Amino-Modified Polymer Immobilized Ionic Liquid Stabilized Ruthenium Nanoparticles: Efficient and Selective Catalysts for the Partial and Complete Reduction of Quinolines

RuNPs stabilised by amino-decorated imidazolium-based polymer immobilized ionic liquids catalyse the dimethylamine borane mediated reduction of quinolines to 1,2-dihydroquinoline (DHQ) and 1,2,3,4-tetrahydroquinoline (THQ). Partial reduction of 3-substituted quinolines to the corresponding 1,2-dihydroquinoline was achieved with 100 % selectivity in toluene under mild conditions. This is the first report of the selective partial reduction of 3-substituted quinolines to the corresponding 1,2-dihydroquinolines with a heterogeneous nanoparticle-based catalyst. A wide range of substituted quinolines have also been reduced to the corresponding 1,2,3,4-tetrahydroquinoline with high selectivity and good yields by adjusting the reaction time. The 1,2-dihydroquinolines readily release dihydrogen in toluene at 60 °C in the absence of catalyst with no evidence for disproportionation and as such are potential organo-hydride reagents. The initial TOF of 610 mol quinoline converted mol Ru−1 h−1 for the reduction of quinoline is among the highest to be reported for a metal nanoparticle-based catalyst and the conversion of 96 % obtained after 4 h at 65 °C is significantly higher than its platinum nanoparticle counterpart PtNP@NH2-PEGPIILS as well as 5 wt/% Ru/C, which only reached 9 % and 11 % conversion, respectively, at the same time. Hot filtration experiments showed that the active species was heterogeneous.