Utilization of common ligands for the ruthenium-catalyzed amination of alcohols

Article abstract of DOI:10.1002/chem.201302774

Simultaneous presence of bidentate phosphines with surprisingly simple structure and of the ligand triphenylphosphine were revealed as structural characteristics of new Ru catalysts for the selective conversion of primary and secondary alcohols and diols into their corresponding primary amines and diamines (see scheme). Copyright

Full text of DOI:10.1002/chem.201302774

DOI: 10.1002/chem.201302774
Utilization of Common Ligands for the Ruthenium-Catalyzed Amination of
Alcohols
[
a]
[a]
[b]
[b]
Wolfgang Baumann, Anke Spannenberg, Jan Pfeffer, Thomas Haas,
[
a]
[a]
[a]
Angela Kçckritz, Andreas Martin, and Jens Deutsch*
Primary amines are valuable organic compounds, which
are used as intermediates of final products for the manufac-
ture of dyes, agrochemicals, pharmaceuticals, surfactants,
coatings, lubricants, and specialty chemicals. Linear a,w-dia-
mines containing two primary amino groups are utilized as
tion of highly active and selective amination catalysts. The
first feasible selective synthesis of primary amines from pri-
mary alcohols and ammonia was achieved by Milstein and
co-workers by using a ruthenium complex with an expensive
acridine-based PNP pincer ligand as homogeneous catalyst
[1]
[8]
building blocks for polymers.
(Scheme 1). Our group used Milsteinꢁs complex successful-
Various methods of nucleophilic substitution have former-
ly been applied to generate primary amines from alkyl halo-
genides, tosylates, or alcohols as starting materials. The ni-
trogen atom of the amine to be synthesized was introduced
by means of special nitrogen sources, such as hexamethyle-
[2]
netetramine (Delepinꢀ reaction), phthalimide (Gabriel
[
3]
[4]
synthesis), or azides (Mitsunobu reaction). The inter-
mediates obtained in this way were transformed in a subse-
[2,3]
[3]
quent step (acid hydrolysis,
hydrazinolysis, Staudinger
[
5]
[6]
reaction, or hydrogenation ) into primary amines as
target compounds. Due to the requirement of consecutive
reaction steps followed by the purification of each inter-
mediate product, due to the formation of effluents and use-
less by-products, and because of their unfavorable atom
economy, the mentioned synthesis routes are laborious and
costly.
Scheme 1. Reported catalysts and catalyst systems for the amination of
alcohols with ammonia. A) Milstein (amination of primary alcohols, cata-
lyst loading 0.1 mol%). B) Beller (amination of primary and secondary
The direct catalytic synthesis of amines from primary or
secondary alcohols and cost-efficient ammonia gas provides
an attractive and environmentally friendly alternative to the
procedures described above. Such reactions are performed
heterogeneously catalyzed on industrial scale. These pro-
cesses give mainly secondary and tertiary amines and have
to be conducted in presence of hydrogen to transfer the in-
termediately formed imines into amines and to maintain cat-
alcohols, catalyst loading 2 mol% [Ru
3
(CO)12], 6 mol% ligand), Vogt
(CO)12],
(
amination of secondary alcohols, catalyst loading: 1 mol% [Ru
3
6 mol% ligand). C) Beller (amination of primary and secondary alcohols,
diols and hydroxy acid esters, catalyst loading 3 mol% Ru compound
and ligand). D) Beller (amination of a-hydroxy acid amides, catalyst
3
loading 2 mol% [Ru (CO)12], 6 mol% ligand).
ly for the conversion of 1,19-nonadecanediol into 1,19-nona-
[7]
[9]
alyst activity.
decanediamine. Catalyst systems containing a ruthenium
The desirable development of more practicable proce-
dures for one-step transformations of alcohols and ammonia
into primary amines depends significantly on the identifica-
compound and commercially available phosphines as li-
gands, such as 2-(dicyclohexylphosphino)-1-phenyl-1H-pyr-
[10]
role (CataCXiumPCy), 4,5-bis(diphenylphosphino)-9,9-di-
[
11]
methylxanthene (Xantphos),
and 1,2-bis(dicyclohexyl-
[12]
phosphino)ethane proved to be alternatives to Milsteinꢁs
catalyst (Scheme 1). The state of the art of the alcohol ami-
nation with ammonia was summarized in several review arti-
cles.
The alcohol amination with ammonia is an integral part
[
a] Dr. W. Baumann, Dr. A. Spannenberg, Dr. A. Kçckritz,
Dr. A. Martin, Dr. J. Deutsch
Leibniz-Institut fꢂr Katalyse an der Universitꢃt Rostock e.V.
Albert-Einstein-Strasse 29a, 18059 Rostock (Germany)
Fax : (+49)381128151266
[13]
E-mail: jens.deutsch@catalysis.de
[14]
of the modern “borrowing-hydrogen” or “hydrogen-auto-
[
b] Dr. J. Pfeffer, Dr. T. Haas
[15]
transfer” methodology, which can be used to replace the
established environmentally unfriendly stoichiometric alky-
lation of C- and N-nucleophiles by elegant catalytic proce-
dures. The mechanism of the alcohol amination includes an
Evonik Industries AG, CREAVIS Technologies & Innovation
Paul-Baumann-Strasse 1, 45772 Marl (Germany)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201302774.
17702
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 17702 – 17706

COMMUNICATION
initial dehydrogenation of a primary or secondary alcohol,
the reaction of the formed aldehyde or ketone with the N-
nucleophile ammonia to the corresponding imine, and the
final re-hydrogenation of the imine to the amine
aromatic solvent indicated appropriate conditions for the
formation of the catalyst and the target product.
Except for Milsteinꢁs complex, the structures of the ami-
[8]
nation catalysts formed under real reaction conditions were
[8,10–16]
[10–12]
(
Scheme 2).
not investigated.
To identify the nature of the catalyti-
cally active ruthenium complex in our experiments, we
heated [Ru(CO)ClH(PPh ) ] with DPEphos in toluene and
AHCTUNGTRENNUNG
3
3
observed the precipitation of colorless crystals from the
cooled clear reaction mixture. Single-crystal XRD analysis
of the isolated solid surprisingly revealed that one molecule
of triphenylphosphine remained in the ruthenium complex.
[8]
In contrast to Milsteinꢁs PNP pincer compound, DPEphos
was found to coordinate as a bidentate ligand at the rutheni-
um center (Scheme 4 and Figure 1). The synthesized new
Scheme 2. “Borrowing-hydrogen” mechanism suggested for the conver-
sion of alcohols with ammonia into primary amines.
Scheme 4. Synthesis of the catalyst [Ru(CO)ClH
action conditions: 2 mmol [Ru(CO)ClH(PPh
0 mL toluene, 858C, 4 h.
A
T
N
T
N
U
G
3
ACHTUNGTNERNUNG( PPh )]. Re-
However, these successful catalysts and, in particular, the
ligands are still quite expensive. It should be considered that
the recovery of the noble metal ruthenium from the reaction
residues is generally less problematic than that of the li-
gands, which are normally decomposed after use. Based on
this, the structural simplification of known successful ligands,
the exposition of their catalytically relevant functionalities,
and the reduction of their prices are attractive research ob-
jectives. With respect to potential applications on industrial
scale, it was challenging to find such ligands for the catalytic
conversion of primary and secondary alcohols and diols into
the resulting primary amines and diamines with high selec-
tivity and yield.
A
H
U
G
R
N
N
3 3
)
5
In preliminary experiments on the amination of cyclohex-
anol with ammonia, we tested a potential catalyst system
consisting of [Ru(CO)ClH ACHTUNGNRTEUNG( PPh ) ] as ruthenium precursor
3 3
and (oxydi-2,1-phenylene)-bis(diphenylphosphine) (DPE-
phos) as ligand in tert-amyl alcohol and toluene as common-
[8–12]
ly used reaction media for aminations (Scheme 3).
The
faster and nearly complete cyclohexanol conversion in the
3
Figure 1. Molecular structure of [Ru(CO)ClH ACHTGNUTERNN(UGN DPEphos) ACTHUNGTRENNUNG( PPh )] with
numbering scheme (the same numbering was used for the assignment in
the NMR spectra). Displacement ellipsoids are drawn at the 30% proba-
bility level. Hydrogen atoms (except the hydride) are omitted for clarity.
complex [Ru(CO)ClH AHCUTNGRENUN(G DPEphos) CAHTUNGTRNNEUN(G PPh )] crystallizes as a sol-
3
vate with toluene (possible removal of the solvent at 808C
in fine vacuum) and shows a strongly distorted octahedral
geometry with chloride and carbon monoxide in trans posi-
tions. Williams et al. evaluated the structurally closely relat-
ed compound [Ru(CO)H ACHTUNGTRENNUG( DPEphos) ACHTUNGTERNNNU(G PPh )] as catalyst pre-
2 3
cursor in the benzylation of tert-butyl cyanoacetate.
The NMR spectra of the complex showed line broadening
for several signals, particularly for those of the DPEphos
Scheme 3. Ruthenium-catalyzed direct amination of cyclohexanol with
ammonia. Reaction conditions: 10 mmol cyclohexanol, 117 mmol=3 mL
[
17]
liquid ammonia, 25 mL solvent, 0.15 mmol [Ru(CO)ClH
.15 mmol DPEphos, 1708C.
3 3
ACHTUNGTRNENUG( PPh ) ],
0
Chem. Eur. J. 2013, 19, 17702 – 17706
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
17703

J. Deutsch et al.
ligand. At 528C, they were sufficiently resolved to allow fur-
action was explained in detail in earlier publications on cata-
[8,10,11]
ther analysis. The complex was characterized by three
lytic alcohol aminations with ammonia.
The phenyl
3
1
3
1
2
P NMR signals: 43.9 (P ), 25.5 (P ), and 6.4 ppm (P ;
Figure 1). The hydride ligand exhibited an eight-line pattern
group in benzyl alcohol seems to exert an activating influ-
ence on the substrate and, because of its bulkiness, an inhib-
iting influence on the tendency of the reaction product to
form higher substituted side products. Both effects may be
plausible reasons for the excellent yield of 93% achieved
for benzylamine (entry 2). Due to an observed “sluggish” re-
action of 2-ethylhexanol at 1408C and to achieve an accept-
able yield of the target compound, we increased the reaction
temperature for the synthesis of 2-ethylhexyla-
1
2
at d( H)=À7.08 ppm with coupling constants J of 110.8
P,H
2
3
1
(
DPEphos, P ), 30.9 (PPh , P ), and 18.4 Hz (DPEphos, P ).
3
Next, the applicability of our new catalyst for the transfor-
mation of primary and secondary alcohols, hydroxy esters,
and diols with ammonia into the corresponding primary
amines was examined (Table 1).
[
a]
mine to 1708C (entry 4). The lower reactivity of
Table 1. Amination of various alcohols by using ammonia.
2
-ethylhexanol should be related to the sterical
hindrance of its functional group.
Amination of the less reactive secondary alco-
hols demanded reaction temperatures of 170–
Entry Catalyst loading per
OH group [mol%]
T
t
Product
Conv. Yield
[b]
[b]
[8C] [h]
[%]
[%]
1
808C (Table 1, entries 5–8). Additionally, an in-
1
1
1.5
140 48
140 24
140 48
96
96
>99
65
71
93
creased catalyst loading of 3 mol% proved to be
useful for the transformations of 2-octanol and 1-
phenylethanol into primary amines. Cyclohexanol
showed an outstanding reactivity and gave cyclo-
hexylamine in high yield within 24 h (entry 8).
The obtained reaction mixtures contained low
amounts of the ketones as dehydrogenation prod-
ucts of the secondary alcohols formed in the first
step of the reaction mechanism (Scheme 2).
Beside the amination of 2-octanol, the formation
of secondary imines and/or amines occurred to
a lower degree than for the aminations of the pri-
mary amines reported above.
1
.5
2
3
1.5
140 24
97
73
4
5
6
1.5
3
170 48
95
77
180 48
90
64
3
3
170 24
170 48
88
95
76
87
7
1.5
170 48
98
92
1
1.5
170 48
170 24
92
98
84
92
8
9
In addition, we tested the catalytic conversion
of hydroxy esters into their amino derivatives,
which was successfully performed by Bellerꢁs
group for the first time (Table 1, entries 9 and
[
[
c]
c]
3
3
135 48
140 48
97
57
85
1
1
1
0
1
2
>99
[11]
1
0). In agreement to their investigations, we re-
[
[
d]
d]
1.5
150 48
>99
68
duced the reaction temperature applied in the
aminations to minimize the possible condensation
between the present amino and ester functions in
the reaction system to undesired higher molecular
amides. The catalyst was used in double amount
to compensate the expected decreased reaction
rate. The amination of 12-hydroxydodecanoic
acid methyl ester gave a considerable amount of
insoluble and, possibly, higher molecular material
1
2
.5
170 48
180 48
97
99
58
78
[
a] Reaction conditions: 10 mmol alcohol, 117 mmol=3 mL liquid ammonia per OH
group, 25 mL toluene. [b] Conversion and yields were analyzed by means of GC and
are based on n-hexadecane as internal standard. [c] Isolated yield. [d] Reaction in
a mixture of 20 mL toluene with 5 mL tert-amyl alcohol.
(
oligomer and/or polymer amides), which was fil-
As was expected, primary alcohols revealed the highest
reactivity of all substrates investigated in our experiments
and reacted at 1408C with ammonia in presence of 1–
tered from the cooled reaction mixture. However, we were
able to isolate 12-aminododecanoic acid methyl ester as the
main product after distillation in 57% yield (entry 9). In
contrast, 4-aminocyclohexanecarboxylic acid ethyl ester con-
tains a more sterically hindered amino group and showed
a lower tendency to form insoluble intermolecular conden-
sation products. Thus, the amine was obtained in a yield of
85% (entry 10).
1.5 mol% of the catalyst (Table 1, entries 1–3). Differences
between the alcohol conversion and the achieved target
product yield resulted from the formation of secondary
imines and/or amines as unwanted consecutive products.
The formation of such higher substituted derivatives was
caused by the reaction of the primary amines, which are
stronger nucleophiles than the reactant ammonia, with the
intermediately formed aldehydes to secondary imines, and
their terminal rehydration to secondary amines. This side re-
Concluding investigations to determine an approximate
range of application for our catalyst [Ru(CO)ClH-
A
H
U
G
R
N
U
G
ACHTUNGTNERNUNG( PPh )] were focused on direct syntheses of di-
3
AHCTUNGTRENNUNG
17704
www.chemeurj.org
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 17702 – 17706

Common Ligands for the Ruthenium-Catalyzed Amination
solubility of the educts 1,4-bis-(hydroxymethyl)-benzene and
COMMUNICATION
complex C. The intermediate C may react with the alcohol
as educt in a terminal step to the initially formed species A
and the primary amine as the target product. To identify
1,4-cyclohexanediol in toluene, tert-amyl alcohol was added
as a second and more polar solvent component to the reac-
tion mixture. The synthesis of 1,4-bis-(aminomethyl)-ben-
zene proceeded with a yield of 68% and was accompanied
by the formation of secondary amines and imines (Table 1,
entry 11). The observed increased appearance of such com-
pounds in this reaction (for comparison, see the higher se-
lective synthesis of benzylamine given in Table 1, entry 2)
may be explained by the presence of two reactive primary
groups in the target product, and, accordingly, by a higher
statistical probability of consecutive reactions. The simulta-
neous rise of the reaction temperature and the catalyst load-
ing proved to be beneficial to complete the transformation
of 1,4-cyclohexanediol into 1,4-cyclohexanediamine and to
diminish the amount of the intermediately formed mono-
amine (entry 12).
one of the assumed intermediates, [Ru(CO)ClH
ACHTUNGTRENNUNG( DPEphos)-
AHCTUNGTREG(NNNU PPh )] was reacted in toluene with the sodium salt of cyclo-
3
hexanol (908C, 3 h). The main component in the obtained
1
product mixture exhibited H NMR signals, which may be
assigned to two hydride ions (À6.31 and À8.20 ppm). The
3
1
corresponding P NMR spectrum showed three phospho-
rous signals (60.6, 50.2, and 39.3 ppm) indicating the pres-
ence of DPEphos and triphenylphosphine in the complex.
In view of these facts, the existence of the intermediate B,
[17]
which was already reported in the literature, seems to be
likely. In addition, the formation of cyclohexanone in the
GC analysis of the experiment was detected.
Our final experiments were focused on the replacement
of the diphenylether moiety in the ligand for more basic
structure elements, such as alkylene groups (Scheme 6). We
With regard to the structure elucidated for the catalyst
[
Ru(CO)ClH ACHTUNGTRENNUNG( DPEphos) ACTHUNGTRENUNNG( PPh )], we are able to propose
3
a hypothetic mechanism for the successful alcohol amina-
tions observed (Figure 1 and Scheme 5).
Scheme 6. Catalytic amination of cyclohexanol, reaction conditions ac-
cording to Scheme 3. Variation of the backbone in the used bidentate
phosphine ligand (loading 0.15 mmol). Conversion of cyclohexanol and
yield of cyclohexanamine.
tested the diphosphines L1–L4 as catalyst components in
the amination of cyclohexanol. These ligands possess back-
bones of varying chain length and showed, consequently, dif-
ferent catalytic performances. Ruthenium complexes formed
from [Ru(CO)ClH
ACHTUNGTNRENUNG( PPh ) ] and L1–L3 were synthesized by
3 3
Santos et al. and used for the hydroruthenation of al-
[18]
kynes.
The diphosphine L3 (1,3-bis(diphenylphosphino)-
butane, DPPB) was identified as a potential substitute for
the useful ligand DPEphos in our screening and gave the
highest yield of cyclohexylamine (Scheme 6). In contrast,
only poor activities were reported for ruthenium catalysts
generated in situ from L1–L4 and [Ru (CO) ] during the
3
12
course of the amination of 2-hydroxypropanoic acid amide
[12]
with aniline.
In summary, the suitability of DPEphos and DPPB as
more common alternatives to the previously used ligands in
ruthenium-based amination catalysts was proved. The appli-
cation of such ligands might save a considerable part of the
ligand costs (of ca. 80% compared with XANTPHOS, of
more than 99% compared with Milsteinꢁs PNP pincer
ligand). Furthermore, the new complex [Ru(CO)ClH-
Scheme 5. Proposed mechanism for the catalytic amination of alcohols in
the presence of [Ru(CO)ClH ACTHUNGTERNNN(UG DPEphos) ACHTNUGTRENNUNG( PPh )].
3
In compliance with the publication of Gunanathan and
[8]
Milstein, we assumed the substitution of the chloride for
an alcoholate ion (deprotonation product of the alcohol to
be aminated) in the catalyst complex to give the compound
A in the introductory reaction step of the catalytic cycle.
The alcoholate complex A might be decomposed under the
applied reaction conditions into the dihydrido compound B
and a ketone. The imine generated from the released ketone
and ammonia should be able to transform B into the amido
AHCTUNGTRENNUG( DPEphos) ACHTUGNTRENNUGN( PPh )] was synthesized, its molecular structure
3
was elucidated, and its catalytic suitability for the conven-
ient one-step conversion of various primary and secondary
alcohols into primary amines was proved. The simultaneous
presence of a bidentate phosphine and of triphenylphos-
phine as ligands in the octahedral ruthenium complex, as
Chem. Eur. J. 2013, 19, 17702 – 17706
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
17705

J. Deutsch et al.
well as the redundancy of an ether function in the diphos-
phine, revealed as structural characteristics of the amination
catalysts.
[5] P. L. Anelli, L. Lattuada, F. Uggeri, Synth. Commun. 1998, 28, 109–
1
17.
[
[
6] A. Bertho, J. Maier, Justus Liebigs Ann. Chem. 1932, 498, 50–61.
7] For reviews on the heterogeneously catalyzed amination of alcohols,
see: a) K. S. Hayes, Appl. Catal. A 2001, 221, 187–195; b) A. Fisch-
er, T. Mallat, A. Baiker, Catal. Today 1997, 37, 167–189; c) A.
Baiker, J. Kijenski, Catal. Rev. 1985, 27, 653–697.
Experimental Section
[
8] C. Gunanathan, D. Milstein, Angew. Chem. 2008, 120, 8789–8792;
Angew. Chem. Int. Ed. 2008, 47, 8661–8664.
Preparation of the catalyst [Ru(CO)ClH
sion of [Ru(CO)ClH(PPh ] (1.904 g, 2 mmol) and (oxydi-2,1-phenyl-
ene)-bis(diphenylphosphine) (1.077 g, 2 mmol) in oxygen-free toluene
25 mL) was heated in an argon atmosphere whilst being stirred and kept
3
ACHTUNGTNERNGNU( DPEphos) ACTHUNGTRENNUNG( PPh )]: A suspen-
[
9] G. Walther, J. Deutsch, A. Martin, F.-E. Baumann, D. Fridag, R.
Franke, A. Kçckritz, ChemSusChem 2011, 4, 1052–1054.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3 3
)
[
10] a) S. Imm, S. Bꢃhn, L. Neubert, H. Neumann, M. Beller, Angew.
Chem. 2010, 122, 8303–8306; Angew. Chem. Int. Ed. 2010, 49, 8126–
(
at 858C for 4 h. The obtained clear solution was subsequently cooled to
RT. The precipitated colorless crystalline toluene solvate of the rutheni-
um complex was separated, washed with ice-cold toluene (2.5 mL),
8
8
129; b) D. Pingen, C. Mꢂller, D. Vogt, Angew. Chem. 2010, 122,
307–8310; Angew. Chem. Int. Ed. 2010, 49, 8130–8133.
[
[
[
11] S. Imm, S. Bꢃhn, M. Zhang, L. Neubert, H. Neumann, F. Klasovsky,
J. Pfeffer, T. Haas, M. Beller, Angew. Chem. 2011, 123, 7741–7745;
Angew. Chem. Int. Ed. 2011, 50, 7599–7603.
À2
crushed, and dried at 808C in vacuum (10 mbar) to remove the toluene.
The ruthenium complex was isolated as a white powder (1.547 g, yield
8
0%). An alternative preparation method (yield 90%) is given in the
12] M. Zhang, S. Imm, S. Bꢃhn, H. Neumann, M. Beller, Angew. Chem.
Supporting Information.
2
011, 123, 11393–11397; Angew. Chem. Int. Ed. 2011, 50, 11197–
General procedure for the amination of primary or secondary alcohols
and diols: The alcohol (10mmol) and the catalyst [Ru(CO)ClH-
1
1201.
13] For reviews on the homogeneously catalyzed amination of alcohols,
see: a) S. Bꢃhn, S. Imm, L. Neubert, M. Zhang, H. Neumann, M.
Beller, ChemCatChem 2011, 3, 1853–1864; b) G. E. Dobereiner,
R. H. Crabtree, Chem. Rev. 2010, 110, 681–703; c) G. Guillena, D. J.
Ramon, M. Yus, Chem. Rev. 2010, 110, 1611–1641.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(DPEphos)
3
ACHTUNGTRENNUNG( PPh )] (0.1–0.3mmol=1–3mol%) were dissolved in toluene
(
25mL) under argon atmosphere in a steel autoclave (100mL, Hastelloy
with glass beaker). Diols were aminated with the double amount of am-
monia and of the catalyst in a solvent mixture of toluene (20mL) with
tert-amyl alcohol (5mL). Next, the autoclave was closed and pressurized
with argon three times (15 bar). Finally, liquid ammonia (2g, 117mmol;
for diols 4g, 234mmol, cooled to À188C) was pumped into the pressur-
ized autoclave (final pressure at RT between 21.0 and 22.5 bar). The re-
action mixture was then heated whilst being stirred (600 rpm) and kept
at 135–1808C for 24–48h. After cooling to RT and careful expansion of
the mixture, the autoclave was again pressurized with argon (20 bar)
three times to remove the ammonia excess from the gas phase in the au-
toclave. After the final expansion, the obtained solution was filtered
through Celite and analyzed by GC.
[
14] For reviews about borrowing hydrogen methodology, see: a) T. D.
Nixon, M. K. Whittlesey, J. M. J. Williams, Dalton Trans. 2009, 753–
7
62; b) G. W. Lamb, J. M. J. Williams, Chim. Oggi 2008, 26, 17–19;
c) M. H. S. A. Hamid, P. A. Slatford, J. M. J. Williams, Adv. Synth.
Catal. 2007, 349, 1555–1575.
[
15] For hydrogen autotransfer, see: G. Guillena, D. J. Ramon, M. Yus,
Angew. Chem. 2007, 119, 2410–2416; Angew. Chem. Int. Ed. 2007,
4
6, 2358–2364.
16] Selective conversion of primary and secondary alcohols with ammo-
nia into primary amines on 10 wt% Ni/g-Al and 10 wt% Ni/q-
Al was reported recently in the following publication, see: K.-I.
[
2
O
3
2
O
3
Shimizu, K. Kon, W. Onodera, H. Yamazaki, J. N. Kondo, ACS
Catal. 2013, 3, 112–117. The authors assume a “borrowing-hydro-
gen” mechanism for the reactions on these heterogeneous catalysts.
It should be mentioned that the presence of hydrogen was experi-
mentally not excluded for the investigated aminations (cooling of
the reduced catalysts under hydrogen, infilling of the catalysts under
hydrogen). We repeated the amination of 2-octanol over 10 wt%
Acknowledgements
We thank Evonik Industries AG, CREAVIS Technologies & Innovation
for financial support.
2 3
Ni/g-Al O (catalyst preparation according to the given protocol,
catalyst loading: 1.5 mol% of Ni) at 1608C in o-xylene. In contrast
to the reported procedure, the cooling and infilling of the freshly re-
duced Ni-catalyst were done under dry argon (oxygen content
Keywords: alcohols · amines · ammonia · homogeneous
catalysis · ruthenium
<
1 ppm) to exclude strictly the presence of external hydrogen in
the reaction system. Under such conditions, we detected no activity
of the Ni catalyst and no conversion of 2-octanol into 2-octylamine
(reaction time 24 h). According to our observation, the amination of
alcohols to primary amines does not really proceed as a “borrowing-
hydrogen” reaction over heterogeneous Ni catalysts.
[
1] K. Weissermel, H.-J. Arpe in Industrial Organic Chemistry, 6th ed.,
Wiley-VCH, Weinheim, 2007, pp. 261–275.
[
2] For a review on the use of hexamethylenetetramine in organic syn-
ˇ
theses, see: N. Bla zˇ evi c´ , D. Kolbah, B. Belin, V. Sunji c´ , F. Kafje zˇ ,
[17] A. E. W. Ledger, M. F. Mahon, M. K. Whittlesey, J. M. J. Williams,
Dalton Trans. 2009, 6941–6947.
Synthesis 1979, 161–176.
[
3] For a review on the Gabriel synthesis, see: M. S. Gibson, R. W.
Bradshaw, Angew. Chem. 1968, 80, 986–996; Angew. Chem. Int. Ed.
Engl. 1968, 7, 919–930.
[18] A. Santos, J. Lopez, J. Montoya, P. Noheda, A. Romero, A. M.
Echavarren, Organometallics 1994, 13, 3605–3615.
[
4] For a review on the Mitsunobu reaction, see: D. L. Hughes, Org.
Prep. Proced. 1996, 28, 127–164.
Received: July 16, 2013
Published online: November 14, 2013
17706
www.chemeurj.org
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 17702 – 17706