Highly Active and Selective Ru-PNH Catalyst in Aerobic Oxidation of Benzyl Amines

Article abstract of DOI:10.1002/cctc.201900952

Set of [Ru(η⁶-cymene)(R)XCl] (R=L¹SnCl, L¹GeCl L²PPh₂, X=Cl or SnCl₃, L¹=[2-(CH₂NEt₂)-4,6-(tBu)₂C₆H₂]^?, L²=2,6-iPr₂-C₆H₃-NH^?) catalysts was tested in aerobic oxidations of primary amines. The activity of studied catalysts depends on the charge of the Ru atom that has been influenced either by donating ligands R or by character of X. Typical Ru/P catalyst [Ru(η⁶-cymene)(L²PPh₂)Cl₂] (3) with least negative charge on the Ru atom has been observed as the most effective. The design of the phosphine ligand L² containing amino-phosphine PNH moiety provided efficient anchoring of complex 3 to silica gel via hydrogen bonding of the PNH functional group to SiO₂ to give heterogeneous catalyst 3-silica. This complex has been also efficiently tested in aerobic oxidation as recyclable catalyst with cumulative TON up to 6930.

Full text of DOI:10.1002/cctc.201900952

Accepted Article
Title: Highly active and selective Ru-PNH catalyst in aerobic oxidation
of benzyl amines
Authors: Roman Jambor, Michal Aman, Jakub Tremmel, Libor Dostal,
Milan Erben, Jiří Tydlitát, and Josef Jansa
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ChemCatChem
10.1002/cctc.201900952
FULL PAPER
Highly active and selective Ru-PNH catalyst in aerobic oxidation
of benzyl amines
[a]
[a]
[a]
[a]
[b]
[c]
Michal Aman, Jakub Tremmel, Libor Dostál, Milan Erben, Jiří Tydlitát, Josef Jansa and
Roman Jambor*[a]
6
1
1
Abstract: Set of [Ru( -cymene)(R)XCl] (R
=
L SnCl, L GeCl
2
1
–
2
L PPh
iPr -C
2
, X = Cl or SnCl
3
, L = [2-(CH
2
NEt
2
2 6 2
)-4,6-(tBu) C H ] , L = 2,6-
–
2
6
H
3
-NH ) catalysts was tested in aerobic oxidations of primary
amines. The activity of studied catalysts depends on the charge of
the Ru atom that has been influenced either by donating ligands R or
6
2
by character of X. Typical Ru/P catalyst [Ru( -cymene)(L PPh
2 2
)Cl ]
(
3) with least negative charge on the Ru atom has been observed as
2
the most effective. The design of the phosphine ligand L containing
amino-phosphine PNH moiety provided efficient anchoring of
complex 3 to silica gel via hydrogen bonding of the PNH
Scheme 1. Possible approaches to CH=N imine bonds
2
functional group to SiO to give heterogeneous catalyst 3-silica.
This complex has been also efficiently tested in aerobic
oxidation as recyclable catalyst with cumulative TON up to 6930.
This method involves the dehydrogenation of primary amines
that yields NH-imines, generally proposed as the key
intermediates. The reaction of either NH-imines or the aldehydes
formed by their hydrolysis with primary amines may provide
homo-coupled imines. These three oxidative approaches are
investigated intensively, and significant developments in aerobic
oxidation of alcohol and amines to imines were achieved.[
Nowadays, the catalytic systems based on metal,[3] metal-free,[4]
photo[5] and bioinspired[6] catalysts are known, but the most
important properties of the catalysts remain similar. The process
of the aerobic oxidation should contain high active, low cost,
easy to handle and well-separable catalyst.
The imine formation is catalysed by metal-based catalysts,
which can be formally classified as noble and non-noble metals.
Traditionally, the compounds based on Ru are studied as
catalysts. However, it was reported that the oxidation 4-
methylbenzylamine with dioxygen catalysed by simple
Introduction
3]
The presence of reactive C=N bond opens the versatile
utilization of the imines for the synthesis of the fine chemicals,
widely used in pharmaceutical or chemical industry. The most
typical transformation of C=N bond is thus their reductions,
additions or cyclizations.[1] While typical synthetic approach is
Schiff coupling, e.g. dehydrative condensation of amines with
carbonyl compounds (Scheme 1A),[2] new approaches are
based on one-pot oxidative methodologies, that operate with
readily available starting materials and air as the oxidant.[3]
These processes involved the cross-coupling of alcohols with
amines, the procedure that is suitable to prepare diverse
symmetric and un-symmetric imines and the water is the only by
product (Scheme 1B). The use of secondary amines involving
the oxidative dehydrogenation is second possibility (Scheme 1C).
While the advantage of this way is that the substrates cannot be
dehydrogenated into nitriles, it differs since the conversions are
highly dependent on steric demands/protections around the NH
moiety. Alternative synthesis of the imines is also the self-
coupling of primary amines (Scheme 1D).
homogeneous Ru catalysts, such as RuCl
RuCl (dmso) ], [{RuCl (p-cymene)} ], and
bpy=2,2’-bipyridyl) proceed with very low yields (up to 25%).
3
, [RuCl
2
(PPh
3 3
) ],
[
(
2
4
2
2
[RuCl
2
(bpy)
2
[
]
7]
In addition, when the aerobic conditions are used, the presence
of oxygen may provide the problems with over oxidation of
imines and often promote formation of nitriles instead of
imines.[ For this reason, Ru complexes were frequently studied
as homogenous catalysts under inert atmosphere.[9] In the field
8]
of aerobic oxidation of amines, the ruthenium hydrido complexes
II
[
Ru (R-BIAN)(PPh
3
)
2
(CO)(H)]ClO
4
(R = OMe, Me, H, Cl, NO
2
)
with TEMPO were reported as the efficient homogenous
catalytic system (Figure 1A).[10] An elegant system containing
ruthenium transfer hydrogenation catalyst with quninone was
developed by Bꢀckvall (Figure 1B),[11] and [Et
3 2 3
NH] [Ru(dipic)Cl ]
[
a]
Mr. M. Aman, Mr. J. Tremmel, Dr. L. Dostál, Dr. M. Erben, prof. R.
Jambor Department of General and Inorganic Chemistry, Faculty of
Chemical Technology, University of Pardubice, 53210 Pardubice,
Czech Republic, E-mail: roman.jambor@upce.cz,
http://www.upce.cz
Dr. J. Tydlitát Department of Organic Chemistry and Technology,
Faculty of Chemical Technology, University of Pardubice, 53210
Pardubice, Czech Republic
catalyst used by Zhao was active in self-condensation as well
(Figure 1C).[12] However, heterogeneous catalysts are favoured
for large scale productions. In the field of aerobic oxidations,
Mori et al., reported on heterogeneous hydroxyapatite-bound
Ru3+ system,[13] that was active for the oxidation of primary
[
[
b]
c]
amines. Later on, Mizuno and co-workers used Ru(OH)
system, that was highly active and lower metal loading were
achieved.[14] The Ru(OH)
supported by other oxides TiO or
Fe
were also studied.[15]
X 2 3
/Al O
Dr. J. Jansa Research Institute for Organic Syntheses (VUOS),
Rybitví 296, CZ-533 54 Pardubice-Rybitví, Czech Republic
X
2
2
O
3
Supporting information for this article is given via a link at the end of
the document.
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FULL PAPER
Previously, we have reported preparation of the set
6
1
2
[
Ru( -cymene)(R)(X)Cl] (R = L SnCl or L PPh
L1 ]–, L2
[2-(CH NEt )-4,6-(tBu) 2,6-iPr
complexes 1 – 4 (Figure 1) that differed in type of either donor
atom (Sn vs. P) or polar group (Cl vs. SnCl
).[16] The DFT
2
, X = Cl or SnCl
3
,
=
2
2
2
C
6
H
2
=
2
-C H
6 3
-NH–)
3
calculations clearly demonstrated that both factors strongly
influenced the charge of the Ru atom.[16]
Scheme 2. Synthesis of the germylene based arene ruthenium complexes 5
and 6.
1
The H NMR spectra of 5 and 6 showed an AX spin system for
the NCH
approximately 14 Hz for 5 and 
for 6. The ring protons of the cymene ligand in 5 and 6 constitute
an AA´BB´ spin system at  5.40, A´ 5.57,  5.64 and B´ 5.74
with JAB being approximately 6 Hz for 5 ( 5.76, A´ 5.82,  6.15
2
protons at 
A
3.92 and 
X
4.59 with JAX being
A
3.85 and 
X
4.62 (JAX = 15 Hz)
A
B
A
B
and B´ 6.23 with JAB = 5 Hz for 6). The 13C NMR spectrum of 5
showed two signals at  84.9 and 87.7 ppm for the C2,6 of the
cymene ligand ( 84.5 and 89.2 ppm for 6) and two signals at 
8
7.2 and 87.5 ppm for the C3,5 carbon atoms ( 87.0 and 93.2
ppm for 6). The 1 Sn NMR spectrum of 6 showed a singlet at
19

–238.7 ppm for SnCl
3
substituent, close to the value found for
)(Cl)] (–205.8 Hz).[18]
6
[
( -cymene)Ru(PPh
3
)(SnCl
3
Figure 1. Examples of homogenous Ru catalysts used for aerobic oxidations
Homogenous aerobic oxidation
(A – C) and complexes used in this study 1 - 4.
As stated, complex 3 is a typical phosphine-like catalyst,
remaining compounds can be perceived as Ru/Sn and Ru/Ge
analogues of Pt/Sn catalysts that were successfully tested for
aerobic oxidations. Therefore, the set of 1 – 6 was tested in
homogenous aerobic oxidation of primary amines to see the
effect of donating ligand (P vs. Ge and Sn) or polar group (Cl vs.
While complex 3 (Figure 1) is a typical phosphine-like
catalyst, compounds 1, 2 and 4 can be perceived as Sn/Ru
analogues of Pt/Sn catalysts that were successfully tested for
[
17]
aerobic oxidations.
Here, we report on the application of the
1
6
3
SnCl ) on their catalytic activity. Our reaction conditions were
germylene L GeCl as the ligand for [( -cymene)RuCl]
2
(-Cl)
prepare germylene analogues [Ru( -cymene)(L GeCl)Cl ] (5)
)Cl] (6). All complexes 1 – 6
2
to
6
1
similar to Zhao who used complex [Et
3
3
NH][Ru(dipic)Cl ] in 1
2
mol% loading for oxidation of neat benzyl amine.[ Since the
12]
6
1
and [Ru( -cymene)(L GeCl)(SnCl
3
proposed mechanism of the aerobic oxidation predicts the
formation of H O, we have also added 4Å molecular sieves, and
2
used air as an oxidant (Scheme 3).
were tested further in homogenous aerobic oxidation of primary
amines to see the effect of different charges of the Ru atom on
the efficiency of the oxidations. The most efficient complex 3 has
been also used for synthesis of heterogeneous catalyst 3-silica
that has been tested for aerobic oxidation of primary amines as
well.
Results and Discussion
Scheme 3. Aerobic oxidation of benzyl amine catalysed by 1 - 6.
Synthesis and Characterization of 1 – 6.
Starting ligand L1GeCl and Ru complexes [Ru(6-
1
6
1
Our studies showed that the catalytic loading could be lowered
cymene)(L SnCl)Cl
2
] (1), [Ru( -cymene)(L SnCl)(SnCl
3
)Cl] (2),
[Ru( -
6
2
6
10 times in comparison with [Et
3
3
NH][Ru(dipic)Cl ] and we used
[
Ru( -cymene)(L PPh
2
)Cl
2
]
(3),
0.1 mol % of the catalysts only.[ The compounds 1, 3 and 5
12]
2
cymene)(L PPh
2
)(SnCl
3
)Cl] (4) were prepared according to the
[
16]
were very active under these conditions, while complexes
literature procedure. The germylene analogues were prepared
by the reaction of L GeCl with [( -cymene)RuCl]
provide complex [Ru( -cymene)(L GeCl)Cl ] (5) (Scheme 2).
2
1
6
containing SnCl
previous study showed that the SnCl
3
ligand were less effective (Table 1). Our
group increased negative
2
(-Cl)
2
to
6
1
3
[Ru(6-
charge on the ruthenium atom (range of -0.78 to -1.02e) in
The
trimetallic
ruthenium
complex
1
comparison with Cl atom (the charge on the ruthenium -0.34 to -
cymene)(L GeCl)(SnCl
3
)Cl] (6) was obtained via the insertion of
0
.55e).[16] This indicates that negative charge on the Ru atom
2
SnCl into the Ru-Cl bond in 5 (Scheme 2).
decrease the catalytic activity of the catalyst.
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proceeded slowly during the first two hours but, subsequently it
was accelerated and finished within ten hours (see Figure 2 and
Figures S40 – S46 in SI).
Table 1. Yields of aerobic oxidation of benzyl amine catalysed by 0.1 mol% of
1
– 6
Catalyst
Temperature (°C)
Time (h)
10
Yield (%)
>99
85
1
2
3
4
5
6
100
100
100
100
100
100
10
10
>99
60
10
10
>99
21
10
Compounds 1, 3 and 5 were tested further to see the effect of
the substitution of starting benzyl amine. For this reason 2, 3
and 4-fluoro and 2, 3 and 4-methyl substituted benzyl amines
and methyl benzylamine were employed as starting materials
Figure 2. Time course of the benzylamine conversion catalysed by 3 (0.1
mol%). Oxidant air (◆) or oxygen (■).
(
Scheme 4).
Slow initiation of the reaction may be explained by slow
oxidation of Ru(II) atom in 3 by the air in the presence RCH
2 2
NH
amine to give Ru(III) complex (Scheme 5A) and H O. To prove
2
this hypothesis we use an oxygen instead of air as oxidant and
this accelerates the reaction substantively (conversion up to
20% within two hours, Figure 2 and Figures S47 – S50 in SI).
The formation of the Ru(III) complex (Scheme 5A) maybe
accompanied with the elimination of RCH=NH imine to yield the
Ru(III) hydride complex (Scheme 5B) in another step. The
Scheme 4. Aerobic oxidation of substituted benzyl amine catalysed by 1, 3
and 5
2
Ru(III) hydride complex may eliminate H to regenerate complex
Reactions were monitored by 1H NMR spectroscopy and the
3. When stoichiometric amount of 3 and benzyl amine was
heated on the air, the 31P{ H} NMR spectra showed new signals
at  106.3 and 21.7 ppm that may be attributed to the proposed
Ru(III) complexes (Figures S51 – S53 in SI).
1
1
13
1
19
1
products were identified by H, C{ H}, F{ H} NMR and GC-MS
analysis (see Figures S12 – S37 in SI). The results showed
strong influence of +I effect of Me substituents (Table 2). All
fluoro-benzyl amines were oxidized at lower temperatures, while
methyl substituted benzylamines were generally oxidized at
higher temperature (120°C), while temperature at 100°C
provided lower conversions 50-85% (entries 11 - 13). It is also
evident that substitution in ortho position strongly decreased the
reactivity of both ortho substituted substrates, which were
oxidized at lower conversions (entries 1, 4) in comparison to
para substituted ones (entries 3, 6). Therefore, 2-substituted
benzylamines allowed us further comparison of the catalytic
activity of our catalysts. The lowest conversions were obtained
in the case of 5 (Ge-substituted Ru catalysts, entry 18), while
Sn-substituted catalyst gave better yield (compound 1, entry 1).
The best conversions were obtained for complex 3 having the
least negative charge at the Ru atom (entry 8). This catalyst also
provided the best result in the oxidation of methyl
benzylamine (75%) under the same conditions (entry 17), but no
conversion was found for catalyst 5 (entry 24). However, the
conversion 12% was observed after 24h and when the catalytic
loading of 5 was increase to 1 mol%, the conversions was 30%
Scheme 5. Possible mechanism of aerobic oxidation benzyl amine catalysed
by 3.
We also examine the thermal stability of 3 to see if any
degradation could take place under the catalytic conditions.
Thermogravimetric analysis of 3 provided information that the
decomposition starts above 159°C (Figure S6 in SI).
(
see Figures S38 and S39 in SI). The time course of the
benzylamine conversion into the imine catalysed by 3 (0.1
1
mol%) was investigated by H NMR spectroscopy. The reaction
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Table 2. Yields of aerobic oxidation of substituted benzyl amine catalysed by 0.1 mol% of 1, 3 and 5
Entry
Catalyst
Substrate
Temperature (°C)
Time (h)
10
Yield (%)
85
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
3
3
3
3
3
3
3
3
3
3
5
5
5
5
5
5
5
2-F-benzylamine
3-F-benzylamine
4-F-benzylamine
2-Me-benzylamine
3-Me-benzylamine
4-Me-benzylamine
methyl benzylamine
2-F-benzylamine
3-F-benzylamine
4-F-benzylamine
2-Me-benzylamine
3-Me-benzylamine
4-Me-benzylamine
2-Me-benzylamine
3-Me-benzylamine
4-Me-benzylamine
methyl benzylamine
2-F-benzylamine
3-F-benzylamine
4-F-benzylamine
2-Me-benzylamine
3-Me-benzylamine
4-Me-benzylamine
methyl benzylamine
100
100
100
120
120
120
120
100
100
100
100
100
100
120
120
120
120
100
100
100
120
120
120
120
10
>99
>99
50
10
10
10
80
10
>99
40
10
10
>99
>99
>99
50
10
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
10
10
10
75
10
80
10
>99
>99
>99
75
10
10
10
10
70
10
>99
>99
60
10
10
10
70
10
>99
0
10
In addition, the NMR sample (toluene-d8) of 3 has been also
heated on the air at 100°C and no decomposition was observed
analysis (see Figures S54 – S71 in SI). The results showed that
complex 3 is able to oxidize the aliphatic amines, but over
oxidation takes place (for details see Table S1 in SI). While the
corresponding nitriles were prepared with conversions 99% after
24h by oxidation of higher primary aliphatic amines (Scheme 6a,
for characterization see Figures S64-S66, S69 – S71 in SI), the
presence of amides has been detected for heptan and
hexanamine after 24h (Scheme 6b) (for details see Table S1 in
SI).
(
Figure S9 in SI), despite the fact, that phosphine containing
catalysts may be easily oxidised air at elevated temperatures.
Therefore, catalyst 3 is stable at temperatures used during the
aerobic oxidations.
To diversify the scope of the reaction, aerobic oxidations of
primary aliphatic amines catalysed by 3 (0.1 mol%) were tested
under the same conditions (Scheme 6). We tested aliphatic
amines, namely octadecanamine, oleyamine, heptanamine and
hexanamine, with the boiling points above the 100°C. The
1
reactions were monitored by H NMR spectroscopy and GC-MS
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The band characteristic for the presence of NH moiety was not
observed in 3-silica probably due to overlapping by strong OH
stretching of silica or by its weakening caused by hydrogen-
bonding of 3 toward polar matrix. From almost identical spectra
of 3 and 3-silica in far-infrared region is apparent that the
molecule of catalyst is not significantly affected by anchoring to
silica gel and Ru coordination environment remains unchanged.
The Ru–Cl stretching modes were tentatively[19] assigned to IR
absorptions at 295 and 224 cm-1 (cf. 3: 298s and 231m cm ).
-1
Scheme 6. Aerobic oxidation of selected aliphatic primary amines by 3
Synthesis and Characterization of 3-silica
Since the complex 3 has been found as the most effective
catalyst, we also used the PNH moiety of L2 ligand for its
anchoring, since the heterogeneous catalysts are favoured for
large scale productions. We used acidic PNH moiety for
anchoring complex 3 to silica gel via PNH hydrogen bonding
with SiO
easy. The appropriated amount of compound 3 was dissolved in
CH Cl (see Figure 3A) and silica gel was added to this solution.
The CH Cl has been immediately de-colourised, while solid
material become red-orange (see Figure 3B). The CH Cl was
filtrated, the red solid dried under the vacuum and characterised
2
(Figure 3). We found that process is very elegant and
2
2
2
2
2
2
13
31
as 3-silica by C, P MAS NMR (see Figures S7 – S9 in SI) and
IR spectroscopy. Importantly, the 31P MAS NMR spectrum of 3-
silica showed the signal at  58.2 ppm (Figure S7 in SI). The
same chemical shift at  58.1 ppm was found in the 31P{ H} NMR
1
3
spectrum of 3 in CDCl solution (Figure S8 in SI). This clearly
indicates that no decomposition of 3 took place during its
anchoring to silica gel. The IR spectrum of 3-silica was
measured (Figure 4). In IR spectra of 3-silica dominate very
strong and broad absorptions due to vibrational motions of polar
O–H and Si–O bonds of silica matrix. Nevertheless, in region
Figure 4. Infrared spectra of 3-silica (a), silica gel (b) and 3 (c). The arrows
indicate bands due to adsorbed 3. *The spectrum of 3-silica after partial
subtraction of silica gel background is shown
-1
3100-2800, 1500-1350 and 800-680 cm , weak bands
attributable to C–H stretching and deformation vibrations of
catalyst 3 were detected (Figure 4).
Heterogeneous aerobic oxidation
As the data confirmed the complex 3 anchored to silica gel,
obtained 3-silica has been tested as heterogeneous catalysts for
aerobic amine oxidation. The conditions were similar to
homogenous procedure. The substituted benzylamines, 4Å
molecular sieves and 3-silica (prepared from CH Cl solution
2 2
containing 0.1 mol% of 3 and silica gel, for details see SI), were
heated and air has been used as oxidant. To the reaction
mixture, Et
2
O was added after 10 h. Obtained suspension was
filtrated. The filtrate was analysed by GC-MS and 1H and 19
F
NMR spectroscopy and both methods proved the full conversion
of substituted benzylamines to corresponding products, similarly
to homogenous catalysis tests (Table 3). The solid material was
examined by 31P MAS NMR spectrum, where the signal at  58
ppm was observed (Figure S11 in SI). This suggests presence
of 3-silica after the first run. Therefore, another appropriate
amount of benzylamines were added to this solid material
Figure 3. Synthesis of 3-silica, CH
2 2
Cl solution of 3 (A), anchoring of complex
insoluble in Et
run.
2
O (3-silica, molecular sieves) to start the second
3
to silica gel (B) and isolated 3-silica (C).
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Table 3. Results for catalytic activity of 3-silica in the first run heterogeneous aerobic oxidation of benzyl amine substrates
-
1
Catalyst
Substrate
Temperature (°C)
Time (h)
10
Yield (%)
>99
TON
990
990
990
990
990
990
990
TOF (h )
3-silica
3-silica
3-silica
3-silica
3-silica
3-silica
3-silica
Benzylamine
100
100
100
100
120
120
120
99
99
99
99
99
99
99
2-F-benzylamine
3-F-benzylamine
4-F-benzylamine
2-Me-benzylamine
3-Me-benzylamine
4-Me-benzylamine
10
>99
10
>99
10
>99
10
>99
10
>99
10
>99
After 10 hours of heating, the reaction mixture was worked up in
the same manner as in the first run and, in the same way, next 5
runs were carried out. We have found out that the
heterogeneous catalyst 3-silica is active for aerobic oxidation of
substrates like benzylamine, or 3- and 4-fluoro benzylamines
and no decrease of activity was observed after 7 cycles (Figure
was influenced by donating ligands R and by character of X.
Finally, the typical Ru/P catalyst 3 has been found as the most
effective and may be used as homogenous catalyst in 0.1 mol%
loading with high selectivity. No over oxidations of tested benzyl
amines were detected. The high catalytic activity of 3 maybe
attributed to least negative charge on the central Ru atom (-
5). For 2-fluoro benzylamine, the catalytic activity decreased
0.34e)[16] in comparison with others tested compounds. Since
2
significantly after four catalytic cycles. For methyl substituted
benzylamines, the catalytic activity has been lowered during
third cycle, where the conversions about 60 % were obtained.
the efficient complex 3 contains donating ligand L PPh
2
, where
L2 is amino-phosphine with the PNH moiety, complex 3 has
been efficiently anchored to silica gel via NH hydrogen bonding
and heterogeneous catalyst 3-silica was prepared. The 3-silica
is highly active and selective in aerobic oxidations of primary
amines similarly to 3 (0.1 mol% loading, no over oxidation). In
addition, no decrease of activity was observed after 7 cycles
providing 3-silica cumulative TON up to 6930.
Experimental Section
Experimental details, characterization of complexes, products of
the aerobic oxidations are given in supporting information.
Acknowledgements
The authors wish to thank the Ministry of Industry and Trade of
the Czech Republic (project FV-10240) for the financial support
Figure 5. Catalytic activity and recovery of 3-silica in aerobic oxidation
Keywords: Ru complexes • aerobic oxidation • amine •
heterogeneous • catalysis
Conclusions
[
1]
a) S. I. Murahashi, Angew. Chem., Int. Ed. Engl. 1995, 34, 2443−2465;
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1
New Ru/Ge complexes [Ru( -cymene)(L GeCl)Cl
2
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6
1
[
Ru( -cymene)(L GeCl)(SnCl
3
)Cl] (6) were prepared to
complete the set of Ru complexes [Ru( -cymene)(L SnCl)Cl
6
1
2
6
]
6
1
(
1),
[Ru( -cymene)(L SnCl)(SnCl
3
)Cl]
(2),
)(SnCl
[Ru( -
2
6
2
cymene)(L PPh
2
6
)Cl
2
] (3), [Ru( -cymene)(L PPh
2
1
3
)Cl] (4).
1
2
Full set of [Ru( -cymene)(R)XCl] (R = L SnCl, L GeCl, L PPh
2
,
3
X = Cl or SnCl ) was further tested as catalysts in aerobic
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Entry for the Table of Contents
FULL PAPER
6
Complex [Ru( -
Michal Aman, Jakub Tremmel, Libor
Dostál, Milan Erben, Jiří Tydlitát, Josef
Jansa and Roman Jambor
2
cymene)(L PPh
2
)Cl
2
] (3) has been
found as the effective homogenous
catalyst in aerobic oxidation of benzyl
amines to imines. Its anchoring to
silica gel via hydrogen bonding of
PNH group provided highly active
heterogeneous catalyst 3-silica, that
provided cumulative TON up to 6930.
Page No. – Page No.
The highly active and selective Ru-
PNH catalyst in aerobic oxidation of
benzyl amines
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