Activation of Strong Bonds - CENTC
CENTC (Center for Enabling New Technology through Catalysis) and is a collaboration with a number of departments from around the United States. A major focus of the center is in elucidating and applying the fundamental principles necessary for the catalytic transformations of strong chemical bonds including C-H, C-C, C-O, C-N, N-H. Our group's work and contributions to the center include:
Anti-Markovnikov Hydroamination of Alkenes
Listed among the ten great challenges in catalysis in the early 1990s, the hydroamination of alkenes remains, despite tremendous research efforts, an unsolved synthetic problem. If realized, such a transformation would provide an atom-economic, environmentally benign synthesis of alkyl amines directly from relatively inexpensive and abundant alkene feedstock. A process favoring the formation of linear (anti-Markovnikov) products would be particularly valuable. The discovery of viable catalysts for large-scale processes could fundamentally change the bulk production of surfactants, detergents and plasticizers, as well as the synthesis of fine chemicals and pharmaceutical intermediates. Our group is exploring, in collaboration with other research groups participating in CENTC, various strategies to accomplish the transition metal-catalyzed anti-Markovnikov hydroamination of alkenes.
Harnessing and Making Molecular Oxygen
Molecular oxygen, O2, is the greenest, most abundant and inexpensive oxidant imaginable. Yet, it is notoriously difficult to carry out selective oxidation reactions using O2. Some of the obstacles met in using molecular oxygen as a reagent include the difficulty in controlling and modulating its oxidation power, and the current lack of understanding concerning its interaction with transition metal complexes. Through the examination of the reactivity of various transition metal complexes with molecular oxygen, our group, in collaboration with other research groups participating in CENTC, is attempting to develop a general means to activate O2 to achieve the selective oxidation of substrates, particularly alkanes.
A New Generation of Electrophilic Oxidation Catalysts
The direct use of alkanes as a feedstock for the chemical production of alcohols and other organics would significantly impact the chemical industry. Some thirty years after Shilov’s initial discovery of platinum-catalyzed alkane oxidation, platinum-based systems continue to represent some of the most promising leads for the direct conversion of alkanes to alcohols. Surprisingly, other late metals that are also known to activate alkanes via a two-electron couple (e.g. iridium and rhodium), and that could in principle perform similar Shilov-type chemistry, have not been extensively studied for this purpose. Using the large knowledge base gained from detailed mechanistic studies on the well-defined platinum systems, related electrophilic catalysts of other metals are under investigation in our group, in collaboration with other research groups participating in CENTC. Efforts are focused on developing and applying fundamental mechanistic understanding of C-H bond activation processes to the development of new catalytic systems for alkane functionalization.
National Science Foundation (NSF)
The development of new catalyst systems for numerous desirable conversions continues to be a high priority research focus in academic and industrial laboratories. Key to the rational design and optimization of new catalysts is an understanding of the energetics and mechanisms of the fundamental organometallic reactions that comprise the steps of the catalytic cycle. To obtain this knowledge, useful for the design of homogeneous catalysts for transformations involving hydrocarbons, our group has been investigating fundamental organometallic reactions of d8 and d6 metal complexes. A variety of reactions have been studied, including C-C, C-H, and C-heteroatom reductive elimination from d6 metals, oxidative addition of alkyl and aryl C-H bonds, and reactivity with small molecules such as molecular oxygen and ethylene. Novel complexes such as neutral-five coordinate Pt(IV) alkyl species have been synthesized and studied, and the study of their reactivity has lead to the discovery of new catalytic systems.
Epoxidation with O2
The epoxidation of olefins is a tremendously valuable industrial process, yielding chemical intermediates for an array of important commercial products. For propylene oxide alone, the total consumption in 2007 well exceeded ten billion pounds globally, and the market is annually growing by 4-5%. Even though there is considerable research in catalytic olefin epoxidation, the two commercial processes responsible for the majority of propylene oxide production have significant room for improvements, both economically and environmentally. Recent developments in epoxide production have utilized more environmentally benign reactants, such as H2O2 as an oxidant. While H2O2 shows promise, our group is focused on achieving catalytic olefin epoxidation with transition metal complexes and molecular oxygen - an oxidant that is both readily available and envronmentally friendly.