found to be a highly active hydrogenation catalyst for a wide range of alkenes
(Table 15), where the steric hindrance on the C¼C bond seems to play an important
role. In addition, the catalyst was recovered via filtration and reused up to seven
cycles without any significant loss in the activity.
5 Hydrogenation Reactions Catalysed by Iridium
Nanoparticles Generated In Situ Without Stabilising
Agent
There are several examples of hydrogenation by Ir NPs generated and stabilised in
situ with the available species (solvents, precursor components, etc.) that do not
require an extra stabilising agent. The majority of these works were carried out by
Finke’s research group, which has extensively studied the formation mechanism of
Ir NPs and their applications in hydrogenation catalysis. This group reported the
formation of Ir(0) NPs (1.8 nm) by H 2 reduction of [Ir(cod)Cl] 2 in acetone as solvent
(2.76 bar H 2 , 22
C; Scheme 7a) [82]. The reaction proceeds with the concomitant
hydrogenation of acetone to isopropanol with 95% selectivity (TON ¼ 16,400,
initial TOF ¼ 1.9 s
À1 ), the remainder being diisopropyl ether (Scheme 7b). Interestingly, the addition of molecular sieves increased the selectivity up to 100%
Table 15 Hydrogenation of alkenes mediated by Ir nanosponges
Substrate
Product
Time (h)
TOF (h
À1
)
Styrene
Ethylbenzene
4
500
4-Chlorostyrene
4-Chloro ethylbenzene
4
500
4-Methylstyrene
4-methyl ethylbenzene
4
500
1-Hexene
Hexane
4
500
1-Octene
Octane
5
400
1-Hexadecene
Hexadecane
6
333
1-Octadecene
Octadecene
6
333
Cyclohexene
Cyclohexane
4
500
Cyclooctene
Cyclooctane
5
400
1,5-Cyclooctadiene
Cyclooctane
9
222
Ethyl acrylate
Ethyl propionate
3.5
571
t-butyl acrylate
t-butyl propionate
4
500
Methyl methacrylate
Methyl-2-methyl propionate
3.75
533
Cyclohexenone
Cyclohexanone + cyclohexanol (89:11)
3.83
522
4-Vinylcyclohexene
Ethyl cyclohexane
9
222
R-limonene
p-Menth-2-ene
a
4.5
444
R-limonene
p-Menth-2-ene
b
0.5
4,000
Reaction conditions: substrate/Ir ¼ 2,000, substrate (20 mmol), CH 2 Cl 2 , H 2 (4 bar), 30
C
a Substrate/Ir ¼ 1,000
b
Substrate/Ir ¼ 1,000, 75
C, n-heptane
414
L. M. Martínez-Prieto et al.
(Table 15), where the steric hindrance on the C¼C bond seems to play an important
role. In addition, the catalyst was recovered via filtration and reused up to seven
cycles without any significant loss in the activity.
5 Hydrogenation Reactions Catalysed by Iridium
Nanoparticles Generated In Situ Without Stabilising
Agent
There are several examples of hydrogenation by Ir NPs generated and stabilised in
situ with the available species (solvents, precursor components, etc.) that do not
require an extra stabilising agent. The majority of these works were carried out by
Finke’s research group, which has extensively studied the formation mechanism of
Ir NPs and their applications in hydrogenation catalysis. This group reported the
formation of Ir(0) NPs (1.8 nm) by H 2 reduction of [Ir(cod)Cl] 2 in acetone as solvent
(2.76 bar H 2 , 22
C; Scheme 7a) [82]. The reaction proceeds with the concomitant
hydrogenation of acetone to isopropanol with 95% selectivity (TON ¼ 16,400,
initial TOF ¼ 1.9 s
À1 ), the remainder being diisopropyl ether (Scheme 7b). Interestingly, the addition of molecular sieves increased the selectivity up to 100%
Table 15 Hydrogenation of alkenes mediated by Ir nanosponges
Substrate
Product
Time (h)
TOF (h
À1
)
Styrene
Ethylbenzene
4
500
4-Chlorostyrene
4-Chloro ethylbenzene
4
500
4-Methylstyrene
4-methyl ethylbenzene
4
500
1-Hexene
Hexane
4
500
1-Octene
Octane
5
400
1-Hexadecene
Hexadecane
6
333
1-Octadecene
Octadecene
6
333
Cyclohexene
Cyclohexane
4
500
Cyclooctene
Cyclooctane
5
400
1,5-Cyclooctadiene
Cyclooctane
9
222
Ethyl acrylate
Ethyl propionate
3.5
571
t-butyl acrylate
t-butyl propionate
4
500
Methyl methacrylate
Methyl-2-methyl propionate
3.75
533
Cyclohexenone
Cyclohexanone + cyclohexanol (89:11)
3.83
522
4-Vinylcyclohexene
Ethyl cyclohexane
9
222
R-limonene
p-Menth-2-ene
a
4.5
444
R-limonene
p-Menth-2-ene
b
0.5
4,000
Reaction conditions: substrate/Ir ¼ 2,000, substrate (20 mmol), CH 2 Cl 2 , H 2 (4 bar), 30
C
a Substrate/Ir ¼ 1,000
b
Substrate/Ir ¼ 1,000, 75
C, n-heptane
414
L. M. Martínez-Prieto et al.