Insights into the mechanism of the ruthenium-porphyrin-catalysed allylic amination of olefins by aryl azides

Article abstract of DOI:10.1002/ejic.201100763

This paper describes the synthesis of allylic amines by aryl azides (ArN₃) catalysed by [Ru(TPP)CO] (TPP = dianion of tetraphenylporphyrin). The employment of aryl azides renders the methodology sustainable as the formation of molecular nitrogen is the only stoichiometric byproduct. The isolation of catalytic intermediates and spectroscopic and kinetic studies revealed interesting information about the reaction mechanism, which could improve its catalytic efficiency in future research. An important result is the X-ray characterisation of [Ru(TPP)(ArN)₂] [Ar = 3,5-(CF₃)₂C₆H₃], which is active in both stoichiometric and catalytic nitrene transfer reactions. The proposed involvement of carbonyl-monoimido-ruthenium porphyrin complexes in the catalytic cycle is also derived from our kinetic and experimental results. All the data indicate the coexistence of two mechanisms, where the electronic nature of the engaged aryl azide and olefin concentration determine one mechanism or the other. Copyright

Full text of DOI:10.1002/ejic.201100763

FULL PAPER
DOI: 10.1002/ejic.201100763
Insights into the Mechanism of the Ruthenium–Porphyrin-Catalysed Allylic
Amination of Olefins by Aryl Azides
Daniela Intrieri,[a] Alessandro Caselli,[a] Fabio Ragaini,[a] Piero Macchi,[b] Nicola Casati,[c]
and Emma Gallo*[a]
Keywords: Amination / C–H activation / Azides / Metalloporphyrins / Porphyrinoids / Homogeneous catalysis
This paper describes the synthesis of allylic amines by aryl
azides (ArN3) catalysed by [Ru(TPP)CO] (TPP = dianion of
tetraphenylporphyrin). The employment of aryl azides ren-
ders the methodology sustainable as the formation of molec-
ular nitrogen is the only stoichiometric byproduct. The isola-
tion of catalytic intermediates and spectroscopic and kinetic
studies revealed interesting information about the reaction
mechanism, which could improve its catalytic efficiency in
future research. An important result is the X-ray characteri-
sation of [Ru(TPP)(ArN)2] [Ar = 3,5-(CF3)2C6H3], which is
active in both stoichiometric and catalytic nitrene transfer re-
actions. The proposed involvement of carbonyl-monoimido-
ruthenium porphyrin complexes in the catalytic cycle is also
derived from our kinetic and experimental results. All the
data indicate the coexistence of two mechanisms, where the
electronic nature of the engaged aryl azide and olefin con-
centration determine one mechanism or the other.
In view of the potential of porphyrin-based methodolo-
gies to transfer a nitrene moiety to a C–H bond, the com-
Introduction
The insertion of a nitrene “RN” functionality into a C– prehension of reaction mechanisms is crucial to plan new
H bond represents a valuable tool to achieve a wide variety and more efficient catalytic systems in future. To date, some
of nitrogen-containing fine chemicals, which frequently studies have been published on the mechanism of por-
present pharmaceutical and/or biological properties.[1–6] phyrin-catalysed C–H amination,[21,22] and imido com-
Among the nitrogen sources available to perform amination plexes of high-valent metals have often been suggested as
reactions, organic azides (RN3) occupy a prominent role. key intermediates.[23–26]
The activation of an organic azide by a transition-metal cat-
alyst yields the reactive fragment “RN” with N2 as the only
stoichiometric byproduct. The generation of ecofriendly
molecular nitrogen renders the process sustainable and
atom efficient.[7–9] It is worth noting that the reaction of
saturated hydrocarbons with organic azides, which is re-
sponsible for the direct transformation of a C–H into a C–
N bond, is considered as a domain of high impact and ex-
treme synthetic utility. Amongst the transition metal com-
plexes employed as catalysts[4,10–12] for both intra- and
intermolecular C–H aminations, metalloporphyrins[13–20]
exhibit a very good catalytic activity and selectivity.
Several years ago, we investigated the catalytic activity of
porphyrinatocobalt complexes in the amination of benzylic
substrates[27,28] by aryl azides, which were easily synthesised
from commercially available anilines and showed a conve-
nient reactivity–stability relationship. Since then, we have
widely used aryl azides as nitrogen sources in aziridin-
ations[29–32] and aminations[33,34] in the presence of por-
phyrinato-cobalt or -ruthenium complexes. Our kinetic and
spectroscopic studies suggested that the benzylic and allylic
aminations mediated by cobalt– porphyrins occur through
the formation of an azido adduct intermediate.[28,33] Zhang
and de Bruin et al.[35] have proposed, on the basis of DFT
and electron paramagnetic resonance studies, that the azido
adduct evolves into a radical nitrene intermediate before
reacting with the hydrocarbon substrate. On the other hand,
our data on porphyrinatoruthenium(II)-mediated C–H
aminations by aryl azides[34,36] envisages the formation of
ruthenium imido complexes as active intermediates, which
is in accord with that proposed by Che et al.[23–26]
[a] Dipartimento di Chimica Inorganica, Metallorganica e
Analitica, Università di Milano, and ISTM-CNR,
via Venezian 21, 20133 Milano, Italy
Fax: +39-02-50314405
E-mail: emma.gallo@unimi.it
[b] Department of Chemistry & Biochemistry, University of Berne,
Freiestrasse 3, 3012 Berne, Switzerland
[c] Diamond Light Source Ltd., Harwell Science and Innovation
Campus,
This report deals with a mechanistic study of allylic amin-
ations by aryl azides catalysed by ruthenium porphyrin
complexes. A catalytic cycle was proposed on the basis of
kinetic and spectroscopic investigations. The isolation and
characterisation of several compounds involved in the cata-
Chilton OX11 0DE, UK
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100763 or from
the author.
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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E. Gallo et al.
FULL PAPER
lytic cycle shed light on the nitrene transfer reaction. A pre- Table 1. The [Ru(TPP)CO]-mediated allylic amination by ArN3.[a]
liminary communication on the subject has recently been
published.[36]
Results and Discussion
Synthetic Studies
Our recent study on the [Ru(TPP)CO]-mediated (TPP =
dianion of tetraphenyl porphyrin) amination of benzylic
substrates by aryl azides[34] prompted us to examine the
amination of allylic substrates. The scope of the reaction
reported in Scheme 1 was investigated by employing dif-
ferent allylic substrates and aryl azides (Table 1).
Scheme 1. Amination of allylic substrates catalysed by [Ru(TPP)
CO].
The synthesis of allylic amines reported in Table 1 was
firstly performed in benzene, employing the molar ratio
[Ru(TPP)CO]/ArN3/olefin = 1:50:250, and secondly with
the neat olefin as the solvent. Data reported in Table 1 indi-
cate that better yields are generally obtained by using the
latter methodology. In particular, very high yields were
achieved in olefin for the allylic amination of cyclohexene
by almost every azide (Table 1, Run 1). The low yield ob-
served in the reaction of 4-OMeC6H4N3 with cyclohexene
(Run 1, 1h) is probably due to the coordination of the meth-
oxy group to the ruthenium atom, which can partially in-
hibit the catalysis.[30] The reduced chemoselectivity of the
amination of 1,2-dihydronaphthalene was because of the
contemporaneous presence of both allylic and benzylic
[a] General procedure for catalytic reactions: [Ru(TPP)CO] (10 mg,
functionalities (Run 3).[34] The amination of 1-octene oc-
1.34ϫ10–2 mmol) in benzene (30 mL) heated to reflux; molar ratio
1
curred only by a small extent because of its poor reactivity
(Run 6). In all the reactions tested, the secondary products
recovered were the aryl diazene and aniline corresponding
to the azide employed.
catalyst/ArN3/olefin = 1:50:250. [b] Determined by H NMR (2,4-
dinitrotoluene as the internal standard). [c] Time required to reach
complete conversion of the starting ArN3. [d] Reaction carried out
in neat olefin heated to reflux.
In the belief that an important step for the improvement
of the catalytic efficiency of the reported methodology is a
comprehension of the reaction mechanism, we first studied
the catalytic reactivity towards the components of a model
reaction, cyclohexene and 3,5-(CF3)2C6H3N3. No catalyst
1
modification was observed by H NMR when [Ru(TPP)-
CO] was suspended in cyclohexene and heated to reflux for
several hours. However, the reaction between [Ru(TPP)CO]
and an excess of AraN3 (3 equiv.) [Ara = 3,5-(CF3)2C6H3]
Scheme 2. Synthesis of 7.
yielded the bisimido complex [Ru(TPP)(NAra)2] (7) in 70% rapidly disproportionate to the bisimido 7 and [Ru(TPP)-
yield (Scheme 2).
CO], analogous to that proposed for isostructural rutheni-
It is likely that 7 derives from the reaction of the mono- um(IV) oxo porphyrins.[37,38]
imido [RuIV(TPP)(AraN)CO] complex with another mole-
Complex 7 was fully characterised. It remained stable for
cule of aryl azide. Unfortunately, the formation of 7 oc- a long period at room temperature and decomposed only
curred without observable intermediates and every attempt when exposed to a coordinating solvent such as tetra-
to detect a ruthenium(IV) species failed. It is possible that hydrofuran. The NMR spectrum of 7 in CDCl3 revealed a
the intermediate RuIV complex reacts with a second azide chemical shift of the aromatic azide hydrogen atoms due
molecule at
a much faster rate than the starting to the ring current effect of the porphyrin (see Supporting
[Ru(TPP)(CO)]. However, [RuIV(TPP)(AraN)CO] may also Information).
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Ru–Porphyrin-Catalysed Allylic Amination of Olefins
Single-crystal X-ray diffraction confirmed the molecular Table 2. Complex 7-mediated allylic amination by AraN3.[a]
structure of 7 (Figure 1; for crystallographic data and de-
tails see SI). The two ArN ligands are syn-periplanar (i.e.
almost perfectly eclipsed about the N1···N2 axis). The Ru–
N distances, 1.808(4) and 1.806(4) Å for N1 and N2, respec-
tively, are in the range of double bonds, which confirms
the imido nature of the ligand. The nitrogen lone pairs are
available as demonstrated by the Ru–N–C angles, which are
extremely bent [139.8(3) and 143.7(4)° for N1 and N2,
respectively].[39] However, no intermolecular contact occurs
between these two crystallographically independent atoms.
This is certainly due to the absence of any H-bond donor
and the almost hindered nature of the molecule. The por-
phyrin–Ru bonds are in the range 2.04–2.07 Å, and the por-
phyrin is not particularly distorted by the apical ligands.
[a] General procedure for catalytic reactions:
7
(15 mg,
1.28ϫ10–2 mmol) in benzene (30 mL) heated to reflux; molar ratio
catalyst/AraN3/olefin = 1:50:250. [b] Determined by 1H NMR (2,4-
dinitrotoluene as the internal standard). [c] Time required to reach
complete conversion of the starting AraN3. [d] Reaction carried out
in neat olefin heated to reflux. [e] AraN3 conversion = 85%.
possible involvement of 7 in the catalytic cycle. If a phenyl
group was present on the double bond of 1,2-dihydro-
naphthalene (Table 2, Run 6), the formation of the aziridine
ring was also observed in accord with that already reported
Figure 1. Molecular structure of 7, ellipsoids are drawn at 30%
probability.
In view of the nature of the imido–metal interaction in 7 for the Ru(porphyrin)CO-catalysed aziridination of ole-
(Figure 1), we investigated the reactivity of the nitrene fins.[30]
transfer reaction by dissolving 7 (0.02 mmol) in cyclohexene
To better investigate the catalytic role of 7, the reaction
(5 mL) at 75 °C. When TLC analysis showed the complete of cyclohexene with AraN3 was run in C6D6 (1 mL) at 65 °C
consumption of 7, the reaction mixture was evaporated to in the presence of 7 (10 mg, 8.6ϫ10–3 mmol) using a molar
1
dryness to eliminate the unreacted olefin and a H NMR ratio of 7/aryl azide/cyclohexene = 1:10:20. The progress of
1
spectrum of the crude material was measured with 2,4-dini- the reaction was monitored by H NMR spectroscopy. The
trotoluene as the internal standard. The presence of the cor- formation of the corresponding allylic amine was ac-
responding allylic amine in 52% yield indicated that the companied by the disappearance of the signals of 7 and
“AraN” group had efficiently inserted into the C–H bond.
signals attributed to a new ruthenium–porphyrin species 9
Following extensive research carried out by Che et al.[23] became evident. This new complex was visible by 1H NMR
on the mechanism of stoichiometric reactions between spectroscopy until the aryl azide conversion was complete
imidoporphyrin complexes and hydrocarbons, we recently and then the formation of several signals in the porphyrin
decided to study the catalytic activity of ruthenium–imido- region indicated a decomposition process.
porphyrins[36] to better assess their implication in Ru(TPP)-
To isolate the complex observed during the NMR analy-
CO-catalysed C–H amination. Thus, we tested the catalytic sis, the reaction was performed on a larger scale (30 mg of
activity of 7 in allylic aminations of several olefins by AraN3 7, 2.57ϫ10–2 mmol) and followed by IR spectroscopy,
(Table 2), despite the fact that other ruthenium–porphyrins which monitored the intensity of the 2116 cm–1 absorption
are easier to handle and synthetically more accessible than of the N3 group of the azide. The reaction was stopped at
7.[26,40]
90% of the aryl azide conversion to avoid the formation
Comparing the data in Table 2 with those reported in of decomposition products (vide supra) and the reaction
Table 1, we can conclude that in almost all cases the allylic mixture was refrigerated to yield a small amount of purple
amine yields are similar, or even better, which suggests the crystals.
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The X-ray structure reported in Figure 2 shows that 9 is hours, 9 was no longer detectable by 1H NMR spec-
the bisamido complex [Ru(TPP)(AraNC6H9)2] (for crystal- troscopy. If more cyclohexene (60 equiv.) was added to the
lographic data and details see Supporting Information). mixture at this point, 9 was regenerated, which indicates a
1
The molecule sits on an inversion centre and the Ru–N1 reversible process. The H NMR spectra also disclosed the
distance is much larger than that in 7 [1.962(3) Å], which is catalytic formation of the allylic amine.
in the range typical for amido bonds. The Ru1–N3–C31
To date, data collected suggest a mechanism for the all-
and Ru1–N3–C41 angles have typical values of 122.2(3) and ylic amination of cyclohexene in which both 7 and 9 are
124.0(3)°, respectively, with the N3–C31–C41 plane perpen- implicated (Scheme 3).
dicular to the TPP one. The N3–C31 bond length in 9
[1.417(5) Å] is longer than those of N1–C1 [1.361(6) Å] and
N2–C2 [1.392(4) Å] in 7. The porphyrin–Ru bonds are
slightly shorter than those in 7 (2.042–2.047 Å). The inter-
molecular contacts are all quite long in the absence of
strong interactions. Nevertheless, no empty volume is left
in the crystal.
Scheme 3. Mechanistic hypothesis for the reaction between cyclo-
hexene and AraN3 catalysed by 7.
The synthesis of 9 requires the abstraction of two hydro-
gen atoms that, in our opinion, are associated with the 7-
mediated[42,43] reduction of a stoichiometric amount of cy-
clohexene to cyclohexane. The reduction of benzene is ex-
cluded because the allylic amination of cyclohexene also oc-
curred in high yields in neat olefin (Table 2, Run 1). The
complete inhibition of the reaction when the 7-catalysed
amination of cyclohexene was performed in the presence of
Figure 2. Molecular structure of 9, ellipsoids are drawn at 30%
probability.
TEMPO (2,2,6,6-tetramethylpiperidine N-oxide) indicates
that the “NAr” insertion into the C–H bond proceeds via
radical intermediates, which has been previously reported
We tried to synthesise 9 in large amounts but, because of for similar catalytic systems.[23,35] The reversible 9 to 7 pro-
its chemical instability, pure 9 was isolated in low yield cess occurs by a hydrogen atom transfer (HAT) reaction in
(18%) together with the allylic amine and unidentified ru- which cyclohexene is oxidised to 1,3-cyclohexadiene, which
thenium species. Complex 9 is stable for a few days at was identified at the end of the catalytic reaction by GC–
–15 °C in the solid state and for some hours in a benzene MS and 1H NMR spectroscopy. 1,3-Cyclohexadiene was
solution and rapidly decomposes in the majority of sol- not present as an impurity in the starting cyclohexene,
vents, especially coordinating ones. The diamagnetic behav- which was evidenced by the same techniques. Unfortu-
iour of 9 indicates the formation of a ruthenium(IV) com- nately, the presence of cyclohexane could not be detected
pound with S = 0. A recent DFT study is in accord with by GC–MS spectroscopy because its signal overlaps with
our experimental results.[41]
that of cyclohexene.
When 9 was left to stand in pure cyclohexene or benzene/
The hypothesis illustrated in Scheme 3 is supported by
cyclohexene, the fast formation of the corresponding allylic the 1H NMR spectroscopic and GC–MS analyses of the
amine and uncharacterised ruthenium products was ob- amination of 1,2-dihydronaphthalene, which reveals, apart
served. Complex 9 could be accumulated in solution only from the corresponding allylic amine, the presence of
under catalytic conditions in which both AraN3 and cyclo- naphthalene and the benzylic amine of 1,2,3,4-tetrahydro-
hexene are present and the olefin concentration is larger naphthalene. The formation of the latter compound indi-
than that of the azide. Conversely, when [AraN3] Ͼ [cyclo- cates that 1,2-dihydronaphthalene was partly reduced to
hexene], 9 was completely converted into 7. We have studied 1,2,3,4-tetrahydronaphthalene that, being a benzylic sub-
this reaction by dissolving 9 (6.85 mg, 5.15ϫ10–3 mmol) in strate for the nitrene transfer reaction, was aminated. The
a C6D6 (1 mL) solution of AraN3 and cyclohexene in a mo- involvement of the hydrocarbon substrate in the HAT pro-
lar ratio of 9/aryl azide/cyclohexene = 1:50:10. The reaction cess explains the need for an excess of olefin for the catalytic
was monitored by following the pyrrolic signals of the por- reaction to proceed. In fact, if allylic aminations were run
1
phyrin in the H NMR spectrum. After a few minutes at with the olefin as the limiting reagent the consumption of
65 °C, the formation of 7 was observed and after four AraN3 was not complete. It should be emphasised that the
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Ru–Porphyrin-Catalysed Allylic Amination of Olefins
active role of 9 was further supported by its catalytic ac-
tivity in the allylic amination of cyclohexene, which was
maintained for two further runs when additional amounts
of the reagents were added before the complete consump-
tion of AraN3 to avoid the catalyst decomposition.
In order to assess if the formation of a bisimido complex
is a general reaction, we have also studied the reactivity
of [Ru(TPP)CO] towards other aryl azides. The reactions
between [Ru(TPP)CO] and ArN3 (Ar = 4-CF3C6H4N3, 4-
Scheme 4. Synthesis of 11.
1
NO2C6H4N3, 4-CNC6H4N3) were monitored by H NMR
Complex 11 exhibited different spectra in CDCl3 and in
C6D6 due to the aromatic solvent-induced shift[44,45] effect
(Figure 3); however, in both cases a signal at a negative
chemical shift value was observed (–3.43 and –4.08 ppm in
CDCl3 and C6D6, respectively). The signal disappeared on
spectroscopy (C6D6). After the addition of the selected az-
ide, an immediate modification of the NMR spectrum of
[Ru(TPP)CO] was observed. The coordination of the ni-
trene ligand to the metal centre has been suggested on the
basis of the change of the typical porphyrin region and for
the appearance of signals in the same NMR region (2–
7 ppm) where aromatic hydrogen atoms of the azide were
detected for 7 (see SI). In every reaction tested, the newly
formed complex was stable for a short time and the disap-
pearance of the signals, which were attributed to the coordi-
nated aryl group, indicated a decomposition process (see
SI).
2
addition of D2O and the H NMR spectrum in C6D6 dis-
closed the presence of a signal at –13.43 ppm; these data
confirm the coordination of an arylamine to the ruthenium
atom.
The reaction between [Ru(TTP)CO] and AreN3 (Are = 4-
CF3C6H4N3) was repeated on a larger scale and stopped
after 30 min to avoid any decomposition. The purple com-
plex [Ru(TPP)(NAre)2] (10) was isolated in 60% yield and
fully characterised. Unreacted [Ru(TPP)CO] was also pres-
ent in the reaction mixture. Complex 10 was stable in the
solid state under an inert atmosphere for several days but
partially decomposed in solution, which made it difficult
to determine its molecular structure by X-ray diffraction
analysis. Nevertheless, we proposed the formation of the
bisimido complex 10 on the basis of 1D and 2D NMR spec-
tra, which showed a perfect similitude with those of 7. The
1H NMR spectrum (see SI) showed the presence of an
AAЈBBЈ pattern for the aromatic azide moiety at 5.94 and
2.61 ppm. All the other analytical data agreed with the pro-
posed structure.
1
Figure 3. H NMR spectra of 11 in CDCl3 (a) and C6D6 (b).
To explain the formation of 11, we propose that, as al-
Complex 10 was heated to reflux in cyclohexene for ready suggested for the synthesis of 7, the first step of the
three hours to give the allylic amine (54%) and it was cata- reaction between [Ru(TPP)CO] and AreN3 yields a mono-
lytically active in the reaction between cyclohexene and imido ruthenium(IV) complex, which is too reactive to be
AreN3 using a catalytic molar ratio of 10/azide = 1:50 in detected. This intermediate can react with another molecule
hot cyclohexene. After 2.5 hours the allylic amine 1e was of aryl azide to yield 10 or can decompose to regenerate
recovered in 55% yield. Complex 10 was also a competent [Ru(TPP)CO]. The so-formed [Ru(TPP)CO] can be
catalyst in the allylic amination of 1-methylcyclohexene, in- “trapped” by AreNH2 to yield 11. The presence of AreNH2
dene and 1-octene by AreN3; the corresponding allylic in solution is due to partial aryl azide decomposition medi-
amines were formed with yields comparable with those ob- ated by the ruthenium catalyst, which can promote hydro-
tained using [Ru(TPP)CO] as the catalyst.
gen atom abstraction reactions.[35] Clearly, we cannot ex-
[Ru(TPP)CO] and 4 equiv. of AreN3 were heated to re- clude that the direct reaction of [Ru(TPP)CO] with AreNH2
flux in C6H6 for three hours to better understand the ob- can also be responsible in part for the formation of 11.
served decomposition pathway. [Ru(TPP)(AreNH2)CO] (11)
Considering that 11 can also be formed during the cata-
was isolated from the reaction mixture in 37% yield. Un- lytic reaction, we have studied its catalytic activity in the
identified ruthenium compounds derived from the decom- allylic amination of several olefins using the same experi-
position of 10 accounted for the rest of the reaction mass mental conditions reported in Table 1. The data obtained
balance with respect to the starting [Ru(TPP)CO].
(see experimental section) were comparable with those ob-
The structure of 11 was definitively assigned by compar- served in [Ru(TPP)CO]-mediated reactions, which indicate
ing its analytical data with those of the reaction product that AreNH2, formed during the catalytic cycle, is not a
from [Ru(TPP)CO] and 4-CF3C6H4NH2 (Scheme 4).
catalyst inhibitor.
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Synthetic results described to date now suggest that, de- visages that 11 should be the only product accumulated in
pending on the electronic nature of the employed aryl azide, solution, which is in accord with the experimental observa-
both bis- and monoimido complexes can be involved in al- tion (Scheme 5).
lylic aminations of cyclohexene and an active role is proba-
bly also played by monoimido species.
Kinetic Study
To shed some light on the [Ru(TPP)CO]-catalysed allylic
amination of cyclohexene, a kinetic study was undertaken
that employed AreN3 (Are = 4-CF3C6H4N3) or AraN3 [Ara
Scheme 5. Mechanistic hypothesis for the reaction between cyclo-
hexene and 4-CF3C6H4N3 catalysed by [Ru(TPP)CO].
= 3,5-(CF3)2C6H3N3] as nitrogen sources. The reactions
were followed by IR spectroscopy, which monitored the in-
tensity of the aryl azide absorption (AreN3 at 2102 cm–1
and AraN3 at 2116 cm–1). All the kinetic experiments in this
paper were run at 75 °C to avoid boiling benzene in the
reactions in which it was present.
The active role of bisimido 10 under these conditions is
not supported by the kinetic experiments. In particular, it
would be difficult to explain the observation of a ruthenium
carbonyl complex even at the end of the reaction if the co-
ordinated CO had been lost in the formation of 10.
The same kinetics have been observed for the reaction of
4-NO2C6H4N3 with cyclohexene catalysed by [Ru(TPP)CO]
(see the Supporting Information for graphics).
The kinetics of the [Ru(TPP)CO]-catalysed reaction be-
tween AraN3 and cyclohexene were more complex than pre-
viously discussed. A first-order dependence on the aryl az-
ide was observed but the rate order dependence on the ole-
fin concentration is not unique. A first-order dependence
was observed up to an olefin concentration of 3 m and then
the reaction rate was almost independent from the quantity
of cyclohexene present in solution (Figure 5a). This behav-
iour indicates the coexistence of at least two mechanisms
that occur contemporaneously with the prevalence of one
or the other depending on the olefin concentration.
The rate of the reaction between cyclohexene and AreN3
showed a first-order dependence on azide and [Ru(TPP)-
CO] concentrations. However, a zero-order dependence on
cyclohexene concentration (the other solvent was benzene)
was observed (Figure 4). These data led to the kinetic equa-
tion v = –d[AreN3]/dt = kobs[Ru(TPP)CO][AreN3].
Figure 4. Kinetic dependence of the reaction rate with respect to
the concentrations of 4-CF3C6H4N3 (a), cyclohexene (b) and
[Ru(TPP)CO] (c).
Figure 5. Kinetic dependence of the reaction rate with respect to
olefin concentration in the reactions between cyclohexene and 3,5-
(CF3)2C6H3N3 catalysed by [Ru(TPP)CO] (a) or 7 (b).
Sampling the reaction mixture during the catalytic reac-
tion and examining it by TLC allowed the observation of
The kinetics of the reaction between AraN3 and cyclo-
[Ru(TPP)(CO)(AreNH2)] as the only identifiable complex. hexene were also studied in the presence of 7, and a first-
Together with the observed kinetics, this observation is con- order dependence with respect to the aryl azide concentra-
sistent with a reaction mechanism in which the rate-de- tion was observed. The rate dependence on the olefin con-
termining step is the formation of a monoimido complex centration showed both similarities and differences with re-
that very quickly reacts with the olefin to form the allylic spect to that observed with [Ru(TPP)CO] as the catalyst.
amine and regenerate [Ru(TPP)CO]. We suggest that A first-order dependence on cyclohexene concentration was
[Ru(TPP)CO] reacts with aniline, a reaction by-product, again obtained up to a 3 m concentration, but an inhibiting
yielding [Ru(TPP)(CO)(AreNH2)] (11) that was identified effect at higher concentrations was evident (Figure 5b)
during the catalysis. This mechanistic hypothesis en- rather than the flat dependence visible in Figure 5a.
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Ru–Porphyrin-Catalysed Allylic Amination of Olefins
Bearing in mind the results of the synthetic studies dis- give the same behaviour at high olefin concentration be-
cussed above, all the experimental results can be accounted cause no CO is present in the first case and a complex of
for in the general reaction scheme shown in Scheme 6.
type C cannot be formed. Under these conditions, in agree-
ment with the results of the synthetic studies described in
above, the resting state of the complex gradually shifts
towards the bisamido complex E. The rate of the reaction
should be independent of olefin concentration, but it must
be considered that E has a low stability and easily decom-
poses. Thus, faster catalyst deactivation is observed when
this type of complex is accumulated in solution. Such a
gradual decomposition can be difficult to separate in any
single kinetic experiment by the natural rate decrease due
to azide consumption and it easily results in a lower appar-
ent first-order kinetic constant.
It should be noted that the lower slope of the low cyclo-
hexene concentration branch of Figure 5 (a) with respect to
that shown in part b is consistent with the contemporane-
ous competition of two catalytic cycles in the first case, only
one of which is accelerated by an increase in olefin concen-
tration. In theory, it may be possible to calculate the relative
weight of the two catalytic cycles by the observed differ-
ences, but the number of available data points does not al-
low us to perform this calculation reliably.
Scheme 6. Mechanistic hypothesis for the allylic amination of cy-
clohexene by aryl azides catalysed by [Ru(TPP)CO].
The reaction of [Ru(TPP)CO] (B in Scheme 6) with ArN3
initially forms a monoimido complex (C). In the case of Ar
= 4-CF3C6H4, the reaction with cyclohexene to yield the
allylic amine and regenerate B is faster than the reaction
with a second azide molecule for all cyclohexene concentra-
tions tested. Thus, the second cycle in Scheme 6 does not
operate and the kinetics are clearly first order for the azide
and ruthenium complex (r.d.s. formation of the monoimido
complex C) and zero order with respect to cyclohexene (fast
reaction). [Ru(TPP)CO], in equilibrium with 11, is the rest-
ing state of the catalyst, which is in accord with the experi-
mental observations. In the case of the stoichiometric reac-
tion between [Ru(TPP)CO] and 4-CF3C6H4N3, which has
been described previously, this clearly does not hold. In this
case there is no olefin available to trap C and the reaction
evolves to the bisimido complex D.
In the case of Ar = 3,5-(CF3)2C6H3, the situation is more
complex. The higher reactivity of the bis-trifuoromethylated
azide renders the formation of the bisimido complex D
more competitive than when only a single electron-with-
drawing group (CF3 or NO2) is present. The rate depen-
dence of the catalytic reaction on olefin concentration
shown in Figure 5 (a) can be explained by assuming that at
low cyclohexene concentration formation of D is relevant
during the reaction. The reaction of D with cyclohexene
becomes rate determining and the kinetics are first order
with respect to the olefin. At a higher cyclohexene concen-
tration, the reaction of C with the olefin becomes faster
than the reaction with another azide molecule and the same
situation is observed in the case of Ar = 4-CF3C6H4 (zero-
order kinetics in cyclohexene).
Conclusions
The allylic amination of cyclohexene catalysed by ruthe-
nium porphyrin complexes occurs through at least two dif-
ferent mechanisms where one prevails over the other de-
pending on the nature of the employed aryl azide and the
olefin concentration. Experimental and kinetic data indi-
cate that both mono- and bisimido species can be involved
in the nitrene transfer reaction but the high reactivity of
the monoimido derivative precluded any characterisation.
However, the isolation of its decomposition products and
kinetic data suggest that the monoimido complex is mainly
responsible for the catalytic reaction when using aryl azides
that show less electron-withdrawing behaviour. On the
other hand, if an aryl azide that bears two strong electron-
withdrawing substituents, such as two CF3 groups, is em-
ployed, the monoimido complex rapidly reacts with the aryl
azide to be further oxidised to the bisimido complex, which
becomes the reaction catalyst.
To better clarify the role of mono- and bisimido com-
plexes in the nitrene transfer reaction into an allylic C–H
bond, a computational study is currently in progress.
Experimental Section
General: Unless otherwise specified, all reactions were carried out
in a nitrogen atmosphere employing standard Schlenk techniques
and magnetic stirring. Benzene and n-hexane were dried by an M.
Braun SPS-800 solvent purification system. Cyclohexene and 1-oc-
tene were distilled from sodium benzophenone and kept under ni-
trogen. All the other starting materials were commercial products
and used as received. Aryl azides,[30,46] tetraphenylporphyrin[47,48]
and [Ru(TPP)CO][49] were synthesised by methods as reported in
When 7 was employed as the catalyst, the situation at
low olefin concentration parallels that observed for
[Ru(TPP)CO]. However, the two types of kinetics cannot the literature or with minor modifications.[50] The purity of olefins
Eur. J. Inorg. Chem. 2012, 569–580
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
575

E. Gallo et al.
FULL PAPER
and the aryl azides employed was confirmed by GC–MS or 1H
NMR spectroscopy. NMR spectra were recorded at room tempera-
ture with a Bruker AC-300 or a Bruker avance 300-DRX instru-
ments operating at 300 MHz for 1H, 75 MHz for 13C and 282 MHz
for 19F, or with a Bruker Avance 400-DRX spectrometers operating
at 400 MHz for 1H and 100 MHz for 13C. Chemical shifts (ppm)
4-tert-Butyl-N-(cyclohex-2-enyl)aniline (1c): 13% yield obtained by
following method A with [Ru(TPP)CO] as catalyst; 89% yield by
following method B with [Ru(TPP)CO] as catalyst. C16H23N
(229.18): calcd. C 83.79, H 10.11, N 6.11; found C 84.01, H 10.02,
N 6.01. 1H NMR (300 MHz, CDCl3): δ = 7.21 (d, 2 H, J = 8.8 Hz,
HAr), 6.59 (d, 2 H, J = 8.8 Hz, HAr), 5.85 (m, 1 H, CH=CH–
CH2), 5.80 (m, 1 H, CH=CH–CH2), 3.97 (br. s, 1 H, CHNH), 3.55
(br. s, 1 H, NH), 2.06–2.03 (m, 2 H, CH2), 1.95–1.90 (m, 2 H,
CH2), 1.70–1.62 (m, 2 H, CH2), 1.29 [s, 9 H, C(CH3)3] ppm. 13C
NMR (75 MHz, CDCl3): δ = 145.2 (C), 140.3 (C), 130.3 (CH),
129.3 (CH), 126.5 (CH), 113.3 (CH), 48.5 (CH), 34.2 (C), 32.0
(CH3), 29.4 (CH2), 25.6 (CH2), 20.1 (CH2) ppm. EI-MS: m/z = 229
[M]+.
1
are reported relative to Me4Si. The H NMR signals of the com-
pounds described below have been attributed by COSY and
NOESY techniques. Assignments of the resonances in 13C NMR
spectra were made using the APT pulse sequence and heteronuclear
single quantum coherence (HSQC) and HMBC techniques. GC–
MS were performed with a Shimadzu QP5050A instrument. Infra-
red spectra were recorded with a Varian Scimitar FTS 1000 spectro-
photometer. UV/Vis spectra were recorded with an Agilent 8453E
instrument. Elemental analyses and mass spectra were recorded in
the analytical laboratories of Milan University. CCDC-720709 (for
7) and -720710 (for 9) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
4-(Cyclohex-2-enylamino)benzonitrile (1d):[53] 13% yield obtained
by following method A with [Ru(TPP)CO] as catalyst; 89% yield
by following method B with [Ru(TPP)CO] as catalyst. Analytical
data are in accord with the literature.
N-(Cyclohex-2-enyl)-4-(trifluoromethyl)benzenamine (1e):[54] 28%
yield obtained by following method A with [Ru(TPP)CO] as cata-
lyst; 85% yield by following method B with [Ru(TPP)CO] as cata-
lyst; 30% yield by following method A with 10 as catalyst; 55%
yield by following method B with 10 as catalyst. 25% yield by fol-
lowing method A with 11 as catalyst; 99% yield by following
method B with 11 as catalyst. Analytical data are in accord with
the literature.
General Procedure for Catalytic Reactions
Method A: In a typical run, the catalyst (1.3ϫ10–2 mmol) and the
aryl azide (6.3ϫ10–1 mmol) were added to a benzene (30 mL) solu-
tion of the olefin (3.2 mmol). The resulting solution was heated to
reflux using a preheated oil bath. The consumption of the aryl
azide was monitored by TLC up to the point that its spot was no
longer observable, and then by IR spectroscopy, which measured
the characteristic N3 absorbance in the range 2095–2130 cm–1. The
reaction was considered to be finished when the absorbance of the
azide measured was below 0.03 (by using a 0.5 mm thick cell). The
solution was then evaporated to dryness and analysed by 1H NMR
spectroscopy with 2,4-dinitrotoluene as the internal standard. The
residue was purified by flash chromatography on deactivated silica
with 10% Et3N added to the eluent (n-hexane/ethyl acetate) during
the packing of the column.
Methyl-4-(cyclohex-2-enylamino)benzoate (1f):[51] 13% yield ob-
tained by following method A with [Ru(TPP)CO] as catalyst; 85%
yield by following method B with [Ru(TPP)CO] as catalyst. Analyt-
ical data are in accord with the literature.
3,5-Dichloro-N-(cyclohex-2-enyl)benzenamine (1g):[51] 38% yield ob-
tained by following method A with [Ru(TPP)CO] as catalyst; 90%
yield by following method B with [Ru(TPP)CO] as catalyst. Analyt-
ical data are in accord with the literature.
N-(Cyclohex-2-enyl)-4-methoxybenzenamine (1h):[54] 8% yield ob-
tained by following method A with [Ru(TPP)CO] as catalyst; 33%
yield by following method B with [Ru(TPP)CO] as catalyst. Analyt-
ical data are in accord with the literature.
Method B: The synthetic procedure reported above was repeated
using the olefin as the reaction solvent.
N-(Cyclohex-2-enyl)-3,5-bis(trifluoromethyl)benzenamine
(1a):[51]
26% yield obtained by following method A with [Ru(TPP)CO] as
catalyst; 75% yield by following method B with [Ru(TPP)CO] as
catalyst; 74% yield by following method A with 7 as catalyst; 99%
yield by following method B with 7 as catalyst.
3,5-Bis(trifluoromethyl)-N-(3-methylcyclohex-2-enyl)benzenamine
(2aA) and 3,5-Bis(trifluoromethyl)-N-(2-methylcyclohex-2-enyl)-
benzenamine (2aB): 43% yield (A/B = 65:35) obtained by following
method A with [Ru(TPP)CO] as catalyst; 60% yield (A/B = 63:34)
by following method A with 7 as catalyst; 88% (A/B = 56:44) yield
by following method B with 7 as catalyst. 2aA and 2aB: C15H15F6N
(323.11): calcd. C 55.73, H 4.68, N 4.33; found C 56.09, H 4.90, N
4.67. 19F NMR (282 MHz, CDCl3): δ = –63.56 ppm. EI-MS: m/z
Method C: Compound 9 (17 mg, 1.28ϫ10–2 mmol) and trifluoro-
methylphenyl azide (166 mg, 6.51ϫ10–1 mmol) were added to a
benzene (30 mL) solution of cyclohexene (0.325 mL, 3.21 mmol).
The solution was heated to reflux for 18 h, evaporated to dryness
1
and analysed by H NMR spectroscopy with 2,4-dinitrotoluene as
the internal standard (70% of 1a). Analytical data are in accord
with the literature.
1
= 323 [M]+. 2aA: H NMR (300 MHz, CDCl3): δ = 7.11 (s, 1 H,
HAr), 6.93 (s, 2 H, HAr), 5.44–5.43 (m, 1 H, CH=C–CH3), 4.13 (br.
s, 1 H, NH), 4.01 (br. s, 1 H, CHNH), 1.98–1.95 (m, 2 H, CH2),
1.88–1.83 (m, 2 H, CH2), 1.72 (s, 3 H, CH3), 1.71–1.64 (m, 2 H,
CH2) ppm. 13C NMR (75 MHz, CDCl3): δ = 148.7 (C), 139.7 (C),
132.9 (q, J = 30.9 Hz, C–CF3), 124.0 (q, J = 270.9 Hz, CF3), 121.6
(CH), 112.5 (CH), 110.0 (CH), 48.7 (CH), 30.4 (CH2), 28.5 (CH2),
24.1 (CH3), 20.0 (CH2) ppm. 2aB: (300 MHz, CDCl3): δ = 7.11 (s,
N-(Cyclohex-2-enyl)-4-nitrobenzenamine (1b):[52] 23% yield ob-
tained by following method A with [Ru(TPP)CO] as catalyst; 70%
yield by following method B with [Ru(TPP)CO] as catalyst.
C12H14N2O2 (218.11): calcd. C 66.04, H 6.47, N 12.84; found C
1
66.50, H 6.49, N 12.61. H NMR (300 MHz, CDCl3): δ = 8.10 (d,
2 H, J = 9.1 Hz, HAr), 6.55 (d, 2 H, J = 9.1 Hz, HAr), 5.97 (m, 1
H, CH=CH–CH2), 5.73 (m, 1 H, CH=CH–CH2), 4.51 (br. s, 1 H, 1 H, HAr), 6.93 (s, 2 H, HAr), 5.68–5.66 (m, 1 H, CH=C–CH3),
NH), 4.10 (br. s, 1 H, CHNH), 2.09–2.01 (m, 2 H, CH2), 1.98–1.92
4.13 (br. s, 1 H, NH), 3.84 (br. s, 1 H, CHNH), 2.04–2.02 (m, 2 H,
(m, 1 H, CH2), 1.80–1.67 (m, 2 H, CH2), 1.63–1.57 (m, 1 H, CH2) CH2), 1.75 (m, 3 H, CH3), 1.70–1.56 (m, 4 H, CH2) ppm. 13C NMR
ppm. 13C NMR (75 MHz, CDCl3): δ = 152.7 (C), 132.2 (CH), (75 MHz, CDCl3): δ = 148.2 (C), 133.3 (C), 132.9 (q, J = 30.9 Hz,
127.1 (CH), 126.9 (CH), 111.7 (CH), 48.1 (CH), 28.9 (CH2), 25.3
(CH2), 19.7 (CH2) ppm. One quaternary carbon was not detected.
EI-MS: m/z = 218 [M]+.
C–CF3), 127.2 (CH), 124.0 (q, J = 270.9 Hz, CF3), 112.2 (CH),
110.0 (CH), 51.4 (CH), 28.1 (CH2), 25.5 (CH2), 21.9 (CH3), 18.2
(CH2) ppm.
576
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Ru–Porphyrin-Catalysed Allylic Amination of Olefins
1
N-(3-Methylcyclohex-2-enyl)-4-nitroaniline (2bA) and N-(2-methyl-
cyclohex-2-enyl)-4-nitroaniline (2bB):[33] 20% yield (2bA + 2bB) ob-
tained by following method A with [Ru(TPP)CO] as catalyst. Ana-
lytical data are in accord with the literature.
3bA: H NMR (300 MHz, CDCl3): δ = 8.11 (d, 2 H, J = 9.0 Hz,
HAr), 7.27–7.16 (m, 4 H, HAr), 6.69 (d, 1 H, J = 9.6 Hz, CH=CH–
CH), 6.58 (d, 1 H, J = 9.0 Hz, HAr), 6.10 (dd, 1 H, J = 9.6 Hz, J
= 4.5 Hz, CH=CH–CH), 4.51 (m, 1 H, CHNH), 4.46 (m, 1 H,
NH), 3.11 (m, 2 H, CH2) ppm. 13C NMR (75 MHz, CDCl3): δ =
154.2 (C), 152.3 (C), 130.8 (CH), 129.2 (CH), 128.4 (CH), 127.7
(CH), 127.3 (CH), 126.9 (CH), 112.0 (CH), 47.1 (CH), 34.0
(CH2) ppm, two quaternary carbon atoms were not detected. EI-
MS: m/z = 266 [M]+.
N-(3-Methylcyclohex-2-enyl)-4-trifluoromethylaniline (2eA) and N-
(2-methylcyclohex-2-enyl)-4-trifluoromethylaniline (2eB): 26% yield
(A/B = 65:35) obtained by following method A with [Ru(TPP)CO]
as catalyst; 30% yield (A + B) by following method A with 10 as
catalyst; 42% yield (A/B = 66:34) by following method A with 11
as catalyst; 99% yield (A + B) by following method B with 11 as
N-[3,5-Bis(trifluoromethyl)phenyl]-1H-inden-1-amine (4a): 42%
yield obtained by following method A with [Ru(TPP)CO] as cata-
lyst; 55% yield by following method A with 7 as catalyst; 70% yield
by following method B with 7 as catalyst. C17H11F6N (343.08):
1
catalyst. 2eA: H NMR (300 MHz, CDCl3): δ = 7.41 (d, 2 H, J =
8.4 Hz), 6.63 (d, 2 H, J = 8.4 Hz), 5.66 [br. s, 1 H, CH=C(CH3)],
4.01 (br. s, 1 H, NH), 3.86 (br. s, 1 H, CHNH), 2.05–1.88 (m, 3 H,
CH2), 1.77 (s, 3 H, CH3), 1.63–1.56 (m, 3 H, CH2) ppm. 13C NMR
(100 MHz, CDCl3): δ = 150.2 (C), 133.5 (C), 126.7 (CH), 126.4
(CH), 118.1 (CCF3, q, J = 32.1 Hz), 111.8 (CH), 50.8 (CH), 28.0
(CH2), 25.2 (CH2), 21.6 (CH3), 17.7 (CH2) ppm, the CF3 signal
1
calcd. C 59.48, H 3.23, N 4.08; found C 59.68, H 3.38, N 4.05. H
NMR (300 MHz, CDCl3): δ = 7.46 (d, 1 H, J = 7.5 Hz, HAr), 7.38–
7.35 (m, 2 H, HAr), 7.27–7.24 (m, 1 H, HAr), 7.22 (s, 1 H, HAr),
7.04 (s, 2 H, HAr), 6.92 (dd, 1 H, J = 5.7 Hz and 1.8 Hz, CH=CH–
CH), 6.53 (d, 1 H, J = 5.7 Hz and 1.8 Hz, CH=CH–CH), 5.16 (d,
1 H, J = 8.7 Hz, CHNH), 4.34 (d, 1 H, J = 8.7 Hz, NH) ppm. 13C
NMR (75 MHz, CDCl3): δ = 148.5 (C), 144.0 (C), 143.2 (C), 135.3
(CH), 133.7 (CH), 132.8 (q, J = 33.4 Hz, C–CF3), 128.8 (CH),
126.4 (CH), 123.7 (q, J = 273.0 Hz, CF3), 123.4 (CH), 122.0 (CH),
112.8 (CH), 111.0 (CH), 61.2 (CH) ppm. 19F NMR (282 MHz,
CDCl3): δ = –63.57 ppm. EI-MS: m/z = 343 [M]+.
1
was not detected. 2eB: H NMR (300 MHz, CDCl3): δ = 7.40 (d,
2 H, J = 8.7 Hz), 6.62 (d, 2 H, J = 8.7 Hz), 5.48 [br. s, 1 H,
CH=C(CH3)], 4.00 (m, 2 H, CHNH), 1.98 (m, 2 H, CH2), 1.86–
1.84 (m, 1 H, CH2), 1.72 (s, 3 H, CH3), 1.71–1.61 (m, 3 H,
CH2) ppm. 13C NMR (75 MHz, CDCl3): δ = 150.2 (C), 139.1 (C),
127.0 (CH), 122.4 (CH), 118.7 (q, J = 32.6 Hz, CCF3), 112.5 (CH),
48.4 (CH), 30.4 (CH2), 28.7 (CH2), 24.2 (CH3), 20.1 (CH3) ppm,
the CF3 signal was not detected.
N-(4-Nitrophenyl)-1H-inden-1-amine (4b): 42% yield obtained by
following method A with [Ru(TPP)CO] as catalyst; 55% yield by
following method A with 7 as catalyst; 70% yield by following
method B with 7 as catalyst. C15H12N2O2 (252.09): calcd. C 71.42,
H 4.79, N 11.10; found C 71.65, H 4.95, N 10.92. 1H NMR
(300 MHz, CDCl3): δ = 8.12 (d, 2 H, J = 9.3 Hz, HAr), 7.45–7.50
(d, 1 H, J = 7.2 Hz, HAr), 7.36–7.39 (m, 2 H, HAr), 7.27–7.24 (m,
1 H, HAr), 6.94 (dd, 1 H, J = 5.6, J = 1.2 Hz, CH=CH–CH) 6.66
(d, 2 H, J = 9.3 Hz, HAr), 6.53 (dd, 1 H, J = 5.6, J = 1.8 Hz,
CH=CH–CH), 5.21 (dd, 1 H, J = 8.4, J = 1.2 Hz, CHNH), 4.71
(d, 1 H, J = 8.4 Hz, NH) ppm. 13C NMR (75 MHz, CDCl3): δ =
153.3 (C), 144.0 (C), 143.4 (C), 139.6 (C), 135.4 (CH), 134.1 (CH),
129.1 (CH), 126.8 (CH), 126.7 (CH), 123.6 (CH), 122.4 (CH), 112.3
(CH), 61.2 (CH) ppm. EI-MS: m/z = 252 [M]+.
N-[3,5-Bis(trifluoromethyl)phenyl]-1,2-dihydronaphthalen-2-amine
(3aA) and N-[3,5-Bis(trifluoromethyl)phenyl]-1,2-dihydronaphthalen-
1-amine (3aB): 57% yield (A/B = 58:42) obtained by following
method A with [Ru(TPP)CO] as catalyst; 85% yield (A/B = 60:40)
by following method B with [Ru(TPP)CO] as catalyst; 60% yield
(A/B = 65:35) by following method A with 7 as catalyst. 3aA:
C18H13F6N (357.09): calcd. C 60.51, H 3.67, N 3.92; found C 60.80,
1
H 3.82, N 4.00. H NMR (300 MHz, CDCl3): δ = 7.26–7.13 (m, 5
H, HAr), 6.95 (s, 2 H, HAr), 6.65 [d, 1 H, J = 9.3 Hz, CH=CH–
CH(NH)], 6.08 [dd, 1 H, J = 9.3 Hz and 4.5 Hz, CH=CH–
CH(NH)], 4.38 [1 H, dddd, J = 8.4, 6.3, 6.3 Hz and 4.5 Hz,
CH(NH)], 4.16 (d, 1 H, J = 8.4 Hz, NH), 3.12 (dd, 1 H, J = 15.9 Hz
and 6.3 Hz, CH2), 3.02 (dd, 1 H, J = 15.9 Hz and 6.3 Hz, CH2)
ppm. 13C NMR (75 MHz, CDCl3): δ = 147.2 (C), 132.4 (q, J =
32.8 Hz, C–CF3 overlapping with another quaternary carbon),
129.9 (CH), 128.6 (CH), 127.8 (CH), 127.1 (CH, two signals over-
laid), 126.6 (CH), 123.4 (q, J = 270.8 Hz, CF3), 112.1 (CH), 110.2
(CH), 46.4 (CH), 33.3 (CH2) ppm. 19F NMR (282 MHz, CDCl3):
δ = –63.17 ppm. EI-MS: m/z = 357 [M]+. 3aB: C18H13F6N (357.09):
N-[4-(Trifluoromethyl)phenyl]-1H-inden-1-amine (4e): 30% yield ob-
tained by following method A with [Ru(TPP)CO] as catalyst; 14%
yield by following method A with 10 as catalyst; 17% yield by
following method A with 11 as catalyst. C16H12NF3 (275.09): calcd.
1
C 69.81, H 4.39, N 5.09; found C 69.94, H 4.73, N 5.56. H NMR
(300 MHz, CDCl3): δ = 7.50 (d, 1 H, J = 7.5 Hz, HAr), 7.45 (d, 2
H, J = 8.4 Hz, HAr), 7.37 (m, 2 H, HAr), 7.24 (m, 1 H, HAr), 6.90
(dd, 1 H, J = 5.7, J = 1.2 Hz, CH=CH), 6.74 (d, 2 H, J = 8.4 Hz,
HAr), 6.57 (dd, 1 H, J = 5.7 Hz, J = 1.8 Hz, CH=CH), 5.18 (d, 1
H, J = 8.7 Hz, CHNH), 4.23 (d, 1 H, J = 8.7 Hz, NH) ppm. 13C
NMR (75 MHz, CDCl3): δ = 150.2 (C), 144.4 (C), 143.0 (C), 135.9
(CH), 132.9 (CH), 126.9 (CH), 126.7 (C), 126.5 (CH), 112.7 (CH),
110.1 (C), 61.1 (CH) ppm. 19F NMR (282 MHz, CDCl3): δ =
–61.40 ppm.
1
calcd. C 60.51, H 3.67, N 3.92; found C 60.61, H 3.88, N 3.97. H
NMR (400 MHz, CDCl3): δ = 7.34–7.24 (m, 3 H, HAr), 7.19–7.17
(m, 2 H, HAr), 7.01 (s, 2 H, HAr), 6.62 (dt, 1 H, J = 9.6 Hz and
1.6 Hz, CH=CH–CH2), 6.02 (dt, 1 H, J = 9.6 Hz and 4.3 Hz,
CH=CH–CH2), 4.76 (dt, 1 H, J = 8.6 Hz and 6.3 Hz, CH=NH),
4.37 (d, 1 H, J = 8.6 Hz, NH), 2.64 (ddd, 2 H, J = 6.3, 4.3 Hz and
1.6 Hz, CH2) ppm. 13C NMR (100 MHz, CDCl3): δ = 147.7 (C),
134.5 (C), 133.3 (C), 132.6 (q, J = 32.8 Hz, C–CF3), 128.5 (CH),
128.0 (CH), 127.8 (CH), 126.9 (CH, two signals overlaid), 125.7
(CH), 123.5 (q, J = 270.9 Hz, CF3), 112.3 (CH), 110.3 (CH), 50.4
(CH), 29.4 (CH2) ppm. 19F NMR (282 MHz, CDCl3): δ =
–63.50 ppm. EI-MS: m/z = 357 [M]+.
N-(Cyclopent-2-enyl)-4-nitroaniline (5):[33] 30% yield obtained by
following method A with [Ru(TPP)CO] as catalyst. C11H12N2O2
(204.09): calcd. C 64.69, H 5.92, N 13.72; found C 64.54, H 5.83,
N 13.98. 1H NMR (300 MHz, C6D6): δ = 8.12 (d, 2 H, J = 9.0 Hz,
HAr), 5.97 (d, 2 H, J = 9.0 Hz, HAr), 5.75 (m, 1 H, CH=CH), 5.47
(m, 1 H, CH=CH), 4.01 (m, 1 H, CHNH), 3.73 (br. s, 1 H, NH),
2.20–2.12 (m, 2 H, CH2), 1.93–1.91 (m, 1 H, CH2), 1.30–1.24 (m,
1 H, CH2) ppm. 13C NMR (75 MHz, CDCl3): δ = 152.5 (C), 138.8
N-(4-Nitrophenyl)-1,2-dihydronaphthalen-2-amine (3bA) and N-(4-
Nitrophenyl)-1,2-dihydronaphthalen-1-amine (3bB): 54% yield (A/B
= 59:41) obtained by following method A with [Ru(TPP)CO] as
catalyst; 73% yield (A/B = 61:39) by following method B with
[Ru(TPP)CO] as catalyst. 3bA and 3bB: C16H14N2O2 (266.11): (C), 135.2 (CH), 130.7 (CH), 126.5 (CH), 111.6 (CH), 59.1 (CH),
calcd. C 72.16, H 5.30, N 10.52; found C 71.76, H 5.27, N 10.46.
31.4 (CH2), 31.1 (CH2). EI-MS: m/z = 204 [M]+.
Eur. J. Inorg. Chem. 2012, 569–580
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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577

E. Gallo et al.
3,5-Bis(trifluoromethyl)-N-(oct-1-en-3-yl)benzenamine (6A) and H 4.01, N 3.18. H NMR (300 MHz, CDCl3): δ = 7.42–7.37 (m, 5
FULL PAPER
1
(E/Z)-3,5-Bis(trifluoromethyl)-N-(oct-2-enyl)benzenamine
(6B):
H, HAr), 7.28–7.25 (m, 3 H, HAr), 7.19 (s, 1 H, HAr), 7.14–7.12 (m,
1 H, HAr), 7.01 (s, 2 H, HAr), 6.10 [d, 1 H, J = 4.6 Hz, C(Ph)=CH–
CH(NH)], 4.51 [m, 1 H, CH(NH)], 4.26 (d, 1 H, J = 8.9 Hz, NH),
3.22 (dd, 1 H, J = 15.4 Hz and 5.7 Hz, CH2), 3.05 (dd, 1 H, J =
15.4 Hz and 7.2 Hz, CH2) ppm. 13C NMR (75 MHz, CDCl3): δ =
20% yield (A/B = 45:55) obtained by following method A with
[Ru(TPP)CO] as catalyst; 11% yield (A/B = 45:55) by following
method A with 7 as catalyst; 22% yield (A/B = 50:50) by following
method B with 7 as catalyst. 6A: C16H19F6N (339.14): calcd. C
56.63, H 5.64, N 4.13; found C 57.02, H 6.00, N 4.06. 1H NMR 147.8 (C), 142.5 (C), 139.8 (C), 134.2 (C), 134.1 (C), 133.0 (q, J =
(300 MHz, CDCl3): δ = 7.13 (s, 1 H, HAr), 6.94 (s, 2 H, HAr), 5.72 32.8 Hz, C–CF3), 129.3 (CH), 128.8 (CH), 128.4 (CH), 128.3 (CH),
(ddd, 1 H, J = 17.2, 10.3 Hz and 6.1 Hz, CH=CH2), 5.23 (d, J =
17.2 Hz, 1 H, CH=CH2), 5.20 (d, 1 H, J = 10.3 Hz, CH=CH2),
4.09 (d, J = 6.9 Hz, 1 H, NH), 3.87–3.83 [m, 1 H, CH(NH)], 1.65–
127.4 (CH), 126.8 (CH), 126.6 (CH), 123.9 (q, J = 271.0 Hz, CF3),
112.8 (CH), 110.8 (CH), 47.7 (CH), 34.7 (CH2) ppm. 19F NMR
(282 MHz, CDCl3): δ = –63.51 ppm. EI-MS: m/z = 433 [M]+. Com-
1.61 (m, 2 H, CH2), 1.36–1.30 (m, 6 H, CH2), 0.92 (3 H, pst, J = pound 8B was isolated by chromatography as a mixture with 1-
6.9 Hz, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 148.5 (C),
138.9 (CH), 132.6 (q, J = 32.4 Hz, C–CF3), 124.0 (q, J = 270.8 Hz,
CF3), 116.4 (CH2), 112.8 (CH), 110.4 (br., CH), 56.4 (CH), 36.1
phenylnaphthalene because of the very similar Rf values of these
compounds in several solvents on both alumina and silica. The
presence of 1-phenylnaphthalene was confirmed by GC–MS analy-
(CH2), 32.0 (CH2), 25.9 (CH2), 22.9 (CH2), 14.4 (CH3) ppm. 19F sis. The 1H, 13C and 19F NMR spectra of this mixture are reported
1
NMR (282 MHz, CDCl3): δ = –63.57 ppm. EI-MS: m/z = 339
in the Supporting Information. The H and 13C NMR signals of
[M]+. 6B: E/Z = 63:37. C16H19F6N (339.14): calcd. C 56.63, H 5.64,
8B have been attributed by COSY, NOESY, HSQC and HMBC
N 4.13; found C 56.90, H 5.85, N 3.99. 1H NMR (300 MHz, techniques.
CDCl3): E isomer: δ = 7.16 (s, 1 H, HAr), 6.96 (s, 2 H, HAr), 5.77–
Synthesis of 9: Complex 7 (99 mg, 8.5ϫ10–2 mmol) was added to
5.64 (m, 1 H, CH=CH), 5.54–5.51 (m, 1 H, CH=CH), 4.20 (br. s,
1 H, NH), 3.79–3.76 (m, 2 H, CH2), 2.09–2.05 (m, 2 H,
CH2CH=CH), 1.40–1.20 (m, 6 H, CH2), 0.93–0.89 (m, 3 H, CH3)
ppm; Z isomer: δH = 7.17 (s, 1 H, HAr), 6.96 (s, 2 H, HAr), 5.77–
5.64 (m, 1 H, CH=CH), 5.54–5.51 (m, 1 H, CH=CH), 4.12 (br. s,
1 H, NH), 3.84–3.81 (m, 2 H, CH2), 2.17–2.14 (m, 2 H,
CH2CH=CH), 1.40–1.20 (m, 6 H, CH2), 0.93–0.89 (m, 3 H, CH3)
ppm. 13C NMR (75 MHz, CDCl3): δ = 148.7 (C), 134.8 (CH),
134.7 (CH), 132.3 (m, C–CF3), 125.0 (CH), 124.9 (CH), 112.0
(CH), 111.9 (CH), 110.1 (CH), 45.7 (CH2), 40.8 (CH2), 32.3 (CH2),
31.5 (CH2), 31.3 (CH2), 29.1 (CH2), 28.8 (CH2), 27.6 (CH2), 22.4
(CH2), 14.0 (CH3) ppm. 19F NMR (282 MHz, CDCl3): δ =
–63.55 ppm. EI-MS: m/z = 339 [M]+.
a benzene (15 mL) solution of 3,5-bis(trifluoromethyl)phenyl azide
(217 mg, 8.4ϫ10–1 mmol) and cyclohexene (0.42 mL, 4.25 mmol).
The resulting solution was stirred at 75 °C, and the aryl azide con-
version was monitored by IR spectroscopy, which measured the
characteristic N3 absorbance at 2116 cm–1. After 4 h (60% of ArN3
conversion), TLC (alumina, petroleum ether/dichloromethane =
8:2) showed the complete consumption of 7. The reaction mixture
was concentrated to 2 mL and petroleum ether (20 mL) was added.
The resulting suspension was filtered to eliminate a dark insoluble
residue and concentrated to 10 mL. The resulting purple solid was
collected by filtration and dried in vacuo (20 mg, 18%). GC–MS
analysis of the solution revealed the presence of the allylic amine N-
(cyclohex-2-enyl)-3,5-bis(trifluoromethyl)benzenamine. C72H52F12-
N6Ru (1329.47): calcd. C 65.01, H 3.94, N 6.32; found C 65.20, H
4.03, N 6.20. UV/Vis (CH2Cl2): λmax [log(ε/m–1 cm–1)] = 414 [480],
Synthesis of 7: 3,5-Bis(trifluoromethyl)phenyl azide (223 mg,
0.87 mmol) was added to a benzene (60 mL) suspension of
[Ru(TPP)(CO)] (210 mg, 0.28 mmol). The resulting dark solution
was heated to reflux under nitrogen for 4 h until the complete con-
sumption of [Ru(TPP)(CO)] was observed by TLC (SiO2, petro-
leum ether/CH2Cl2 = 7:3). The mixture was evaporated to dryness,
and the residue was purified by chromatography (alumina, petro-
leum ether/dichloromethane = 8:2) to give 7 (230 mg, 70%).
C60H34N6F12Ru (1167.33): calcd. C 61.70, H 2.93, N 7.20; found
C 61.34, H 2.99, N 7.55. UV/Vis (CH2Cl2): λmax [log(ε/m–1 cm–1)]
526 [3.92] nm; IR (nujol): ν = 1013 (oxidation marker) cm–1; IR
˜
(ATR): ν = 1008 (oxidation marker) cm–1. 1H NMR (300 MHz,
˜
CDCl3): δ = 8.44 (s, 8 H, Hβ), 7.90–7.87 (m, 8 H, Ho), 7.75–7.71
(m, 12 H, Hm–p), 6.91 (s, 2 H, HAr), 4.30–4.26 (m, 2 H, CH–
CH=CH), 2.85–2.82 (m, 2 H, HAr), 2.61–2.59 (m, 2 H, HAr), 1.60–
1.54 (m, 2 H, CH=CH–CH2 overlapping with H2O), 0.88–0.82 (m,
2 H, CH=CH–CHH), 0.52–0.43 (m, 2 H, CH=CH–CHH), 0.13–
0.09 (m, 2 H, CH2–CHH–CH2 overlapping with grease), –0.04 to
–0.10 (m, 2 H, CH2–CHH–CH2), –1.57 to –1.62 (m, 2 H, N–CH–
CHH), –1.91 to –1.95 (m, 2 H, N–CH–CHH), –2.10 to –2.13 (m,
2 H, N–CH) ppm. The 13C NMR spectrum is not reported because
9 partly decomposed during the experiment. 19F NMR (282 MHz,
CDCl3): δ = –63.25, –63.00 ppm. ESI-MS: m/z = 1331 [M + 1]+.
= 419 [5.03], 526 [4.00] nm. IR (ATR): ν = 1014 (oxidation marker),
˜
877 (imido band) cm–1; IR (CH2Cl2):
ν = 1016 (oxidation
˜
marker) cm–1; IR (nujol): ν = 1016 (oxidation marker), 878 (imido
˜
1
band) cm–1. H NMR (300 MHz, CDCl3): δ = 8.87 (s, 8 H, Hβ),
8.08 (d, J = 6.9 Hz, 8 H, Ho), 7.83–7.76 (m, 12 H, Hm–p), 6.60 (s,
1
Synthesis of 10: 4-(Trifluoromethyl)phenyl azide (74.0 mg,
0.393 mmol) was added to a benzene (50 mL) suspension of
[Ru(TPP)CO] (145 mg, 0.197 mmol) to give a dark solution, which
was heated to reflux under nitrogen for 30 min. The mixture was
concentrated to 30 mL and filtered to eliminate unreacted
[Ru(TPP)CO]. The resulting solution was evaporated to dryness
and n-hexane (20 mL) was added. The purple solid was collected
by filtration and dried in vacuo (88 mg, 44%). C58H37F6N6Ru
(1032.37): calcd. C 67.44, H 3.61, N 8.14; found C 67.87, H 3.98,
N 8.05. UV/Vis (CH2Cl2): λmax [log(ε/m–1 cm–1)] = 417 [5.42], 530
2 H, HAr), 2.66 (s, 4 H, HAr) ppm. H NMR (300 MHz, C6D6): δ
= 9.00 (s, 8 H, Hβ), 8.17 (d, J = 6.9 Hz, 8 H, Ho), 7.62–7.58 (m,
12 H, Hm–p), 6.58 (s, 2 H, HAr), 2.95 (s, 4 H, HAr) ppm. 13C NMR
(75 MHz, CDCl3): δ = 151.9 (C), 142.5 (C), 141.9 (C), 134.6 (CH),
131.9 (CH), 129.7 (q, J = 33.2 Hz, C–CF3), 128.4 (CH), 127.2
(CH), 123.6 (C), 122.3 (q, J = 271.7 Hz, CF3), 118.1 (CH), 117.8
(CH) ppm. 19F NMR (282 MHz, CDCl3): δ = –64.06 ppm. 19F
NMR (282 MHz, C6D6): δ = –63.75 ppm. ESI-MS: m/z = 1169 [M
+ 1]+.
N-[3,5-Bis(trifluoromethyl)phenyl]-1,2-dihydro-4-phenylnaphthalen-
2-amine (8A) and 1-[3,5-Bis(trifluoromethyl)phenyl]-1a,2,3,7b-tetra-
hydro-7b-phenyl-1H-naphtho[2,1-b]azirine (8B): 61% yield (A/B =
54:46) obtained by following method A with 7 as catalyst. 8A:
C24H17F6N (433.13): calcd. C 66.51, H 3.95, N 3.23; found C 66.65,
[4.27] nm. IR (ATR): ν = 1011 (oxidation marker), 838 (imido
˜
band) cm–1; IR (CH Cl ): ν = 1015 (oxidation marker) cm–1; IR
˜
2
2
(nujol): ν = 1012 (oxidation marker), 842 (imido band) cm–1. 1H
˜
NMR (300 MHz, C6D6): δ = 9.00 (s, 8 H, Hβ), 8.15 (d, 8 H, J =
9.1 Hz, Ho), 7.59–7.58 (m, 12 H, Hm–p), 5.94 (d, 4 H, J = 8.4 Hz,
578
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 569–580

Ru–Porphyrin-Catalysed Allylic Amination of Olefins
HAr), 2.61 (d, 4 H, J = 8.4 Hz, HAr). 13C NMR (75 MHz, C6D6):
δ = 154.0 (C), 144.5 (C), 142.9 (C), 142.6 (C), 142.0 (CCF3, q, J =
27.2 Hz), 134.7 (CH), 131.5 (CH), 126.8 (CH), 122.9 (CH), 121.9
(CF3, q, 185.9 Hz), 118.3 (CH) ppm, the complex partly decom-
posed during the analysis. 19F NMR (282 MHz, C6D6): δ =
–62.6 ppm. ESI-MS: m/z = 1033 [M + 1]+.
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Synthesis of 11. Method I: 4-(Trifluoromethyl)aniline (45.9 mg,
2.85ϫ10–1 mmol) was added to a benzene (50 mL) suspension of
[Ru(TPP)CO] (105.6 mg, 1.4ϫ10–1 mmol). The resulting red solu-
tion was stirred at room temperature for 30 min, concentrated to
2 mL and n-hexane (15 mL) was added. The resulting red solid was
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Method
II:
4-(Trifluoromethyl)phenyl
azide
(151.2 mg,
8.08ϫ10–1 mmol) was added to a benzene (50 mL) suspension of
[Ru(TPP)CO] (149.9 mg, 2.02ϫ10–1 mmol). The resulting dark
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˜
IR (CH Cl ): ν = 1942 (CO stretch), 1009 (oxidation marker) cm–1;
˜
2
2
IR (nujol): ν = 1965 (CO stretch), 1009 (oxidation marker) cm–1.
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= 7.5 Hz, Ho), 8.10 (d, 4 H, J = 7.5 Hz, HoЈ), 7.70 (4 H, pst, J =
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–13.43 ppm due to coordinated ArNH2. 13C NMR (75 MHz,
C6D6): δ = 144.6 (C), 143.0 (C), 135.2 (CH), 134.2 (CH), 132.7
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FULL PAPER
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Received: July 22, 2011
Published Online: November 15, 2011
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