Organosilanols as Universal Donors in Organometallic Chemistry

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In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor Scott E. Denmark will conduct research to implement the use organosilanols to access the catalytic organometallic chemistry of a myriad of transition metal elements. Organosilanols are inexpensive, non-toxic, air- and water-stable compounds that have the remarkable ability to exchange the carbon-silicon bond with many other carbon-metal bonds through the agency of a discrete Si-O-M linkage. The program will involve a rational, structurally-based exploration of the synthesis, reactivity and subsequent catalytic chemistry of transition metal silanolates derived from nickel, copper, rhodium, iridium and chromium. The first component of the research plan will involve detailed mechanistic resolution of the elementary steps in the catalytic cycle for the well-established, palladium-catalyzed, cross-coupling reactions of silanolates. These insights will be of great value for the major thrust of the research plan that involves other, less well-investigated transition metals. The bulk of the research program will involve the exploration of the ability of silanols (silanolates) to form Si-O-M linkages with existing catalytically active intermediates or to create those intermediates in the reactions of transition metal reagents. In many cases, such transition metal silanolate complexes can be independently prepared and studied, whereas in other cases, the in-situ generation and product analysis will be needed. Progress in all areas of chemical synthesis is driven by the creation, optimization and understanding of new chemical reactions. The preparation of molecules with challenging chemical structures (natural products, or molecules of theoretical interest) or molecules with desirable chemical, physical or biological properties (with applications in materials science or the agricultural, pharmaceutical or commercial sectors) will require the ability to design executable synthetic routes. The most important lesson gleaned from the evolution of organic synthesis during the second half of the 20th century is that strategy and planning of synthetic routes is driven by tactics. In other words, the scope, selectivity and efficiency of chemical synthesis are inexorably tied to the discovery, development and optimization of new chemical reactions. These activities to be carried out in this project are ideal for the intellectual and practical training of graduate students and postdoctoral coworkers. The interplay of reaction design, development and application represent the essence of the scientific method. Students will be presented with hypotheses for the outcome of planned experiments and they must learn to collect and interpret data to substantiate or eliminate the hypothesis. The unifying theme of this activity will be the invention of new chemical reactions on the basis of current mechanistic paradigms. This will provide a platform for creativity within the guidelines of the project for students to identify new directions. In addition, the diversity of new types of carbon-carbon bond forming processes that will be accessible from inexpensive, non-toxic, and air and water stable silanolates will be significant.