Computation Study on Copper-Catalyzed Aerobic Intramolecular Aminooxygenative C═C Bond Cleavage to Imides: Different Roles of Mononuclear and Dinuclear Copper Complexes

Abstract

Cu-catalyzed aerobic reactions are a powerful protocol for the synthesis of value-added chemicals based on the ideal oxidant O2. Despite the long research history, the mechanistic studies clarifying the details of the whole catalytic cycle, where Cu-O2 complexes and their derivatives directly participate in the conversion of substrates, are limited, leaving the mechanisms of emerging aerobic reactions far from understanding. Herein, a computational study on the mechanism of Cu-catalyzed aerobic aminooxygenation of alkene-tethered amides to imides is reported. It is found that the Cu(I) precursor is not the active species but can generate two types of Cu(II) complexes LCu(OAc)OH and LCu(OAc)OOR to start the aminooxygenation through the successive formation of dinuclear Cu(III) oxo complex, dinuclear Cu(II) hydroxide complex, and hetero-dinuclear Cu(II)-Cu(I) complex, followed by alkylperoxo radical capture with Cu(I) species. LCu(OAc)OH catalyzes the aminooxygenation via a mononuclear mechanism, while LCu(OAc)OOR is an active intermediate therein. In the initial catalytic stage, LCu(OAc)OH transforms alkene-tethered amides to α-amidated aldehydes through N–H activation, amide isomerization, cyclization, alkyl radical release, alkyl radical capture by O2, alkylperoxo radical capture by in situ-generated Cu(I) species to LCu(OAc)OOR, acetate-assisted proton-coupled electron transfer (PCET), and concerted PCET/O–O bond cleavage. In the second catalytic stage for the generation of imides from α-amidated aldehydes, the previously proposed aldehyde Cα–H pathway is possible, but it is more likely to generate CO2 and H2 as the byproducts. Instead, a more feasible pathway involving C(O)–H activation to acyl radical, decarbonylation, and radical capture to LCu(OAc)OOR′ was discovered. The C(O)–H activation pathway generates CO and H2O as the byproducts and is consistent with the experimental observations. The concerted PCET/O–O bond cleavage steps generating α-amidated aldehydes and imides have close energy barriers and both can be the rate-determining steps. The presented outcome revised and expanded the knowledge of Cu-catalyzed aerobic conversion of CC bonds and amide N–H bonds, highlighting the different roles of mononuclear and dinuclear copper complexes in the aerobic reactions and the in situ generation of Cu(II) catalysts, respectively.

Iron-Promoted Catalytic Activity of Selenium Endowing the Aerobic Oxidative Cracking Reaction of Alkenes

“…Thus, on the basis of the above experimental results as well as the literature reports, ,− a plausible mechanism was proposed (Scheme ). First of all, the Se-catalyzed oxidative cracking of alkenes with H 2 O 2 occurs via the ionic reaction mechanism, and it has already been proposed by us in 2017 (Route a) .…”

“…37 The Se-catalyzed oxidation of Fe(II) to Fe(III) process has been verified via the X-ray photoelectron spectroscopy (XPS) analysis. 38 Oxidation of 3 furnishes the peroxygenic intermediate 4, 39,40 which is converted into 5 after grabbing protons from water. 41 Hydroxyl radicals are also generated during the process.…”

Recent advances in computational studies on Cu-catalyzed aerobic reactions: cooperation of copper catalysts and dioxygen

“…30). 54 This aminooxygenation of alkenes involves the cleavage of the CC double bond and N–H bond along with the formation of the CO bond and C(O)–N bond. The Cu( i ) precursor was found to be not the active species but it can in situ generate an active Cu( ii ) catalyst LCu(OAc)OH 2 182 and an active intermediate LCu(OAc)OOR 2 185 to start the real catalytic cycle.…”