Catalytic Properties of Mechanochemically Exfoliated MoS2 in the Hydrogenation of Bromoquinolines

This study aimed to develop new catalysts, based on MoS2, for the hydrogenation of bromoquinolines without C-Br bond cleavage. The mechanochemical exfoliation of the bulk MoS2 in the presence of NaCl resulted in the formation of the material (MoS2-1), consisting of flat plates of size between ca. 40 × 100 and ca. 250 × 400 nm2. Similar grinding of MoS2 in the presence of NH4Cl produced smaller nanoplates of size between ca. 10 × 30 and ca. 50 × 300 nm2 (MoS2-2). These materials were characterized using powder XRD, TEM, SEM, Raman spectroscopy and XPS. The specific surface area of the MoS2-1 and MoS2-2 samples was estimated using the analysis of N2 adsorption isotherms. Both materials were catalytically active in the hydrogenation of quinoline; 1,2,3,4-tetrahydroquinoline (THQ) was the sole product and its yield grew proportionally to the accessible surface area of the catalyst. The hydrogenation of 5- and 8-bromoquinolines in the presence of MoS2-1 and MoS2-2 led to the respective bromo-THQs with almost quantitative yields, while the hydrogenation of 6-bromoquinoline resulted in the formation of the respective 6-bromo-THQ with the yield up to 30%. In the case of 7-bromoquinoline, N-methylated 7-bromo-THQ was formed almost quantitatively.