L. Keith Woo

Organometallic Chemistry, Catalysis

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Research Interests

The research in my group spans an extensive spectrum of chemistry, ranging from organic synthesis of complex ligand systems to physical studies on the kinetics and thermodynamics of new reactions. In addition, we are interested in the synthesis and reactivity of novel coordination compounds and organometallic complexes. Our research is directed towards understanding fundamental transition metal behavior and reactivity in both biological systems and in new materials. Aspects of our current efforts are summarized below.

Coordination Chemistry. We have recently developed new methods for preparing transition metal and main group porphyrin complexes containing metal-ligand multiple bonds and other novel features. Our discoveries have greatly increased the realm of porphyrin chemistry and continue to be an active area of exploration. Examples of some meso-tetratolylporphyrin (TTP) complexes that we have prepared are shown below. Tolyl groups at the meso positions of the porphyrns have been omitted for viewing clarity.

(TTP)Zr complex with a N,O-bound ureate ligand

(TTP)Ti complex with π-bound 1,4-diphenyl-1,3-butadiyne ligand

First tellurium porphyrin complex, (TTP)TeCl2. Note unusual binding mode of the porphyrin

Catalysis. Through our evolving work in organometallic chemistry, we have demonstrated that osmium and iron porphyrin complexes efficiently catalyze the cyclopropanation of olefins in the presence of diazo reagents. Our catalysts produce some of the highest known stereoselectivities for styrene cyclopropanation. Our research provides strong evidence that the mechanism of this process involves a carbene complex. In fact, we have isolated and structurally characterized several osmium carbene complexes. We are pursuing mechanistic studies and attempting to design enantioselective catalytic systems. This includes the use of C2- and C4-symmetric porphyrin and chiral tetraazaannulene ligands.

We have recently discovered that iron(II) porphyrin complexes are extremely efficient catalysts for the olefination of carbonyl compounds with diazo reaagents. These catalysts are among the most effective and inexpensive known to date.

In our most recent finding, titanium(IV) oxo porphyrins catalytically cleave 1,2-diols to the corresponding carbonyl compounds. The net reaction consumes a half an equivalent of dioxygen

and liberates water. A possible mechanism for this process is shown below. Kinetic and mechanistic studies on this reaction are underway.