Robert Bergman
Professor of Chemistry

Since moving to the new laboratories on the sixth floor of Tan Hall, our research group has made significant advances in organometallic chemistry, the interfacial area between organic and inorganic chemistry.

Activating Nonreactive Bonds
A major focus of our work is activating the normally very inert carbon-hydrogen bonds in alkanes, open-ended chains of hydrogen and carbon, using metal complexes. Shortly after arriving at Berkeley, our group discovered one of the first directly observable “C-H activation” reactions in which we showed that alkanes reacted with complexes containing the metals iridium and rhodium. This opened up a whole new avenue of organic synthesis.

More recently we discovered a new type of C-H activation using a relatively high oxidation state (+3) methyliridium complex:

+ R-H --> Cp*(PMe3)Ir+-R + CH4

After doing extensive studies to determine the chemical mechanism, we found that the compounds that are formed between the starting and final products (where the arrow is) are very unusual and have an even higher (+5) oxidation state at the iridium center. After the move to Tan Hall, we successfully synthesized the intermediate compound. To our surprise, we found that the intermediate hydride compound induces a very rapid catalytic C-H activation reaction and catalyzes deuteration of organic compounds from heavy water (D2O), by far the cheapest source of deuterium available. Deuterium is an isotope of hydrogen that has one proton and one neutron in its nucleus and twice the mass of ordinary hydrogen. It is widely used in chemical synthesis. This reaction could provide an efficient route to labeling organic materials with deuterium in locations that have traditionally been inaccessible to isotopic substitution, which would be useful in many of the tracer experiments used in mechanistic and physiological studies.

Resolving Enantiomers
In another project involving zirconium and titanium, we have generated chemical complexes containing metal-nitrogen multiple bonds that can react with a wide range of organic molecules. Many of these transformations are analogous to organic cycloaddition reactions, in which a chemical reaction leads to ring formation.

In our most dramatic recent finding, we successfully prepared optically active imidozirconium complexes, which are among the first metal-heteroatom multiply-bonded complexes to be enantioresolved. (Enantiomers are compounds whose molecular structures are each other’s mirror image.)

Resolving enantiomers is a difficult task because the two compounds are extremely similar, and many times only one is chemically desirable. In addition to providing information about metal/organic cycloaddition reaction mechanisms, this process will be useful as the allene compounds that result are increasingly important starting materials in organic synthesis.

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