4 MNP Catalysis in Ionic Liquids
123
14–16). NPs stabilised by BIHB.NTf 2 , with a C 7 alkyl chain separating the imidazolium functionality from the pyridine backbone, were considerably more active than
the bipy-stabilised system (with increases in conversion of as much as 68% being
observed), whereas NPs protected by the BIHB.NTf 2 stabiliser with one CH 2 group
between the imidazolium and the pyridine resulted in the lowest activity.
A reduction in the aromatic character of arenes is an important field in industrial
hydrogenation processes. The chemoselective hydrogenation of aromatic compounds
(aromatic ketones, aromatic aldehydes, quinolines, etc.) by Ru NPs in BMIm.BF 4
IL improved the catalytic performance: acetophenone could be hydrogenated to 1phenylethanol with 77% conversion and 99% chemoselectivity. It was essential to use
1-butyl-2,3-dimethylimidazolium hydroxide (BMMIm.OH) IL as a base to improve
the catalytic performance. Konnerth and Prechtl developed a low-cost system using
Ru NPs stabilised by EGMMIm.NTf 2 as catalyst. The best performance was achieved
in the hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline (THQ) with up to
99% selectivity [82].
Metal NPs prepared in nitrile-functionalised ILs have been tested as catalysts in
the hydrogenation of alkynes, and they showed excellent potential for the production
of alkenes. A catalyst system formed by Ni NPs in C 3 CNMMIm.NTf 2 achieved high
selectivity in the hydrogenation of diphenylacetylene to the alkene using the very mild
reaction conditions of 30 °C and 1 bar H 2 . Also, Pd NPs in C 3 CNMIm.NTf 2 presented
similar results. The nitrile group is crucial for the alkene selectivity. Moreover, coordination on the nanoparticle surface involving the nitrile group is suggested. In both
Ni and Pd systems, the methods employed are applicable to internal aliphatic alkynes
as well as to terminal phenylalkynes (Table 4.3, entries 21–24) [83]. Furthermore,
the catalysts are recyclable with stable conversion rates and selectivity for at least
four runs. Interestingly, there is a noticeable difference between the two systems:
the application of higher hydrogen pressure (4 bar) does not affect the selectivity
reached by Ni NPs in C 3 CNMMIm.NTf 2 , while Pd NPs in C 3 CNMIm.NTf 2 tended
towards the formation of alkanes.
ILs, especially imidazolium-based ones, have also been used as solvents for
liquid–liquid biphasic catalysis of hydroformylation. Organometallic Rh complexes
have frequently been used, and their activity depends strongly on the structure
of the ILs used. Rh NPs were investigated for the hydroformylation of 1-octene
in thermoregulated IL/organic biphasic systems composed of [CH 3 (OCH 2 CH 2 ) 16
N
+ Et 3 ][CH 3 SO 3
− ] (IL PEG750 ) IL, producing aldehyde yields above 85% at 99%
conversion [85]. The use of PEG-functionalised ILs and different organic solvents
enabled the separation of the catalysts from the products for reuse. This IL revealed
unique solubility in organic solvent depending on the temperature. It is immiscible with the toluene/n-heptane mixture at room temperature but becomes homogeneous when the temperature is increased to a certain point. Consequently, the
reaction proceeds in a virtually homogeneous system under heating, and upon
cooling to room temperature separates into a biphasic system composed of an IL
phase containing the Rh catalyst and an organic phase containing the products. This
NEtPEG.CH 3 SO 3 /toluene catalytic system also showed efficiency with other olefins
(cyclohexene and styrene). Wang reported on small-sized Rh NPs (2.4 ± 0.3 nm) in
123
14–16). NPs stabilised by BIHB.NTf 2 , with a C 7 alkyl chain separating the imidazolium functionality from the pyridine backbone, were considerably more active than
the bipy-stabilised system (with increases in conversion of as much as 68% being
observed), whereas NPs protected by the BIHB.NTf 2 stabiliser with one CH 2 group
between the imidazolium and the pyridine resulted in the lowest activity.
A reduction in the aromatic character of arenes is an important field in industrial
hydrogenation processes. The chemoselective hydrogenation of aromatic compounds
(aromatic ketones, aromatic aldehydes, quinolines, etc.) by Ru NPs in BMIm.BF 4
IL improved the catalytic performance: acetophenone could be hydrogenated to 1phenylethanol with 77% conversion and 99% chemoselectivity. It was essential to use
1-butyl-2,3-dimethylimidazolium hydroxide (BMMIm.OH) IL as a base to improve
the catalytic performance. Konnerth and Prechtl developed a low-cost system using
Ru NPs stabilised by EGMMIm.NTf 2 as catalyst. The best performance was achieved
in the hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline (THQ) with up to
99% selectivity [82].
Metal NPs prepared in nitrile-functionalised ILs have been tested as catalysts in
the hydrogenation of alkynes, and they showed excellent potential for the production
of alkenes. A catalyst system formed by Ni NPs in C 3 CNMMIm.NTf 2 achieved high
selectivity in the hydrogenation of diphenylacetylene to the alkene using the very mild
reaction conditions of 30 °C and 1 bar H 2 . Also, Pd NPs in C 3 CNMIm.NTf 2 presented
similar results. The nitrile group is crucial for the alkene selectivity. Moreover, coordination on the nanoparticle surface involving the nitrile group is suggested. In both
Ni and Pd systems, the methods employed are applicable to internal aliphatic alkynes
as well as to terminal phenylalkynes (Table 4.3, entries 21–24) [83]. Furthermore,
the catalysts are recyclable with stable conversion rates and selectivity for at least
four runs. Interestingly, there is a noticeable difference between the two systems:
the application of higher hydrogen pressure (4 bar) does not affect the selectivity
reached by Ni NPs in C 3 CNMMIm.NTf 2 , while Pd NPs in C 3 CNMIm.NTf 2 tended
towards the formation of alkanes.
ILs, especially imidazolium-based ones, have also been used as solvents for
liquid–liquid biphasic catalysis of hydroformylation. Organometallic Rh complexes
have frequently been used, and their activity depends strongly on the structure
of the ILs used. Rh NPs were investigated for the hydroformylation of 1-octene
in thermoregulated IL/organic biphasic systems composed of [CH 3 (OCH 2 CH 2 ) 16
N
+ Et 3 ][CH 3 SO 3
− ] (IL PEG750 ) IL, producing aldehyde yields above 85% at 99%
conversion [85]. The use of PEG-functionalised ILs and different organic solvents
enabled the separation of the catalysts from the products for reuse. This IL revealed
unique solubility in organic solvent depending on the temperature. It is immiscible with the toluene/n-heptane mixture at room temperature but becomes homogeneous when the temperature is increased to a certain point. Consequently, the
reaction proceeds in a virtually homogeneous system under heating, and upon
cooling to room temperature separates into a biphasic system composed of an IL
phase containing the Rh catalyst and an organic phase containing the products. This
NEtPEG.CH 3 SO 3 /toluene catalytic system also showed efficiency with other olefins
(cyclohexene and styrene). Wang reported on small-sized Rh NPs (2.4 ± 0.3 nm) in