Recent Advances in Electrocatalytic C-H Activation

Electrolysis in synthetic organic chemistry has a rich history dating back to the 19th century. Many advances have been done with the use of electrolysis in the past, e.g. Kolbe’s decarboxylative dimerization, ¹ Tafel’s electrolytic rearrangement, ² Simmons’s C-H fluorination.³ Since then the popularity of the electrolysis in synthetic organic chemistry has drastically decreased.

In the past decade transition metal-catalyzed C-H functionalization has become a very popular tool in the hands of synthetic organic chemists allowing a wide variety of useful direct conversions of C-H bonds into diverse functional groups in the single synthetic step.^4-6 However, several issues still remain unresolved in the various catalytic C-H functionalization reactions. First, stoichiometric amounts of oxidant are required in the reaction vessel, which can cause generation of undesirable byproducts and selectivity issues during reductive elimination from transition metal.⁷ Second, limited catalyst turnover which results in high catalyst loadings. Introduction of electrochemical methods into transition metal-catalyzed C-H activation can potentially solve the issue with stoichiometric amounts of oxidant being present in the reaction mixture, thereby improving the efficiency and atom-economy of such reactions. One of the advantages of electrochemistry is the ability to precisely control oxidative potential, thereby increasing the substrate scope, as functionalities sensible to the strong oxidants can be used in such reactions. Another advantage of the electrochemical methods is that the reaction schedule can be controlled by “On”/”Off” switch on the ElectraSyn plate.^{7- 8} In electrochemical transition metal-catalyzed chemistry reactions anodic oxidation generally can be used to either oxidize an organometallic intermediate to a high-valent species which promote subsequent reductive elimination with regeneration of the catalyst or to regenerate active metal catalyst by oxidation.

Therefore, electrochemical metal-catalyzed C-H activation is a promising method in organometallic chemistry, although there are still some challenges to be resolved before this method will be widely adopted in academic or industrial settings.

1.   Kolbe, H., Beobachtungen über die oxydirende Wirkung des Sauerstoffs, wenn derselbe mit Hülfe einer elektrischen Säule entwickelt wird. Journal für Praktische Chemie 1847, 41 (1), 137-139.

2.   Tafel, J.; Hahl, H., Complete reduction of benzyl acetic ester. Berichte Der Deutschen Chemischen Gesellschaft 1907, 40, 3312-3318.

3.   Simons, J. H., The electrochemical process for the production of fluorocarbons. J. Electrochem. Soc. 1949, 95 (2), 47-47.

4.   Lyons, T. W.; Sanford, M. S., Palladium-Catalyzed Ligand-Directed C-H Functionalization Reactions. Chem. Rev. 2010, 110 (2), 1147-1169.

5.   Ye, B. H.; Cramer, N., Chiral Cyclopentadienyls: Enabling Ligands for Asymmetric Rh(III)-Catalyzed C-H Functionalizations. Acc. Chem. Res. 2015, 48 (5), 1308-1318.

6.   Gandeepan, P.; Ackermann, L., Transient Directing Groups for Transformative C-H Activation by Synergistic Metal Catalysis. Chem 2018, 4 (2), 199-222.

7.   Ma, C.; Fang, P.; Mei, T.-S., Recent Advances in C–H Functionalization Using Electrochemical Transition Metal Catalysis. ACS Catalysis 2018, 8 (8), 7179-7189.