Efficient and selective solvent-free homogeneous hydrogenation of aldehydes under mild reaction conditions using [RuCl2(dppb)(ampy)]

Article abstract of DOI:10.1016/j.tetlet.2020.151677

The efficient, solvent-free homogeneous hydrogenation of aldehydes has been accomplished using the catalysts [RuCl₂(dppb)(ampy)] and [RuCl₂(dppf)(ampy)], providing high conversion to the corresponding alcohols at molar catalyst loadings of 10,000/1–50,000/1. A solvent-free protocol has been developed, allowing aldehydes to be efficiently reduced avoiding by-product formation and with minimal waste generation.[Formula presented]

Full text of DOI:10.1016/j.tetlet.2020.151677

Journal Pre-proofs
Efficient and Selective Solvent-free Homogeneous Hydrogenation of Alde-
hydes under Mild Reaction Conditions using [RuCl2(dppb)(ampy)]
Antonio Zanotti-Gerosa, Tommaso Angelini, Stephen Roseblade
PII:
S0040-4039(20)30096-4
DOI:
https://doi.org/10.1016/j.tetlet.2020.151677
TETL 151677
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
27 November 2019
14 January 2020
24 January 2020
Please cite this article as: Zanotti-Gerosa, A., Angelini, T., Roseblade, S., Efficient and Selective Solvent-free
Homogeneous Hydrogenation of Aldehydes under Mild Reaction Conditions using [RuCl2(dppb)(ampy)],
Tetrahedron Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.151677
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Efficient and Selective Solvent-free Homogeneous Hydrogenation of
Aldehydes under Mild Reaction Conditions using [RuCl2(dppb)(ampy)]
Antonio Zanotti-Gerosa, Tommaso Angelini and Stephen Rosebladea
a Johnson Matthey, 28 Cambridge Science Park, Milton Road, Cambridge, CB4 0FP
Abstract
The efficient, solvent-free homogeneous hydrogenation of aldehydes has been accomplished using
the catalysts [RuCl2(dppb)(ampy)] and [RuCl2(dppf)(ampy)], providing high conversion to the
corresponding alcohols at molar catalyst loadings of 10,000/1 – 50,000/1. A solvent-free protocol
has been developed, allowing aldehydes to be efficiently reduced avoiding by-product formation
and with minimal waste generation.
Keywords: Homogeneous hydrogenation; aldehydes; carbonyl reduction;
solvent-free reactions; industrial chemistry
The reduction of carbonyl compounds to alcohols is an important transformation for
industrial processes1 and primary alcohols, accessible either by reduction of the corresponding esters
or aldehydes, are important targets. Large scale batch reductions are still often performed using
stoichiometric reducing agents such as hydrides due to their speed of development and well-
understood protocols. However, catalytic hydrogenation provides a cost-effective alternative that
simplifies reaction processes and reduces the amount of waste generated. While heterogeneous
hydrogenation catalysts offer the advantage of recyclability of the catalyst, they often lack the
selectivity required for use on complex, polyfunctionalised molecules. Homogeneous hydrogenation
catalysts have been used for decades in industry in a variety of enantioselective reductions but
applications to the reduction of non-prochiral substrates such as aldehydes have been scarce.
Achiral reductions are much more sensitive to catalyst cost contribution and, to meet
economic targets, a clean, fast, selective reduction is required at very low catalyst loadings.2 We
have recently highlighted how the use of a tridentate phosphine can provide very high turnover
numbers.3 Noyori-type catalysts, with their ‘outer sphere’ reaction mechanism, brought a step
Page 1 of 13

change in the catalytic reduction of carbonyl groups.4 Their application to the reduction of aldehydes
has been limited, however, by the requirement for basic conditions: the use of base to activate the
catalyst can promote side reactions, such as aldol condensation, Cannizzaro reaction and Claisen-
Tishchenko reaction and although the reduction of aldehydes is thermodynamically favourable, it is
a challenging process since aldehydes are prone to oxidation or decomposition and the use of
commercial grade reagents often requires purification by distillation. During the hydrogenation
process, several by-products can be formed, such as acetals, ethers, esters and acids, due to the
interaction between the reactive substrate and the other components of the reaction.
Using Noyori-type catalysts in a way that retain high activity while avoiding base-catalysed
side reactions is
a
non-trivial problem. Researchers at Firmenich have designed
[(diphosphine)Ru(carboxylate)2(diamine)] catalysts that not only work under neutral conditions but
also show selectivity for aldehydes versus ketones.5 We have been for some time involved in the
search for adequate reaction conditions for the use of [(diphosphine) RuCl2 (ampy)] ‘Baratta-type’
catalysts in the reduction of aldehydes. Some examples of aldehyde reduction with high TON and
TOF were presented in Baratta’s original papers with hydrogen transfer in iso-propanol/base.6, 7 We
were interested in finding conditions that worked on non-distilled, commercial grade aldehydes and
with minimal requirement for anhydrous conditions. This work has led to the development of
suitable hydrogenation conditions in the presence of potassium carbonate8 as well as biphasic
transfer hydrogenation in the presence of ammonium formate9. In both cases, but especially in the
latter, it was found that the more robust pincer ‘second generation’ catalysts of the type
[(diphosphine) RuCl (AMBQ)] (AMBQ = 2-aminomethylquinoline and their derivatives) provided
much higher performance than the original [(diphosphine) RuCl2 (ampy)] catalysts.
We describe herein an alternative solution based on the observation that unmodified
[(diphosphine) RuCl2 (ampy)] catalysts (ampy = 2-aminomethyl pyridine), when used under solvent
free conditions in the presence of a small amount of aqueous base, provide clean reduction to
primary alcohols with very high activity and avoiding undesired side reactions. Solvent-free
processes are of general interest in reducing the amount of waste produced in large scale processes,
helping to lower costs, environmental impacts and improve efficiency.10
In the initial experiments, hydrogenation of laboratory grade benzaldehyde (approx. 95%
1
purity by H NMR) was examined using [RuCl2(dppb)(ampy)] as catalyst. A range of temperatures
were tested with catalyst loading of 2000/1, in combination with 1N KOH (1 mol%) as a basic
additive. MeOH was initially used as solvent at varying substrate concentrations. Temperatures of
50–90 oC were probed with a moderate hydrogen pressure of 10 bar (150 PSI) (Table 1, entries 1 -7).
Page 2 of 13

Table 1: Hydrogenation of benzaldehyde at different reaction temperatures and concentrations.
Entry Solvent T (oC)
Conversion to
benzyl alcohol
(%)
S/C = 2000/1, 10 bar H2, 1 mol % KOH
1
2
3
4
5
6
7
MeOH
2M
MeOH
2M
MeOH
2M
MeOH
5M
MeOH
5M
MeOH
5M
50
70
90
50
70
90
90
3
14
93
3
19
86
>99
SolFC
S/C = 10,000/1, 20 bar H2, 0.1 mol % KOH
8
SolFC
SolFC
SolFC
100
110
120
>99
>99
>99
9
10
Experimental procedure: In a glass reaction vial was weighed catalyst [RuCl2(dppb)(ampy)] (S/C =
2000/1 or 10000/1) and benzaldehyde (8 – 40 mmol), followed by solvent (1 – 3 mL) if required and
a 1N solution of KOH (0.1-1 mol%). The vial was transferred to a Biotage Endeavour, purged with N2
and H2 and heated to 50 – 90 oC under 10 - 20 bar (150 - 300 PSI) H2 for 16 hours. The reactions were
cooled, vented and analysed by GC and/or 1H NMR spectroscopy.
In these experiments, low conversion was observed at temperatures of 50 and 70 °C. At 90
°C, much higher conversion was obtained and the solvent-free reaction gave complete consumption
of the benzaldehyde and >98 % benzyl alcohol by GC analysis (Entry 7). The reactions with MeOH as
solvent also contained a side-product which was assigned as the dimethoxyacetal formed from the
condensation of benzaldehyde with methanol. Reaction temperatures greater than 90 °C were
tested in the hydrogenation of benzaldehyde to understand their effect on reaction rate and product
purity. Temperatures of 90, 100, 110 and 120 °C were tested under the conditions: S/C = 10000/1,
neat, 0.1 mol% 1N KOH, 20 bar H2, 16 hours (Table 1, entries 8–10). In all of the reactions the
aldehyde was fully reduced and benzyl alcohol was formed in >98 % purity by GC analysis. There was
a strong effect of reaction temperature on rate as assessed by hydrogen uptake curves. At 120 °C
Page 3 of 13

the reaction appeared to be complete within 3 hours and at 110 °C hydrogen uptake finished after
4–5 hours, whereas at 90 °C 16 hours were needed.
In further experiments the reaction temperature of 90 °C was held constant and different
alcohol solvents were tested in the hydrogenation of benzaldehyde. A catalyst loading of S/C =
5000/1 was used under 6 bar H2 pressure with 0.2 mol% 1N KOH. The solvents MeOH, EtOH, IPA and
1-PrOH were added in 25% volume to probe their effect on the rate of benzaldehyde hydrogenation.
Table 2: Hydrogenation in different solvents.
Entry Solvent T (oC)
Conversion to
benzyl alcohol by
GC (%)
S/C = 5000/1, 6 bar H2, 0.2 mol % KOH
1
2
3
4
5
None
90
90
90
90
90
99
96
95
98
94
MeOH
7.5M
EtOH
7.5 M
2-PrOH
7.5 M
1-PrOH
7.5M
Experimental procedure: In a glass reaction vial was weighed catalyst [RuCl2(dppb)(ampy)] (S/C =
5000/1) and benzaldehyde (30 mmol), followed by solvent (1 mL) if required and a 1N solution of
KOH (0.2 mol%). The vial was transferred to a Biotage Endeavour, purged with N2 and H2 and heated
to 90 oC under 6 bar (100 PSI) H2 for 16 hours. The reactions were cooled, vented and analysed by GC
and/or 1H NMR spectroscopy.
The highest conversion to benzyl alcohol (99% by GC) was observed under solvent-free
conditions and this reaction was also found to give the highest reaction rate as observed by
hydrogen uptake curves. The reaction in which 2-PrOH was added to the reaction was the next best
giving 98% conversion. The addition of MeOH, EtOH and 1-PrOH gave lower conversions (94–96%)
and slower reaction rates. Although solvent-free conditions have been found to be very effective,
this information on solvent compatibility could be useful for synthetic applications in which a solvent
is needed to dissolve a solid substrate for example.
Next the hydrogenation of benzaldehyde was carried out under solvent-free conditions at 6-
30 bar H2 pressure with 1N KOH added in 0.1 mol% loading (90 oC, 16 hours) and a range of catalyst
Page 4 of 13

loadings were tested (Table 3). For a cost-effective process at scale the use of low catalyst loadings
would be required.
Table 3: Hydrogenation of benzaldehyde at low catalyst loadings.
H2
pressure
(bar)
6
Conversion
to benzyl
alcohol (%)
>99
Entry
Catalyst
Loading
2000/1
1
2
3
4
5
6
7
8
9
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppf)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppf)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppf)(ampy)]
5000/1
6
99
95
10000/1
10000/1
10000/1
20000/1
20000/1
40000/1
40000/1
6
20
30
30
30
30
30
>99
>99
93
>98
48
11
With pure benzaldehyde batch
10
11
12
[RuCl2(dppb)(ampy)] 20,000/1
[RuCl2(dppb)(ampy)] 30,000/1
[RuCl2(dppb)(ampy)] 40,000/1
30
30
30
>99
>99
>99
Experimental procedure: In a glass reaction vial was weighed catalyst [RuCl2(dppb)(ampy)] (1–20 mg)
and benzaldehyde (30–60 mmol, 3–6 mL), followed by a 1N solution of 1 N aqueous KOH (0.1 mol%,
30- 75 L). The vial was transferred to a Biotage Endeavour, purged with N2 and H2 and heated to 90
1
oC under H2 for 16 hours. The reactions were cooled, vented and analysed by GC and/or H NMR
spectroscopy.
At 6 bar H2 pressure, complete conversion was found at 2000/1. At 5000/1, 99% conversion
to benzyl alcohol was obtained and at 10,000/1 some of the benzaldehyde remained (96%
conversion to benzyl alcohol). At S/C = 10,000/1 high conversion to benzyl alcohol was observed
under 20 bar hydrogen pressure. When 30 bar hydrogen pressure was employed and catalyst
loadings were reduced further (S/C = 20,000/1–40,000/1) incomplete conversion to the benzyl
Page 5 of 13

alcohol resulted. A series of reactions was carried out using the catalyst [RuCl2(dppf)(ampy)] and a
similar performance was observed when compared to [RuCl2(dppb)(ampy)] (Table 3, entries 5, 7 and
9).
To examine the effect of aldehyde purity on the hydrogenation, a freshly opened batch of
benzaldehyde (ReagentPlus, >99 % purity) was hydrogenated with [RuCl2(dppb)(ampy)] at loadings
of 10,000/1 – 40,000/1. The reaction conditions were: KOH (0.1 mol% as a 1N solution), neat, 90 oC,
28 bar H2, 16 hours. Complete conversion was obtained in these reactions (Entries 10–12) showing
that the use of a freshly opened, more highly pure benzaldehyde batch gave improved performance.
Evidence from 1H NMR spectroscopy suggested that the main impurity was benzoic acid, which could
explain the difference in reaction rate if catalyst activation was affected. Experiments performed
under these conditions have also shown that the order of addition of the reagents did not affect the
reaction performance.
To investigate the effect of different bases on the hydrogenation of benzaldehyde,
[RuCl2(dppb)(ampy)] was tested at S/C = 10,000/1 under the following conditions: base (0.2 mol%),
neat, 100 oC, 20 bar H2, 16 hours. A range of potassium salts were tested as bases in the reaction.
Table 4: Benzaldehyde hydrogenation at S/C = 10,000/1 using different bases.
GC
Entry
Base
KOAc
conversion to
benzyl alcohol (%)
>99
1
2
3
4
5
6
7
8
(CH3)3CO2K
KOMe
>99
>99
>99
>99
>99
>99
>99
KOtBu
K3PO4
K2CO3
KOH (s)
KOH
(1 N aq)
Experimental procedure: In a glass vial was weighed the catalyst (approx. 1.8 mg). Solid base (0.2
mol%) was weighed out if necessary and benzaldehyde (50 mmol, 5 mL) was added. Liquid base was
added if necessary (0.2 mol%) and the vial was transferred to a Biotage Endeavour, purged with N2
o
and H2 and heated to 100 C under 20 bar H2 for 18 hours. The reaction was cooled, vented and
analysed by GC.
Page 6 of 13

Full conversion was obtained after 16 hours using all of the bases tested under these
conditions, including weak bases such as KOAc (Entry 1). Hydrogen uptake curves showed some
difference in the reaction rates with (CH3)3CO2K giving the fastest rate (complete consumption after
approximately 7 hours). When a freshly opened batch of aldehyde was used under identical
conditions, faster reaction rates were obtained: in all of the reactions hydrogen uptake had finished
1
within 3–4 hours. H NMR analysis of the reaction mixtures showed a high purity of benzyl alcohol
after sampling of the crude reaction mixtures (see ESI for spectra).
With these encouraging results in hand for the efficient solvent-free hydrogenation of
aldehydes, a variety of different aldehydes was hydrogenated. The [RuCl2(dppb)(ampy)] or
[RuCl2(dppf)(ampy)] catalyst was used under the conditions: KOH (0.2 mol% as a 1N solution), neat,
o
90-120 C, 28 bar H2, 16 hours. Hydrogen uptake was observed using the Biotage Endeavour. The
reactions were analysed by 1H NMR and GC.
Table 5: Hydrogenation of various aldehyde substrates under solvent-free conditions.
Catalyst
loading
GC
Conversion
(%)
Entry
1
Catalyst
Substrate
[RuCl2(dppb)(ampy)]
[RuCl2(dppf)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
Benzaldehyde
Benzaldehyde
10,000/1
10,000/1
10,000/1
20,000/1
20,000/1
10,000/1
5,000/1
>99
2
>99
>99
>99
95
3
p-MeO-
benzaldehyde
p-MeO-
4
benzaldehyde
5
p-F-
benzaldehyde
o-MeO-
6
69
benzaldehyde
7
o-MeO-
benzaldehyde
2-Cl-
>99
97
8
10,000/1
20,000/1
10,000/1
10,000/1
benzaldehyde
9
2-Cl-
benzaldehyde
3-Cl-
88
10
11
>99
>99
benzaldehyde
4-Cl-
benzaldehyde
Page 7 of 13

H
H
12
13
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
10,000/1
20,000/1
>99
>99
Ph
Ph
O
O
14
15
16
[RuCl2(dppb)(ampy)] iso-valeraldehyde 10,000/1
>99
<5
[RuCl2(dppb)(ampy)]
[RuCl2(dppb)(ampy)]
trans-
cinnamaldehyde
trans-
10,000/1
2,500/1
29
cinnamaldehyde
2-furaldehyde
>98% ACS
17
[RuCl2(dppb)(ampy)]
10,000/1
64
reagent grade
2-furaldehyde
>98% ACS
reagent grade
2-furaldehyde
98%
18
19
20
[RuCl2(dppf)(ampy)]
[RuCl2(dppb)(ampy)]
[RuCl2(dppf)(ampy)]
10,000/1
10,000/1
10,000/1
99
23
25
2-furaldehyde
98%
Experimental procedure: In a glass vial was weighed [RuCl2(dppb)(ampy)] or [RuCl2(dppf)(ampy)] and
aldehyde (30 mmol). A 1N solution of aqueous KOH (0.2 mol%, 60 L) was added and the vial was
transferred to a Biotage Endeavour, purged with N2 and H2 and heated to 90-120 oC under 28 bar H2
for 16 hours. The reaction was cooled, vented and analysed by 1H NMR (CDCl3) and GC.
Good conversion to the alcohol was obtained in most cases, for instance benzaldehyde was
reduced completely to benzyl alcohol without the formation of side-products using either the
[RuCl2(dppb)(ampy)] or [RuCl2(dppf)(ampy)] catalysts. p-MeO-benzaldehyde and p-F-benzaldehyde
gave full conversion at S/C = 20000/1. 2-MeO-benzaldehyde proved less reactive (Entry 6) giving
incomplete conversion with S/C = 10000/1 at 90 °C under 28 bar H2. Full conversion could be
obtained using S/C = 5000/1 (Entry 7). It was also observed that performing the reaction with S/C =
10,000/1 gave full conversion within 5 hours if reaction temperatures of 110 or 120 °C were used.
Chlorobenzaldehyde was also effective and gave the benzylic alcohol in high purity, with the 2-chloro
isomer being somewhat less reactive than the 3- and 4- regio-isomers. It can be seen that a variety
of aldehydes, including those which are low melting solids, can be hydrogenated to the
corresponding benzylic alcohols with high levels of conversion and product purity under neat
reaction conditions. It should be noted that performing the reaction at higher reaction temperature
(110–120 °C) gives improved reactivity and faster reaction rates. trans-Cinnamaldehyde proved to be
a rather unreactive substrate giving <5% conversion to cinnamyl alcohol under the standard
hydrogenation conditions (Entry 15, S/C = 10,000/1, 90 °C, 28 bar H2, 0.2 mol% 1N KOH, 16 hours).
At higher catalyst loadings of 2500/1, a 29% conversion to cinnamyl alcohol was obtained and at 120
Page 8 of 13

°C with S/C = 10000/1 a 38% conversion to cinnamyl alcohol was obtained. These results are in
contrast to the hydrogenation of the saturated aldehyde phenylacetaldehyde, which gave full
conversion to phenethyl alcohol (2-phenyl ethanol) at low catalyst loadings (Entries 12–13). The
reduction of furfural was also examined and the best results were obtained using the
[RuCl2(dppf)(ampy)] catalyst in combination with > 98% ACS reagent grade substrate (Entries 17-20)
which allowed high conversion to be obtained under the standard conditions.
Reactions at larger scale in stand-alone autoclaves have been carried out. For example, the
hydrogenation of benzaldehyde (95% purity) at S/C = 10000/1 with 0.1 mol% 1N KOH at 90 °C and
approximately 6 bar H2 pressure at 10 g scale was successful, although an extended reaction time
was needed to obtain complete hydrogenation (>24 hours). As found in the prior experiments
improved performance can be expected at increased reaction temperature and hydrogen pressure.
When the pressure and temperature was increased to 110 °C and 25 bar H2, respectively, the
reaction on 30 g scale could be carried out using S/C = 30,000/1 (0.1 mol% 1N KOH, 18 hours). When
a freshly opened bottle of benzaldehyde (>99%) was used at a loading of S/C = 50,000/1 under the
o
1
conditions: (CH3)3CO2K (0.1 mol%), neat, 110 C, 25 bar H2 GC analysis and H NMR spectroscopy
showed >99% conversion to benzyl alcohol after 24 hours.
In conclusion, the hydrogenation of benzaldehyde using the readily available catalysts
[RuCl2(dppb)(ampy)] and [RuCl2(dppb)(ampy)] has been studied. Solvent free conditions were found
to be especially effective in promoting high reaction rates and when a minimal amount of base and
catalyst was used high levels of purity were obtained (>98%). A variety of functionalised aldehydes
were hydrogenated with catalyst loadings of 5000/1–50,000/1 under solvent free conditions. A
range of bases can be used, including 1N KOH. Effective hydrogen pressures range from 5–30 bar
and reaction temperatures of 90–120 °C have been employed. The hydrogenation reaction can work
effectively using aldehyde which was not freshly distilled, showing it is a robust and practical method
for the reduction of aldehydes to alcohols which minimises waste production. Solvent-free aldehyde
hydrogenation reactions have been carried out at multi-gram scale in a straightforward manner with
reduced catalyst loadings of S/C = 50,000/1 so far.
References
1
2
3
J. Magano, J. R. Dunetz, Org. Process. Res. Dev., 2012, 16, 1156 and references therein.
P. D. de Koning, M. Jackson, I. C. Lennon, Org. Process Res. Dev., 2006, 10, 1054-1058.
F. Christie, A. Zanotti-Gerosa, D. Grainger, Chem.Cat.Chem., 2018, 10 (5), 1012-1018.
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4
T. Ohkuma, H. Ooka, T. Ikariya, R. Noyori, J. Am. Chem. Soc., 1995, 117, 10417-10418; H. Doucet, T. Ohkuma, K.
Murata, T. Yokozawa, M. Kozawa, E. Katayama, A. F. England, T. Ikariya, R. Noyori, Angew. Chem. Int. Ed., 1998,
37, 1703 – 1707.
5
6
7
P. Dupau, L. Bonomo, L. Kermorvan, Angew.Chem.Int.Ed., 2013, 52, 1 – 5; L. Bonomo, L. Kermorvan, P. Dupau,
ChemCatChem, 2015, 7, 907-910.
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9
S. Baldino, S. Facchetti, A. Zanotti-Gerosa, H. G. Nedden, W. Baratta, ChemCatChem, 2016, 8, 2279-2288.
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10 For selected examples see: S. Hermans, R. Raja, J. M. Thomas, B. F. G. Johnson, G. Sankar, D. Gleeson,
Angew.Chem.Int.Ed., 2001, 40, 1211; B. F. M. Kimmich, P. J. Fagan, E. Hauptman, R. M. Bullock, Chem Comm,
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Page 10 of 13

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be
considered as potential competing interests:
Page 11 of 13

[RuCl2(dppb)(ampy)] or [RuCl2(dppf)(ampy)],
Molar substrate/catalyst ratio = 10,000/1 - 40,000/1
H
R
OH
R
O
solvent-free conditions
90-120 oC, 5 - 30 bar H2,
0.1 - 0.2 mol % mild base
R = aryl, alkyl
Page 12 of 13

Highlights for Tetrahedron Letters article




User-friendly hydrogenation method for aldehyde to alcohol reduction
Solvent-free conditions aid work-up, product isolation and reduce waste
Very low loadings of a homogeneous ruthenium hydrogenation catalyst
Commercial grade aldehydes can be used without additional purification
Page 13 of 13