The (porphyrin)ruthenium-catalyzed aziridination of olefins using aryl azides as nitrogen sources

Article abstract of DOI:10.1002/ejoc.200700678

Aryl azides have been used as atom-efficient nitrene transfer reagents in the (porphyrin)ruthenium-catalyzed amination of olefins. Several azides, olefins and [Ru(porphyrin)CO] complexes were tested to investigate the scope and limits of the reaction. Quantitative yields and short reaction times were achieved by using terminal olefins and aryl azides bearing electron-withdrawing groups on the aryl moiety. The reactions were influenced by steric factors. Internally disubstituted olefins exhibited a lower reactivity and tri- and tetra-substituted olefins did not react at all. A very high turnover number (TON) for the [Ru(TPP)CO] (TPP = tetraphenylporphyrin dianion) catalyzed amination of α-methylstyrene by p-nitrophenyl azide was obtained. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700678

FULL PAPER
DOI: 10.1002/ejoc.200700678
The (Porphyrin)ruthenium-Catalyzed Aziridination of Olefins Using Aryl
Azides as Nitrogen Sources
Simone Fantauzzi,[a] Emma Gallo,*[a] Alessandro Caselli,[a] Cristiana Piangiolino,[a]
Fabio Ragaini,[a] and Sergio Cenini[a]
Keywords: Azides / Aziridines / Ruthenium / Porphyrins / Catalysis
Aryl azides have been used as atom-efficient nitrene transfer
reagents in the (porphyrin)ruthenium-catalyzed amination of
olefins. Several azides, olefins and [Ru(porphyrin)CO] com-
plexes were tested to investigate the scope and limits of the
reaction. Quantitative yields and short reaction times were
achieved by using terminal olefins and aryl azides bearing
electron-withdrawing groups on the aryl moiety. The reac-
tions were influenced by steric factors. Internally disubsti-
tuted olefins exhibited a lower reactivity and tri- and tetra-
substituted olefins did not react at all. A very high turnover
number (TON) for the [Ru(TPP)CO] (TPP = tetraphenylpor-
phyrin dianion) catalyzed amination of α-methylstyrene by
p-nitrophenyl azide was obtained.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
thetic versatility of this class of molecules. The lability of
the Nα–Nβ bond of the N3 group allows the generation of
a nitrene [RN] with the ecofriendly molecular nitrogen be-
ing the only reaction side-product. Therefore, organic az-
ides can be considered as atom-efficient nitrene transfer rea-
gents. Nitrene transfer from RN3 to an organic substrate
can be performed by thermal[40] or photochemical acti-
vation,[41,42] but very often the chemoselectivity of the reac-
tion is low. On the other hand, the presence of transition-
metal catalysts can drive the amination reaction to the de-
sired product under milder conditions. Recently, several re-
views on the use of organic azides as nitrogen sources in
amination reactions have been published.[43–46] Very inter-
esting results were achieved by using tosyl azide,[45,47–50] 2-
(trimethylsilyl)ethanesulfonyl azide[51] and diphenylphos-
phoryl azide[52] as nitrene precursors even in enantioselec-
tive reactions.
In the last few years we have reported on the use of aryl
azides as aminating agents. They represent very convenient
reagents because (i) they can be easily synthesized from the
corresponding substituted anilines by a simple procedure,
(ii) they allow the introduction of a great variety of N-aryl
groups into the molecule and (iii) they are stable enough to
be safely handled in the laboratory. Moreover, it is impor-
tant to point out that the aryl group on the aziridine nitro-
gen atom should be considered as part of the molecule that
can play an important role in further aziridine rearrange-
ments.[53,54]
Introduction
The development of new methods for the direct and se-
lective synthesis of organonitrogen compounds represents
an important goal for both academia and industry. Azirid-
ines exhibit various biological properties,[1–3] and they are
useful building blocks in organic synthesis[4–10] due to easy
opening of the three-membered ring.[11–15] Two of the most
effective routes for the synthesis of this class of compound
are the carbene transfer reaction to imines[16–20] and the
nitrene transfer to olefins.[4] The direct aziridination of un-
saturated hydrocarbons has been extensively studied by em-
ploying [N-(arylsulfonyl)imino]phenyliodinane compounds
[PhI=N(SO2)Ar][21–26] as nitrogen sources which can be pre-
pared in situ from the corresponding sulfonylamine and
iodosylbenzene[27] or (diacetoxyiodo)benzene.[28–31] It
should be noted that by using these synthetic procedures
the side-product of the reaction is iodobenzene, and a sul-
fonyl group is always introduced into the aminated com-
pound. To overcome some of the limitations associated with
the use of iminoiodinane compounds, alternative nitrene
sources such as chloramine-T[32–35] or bromamine-T[36–39]
have been employed. In any case, the N-protecting group is
a sulfonyl derivative.
In the last few years the use of organic azides RN3 as
nitrogen sources has been explored due to the high syn-
[a] Dipartimento di Chimica Inorganica, Metallorganica e Analit-
ica, Università degli Studi di Milano and ISTM-CNR,
Via Venezian 21, 20133 Milano, Italy
Aryl azides react with benzylic C–H bonds to form
amines and imines,[55,56] with conjugated dienes to give N-
aryl-2-vinylaziridines[54] and with styrenes to form N-aryl-
aziridines.[57] The amination reactions of benzylic com-
Fax: +39-0250-314-405
E-mail: emma.gallo@unimi.it
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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E. Gallo et al.
FULL PAPER
pounds are catalyzed by [Co(porphyrin)] complexes and the lyst.[58] In fact, if the sample was not dried at a high tem-
aziridination reactions are efficiently catalyzed by [Ru(por- perature, a decrease in the reaction rate was observed owing
phyrin)CO] complexes.
to the presence of variable amounts of the less active [Ru-
Herein we report a full account of our synthetic results (porphyrin)CO(H2O)] complex.
on the amination of olefins by aryl azides catalyzed by car-
As reported in Table 1, the presence of β-substituted pyr-
bonyl(porphyrin)ruthenium complexes. A preliminary com- rolic moieties in the tetraphenylporphyrin skeleton yielded
munication on this reaction, mainly concerning the mech- high aziridine selectivities in short reaction times (Entries 2
anistic aspects of the reaction, has already been pub- and 3, Table 1). It is important to point out that if a hydro-
lished.[57] The effect of the coordination sphere of the ruthe- gen atom is present in the meso-porphyrin position, as in
nium atom on the catalytic activity has been investigated in the case of [Ru(OEP)CO] (4) (OEP = octaethylporphyrin
detail. To extend the scope of the reaction, we have also dianion) (Entry 4, Table 1), this positive catalytic effect is
studied the effect of different functional groups on the azide suppressed. Complex 4, with flexible ethyl groups, is proba-
and the olefin on the reaction efficiency.
bly able to stack more efficiently than (meso-substituted
porphyrin)ruthenium complexes, thus reducing the access
of organic substrates to the active metal centre. The effect
of the ethyl groups on the overall packing of (porphyrin)-
ruthenium complexes has already been reported.[59]
Results and Discussion
To study the effect on the catalytic activity of the elec-
tronic and/or steric behaviour of different substituents on
(porphyrin)ruthenium complexes, the reaction between α-
methylstyrene and p-nitrophenyl azide was carried out in
the presence of several catalysts (Scheme 1, Table 1).
Several para-substituted meso-arylporphyrins were also
tested. Although precise kinetic measurements were not
taken at this stage, it is apparent that electron-withdrawing
groups on the meso-aryl moiety accelerate the reaction.
However, if substituents are placed at the meta or ortho po-
sitions of the meso-aryl groups, steric effects also become
evident. In fact, the rate of the reaction catalyzed by 11
(Entry 11, Table 1) is lower than may have been expected
based on the high electron-withdrawing power of the two
CF3 groups. Not surprisingly, complex 12, which is deacti-
vated both electronically and sterically, is a less active cata-
lyst. The catalytic behaviour of the methoxy-substituted
(porphyrin)ruthenium complex 13 (Entry 13, Table 1) de-
serves special comment.
It is common for a catalytic cycle to be negatively affec-
ted by the presence of a coordinating group, such as OCH3,
which can compete with the organic substrate for the metal
centre. Therefore, it is not surprising that the rate of the 13-
catalyzed reaction is lower than those observed by using
catalysts containing non-coordinating electron-donating
groups (Entries 8 and 10, Table 1).
In order to mimic the effect of a methoxy group linked
to an aryl ring, such as that present in the ruthenium com-
plex 13, the 1-catalyzed reaction between p-nitrophenyl az-
ide and α-methylstyrene was carried out in the presence of
4-methylanisole by using a catalytic molar ratio 1/azide/4-
methylanisole/olefin of 1:50:50:250. The consumption of
the azide was monitored by IR spectroscopy, measuring the
intensity of the 2121 cm–1 absorption of the N3 group. The
A/A0 vs. time dependence of the [Ru(TPP)CO]-catalyzed re-
actions of p-nitrophenyl azide with α-methylstyrene in the
presence or absence of 4-methylanisole was measured. The
reaction rate was 2.5 times lower when 4-methylanisole was
added to the reaction mixture, which indicates competition
for the ruthenium centre between the methoxy group of 4-
methylanisole and the N3 group of the aryl azide.
Scheme 1. Aziridination reaction of α-methylstyrene by p-ni-
trophenyl azide catalyzed by [Ru(porphyrin)CO] complexes.
Table 1. Aziridination reaction of α-methylstyrene by p-nitrophenyl
azide catalyzed by [Ru(porphyrin)CO] complexes 1–13.[a]
Entry Catalyst
R
RЈ
RЈЈ Time Selectivity
[h][b]
[%][c]
1
2
3
4
5
6
7
8
9
10
11
12
13
1
2
3
4
5
6
7
8
9
10
11
12
13
C6H5
C6H5
C6H5
H
Br
Ph
Et
H
H
H
H
H
H
H
H
H
H
H
H
Et
H
H
H
H
H
H
H
H
H
0.75
0.5
0.5
1.5
0.5
0.75
1
99
98
99
96
98
93
95
99
98
94
97
95
88
H
4-CF3C6H4
4-CH3OCOC6H4
4-ClC6H4
4-nBuC6H4
4-FC6H4
4-tBuC6H4
3,5-(CF3)2C6H3
2,4,6-(CH3)3C6H2
4-CH3OC6H4
1
1.5
1.5
1
2
2
[a] General procedure for the reaction: catalyst (1.20ϫ10–2 mmol)
in refluxing benzene (30 mL), molar ratio catalyst/azide/olefin =
1:50:250. [b] Time required for complete conversion of the starting
1
azide. [c] Determined by H NMR (2,4-dinitrotoluene used as the
internal standard) on complete conversion of the starting azide.
We then investigated the reactivity of different aryl azides
All catalysts employed for the reactions reported in this by using styrene or α-methylstyrene as olefins and [Ru(TPP)-
study were dried in vacuo at 120 °C for 3 h before use. This CO] (1) as the catalyst (Scheme 2, Table 2). [Ru(TPP)CO]
procedure had been shown earlier to be effective in remov- was chosen because it is the synthetically most accessible of
ing all coordinated water without decomposing the cata- the complexes found to have a high catalytic activity.
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(Porphyrin)ruthenium-Catalyzed Aziridination of Olefins
Table 2. Aziridination reactions of styrene and α-methylstyrene by different aryl azides catalyzed by 1.[a]
Entry
Ar
R = H
R = CH3
Time [h][b]
Selectivity [%][c]
Product
Time [h][b]
Selectivity [%][c]
Product
1
2
3
4
5
6
7
8
4-O2NC6H4
4-ClC6H4
4-BrC6H4
4-NCC6H4
4-CH3OC6H4
4-CH3C6H4
1.2
2
2
2
4
4
4
3.2
3.5
1
1.3
3
99
90
95
94
69
40
90
93
99[e]
99
96
85
14
16
18
20
22
24
26
28
30
32
34
36
0.75[d]
1
1.5
1
6
2.5
4
99[d]
95
94
99
54
15
17
19
21
23
25
27
29
31
33
35
37
30
96
4-tBuC6H4
2-O2NC6H4
2,6-(O2N)2C6H3
3,5-(CF3)2C6H3
3,5-Cl2C6H3
3,4,5-(CH3O)3C6H2
3
91
9
3.5
0.5
1
90[f]
97
10
11
12
93
90
2.5
[a] General procedure for the reaction: 1 (9.0 mg, 1.20؋10–2 mmol) in refluxing benzene (30 mL); molar ratio 1/azide/olefin = 1:50:250.
1
[b] Time required for complete conversion of the starting azide. [c] Determined by H NMR (2,4-dinitrotoluene was used as the internal
standard). [d] These data, already present in Table 1 (Entry 1), are reported here for a better comparison of the experimental results. [e]
1
The H NMR spectrum showed the presence of both 1,2-trans/cis isomers in a ratio of 83:17. [f] Only the 1,2-trans isomer was obtained.
Scheme 2. Aziridination reactions of styrene and α-methylstyrene
by different aryl azides catalyzed by 1.
Scheme 3. The pyramidal inversion of the nitrogen atom in com-
pounds 30 and 31.
The data reported in Table 2 suggest that the results de-
pend on both the electronic and the steric characteristics of charge density formed during the nucleophilic attack of the
the azide. In general, the presence of electron-withdrawing azide by the olefin.
groups on the aryl moiety of the azide is responsible for
On the other hand, the presence of an electron-donating
high aziridine selectivities and short reaction times. The group in the para position of the aryl group (Entries 6 and
best results were observed by using para- or meta-substi- 7, Table 2) is responsible for longer reaction times and a
tuted aryl azides (Entries 1–4 and 10 and 11, Table 2). The decrease in aziridine selectivity. When the electron-donating
use of ortho-substituted aryl azides (Entries 8 and 9, group is also a coordinating one, such as the methoxy group
Table 2), in which the N3 group is sterically hindered, re- (Entries 5 and 12, Table 2), this negative effect is enhanced
sulted in longer reaction times. It is worth noting that the for all the reasons illustrated above. This effect is more pro-
1,2-trans and -cis isomers of compound 30 are observable nounced with 4-CH3OC6H4N3 than with 3,4,5-(CH3O)3-
1
as separate products in a ratio of 83:17 in the H NMR C6H2N3 due to the better coordinating capability of an un-
spectrum. The pyramidal inversion of the aziridine nitrogen hindered methoxy group compared with three adiacent
atom is a very well-known process,[60] and usually the in- ones. When the aziridination reaction was performed with
terconversion occurs at room temperature because the en- 4-CH3OC6H4N3 and 4-CH3C6H4N3 (Entries 5 and 6,
ergy barrier is relatively small (ca. 25 kJ/mol). But if, for Table 2), the corresponding aniline was the major by-prod-
any reason, the energy barrier increases, it would be pos- uct of the reaction.
sible to isolate both the cis and trans isomers. The steric
The amination reactions of styrene and α-methylstyrene
hindrance around the N-aryl group in the case of 30 proba- were also performed in the presence of 1 with non-aromatic
bly increases the barrier to cis/trans inversion of the azirid- azides such as benzoyl azide, trimethylsilyl azide and tri-
ine nitrogen atom relative to those of the other aziridines phenylmethyl azide. With benzoyl azide the corresponding
reported in Table 2 (Scheme 3).[6] The reaction of 2,6-(O2N)2- aziridine was formed only in trace amounts. No reaction
C6H3N3 with α-methylstyrene yielded only the 1,2-trans was observed by employing the other two azides which con-
isomer 31 (Entry 9, Table 2).
firms the electrophilic role of the azide.
The correlation observed between the electronic charac-
In order to extend the scope of the reaction, we employed
teristics of the aryl azides and the synthetic results reveals p-nitrophenyl azide to aminate, in the presence of 1, several
the electrophilic role of the azide in the catalytic cycle. olefins. The reactions that gave positive results are reported
Furthermore, as reported in Table 2, α-methylstyrene al- in Table 3; with tri- or tetrasubstituted olefins such as (E)-
ways exhibited better reactivity than styrene. This could be β-methyl-β-nitrostyrene, 2-methyl-1-phenyl-1-propene, α-
due to the presence of the methyl group at the α position methylstilbene and tetraphenylethylene, no reaction was ob-
of the double bond which can stabilize the transient positive served.
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E. Gallo et al.
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Table 3. Aziridination reaction of different olefins by p-nitrophenyl azide catalyzed by 1.[a]
[a] General procedure for the reaction: 1 (9.0 mg, 1.20ϫ10–2 mmol) in refluxing benzene (30 mL); molar ratio 1/p-nitrophenyl azide/
1
olefin = 1:50:250. [b] Time required for complete conversion of the starting azide. [c] Determined by H NMR (2,4-dinitrotoluene was
1
used as the internal standard). [d] The H NMR spectrum showed the presence of both 2,3-cis/trans isomers in a ratio of 3:1.
The reaction efficiency depended on both the electronic
In accord with the poor reactivity of internal olefins, the
and the steric characteristics of the olefins. The best cata- aziridine of (Z)-stilbene was obtained in a low yield and
lytic results were observed by using terminal styrenes bear- after a very long reaction time (Entry 7, Table 3); again the
ing electron-donating substituents either at the α position aniline is the by-product of the reaction. The lack of stereo-
of the double bond (Entry 1, Table 1 and Entries 2 and 3, specificity of the reaction between p-nitrophenyl azide and
Table 3) or on the aryl moiety (Entry 1, Table 3, compound (Z)-stilbene indicates a two-step mechanism, which allows
38), which again indicates the electrophilic role of the azide isomerization to proceed, rather than a concerted nitrogen
in the reaction. This hypothesis is in agreement with the atom transfer (Entry 7, Table 3).[23,61] Nevertheless, with
very low reactivity of the electron-deficient 2,3,4,5,6-penta- (E)-β-methylstyrenes, the aziridination reaction is stere-
fluorostyrene (Entry 5, Table 3).
ospecific probably because, in the stepwise process, the rate
On the other hand, the presence of substituents on the β- of ring closure is fast relative to the rate of Cα–Cβ bond
carbon atom of the double bond (Entries 6 and 7, Table 3) rotation (Entry 6, Table 3).
produces a lowering of the yields and longer reaction times
The reaction of 2-vinylpyridine with p-nitrophenyl azide
for steric reasons. It should be noted that 46 is formed in occurred in 3 h with an aziridine selectivity of 85% despite
good yield and in a short reaction time in spite of the pres- the presence of a coordinating pyridine unit (Entry 8,
ence of a methyl group on the β-carbon atom and of a Table 3). In this case, the inhibiting effect is probably not
methoxy group on the aryl moiety (Entry 6, Table 3). This significant because of the low accessibility of the pyridine
experimental result suggests that in this case the electron- nitrogen atom. In fact, if 4-vinylpyridine, in which coordi-
donating capability of the methoxy group strongly pro- nation is sterically not inhibited, was used as the unsatu-
motes the reaction and balances the negative catalytic effect rated substrate, no reaction would be observed.
arising from the presence of steric hindrance on the double
bond and of a coordinating group on the aryl moiety.
In contrast with the low reactivity of (Z)-stilbene, 5-di-
benzosuberenone reacted with p-nitrophenyl azide to yield
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(Porphyrin)ruthenium-Catalyzed Aziridination of Olefins
Table 4. Optimization of the catalyst loading of 1 for the reaction of α-methylstyrene with p-nitrophenyl azide.[a]
Entry
1 [mol-%]
Molar ratio 1/azide/olefin
Time [h][b]
Conversion [%][c]
Selectivity [%][d]
TON
1
2
3
4
5
2
1:50:250
1:250:1250
1:500:2500
1:1000:5000
1:2500:12500
1
4
6
10
25
100
100
96.5
96.5
92.5
99
97
95
95
92
50
250
482
965
2300
0.4
0.2
0.1
0.04
[a] General procedure for the reaction: catalyst 1 was refluxed in benzene (60 mL) with α-methylstyrene (0.8 mL, 6.15 mmol) and p-
nitrophenyl azide (200 mg, 1.22 mmol). [b] Time required for the reported conversion of the starting azide. [c] Determined by IR spec-
troscopy measuring the absorbance of the azide band at 2121 cm–1. [d] Determined by 1H NMR (2,4-dinitrotoluene was used as the
internal standard).
the corresponding aziridine with a high selectivity in a short lyzed by [CoII(porphyrin)][55,56] and [MnIII(corrole)][64] com-
time (Entry 9, Table 3). We presume that the presence of a plexes, respectively.
conjugated carbonyl group can drive the reaction and that
The pocket conformation of the azide moiety prevents
a different mechanism is involved.[62] As a matter of fact, a close approach of the whole hydrocarbon molecule and
when the carbonyl group of 5-dibenzosuberenone was pro- accounts for the effect that the steric hindrance of the RЈЈ
tected as a cyclic ketal (Entry 10, Table 3), the reaction group has on the reaction rate and selectivity. We do not
slowed down considerably and also the selectivity dropped. discuss the mechanistic aspects of this reaction in this paper
Compound 50 has only been characterized in solution be- because we are still investigating them, and a complete
cause it hydrolyzed to 49 during attempts to purify it by study will be reported in a following paper.[65]
chromatography in the presence of Et3N in the eluent (see
All the catalytic reactions described up to now in this
Exp. Sect.). Since the reaction had been performed to pro- paper were carried out with 2 mol-% catalyst. Although this
vide mechanistic information rather than to obtain a new is a suitable amount on a laboratory scale, a lower catalyst
compound, no further attempt to isolate pure 50 was made. loading would be preferable for industrial applications. We
Overall, the trends in reactivity observed with different have thus studied the effect of decreasing amounts of cata-
olefins strongly point to an end-on approach of the olefin lyst on the aziridination reaction between p-nitrophenyl az-
towards the electrophilic aminating species. This is also in ide and α-methylstyrene catalyzed by 1 taken as a model
full agreement with the higher reactivity of aryl azides bear- case. The results are reported in Table 4.
ing electron-withdrawing groups and the better catalytic
performances of (porphyrin)ruthenium complexes having tios, 92% selectivity in the aziridine was observed even
electron-withdrawing substituents. when only 0.04 mol-% of catalyst was employed (Entry 5,
Although the selectivity was reduced at high catalytic ra-
Figure 1 shows a plausible transition state for the reac- Table 4). It is important to point out that, to the best of
tion which accounts for all the experimental observations our knowledge, the resulting turnover number (TON) of
discussed.
2300 is the highest value reported for the intermolecular
aziridination of olefins[31,50,51,66] and is compatible with an
application in the fine chemicals industry.
Conclusions
We have investigated the synthetic applicability of aryl
azides as nitrogen sources for the aziridination of olefins.
Data collected indicate that by using this methodology a
wide range of aziridines can be obtained as it is possible to
introduce several functional groups onto both the azide and
the olefin. In several cases the high selectivity achieved al-
Figure 1. Proposed transition state for the aziridination reaction
catalyzed by 1.
We propose the formation of an azido(porphyrin)ruthe- lows the aziridine to be obtained as the only reaction prod-
nium(II) adduct, [(ArN3)RuII(porphyrin)(CO)], instead of uct, which confirms the atom efficiency of the reaction. It
an imido(porphyrin)ruthenium(IV) complex, [ArN=RuIV- is important to point out that the large turnover number
(porphyrin)(L)],[51,63] obtained by N2 loss from a metal of 2300 observed in one case also minimizes the problems
azide adduct on the basis of a preliminary kinetic study that associated with catalyst recovery and allows the reaction
indicated that the first step of the reaction is an equilibrium crude to be used for further aziridine modifications. The
and not an irreversible step. Any attempt to spectroscopi- presence of different substituents on the nitrogen atom and
cally observe the species [(ArN3)Ru(TPP)(CO)] failed. Evi- at other positions in the ring allows the aziridines reported
dence that an imidometal complex is not always the group in this paper to be employed in the synthesis of organic
transfer reagent has already been provided by the amination compounds of biological importance.[9] Further studies will
of benzylic groups and by the aziridination of styrenes cata- be directed towards this goal.
Eur. J. Org. Chem. 2007, 6053–6059
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E. Gallo et al.
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are reported in Tables 1, 2, and 3. Analytical data for compounds
14–49 are reported in the Supporting Information.
Experimental Section
General: 1H NMR spectra were recorded with an Avance 300-DRX
Bruker instrument operating at 300 MHz for 1H, at 75 MHz for
13C and at 282 MHz for 19F and with an Avance 400-DRX Bruker
Cyclic Ethyl Ketal of 5H-Dibenzo[a,d]cyclohepten-5-one: 5H-Di-
benzo[a,d]cyclohepten-5-one (506 mg, 2.45 mmol) was refluxed in
toluene (50 mL) with ethylene glycol (10 mL, 180 mmol) and p-
toluenesulfonic acid (51 mg, 0.270 mmol) for 10 h. During the reac-
tion, the Dean–Stark apparatus was used for continuous removal
of the water. Then the reaction mixture was washed with water
(3ϫ10 mL), and the solvents were evaporated to dryness to yield
the title compound (550 mg, 90%). 1H NMR (300 MHz, CDCl3,
300 K): δ = 7.96–7.93 (m, 2 H, ArH), 7.46–7.36 (m, 6 H, ArH),
7.14 (s, 2 H, CH2), 4.17 (br., 2 H, CH2), 3.82 (br., 2 H, CH2) ppm.
13C NMR (75 MHz, CDCl3, 300 K): δ = 138.5 (C), 133.7 (C), 131.5
(CH), 129.8 (CH), 128.4 (CH), 128.1 (CH), 124.4 (CH), 66.0 (CH2),
64.0 (CH2) ppm. C17H14O2 (250.3): calcd. C 81.58, H 6.64; found
C 80.35, H 6.49. MS (EI): m/z = 250 [M+].
instrument operating at 400 MHz for H and at 100 MHz for 13C.
1
Chemical shifts (ppm) are reported relative to TMS. The 1H NMR
signals of compounds described in the following have been assigned
by COSY and NOESY techniques. Assignments of the resonances
in the 13C NMR spectra were made by using the APT pulse se-
quence, HSQC and HMQC techniques. Infrared spectra were re-
corded with a BIO-RAD FTS or with a Varian Scimitar FTS 1000
spectrophotometer. UV/Vis spectra were recorded with an Agilent
8453E instrument. Elemental analyses and mass spectra were re-
corded in the analytical laboratories of Milan University. Unless
otherwise specified, all reactions were carried out under nitrogen
by employing standard Schlenk techniques and magnetic stirring.
Solvents were dried prior to use by standard procedures and stored
under nitrogen. All starting materials were commercial products
and were used as received unless otherwise reported. Aryl az-
ides,[67–69] meso-tetraphenylporphyrins,[70,71] β-substituted meso-tet-
raphenylporphyrins[72,73] and their ruthenium complexes,[54,74,75]
were synthesized according to methods reported in the literature or
by using minor modifications of them. [Ru(OEP)(CO)] (Aldrich)
was used as received. The purity of the azides and olefins employed
Kinetic Measurements: Complex 1 (9.1 mg, 12.3 µmol), p-ni-
trophenyl azide (101.1 mg, 0.617 mmol) and α-methylstyrene
(400 µL, 3.08 mmol) were added to benzene (30 mL) in a Schlenk
flask under N2. The solution was stirred for 1 min to dissolve all
the reagents, and then a sample (0.2 mL) was withdrawn for IR
analysis. The consumption of the azide was monitored by IR spec-
troscopy, measuring the azide absorbance at 2121 cm–1, by with-
drawing samples of the solution at regular times. The absorbance
of the azide was below 1% of the starting value after 1.5 h. The
reaction was repeated in the presence 4-methylanisole. Complex 1
(9.0 mg, 12.1 µmol), p-nitrophenyl azide (99.5 mg, 0.607 mmol), 4-
methylanisole (80 µL, 0.635 mmol) and α-methylstyrene (400 µL,
3.08 mmol) were added to benzene (30 mL) in a Schlenk flask un-
der N2. The procedure reported above was followed. The ab-
sorbance of the azide was below 1% of the starting value after 4 h
(the graphics are reported in the Supporting Information).
1
was checked by GC-MS or H NMR analyses. The [Ru(porphyr-
in)(CO)] complexes employed were kept under vacuum at 120 °C
for 3 h prior to use. The collected analytical data for N-(4-chlo-
rophenyl)-2-phenylaziridine (16)[76] and N-(4-cyanophenyl)-2-phen-
ylaziridine (20)[77] are in agreement with those reported in the lit-
erature.
Synthesis of [Ru(β-Ph4TPP)(CO) (3)]: [Ru3(CO)12] (30.0 mg,
4.69ϫ10–5 mol) and β-Ph4TPPH2
(50.2 mg, 5.47ϫ10–5 mol)
[73]
Supporting Information (see footnote on the first page of this arti-
cle): Analytical data for all reaction products and kinetic graphics.
were dissolved in dry toluene (30 mL), and the resulting purple
solution was refluxed under nitrogen for 18 h. Oxidation of the
crude by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)[78] fol-
lowed by solvent evaporation and purification by flash chromatog-
raphy on silica (eluent n-hexane/dichloromethane, 8:2) yielded pure
[Ru(β-Ph4TPP)(CO)] (37.2 mg, 65%). 1H NMR (300 MHz, CDCl3,
300 K): δ = 8.24 (s, 4 H, Hβ), 7.75–7.68 (m, 8 H, HAr), 7.19–6.78
(m, 32 H, HAr) ppm. 13C NMR (75 MHz, CDCl3, 300 K): δ = 147.7
(C), 146.7 (C), 142.1 (C), 141.5 (C), 139.2 (C), 135.6 (CH), 135.0
(CH), 132.6 (CH), 132.2 (CH), 127.4 (CH), 127.1 (CH), 126.8
(CH), 126.3 (CH), 126.1 (CH), 125.6 (CH), 123.3 (C) ppm.
C69H44N4ORu (1046.2): calcd. C 79.22, H 4.24, N 5.36; found C
Acknowledgments
We thank the Ministero dell’Università e della Ricerca (MIUR),
Programmi di Ricerca Scientifica di Rilevante Interesse Nazionale
(PRIN 2005035123) for financial support and Metalor Technol-
ogies SA for a generous supply of ruthenium trichloride.
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6058
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Eur. J. Org. Chem. 2007, 6053–6059

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Published Online: October 24, 2007
Eur. J. Org. Chem. 2007, 6053–6059
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6059