Schlough '08, and I both benefited especially from the opportunity to carry out funded research over the summer.  As expected, Jennifer was vastly more productive through working complete days compared to the intermittent nature of undergraduate research during the semester, and she had the opportunity to focus more exclusively on her project.  Jennifer has personally learned the value of persistence and repetition, and as a scientist, she has also learned the importance of letting the data inspire their own interpretation rather than having a researcher impose her will on what the data are supposed to indicate.  That lesson has been particularly important on this project.

References

1.  Nunes, G. S.; Alexiou, A. D. P.; Araki, K.; Formiga, A. L. B.; Rocha, R. C.; Toma, H. E. Eur. J. Inorg. Chem. 2006, 1487-1495.

2.  Meyer, T. J.; Huynh, M. H. V. Inorg. Chem. 2003, 8140.

3.  Pink. C. C.; Saad, N. L.; Schlough, J. M.; Mugge, A. M.; Pence, L. E. manuscript in preparation.

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