Biradical-like Reactive Intermediates

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With the support of the Organic Dynamics Program in the Chemistry Division, Professor Josef Michl of the University of Colorado-Boulder and his collaborators will work on two projects in the area of their traditional interests, photophysics and photochemistry and on a third project that involves reactive intermediates and their isolable analogs in the field of carborane chemistry. The first project is related to their current effort to understand the electronic structure of oligosilanes, prototypical sigma-conjugated systems, and deals with the relaxation of their vertical excited states that are associated with excitation energy localization, and with an attempt to discover and assign their triplet excited states. The geometrical relaxation of the excited singlets will be examined using time-resolved Raman spectroscopy. The detection of the triplet states connects oligosilane spectroscopy to the second project, which takes advantage of the accomplishments attained in the current grant period with respect to improving the sensitivity of an electron energy loss spectrometer. This is expected to permit the detection of spin-forbidden transitions in oligosilanes, but also in fluorocarbons, in various matrix-isolated species, and additional samples. The third project deals with the chemistry of compounds derived from the anionic icosahedral carborane, HCB11Me11(-). It is still relatively new to this research group and builds on the discovery of a new type of reactive intermediates that was made in the current grant period. These are the isomeric carbonium and boronium ylides HCB11Me11, which show unusual reactivity in preliminary experiments and will now be examined in detail. Peralkylated and perfluoroalkylated carborane anions will also be used as sterically bulky protecting groups to stabilize structures containing electron-deficient atoms of main group elements for structural and spectroscopic studies and well as an examination of chemical reactivity. Perfluorinated anions of the type CB11Fx(CF3)12-x will be used for the stabilization of highly reactive cations. The Organic and Macromolecular Chemistry Program supports the research of Professor Josef Michl of the University of Colorado-Boulder that will impact the field of reactive intermediate chemistry. Contributions to this field will be communicated through publications in scientific journals in the areas of synthetic organic, inorganic, physical, and theoretical chemistry. The work is expected to contribute to the education and training of undergraduate, graduate, and postdoctoral students in a range of interdisciplinary experimental and theoretical methods spanning an area from bonding theory, photophysics, spectroscopy, and photochemistry to physical organic and inorganic as well as preparative chemistry.