Copper-catalyzed photoinduced carbonylation of C1-C3 gaseous alkanes

Abstract

The catalytic conversion of carbon monoxide (CO) provides an enormous opportunity to construct carbonyl-containing molecules. Among them, the direct carbonylation of C-H bonds on gaseous hydrocarbon feedstocks provides a straightforward approach to access industrially important short-chain carboxylic acid derivatives. Here, we report a general and mild direct carbonylation of methane, ethane, and propane under blue LED irradiation at ambient temperature, enabling the direct formation of short-chain carboxylic acid derivatives. Notably, the direct carbonylation of ethane offers the potential for a more cost-efficient route to produce MMA. The combination of copper reduction and chlorine radical released via a ligand-to-metal charge transfer (LMCT) process facilitates the activation of gaseous hydrocarbon in a mild and atom-economical mode.

Fig. 1. Background and introduction of C1-C3 gaseous alkanes carbonylation.

a Application examples of CO in industrial synthesis. b General strategies for the synthesis of short-chain carboxylic acid derivatives by carbonylation. c Distribution of C1-C3 gaseous alkanes in natural gas. d Bond dissociation energy (BDE) of various gaseous alkanes. e The low solubility and competition of gaseous starting materials in organic solvents. f A net oxidative process in photoinduced ligand-to-metal charge of CuCl₂. g This work, a copper-catalyzed C1-C3 gaseous alkanes carbonylation via photoinduced ligand-to-metal charge transfer. MMA, methyl methacrylate, production volume not yet announced.

Fig. 2. Exploration of reaction conditions.

a Optimization of the reaction conditions with ethane and substrate 2a under blue light irradiation in the presence of CO, (b) Investigating the effect of catalyst loading on yield and TON, (c) Proposed mechanisms. ^a Ethane (1 bar), 2a (0.2 mmol), CuCl₂ (5 mol%), ^tBuCOCl (1.5 equiv.), TBACl (10 mol%), MeCN (0.1 M), CO (49 bar), 40 W blue LEDs, r.t., 20 h. ^b Ethane (20 bar), CO (40 bar). TON turnover numbers, TBACl tetrabutyl ammonium chloride, PBC 4-bromobenzoyl chloride.

Fig. 3. Evaluating the reaction scope.^a

^a General reaction conditions: 1 (1 bar), 2a (0.2 mmol), CuCl₂ (5 mol%), ^tBuCOCl (1.5 equiv.), TBACl (10 mol%), MeCN (0.1 M) at r.t. for 20 h under CO (49 bar), irradiated by 40 W blue LEDs. ^b CuCl₂ (10 mol%), ethane (10 bar). CO (50 bar). ^c 0.1 mmol scale, CuCl₂ (10 mol%), methane (30 bar), CO (40 bar), MeCN (0.05 M). The regioisomeric ratios (r.r.) were determined by ¹H NMR analysis. All yields are isolated yields.

Fig. 4. Synthetic applications and Mechanistic studies.

a 1 mmol scale-up reaction. b Cu-catalyzed carbonylation of ethane with DEAD. c Synthetic methyl methacrylate (MMA). d Capture of chlorine radical species. e Key intermediates of this carbonylation. f S-(p-tolyl) benzenesulfonothioate experiment. ^a 1 mmol Scale-up carbonylation. ^b Added KOH (1 equiv.), MeOH (10 equiv.), r.t., 4 h.