Synthesis of Dimeric Molecules via Ag-Catalyzed Electrochemical Homocoupling of Organic Bromides Paired with Electrooxidation of Urea

Abstract

We present a sacrificial anode-free approach to reductive homocoupling of organohalides that does not require a co-catalyst. In this approach, a divided electrochemical cell with aprotic and aqueous compartments separated by an anion exchange membrane enables coupling of the cathodic homocoupling reaction with anodic oxidation of urea. We show that, in contrast with traditional one-compartment cells relying on sacrificial anodes, the proposed cell configuration maintains stable cell voltage in the course of galvanostatic electrolysis. A synthetic potential of this method was assessed using a series of 13 organic bromides that demonstrated a strong dependence of the reaction outcome on the structure of the organic substrate, more specifically, the dissociation energy of the C–Br bond and the redox properties of formed radicals, which are discussed in detail. While not being suitable for the synthesis of byarylstructures, this method is excellent for C(sp3)-C(sp3) coupling to corresponding dimeric products with up to quantitative yields. Simultaneous electrochemical treatment of nitrogenous waste in the adjacent half-cell provides an additional incentive for wide adaptation of this sustainable synthetic approach.

Suppressing carboxylate nucleophilicity with inorganic salts enables selective electrocarboxylation without sacrificial anodes

“…GCMS-FID analysis revealed lower substrate conversions and lower AARs for tertiary alkyl halides. Given that several studies have implicated the presence of a carbanion intermediate in the reduction of aliphatic carbon-halide bonds, 74,75 we hypothesize the yield trend can be rationalized by the greater instability of carbanions with greater degrees of carbon substitution. The inductive electron donation from these surrounding carbon atoms increase the negative charge of the carbanion, making it more unstable.…”

Translating Tactics from Direct CO2 Electroreduction to Electroorganic Coupling Reactions with CO2

“…The specificities of the EC reaction mechanism dictate certain requirements for the availability and relative concentrations of the organic precursor and CO 2 . Specifically, when the anion formation is a result of two single‐electron transfers, the concentration of the organic precursor cannot be too high; otherwise, radical coupling [ 62 ] would dominate over the second electron transfer. When carbanions are formed, the concentration of CO 2 has to be high; i.e., it should be omnipresent at the electrode surface to minimize the reaction of the carbanions with species other than CO 2 .…”

Nickel‐Electrocatalyzed Synthesis of Bifuran‐Based Monomers

“…[57] While sacrificial anodes offer some benefits in organic electrosynthesis, [60,61] the dissolution of the anode can complicate electrolysis, altering the inter-electrode gap as reaction progresses, [62] and the generation of stoichiometric metal waste can complicate waste disposal on a larger scale. [63] A few methods in the literature have avoided the use of sacrificial anodes in nickel-mediated electrohomocouplings by utilizing water [56] and urea oxidations [64] as counter-reactions in a divided cell. However, the use of cell separators increases cell resistivity and adds complexity to the system, therefore, undivided electrosynthesis without a sacrificial anode in nickelcatalyzed electrohomocouplings would be desirable.…”