Abstract:Transition metal hydrides represent a class of promising hydrogen atom transfer reagents to replace tin hydrides. Due to their typically weaker M-H bonds, transition metal hydrides are often able to transfer H• to C=C and generate radicals — a reaction that tin hydrides cannot do. Furthermore, many transition metal hydrides can be regenerated from hydrogen gas. We have employed H• transfer ability of transition metal hydrides to develop various new reactivities. First, I developed a Ti/Cr cooperative catalytic system for anti-Markovnikov hydrogenation of epoxides, which features multiple interactions between the two metal systems. This reactivity was also extended to reductive cyclization of epoxy enones under H2, which was successfully incorporated in natural product synthesis in collaboration with Prof. Snyder’s group at UChicago. Second, hydrodefluorination of CF3-substituted olefins catalyzed by a nickel hydride will be discussed. Last, I developed a method to achieve a broad range of hydrofunctionalizations of olefins with hydrogen atom transfer from metal hydrides in situ. Hydrogen atom transfer to olefins was followed by TEMPO trapping to form TEMPO adducts. A subsequent photocatalytic substitution on those TEMPO adducts with different nucleophiles affords various hydrofunctionalized products.
