Research Overview

Inorganic and Organometallic Chemistry

Our work is aimed at understanding the fundamental details of transition-metal catalyzed atom and group transfer reactions and to use this knowledge for the development of new catalytic reactions and for the construction of novel materials. Our approach involves the rational design of new reagents and ligands for achieving these goals. Our research cuts through the traditional boundaries of Organic, Inorganic, Organometallic and Main Group Chemistry.

1) Novel Materials for Molecular Electronics and Nanotechnology:

Transition Metal- and Main Group-Phosphinidene Complexes for Precursors to Hybrid Polymeric Materials

We are interested in the construction of novel conjugated materials that incorporate multiply bonded low coordinate phosphorus centers. For example, many fascinating conducting polymers having backbones comprised of C=C units in a conjugated fashion are being intensely studied for new electronic and optical properties. Using the well-known diagonal relationship between carbon and phosphorus, our goal is to prepare new materials having having P=C and P=P double bonds along the conjugation pathway. One recent successful polymer (left) is compared to a model oligomer (right) below .

As the pi-bonds involving phosphorus are weaker than for carbon, these redox active sites have smaller HOMO-LUMO gaps and should add new mechanisms for modulating electronic and optical properties of the materials. An added challenge to this work is the need to design new multifunctional ligands for phosphorus that also are sterically encumbered. In addition, we are exploring new modes of synthesis of such materials. recently we discovered a new type of "phospha-Wittig" reaction (equation 1). The "phospha-Wittig" reaction allows for rapid construction of P=C bonds in a selective manner.

During the course of our work we have devloped new protective groups for phosphorus based on m-terphenyl and tertra-arylphenyl ligands. A structurally characterized conjugated bis-diphosphene, DmpP=P(C6Ar4)P=PDmp (below) has been prepared, and discovered to undergo novel structural changes upon 1 and 2 electron reductions. Such behavior is akin to a "molecular switch"..

Some Recent Papers:

2) Mechanistic & Catalytic Reactions:

New Ligands for Catalysis based on meta-Terphenyls

Meta-Terphenyls that are being used in our labd also make great platforms upon which we can build many new exciting ligands. Shown above is one of our new ligands and its palladium complex. The trans spanning mode of this ligand is unusual. These materials also act as catalysts for many important Suzuki and Heck coupling reactions that we are currently studying.

Some Recent Papers:

Oxo- and Nitrene-Transfer Reactions of Organoiodine(III) Complexes

Iodosylbenzene, (PhI=O)n, and (Tosyliminoiodo)benzene, (PhI=NTs)n, are two of the most important sources of oxygen atoms and tosylimino groups for transition metal catalyzed processes such as epoxidation and aziridination (left, S = olefin). A full understanding of these powerful oxidants containing a hypervalent iodine(III) center is currently lacking due to their limited solubility and polymeric essence. Any sort of mechanistic studies of the catalytic reactions are therefore impeded by the heterogeneous nature of the reaction medium.We have recently gained important insights to the nature of the insolubility of these reagents by the characterization of the solid state details of ArI=NTs by single crystal X-ray studies. An analysis of this data has led to the successful design of new reagents that incorporate intramolecular secondary bonds (analogues of hydrogen bonds that involve heavy atoms) between iodine and oxygen atoms (below). These newly developed species display unprecedented solubility in conventional organic solvents and allow for standard spectroscopic measurements. Work is currently in progress to determine how the solid state structures of these new materials pertain to their solution behavior and to their atom and nitrene transfer proficiency. These new organoiodine(III) reagents will thus allow us to fully maximize the potential of transition metal catalyzed atom and group transfer reactions. New applications are also anticipated.

Some Recent Papers: