Vaska’s complex is a catalyst molecule that is important for improving the rates of chemical reactions. This molecule consists of organic (carbon-based) regions surrounding an iridium metal atom. The interactions of this complex with reactants during a catalytic process involve binding of reactants to the metal and rearrangement of the surrounding organic regions. Throughout this process, the solvent in which the reaction is occurring is also
rapidly rearranging. These rearrangements have recently been studied by the Massari
group at the University of Minnesota (Jones, B. H.; Huber, C. J.; Massari, A. M. Solvation
Dynamics of Vaska’s Complex by 2D-IR Spectroscopy J. Phys. Chem. C 2011, 115, 24813-24822.). The role of solvents in the catalytic reactions of Vaska’s complex can be further studied by Fourier transform IR (FTIR) spectroscopy, which measures the molecular vibrations of the molecules at work. In this project, bromine and sulfur were bound to the Vaska’s complex in a broad range of solvents. The carbonyl bond stretch frequency in the Vaska’s complex in these solutions was analyzed using FTIR spectroscopy to determine if there was a
solvent dependency. The solvent dependence of the carbonyl stretch had been previously
observed to differ by about 10 cm-1 in different solvents. Addition of sulfur and bromine respectively to Vaska’s complex increased the carbonyl stretching vibration. Addition of bromine increased the carbonyl vibration more than the addition of sulfur to the Vaska’s complex, indicating that the bond between carbon from carbonyl and iridium was weakened to a greater extent by the bromine. Surprisingly, it was found that the frequency of the carbonyl was nearly insensitive to the nature of the solvent, while the sulfur complexes experienced moderate frequency shifts. This was explained by considering the differences
in the way that the bromine and sulfur bind to the iridium metal.
This research was supported by the Undergraduate Research Opportunities Program (UROP).
Changes of carbonyl bond stretch frequency of Vaska’s complex with added bromine and sulfur respectively in different solvents.
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