398
I. Cano and P. W. N. M. van Leeuwen
them more electron-deficient and thus activates the carbonyl functionality. However,
the mechanism of action of alloyed MNPs may be different, such as a cooperation
between an electron-deficient and an electron-rich metal, or a synergistic effect in
which one metal serves for the generation of hydrogen species (for example, through
a spillover mechanism) and the other metal activates the C=O group or acts as active
hydrogen acceptor. As regards solvents, many authors have reported increased allyl
alcohol selectivity for protic solvents, but there are notable exceptions; when the
catalyst has a strong intrinsic preference for heterolytic transfer, the solvent is less
important.
In addition, a steric impediment can avoid the reduction of the internal C=C bond,
thus favouring the selective hydrogenation of the C=O functionality. This effect can
be achieved in different ways: bulky groups in the vicinity of the C=C bond, flat metal
surfaces, steric repulsion between large nanoparticles and aromatic substituents on
the substrate, etc. Finally, it is worth noting the use of additives and ligands that
promote the heterolytic cleavage of H 2 through a cooperative effect with the metal,
and thus lead to the selective reduction of the polar C=O group. This successful
approach has allowed to obtain very high selectivities towards the unsaturated alcohol
product, either with supported and unsupported MNPs.
In summary, important developments in the partial hydrogenation of unsaturated aldehydes and ketones mediated by metallic nanoparticles have been recently
described. However, new approaches and strategies are required to make this process
worthwhile from an industrial point of view. Due to the increasing number of
researchers working in the area of MNP catalysis, there is no doubt that new and
exciting advances in this transformation will appear in the near future.
References
1. Cao XM, Burch R, Hardacre C, Hu P (2011) Reaction mechanisms of crotonaldehyde hydrogenation on Pt(111): density functional theory and microkinetic modeling. J Phys Chem C
115:19819–19827
2. Leffingwell JC, Leffingwell D (2011) Chiral chemistry in flavours & fragrances. Speciality
Chem Mag March 2011:30–33. http://www.leffingwell.com/menthol13/menthol_basf.htm.
Accessed 3 May 2019
3. Gallezot P, Richard D (1998) Selective hydrogenation of α,β-unsaturated aldehydes. Catal
Rev Sci Engin 40:81–126
4. Rylander PN, Steele DR (1968) Hydrogenation of unsaturated aldehydes to unsaturated
alcohols. US Patent 3,655,777 to Engelhard Minerals and Chemicals Corp. April 11, 1972
5. Mitsumode T, Kaneda K (2013) Gold nanoparticle catalysts for selective hydrogenations.
Green Chem 15:2636–2654
6. Mertens PGN, Poelman H, Ye X, Vankelecom IFJ, Jacobs PA, De Vos DE (2007) Au0 nanocolloids as recyclable quasihomogeneous metal catalysts in the chemoselective hydrogenation
of α,β-unsaturated aldehydes and ketones to allylic alcohols. Catal Today 122:352–360
7. Mertens PGN, Vandezande P, Ye X, Poelman H, Vankelecom IFJ, De Vos DE (2009)
Recyclable Au0, Ag0 and Au0–Ag0 nanocolloids for the chemoselective hydrogenation of
α,β-unsaturated aldehydes and ketones to allylic alcohols. Appl Catal A 355:176–183
I. Cano and P. W. N. M. van Leeuwen
them more electron-deficient and thus activates the carbonyl functionality. However,
the mechanism of action of alloyed MNPs may be different, such as a cooperation
between an electron-deficient and an electron-rich metal, or a synergistic effect in
which one metal serves for the generation of hydrogen species (for example, through
a spillover mechanism) and the other metal activates the C=O group or acts as active
hydrogen acceptor. As regards solvents, many authors have reported increased allyl
alcohol selectivity for protic solvents, but there are notable exceptions; when the
catalyst has a strong intrinsic preference for heterolytic transfer, the solvent is less
important.
In addition, a steric impediment can avoid the reduction of the internal C=C bond,
thus favouring the selective hydrogenation of the C=O functionality. This effect can
be achieved in different ways: bulky groups in the vicinity of the C=C bond, flat metal
surfaces, steric repulsion between large nanoparticles and aromatic substituents on
the substrate, etc. Finally, it is worth noting the use of additives and ligands that
promote the heterolytic cleavage of H 2 through a cooperative effect with the metal,
and thus lead to the selective reduction of the polar C=O group. This successful
approach has allowed to obtain very high selectivities towards the unsaturated alcohol
product, either with supported and unsupported MNPs.
In summary, important developments in the partial hydrogenation of unsaturated aldehydes and ketones mediated by metallic nanoparticles have been recently
described. However, new approaches and strategies are required to make this process
worthwhile from an industrial point of view. Due to the increasing number of
researchers working in the area of MNP catalysis, there is no doubt that new and
exciting advances in this transformation will appear in the near future.
References
1. Cao XM, Burch R, Hardacre C, Hu P (2011) Reaction mechanisms of crotonaldehyde hydrogenation on Pt(111): density functional theory and microkinetic modeling. J Phys Chem C
115:19819–19827
2. Leffingwell JC, Leffingwell D (2011) Chiral chemistry in flavours & fragrances. Speciality
Chem Mag March 2011:30–33. http://www.leffingwell.com/menthol13/menthol_basf.htm.
Accessed 3 May 2019
3. Gallezot P, Richard D (1998) Selective hydrogenation of α,β-unsaturated aldehydes. Catal
Rev Sci Engin 40:81–126
4. Rylander PN, Steele DR (1968) Hydrogenation of unsaturated aldehydes to unsaturated
alcohols. US Patent 3,655,777 to Engelhard Minerals and Chemicals Corp. April 11, 1972
5. Mitsumode T, Kaneda K (2013) Gold nanoparticle catalysts for selective hydrogenations.
Green Chem 15:2636–2654
6. Mertens PGN, Poelman H, Ye X, Vankelecom IFJ, Jacobs PA, De Vos DE (2007) Au0 nanocolloids as recyclable quasihomogeneous metal catalysts in the chemoselective hydrogenation
of α,β-unsaturated aldehydes and ketones to allylic alcohols. Catal Today 122:352–360
7. Mertens PGN, Vandezande P, Ye X, Poelman H, Vankelecom IFJ, De Vos DE (2009)
Recyclable Au0, Ag0 and Au0–Ag0 nanocolloids for the chemoselective hydrogenation of
α,β-unsaturated aldehydes and ketones to allylic alcohols. Appl Catal A 355:176–183