Our group applies "state-of-the-art" theoretical techniques to chemical problems of current interest to practicing inorganic, organometallic, and biological chemists. We also develop new algorithms that are especially suited to electronic structure problems in large transition metal molecules. Some examples of our current problems are given below.
Our underutilized reserves of methane have provided the impetus for many research groups to study C-H bond activation. Detailed kinetics of the early stages of the C-H bonds activated by a tris-pyrazolylborate(Tp) rhodium carbonyl show the formation of two successive intermediates. Our preliminary calculations have identified these as a weakly solvated trihapto-Tp followed by a more strongly solvated dihapto-Tp complex, an interpretation that is quite different from the original ones suggested in the experimental work. This investigation will be completed by determining the nature and energy of the transition states connecting these proposed intermediates and determining if similar intermediates are possible for the analogous CpML reactions, where a slipped Cp might be involved. The figure shows the transition state structure for the intramolecular C-H bond activation in an iridium complex.
Much of our recent work has involved new developments in transition metal polyhydride complexes, particularly the transformation between non-classical dihydrogen complexes and classical hydrides. Among several studies are the recently reported, unexpected protonation of some group 6d pentahydrides. Oxygen transfer and insertion reactions are being examined in a model system that mimics enzymes. The stability and structure of transition metal carbon clusters, particularly the MCx systems studied by mass spectroscopy and the growth of MxCy clusters, are being investigated.
The most significant theoretical development has been the derivation and implementation of our new Generalized Molecular Orbital Theory, which begins with a pair-excited multi-configuration self-consistent field for the orbital optimization, and is followed by a multi-reference configuration interaction calculation. The method has the advantage of being variational, of handling large numbers of active electrons, and of only needing the user to specify the number of active electrons and orbitals and not pick a dominant configuration.
"Theoretical Characterization of the Reaction Intermediates in a Model of the Nickel-Iron Hydrogenase of Desulfovibrio gigas" Niu, S. Thomson, L., and Hall, M.B. J. Am. Chem. Soc. 1999, 121, 4000.
"Theoretical Studies of Inorganic and Organometallic Reaction Mechanisms 15. Catalytic Alkane Dehydrogenation by Iridium(III) Complexes" Niu, S. and Hall, M.B. J. Am. Chem. Soc. 1999, 121, 3992.
"Prediction of the Geometries of Simple Transition Metal Polyhydride Complexes by Symmetry Analysis" Bayse, C.A., and Hall, M.B. J. Am. Chem. Soc. 1999, 121, 1348.
"Structural and Bonding Trends in Platinum-Carbon Clusters" III Miller, T.F., and Hall, M.B. J. Am. Chem. Soc. 1999, 121, 7389.
"Theoretical Calculations on Reactions of Transition Metal Complexes" Niu, S., and Hall, M.B. Chemical Reviews 2000, 100, 353.