Highly efficient sulfurized Re–Ir catalysts for multiple N-methylation of ethylenediamine and its homologous series with CO2 and H2 in water solvent

Abstract

Sulfurized Re–Ir clusters on a carbon black support were demonstrated to be highly active catalysts for the quadruple N-methylation of ethylenediamine (EDA) with CO₂ and H₂ to yield N,N,N′,N′-tetramethylethylenediamine (TetraM-EDA). The catalytic activity of this catalyst was 6.4-fold higher than that of the previously reported sulfurized Re catalyst. This bimetallic catalyst was applicable to the multiple N-methylation of various diamines that consisted of C2/C3 units sandwiched between two amino groups, and their strong interaction arising from the chelating effect played a key role in the progress of N-methylation over the catalyst, as indicated by the kinetic study. Furthermore, the sulfurized Re–Ir species were mandatory for the N-methylation of EDA (namely, the hydrogenation step of N-formylated intermediates into N-methylated EDAs), and a lack of sulfurized species resulted in the formation of N-formylated compounds as major products instead of N-methylated ones. Detailed characterization suggested that the role of Ir species was to substantially reduce Re species. These functions offered not only high catalytic activity but also stability against air, the latter of which contributed to the suppression of oxidation and leaching of Re species after catalyst exposure to air.