Pairing Iron and Nickel Catalysis for Electrochemical Esterification of Aryl Halides with Carbazates

Abstract

We report an electrocatalytic approach for esterification of aryl halides by pairing iron and nickel electrocatalysis. The reaction involves anodically iron-catalyzed oxidation of carbazates to produce alkoxycarbonyl radicals. The carboncentered radicals then enter nickel catalysis that is powered by cathodic reduction to deliver the radical coupling products. Mechanistic data are consistent with arylnickel(II) species as the key intermediates enabling the desired carbon−carbon bond formation.

Electrochemical Metal‐Catalyzed Azidoesterification of Alkenes

“…Taken together, all experimental data are in agreement with the mechanistic scenario detailed in Figure 1D. The oxidative generation of methoxycarbonyl radical ( III ) from methyl carbazate 1 was mediated by anodically generated PcFe III species in the electrolytic system [12,13] . The alkene substrate then reacted with methoxycarbonyl radical ( III ) to form the C‐centered radical ( I ).…”

“…Notably, this wave further increased in intensity in the presence of methyl carbazate 1 (Figure 1B, a, red), indicating redox events occurred between Fe(III) species and the methyl carbazate 1. [12] In contrast, replacement of PcFe with MnBr 2 did not show the same phenomenon (Figure 1B, b). This is consistent with the control experiment results in Table 1 that the sole use of Mn catalyst was not capable of catalyzing the reaction (Table , entry 3).…”

“…We assigned this peak to the Fe II /Fe III oxidation and azide anion likely served as a ligand on Fe and reduced the potential needed for its oxidation. Notably, this wave further increased in intensity in the presence of methyl carbazate 1 (Figure 1B, a, red), indicating redox events occurred between Fe(III) species and the methyl carbazate 1 [12] . In contrast, replacement of PcFe with MnBr 2 did not show the same phenomenon (Figure 1B, b).…”

“…The oxidative generation of methoxycarbonyl radical (III) from methyl carbazate 1 was mediated by anodically generated PcFe III species in the electrolytic system. [12,13] The alkene substrate then reacted with methoxycarbonyl radical (III) to form the C- centered radical (I). This nascent transient radical species subsequently coupled with the persistent open-shell intermediate PcFe III À N 3 to deliver the final product.…”

Taming Challenging Radical-Based Convergent Paired Electrolysis with Dual-Transition-Metal Catalysis

“…The strategy of transition-metal-catalyzed convergent paired electrolysis was also employed in our esterification protocol. 16 Aryl halides are converted into methyl benzoates by using iron phthalocyanine (PcFe) and a Ni complex as catalysts with methyl carbazate (11) as a source of methoxycarbonyl radicals and phthalimide as an additive in DMF under electrochemical conditions. A plausible mechanism is outlined in Scheme 3.…”