Professor of Chemistry
Our move from the second floor of Lewis Hall to the fifth floor of Tan Hall in 1997 came just two years after a move to Berkeley from UCSD. The new location brought us closer to our inorganic colleagues in Latimer Hall and to our collaborators, Professors Bergman and Bell. We have since been busy developing new synthetic approaches to novel inorganic, organometallic, and organic systems.
Some of our research has targeted molecular chemistry, and we have developed new structures and reactions for compounds containing transition metals. Along these lines, our group is developing new homogeneous catalysts for organic reactions. Other research in the lab focuses on the design of synthetic pathways using organometallic compounds to make new organic materials, including polymers with unusual electronic properties.
An important theme throughout our research in organometallic chemistry is the role of sigma-bond metathesis in activating substrate molecules. In this process, single bonds in the substrate (M-R, where R is a carbon-containing group) break as new bonds form at the metal center (M), via a so-called four-center transition state (below).
We have shed light on possible catalytic pathways involving readily occurring reactions of bonds to carbon (e.g., C-H and C-Si.). For example, a positively charged hafnium (element 72) complex [Cp2Hf-SiHR2]+ reacts rapidly with arenes (ArH) to produce aryl-hafnium products [Cp2Hf-Ar]+ and the silane R2SiH2. We are working to incorporate this reaction type into catalytic cycles. This reaction would represent a new method to make inert hydrocarbons into more useful chemicals by adding functional groups. Currently, there are few ways to do this under mild conditions.
We also study polymer synthesis, creating compounds consisting of repeating structural units by coordinating polymerizing reactions with either transition-metal catalysts or organometallic reagents. In particular, we are developing electron-delocalized polymers, which show great promise as materials such as conductors, semiconductors, photoconductors, nonlinear optical materials, and light-emitting materials.
A similar approach to make new classes of heterogeneous catalysts also involves a molecular design strategy, but this one is based on the assembly of nanoscopic building blocks into networks with tailored properties. We have had success using a sol-gel method to link dendrimers (regular, highly-branched monomers) into hybrid organic-inorganic materials that have large surface areas with well-defined Si-OH surface functionality. This approach holds great promise for controlling the structure and properties of the active sites of a heterogeneous catalyst.