In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor John F. Hartwig at the University of California, Berkeley will develop reactions at typically unreactive carbon-hydrogen (C-H) bonds. Prof. Hartwig's group discovered the borylation of methyl C-H bonds in alkanes and alkyl groups of functionalized molecules and developed iridium complexes that catalyze the borylation of aryl and alkyl C-H bonds under mild conditions, with sterically controlled selectivity, including reactions that occur with high turnovers. The proposed research builds upon several sets of preliminary data on the silylation of C-H bonds, the borylation of aliphatic C-H bonds with a new iridium catalyst, and the factors that control selectivity in these C-H bond functionalizations. The proposed research will broaden the scope of the borylations of alkyl C-H bonds to include the borylation of secondary C-H bonds and activated primary C-H bonds, directed borylations by strategies related to this group's recently discovered directed silylations of alkyl C-H bonds, and aspects of intermolecular C-H bond silylations of arenes, heteroarenes, and alkenes. The proposed research will also gain insight into the mechanism of silylations and borylations of C-H bonds by preparing boryl and silyl complexes that are competent to be intermediates in the recently discovered borylations of aliphatic C-H bonds and silylations of aliphatic and aromatic C-H bonds.
For many years, chemical synthesis has focused on reactions at particular points of a molecule that contains a reactive array of atoms called "functional groups." The C-H bonds distal from these functional groups are usually unreactive with reagents used for conventional synthetic chemistry. The proposed research focuses on reactions that occur selectively at the C-H bonds of a molecule that are typically unreactive. One challenge that must be met to achieve this goal is the selective functionalization of a specific C-H bond in a molecule. In some cases, the selectivity for one C-H bond results from the spatial availability of the bond, in some cases from the distribution of electrons around the bond, and in other cases from the position of a functional group several atoms away from the C-H bond. Methods to exploit each of these properties for selectivity will be uncovered. This research will lead to new methods to conduct chemical synthesis in fewer steps, with less waste, and with less reliance on the installation and protection of functional groups. In addition, this research creates the underlying principles on which future design of catalysts and processes for more efficient synthesis are based. This may impact the synthesis of useful materials such as polymers containing new properties, organic molecules with enhanced abilities to emit light, components of catalysts for other reactions, organic probes for understanding biological systems, and components of medicinally important molecules. Work emanating from the proposed research has become part of new curricula for the classroom, short-courses, many external lectures, and a major textbook project that was recently completed by the PI.
