NEW REACTIONS VIA EARTH ABUNDANT ELEMENT PHOTOCATALYSIS

Abstract

The alkene is a central functional group in organic synthesis. While myriad reliable methods exist to access this moiety from other functionalities, acceptorless dehydrogenation, or the direct synthesis of alkenes from alkanes with hydrogen gas as the sole byproduct, remains a challenging, albeit highly desirable, transformation. Careful study of both organometallic and enzymatic approaches to dehydrogenation have allowed us to design a dual catalytic system capable of dehydrogenative transformations using earth abundant elements and light energy. This noble metal-free catalyst combination follows a nature-inspired pathway of high- and low-energy hydrogen atom abstractions. Not only is this system effective for the dehydrogenation of alkanes and alcohols but, also, it is capable of catalyzing acceptorless dehydroformylation, or the conversion of aldehydes into alkenes, carbon monoxide, and hydrogen gas.

During the course of developing our dehydrogenation system we became interested in finding new earth abundant element visible light photo-hydrogen atom transfer (photo-HAT) catalysts. Our studies of the physical inorganic literature suggested the depleted uranyl cation (UO22+) to be one such species, prompting us to investigate its use. Using C–H fluorination, an important reaction for pharmaceutical, agrochemical, and materials sciences, as a litmus test, we were able to demonstrate the uranyl cation as an effective visible light photo-HAT catalyst. Importantly, the uranyl cation exhibits idiosyncratic reactivity when compared to other photo-HAT driven fluorination reactions.