Synthesis and catalytic activity of μ-oxo ruthenium(IV) porphyrin species to promote amination reactions

Article abstract of DOI:10.1142/S1088424616500814

This work describes the synthesis of ruthenium(IV) m-oxo porphyrin complexes of general formula [Ru^IV(TPP)(X)]₂O which have been applied as catalysts in nitrene transfer reactions using aryl azides (ArN₃) as nitrene sources. Collected data indicated that the catalytic efficiency of [Ru^IV(TPP)(OCH₃)]₂O was comparable to that of Ru^II(TPP)CO because of their analogous reactivity towards aryl azides to give the same catalytically active bis-imido species Ru^VI(TPP)(ArN)₂. The reaction of [Ru^IV(TPP)(OCH₃)]₂O with Ph₃CN₃ or (CH₃)₃SiN₃ afforded [RuIV(TPP)(N₃)]₂O which was fully characterised, its molecular structure was also determined by single crystal X-ray analysis.

Full text of DOI:10.1142/S1088424616500814

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2016; 20: 1–10
DOI: 10.1142/S1088424616500814
Published at http://www.worldscinet.com/jpp/
Synthesis and catalytic activity of m-oxo ruthenium(IV)
porphyrin species to promote amination reactions
Paolo Zardia, Daniela Intrierib, Daniela Maria Carminatib, Francesco Ferrettib,
Piero Macchic and Emma Gallo*b◊
a Department of Chemical Sciences of Padua University, Via F. Marzolo, 1-35131 Padua, Italy
b Chemistry Department of Milan University, Via C. Golgi 19, 20133 Milan, Italy
c Department of Chemistry and Biochemistry of University of Berne, Freiestrasse 3, CH-3012 Berne, Switzerland
Dedicated to Professor Tomás Torres on the occasion of his 65th birthday
Received 29 January 2016
Accepted 18 March 2016
ABSTRACT: This work describes the synthesis of ruthenium(IV) m-oxo porphyrin complexes of
general formula [RuIV(TPP)(X)]2O which have been applied as catalysts in nitrene transfer reactions
using aryl azides (ArN3) as nitrene sources. Collected data indicated that the catalytic efficiency of
[RuIV(TPP)(OCH3)]2O was comparable to that of RuII(TPP)CO because of their analogous reactivity
towards aryl azides to give the same catalytically active bis-imido species RuVI(TPP)(ArN)2. The
reaction of [RuIV(TPP)(OCH3)]2O with Ph3CN3 or (CH3)3SiN3 afforded [RuIV(TPP)(N3)]2O which was
fully characterised, its molecular structure was also determined by single crystal X-ray analysis.
KEYWORDS: homogeneous catalysis, ruthenium, amination, azide.
17] porphyrin catalysts were tested and their catalytic
INTRODUCTION
efficiency were compared to that of ruthenium(II)
The development of efficient synthetic procedures to
porphyrin complexes. Recorded data showed that high-
attain aminated compounds is of paramount importance
valent ruthenium species are competent amination
due to pharmaceutical and/or biologic behaviors of aza-
catalysts which strongly reinforce the hypothesis of their
containing molecules [1]. Amongst all the catalysts
formation during ruthenium(II)-catalysed reactions, as
capable of promoting amination reactions, ruthenium(II)
suggested by several theoretical investigations [18–20].
porphyrin complexes [2–4] show a good efficiency in
Concerning the use of ruthenium(IV) porphyrin cat-
catalysing the amination of saturated and unsaturated
alysts, C. M. Che and co-authors reported very good
hydrocarbons by using different classes of aminating
results on the activity of differently substituted
agents such as aryl iminoiodinanes (RN=IAr) [5], amines
in the presence of oxidant species [6] and organic azides
(RN3) [7–11]. Numerous structural modifications of
the porphyrin skeleton were carried out to improve the
catalytic performance which can also be modulated
by the electronic nature of the axial ligands onto the
ruthenium(II) center [12, 13]. Based on the fact that the
catalytic activity can be fine-tuned by the metal oxidation
state, ruthenium(IV) [14, 15] and ruthenium(VI) [10, 16,
RuIV(porphyrin)Cl2 [14, 15] complexes to promote C–H
bond nitrene insertions but, to the best of our knowledge,
the catalytic activity of dimeric ruthenium(IV) porphyrin
species to promote amination reactions have not yet been
reported. The synthesis of oxo-bridged dimers was studied
in the early 80’s [21] and is favored by using ruthenium(II)-
carbonyl complexes of unhindered porphyrin ligands [22,
23], such as TPP (TPP = dianion of tetraphenylporphyrin)
and OEP (OEP = dianion of octaethylporphyrin) as star-
ting materials. The first report concerns the oxidation of
RuII(OEP)CO by tert-butylhydroperoxide to yield the
m-oxo complex [RuIV(OEP)(OH)]2O [24], which showed
◊ SPP full member in good standing
*Correspondence to: Emma Gallo, email: emma.gallo@unimi.it
Copyright © 2016 World Scientific Publishing Company

2
P. ZARDI ET AL.
an unexpected stability. In fact m-oxo dimers can easily
exchange the axial ligand under acidic conditions achieving
compounds of the general formula [RuIV(porphyrin)(L)]2O
[21]. The catalytic employment of m-oxo ruthenium
porphyrins is scarce and only recently R. Zhang and
co-workers [25, 26] reported on the use of these dimeric
species in promoting the oxidation of hydrocarbons upon
photochemical activation.
in a 40% yield and recorded analytical data were in
accord to those reported in literature [21].
We synthesised complex 3 in high yields (81% yield)
by reacting complex 1 with a slight excess of the oxidant
mCPBA (8,0 eq.) in a MeOH/CH2Cl2 mixture in the
convenient ratio of 10:1, which limited the formation of
complex 2 and assured the complete conversion of the
starting complex 1.
Hence, we focused our attention on the synthesis of
m-oxo ruthenium porphyrin complexes to investigate
their reactivity with organic azides and their catalytic
activity in amination reactions.
Complexes 2 and 3 were both tested as catalysts of
the cumene amination and only complex 3 promoted the
synthesis of the corresponding benzylic amine in 65%
yield (entry 1, Table 1). Thus, complex 3 was tested as
the catalyst for the nitrene transfer reactions shown in
Scheme 1 by using aryl azides as nitrogen sources and
obtained aza-derivatives are reported in Table 1.
RESULTS AND DISCUSSION
As shown in Table 1, compound 3 was active in
promoting benzylic (entries 1–7) and allylic (entry 8)
aminations as well as aziridination reactions (entry 9).
In order to evaluate the catalytic efficiency of 3 for the
benzylic amination, the amination of cumene was run in
the presence of the low catalyst loading of 0.025% mol
to obtain 4 in 65% yield. Complex 3 was also active
in promoting the amination of less reactive benzylic
substrates such as methyl phenylacetate (entry 6)
and methyl dihydrocinnamate (entry 7), which were trans-
formed into corresponding amino esters 9 and 10.
Concerning the allylic amination of cyclohexene (entry 8)
the reaction efficiency was independent from the electronic
featureofthestartingazideandsimilaryieldswereachieved
in the synthesis of compounds 11 and 12. The low yield
obtained in the synthesis of compound 13 can be due to a
We started studying the reaction of [RuII(TPP)
(CO)(MeOH)] (1) with mCPBA (meta-chloroperbenzoic
acid) which formed [RuIV(TPP)(mCB)]2O complex (2)
where two meta-chlorobenzoate (mCB) anions were
present on the ruthenium axial positions. Complex 2 was
unequivocally identified by MS and NMR spectroscopy
which showed strongly shifted signals for the aromatic
protons of mCB moieties. We also observed the typical
signal pattern of a m-oxo tetraphenylporphyrin complex,
where the aromatic protons of the meso-phenyl groups
were split into five different signals (Fig. 1). Complex
2 was obtained in a 39% yield and the missing mass
balance was due to the partial decomposition of 2 into
[RuIV(TPP)(OCH3)]2O (3) during the chromatographic
purification with CH2Cl2/MeOH. Complex 3 was obtained
Fig. 1. Structure and 1H NMR spectrum of [RuIV(TPP)(mCB)]2O complex (2)
Copyright © 2016 World Scientific Publishing Company
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SYNTHESIS AND CATALYTIC ACTIVITY OF m-OXO RUTHENIUM(IV) PORPHYRIN SPECIES
3
benzylic amination
partial inhibition of thecatalytic activityby thecoordination
of the substrate methoxy group to the ruthenium center. As
reported in entry 9 of Table 1, complex 3 was also a very
goodcatalystfortheaziridinationofa-methylstyrenewhich
afforded the desired aziridine 14 in a very short reaction
time and a quantitative yield. Even if 3 demonstrated to
be a competent and versatile amination catalyst, collected
catalytic data are comparable to those already achieved
by using Ru(TPP)CO (15) as the catalytic species
[10, 11, 18, 27].
R
R
R’
R’
NHAr
ArN3, -N2
a)
b)
c)
Ar'
Ar'
H
3
allylic amination
NHAr
ArN3, -N2
3
aziridination
ArN3, -N2
Ph
Ph
N
Ar
3
In view of the observed similarity between the catalytic
behavior of complexes [RuIV(TPP)(OCH3)]2O (3) and
RuII(TPP)(CO) (15), we reacted m-oxo derivatives 2 and
Scheme 1. Nitrene transfer reactions catalysed by complex 3
Table 1. Synthesis of aza-derivatives 4–14 catalysed by [RuIV(TPP)(OCH3)]2O (3)a
Reagent Product Ar
T, hb
Entry
1
Yield, %c
65
3,5(CF3)2C6H3, 4
0.5
2
3
3,5(CF3)2C6H3, 5
3,5(CF3)2C6H3, 6
1.5
5.5
55
80
4
3,5(CF3)2C6H3, 7
2
65
5
3,5(CF3)2C6H3, 8
3,5(CF3)2C6H3, 9
1.5
6
90
44
6d
7d
3,5(CF3)2C6H3, 10
5
70
3,5(CF3)2C6H3, 11
4(tBu)C6H4, 12
0.75
3
65
60
20
8e
9f
4(OCH3)C6H4, 13
1.5
3,5(CF3)2C6H3, 14
0.1
99
a Catalyst 3 (2.6 × 10-5 mol, 1.0% with respect to ArN3) in 25.0 mL of refluxing substrate. b Time required
for the complete azide conversion monitored by IR spectroscopy. c Determined by 1H NMR spectroscopy
(2,4-dinitrotoluene as the internal standard). d Catalytic ratio 3 (2.6 × 10-4 mol)/azide/substrate = 1:10:250
e
in 25.0 mL of refluxing benzene. Catalytic ratio 3 (5.2 × 10-5 mol)/azide/substrate = 1:50:250 in
25.0 mL of refluxing benzene. f Catalytic ratio 3 (2.6 × 10-5 mol)/azide/substrate = 1:100:250 in 25.0 mL
of refluxing benzene.
Copyright © 2016 World Scientific Publishing Company
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4
P. ZARDI ET AL.
OMe
RuIV
mCB
RuIV
O
1
2
3
4
5
6
7
8
9
complexes which cannot be obtained by directly reacting
ruthenium(II) porphyrin derivatives with aryl azides. As
already reported [10, 17], this synthetic strategy was
effective by using electron poor aryl azides as the starting
material whereas bis-imido complexes were not obtained
when electron rich aryl azides were employed. This
can be due to the reaction of the initially formed mono-
imido RuIV(porphyrin)(ArN)CO with traces of water to
yield RuII(porphyrin)(ArNH2)CO. This decomposition
pathway was previously observed in the reaction between
RuII(TPP)CO and 4-tert-butylphenyl azide (4-tBuC6H4N3)
which formed RuII(TPP)(4-tBuC6H4NH2)CO (17) in
good yields (Scheme 3) [10]. Analytical data of 17 were
in accord with those of the compound synthesised by
directly reacting Ru(TPP)CO (15) with 4-tBuC6H4NH2.
The replacement of RuII(TPP)CO (15) by [RuIV(TPP)
(OCH3)]2O (3) in the reaction with 4-tBuC6H4N3 afforded
complex RuVI(TPP)(4-tBuC6H4N)2 (18) to suggest an
important effect of the metal oxidation state of the starting
ruthenium complexes in the reaction with aryl azides.
It can be suggested that the reaction between 3 and
4-tBuC6H4N3 followed a different pathway during
which the unstable ruthenium(IV) mono-imido complex
was not formed and consequently the decomposition
process leading to 17 was avoided. Complex 18 was
fully characterised and its reactivity was tested in both
stoichiometric nitrene transfer and catalytic reactions by
using cyclohexene as the substrate. In both cases complex
18 was completely inactive to indicate that the reactivity
of nitrene functionalities is strongly related to the electron
density on ruthenium-imido functionality which in turn
depends on the electronic nature of substituents onto
the “ArN” moiety as proposed by a previous theoretical
study [19].
1
2
3
4
5
6
7
8
NAr
+ ArN3
+ ArN3
-N2
O
RuVI
X
-N2
RuIV
OMe
(3)
RuIV
mCB
(2)
NAr
(16)
+ ArN3
- N2
9
= TPP
RuII
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
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37
38
39
40
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42
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44
45
46
47
48
49
50
51
52
53
54
55
56
57
Ar = 3,5(CF3)2C6H3
CO
(15)
Scheme 2. Stoichiometric reaction of complexes 2 and 3 with
3,5-bis(trifluoromethyl)phenyl azide
3 with a slight excess of 3,5-bis(trifluoromethyl)phenyl
azide (Ru/azide =1:3) in order to discover the nature of
catalytic intermediates and to investigate whether similar
or different mechanistic pathways are involved when
ruthenium(IV) catalysts are used instead of ruthenium(II)
complexes.
Complex 2 did not react with 3,5-bis(trifluoromethyl)
phenyl azide even under light irradiation, whilst 3 was
converted into the bis-imido RuVI(TPP)(3,5-(CF3)2C6H3N)2
(16) after 4 h (Scheme 2). As already reported [10, 17],
complex 16 can be also obtained from the stoichiome-
tric reaction of complex Ru(TPP)CO (15) with 3,5-bis-
(trifluoromethyl)phenyl azide.
These results suggested that the formation of bis-imido
ruthenium(VI) active species was independent from the
oxidation state of the starting ruthenium complex which
can be considered a pre-catalyst of the amination reaction.
Achieved data also explain the catalytic inactivity shown by
complex 2 in the amination of cumene, it did not react with
the involved azide and consequently it was not converted
into the catalytically active ruthenium(VI) intermediate.
Given the reactivity of complex 3 towards azides,
it was investigated for the synthesis of bis-imido
In order to expand the reaction scope, complex 3 was
reacted with a stoichiometric amount of tosyl azide,
adamantyl azide and benzyl azide. In the first two
cases no reaction occurred, whilst in the last case the
reaction achieved unidentified products. When complex
3 was reacted with organic azides (RN3) displaying a
good R leaving group for electrophilic substitutions
NH2Ar
NAr
+ ArN3
+ ArNH2
[H]
RuII
RuII
RuII
RuIV
-N2
CO
CO
CO
CO
(15)
(17)
(15)
OMe
RuIV
NAr
+ ArN3
O
RuVI
NAr
= TPP
-N2
RuIV
Ar = 4-tBuC6H4
(18)
OMe
(3)
Scheme 3. Synthesis of complexes 17 and 18
Copyright © 2016 World Scientific Publishing Company
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SYNTHESIS AND CATALYTIC ACTIVITY OF m-OXO RUTHENIUM(IV) PORPHYRIN SPECIES
5
1
1
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2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
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12
13
14
15
16
17
18
19
20
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10
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Scheme 4. Synthesis and 1H NMR spectrum of complex 19
Fig. 2. Top and side view of the molecular structure of 19.Atomic displacement parameters are shown as ellipsoids at 50% probability
level. Ru atoms are in green, O atom is in red, N atoms are in blue, C atoms are in dark grey and H atoms in light grey. For sake of
clarity, the disorder of azido group has been removed and only the dominant orientation of each group is shown
(R = trityl or trimethylsilyl) a new m-oxo dimer
complex [RuIV(TPP)(N3)]2O (19) was obtained at room
temperature (Scheme 4).
Compound 19 was completely characterised and a
slow diffusion of a CHCl3 solution of [Ru(TPP)(N3)]2O
into n-hexane gave crystals suitable for the molecular
structure determination by X-ray diffraction analysis
(Fig. 2, Table 2).
The crystal has a monoclinic P21/n space group,
with one independent molecule in the asymmetric unit
and therefore four molecules in the unit cell. At least
one molecule of the crystallization solvent is localised
(although refined with a disordered model). A rather large
void volume (780 Å3 per unit cell) indicates that very
likely other solvent molecules (3 per asymmetric unit)
may be present, but their disorder is so strong that they
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J. Porphyrins Phthalocyanines 2016; 20: 5–10

6
P. ZARDI ET AL.
Table 2. Crystal data and structure refinement for 19
Empirical formula
C88H56N14ORu2 . CHCl3
1646.96
Formula weight
Temperature
173(2) K
Wavelength
0.71069 Å
Crystal system
Space group
Monoclinic
P 21/n
Unit cell dimensions
a = 13.89880 (10) Å
b = 31.9489 (3) Å
c = 18.4576 (2) Å
7815.79 (13) Å3
4
a = 90°.
b = 107.5230 (10)°.
g = 90°.
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
1.399 Mg/m3
0.547 mm-1
3340
Crystal size
0.3 × 0.2 × 0.1 mm3
Theta range for data collection
Index ranges
1.621 to 25.347°.
-16←h←16, -38←k←38, -22←l←22
58274
Reflections collected
Independent reflections
14312 [R(int) = 0.0336]
Completeness to theta = 25.000° 100.0%
Refinement method
Full-matrix least-squares on F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
14312/72/1031
1.041
R1 = 0.0663, wR2 = 0.1932
R1 = 0.0754, wR2 = 0.2030
5.011 and -1.593 e.Å-3
Largest diff. peak and hole
cannot be easily localised even analysing the residual
electron density. The molecular structure of 19 (see Fig. 2)
is dominated by the sandwich-like aggregation of the two
porphyrins that trap the O atoms exactly in the middle
between the two Ru atoms (1.796(3) and 1.798(3) Å for
O12-Ru1 and O12-Ru2, respectively). The two average
planes are almost exactly parallel to each other, although
the porphyrin skeletons are not exactly flat. Moreover, the
phenyl substituents clearly produce large steric hindrance
andtheyhaveaconformationtiltedby50–65°withrespect
to the porphyrin planes. Repulsions between atoms of
the two porphyrin skeletons and repulsion between the
phenyl rings of the two porphyrins, induce a staggered-
like conformation by making the two porphyrins rotated
by ca. 28° with respect to the Ru–Ru axis. This feature is
rather common in M–M bonded di-porphyrin complexes
with the only exception of (TPP)Mo-Re(OEP), featuring
a quadruple M–M bond [28], which is perfectly eclipsed.
For systems like 19, with a bridging atom making the
porphyrin–porphyrin distance larger, the staggered
conformation is still the most common, although many
eclipsed structures are also known. On each Ru atom,
trans to the bridging O, an azide group is coordinated.
The potential around this ligand is rather flat, producing a
large dynamic disorder that could not be eliminated even
with a data collection at low temperature. Each azide has
at least two orientations (only the major component is
shown in Fig. 2), anyway the coordination to Ru features
the classical bent mode: Ru–N–N angles are 126.7(4) and
121.2(10)° for the main orientations of azide at Ru(1) and
Ru(2), respectively. This is in keeping with the average
values known for Ru-azido complexes. The Ru–N bonds
are instead somewhat shorter than the average values
from the literature for RuIV–N3 bonds (2.05 vs. 2.13 Å),
which could reflect the large atomic motion. The N–N
distances of the azides are even more affected by the
orientational disorder and the large thermal motion,
therefore their accuracy is lower and does not allow
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SYNTHESIS AND CATALYTIC ACTIVITY OF m-OXO RUTHENIUM(IV) PORPHYRIN SPECIES
7
precise comparisons with other structures. The bonds
of the porphyrin skeleton to Ru atoms are perfectly
matching the standard values (2.05 Å).
(trifluoromethyl)aniline (11) [10]; 4-(tert-butyl)-N-
(cyclohex-2-en-1-yl)aniline (12) [10]; N-(cyclohex-
2-en-1-yl)-4-methoxyaniline (13) [10]; 2-methyl-1-
(4-nitrophenyl)-2-phenylaziridine (14) [34] were in
agreement with those reported in literature.
EXPERIMENTAL
Synthesis
General
Synthesis of [RuIV(TPP)(mCB)]2O (2). Complex
1 (102 mg, 1.32 × 10-4 mol) was suspended in CH2Cl2
(20 mL) and a solution of mCPBA (123 mg, 7.13 ×
10-4 mol) in CH2Cl2 (25 mL) was added dropwise in
30 min and in air. The initial red suspension turned into a
dark red solution. The reaction was stirred for 1.5 h and
the TLC analysis (Al2O3, CH2Cl2) revealed the presence
of unreacted complex 1.An additional amount of mCPBA
(52 mg, 3.0 × 10-4 mol) was added and the solution was
stirred for 3 h. TLC and IR analyses (nujol, nC=O of
1 at 1939 cm-1) showed the complete consumption of
starting 1. The solution was concentrated to about 20 mL
and filtered through a short (5 cm) alumina column.
The product fraction was evaporated to dryness and the
resulting dark solid was dried in vacuo (47 mg, 39%). 1H
NMR (300 MHz, CDCl3): d, ppm 8.96 (8H, d, J = 7.6 Hz,
Ho), 8.67 (16H, s, Hb), 7.98 (8H, t, J = 7.2 Hz, Hm), 7.82
(8H, t, J = 7.5 Hz, Hp), 7.50 (8H, t, J = 7.6 Hz, Hm′), 7.25
(8H, overlaps with chloroform signal, Ho′), 6.14 (2H, d,
J = 7.9 Hz, H3), 5.66 (2H, t, J = 7.8 Hz, H2), 3.54 (2H, d, J =
7.8 Hz, H1), 2.74 (2H, s, H4). 13C NMR (75 MHz, CDCl3):
d, ppm 142.1 (Ca), 141.3 (C–Cmeso), 136.2 (CHo′), 135.0
(CHo), 131.6 (CHb), 128.9 (C–H3), 127.9 (CHp), 126.9
(CHm′), 126.8 (C–H2), 126.6 (CHm), 126.1 (C–H4), 124.2
(C–H1), 121.1. The Cmeso, C–Cl, carbonyl and C–COO–
Unless otherwise specified, all the reactions were
carried out in a nitrogen atmosphere employing
standard Schlenk techniques and magnetic stirring.
Toluene, n-hexane and benzene were dried by
M. Braun SPS-800 solvent purification system. THF,
a-methylstyrene, cyclohexene, cumene and decalin over
sodium and stored under nitrogen. 1,2-Dichloroethane
and CH2Cl2 were distilled over CaH2 and immediately
used. Commercial mCPBA (77%) was purified using
a reported procedure [29] and stored at -20°C. Aryl
azides [27, 30], [RuII(TPP)(CO)(CH3OH)] (1) [31],
[RuIV(TPP)(OCH3)2]O (3) [21], RuII(TPP)CO (15)
[22] and RuVI(TPP)(3,5-(CF3)2C6H3N)2 (16) [17] were
synthesised by methods reported in the literature or
using minor modifications. The purity of hydrocarbons
and aryl azides employed was checked by GC-MS
1
or H NMR analysis. All the other starting materials
were commercial products used as received. NMR
spectra were recorded at room temperature, unless
otherwise specified, on a Bruker avance 300-DRX,
1
13
operating at 300 MHz for H, at 75 MHz for C and at
282 MHz for 19F. Chemical shifts (ppm) are reported
relative to TMS. The 1H NMR signals of the compounds
described in the following have been attributed by
COSY and NOESY techniques. Assignments of the
resonances in 13C NMR were made using the APT pulse
sequence and HSQC and HMBC techniques. GC-MS
analyses were performed on a Shimadzu QP5050A
equipped with Supelco SLB -5 ms capillary column (L
30 m × I.D. 0.25 mm × 0.25 mm film thickness). GC
analyses were performed on a Shimadzu GC -2010
equipped with a Supelco SLB -5ms capillary column
(L 10 m × I.D. 0.1 mm × 0.1 mm film thickness).
Infrared spectra were recorded on a Varian Scimitar
FTS 1000 spectrophotometer. UV-vis spectra were
recorded on an Agilent 8453E instrument. Elemental
analyses and mass spectra were recorded in the
analytical laboratories of Milan University. The collec-
ted analytical data for N-(2-phenylpropan-2-yl)-3,5-
bis(trifluoromethyl)aniline(4) [11]; N-phenyl-3,5-
bis(trifluoromethyl)aniline (5) [11]; N-(1-phenylethyl)-
3,5-bis(trifluoromethyl)aniline (6) [32]; N-(2-methyl-1-
phenylpropyl)-3,5-bis(trifluoromethyl)aniline (7) [17];
N-(3,5-bis(trifluoromethyl)phenyl)-2,3-dihydro-1H-
inden-1-amine (8) [11]; methyl 2-((3,5-bis-(trifluo-
romethyl)phenyl)amino)-2-phenylacetate (9)[33];methyl
3-((3,5-bis(trifluoromethyl)phenyl)amino)-3-phenyl-
propanoate (10) [33]; N-(cyclohex-2-en-1-yl)-3,5-bis
Ru signals were not detected. UV-vis (CH2Cl2): lmax
,
nm (log e) 392 (5.42), 522 (4.24), 591 (4.25), 527 (sh).
IR (ATR): n, cm-1 1735 (nC=O), 1014 (oxidation marker
band). Elemental analysis calcd. for C102H64Cl2N8O5Ru2
C, 69.82; H, 3.68; N, 6.39. Found C, 69.54; H, 3.42; N,
6.05. MS (ESI+): m/z 1599 [M – 155(mCB)]+.
Synthesis of RuII(TPP)(4-tBuC6H4NH2)CO (17).
The amine 4-tBuC6H4NH2 (97.6 μL, 6.13 × 10-4 mol) was
added to a benzene (90 mL) suspension of Ru(TPP)CO
(15) (150 mg, 2.02 × 10-4 mol). The resulting red solution
was stirred at room temperature for 30 min, concentrated
to 2 mL and n-hexane (20 mL) was added. The resulting
red solid was collected by filtration and dried in vacuo
(155 mg, 86%). 1H NMR (300 MHz, C6D6): d, ppm 8.83
(8H, s, Hb), 8.23 (4H, d, J = 8.0 Hz, Ho), 8.04 (4H, d, J =
8.0 Hz, Ho’), 7.52 (8H, Hm+p), 7.40 (4H, Hm’), 5.29 (2H, d,
J = 8.7 Hz, HAr), 2.41 (2H, d, J = 8.7 Hz, HAr), 0.89 (9H, s,
HtBu). 13C NMR (75 MHz, C6D6): d, ppm 144.6 (C), 143.0
(C), 135.1 (CH), 134.3 (CH), 132.5 (CH), 127.8 (CH),
126.6 (CH), 123.8 (CH). UV-vis (CH2Cl2): lmax, nm (log e)
413 (5.32), 532 (4.18). IR (ATR): n, cm-1 1948 (nC=O),
1008 (oxidation marker band). Elemental analysis calcd.
for C55H43N5ORu C, 74.14; H, 4.86; N, 7.86. Found C,
74.35; H, 4.95; N, 7.60. MS (ESI+): m/z 892.6 [M + 1].
Copyright © 2016 World Scientific Publishing Company
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P. ZARDI ET AL.
Synthesis of RuVI(TPP)(4-tBuC6H4N)2 (18). The
azide 4-tBuC6H4N3 (32 mg, 1.8 × 10-4 mol) was added to
a benzene (35 mL) solution of complex 3 (42.0 mg, 2.8 ×
10-5 mol). The resulting dark mixture was refluxed for
8 h till the complete consumption of the organic azide
(IR monitoring nN=N = 2124–2092 cm-1). The solution was
concentrated to 5 mL and n-hexane (15 mL) was added.
By cooling the solution in an ice bath, the formation of a
violet precipitate was observed. The dark violet solid was
collected by filtration and dried in vacuo. (55% yield).
1H NMR (300 MHz, C6D6): d, ppm 8.93 (8H, s, Hb), 8.12
(8H, m, HPh-ortho), 7.47 (12H, m, HPh-meta and -para), 5.78 (4H, d,
J = 8.7 Hz, HAr-meta), 2.77 (4H, d, J = 8.7 Hz, HAr-ortho), 0.64
(9H,s,HtBu).13CNMR(100MHz,C6D6):d,ppm143.0(Ca),
134.7 (CHPh-ortho), 131.6 (CHb), 126.7 (CHPh-meta and -para),
123.1 (CH HAr-meta), 119.1 (CHAr-ortho), 30.75 (CHtBu).
A little amount of the complex decomposed during the
carbon spectrum acquisition, five quaternary carbons
were not detected. UV-vis (CH2Cl2): lmax, nm (log e) 39
(4.59), 532 (3.66). IR (ATR): n, cm-1 2954 (nC–H), 1012
(oxidation marker band). Elemental analysis calcd. for
C64H54N6Ru C, 76.24; H, 5.40; N, 8.34. Found C, 76.55;
H, 5.62; N, 8.11. MS (ESI+): m/z 1009.2 [M + 1].
General procedure for catalytic reactions
Method A. In a typical run, complex 3 (39.0 mg,
2.60 × 10-5 mol) and the opportune amount of azide
were dissolved into the desired hydrocarbon substrate
(25 mL). The reaction solution was then heated to reflux
by using a preheated oil bath. The consumption of the
azide was monitored by TLC up to the point that its spot
was no longer observable, and then by IR spectroscopy
measuring the characteristic azide absorbance in the
region 2095–2130 cm-1. The reaction was considered to
be finished when the absorbance of the latter peak was
below 0.03 (using a 0.5 mm thick cell). The solution was
then concentrated to dryness and the residue was purified
by flash chromatography using n-hexane/ethyl acetate =
1
9:1 as the eluent mixture or analysed by H NMR with
2,4-dinitrotoluene as the internal standard. All reaction
times and products yields are reported in Table 1.
Method B. In a typical run, compound 3 (39.0 mg,
2.60 × 10-5 mol) and the opportune amount of azide and
hydrocarbon were dissolved in benzene (25 mL). The
solution was then heated to reflux by using a preheated
oil bath. The consumption of the azide was monitored
by TLC until its spot was no longer observable, and then
by IR spectroscopy measuring the characteristic azide
absorbance in the region 2095–2130 cm-1. The reaction
was considered to be finished when the absorbance of
the latter peak was below 0.03 (using a 0.5 mm thick
cell). The solution was then concentrated to dryness
and the residue was purified by flash chromatography
using n-hexane/ethyl acetate = 9:1 as the eluent mixture
Synthesis of [RuIV(TPP)(N3)]2O (19). Method A.
[RuIV(TPP)(OMe)]2O (3) (102 mg, 6.77 × 10-5 mol)
was dissolved in benzene (20 mL) and trimethylsilyl
azide was added (36 ml, 2.7 × 10-4 mol). The solution
immediately turned form dark red to dark green, the
mixture was stirred for 1 h at RT and monitored by TLC
and IR analyses. The solution was evaporated to dryness
and n-hexane (10 mL) was added to the residue. The
resulting dark violet solid was collected by filtration
and washed with n-hexane (10 mL) (90 mg, 87%).
Method B. [Ru(TPP)(OMe)]2O (3) (108 mg, 7.17 ×
10-5 mol) was dissolved in benzene (30 mL) and
trityl azide was added (217 mg, 7.60 × 10-4 mol). The
solution was heated to reflux for 4 h and the reaction
was monitored by TLC and IR analyses. The solution
was evaporated to dryness, the crude was washed with
n-hexane (2 × 30 mL) and purified by chromatography
(Al2O3, n-hexane/CH2Cl2 = 6:4). A dark violet solid was
obtained (46 mg, 41%). 1H NMR (300 MHz, CDCl3): d,
ppm 8.87 (8H, d, J = 7.6 Hz, Ho), 8.65 (16H, s, Hb), 7.97
(8H, t, J = 7.6 Hz, Hm), 7.84 (8H, t, J = 7.5 Hz, Hp), 7.56
(8H, t, J = 7.5 Hz, Hm’), 7.43 (8H, d, J = 7.6 Hz, Ho’).
13C NMR (75 MHz, CDCl3): d, ppm 141.69 (Ca), 141.22
(C-Cmeso), 136.27 (CHo’), 135.41 (CHo), 131.78 (CHb),
127.97 (CHp), 127.00 (CHm’), 126.62 (CHm), 120.83
(Cmeso). UV-vis (CH2Cl2): lmax, nm (log e) 280 (4.43),
393 (5.46), 554 (4.18), 592 (4.21). IR (ATR): n, cm-1
2023 (nN=N), 1012 (oxidation marker band). Elemental
analysis calcd. for C88H56N14ORu2 C, 69.19; H, 3.69;
N, 12.84; O, 1.05; Ru, 13.23. Found C, 69.31; H,
3.55; N, 12.47. MS (ESI-): m/z 1529.0 [M + 1]. X-ray
quality crystals were obtained by slow diffusion of a
CHCl3 solution of [Ru(TPP)(N3)]2O into n-hexane (see
Table 2 and SI).
1
or analysed by H NMR with 2,4-dinitrotoluene as the
internal standard. All reaction times and products yields
are reported in Table 1.
Single crystal X-ray diffraction
of [RuIV(TPP)(N3)]2O (19)
A crystal of species 19, was mounted in air and used
for X-ray structure determination. All measurements
were made on a Rigaku Oxford Diffraction SuperNova
area-detector diffractometer using mirror optics
monochromated Mo Ka radiation (l = 0.71073 Å) and
Al filtered [35]. The unit cell constants and an orientation
matrix for data collection were obtained from a least-
squares refinement of the setting angles of reflections in
the range 1.6° < q < 25.2°. A total of 554 frames were
collected using w scans, with 15 + 15 s exposure time,
a rotation angle of 1.0° per frame, a crystal-detector
distance of 65.1 mm, at T = 173(2) K. Data reduction
was performed using the CrysAlisPro program [36]. The
intensities were corrected for Lorentz and polarization
effects, and an absorption correction based on the multi-
scan method using SCALE3 ABSPACK in CrysAlisPro
was applied. Data collection and refinement parameters
are given in Table 2.
The structure was solved by direct methods using
SHELXS-97 [37], which revealed the positions of all
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SYNTHESIS AND CATALYTIC ACTIVITY OF m-OXO RUTHENIUM(IV) PORPHYRIN SPECIES
9
non-hydrogen atoms of the title compound. The non-
4. Collet F, Lescot C and Dauban P. Chem. Soc. Rev.
2011; 40: 1926–1936.
5. Chang JWW, Ton TMU and Chan PWH. Chem.
Rec. 2011; 11: 331–357.
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100–105.
7. Intrieri D, Zardi P, Caselli A and Gallo E. Chem.
Commun. 2014; 50: 11440–11453.
hydrogen atoms were refined anisotropically.All H-atoms
were placed in geometrically calculated positions and
refined using a riding model where each H-atom was
assigned a fixed isotropic displacement parameter with a
value equal to 1.2Ueq of its parent atom.
Refinement of the structure was carried out on F2 using
full-matrix least-squares procedures, which minimised
the function Sw(Fo2 – Fc2)2. The weighting scheme was
based on counting statistics and included a factor to
downweight the intense reflections. All calculations were
performed using the SHELXL-97 program.
8. Tseberlidis G, Zardi P, Caselli A, Cancogni D,
Fusari M, Lay L and Gallo E. Organometallics
2015; 34: 3774–3781.
9. Intrieri D, Mariani M, Caselli A, Ragaini F and
Gallo E. Chem. Eur. J. 2012; 18: 10487–10490.
10. Intrieri D, Caselli A, Ragaini F, Macchi P, Casati N
and Gallo E. Eur. J. Inorg. Chem. 2012; 569–580.
11. Intrieri D, Caselli A, Ragaini F, Cenini S and
Gallo E. J. Porphyrins Phthalocyanines 2010; 14:
732–740.
12. Manca G, Mealli C, Carminati DM, Intrieri D and
Gallo E. Eur. J. Inorg. Chem. 2015; 4885–4893.
13. Chan K-H, Guan X, LoVK-Y and Che C-M. Angew.
Chem. Int. Ed. 2014; 53: 2982–2987.
14. Xiao W, Wei J, Zhou C-Y and Che C-M. Chem.
Commun. 2013; 49: 4619–4621.
15. Xiao W, Zhou C-Y and Che C-M. Chem. Commun.
2012; 48: 5871–5873.
16. Guo Z, Guan X, Huang J-S, Tsui W-M, Lin Z and
Che C-M. Chem. Eur. J. 2013; 19: 11320–11331.
17. Fantauzzi S, Gallo E, Caselli A, Ragaini F, Casati
N, Macchi P and Cenini S. Chem. Commun. 2009;
3952–3954.
18. Zardi P, Pozzoli A, Ferretti F, Manca G, Mealli C
and Gallo E. Dalton Trans. 2015; 44: 10479–10489.
19. Manca G, Gallo E, Intrieri D and Mealli C. ACS
Catal. 2014; 823–832.
CONCLUSION
This work deals with the synthesis of m-oxo dimeric
ruthenium(IV) porphyrin species to investigate their
catalytic efficiency in amination reactions by using aryl
azides as nitrogen sources. Recorded data were compared
to those achieved by using ruthenium(II) porphyrins in
order to study the effect of the metal oxidation state on the
catalytic performance of ruthenium porphyrin species.
Similar catalytic results were achieved to indicate the
probable formation of same active intermediates during
the amination and in fact, the study of the reactivity of
ruthenium(IV) species towards aryl azides disclosed the
formation in both cases of a bis-imido ruthenium(VI)
intermediate which is responsible for the nitrene transfer
reaction. The stoichiometric reaction between [RuIV(TPP)
(OCH3)]2O (3) and 4-tBuC6H4N3 or RN3 (R = Ph3C or
(CH3)3Si) afforded RuVI(TPP)(4-tBuC6H4N)2 (18) and
[RuIV(TPP)(N3)]2O (19) respectively. Both complexes
were fully characterised and the molecular structure of
complex 19 was determinated by X-ray single crystal
diffraction.
20. Au S-M, Huang J-S, Yu W-Y, Fung W-H and Che
C-M. J. Am. Chem. Soc. 1999; 121: 9120–9132.
21. Collman JP, Barnes CE, Brothers PJ, Collins TJ,
Ozawa T, Gallucci JC and Ibers JA. J. Am. Chem.
Soc. 1984; 106: 5151–5163.
22. Gallo E, Caselli A, Ragaini F, Fantauzzi S, Mascioc-
chi N, Sironi A and Cenini S. Inorg. Chem. 2005; 44:
2039–2049.
23. Groves JT and Quinn R. Inorg. Chem. 1984; 23:
3844–3846.
24. Masuda H, Taga T, Osaki K, Sugimoto H, Mori M and
Ogoshi H. J. Am. Chem. Soc. 1981; 103: 2199–2203.
25. Vanover E, HuangY, Xu L, Newcomb M and Zhang
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Supporting information
Table S1 is given in the supplementary material. This
material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Center (CCDC) under
numberCCDC-1450326. Copiescanbeobtainedonrequest,
free of charge, via www.ccdc.cam.ac.uk/data_request/cif
or from the Cambridge Crystallographic Data Center, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223-
336-033 or email: data_request@ccdc.cam.ac.uk).
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