Search

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO2 to formate; the initial TOF of 500 h−1 is markedly higher than either unmodified catalyst or its benzylamine and N,N-dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles stabilized by imidazolium‐based phosphine‐decorated Polymer Immobilized Ionic Liquids (PPh2‐PIIL) catalyze the hydrolytic evolution of hydrogen from sodium borohydride with remarkable efficiency, under mild conditions. The composition of the polymer influences efficiency with the catalyst based on a polyethylene glycol modified imidazolium monomer (PtNP@PPh2‐PEGPIILS) more active than its N‐alkylated counterpart (PtNP@PPh2‐N‐decylPIILS). The maximum initial TOF of 169 moleH2.molcat−1.min−1 obtained at 30 °C with a catalyst loading of 0.08 mol% is among the highest to be reported for the aqueous phase hydrolysis of sodium borohydride catalyzed by a PtNP‐based system. Kinetic studies revealed that the apparent activation energy (Ea) of 23.9 kJ mol−1 for the hydrolysis of NaBH4 catalyzed by PtNP@PPh2‐PEGPIILS is significantly lower than that of 35.6 kJ mol−1 for PtNP@PPh2‐N‐decylPIILS. Primary kinetic isotope effects kH/kD of 1.8 and 2.1 obtained with PtNP@PPh2‐PEGPIILS and PtNP@PPh2‐N‐decylPIILS, respectively, for the hydrolysis with D2O support a mechanism involving rate determining oxidative addition or σ‐bond metathesis of the O−H bond. Catalyst stability and reuse studies showed that PtNP@PPh2‐PEGPIILS retained 70 % of its activity across five runs; the gradual drop in conversion appears to be due to poisoning of the catalyst by the accumulated metaborate product as well as the increased viscosity of the reaction mixture. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrafine RuNPs stabilised by a phosphine oxide-modified polymer immobilized ionic liquid. • Complete selectivity for the partial reduction of aromatic and heteroaromatic nitroarenes to the corresponding N -arylhydroxylamine. • Highest initial turn over frequency to be reported for a RuNP catalysed partial reduction of nitrobenzene to N -phenylhydroxylamine. • Reduction of electron rich amino nitroarenes to the aniline proposed to occur via a quinondiimine-derived iminium. • High activity and selectivity retained over five reuses with only a minor reduction in conversion. RuNPs stabilised by a polymer immobilised ionic liquid derived from co-polymerisation of a PEG-substituted imidazolium-based styrene monomer and diphenyl(4-vinylphenyl)phosphine oxide, RuNP@O = PPh 2 -PEGPIILS, (2) is a remarkably efficient and selective catalyst for the hydrazine hydrate-mediated partial reduction of nitroarenes to the corresponding N -arylhydoxylamine. Near quantitative conversion to N -phenylhydroxylamine with > 99 % selectivity was obtained after only 2 h when the reaction was conducted at 25 °C in ethanol under an inert atmosphere using 0.1 mol% catalyst. Under these conditions, the composition-time profile showed that the reduction occurred via the direct pathway whereas reactions in air gave a mixture of azoxy-based products due to competing condensation resulting from reversible formation of N -phenylhydroxylamine. The initial TOF of 6,100 h−1 obtained after 10 min at 40 °C with 0.1 mol% 2 is among the highest to be reported for the metal nanoparticle catalysed reduction of nitrobenzene to N -phenylhydroxylamine and a significant improvement on 5 wt% Ru/C which gave a modest conversion of 21 % (initial TOF = 240 h−1) to a mixture of N -phenylhydroxylamine and aniline. A broad range of substituted N -aryl and N -heteroaryl nitroarenes were reduced to the corresponding N -arylhydroxylamine in high yield and with excellent selectivity by adjusting the reaction times. However, reduction of electron rich amino-substituted nitroarenes was extremely slow and resulted in reduction to the aniline with no evidence for the corresponding hydroxylamine. Complete reduction of amino substituted nitroarene is proposed to be facilitated by amine-assisted elimination of hydroxide from the hydroxylamine to afford a readily reducible quinondiimine-derived iminium intermediate that reacts with a surface hydride to liberate the amine. Under optimum conditions the catalyst could be reused five times for the reduction of nitrobenzene to N -phenylhydroxylamine with no detectable change in activity and only slight decrease in selectivity. [ABSTRACT FROM AUTHOR]