Quadruple <i>N</i>‐Methylation of Ethylenediamine with CO₂ and H₂ over Supported Sulfurized Re Catalysts

Abstract Sulfurized Re clusters supported on carbon black were demonstrated to exhibit high catalytic activity and stability in the quadruple N ‐methylation of ethylenediamine (EDA) using CO 2 and H 2 as a C1 source and reductant, respectively. EDA underwent the step‐by‐step N ‐functionalization consisting of N ‐formylation and N ‐methylation to be the target product N , N , N ′, N ′‐tetramethylethylenediamine (TetraM‐EDA), whose maximum yield reached 84% under the optimum conditions. In this reaction, N , N ′‐dimethylethylenediamine and its N ‐formylated compounds were found as the important intermediates. The ReS x species in the clusters consisting of both metallic and sulfurized Re were assumed from various characterizations and control experiments to exhibit the better activity for the hydrogenation of N ‐formylated compounds than the clusters composed of metallic and oxidized Re species, enabling the high‐yielding production of TetraM‐EDA. Another plausible role of sulfurized Re species was assumed to offer high resistance against highly basic N ‐methylated EDAs in this reaction. The synergy between metallic and sulfurized Re species is the key to the high activity for the quadruple N ‐methylation of EDA.