Sulfonate-functionalized NHC-based ruthenium catalysts for the isomerization of allylic alcohols in water. recyclability studies

Article abstract of DOI:10.1021/om100601r

Two new complexes of the type [Ru(CO₃)(η⁶-arene) (NHC)]Cs, in which the NHC ligand incorporates a sulfonate functionality, have been prepared and fully characterized. The two water-soluble complexes have been tested in the catalytic isomerization of allylic alcohols in water. The p-cymene compound (labeled as 1) was shown to be an excellent catalyst when compared to other related Ru catalysts. This catalyst can be recycled by simple liquid-liquid extractions several times without detected loss of activity.

Full text of DOI:10.1021/om100601r

Organometallics 2010, 29, 3661–3664 3661
DOI: 10.1021/om100601r
Sulfonate-Functionalized NHC-Based Ruthenium Catalysts for the
Isomerization of Allylic Alcohols in Water. Recyclability Studies
Arturo Azua, Sergio Sanz, and Eduardo Peris*
´
ꢀ
Departamento de Quımica Inorganica y Organica, Universitat Jaume I. Avenida Vicente Sos Baynat s/n,
ꢀ
Castellon, E-12071 Spain
ꢀ
Received June 21, 2010
Two newcomplexesof the type [Ru(CO3)(η6-arene)(NHC)]Cs,inwhichtheNHCligandincorporates
a sulfonate functionality, have been prepared and fully characterized. The two water-soluble complexes
have been tested in the catalytic isomerization of allylic alcohols in water. The p-cymene compound
(labeled as 1) was shown to be an excellent catalyst when compared to other related Ru catalysts. This
catalyst can be recycled by simple liquid-liquid extractions several times without detected loss of
activity.
Introduction
have been described in the literature,5,6 but we found only
three recent examples in which the complexes obtained were
used as water-soluble catalysts.5
During the last two decades, there has been an increasing
interest in the use of water as solvent for many homoge-
neously catalyzed reactions.1,2 The potential advantages of
water over usual organic solvents may include cost, safety,
and environmental concerns.2 Water-soluble versions of al-
most any kind of ligand are nowadays known, although
phosphines are by far the ones that have been more widely
studied,1,3 probably because they have been extensively used
in the preparation of homogeneous catalysts. Despite the
increasing interest in the use of N-heterocyclic carbenes
(NHCs) in the design of homogeneous catalysts during the
last two decades, it is rather surprising that these types of
ligands have rarely been prepared in their water-soluble
versions for homogeneously catalyzed reactions in water.4
NHCs may introduce a series of advantages over phosphines
in the design of water-soluble catalysts. For example, (i)
NHCs are considered as stabilizing ligands for transition
metal complexes; thus they may improve the stability of the
catalyst in water; (ii) phosphines are easily oxidized and may
generate undesirable residues; and (iii) NHCs are known to
be less toxic than phosphines. A few examples of NHC
ligands containing hydrophilic groups (mainly sulfonates)
Aiming to obtain suitable complexes that can facilitate
homogeneously catalyzed reactions in water, we now report
the preparation of two new Ru(η6-arene)(NHC) compounds
in which the NHC ligand has a sulfonate group. The two new
compounds have been studied in the water-catalyzed iso-
merization of allylic alcohols.
Results and Discussion
Compounds 1 and 2 were prepared from the reaction of
[RuCl2(η6-arene)]2 (arene = hexamethylbenzene or p-cymene)
and N,N0-(methyl)(propanesulfonate)imidazolium in the pre-
sence of cesium carbonate in refluxing acetonitrile (Scheme 1).
Both complexes were insoluble in most organic solvents, al-
though they were soluble in MeOH and water (water solu-
bility >300 g/L). Compounds 1 and 2 were characterized by
NMR spectroscopy, electrospray mass spectrometry (ESI-
MS), and elemental analysis. The most representative NMR
data arise from the 13CNMR spectra, which show the signals
due to the Ru-Ccarbene carbons at δ 176.4 (1) and 179.4 (2).
The 13C NMR signals due to the carbon at the carbonate
ligand appear at δ 167.3 (1) and 167.1 (2). The presence of the
carbonate ligand is also confirmed by the presence of a broad
band at 1595.8 (1) and 1586.2 (2) cm-1, in accordance with
the frequencies shown for other related Ru(CO3)(η6-arene)-
(NHC) complexes previously reported.7
*To whom correspondence should be addressed. E-mail: eperis@
qio.uji.es.
(1) Herrmann, W. A.; Kohlpaintner, C. W. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1524.
(2) Lamblin, M.; Nassar-Hardy, L.; Hierso, J. C.; Fouquet, E.;
Felpin, F. X. Adv. Synth. Catal. 2010, 352, 33. Lindstrom, U. M. Chem.
Rev. 2002, 102, 2751.
(3) Shaughnessy, K. H. Chem. Rev. 2009, 109, 643. Pinault, N.; Bruce,
D. W. Coord. Chem. Rev. 2003, 241, 1.
(4) A full and detailed review on the synthesis of hydrophilic carbene
ligands can be found in: Shaughnessy, K. H. Chem. Rev. 2009, 109, 643.
(5) Turkmen, H.; Can, R.; Cetinkaya, B. Dalton Trans. 2009, 7039.
Fleckenstein, C.; Roy, S.; Leuthausser, S.; Plenio, H. Chem. Commun. 2007,
2870. Papini, G.; Pellei, M.; Lobbia, G. G.; Burini, A.; Santini, C. Dalton
Trans. 2009, 6985.
(6) Virboul, M. A. N.; Lutz, M.; Siegler, M. A.; Spek, A. L.; van
Koten, G.; Gebbink, R. Chem.;Eur. J. 2009, 15, 9981. Nagai, Y.; Kochi,
T.; Nozaki, K. Organometallics 2009, 28, 6131.
The presence of the carbonate ligand in the Ru complex
offered us a good opportunity to study the reaction of this
complex with H2, in connection with our previous studies
on the reduction of CO2 with Ir and Ru NHC-based com-
plexes.8 The reaction of 1 in the presence of KOH (1 M) and
50 atm of H2 affords the formation of KCHOO, so the
(7) Demerseman, B.; Mbaye, M. D.; Semeril, D.; Toupet, L.; Bruneau,
C.; Dixneuf, P. H. Eur. J. Inorg. Chem. 2006, 1174.
(8) Sanz, S.; Azua, A.; Peris, E. Dalton Trans. 2010, 39, 6339. Sanz, S.;
Benitez, M.; Peris, E. Organometallics 2010, 29, 275.
r
2010 American Chemical Society
Published on Web 07/19/2010
pubs.acs.org/Organometallics

3662 Organometallics, Vol. 29, No. 16, 2010
Azua et al.
Scheme 1
Table 1. Isomerization of Allylic Alcohols in H2Oa
formation of carbonate-Ru intermediates may be considered
as possible reaction intermediates in the reduction of CO2
under basic reaction conditions. Unfortunately, we did not
obtain any clear evidence about the nature of the resulting
Ru species after this process.
We tested the catalytic activity of complexes 1 and 2 in the
isomerization of allylic alcohols. This reaction proceeds with
total atom economy and allows the direct preparation of the
corresponding carbonyl compounds, thus simplifying the
conventional two-step organic procedures.9 Several ruthe-
nium complexes have been reported to show high activities in
this catalytic reaction,10-14 and some of them have provided
excellent outcomes using water as solvent,10,11,13,15 although
there are just a few studies reporting the recycling of the
catalyst for its reuse in further catalytic cycles.10,11,13,16
The reactions were carried out in water with a 0.2 mol %
catalyst loading at 100 °C. For comparative purposes we
entry
R
catalyst
time (h)
yieldb
1
2
3
4
5
6
7
8
H
H
Et
2
1
2
1
2
1
1
1
4
2
4
4
4
4
4
4
4
99
99
6
98
2
98
90
92
0
20
99
Et
nPr
nPr
nPr
nPr
nPr
nBu
nBu
[RuCl2(p-cymene)(IMe)]
[RuCl2(p-cymene)]2
RuCl3 3H2O
9
10
11
3
2
1
a Reactions performed in a sealed tube under N2 atmosphere at 100 °C,
allylic alcohol (0.5 mmol), catalyst (0.2 mol %), using 1 mL of H2O as
solvent. b Yields and conversions determined by GC and 1H NMR
spectroscopy, using anisole as internal standard.
also tested RuCl3 3H2O, [RuCl2(p-cymene)]2, and [RuCl2(p-
3
cymene)(IMe)] (IMe = N,N-dimethylimidazolylidene). As
can be seen from the data shown in Table 1, compound 1
is far more active than 2, in agreement with previously re-
ported results by Crochet and co-workers, where the cata-
lytic activityof Ru(p-cymene) complexes is shown to be higher
than the Ru(hexamethylbenzene) analogues.13 This result
may indicate that the decoordination of the η6-arene ligand
may also be playing a role in the activation of the catalyst.
[RuCl2(p-cymene)]2 and [RuCl2(p-cymene)(IMe)] also affor-
ded very good catalytic outcomes (entries 7 and 8), although
slightly lower than that shown by 1 (entry 6). The differences
in catalytic activities between 1, [RuCl2(p-cymene)]2, and
[RuCl2(p-cymene)(IMe)] are more important when shorter
reaction times are used. For example, for catalyst 1, the
reaction is almost complete after 1 h (yield: 85%), while for
[RuCl2(p-cymene)]2 and [RuCl2(p-cymene)(IMe)] yields are
below 60%.
Remarkably, all the reactions proceed without the need of
the addition of an external base, which not only simplifies the
reaction procedure but also increases the atom economy of
the overall process.
We also monitored the isomerization of 1-hexen-3-ol using
catalyst 1 in H2O and D2O in order to determine if there is a
measurable kinetic isotopic effect (KIE) for this process.
According to Figure 1, we calculated a KIE value of kH/kD =
1.33 (based on the determination of t1/2 values at 100 °C), but
this low value is likely to be due to a solvent isotopic effect
rather than an effect attributed to the intrinsic reaction mec-
hanism. The time-course plots show a sigmoidal shape, indi-
cating that the catalyst needs an activation period of ca.
30 min, which is probably the time needed for the loss of the
carbonate ligand. In a recent study we observed that the KIE
measured for the isomerization of an O-deuterated allylic
alcohol was negligible, indicating that the O-H(D) bond
activation is not the rate-determining step of the reaction.14
Due the great solubility of 1 in water, the reaction products
can be easily separated from the catalyst by simple liquid-
liquid extraction once the reaction is complete. Also, the high
activity of the catalyst in the absence of any external base
simplifies the experimental workup for the catalyst reuse.
The reactions were carried out using a 1 or 0.5 mol % catalyst
loading at 100 °C. The isomerization of two allylic alcohols
(1-hepten-3-ol and 1-hexen-3-ol) was studied. After each
cycle, the organic products were extracted with CHCl3, and
(9) Cadierno, V.; Crochet, P.; Gimeno, J. Synlett 2008, 1105. Cadierno,
V.; Crochet, P.; Garcia-Garrido, S. E.; Gimeno, J. Dalton Trans. 2010, 39, 4015.
Uma, R.; Crevisy, C.; Gree, R. Chem. Rev. 2003, 103, 27.
(10) Crochet, P.; Diez, J.; Fernandez-Zumel, M. A.; Gimeno, J. Adv.
Synth. Catal. 2006, 348, 93.
(11) Cadierno, V.; Garcia-Garrido, S. E.; Gimeno, J. Chem. Com-
mun. 2004, 232. Cadierno, V.; Crochet, P.; Garcia-Garrido, S. E.; Gimeno, J.
Dalton Trans. 2004, 3635.
(12) Ito, M.; Kitahara, S.; Ikariya, T. J. Am. Chem. Soc. 2005, 127,
6172. Crochet, P.; Fernandez-Zumel, M. A.; Gimeno, J.; Scheele, M.
Organometallics 2006, 25, 4846. Doppiu, A.; Salzer, A. Eur. J. Inorg.
Chem. 2004, 2244. Fekete, M.; Joo, F. Catal. Commun. 2006, 7, 783.
Martin-Matute, B.; Bogar, K.; Edin, M.; Kaynak, F. B.; Backvall, J. E.
Chem.;Eur. J. 2005, 11, 5832. Campos-Malpartida, T.; Fekete, M.; Joo, F.;
Katho, A.; Romerosa, A.; Saoud, M.; Wojtkow, W. J. Organomet. Chem.
2008, 693, 468. Cadierno, V.; Crochet, P.; Francos, J.; Garcia-Garrido, S. E.;
Gimeno, J.; Nebra, N. Green Chem. 2009, 11, 1992. Takai, Y.; Kitaura, R.;
Nakatani, E.; Onishi, T.; Kurosawa, H. Organometallics 2005, 24, 4729.
Lastra-Barreira, B.; Diez, J.; Crochet, P. Green Chem. 2009, 11, 1681.
(13) Diaz-Alvarez, A. E.; Crochet, P.; Zablocka, M.; Duhayon, C.;
Cadierno, V.; Gimeno, J.; Majoral, J. P. Adv. Synth. Catal. 2006, 348,
1671.
(14) da Costa, A. P.; Mata, J. A.; Royo, B.; Peris, E. Organometallics
2010, 29, 1832.
(15) Cadierno, V.; Garcia-Garrido, S. E.; Gimeno, J.; Varela-Alvarez,
A.; Sordo, J. A. J. Am. Chem. Soc. 2006, 128, 1360.
(16) Knight, D. A.; Schull, T. L. Synth. Commun. 2003, 33, 827.
Bianchini, C.; Meli, A.; Oberhauser, W. New J. Chem. 2001, 25, 11.

Article
Organometallics, Vol. 29, No. 16, 2010 3663
Figure 1. Time course of isomerization of 1-hexen-3-ol using catalyst 1 (0.5 mol %) in H2O and D2O at 100 °C.
Table 2. Catalyst Recycling in the Isomerization Reactions of
Allylic Alcohols Running in H2Oa
to activate the catalyst. In a more recent example, Caminade
and co-workers reported a Ru-based dendrimer terminated
with water-soluble phosphines that was also recycled in the
catalytic isomerization of allylic alcohols,17 although in this
example the reactions took longer (24 h each run) and the loss
of activity was detected after four runs.
entry
R
% Ru
1
run
yieldb
TONc
Conclusions
1
2
3
4
5
6
7
8
nBu
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
99
99
99
99
99
99
99
99
26
10
99
99
99
99
99
99
97
90
34
20
99
99
92
88
86
5
99
198
297
396
495
594
693
792
818
828
99
198
297
396
495
594
691
781
815
835
198
396
580
756
928
938
We have prepared two new complexes of the type [Ru-
(CO3)(η6-arene)(NHC)]Cs, in which the NHC ligand incor-
porates a sulfonate functionality. Both compounds are solu-
ble in water, but very insoluble in most organic solvents, for
whichthe complexesarea priorigoodcandidates fordesigning
recyclable catalytic systems in which the catalyst is separated
with the H2O phase by simple liquid-liquid extraction. The p-
cymene complex 1 resulted in being a very effective catalyst in
the isomerization of allylic alcohols, but the most remarkable
result is its capability to be recycled several times without loss
of activity. To the best of our knowledge, catalyst 1 is the best
catalyst in terms of reuse capacity together with a previous
example reported by Crochet, Gimeno, and co-workers,10 but
our system has the advantage that the reaction can be carried
out in the absence of an external base, which in fact simplifies
the reaction procedure and transforms the reaction into a
more environmental friendly process.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
nPr
1
nPr
0.5
Our work constitutes a new report of the very few exam-
ples of the use of NHC-based catalysts incorporating a
hydrophilic functionality for the study of a homogeneously
catalyzed reaction in water.
a Reactions performed in a sealed tube under N2 atmosphere at 100 °C,
allylic alcohol (0.5 mmol) and catalyst, using 1 mL of H2O as solvent.
1
Reaction time: 2 h. b Yields and conversions determined by GC and H
Experimental Section
NMR spectroscopy, using anisole as internal standard. c Cumulative TONs.
NMR spectra were recorded on Varian Innova 300 and 500
MHz spectrometers, using CD3OD and D2O as solvents. Elemen-
tal analyses were carried out in an EA 1108 CHNS-O Carlo Erba
analyzer. Electrospray mass spectra (ESI-MS) were recorded on
a Micromass Quatro LC instrument, and nitrogen was employed
as drying and nebulizing gas. [RuCl2(p-cymene)]2,18 [RuCl2-
(C6Me6)]2,19 and [Ru Cl2(p-cymene)(IMe)]20 were prepared
the aqueous phase containing the catalyst was reused for the
successive cycles. In order to compare the activity of each
individual cycle in each of the sequences, we decided to
perform cycles with a fixed reaction time of 2 h. As can be
seen from the data shown in Table 2, catalyst 1 can be recycled
up to eight times, without important loss of activity, when an
initial 1 mol % catalyst loading was used. For the reactions
carried out with a 0.5 mol % catalyst loading, up to five runs
could be made before the catalyst showed any important loss
of activity. These data compare well with the results reported
by Crochet and Gimeno,10 which are considered the best
reported so far in terms of recycling capacity, although in
their case KOtBu was added to the reaction medium in order
(17) Servin, P.; Laurent, R.; Gonsalvi, L.; Tristany, M.; Peruzzini,
M.; Majoral, J. P.; Caminade, A. M. Dalton Trans. 2009, 4432.
(18) Bennett, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans. 1974,
233.
(19) Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1982, 21, 74.
(20) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus,
G. R. J. Chem.;Eur. J. 1996, 2, 772.

3664 Organometallics, Vol. 29, No. 16, 2010
Azua et al.
according to literature procedures. Solvents and reagents were
used as received from commercial suppliers.
O6SH29RuCs (mol wt 659.49): C, 36.42; H, 4.43; N, 4.25. Found:
C, 36.83; H, 4.73; N, 4.49.
Synthesis of 1. A solution of [RuCl2(p-cymene)]2 (61 mg, 0.1
mmol), (N,N0-(methyl)(propanesulfonate)imidazolium) (41 mg,
0.2 mmol), and cesium carbonate (391 mg, 1.2 mmol) was refluxed
in CH3CN (30 mL) overnight. The suspension was filtered through
Celite, and the solvent was evaporated under reduced pressure. The
crude solid was purified by column chromatography. If it is
necessary, elution with CH3OH/acetone afforded the separation
of a light brown band that contained the compound. The complex
was obtained as a light brown solid by precipitation from MeOH/
Et2O solution (yield: 106.1 mg, 84%). 1H NMR (D2O, 500 MHz):
δ 7.29 (s, 1H, Himid), 7.22 (s, 1H, Himid), 5.76-5.70 (m, 2H, C6H4),
5.36-5.29 (m, 2H, C6H4), 4.21-4.13 (m, 1H, NCH2), 4.00-3.91
(m, 1H, NCH2), 3.61 (s, 3H, CH3N), 2.92-2.83 (m, 1H, CH2-
CH2SO3), 2.81-2.69 (m, 2H, CH2CH2SO3, CHCH3), 2.19-2.09
(m, 2H, CH2CH2SO3), 1.92 (s, 3H, CH3(C6H4)), 1.20-1.11
(m, 6H, CH(CH3)2). 13C{1H} NMR (CD3OD, 300 MHz):
δ 176.37 (1C, Cimid), 167.31 (1C, CO3), 123.92 (1C, Cimid),
121.42 (1C, Cimid), 108.10 (1C, CiPr, p-cymene), 97.64 (1C,
CMe, p-cymene), 83.47 (2C, C6H4), 80.07 (2C, C6H4), 49.47
(1C, CH2SO3), 48.68 (1C, NCH2), 36.94 (1C, NCH3), 31.85 (1C,
CHMe2), 26.79 (1C, CH2CH2SO3), 22.05 (2C, CHMe2), 17.81
(1C, MeC6H4). IR (KBr, cm-1): 1595.81 sbr (CdO), 1199.51 sbr
(SO3), 1041.37 s (SO3). Electrospray HR MS(15V, m/z): 499.0478
[M]-. Anal. Calcd for C18N2O6SH25RuCs (mol wt 631.44): C,
34.24; H, 3.99; N, 4.44. Found: C, 34.51; H, 4.23; N, 4.81.
Synthesis of (N,N0-(Methyl)(propanesulfonate)imidazolium).
A solution of N-(methyl)imidazole (235 mg, 2.8 mmol) and
propanesufate (2.05 g, 16.8 mmol) reacted in 5 mL of CH2Cl2 at
60 °C in a pressure tube for 15 h. The white precipitate was filtered
and washed with CH2Cl2, forming a pure white product (yield:
1
542.64 mg, 95%). H NMR (D2O, 300 MHz): δ 8.83 (s, 1H,
Himid), 7.61 (s, 1H, Himid), 7.56 (s, 1H, Himid), 4.50-4.39 (m, 2H,
NCH2), 3.98 (s, 3H, CH3N), 3.04-2.94 (m, 2H, CH2CH2SO3),
2.47-2.34 (m, 2H, CH2CH2SO3). 13C{1H} NMR (D2O, 300
MHz): δ 136.33 (1C, Cimid), 123.88 (1C, Cimid), 122.31 (1C, Cimid),
47.85 (1C, CH2SO3), 47.32 (1C, NCH2), 35.82 (1C, CH3N), 25.22
(1C, CH2CH2SO3)). Electrospray MS (15 V, m/z): 203.1 [M -
H]-. Anal. Calcd for C7N2O3SH12 (mol wt 204.25): C, 41.16; H,
5.92; N, 13.72. Found: C, 41.32; H, 6.11 N, 13.97.
Catalytic Isomerization of Allylic Alcohols in Water. In a sealed
tube, catalyst (0.005 mmol) and the corresponding allylic alcohol
(0.5 mmol) were mixed in 1 mL of desoxigenated water under inert
atmosphere and stirred at 100 °C for the appropiate time. The pro-
ducts were extracted twice with 2 mL of CHCl3, and anisole
(0.5 mmol) was added to the resulting solution. The reaction mix-
ture was analyzed by NMR and gas chromatography.
Recycling Procedure. After cooling the reaction mixture, the
product was extracted twice with 2 mL of CHCl3, and anisole
(0.5 mmol) was added to the resulting solution. The resulting
solution was analyzed by NMR and gas chromatography. The
traces of organic solvent were eliminated at reduced pressure.
Substrate (0.5 mmol) was added and the mixture was heated
at 100 °C.
Synthesis of 2. A solution of [RuCl2(C6Me6)]2 (69 mg, 0.1
mmol), (N,N0-(methyl)(propanesulfonate)imidazolium) (41 mg,
0.2 mmol), and cesium carbonate (391 mg, 1.2 mmol) was refluxed
in CH3CN (30 mL) overnight. The suspension was filtered
through Celite, and the solvent was evaporated under reduced
pressure. The crude solid was purified by column chromatogra-
phy. If it is necessary, elution with CH3OH/acetone afforded the
separation of a yellow band that contained the compound. The
complex was obtained as a yellow solid by precipitation from
Reaction of 1 with Pressurized Hydrogen. Ten mg of com-
pound 1 and 120 mg of KOH were dissolved in 2 mL of D2O.
This solution was pressurized up to 50 bar of H2 in a Hastelloy
Autoclave Mini-Reactor system for 16 h. After this time the
KCHOO signal is observed by 1H NMR.
1
MeOH/Et2O solution (yield: 101.6 mg, 77%). H NMR (D2O,
Acknowledgment. We gratefully acknowledge finan-
ꢀ
300 MHz): δ 7.42 (s, 1H, Himid), 7.33 (s, 1H, Himid), 4.32-4.23 (m,
1H, NCH2), 3.98-3.89 (m, 1H, NCH2), 3.64 (s, 3H, CH3N),
2.98-2.90 (m, 1H, CH2CH2SO3), 2.81-2.71 (m, 1H, CH2CH2-
SO3), 2.32-2.18 (m, 2H, CH2CH2SO3), 2.11 (s, 18H, C6Me6).
13C{1H} NMR (CD3OD, 300 MHz): δ 179.37 (1C, Cimid), 167.10
(1C, CO3), 123.91 (1C, Cimid), 121.34 (1C, Cimid), 92.79 (6C,
C6Me6), 49.25 (1C, CH2SO3), 48.24 (1C, NCH2), 36.59 (1C,
NCH3), 26.77 (1C, CH2CH2SO3), 14.96 (6C, C6Me6). IR (KBr,
cm-1): 1586.16 sbr (CdO), 1185.04, sbr (SO3), 1039.44 s (SO3).
Electrospray MS (15 V, m/z): 527.0 [M]-. Anal. Calcd for C20N2-
cial support from the Ministerio de Ciencia e Innovacion
of Spain (CTQ2008-04460 and CTQ2007-31175-E/BQU)
and Bancaixa (P1.1B2007-04). The authors are grateful to
ꢀ
the Serveis Centrals d’Instrumentacio Cientıfica (SCIC)
´
of the Universitat Jaume I for providing us with spectro-
scopic facilities.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.