the aldehydes, giving high selectivities towards the unsaturated alcohol. However,
preference for the C¼C bond adsorption would occur when the substrate is a ketone.
It was proposed that ligands bound to the NP surface constrain the surface site
geometries which only allow certain adsorption models.
As commented above, there are also several examples on hydrogenation by Ir
NP-based catalytic systems in which the ligand only acts as a stabilising agent.
Table 3 Catalytic hydrogenation of substituted aldehydes by SPO-stabilised Ir NPs
Substrate
Product
P (bar) Conv. (%) Sel. (%) TOF (h
À1
)
10
99
99
22
20
>99
95
22
40
>99
>99
11
O
OH 40
80
96
18
Reaction conditions: Substrate/Ir ¼ 400, Ir NPs (0.0025 mmol Ir), THF (0.75 mL), RT. 18 h
Table 4 Hydrogenation of α,β-unsaturated carbonyl compounds mediated by Ir NPs stabilised by
Ph 2 P(CH 2 CH 2 O) 22 CH 3
Substrate
Product
Time (h)
Conv. (%)
Selec. (%)
a
3
9 6
>99
7
9 0
>99
7
7 2
9 8
3
>99
96
3.5
>99
94
9
9 8
>99
2.5
76
90
3.5
>99
>99
4
>99
>99
1
>99
>99
Reaction conditions: Substrate/Ir ¼ 100, 1-pentanol (4 mL), H 2 O (4 mL) containing 0.0067 mmol Ir
NPs. 10 bar H 2 , 70
C
a The remainder is the saturated alcohol
Iridium Nanoparticles for Hydrogenation Reactions
403