Selective functionalization of crown ethers via arene chromium tricarbonyl complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.09.090

The crown ethers dibenzo-16-crown-4 and dibenzo-18-crown-5 and a diaryl polyether were complexed by the chromium tricarbonyl group for the purpose of selective functionalization. This complexation did indeed permit exclusive functionalization of the complexed ring. CHO and CH₂OH functionalities were introduced ortho to the ether group. It was noted that the nature of the two ether chains had a strong influence on the regioselectivity of the functionalization, which occurred preferentially on the side with the polyether chain. Photochemical decomplexation produced functionalized organic crown ethers.

Full text of DOI:10.1016/j.jorganchem.2004.09.090

Journal of Organometallic Chemistry 690 (2005) 847–856
www.elsevier.com/locate/jorganchem
Selective functionalization of crown ethers via arene chromium
tricarbonyl complexes
a
Abir Ben Hadj Amor , Siden Top , Faouzi Meganem , Gerard Jaouen
b,
a
b,
*
*
´
a
` ´
Laboratoire de Synthese Organique, Faculte des Sciences de Bizerte, 7021 Jarzouna, Bizerte Tunisie
´ ´
Laboratoire de Chimie et Biochimie des Complexes Moleculaires, Ecole Nationale Superieure de Chimie de Paris,
b
UMR C.N.R.S. 7576, 11, Rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
Received 16 June 2004; accepted 10 September 2004
Available online 19 November 2004
Abstract
The crown ethers dibenzo-16-crown-4 and dibenzo-18-crown-5 and a diaryl polyether were complexed by the chromium tricar-
bonyl group for the purpose of selective functionalization. This complexation did indeed permit exclusive functionalization of the
complexed ring. CHO and CH2OH functionalities were introduced ortho to the ether group. It was noted that the nature of the two
ether chains had a strong influence on the regioselectivity of the functionalization, which occurred preferentially on the side with the
polyether chain. Photochemical decomplexation produced functionalized organic crown ethers.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Crown ether; Chromium tricarbonyl; Polyether; Aldehyde; Alcohol; Arene activation
1. Introduction
concept may be outlined as follows. One of the reasons
for the current interest in the chemistry of crown ethers,
which selectively complex cations, is that they may be
capable of selective coupling with biological species
(peptides, proteins) [8] and even with solid supports
[9]. This is made possible by the selective addition of a
functional group to a crown ether, which is not initially
capable of coupling in this way.
Crown ethers containing 4 or 5 oxygen atoms are
known to complex Li+ and K+ cations, respectively
[1a,10]. We thought that crown ethers 1 and 2 would
be good candidates for the application of the concept
of selective functionalization of one of the arenes by
temporary activation due to the Cr(CO)3 moiety.
The approach is based on ideas that we introduced in
the 1970s [11] and which have since been extended [12],
although curiously not in the context of selective activa-
tion of crown ethers. The CHO and CH2OH functional-
ities were chosen for attachment to the arene. These
functionalities can of course be used to establish a bond
between the crown ether and a selected substrate. The
The chemistry of crown ethers has been considerably
developed since PedersenÕs studies were first published
[1]. In particular, the organometallic crown ethers have
already been the subject of study, principally with the
aim of using the organometallic entity as an analytical
probe in electrochemistry. For this reason the organo-
metallic crown ethers are chiefly known in the form of
ferrocene derivatives [2]. Other organometallic crown
ethers have been reported with complexes of an
Fe–Mo cluster [3], ruthenium [4], cymantrene [5], cobalto-
cene [5], platinum [6], or arene chromium tricarbonyl
[4,6a].
Here, we present a new way of exploiting the proper-
ties of organometallics in the crown ether series. The
*
Corresponding authors. Tel.: +33 144 27 6699; fax: +33 143 26
0061 (S. Top), Tel.: +33 143 26 9555; fax: +33 143 26 0061 (G. Jaouen).
E-mail addresses: siden@ext.jussieu.fr (S. Top), gerard-jaouen@
enscp.jussieu.fr (G. Jaouen).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.09.090

848
A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
a mixture of THF/dibutyl ether [13] or use of the rea-
gents Cr(CO)3(NH3)3 [14], Cr(CO)3(MeCN)3 [15], or
(naphthalene)Cr(CO)3 [16]. We first chose to use the
classic method which involves heating the arene with
chromium hexacarbonyl in the THF/dibutyl ether mix-
ture in an apparatus described by Toma [16a].
C8H17
O
C8H17
O
O
O
O
O
O
O
O
O
O
O
O
O
1
2
3
The crown ethers 1, 2 and 3 were thus heated with
chromium hexacarbonyl in dibutyl ether containing
10% THF (Scheme 1) [13]. This was expected to give a
mixture of the monocomplexed and the dicomplexed
compound.
work was also extended to a polyether, 3, considered as
an open chain, to complete the study. In addition, we
show that the nature of the substituents on the com-
plexed arene ring plays an important part in regioselec-
tivity when new substituents are introduced.
After 20 h heating, the monocomplexed compound 4
was produced in 28% yield and the dicomplexed com-
pound 5 in 3.9% yield. With the ether 2, the monocom-
plexed compound 6 was obtained in 30% yield and the
dicomplexed compound 7 in 3% yield. Compound 3
gave only 14.5% of the monocomplexed 8 and 5.2% of
the dicomplexed compound 9. The X-ray structures of
the mono chromium complex 4 and the dichromium
complex 7 have been submitted for publication [17,18].
Using this complexation route, yields of the desired
complexes remain mediocre. These unsatisfactory results
led us to test the reagent Cr(CO)3(NH3)3 in an attempt
to achieve an acceptable yield level [14]. The crown ether
and Cr(CO)3(NH3)3 were heated under reflux in dioxane
for 2 h. In this case, the yield for the ether 2 was similar
to the previous result, but the yield of complex 8 was
much improved at a level of 36.7%, and the dicomplexed
compound 9 was not found in any noticeable quantity,
facilitating recovery of 8.
2. Results and discussion
Access to functionalized crown ethers involves three
reaction steps: complexation, the functionalization itself,
and decomplexation. Several methods have been de-
scribed for the complexation of an arene by a chromium
tricarbonyl group to obtain a variety of complexes. As
far as crown ethers are concerned, a method has been
published [7a] which consists of heating a mixture of
the crown ether and chromium hexacarbonyl under re-
flux in THF/2,2,4-trimethylpentane while irradiating
the mixture with a UV lamp. However, the characteris-
tics of the lamp were not given. This complexation
method was tested on compounds 1, 2 and 3 but without
irradiation. After 8 hours of heating, no noticeable
quantities of complexed products were produced. There
are several other complexation methods given in the lit-
erature, such as heating with chromium hexacarbonyl in
It is clear that the crown ethers do not lend themselves
particularly well to the complexation reaction with the
Cr(CO)6. It is likely that the chromiumtricarbonyl group
15
16
2
5
O
O
O
O
1
O
O
O
O
3
4
14
13
Cr(CO)6
1
11
6
n-Bu2O/THF
reflux, 20 h
12
Cr(CO)
Cr(CO)
10
7
Cr(CO)
3
3
3
8
9
5
4
3.9 % yield
28 % yield
18
20
17
16
21
2
15
12
19
O
O
1
3
4
O
O
O
O
14
13
Cr(CO)6
2
3
O
O
11
10
n-Bu2O/THF
reflux, 18 h
6
5
Cr(CO)
Cr(CO)
3
O
Cr(CO)
3
7
3
O
9
8
7
6
3 % yield
30 % yield
C H
8
C H
8
C H
C H
8 17
17
17
8
17
15
2
5
16
O
O
O
O 1
3
4
14
13
Cr(CO)6
O
O
O
O
6
11
n-Bu2O/THF
reflux, 8.5 h
12
Cr(CO)
3
Cr(CO)
Cr(CO)
O
O
a
7
3
10
8
9
5.2 % yield
14.5 % yield
9
8
Scheme 1.

A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
849
complexed ring. The complexation thus permits selective
activation of one of the arene rings.
O
O
A
To obtain the purely organic functionalized crown
ether requires only decomplexation of compound 10
by exposing it to sunlight in an ethereal solution, as de-
scribed in the literature [20]. The aldehyde 11 was ob-
tained in this manner in 75% yield. Furthermore, the
addition of NaBH4 to the solution of the aldehyde 11
rapidly gave the alcohol 12 in 67% yield. The same reac-
tions were carried out on the complexed crown ether 6.
Scheme 3 summarizes the reactions employed and the
yields obtained.
In the case of the crown ether 6, the two chains link-
ing the two arene rings are not identical. Consequently,
substitution at position 2 does not give the same com-
pound as that in position 5. In theory a mixture of
two isomers, 13a and 13b, is formed, and a mixture of
these two isomers was indeed obtained with an overall
yield of 40% after addition of DMF to the organolith-
ium precursor. The NMR spectrum clearly shows the
mixture of the two isomers, but with strong selectivity,
in a ratio of 80/20. The pure isomer 13a was isolated
by fractional crystallization and identified by 2D
NMR. It is clear that the high level of selectivity be-
tween 13a and 13b is due to the nature of the two ether
chains. In the case of the more abundant isomer 13a,
functionalization occurs ortho to the OCH2CH2OCH2-
CH2O chain, while 13b is functionalized ortho to the
OCH2CH2CH2CH2CH2O chain. Clearly the ether func-
tionality in the middle of the chain is responsible for the
observed selectivity. It is in fact well known that an ether
or amine functionality in a carbon chain stabilizes the
lithium substitution in the ortho position [19g,21]. Con-
sequently, the most abundant species in the substitution
reaction may be described by the intermediate B (Fig. 2)
Cr(CO)3
O
O
O
Fig. 1.
binds first to oxygen atoms of the ether functionality. In
this case, we may posit the formation of several interme-
diates of which one is the A isomer (Fig. 1). This interme-
diate would have to possess a certain degree of stability
which, owing to the complexation by oxygen of the chro-
mium tricarbonyl group, would disfavor the direct
attachment of the chromium tricarbonyl moiety onto
the arene ring for steric reason. This hypothesis is
strengthened by the rapid formation of a yellow com-
pound, the characteristic colour of a chromium complex,
when the crown ether was heated with Cr(CO)3(NH3)3.
This intermediate progressively disappeared as heating
continued, to be replaced by the final complex.
Functionalization of the complexes by addition of the
formyl group occurs via the generation of an organolith-
ium compound under the action of n-BuLi, followed by
addition of DMF or dry ice. It has been shown that
addition of TMEDA to the solution containing the
organolithium improves the yield of the functionalized
product [12]. The organolithium compound of complex
4 is thus generated by addition of n-BuLi at ꢀ78 ꢁC in
the presence of TMEDA. The addition of DMF to the
formed organolithium compound derivative generates
the complexed aldehyde 10 (Scheme 2).
Normally functionalization occurs at the ortho posi-
tion relative to the ether functionality [19]. This substitu-
tion position is confirmed by the NMR spectrum which
shows two doublets and a triplet for the protons of the
CHO
1) n-BuLi, THF,
O
O
O
O
TMEDA, -78˚C
4
2) DMF, -78˚C
Cr(CO)3
10
31 % yield
hν
Et2O
CH2OH
CHO
O
O
O
O
O
O
O
O
NaBH4
MeOH/H2O
75 % yield
12
11
67 %
Scheme 2.

850
A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
CHO
O
O
O
O
2
13b
Cr(CO)
O
3
1) n-BuLi, THF,
-78˚C
Cr(CO)
3
O
O
O
O
NaBH4
6
MeOH/H2O
2) DMF, -10˚C
CH OH
2
O
Cr(CO)
3
O
O
5
15a,b
56 % yield
O
O
13a
O
CHO
hν
Et2O
O
O
O
O
O
O
O
NaBH4
14a
14b
52 % yield
12 % yield
MeOH/H2O
O
O
CHO
O
CH OH
2
16a
64 % yield
CHO
2
O
O
O
O
O
Scheme 3.
with the lithium further stabilized by complexation by
the oxygen in the middle of the carbon chain.
18a in 53% yield. Reduction of 17a by NaBH4 gave the
alcohol 19. 2D NMR spectra of 19 show a correlation be-
tween H-2 and the OCH2 protons of the C8H17 chain on
the one hand, and between the CH2OH protons and the
OCH2CH2O protons on the other hand. It is interesting
to note that the two CH2OH protons and the two OCH2
protons at position 8 are non-equivalent, proving that
the CHO group must be at position 5. The high selectiv-
ity at position 5 relative to that of position 2 confirms the
hypothesis stated above. In fact the ether chain has a sta-
bilizing effect on the organolithium precursor at position
5 while the C8H17 alkyl chain does not produce this ef-
fect. Exposure of the ethereal solution of 19 to sunlight
gave the non-complexed alcohol 20 in 87.5% yield.
The ethereal solution of the mixture of 13a and 13b
was exposed to sunlight to induce decomplexation. In
this case it was possible to separate the non-complexed
aldehydes 14a and 14b with yields of 52% and 12%,
respectively. Reduction of the mixture of 13a and 13b
with NaBH4 gave the alcohol complexes 15a and 15b.
Reduction of 14a with NaBH4 gave the alcohol 16a.
Scheme 4 summarizes the reactions carried out on the
complexed polyether 8.
In the case of complex 8, the addition of TMEDA to
the organolithium solution gave increased yields of the
complexed aldehydes. The aldehydes 17a and 17b were
obtained in yields of 59% and 3%, respectively, compared
to 28% and 6% when TMEDA was not present. The ratio
of the two isomers was 82/18. The more abundant isomer
17a was unambiguously identified, by 2D NMR,
NOESY, HMBC and HMQC on the non-complexed
aldehyde 19 and the alcohol 20, as the compound substi-
tuted at position 5. Exposure of the ethereal solution of
17a to sunlight produced the non-complexed aldehyde
3. Conclusion
This work has shown that complexation of one of
the two aromatic rings of the crown ethers dibenzo-
16-crown-4 and dibenzo-18-crown-5, plus a diaryl poly-
ether, by the chromium tricarbonyl group permits
exclusive and selective functionalization of the com-
plexed ring, which is activated for directed lithiation
at the position adjacent to the OR groups. The nature
of the two ether chains plays a large part in regioselec-
tive control of the functionalization, which occurs pref-
erentially on the side where the polyether chain is
located. This approach may be useful not only for
the selective functionalization of crown ethers but also
for their detection, thanks to the Cr(CO)3 group which
can act as a very sensitive infra-red probe [22]. Further
Cr(CO)
3
O
O
Li
B
O
O
O
Fig. 2.

A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
851
C H
H C
17 8
CHO
8
17
O
O
O
6 % yield
17b
O
Cr(CO)
O
3
1) n-BuLi, THF,
TMEDA, -78˚C
8
2) DMF, -78˚C
C H
C H
8
17
8
17
C H
C H
8 17
8
17
Cr(CO)
3
2
3
Cr(CO)
3
O
O
1
O
O
NaBH4
6
4
O
O
MeOH/H2O
O
O
5
7
8
O
CHO
O
CH OH
2
28 % yield
17a
19
59,4 % yield
hν
Et2O
h
Et2O
C H
C H
8 17
8
17
C H
C H
8 17
8
17
O
O
O
O
O
O
O
O
O
CHO
O
CH OH
2
53 % yield
18a
20
87.5 % yield
Scheme 4.
studies will be undertaken to further explore these
possibilities.
tained (2.030 g) was chromatographed on a silica gel col-
umn using diethyl ether:petroleum ether 2:1 as eluent.
The mono-complexed compound, 4, was first eluted,
0.648 g (28% yield). Recrystallization from diethyl
ether/pentane furnished yellow crystals, m.p. 112 ꢁC.
1H NMR (200 MHz, CDCl3): d 6.89 (m, 4H, non-com-
plexed aromatic ring), 5.30 and 5.05 (m, m, 2H, 2H,
complexed aromatic ring), 4.04 (m, 8H, OCH2), 2.04
(m, 8H, CH2). 13C NMR (100 MHz, CDCl3): d 233.9
(CO), 149.8 (C11, C16, non-complexed aromatic ring),
133.5 (C1, C6, complexed aromatic ring), 121.5 and
114.9 (C12–C15, non-complexed aromatic ring), 87.4
and 81.5 (C2–C5, complexed aromatic ring), 72.1 and
69.4 (OCH2), 26.7 and 26.5 (CH2). IR (KBr, cmꢀ1):
4. Experimental
4.1. General data
Starting materials were synthesized using standard
Schlenk technique under an argon atmosphere. Anhy-
drous THF and di-n-butyl ether were distilled from so-
dium/benzophenone. Thin layer chromatography was
performed on silica gel 60 GF254. FT-IR spectra were
recorded on a BOMEM Michelson-100 spectrometer.
1H and 13C NMR spectra were acquired on Bruker
200 or 400 MHz spectrometers. Mass spectrometry
was performed on a Nermag R 10-10C spectrometer.
Melting points were measured with a Kofler device
and DSC apparatus. Elemental analyses were performed
by the Regional Microanalysis Department of Univer-
m
CO = 1944, 1858. MS (DCI) 482 [M + NH4]+, 465
[M + H]+, 380 [M ꢀ 3CO]+, 346. Anal. Calc. for
C23H24O7Cr: C, 59.48; H, 5.21. Found: C, 59.56; H,
5.34%. After isolation of the mono-complexed com-
pound, the eluent was switched to diethyl ether:petrole-
um ether 3:1. The di-complexed compound, 5, was then
isolated (0.119 g, 3.9% yield). Recrystallization from
diethyl ether/pentane furnished yellow crystals, m.p.
´
site Pierre et Marie Curie.
1
4.2. Synthesis of complexes 4 and 5
212 ꢁC. H NMR (200 MHz, CDCl3): d 5.27 and 5.04
(m, m, 4H, 4H, complexed aromatic ring), 4.00 (m,
8H, OCH2), 2.04 (m, 8H, CH2). 13C NMR (100 MHz,
CDCl3): d 133.8 (C1, C6, C11, and C16, complexed aro-
matic ring), 86.9, and 80.1 (C2–C5, C12–C15, com-
plexed aromatic ring), 71.2 (OCH2), 26.1 (CH2). IR
Crown ether 1 (1.641 g, 5 mmol) and chromium hexa-
carbonyl (2.200 g, 10 mmol) were placed in a 250 mL
flask equipped with a condenser. n-dibutyl ether (150
mL) and THF (15 mL) were added into the flask. The
mixture was then heated at reflux for 20 h. The yellow
solution obtained was allowed to cool to room temper-
ature and then was put in a refrigerator in order to pre-
cipitate the unreacted chromium hexacarbonyl. After
filtration and evaporation of solvent, the yellow oil ob-
(KBr, cmꢀ1):
mCO = 1946, 1847. MS (DCI) 618
[M + NH4]+, 601 [M + H]+, 482 [M ꢀ 3COCr]+,
465[M + H ꢀ 6CO ꢀ Cr]+,
346[M + NH4 ꢀ 6CO ꢀ
2Cr]+. Anal. Calc. for C26H24 Cr2O10: C, 52.05; H,
4.03. Found: C, 51.96; H, 4.15%.

852
A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
4.3. Synthesis of complexes 6 and 7
NMR (200 MHz, CDCl3): d 6.90 (m, 4H, non-com-
plexed aromatic ring), 5.42, 5.23, 5.07, and 4.96 (d, d,
t, t, 1H, 1H, 1H, 1H, complexed aromatic ring), 4.18
(t, OCH2, 2H), 4.11 (t, 2H, OCH2), 3.90 (m, 8H,
OCH2), 1.77, 1.44, and 1.28 (m, s, s, 4H, 4H 16H,
–CH2), 0.88 (m, 6H, 2 CH3). 13C NMR (100 MHz,
CDCl3): d 233.8 (CO), 149.6 and 148.8 (non-complexed
aromatic ring), 133.8 and 132.3 (complexed aromatic
ring), 121.9, 121.0, 115.3, and 113.9 (non-complexed
aromatic ring), 88.01, 86.7, 82.1, 79.1 (complexed aro-
matic ring), 71.6, 70.8, 70.2, 69.9, and 69.2 (OCH2),
31.9-22.7 (CH2), 14.2 (CH3). IR (CH2Cl2, cmꢀ1):
The complexation procedure is identical to that of
1. Crown ether 2 (1.790 g, 5 mmol), chromium hexa-
carbonyl (2.200 g, 10 mmol), di-n-butyl ether (150
mL) and THF (15mL) were combined in a flask equi-
ped with a condensor. The mixture was heated at re-
flux for 18 h. After filtration and evaporation of
solvent, the yellow oil obtained (2.30 g), was chroma-
tographed on silica gel column using diethyl ether:pe-
troleum ether 2:1 as eluent. The mono-complexed
compound, 6, was first eluted, 0.751 g (30% yield).
Recrystallization from diethyl ether/pentane furnished
yellow crystals, m.p. 142 ꢁC. 1H NMR (200 MHz,
CDCl3): d 6.86 (s, 4H, non-complexed aromatic ring),
5.32 and 5.23 (dd, dd, 1H, 1H, J = 6.4 Hz and J = 1.2
Hz, H2 and H5), 5.09 and 4.97 (t, t, 1H, 1H, J = 6.4
Hz and J = 1.2 Hz, H3 and H4), 4.01 (m, 12H,
OCH2), 1.90 (m, 6H, –CH2). 13C NMR (100 MHz,
DMSO): d 233.8 (CO), 149.2 and 148.4 (non-com-
plexed aromatic ring), 133.6 and 131.7 (complexed
aromatic ring), 121.3, 120.5, 113.5, and 112.3 (non-
complexed aromatic ring), 88.1, 86.3, 81.4, 78.2 (com-
plexed aromatic ring), 71.0, 70.2, 69.6, 68.7, and 68.0
(OCH2), 29.5, 29.2, 23.8 (CH2). IR (KBr, cmꢀ1):
m
CO = 1960, 1877. MS (DCI) 668 [M + NH4]+, 566
[M + H ꢀ 3CO]+, 532 [M + NH4 ꢀ 3CO ꢀ Cr]+. Anal.
Calc. for C35H50O8Cr: C, 64.53; H, 7.74. Found: C,
64.45; H, 7.86%. After isolation of the mono-com-
plexed compound, the eluent was switched to diethyl
ether:petroleum ether 4:1. The di-complexed com-
pound, 9, was then isolated as a yellow oil (0.204 g,
5.2% yield). 1H NMR (400 MHz, CDCl3): d 5.42,
5.24, 5.09, and 5.00 (m, m,m, m, 8H, aromatic ring),
4.20–4.38 (m, 12H, OCH2), 1.78, 1.44, 1.28 (m, m, m,
4H, 4H, 16H, CH2), 0.88 (m, 4H, CH3). 13C NMR
(100 MHz, CDCl3): d 133.8 and 132.2 (C1, C6, aro-
matic ring), 88.1, 86.8, 82.2, and 79.0 (C2, C3, C4,
and C5, aromatic ring), 71.6, 70.8, 69.8 (OCH2), 31.8,
29.3, 29.1, 25.9, 22.7 (CH2), 14.2 (CH3). IR (KBr,
cmꢀ1): mCO = 1961, 1877. MS (electrospray) 809.4
[M + Na]+. MS (EI) 618 [M ꢀ 6CO]+, 566
[M ꢀ 6CO ꢀ Cr]+, 514 [M ꢀ 6CO ꢀ 2Cr]+,. Anal. Calc.
for C38H50O11Cr2: C, 58.01; H, 6.85. Found: C, 58.63;
H, 6.61%.
m
CO = 1951, 1855. MS (DCI) 512 [M + NH4]+, 376
[M + NH4 ꢀ 3CO ꢀ Cr]+. Anal. Calc. for C24H26O8Cr:
C, 58.29; H, 5.29. Found: C, 58.04; H, 5.50%. After
isolation of mono-complexed compound, the eluent
was switched to diethyl ether:petroleum ether 3:1.
The di-complexed compound, 7, was then isolated
(0.100 g, 3.1% yield). Recrystallization from diethyl
ether/pentane furnished yellow crystals, m.p. 234 ꢁC.
1H NMR (400 MHz, DMSO): d 5.88 and 5.86 (d, d,
2H, 2H, aromatic ring), 5.42 and 5.35 (t, t, 2H, 2H,
aromatic ring), 4.12, 4.00, 3.85, 3.73 (m, m, m, 12H,
OCH2), 1.72 (m, 6H, CH2). 13C NMR (100 MHz,
DMSO): d 133.7 and 132. 5 (aromatic ring), 89.7,
88.7, 82.2, and 80.8 (aromatic ring), 69.6, and 68.6
(OCH2), 28.5 (2 CH2), 23.2 (CH2). IR (KBr, cmꢀ1):
4.5. Synthesis of aldehyde 10
Complex 4 (0.464 g, 1 mmol) was dissolved in THF
(20 mL). The solution was cooled to ꢀ78 ꢁC. Then
0.40 mL of n-BuLi solution (1 mmol, 2.56 M in hexane)
was added dropwise. After 2 h stirring, the temperature
was raised to ꢀ10 ꢁC, and 0.155 mL of DMF was added.
Stirring was continued for 15 min, and the mixture was
poured into a diluted HCl aqueous solution. The com-
pound was extracted with 100 mL of CH2Cl2. After fil-
tration and evaporation of solvent, the orange oil
obtained (0.534 g) was chromatographed on a silica
gel column by using diethyl ether:petroleum ether 2:1
as eluent. The aldehyde 10 was isolated as an orange
oil (0.153 g, 31% yield). Recrystallization from diethyl
ether/pentane furnished orange crystals, m.p. 52 ꢁC.
1H NMR (200 MHz, CDCl3): d 10.10 (s, 1H, CHO),
6.89 (m, 4H, non-complexed aromatic ring), 5.66 (d, 1
H, J = 6.6 Hz, complexed aromatic ring), 5.48 (d, 1 H,
J = 5.5 Hz, complexed aromatic ring), 5.12 (t, 1H,
J = 5.9 Hz, complexed aromatic ring), 4.65, 4.40, 4.05,
3.84 (m, m, m, m, 8H, OCH2), 2.04 (m, 8H, CH2). IR
(KBr, cmꢀ1): mCO = 1966, 1888, mC@O = 1683. MS
m
CO = 1954, 1866. MS (DCI) 648 [M + NH4]+, 512
[M + NH4 ꢀ 3CO ꢀ Cr]+, 376 [M + NH4 ꢀ 6CO ꢀ
2Cr]+. Anal. Calc. for C27H24O11Cr2: C, 51.42; H,
4.15. Found: C, 51.52; H, 4.27%.
4.4. Synthesis of complexes 8 and 9
The complexation procedure is identical to that of 1,
using ether 3 (2.570 g, 5 mmol), chromium hexacarbo-
nyl (2.200 g, 10 mmol), di-n-butyl ether (150 mL) and
THF (15 mL). The mixture was heated at reflux for 8.5
h. After filtration and evaporation of solvent, the yel-
low oil obtained (1.15 g), was chromatographed on a
silica gel column using diethyl ether:petroleum ether
2:1 as eluent. The mono-complexed compound, 8,
1
was first eluted, 0.471 g (yellow oil, 14.5% yield). H

A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
853
(DCI) 510 [M + NH4]+, 493 [M + H]+, 374
[M + NH4 ꢀ 3CO ꢀ Cr]+, 357 [M + H ꢀ 3CO ꢀ Cr]+.
Anal. Calc. for C24H24O8Cr: C, 58.53; H, 4.91. Found:
C, 59.02; H, 5.49%.
hyde 13a,b was isolated as an orange oil (0.400 g,
40% yield). The NMR spectrum showed a mixture
of two isomers in 80:20 proportion. 1H NMR (200
MHz, CDCl3) of major isomer: d 10.12 (s, 1H,
CHO), 6.87 (m, 4H, non-complexed aromatic ring),
5.58 (d, 1 H, J = 6.4 Hz, complexed aromatic ring),
4.6. Synthesis of aldehyde 11
5.42 (d,
ring), 5.20 (t, 1H, J = 6.5 Hz, complexed aromatic
1 H, J = 6.5 Hz, complexed aromatic
Aldehyde complex 10 (0.050 g, 0.10 mmol) was dis-
solved in 20 mL diethyl ether. The solution was ex-
posed to sunlight for 2 h. The colourless solution was
then filtered on silica gel pad to give 0.040 g of a solid
after evaporation of the solvent. The crude product
was purified by TLC using diethyl ether:pentane 1:1
as eluent. Aldehyde 11 was obtained as a colourless so-
ring), 4.55, 4.30, 4.15 and 4.03 (4 m, OCH2), 1.87
6
H, CH2CH2CH2). 13C NMR (100 MHz,
(m,
C6D6): d 231.5 (CO), 187.5 (CHO), 149.9 and 148.4
(C11, C16), 132.8 and 132.2 (C1, C6), 121.2, 120.7,
113.6, and 112.4 (C12, C13, C14, and C15), 92.6,
87.3, 84.9, 78.8 (C2, C3, C4, C5), 70.4, 69.8, 69.2,
67.8 (C7, C8, C9, C10, C17, C21), 29.5, 29.2 and
23.8 (CH2CH2CH2). IR (KBr, cmꢀ1): mCO = 1967,
1885, mC@O = 1684. MS (DCI) 540 [M + NH4]+, 523
[M + H]+, 404 [M + NH4 ꢀ 3CO ꢀ Cr]+, 387 [M +
H ꢀ 3CO ꢀ Cr]+, 376 [M + H ꢀ 4CO ꢀ Cr]+. Anal.
Calc. for C25H26O9Cr: C, 57.42; H, 5.01. Found: C,
57.65; H, 5.26%.
1
lid (0.027 g, 75.0% yield, m.p. 99 ꢁC). H NMR (200
MHz, CDCl3): d 10.40 (s, 1H, CHO), 7.32 (dd, 1 H,
J = 6.6 Hz and 2.8 Hz, H4), 7.03 (m, 2 H, H2 and
H3), 6.83 (m, 4H, non-substituted ring), 4.27 (t, 2 H,
CH2O), 3.99 (m, 6 H, CH2O), 2.04 (m, 8 H, CH2-
CH2). 13C NMR (100 MHz, CDCl3): d 190.7 (CHO),
152.9 and 152.6 (C1, C6), 149.7 and 149.5 (C11,
C16), 129.9 (C5), 123.7, 121.5, 118.9 and 114.7 (C2,
C3, C4, C12, C13, C14, C15), 75.7 (C7), 69.4 (C8),
69.0 (C9), 68.5 (C10, C17, C20), 27.9, 26.9, 26.0 and
25.3 (C8, C9, C18 and C19). IR (KBr, cmꢀ1):
4.9. Synthesis of aldehydes 14a and 14b
The aldehyde complex 13 (0.052 g, 0.1 mmol) was
dissolved in 10 mL of diethyl ether. The solution was
exposed to sunlight for 2 h. The colourless solution
was then filtered on a silica gel pad to give 0.035 g
of a solid after evaporation of the solvent. The crude
product was purified by TLC using CH2Cl2:CHCl3
2:3 as eluent. Aldehyde 14a, the major isomer, was ob-
tained as a colourless solid (0.020 g, 52.0% yield, mp
119 ꢁC). 1H NMR (200 MHz, CDCl3): d 10.49 (s,
1H, CHO), 7.38 (dd, 1 H, J = 5.6 Hz and 3.8 Hz, sub-
stituted ring), 7.10 (d, 1 H, J = 3.8 Hz, substituted
ring), 7.09 (d, 1 H, J = 5.6 Hz, substituted ring), 6.87
(m, 4 H, non-substituted ring), 4.37 (t, 2 H, J = 3.7
Hz, CH2O), 4.17 (m, 2 H, CH2O), 4.00 (m, 8 H, 4
CH2O), 1.90 (m, 6 H, CH2CH2CH2). 13C NMR (100
MHz, CDCl3): d 190.5 (CHO), 152.4 (C1), 151.5
(C6), 148.9 (C16), 148.3 (C11), 129.9 (C5), 124.0
(C3), 121.1, and 120.7 (C13, C14), 118.7 (C4), 118.1
(C2), 112.7, and 112.3 (C12 and C15), 73.7 (C7), 70.7
(C8), 69.6 (C9), 69.3 (C10), 68.4 (C21), 67.9 (C17),
29.6 and 29.5 (C18 and C20), 24.0 (C19). IR (KBr,
cmꢀ1): mC@O = 1684. MS (EI) 386 [M+Å]. Anal. Calc.
for C22H26O6: C, 68.39; H, 6.73. Found: C, 68.30; H,
6.91%. 0.005 g of aldehyde 14b, the minor isomer,
was also isolated (12% yield, mp 96 ꢁC). 1H NMR
(200 MHz, CDCl3): d 10.37 (s, 1H, CHO), 7.34 (m, 1
H, substituted ring), 7.02 (m, 2 H, substituted ring),
6.84 6.87 (m, 4 H, non-substituted ring), 4.16–3.90
(m, 12 H, CH2O), 1.81 (m, 6 H, CH2CH2CH2). IR
(KBr, cmꢀ1): mC@O = 1686. MS (ES) 411 [M + Na]+,
406 [M + NH4]+. Anal. Calc. for C22H26O6: C, 68.39;
H, 6.73. Found: C, 69.31; H, 7.22%.
m
C@O = 1684. MS (ES) 379 [M + Na]+. Anal. Calc. for
C21H24O5: C, 70.76; H, 6.78. Found: C, 70.58; H,
6.97%.
4.7. Synthesis of alcohol 12
Aldehyde 11 (0.090 g, 0.25 mmol) was dissolved in
10 mL of ethanol. A solution of NaBH4 (0.125 g) in 2
mL of water was added to the first solution. After
stirring for 30 min, the mixture was poured in 10
mL of a 10% HCl solution. The product was extracted
with diethyl ether. The organic layer was washed with
20 mL of water. After drying on MgSO4, filtration,
and solvent removal, 0.070 g of crude product was ob-
tained as a solid. Crystallization in CH2Cl2:hexane
gave 0.060 mg of alcohol 13 (67% yield, m.p. 87
ꢁC). 1H NMR (200 MHz, CDCl3): d 6.91–6.74 (m,
7H, aromatic ring), 4.63 (d,
2 H, J = 5.1 Hz,
CH2OH), 4.16 and 4.00 (t, m, 2 H, 6 H, CH2O),
1.98 (m, 8 H, CH2-CH2). MS (EI) 381 [M + Na]+.
Anal. Calc. for C21H26O5: C, 70.37; H, 7.31. Found:
C, 70.28; H, 7.38%.
4.8. Synthesis of aldehyde 13a and 13b
The procedure is identical to that for 10, using
complex 6 (0.99 g, 2 mmol), THF (30 mL), n-BuLi
solution (0.80 mL, 2 mmol), and DMF (0.31 mL, 4
mmol). After work-up, the orange oil obtained (1.70
g) was chromatographed on a silica gel column using
diethyl ether:petroleum ether 2:1 as eluent. The alde-

854
A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
4.10. Synthesis of alcohol 15a and 15b
plexed aromatic ring), 5.42 (dd, 1 H, J = 6.5 and 1.0
Hz, complexed aromatic ring), 5.11 (t, 1H, J = 6.5
Hz, complexed aromatic ring), 4.37, 4.13 and 3.90
(m, m, m, 2 H, 4 H, and 6 H, OCH2), 1.79, and 1.28
(m, m, 4 H, and 24 H, 6 CH2), 0.88 (m, 6H, 2 CH3).
13C NMR (100 MHz, DMSO): d 231.4 (CO), 187.8
(CHO), 149.5 and 148.6 (C11, C16), 134.1 and 132.5
(C1, C6), 121.9, 121.0, 113.8, and 113.9 (C12, C13,
C14, and C15), 91.8, 86.7, 85.3, 79.6, 75.6 (C2, C3,
C4, C5, and C7), 70.9, 70.5, 69.9, 69.3, and 69.0 (C8,
C9, C10, C10, C100), 31.9–22.7 (C20–C70 and C200–
C700), 14.2 and 14.0 (C80 and C800). IR (CH2Cl2,
cmꢀ1): mCO = 1976, 1902, mC@O = 1679. MS (DCI) 713
[M + NH3 + NH4]+, 696 [M + NH4]+, 679 [M + H]+,
560 [M + NH4 ꢀ 3CO ꢀ Cr]+, 543 [M + H ꢀ 3CO ꢀ
Cr]+, 532 [M + NH4 ꢀ 4CO ꢀ Cr]+. Anal. Calc. for
C36H50O9Cr: C, 63.70; H, 7.42. Found: C, 63.11; H,
7.72%. The minor aldehyde 17b was eluted after 17a
The aldehyde complexes 13a and 13b (0.150 g, 0.3
mmol) were dissolved in 20 mL ethanol. A solution of
NaBH4 (0.20 g) in 1 mL water was added to the first
solution. The mixture immediately turned yellow. After
stirring for 30 min, the mixture was poured into 10 mL
of water. The product was extracted with diethyl ether.
The organic layer was washed with 20 mL water. After
drying on MgSO4, filtration and solvent removal, the
product was purified by TLC using diethyl ether:pen-
tane 3:1 as eluent. Alcohols 15a,b were obtained as an
yellow solid (0.090 g, 56% yield, m.p. 139 ꢁC). Major
1
isomer : H NMR (200 MHz, CDCl3): d 6.86 (m, 4H,
non-substituted ring), 5.38 (t, 1 H, J = 6.5 Hz, substi-
tuted ring), 5.05 (d, 1 H, J = 6.8 Hz, substituted ring),
4.96 (d, 1 H, J = 6.1 Hz, substituted ring), 4.80 and
4.42 (dd, dd, 1H, 1H,, J = 14.3 Hz and J = 4.8 Hz,
CH2OH), 4.59 (t, 1H, OH), 4.38 and 4.01 (m, m, 2H,
10 H, CH2O), 2.03 (m, 6 H, CH2CH2CH2). IR (KBr,
cmꢀ1): mOH 3416, mCO = 1955, 1874. MS (EI) 388
[M ꢀ 3CO ꢀ Cr]+. Anal. Calc. for C25H28O9Cr: C,
57.25; H, 5.38. Found: C, 57.22; H, 5.58%.
1
and isolated as an orange oil (0.049 g, 6% yield). H
NMR (200 MHz, CDCl3): d 10.04 (s, 1H, CHO),
6.92 (m, 4H, non-complexed aromatic ring), 5.67 (dd,
1 H, J = 6.5 and 1.1 Hz, complexed aromatic ring),
5.59 (dd, 1 H, J = 6.5 and 1.1 Hz, complexed aromatic
ring), 5.07 (t, 1H, J = 6.5 Hz, complexed aromatic
ring), 4.20, and 3.90 (m, m, 4 H, and 8 H, OCH2),
1.77, and 1.27 (m, m, 4 H, and 24 H, 6 CH2), 0.88
(m, 6H, 2 CH3). 13C NMR (50 MHz, CDCl3): d
231.3 (CO), 187.1 (CHO), 149.5 and 148.6 (C11,
C16), 122.7, 122.1, 121.1, 120.9, 115.2, and 113.8 (C1,
C6, C12, C13, C14, and C15), 91.3, 86.5, 86.0, 81.8,
74.4 (C2, C3, C4, C5, and C7), 71.2, 70.2, 69.7, 69.4,
and 69.0 (C8, C9, C10, C10, C100), 31.3–22.7 (C20–C70
and C200–C700), 14.2 (C80 and C800). IR (CH2Cl2,
cmꢀ1): mCO = 1977, 1907, mC@O = 1684. MS (ES) 701
[M + Na]+, 565 [M + Na ꢀ 3CO ꢀ Cr]+. Anal. Calc.
for C36H50O9Cr: C, 63.70; H, 7.42. Found: C, 63.44;
H, 7.67%.
4.11. Synthesis of alcohol 16a
The aldehyde 14a (0.040 g, 0.1 mmol) was dissolved
in 10 mL ethanol. A solution of NaBH4 (0.050 g) in 1
mL water was added to the first solution. The mixture
turned yellow immediately. After stirring for 30 min,
the mixture was poured into 10 mL water. The product
was extracted with diethyl ether. The organic layer was
washed with 20 mL of water. After drying on MgSO4,
filtration and solvent removal, 0.030 g of the alcohol
16a was obtained as a colourless solid. A crystallization
in CH2Cl2:hexane gave colourless crystals, 0.025 g, 64%
yield, m.p. 205 ꢁC. 1H NMR (200 MHz, CDCl3): d 6.80
(m, 7H, aromatic ring), 4.60, 4.32, 4.09 and 3.98 (d, m,
m, m, 15 H, CH2O, CH2OH and OH), 1.80 (m, 6 H,
CH2CH2CH2). IR (KBr, cmꢀ1): mOH 3435. MS (EI)
388 [M]+. Anal. Calc. for C22H28O6: C, 68.02; H, 7.27.
Found: C, 67.77; H, 7.58%.
1"
8" 7" 6" 5" 4" 3" 2"
1' 2' 3' 4' 5' 6' 7'
8'
CH3CH2CH2CH2CH CH2CH2CH2
CH2CH2CH2CH2CH CH2CH2CH3
2
2
15
2
1
O
O
O
3
14
16
6
4Cr(CO)3
13
11
O
5
12
10
O
CHO
7
17
4.12. Synthesis of aldehyde 17a and 17b
8
9
The procedure is identical to that of 10 using com-
plex 8 (0.700 g, 1.07 mmol), THF (10 mL), n-BuLi
2.5 M solution (0.48 mL, 1.2 mmol), and DMF (0.5
mL). After a work-up, the orange oil obtained (1.07
g), was chromatographed on silica gel plates (TLC)
by using diethyl ether:petroleum ether 1:1 as eluent.
Two aldehyde complexes were isolated. The major
aldehyde 17a was first isolated as an orange oil
4.13. Synthesis of aldehyde 18a
Aldehyde complex 17a (0.090 g, 0.13 mmol) was dis-
solved in 10 mL of diethyl ether. The solution was ex-
posed to sunlight for 30 min. The colourless solution
was then filtered on a silica gel pad to give 0.062 g
of oil after evaporation of the solvent. The crude prod-
uct was purified by TLC using diethyl ether:petroleum
ether 1:2 as eluent. The aldehyde 18a was obtained as a
1
(0.211 g, 28% yield). H NMR (200 MHz, CDCl3): d
10.13 (s, 1H, CHO), 6.90 (m, 4H, non-complexed aro-
matic ring), 5.58 (dd, 1 H, J = 6.5 and 1.0 Hz, com-

A. Ben Hadj Amor et al. / Journal of Organometallic Chemistry 690 (2005) 847–856
855
colourless oil (0.038 g, 53.0% yield). 1H NMR (400
4.15. Synthesis of alcohol 20
MHz, CDCl3): d 10.52 (s, 1H, CHO), 7.40 (dd, 1 H,
J = 7.1 and 2.1 Hz, H4), 7.10 (m, 2 H, H2 and H3),
6.90 (m, 4H, non-substituted ring), 4.36 (m, 2 H,
H7), 4.15 (t, 2 H, J = 3.6 Hz, H10), 4.00 (t, 2 H,
J = 6.5 Hz, H10), 3.96 (t, 2 H, J = 6.7 Hz, H100), 3.90
(m, 4 H, H8 and H9), 1.81 (m, 4 H, H20 and H200),
1.30 (m, 4 H, H30 and H300), 1.27 (m, 16 H, H40–H70
and H400–H700), 0.88 (m, 6H, H80 and H800). 13C
NMR (100 MHz, CDCl3): d 191.0 (CHO), 152.4 and
151.6 (C1, C6), 149.5 and 148.7 (C11, C16), 130.2
(C5), 124.0 (C4), 121.8, 121.0, 118.9, 118.8, 115.1,
and 113.8 (C2, C3, C12, C13, C14, and C15), 73.2,
70.7, 69.8, 69.2, 69.1, and 34.2 (C10, C100, C7, C8,
C9, C10), 31.9 (C60, C600), 29.4, 29.4, 29.3 (C20, C200,
C40, C400, C50, C500, C60, C600), 26.2, 26.1 (C30, C300),
22.7 (C70, C700), 14.1 (C80, C800). IR (CH2Cl2, cmꢀ1):
Alcohol complex 19 (0.060 g, 0.09 mmol) was dis-
solved in 5 mL of diethyl ether. The solution was ex-
posed to sunlight for 30 min. The colourless solution
was then filtered on a silica gel pad to give 0.042 g of
20 as an oil after evaporation of the solvent (87.5%
1
yield). H NMR (400 MHz, CDCl3): d 6.80 (m, 7 H,
arene ring), 4.55 (d, 2 H, J = 6.3 Hz, CH OH), 4.25
2
(m, 2 H, H7), (t, 2 H, J = 5.2 Hz, H10), 3.87 (m, 9 H,
H10, H100, H8, H9, OH), 1.73 (m, 4 H, H20 and H200),
1.21 (m, 20 H, H30-H70 and H300–H700), 0.81 (m, 6H,
H80 and H800). 13C NMR (50 MHz, CDCl3): d 151.7
(C1), 149.4 (C16), 148.5 (C11), 146.5 (C4), 135.1 (C5),
123.6, 121.8, 121.5, 121.0, 115.2, 113.9, 113.2 (C2, C3,
C4, C12, C13, C14, and C15), 72.1, 71.2, 69.7, 69.1,
68.6, and 65.8 (C10, C100, C7, C8, C9, C10), 61.8
(CH2OH), 31.8, 29.3, 26.1, 26.0, 22.6 (C20–C70 and
C200–C700), 15.2 and 14.1 (C80, C800). IR (CH2Cl2,
cmꢀ1): mCO = 1592. MS (EI) 544 [M]+, 527 [M ꢀ OH]+.
Anal. Calc. for C33H52O6: C, 72.76; H, 9.62. Found:
C, 72.53; H, 9.83%.
m
C@O = 1684. MS (EI) 542 [M]+, 514 [M + CO]+. Anal.
Calc. for C33H50O6: C, 73.03; H, 9.39. Found: C,
72.52; H, 9.78%.
4.14. Synthesis of alcohol 19
The aldehyde complex 17a (0.160 g, 0.23 mmol) was
dissolved in 3 mL of ethanol. A solution of NaBH4
(0.038 g, 1 mmol) in 1 mL water was added to the first
solution. The mixture turned yellow immediately. After
stirring for 15 min, the mixture was poured into 30 mL
water. The product was extracted with diethyl ether
(2 · 30 mL). The organic layer was washed with 20
mL water. After drying on MgSO4, filtration and sol-
vent removal, the product was purified by TLC using
diethyl ether:petroleum ether 1:1 as eluent. Alcohol
19 was obtained as a yellow oil (0.093 g, 59.4% yield).
1H NMR (400 MHz, CDCl3): d 6.90 (m, 4H, H12,
H13, H14, H15), 5.27 (t, 1 H, J = 6.5 Hz, H3), 5.08
(dd, 1 H, J = 6.6 Hz and J = 0.9 Hz, H2), 4.94 (dd, 1
H, J = 6.2 Hz and J = .9 Hz, H4), 4.82 and 4.30 (dd,
dd, 1H, 1H,, J = 12.9 Hz and J = 5.9 Hz, H17,
CH2OH), 4.30 and 4.20 (m, m, 1H, 1H, H7), 4.20
(m, 2 H, H10), 4.00 (t, 4 H, J = 6.7 Hz, H10 and
H100), 3.93 (m, 4 H, H8 and H9), 1.80 (m, 4 H, H20
and H200), 1.44 (m, 4 H, H30 and H300), 1.30 (m, 16
H, H40–H70 and H400–H700), 0.88 (m, 6H, H80 and
H800). 13C NMR (100 MHz, CDCl3): d 233.4 (CO),
149.3 (C16), 148.5 (C11), 136.9 (C1), 128.0 (C1),
122.0, 121.1, 115.1, 114.0 (C12, C13, C14, and C15),
109.1 (C5), 90.9 (C3), 85.4 (C4), 76.4 (C7), 75.2 (C2),
70.6, 69.9 and 69.7 (C10, C8, C9), 69.2 (C100), 69.0
(C10), 60.8 (C17), 31.9 and 31.8 (C60, C600), 29.4,
29.3, 29.2, and 29.0 (C20, C200, C40, C400, C50, C500),
26.0, 25.9 (C30, C300), 22.7 (C70, C700), 14.2 (C80, C800).
IR (CH2Cl2, cmꢀ1): mOH = 3459, mCO = 1962, 1881.
MS (ES) 703 [M + Na]+, 567 [M + Na ꢀ 3CO ꢀ Cr]+.
Anal. Calc. for C36H52O9Cr: C, 63.51; H, 7.70. Found:
C, 63.05; H, 8.15%.
Acknowledgements
`
Financial support from the Ministere de la Recher-
che, the Centre National de la Recherche Scientifique
and the Tunisian Ministere de lÕenseignement superieur
et de la recherche scientifique are gratefully acknowl-
edged. We thank B. McGlinchey for translating the
manuscript.
`
´
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