γ-Methylene chalcogenapyrans and benzopyrans as proaromatic donors in push-pull Fischer type carbene complexes: Influences of chalcogen atom and chain length on the electronic and N.L.O. properties of these molecules

Article abstract of DOI:10.1016/j.jorganchem.2005.07.049

A new class of push-pull molecules bearing γ-methylene chalcogenapyran and benzopyran nucleus as proaromatic donors and methoxypentacarbonyltungstene carbene fragment as acceptors is described. N.L.O. properties (as μβ by EFISH) of these complexes have been investigated. The influence of the unsaturated chain length, of the presence of the fused aromatic ring and of the chalcogen atom on the first hyperpolarizability values are shown.

Full text of DOI:10.1016/j.jorganchem.2005.07.049

Journal of Organometallic Chemistry 690 (2005) 4982–4988
www.elsevier.com/locate/jorganchem
Note
c-Methylene chalcogenapyrans and benzopyrans
as proaromatic donors in ‘‘push–pull’’ Fischer type carbene
complexes: Influences of chalcogen atom and chain length
on the electronic and N.L.O. properties of these molecules
a
a,
a
b
c
c
N. Faux , B. Caro *, F. Robin-Le Guen , P. Le Poul , K. Nakatani , E. Ishow
a
Laboratoire de chimie organometallique et he´te´rocyclique, U.M.R. CNRS 6509, Organome´talliques et catalyse,
Institut de Chimie de Rennes, I.U.T. Lannion, rue E. Branly, 22300 Lannion, France
b
U.C.O. 22200 Guingamp, France
Laboratoire de Photophysique et de Photochimie Supra et Macromole´culaires, UMR 8531, Ecole Normale Supe´rieure de Cachan,
61 avenue du pre´sident Wilson, 94235 Cachan ce´dex, France
c
Received 14 June 2005; received in revised form 13 July 2005; accepted 13 July 2005
Available online 13 September 2005
Abstract
A new class of push–pull molecules bearing c-methylene chalcogenapyran and benzopyran nucleus as proaromatic donors and
methoxypentacarbonyltungstene carbene fragment as acceptors is described. N.L.O. properties (as lb by EFISH) of these complexes
have been investigated. The influence of the unsaturated chain length, of the presence of the fused aromatic ring and of the chal-
cogen atom on the first hyperpolarizability values are shown.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Chalcogenapyran; Fischer type carbene complexes; N.L.O. properties
1. Introduction
portional to Dleg, the difference between the excited and
the ground state dipole moment, to feg the transition di-
pole moment, and inversely proportional to the energy
of the electronic transition DEge implied in the N.L.O.
phenomena ðbað3fe2gDle2gÞ=ðDEg2eÞÞ.
Due to the potential applications in the field of opto-
electronics during the last two decades, intense research
has been conducted to discover organic or organometal-
lic molecular materials with non-linear optical proper-
ties [1]. From a simple theoretical model developped
by Chemla and Oudar [2] about thirty years ago, based
on a sole electronic transition (the two-level model), or-
ganic and organometallic compounds with large first
hyperpolarisability b have been synthesized. In the
approximation of the two-level model, b is directly pro-
Purely organic push–pull molecules in which donor
and acceptor groups are linked via unsaturated p spacers
(Fig. 1) fit the model since they are characterized, partic-
ularly for extended spacers, by a low energy intramolecu-
lar charge transfer electronic transition DEge, a large
transition dipole moment feg, and a significant Dleg [3].
The two-level model has been applied, but with some
limitations, to organometallic push–pull molecules
which possess a low energy metal to ligand electronic
charge transfer transition [4]. For example, in ferrocenyl
push–pull molecules, the presence of two electronic
*
Corresponding author. Tel.: +33 2 96485748; fax: +33 2 96485797.
E-mail addresses: bertrand.caro@iut-lannion.fr (B. Caro), francoise.
le-guen@univ-rennes1.fr (F. Robin-Le Guen).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.049

N. Faux et al. / Journal of Organometallic Chemistry 690 (2005) 4982–4988
4983
liquid crystals materials [10], in photodynamic therapy
[11] and in molecular machines [12].
A
D
spacer
A
D
spacer
In addition, c-methylene pyran structure bearing two
cyano groups has been tested as proaromatic acceptors
for N.L.O. purposes [13]. We anticipate that this hetero-
cyclic fragment could also act as a proaromatic donor in
push–pull type molecules.
Fig. 1. Schematic representation of push–pull chromophore.
transitions in the visible spectrum, which play a role in
the N.L.O. phenomena does not allow a simple analysis
based on this model [5].
In this paper, we wish to report on the synthesis and
N.L.O. properties of c-methylene chalcogenapyran and
benzochalcogenapyran Fischer type methoxy carbene
complexes. In these molecules, a strong electron with-
drawing organometallic acceptor fragment is linked via
an unsaturated carbon–carbon chain of various lengths
to the heterocycle. It can be noted that methoxy and
amino Fischer carbene complexes containing classic di-
methyl amino and ferrocenyl donor groups have given
large first hyperpolarisability b values determined by
the HRS technique and the results have been analysed
in the context of the two-level model [14] despite the
presence of more than one transition in the visible part
of the electronic spectrum. In fact, the role of the orga-
nometallic carbene fragment is not well understood. For
amino carbene complexes, polarisation of p cloud of the
unsaturated link by the electronic inductive effect of the
metal carbonyl would be responsible for the important
N.L.O. response. The role of the MLCT (metal to ligand
charge transfer) is minimized due to the lack of conjuga-
tion between the unsaturated chain and the carbenic
fragment.
For this study, we focussed on the influences of chal-
cogen (O, S, and Te) and the unsaturated chain length,
both on the electronic ground state structure and on
the second order non linear optical properties. As the
group 6 atom becomes more and more electropositive
(O < S < Te), the conjugation with the acceptor group
should increase. However, this favourable effect is offset
by a less efficient overlap of the lone pair orbitals of the
heteroatom with those of the p framework [15]. The
existence of two opposite electronic effects, which also
determines the aromaticity of the heterocycle [16], does
not allow, ‘‘a priori’’ an estimate of the second order
non-linear optical properties.
Semi-empirical calculations [6] and experimental
work [3c] have shown that b can be correlated with
the ground state polarization. In a simple description
of donor–acceptor molecules as a mixture of neutral
and zwitterionic limit resonance forms (Fig. 1), b values
peak positively when there is at least 75% of the neutral
form present, decreases to zero when both forms have
been equally (the so-called cyanine limit) present and
becomes negative when the zwitterionic form prevails.
It has been emphasized that the b evolution closely fol-
lows that of Dleg [6a].
For a given molecular structure, several factors can
influence the balance between the two limit resonance
forms. For example, increasing the donor or acceptor
strength of the end groups tends to increase the weight
of the zwitterionic form. Increasing the length of the
p-spacer favours the neutral form. Aromaticity and pro-
aromaticity of the end capped groups can also play a
major role by stabilizing, respectively, the neutral and
the zwitterionic limit forms. Among the used acceptor
groups, heterocyclic proaromatic substituents (barbitu-
ric group for example [3c]) have shown their efficiency,
particularly in molecule containing aromatic donor
groups. In these cases, the decrease of resonance energy
upon charge transfer was offset by the gain of aromatic-
ity at the other end of the molecule.
On the other hand, the influence of proaromatic het-
erocyclic donors on N.L.O. properties of this class of
molecules have been less studied. Studies focused on
N.L.O.-phores containing five atom proaromatic het-
erocycles (dithiafulvene for example [7]).
c-Methylene chalcogenapyran and benzochalcogena-
pyran nucleus and chalcogenaxanthene act as versatile
six atom nucleus in heterocyclic chemistry (Fig. 2). We
can find them in many compounds with potential appli-
cations in the field of conductive [8], magnetic [9] and
2. Results and discussion
2.1. Synthesis
We have previously described the synthetic methodol-
ogy which has allowed the formation of the complexes
necessary for this study. The first molecule of the series
1a (Scheme 1) was obtained from unsubstituted c-pyry-
lium salts and Fischer carbene complexes [17]. The use
of the c-methoxytelluropyrylium salt (Y = OMe, Scheme
1), allowed the formation of the carbene 1b in good yield.
This synthetic approach should open the route to a great
R1
R2
R3
R4
X
X = O, S, Se, Te
Fig. 2. Methylenepyrane core.

4984
N. Faux et al. / Journal of Organometallic Chemistry 690 (2005) 4982–4988
M+ = Li+, Y = H
Ph
O
H3CO
Y = H
Ph
X
W(CO)5
X = O
A = BF4
Ph3C+ BF4
-
Y
Ph
Ph
1a
A-
Ph
H3CO
-
Ph3C+ BF4
H2C
OCH3
M
W(CO)5
C
M+ = NH(CH2CH3)3
Y = OCH3
Te
Ph
W(CO)5
X = Te
A = CF3SO3
1b
Scheme 1.
variety of heterocyclic carbene complexes and will be the
subject of a future communication [18].
double bonds. We have reported, respectively, in Tables
1 and 2 a summary of the linear optical data obtained
for chalcogenapyran and benzochalcogenapyran car-
bene complexes in two solvents of different polarity.
The second order non linear properties were studied
in CHCl3 solution at 1.97 lm by an electrical field in-
duced second harmonic generation technique, which
provides information about the scalar product lb (2x)
of the vectorial part of the first hyperpolarisability ten-
sor and the dipole moment vector l.
The type 2 molecules were obtained from Aumann
condensation [19] using heterocyclic aldehydes n = 0
(Scheme 2) and the carbanion of the corresponding car-
bene, in the presence of N(Et)3 and (CH3)3 SiCl (Scheme
2) [20]. Action of the propenyl carbene complex (Scheme
2, n0 = 1), under the same conditions, on the aldehyde
n = 0 (Scheme 2), gave the unsaturated carbene 3 with
good to moderate yield [20]. The most extended mole-
cule 4a was obtained in low yield from the heterocyclic
aldehyde n = 1 (Scheme 2) and the propenyl Fischer
type carbene complex (n0 = 1).
All complexes were thus tested away from resonance.
These values are reported in Table 3 together with the
3
DJ calculated from JHH coupling constants relating to
All the new compounds were characterized by FT-IR,
the hydrogen atoms of the unsaturated chain. It is well
established that these values provide information about
the degree of bond length alternation of unsaturated
carbon–carbon chains [3c]. Therefore, the reported DJ
values could be indicative of the pyrylium character of
the heterocycles.
1
NMR (13C and H), UV–Vis spectroscopy and elemen-
tary analysis or mass spectroscopy (2b, 2c, 3b, 3c, 4a,
2d–f, 3d–f). For the highly unsaturated complexes, the
3JHH coupling constant values are consistent (see exper-
imental part) with a trans configuration for the C–C
H3CO
H
W(CO)5
R
X
O
R
X
N(C2H5)3
n''
n
(CH3)3SiCl (THF)
n = 0 ; n = 1
R'
R''
R'
R''
2a
2b
2c
3a
3b
3c
4a
n'' = 1, R = Ph, X = O, R' = R'' = (CH)
4
n'' = 1, R = Ph, X = S, R' = R'' = (CH)4
n'' = 1, R = Th, X = O, R' = R'' = (CH)4
n'' = 1, X = O, R = Ph, R' = Ph, R'' = H
n'' = 1, X = S, R = Ph, R' = Ph, R'' = H
n'' = 1, X = Te, R = Ph, R' = Ph, R'' = H 2f
n'' = 2, X = O, R = Ph, R' = Ph, R'' = H
n'' = 2, X = S, R = Ph, R' = Ph, R'' = H
n'' = 2, X = Te, R = Ph, R' = Ph, R'' = H
n'' = 3, X = O, R = Ph, R' = Ph, R'' = H
2d
2e
H3C
CH
OCH3
n'' = 2, R = Ph, X = O, R' = R'' = (CH)
3d
3e
3f
CH
C
4
n'
n'' = 2, R = Ph, X = S, R' = R'' = (CH)4
n'' = 2, R = Th, X = O, R' = R'' = (CH)4
W(CO)5
n' = 0 ; n' = 1
Ph=Phenyl, Th=thienyl
Scheme 2.

N. Faux et al. / Journal of Organometallic Chemistry 690 (2005) 4982–4988
4985
Table 1
Absorption data of c-methylenechalcogenapyran carbene complexes in CCl4 and DMSO (Schemes 1 and 2), k (nm) e (·10ꢀ4 molꢀ1 L cmꢀ1
)
CCl4
DMSO
k1 (e)
k2 (e)
k1 (e)
k2 (e)
1a
1b
2a
2b
2c
3a
3b
3c
4a
a
334 (1.2)
442 (0.9)
449 (0.35)
468 (1.2)
542 (2.3)
583 (3.4)
569 (1.1)
585 (4.5)
598 (5.7)a
594 (7.6)a
605 (7.3)a
613 (5.7)a
619 (2.3)a
356 (0.87)
515 (1.8)
440 (1.3)(CH3CN)b
454 (0.61)
573 (1.7)(CH3CN) 590c
590 (2.7)
464 (1.1)
612 (4.2)
628 (2.6)a
653 (2.3)a
652 (2.4)a
639 (3.2)a
665 (2.4)a
A sole band is observable for the two electronic transitions.
In DMSO, an oxidation leads to the production of an ester.
e undetermined.
b
c
Table 2
Absorption data of methylenebenzochalcogenapyran carbene complexes in CCl4 and DMSO (Scheme 2), k (nm) e (·10ꢀ4 molꢀ1 L cmꢀ1
)
CCl4
DMSO
k1 (e)
k1 (e)
k2 (e)
k2 (e)
2d
2e
2f
3d
3e
3f
a
450 (1.2)
558 (3.6)
571 (3.6)a
565 (3.6)
576 (2.6)a
583 (2.0)a
579 (2.3)a
446 (0.8)
575 (2.6)
582 (1.8)a
580 (2.6)
599 (2.0)a
601 (1.6)a
607 (1.5)a
463 (1.2)
450 (0.9)
A sole band is observable for the two electronic transitions.
Table 3
lb and DJ values for complexes 1–4
1a
1b
2a
2b
2c
3a
3b
3c
4a
2d
2e
2f
3d
3e
3f
lbb · 10ꢀ48 esu
DJ ðHzÞ ðTHF-d8Þ
ꢀ51
19
505
0.4
665
0.7
673
1.1a
1219
1.2
2348
1.9
1615
1.4a
2894
2.2a
219
1.8
402
0.6
505
1.3
1027
2.0
870
1.9
937
2.4
DJ values average difference in JHH values (1H–1H coupling constants) across adjacent C@C and C–C bonds.
3
a
Measurements in CDCl3.
b
Molecular concentrations used for the measurements were in range 10ꢀ3–10ꢀ2 M; 3-methyl-4-nitrosaniline (MNA) for which lb
(CHCl3) = 71.06 · 10ꢀ48 esu was used as an external reference. lb 20%.
2.2. Electronic transitions and N.L.O. properties
solvatochromic bands (Tables 1 and 2) [3,14]. However,
the p–p* transition (ILCT) seems to be more sensitive
to this factor. This result leads, for compounds 3–4, to
the observation of an overlap of the ILCT and MLCT
bands. As a consequence, for two transitions it was not
possible to obtain values of the oscillator strength (feg).
Under the influence of the heteroatomic substitution
(O–S–Te), a bathochromic shift was observed. Such
behaviour has been previously noted by Detty for
pyrylium and chalcogenapyrylium salts [15]. For these
cations a concomitant lowering and increase, respec-
tively, of p and p* (HOMO, LUMO) levels as the size of
the heteroatom raises, is responsible for the red shift. Sub-
stitution of a phenyl group by a thiophenyl group (com-
pounds 2f, 3f) leads to a red shift for the ILCT (when it
is observable) and for the MLCT (Table 2). Finally, it
can be noted that the high MLCT wavenumber values
The first compounds of the series examined in this
study (1a, 1b) have shown two strong absorption bands
in the UV–Vis, which exhibit solvatochromic behaviour
(Table 1). The corresponding electronic transitions
should play a role in the first quadratic hyperpolarisabil-
ity. On the base of DFT calculations performed on the
model of 1a [17], the lower and the higher energy bands
can be assigned, respectively, to a metal to ligand charge
transfer transition (MLCT or HOMO–LUMO) and to a
p–p* intra ligand charge transfer transition (ILCT). The
electronic spectra show a third band in the UV (not
shown in Table 1). This band, insensitive to solvent polar-
ity, can be tentatively assigned to a d–p*CO transition.
As observed earlier for other ‘‘push–pull’’ molecules,
increasing conjugation length leads to a red shift of the

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N. Faux et al. / Journal of Organometallic Chemistry 690 (2005) 4982–4988
are consistant with a conjugation between the carbenic
C(OMe)W(CO)5 fragment and the unsaturated part of
the molecule, a situation which is different to that found
for push–pull amino carbenes [14a].
The lb values are presented in Table 3. Since multiple
states seem to contribute to the non-linear response, no
attempt has been made to correct the values for disper-
sion using the two-level model.
Appending a benzene ring to the pyran nucleus pro-
duces a decrease in the quadratic hyperpolarizability,
for homologous ‘‘push–pull’’ carbene complexes of
similar length. This is in accordance with the higher en-
ergy of the electronic transitions (MLCT and ILCT)
corresponding to the chalcogenabenzopyran derivatives
(Tables 1 and 2). From a comparison of thevalues Ta-
ble 3), it appears that the ground state of the chalco-
Apart from compounds 1 which gave low negative
(1a) or positive (1b) values, the observed lb values for
complexes 2–4 are large and positive indicative of ex-
cited states, which are more polarized than the ground
state (le > lg). In addition, this implies that the ground
and excited states are polarized in the same direction.
The positive values are in accordance with the solvato-
chromism observed for the lower MLCT energy band
(Tables 1 and 2). However, if we assume a mainly s-trans
conformation for the carbene complexes, then this result
does not concord with the ‘‘direction’’ of metal to ligand
charge transfer which is, as suggested by the valence
bond description [14a], opposite to that of the ground
state dipole moment. Calculations have shown that
ground state dipole moment direction is governed by
the pyrylium character of these molecules [21] (Scheme
2). It can be noticed that the DJ values ranged from
2.4 to 0 Hz depending on the polyenic chain length,
are indicative of reduced bond length alternation and
therefore of a pyrylium character [14c] (see Fig. 3).
On the other hand, the negative lb value found for
1a, which is in line with the negative solvatochromism
observable for the MLCT band, reflects an opposite sign
for le and lg values, or a lg value greater than that of le.
For the telluro complex 1b, the low positive lb product,
should be relevant to the low solvent influence on the
UV–Vis electronic spectrum (Table 1).
Despite the apparent failure of the two-level model
(calculations will have to be carried out to explain this
behaviour [21]), as it can be noted from Table 3, struc-
tural changes affect the N.L.O. response.
As expected from other N.L.O. studies, lengthening
the polyenic chain induces a significant increase in the
first quadratic non-linearity [3,14]. The enhancement
of the first hyperpolarisability is found in the two series
(benzo and pyran series). This leads to large lb values,
particularly for the longest complex 4a reported here
(lb 2894 · 10ꢀ48 esu).
genapyran chromophores seems to have a more
pronounced chalcogenapyrylium character. Therefore,
the pyran nucleus is a better electron donating group
than the benzopyran group. Moreover, the presence
of a benzene ring (benzopyran derivatives) should
partly inhibit the p electron mobility upon photoexcita-
tion influence and as expected, a lower lb value is
observed.
It is noteworthy that an opposite trend has been
found for analogous phenylthiocarbene complexes for
which, in particular for the pyran series, the contribu-
tion of the zwitterionic form is more pronounced (a
more important pyrylium character) [14c].
Replacing the oxygen atom of the pyrylium ring with
a sulfur atom enhances the N.L.O. response for all com-
pounds of the heterocycle series, except for3d and 3e for
which a slight decrease in the lb product is observed.
Thus, the thiopyran complex 3b exhibits a lb value of
2348 · 10ꢀ48 esu, about twice high as that of the homol-
ogous pyran complex 3a.
In the pyran series, the increase of the lb products
should be relevant to the greater polarizability of the
sulfur valence shell electrons, and to a certain extent
to a decrease of heterocyclic aromatic character relative
to that of the oxygenate derivatives [15]. This is in a
line with the DJ values reported in Table 3 for 2a–2b
and 3a–3b. The relative sensitivity of the N.L.O.
response toward the O to S atom change, is not in
accordance with the result of a recent theoretical anal-
ysis which showed that styrene based chromophores
bearing pyrylium and thiopyrylium ring, gave similar
lb values [23]. In the benzopyran series, the presence
of an aromatic benzene ring affects the polarization
and the polarizability of the p electrons and the evolu-
tion of the first hyperpolarizability, upon O–S substitu-
tion could reflect subtle differences in the p electronic
transmission capability. Note that in these cases, the
effect of the substitution on the lb values is sensitive
H3CO
H3CO
(OC)5W
W(CO)5
W(CO)5
Ph
X
Ph
X
µg
OCH3
Ph
X
µg
n
n
n
Ph
Ph
Ph
s-trans
s-cis
Fig. 3. Orientation of the dipole moment for s-cis and s-trans.

N. Faux et al. / Journal of Organometallic Chemistry 690 (2005) 4982–4988
4987
to the length of the unsaturated chain (Table 3: com-
pared 2d–2e values and 3d–3e values).
4.2. General procedure for preparation of carbenes 2b, 2c,
3b, 3c, 4a, 2d, 2e, 2f, 3d, 3e, 3f
On the other hand, the telluropyran complexes
showed lb values close to those of their thio counter-
parts for compounds of type 2 and lower values for mol-
ecules of type 3. It is well established that the
aromaticity of telluropyrylium is weak. In addition, X-
ray structure of a telluromethylenepyran pyrylium salt
has shown the great distance between the Ca and Te
atoms and the significant distortion of the tellurohetero-
cyclic ring [15]. The tellure atom is bent 8.7ꢁ out of the
plane formed by the five carbon atoms of the ring.
Therefore, the N.L.O. results could be the consequence
of a poor overlap between the lone pair electrons of
the tellure atom and the p cloud.
In a 100-ml schlenk, 1.3 · 10ꢀ3 mol of the corre-
sponding heterocyclic aldehyde was added to 20 ml of
freshly distilled THF, under a stream of nitrogen.
N(Et)3 (3.9 · 10ꢀ3 mol), (CH3)3 SiCl (3.9 · 10ꢀ3 mol)
and the corresponding methoxy carbene (1.3 ·
10ꢀ3 mol) were then added successively to the stirred
solution at room temperature. The de-gassed reaction
mixture was monitored with TLC chromatography.
The solution was quenched with iced and de-gassed
water under a stream of nitrogen. The complex was then
extracted with de-gassed diethylether (3 · 100 ml) and
dried with MgSO4. Solvents were removed under vac-
uum. The obtained residue was then purified on layer
chromatography and the complex was then isolated
(blue to purple solids). Yields: 2b, 90%; 2c, 69%; 3b,
52%; 3c, 31%; 4a, 20%; 2d, 65%; 2e, 48%; 2f, 64%; 3d,
27%; 3e, 24%; 3f, 31%.
Finally, note that substitution of phenyl by thiophe-
nyl group in a position of the heterocycle doubles the
N.L.O. response for shorter complexes (2d and 2f) but
has no influence on the carbenes of type 3 (3d and 3f).
3. Conclusion
4.3. Selected data for 2b
To summarize, we have shown the efficiency of chalco-
gena and benzochalcogenapyran ring as proaromatic do-
nors in push–pull carbene complexes for N.L.O.
purposes. The compounds containing pyran heterocycle,
gave a better non-linear response than those bearing a
benzopyran ring. The lower values of lb for the fused ring
compounds should be the consequence of the presence of
the benzene ring which limits the p electron circulation.
Among the tested proaromatic chalcogenapyran hetero-
cycles (O, S, Te) tested, the thiopyran ring gave the largest
lb values. This result can be explained by the sulphur
atom electronegativity and the polarizability of lone pair
electrons, which allow good transmission of the electrons
upon photoexcitation.
1H NMR (THF-d8, 500 MHz): d 4.39 (s, 3H), 6.15 (d,
J = 12.9 Hz, 1H), 7.15 (d, J = 13.6 Hz, 1H), 7.19 ( s, 1H),
7.45 (m, 6H), 7.61 (s, 1H), 7.67 (m, 4H), 7.94 (t,
J = 13.2 Hz, 1H). 13C NMR (THF-d8, 500 MHz):
d 67.4, 120.6, 122.7, 127.0, 127.4, 127.5, 130.1, 131.0,
131.1, 137.8, 138.2, 139.0, 141.7, 143.7, 145.1, 148.0,
199.6, 204.7, 292.9. Anal. Calc. for C27H18O6SW: C,
49.56; H, 2.77; S, 4.90. Found: C, 49.39; H, 3.17; S,
5.29%. FTIR (KBr): 2922, 2050, 1929, 1885, 1547,
1488, 1143, 1096, 964, 897, 868, 748, 686. M.p. = 138 ꢁC.
Acknowledgements
Financial support by CNRS and by ÔLe Conseil
Calculations are in progress to obtain more informa-
tion concerning the electronic transitions implied in the
N.L.O. phenomena.
´ ´
ˆ
´
General des Cotes dÕArmor et la communaute des com-
´
munes du TregorÕ are gratefully acknowledged.
Appendix A. Supplementary materials
4. Experimental section
Supporting characteristic data for the new com-
pounds are available. Supplementary data associated
with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2005.07.049.
4.1. Materials
All operations were carried out under a nitrogen
atmosphere. Tetrahydrofuran (THF) was distilled from
Na/benzophenone under N2. Chromatographic purifica-
tion was performed with Silica Gel 60 (0.063–0.200 lm).
References
NMR analysis was done using Brucker 500 MHz spec-
¨
trometer. IR analysis were recorded on Perkin–Elmer
Spectrum 1000 FT-IR spectrophotometer using KBr
plates and elementary analysis or mass spectroscopy
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