Room Temperature Electroreductive Carboxylation of Unactivated Alkyl Chlorides with CO2 Using a Ni(II) NNN-Pincer Complex. Towards Polyvinyl chloride (PVC) Upgrading

In organic synthesis, direct carboxylation of organohalides with carbon dioxide is a highly desirable transformation because it uses feedstock chemicals and produces carboxylic acids, which are among the most widely used classes of organic compounds. Alkyl carboxylic acids are favored motifs in many medicines and physiologically active substances. Carbon dioxide (CO2) is an ideal C1 source for organic synthesis because of its high abundance, low cost, nontoxicity, and recyclability. This article describes a nickel-catalyzed electrochemical method for producing alkyl carboxylic acids via carboxylation of unactivated alkyl chlorides with CO2. The development of a Ni pincer complex (complex 1) with a redox-active ligand as an electrocatalyst to convert unactivated alkyl chlorides to the corresponding acids over less desirable homocoupling products is presented. Electronic structure calculations revealed that CO2 binding occurs in a resting state to yield an 2-CO2 adduct and that the C-Cl bond activation step is the TOF-determining transition state, which has an activation energy of 19.3 kcal/mol. A combination of electroanalytical methods, control experiments, and computational studies revealed the mechanism of the electrocarboxylation reaction. In addition, complex 1 has been demonstrated as an efficient catalyst to upgrade polyvinyl chloride to polyacrylate in 95% yield.