Theoretical Study on the Rhodium-Catalyzed Electrochemical C–H Phosphorylation: Insights into the Effect of Electro-oxidation on the Reaction Mechanism

Abstract

The merging of transition-metal-catalyzed C–H bond activation with electro-oxidation has evolved into an appealing protocol for oxidative C–H bond functionalization. Nevertheless, specific effects of the electro-oxidation process on the reaction mechanism of transition-metal catalysis have rarely been investigated. Herein, we present a comprehensive computational study on the rhodium-catalyzed electrochemical C–H phosphorylation of 2-phenylpyridine by diphenylphosphine oxide to reveal the mechanistic details. The effects of electro-oxidation on the three major chemical processes, i.e., C–H activation, P–H activation, and reductive elimination/C–P bond formation, were thoroughly addressed by considering the chemical steps at the Rh­(III), Rh­(IV), and Rh­(V) oxidation states. The calculations demonstrated that the C–H activation prefers to take place at the Rh­(III) state, P–H activation at the Rh­(IV) state, and reductive elimination at the Rh­(V) state. Without electrochemical oxidation, the total barrier for the reductive elimination occurring at the Rh­(III) center is unsurmountable under the experimental temperature. The mechanistic insights disclosed in the present study are expected to be beneficial in understanding the transition-metal-catalyzed electro-oxidative C–H bond functionalization.

Rh(iii)-catalyzed selective C2 C–H acyloxylation of indoles

“…These results implied that Rh IV or Rh V species might be involved in this catalytic process. 14 Accordingly, all the above results also demonstrated that the oxidation of Rh III to Rh IV/V might be the rate-limiting step.…”

“…Then, the intermediate III might be oxidized by MnO 2 to form Rh IV complex IV , followed by reductive elimination to yield the target product 2aa and further oxidation of Rh I salt VII to regenerate the active catalyst. 14 Alternatively, a key Rh V intermediate V might also be produced by the oxidation of MnO 2 , which undergoes reductive elimination to give the desired product 2aa and Rh III catalyst, thus fixing the catalytic cycle.…”