Photochemical Reactivity of \(\alpha\)-Diimine Organopalladium Complexes: Exploring Ligand Control for Selective Visible Light-Induced Alkyl Radical Formation

Abstract

Methods to functionalize C–H bonds are sought after to achieve late-stage transformations of complex molecules, thereby streamlining synthetic routes and helping to lower the amount of chemical waste produced globally. However, the development of a general, non-directed method to functionalize primary aliphatic C–H bonds remains a challenging goal due to the thermodynamic strength of this bond. Herein, I investigate the photochemical reactivity of \(\alpha\)-diimine-ligated palladium alkyl complexes and their potential to achieve this elusive transformation selectively and under mild conditions. I report that these complexes, generated in situ through carbometallation of alkenes, undergo homolytic cleavage of the strong metal-carbon bond upon irradiation with visible light, and insights into the factors that affect the rate of these photochemical reactions were obtained. In addition, I show that fast isomerization of these organometallic intermediates via “chain walking” can alter the selectivity of bond homolysis and allows for a formal H-atom abstraction from a primary site after migration of the metal complex to the terminal position. I hypothesize that the resulting primary alkyl radical from this process can act as a general intermediate for a variety of bond-forming events, and that this photochemical reactivity provides the basis for selective functionalization of the primary position in a non-directed fashion.