Terminal organylchalcogenoethyl- and -propylamines and their Schiff base derivatives

Article abstract of DOI:10.1055/s-2005-865310

A series of organoselanyl- and organotellanyl-substituted ethyl- and propylamines and their hydrochlorides, as well as 2-(methylsulfanyl)ethylamine have been synthesized. Efficient general synthetic routes have been developed to chalcogen(S, Se, Te)-conta

Full text of DOI:10.1055/s-2005-865310

PAPER
1641
Terminal Organylchalcogenoethyl- and -propylamines and Their Schiff Base
Derivatives
T
ermina
l
O
rga
v
nylchalcoge
e
noethyl- an
t
d
-prop
l
ylamin
a
es na V. Amosova,*a Natalia A. Makhaeva,a Alexander V. Martynov,a Vladimir A. Potapov,a Barry R. Steele,b
Ioannis D. Kostasb
a
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1, Favorsky Str., Irkutsk 664033,
Russia
Fax +7(3952)425885; E-mail: amosova@irioch.irk.ru
National Hellenic Research Foundation, Institute of Organic and Pharmaceutical Chemistry, Vas. Constantinou 48, 11635 Athens,
b
Greece
Received 17 November 2004; revised 4 February 2005
Taking into account the potential of these Schiff bases as
Abstract: A series of organoselanyl- and organotellanyl-substitut-
tridentate ligands,1 and at the same time the extremely
ed ethyl- and propylamines and their hydrochlorides, as well as 2-
scarce knowledge about these compounds, which is limit-
ed mainly to sulfur-containing derivatives, we have syn-
(methylsulfanyl)ethylamine have been synthesized. Efficient gener-
al synthetic routes have been developed to chalcogen(S, Se, Te)-
containing Schiff bases with di- and trimethylene bridges between thesized salicylaldimines bearing sulfide-, selenide- and
the nitrogen atom of the imino group and the chalcogen, by conden-
telluride functions connected to nitrogen by a polymethyl-
sation of 3-(tert-butyl)- and 3-(1-ethylpropyl)-2-hydoxybenzene-
ene bridge (CH2)n (n = 2,3) starting from 3-(tert-butyl)-
carbaldehydes with the amines. The influence of the organylchal-
and 3-(1-ethylpropyl)-2-hydroxybenzenecarbaldehydes
cogenyl-group on some spectral characteristics (1H, 13C, 77Se NMR
and a series of 2-(organylselanyl)ethylamines 6, 2-(orga-
nyltellanyl)ethylamines 7, 3-(organylselanyl)propyl-
spectroscopy) of both amines and Schiff bases is discussed.
Key words: amines, Schiff bases, condensation, spectroscopy, or-
ganometallic reagents
amines 8, and 3-(organyltellanyl)propylamines
9
synthesized by us. For comparison purposes we have also
prepared the analogous Schiff bases using 2-(methylsulfa-
nyl)ethylamine 5.
Schiff bases are among the most investigated ligands in
coordination chemistry,1 but interest in them remains
high, due partly to the wide range of possibilities for vary-
ing the substituents in these ligand systems and also be-
cause of their potential applications in homogeneous
catalysis. One class of Schiff bases, which has received
particular attention, is that of the bidentate salicylaldi-
mines formed by the reaction of o-hydroxybenzaldehydes
with the corresponding amines. Use of amines which in-
corporate alkylamino-, hydroxy-, alkoxy-, alkyl- and
arylthio groups capable of additional coordination leads to
the possibility of an increase in denticity of the ligand in
complex formation.2
It should be pointed out that terminal organylchalcogenyl-
alkylamines in themselves are prospective ligands, which
has been shown for N-{2-(4-methoxyphenyltellanyl)eth-
yl}morpholine,7 bis-{2-(N-morpholino)ethyl}telluride,7b
3-organylselanyl(tellanyl) propylamines,8 2-organylsela-
nylethylamine,9 N,N-dialkyl(thioalkyl)amines,10 and
hence are interesting per se.
Of the organylchalcogenylalkylamines 5–9, only the sul-
fur derivatives are well-known.11 Selenium and tellurium
derivatives are represented solely by a few compounds: 2-
(methylselanyl)ethylamine hydrochloride (1a),12 2-(phe-
nylselanyl)ethylamine (6c),13 3-(phenylselanyl)- and 3-
(phenyltellanyl)propylamines 8b and 9b, 3-(4-methoxy-
phenyltellanyl)propylamine,8 but to date terminal orga-
nylselanyl- and tellanylalkylamines remain a poorly
studied type of alkylamines. The most general method for
their preparation is by nucleophilic substitution of halo-
gen in w-halogenoalkylamines by organylchalcogenolate
anions.8,11a–c,13 Alternative methods for the preparation of
2-(alkylsulfanyl)ethylamines include substitution of the
iodine atom in methyl iodide by the cysteamine an-
ion,11e–h substitution of chlorine in chloroethylsulfide by
phthalimido anion followed by alkaline hydrolysis of the
product,11i reduction of 2-methylsulfanylethyl nitrate with
hydrogen in the presence of nickel at 50–60 °C and a pres-
sure of 100 atm11j or rupture of ethylenimine with thi-
ol.11c,e On rupture of ethylenimine with potassium
selenosulfate followed by alkaline hydrolysis, selenocys-
teamine is formed12a,b and subsequent treatment with
methyl iodide affords 2-(methylselanyl)ethylamine.12b,c
An alternative procedure for the preparation of this type of
ligands containing sulfur consists of electrochemical rup-
ture of the disulfide bond of the corresponding bis-2-sali-
cylaldiminoethyl disulfides.3 Large 24- and 28-membered
macrocyclic Schiff bases are also known with selenide
and telluride functions linked to the nitrogen atom of the
imine bond through polymethylene bridges (CH2)n (n =
2,3).4 Schiff bases bearing a sulfide group connected to
the nitrogen atom of the imine function by a dimethylene
bridge are formed by condensation of 2-(organosulfa-
nyl)ethylamine, 2-[(2-aminoethyl)thiomethyl]benzimida-
zole or imidazole, with substituted salicylaldehydes,5
acetophenone or acetylacetones.6
SYNTHESIS 2005, No. 10, pp 1641–1648
x
x.
x
x
.
2
0
0
5
Advanced online publication: 12.04.2005
DOI: 10.1055/s-2005-865310; Art ID: Z21804SS
© Georg Thieme Verlag Stuttgart · New York

1642
S. V. Amosova et al.
PAPER
To prepare a series of terminal organylselanyl- and orga- rides 1a–c, 2a,b, 3a,b, 4a,b was proved by spectral meth-
13
77
nyltellanylethyl- and propylamines 6–9 we modified the ods (NMR 1H, C and Se, IR), GC–MS and elemental
most studied method of nucleophilic substitution of a analysis (experimental section, Tables 1 and 2).
chlorine atom in w-chloroalkylamines by chalcogenolate
anion.8,11a–c,13 Treatment of 2-chloroethylamine and 3-
chloropropylamine with organylselenolate and organyl-
tellurolate anions generated in situ by treatment of the cor-
responding diorganyl diselenide and ditelluride with
sodium tetrahydroborate in EtOH leads to the correspond-
ing 2-(organylselanyl)ethylamines 6, 2-(organyltella-
nyl)ethylamines 7, 3-(organylselanyl)propylamines 8 and
3-(organyltellanyl)propylamines 9 (Scheme 1). 2-Chloro-
ethylamine and 3-chloropropylamine were generated in
turn from the corresponding hydrochlorides by treatment
with sodium ethylate and used without separation.
1H NMR spectra of the chalcogeno-substituted alkyl-
amines 6–9 and their salts 1–4 (Table 1) are characterized,
apart from singlet signals for the methyl groups in the case
of methylchalcogenyl derivatives or aromatic signals in
the case of phenylchalcogenyl derivatives, with two dis-
tinct triplets of methylene groups in the case of ethyl-
amines 1, 2, 6, 7 and two triplets and a quintuplet for the
three methylene groups in the case of propylamines 3, 4,
8, 9. The NH2 group of the amine hydrochlorides in D2O
manifests itself as a singlet in the range 4.91–4.59 ppm.
The signal for the NH2 group for free amines appears in
the wide range of 1.80–0.85 ppm. Comparison of the
spectra for alkylamines 6–9 and hydrochlorides 1–4 with
the spectra for the parent 2-chloroethylamine, 3-chloro-
propylamine and their hydrochlorides indicates that the
influence of the organylchalcogenyl group extends only to
the adjacent methylene group of the alkyl moiety. The sig-
nals for the CH2X groups (X = Se, Te) are shifted towards
higher field compared to those for the CH2Cl-group of 2-
chloroethyl- (3.76 ppm) and 3-chloropropylamines (3.60
ppm). For methylchalcogenylalkylamines the chemical
shift of XCH2-group depends on chalcogen atom and in
the case of tellanyl derivatives is shifted to lower field
(2.72–2.57 ppm) compared to the selanyl derivatives
(2.63–1.98 ppm). For the phenylchalcogenyl derivatives
chemical shifts of the XCH2 group (X = Se, Te) practical-
ly do not depend on chalcogen atom and lie in the range
of 3.01–2.72 ppm.
NaOEt
Cl(CH2)nNH2·HCl
Cl(CH2)nNH2
1. EtOH
R2X2 + NaBH4 + Cl(CH2)nNH2
RX(CH2)nNH2·HCl
2. HClaq
1a–c; 2a,b; 3a,b; 4a,b
Scheme 1
The synthesized compounds were isolated in good yields
(up to 90%) as amine hydrochlorides (1a–c; 2a,b; 3a,b;
4a,b) on treatment of the reaction mixtures with concen-
trated hydrochloric acid (Scheme 1). The method de-
scribed allows preparation of the pure products 1–4
without additional purification. Unlike free amines 6–9,
their salts 1–4 are more stable on storage and lack any
odor.
As individual compounds, amines 6a–c, 7a,b, 8a,b, 9a,b
were prepared by treatment of the salts 1–4 with 50%
aqueous solution of KOH (Scheme 2). In contrast to a re-
port that propylamines 8b and 9b are crystals,8 all our
compounds 6–9 are liquids. The variance of our data as re-
gards to amines 8b and 9b with those reported8 are prob-
ably due to the fact that we had prepared these compounds
in metastable form.
13
In the C NMR spectra of the methylchalcogenyl-alkyl-
amines 6–9 (Table 2), the methyl group signal, identified
by its characteristic multiplicity (quartet), lies in the range
of 4.4–1.5 ppm for the selenium derivatives, while, in the
case of tellurium, a very marked shift to higher field
(–23.2 to 21.6 ppm) is observed. It is rather hard to assign
other signals of aliphatic carbons to specified methylene
groups of ethylamines 6 and 7 and propylamines 8 and 9,
but it can be assumed that the signal found in the spectra
of all alkylamines 5–9 in the range of 38.9–43.7 ppm cor-
responds to the CH2N group and that, as in the 1H spectra,
it is not influenced by the organylchalcogenide group.
KOH 50%
RX(CH2)nNH2·HCl
RX(CH2)nNH2
1a–c; 2a,b; 3a,b; 4a,b
6a–c; 7a,b; 8a,b; 9a,b
1,6: X = Se, n = 2, R = Me (a), Ph (b), Et (c)
2,7: X = Te, n = 2, R = Me (a), Ph (b)
3,8: X = Se, n = 3. R = Me (a), Ph (b)
4,9: X = Te, n = 3, R = Me (a), Ph (b)
Lengthening of the methylene chain between the selenium
and nitrogen atoms leads to a downfield shift of the sele-
nium signal in the Se spectra both for alkylseleno-sub-
77
Scheme 2
stituted amines and their salts (Table 2), and for aromatic
derivatives.
It should be pointed out that for both salts and free amines
the yields of (phenylchalcogenyl)alkylamines were higher
than those of the aliphatic derivatives. A similar compari-
son can be made for seleno- and telluro-substituted alkyl-
amines and their salts; in the case of selanyl derivatives
the yields are higher than for the tellanyl ones.
In the IR spectra, the free amines 5–9 are characterized by
two bands for N–H bond valence vibrations at 3367–3348
and 3291–3256 cm–1 that shift to the lower frequency re-
gion 3020–2926 cm–1 in the case of salts 1–4.
The mass-spectra of the free amines 6–9 are characterized
along with the molecular ions, by fragment ions resulting
from rupture of C–X (X = Se, Te) and C–N bonds. As a
result, these spectra indicate the presence of the ions
The structure of 2-(organylselanyl)- 6a–c and 2-(organyl-
tellanyl)ethyamines 7a,b, 3-(organylselanyl)- 8a,b and 3-
(organyltellanyl)propylamines 9a,b and their hydrochlo-
[RX]+,
[NH2(CH2)n]+
(or
[NH2CH=CH]+,
Synthesis 2005, No. 10, 1641–1648 © Thieme Stuttgart · New York

PAPER
Terminal Organylchalcogenoethyl- and -propylamines
1643
[NH2CH=CHCH3]+) and [RX(CH2)n]+ (or [RXCH=CH]+, bases 10 and 11, due to the influence of the imine group
[RXCH=CHCH3]+) (n = 2, 3). C–C bond scission to form and the phenol ring occur to lower field (3.87–3.79 ppm
fragments [RXCH2]+ and [NH2CH3]+ is characteristic of in the case of sulfur- and selenium-containing Schiff bases
ethylamines 6,7. The same C–C bond scission is also and 3.99–3.95 ppm in the case of tellurium-containing
found for the propylamines 8, 9 but with formation of ones) compared to the parent amines 5–9 and demonstrate
fragments [RXCH2CH2]+ (or [RXCH=CH]+) and the same splitting pattern with 4JHH 1.22 Hz. The signal of
[NH2CH2CH2]+ (or [NH2CH=CH]+). Both selenium- and the methyl group on the chalcogen atom and the triplet
tellurium-containing amines form the [Se]+ and [Te]+ ions signal of the methylene group adjacent to the methylsulfa-
on electron impact. Exceptions are the 2-, 3-(phenylsela- nyl, organylselanyl and organyltellanyl groups of bases 10
nyl)alkylamines.
and 11 are shifted to lower field compared to the starting
amine. The presence of an additional methylene in the
methylselanylpropyl derivatives of the Schiff bases 10f,
11f leads to an up-field shift of the NCH2 group signal as
compared to the ethyl derivatives.
We prepared the organylselanyl- and organyltellanylal-
kylamines-based Schiff bases by condensation of the cor-
responding benzaldehydes with free amine (method 1) or
amine generated in situ from amine hydrochloride on
treatment with sodium methylate in MeOH (method 2) Comparison of the 13C NMR spectra for the parent benzal-
(Scheme 3). The first method was used to synthesize the dehydes and those of the salicylaldimines 10 and 11
Schiff bases from 2-(methylsulfanyl)ethylamine 5 pre- (Table 4) prepared from them allows rather simple assign-
pared from cysteamine according to the known proce- ment of observable signals of the carbon atoms to corre-
dure.11e–h Yields of the bases reach 99% in this case, in the sponding groups. Thus, the carbon signals in the region of
second method they were 60–97% and, in general, de- sp2-hybridized atoms (166.5–165.4 ppm) evidently corre-
creased in the order S > Se > Te, being higher for the spond to the imino group CH=N, the doublet splitting ob-
methylchalcogenyl-derivatives compared to the phenyl served in some cases is probably due to residual coupling
ones.
to the low-field phenolic proton. The signals of the MeX
group (X = S, Se, Te) are found in the range of 15.7 to
–21.9 ppm and shift from lower to higher field in the order
S, Se, Te. A similar tendency is found for the CH2X group
(X = S, Se, Te) which is observed in the wide range of
35.0–4.1 ppm, an up-field shift being observed on going
from sulfur (35.0 ppm) to selenium (30.8–25.8 ppm) and
tellurium (4.1–9.1 ppm), and also on going from MeX to
PhX (X = S, Se) and from the ethyl to propyl derivatives.
The methylene group connected to the imino group is
strongly deshielded compared to the parent amines. As a
result, its signals manifest themselves in the range of
61.3–58.8 ppm with a slight down-field shift observed in
the order S, Se, Te. The central methylene group in the
propyl derivatives manifests itself at 22.6 ppm.
It is known that the Schiff bases prepared from salicylal-
dehyde and primary amines possess the E-configuration
due to H-bonding between the hydroxyl and the nitrogen
of the imine group.14 Since the H NMR spectral data of
1
the products 10 and 11 (Table 3) are similar to those of re-
ported salicylaldimines,14 this fact clearly speaks in favor
of an E-configuration for the Schiff bases 10a–f and 11a–
f. In the 1H NMR spectra of the compounds 10, 11, the hy-
droxy-group manifests itself as a singlet in the range
14.00–13.77 ppm for tert-butyl derivatives, and in the
range 13.62–13.41 ppm for 1-ethylpropyl derivatives, be-
ing shifted to lower field compared to the starting alde-
hydes (11.87 and 11.33 ppm respectively). The CH=N
group of Schiff bases manifests itself in the range 8.39–
8.31 ppm as a broad singlet or doublet with a 4JH-H split- In conclusion, we have developed a fairly efficient gener-
ting constant of 1.22 Hz. The signals for the methylene al synthetic route to S-, Se-, Te-containing Schiff bases,
groups bonded to nitrogen atom of the imine group of
Scheme 3
Synthesis 2005, No. 10, 1641–1648 © Thieme Stuttgart · New York

1644
S. V. Amosova et al.
PAPER
rinsed with EtOH (20 mL) and the combined ethanolic solution was
acidified with concd HCl to pH 5 (1 mL) and dried in vacuum to af-
ford PhSe(CH2)2NH2·HCl [1b, 1.60 g (52.6%)]; mp 115–117 °C
(EtOH).
potential tridentate hemilabile ligands for homogeneous
catalysis.15
3-(tert-Butyl)-2-hydroxybenzenecarbaldehyde and 3-(1-ethylpro-
pyl)-2-hydroxybenzenecarbaldehyde were prepared using a litera-
ture procedure.16 Dimethyl diselenide, diethyl diselenide, diphenyl
diselenide, dimethyl ditelluride and diphenyl ditelluride were pre-
pared according to known procedures.17 2-(Methylsulfanyl)eth-
ylamine 5 was prepared according to a known procedure.11f 1H (400
MHz), 13C (100.6 MHz) and 77Se (76.3 MHz) NMR spectra of
amines 5–9 and their salts 1–4 were recorded in CDCl3 or D2O
(amine hydrochlorides 1–4) on a Bruker DPX-400 spectrometer us-
IR (KBr): 2942 (br), 1583, 1503, 1251, 889 cm–1.
Anal. Calcd for C8H12NSeCl: C, 40.10; H, 5.07; N, 5.90. Found: C,
40.61; H, 5.11; N, 5.92.
Ethyl- and propyl amine hydrochlorides 1–4 were prepared from the
corresponding dichalcogenides by analogous procedures.
2-(Methylselanyl)ethylamine Hydrochloride (1a)
Yield: 29.5%; mp 153–155 °C (EtOH).
IR (KBr): 2980 (br), 1599, 1464, 1478, 1226, 883 cm–1.
1
ing hexamethyldisiloxane as internal standard. H (300 MHz) and
13C (75.5 MHz) NMR spectra of Schiff bases 10, 11 were recorded
in CDCl3 on a Bruker AC-300 spectrometer using CHCl3 as internal
standard. EI mass spectra were obtained at 70 eV ionization energy
on a HP 5971A spectrometer, which was interfaced to a HP-5890
gas chromatograph. IR spectra were recorded on a Bruker IPS 25
spectrometer in KBr (amine hydrochlorides) or neat.
Anal. Calcd for C3H10NSeCl: C, 20.65; H, 5.78; N, 8.03. Found: C,
20.40; H, 5.54; N, 7.97.
2-(Ethylselanyl)ethylamine Hydrochloride (1c)
Yield: 98.0%; mp 80–83 °C (EtOH).
IR (KBr): 2969 (br), 1599, 1475, 1461, 1222 cm–1.
2-(Phenylselanyl)ethylamine Hydrochloride (1b)
NaBH4 was slowly added under an Ar atmosphere to a solution of
Ph2Se2 (2.00 g, 6.41 mmol) in EtOH (40 mL) and the mixture stirred
until discoloring of the solution occurred. 2-Chloroethylamine gen-
erated from Cl(CH2)2NH2·HCl (1.49 g, 12.82 mmol) and sodium
(0.29 g, 12.82 mmol) in EtOH (25 mL) was then added under Ar to
a resulting solution of selenolate. This reaction mixture was re-
fluxed for 3 h. On cooling the precipitated NaCl was filtered off,
Anal. Calcd for C4H12SeNCl: C, 25.48; H, 6.41; N, 7.43. Found: C,
24.87; H, 7.05; N, 8.20.
2-(Methyltellanyl)ethylamine Hydrochloride (2a)
Yield: 84.5%; mp 124–126 °C (decomp.) (EtOH).
IR (KBr): 2963 (br), 1597, 1461, 1228, 889 cm–1.
Table 1 1H NMR Data for Amine Hydrochlorides RX(CH2)nNH3 Cl– 1–4 and Amines RX(CH2)nNH2 5–9
+
Compound RX
1H NMR data, δ, ppm (multiplicity, 2JHH, Hz)
R
XCH2
-CH2-
CH2N
NH2
1a
1b
1c
2a
2b
3a
3b
4a
4b
5
MeSe
1.85 (s)
2.62 (t, 7.08)
2.95 (t, 6.55)
2.65 (t, 7.08)
2.65 (t, 8.00)
3.01 (t, 7.84)
2.50 (t, 7.29)
2.92 (t, 7.18)
2.57 (t, 7.56)
2.80 (br s)
–
3.08 (t, 7.01)
2.98 (t, 6.55)
3.07 (t, 7.23)
3.18 (t, 8.06)
3.22 (t, 8.22)
2.97 (t, 7.51)
3.00 (t, 7.51)
2.99 (t, 7.45)
2.92 (br s)
4.65 (s)
4.59 (s)
4.65 (s)
4.62 (s)
4.91 (s)
4.61 (s)
4.67 (s)
4.67 (s)
4.70 (s)
1.56 (s)
1.80 (s)
1.58 (s)
1.36 (s)
1.31 (s)
1.32 (s)
1.29 (s)
1.05 (s)
1.69 (s)
1.14 (s)
PhSe
EtSe
7.16–7.39 (m)
1.19 (t, 7.46), 2.47 (q, 7.51)
1.79 (s)
–
–
MeTe
PhTe
MeSe
PhSe
MeTe
PhTe
MeS
–
7.22–7.45 (m)
1.88 (s)
–
1.90 (m, 7.26)
7.28–7.49 (m)
1.84 (s)
1.93 (m, 7.42)
2.01 (m, 7.51)
7.20–7.82 (m)
2.08 (s)
1.99 (br s)
2.59 (t, 6.24)
2.63 (t, 6.47)
2.95 (t, 9.0)
2.66 (t, 7.08)
2.72 (t, 6.85)
2.95 (t, 4.87)
2.58 (7.32)
–
2.87 (t, 6.55)
2.92 (t, 6.41)
2.97 (t, 8.5)
2.90 (t, 6.55)
2.95 (t, 6.85)
2.99 (t, 5.18)
2.78 (t, 6.92)
2.92 (t, 7.34)
2.73 (t, 6.91)
2.90 (t, 7.45)
6a
6b
6c
7a
7b
8a
8b
9a
9b
MeSe
PhSe
EtSe
1.98 (s)
–
7.22–7.48 (m)
1.39 (t, 7.61), 2.57 (q, 7.51)
1.87 (s)
–
–
MeTe
PhTe
MeSe
PhSe
MeTe
PhTe
–
7.16–7.42 (m)
1.98 (s)
–
1.80 (m, 7.20)
1.79 (m, 7.10)
1.85 (m, 7.07)
1.92 (m, 7.07)
7.20–7.46 (m)
1.88 (s)
2.75 (t, 6.85)
2.63 (t, 7.45)
2.72 (t, 6.80)
7.16–7.72 (m)
Synthesis 2005, No. 10, 1641–1648 © Thieme Stuttgart · New York

PAPER
Terminal Organylchalcogenoethyl- and -propylamines
1645
Table 2 13C NMR and 77Se NMR Data for Amine Hydrochlorides RX(CH2)nNH3 Cl– 1–4 and Amines RX(CH2)nNH2 5–9
+
77Se NMR
Compound
RX
13C NMR, δ, ppm (multiplicity, 3JC–H, Hz)
R
XCH2
CH2
CH2N
δ, ppm
41.2
1aa
1ba
1ca
2ab
2ba
3ab
3bb
4ab
4bb
5a
MeSe
PhSe
EtSe
4.4 (q, 142)
21.6 (t, 143)
24.0 (t, 144)
18.8 (t, 141)
–2.7
–
–
–
–
–
39.8 (t, 143)
39.6 (t, 145)
39.4 (t, 145)
41.6
134.6, 133.0, 131.0, 129.4, 127.8
261.3
154.8
15.0 (t, 148), 17.4 (q, 128)
MeTe
PhTe
MeSe
PhSe
MeTe
PhTe
MeS
–21.6
127.1–134.6 (m)
2.9 (t, 138)
20.8, 27.1
23.0, 26.9
–2.3
43.5 (t, 141)
39.5
3.5
62.9
132.4, 129.2, 127.2
38.9
281.7
–22.2
28.9
41.1
138.2, 129.8, 128.5
3.9
29.0
41.0
14.5 (q, 139)
37.8 (t, 138)
30.1
–
–
–
–
–
–
39.8 (t, 135)
41.4
6ab
6ba
6ca
7ab
7ba
8ab
8bb
9ab
9bb
MeSe
PhSe
EtSe
3.8
126.1–133.6 (m)
32.5 (t, 141)
27.9 (t, 138)
9.3
41.6 (t, 137)
41.7 (t, 136)
42.8
259.2
155.9
16.6 (t, 141), 15.6 (q, 127)
MeTe
PhTe
MeSe
PhSe
MeTe
PhTe
–23.2
129.9, 129.5, 128.3, 127.9, 126.8, 126.3
14.6 (t, 142)
14.8, 26.4
25.0, 33.8
–1.0
43.2 (t, 135)
41.0
1.5
77.0
132.4, 128.9, 126.6
–23.3
41.8
292.3c
34.4
35.3
42.7
138.3, 137.7, 129.2, 128.9, 127.6, 127.3,
112.0
5.2
43.7
a Without 13C–H decoupling.
b With 13C–H decoupling.
c Lit.8: d = 306.
Anal. Calcd for C3H10TeNCl: C, 16.15; H, 4.52; N, 6.28. Found: C,
16.04; H, 4.99; N, 6.27.
3-(Methyltellanyl)propylamine Hydrochloride (4a)
Yield: 46.4%; mp 85–87 °C (EtOH).
IR (KBr): 3020 (br), 2922, 1618, 1510, 1187, 833 cm–1.
2-(Phenyltellanyl)ethylamine Hydrochloride (2b)
Yield: 98.6%; mp 79–81 °C (EtOH).
IR (KBr): 3007 (br), 1597, 1572, 1509, 1476, 1204, 730 cm–1.
Anal. Calcd for C4H12TeNCl: C, 20.25; H, 5.10; N, 5.91. Found: C,
19.80; H, 4.81; N, 5.84.
Anal. Calcd for C8H12TeNCl: C, 33.69; H, 4.24; N, 4.91. Found: C,
33.78; H, 4.00; N, 5.12.
3-(Phenyltellanyl)propylamine Hydrochloride (4b)
Yield: 39.9%; mp 81–83 °C (EtOH).
IR (KBr): 2967 (br), 1573, 1505, 1487, 1180, 786 cm–1.
3-(Methylselanyl)propylamine Hydrochloride (3a)
Yield: 46.6%; mp 147–148 °C (EtOH).
IR (KBr): 2926 (br), 1593, 1570, 1520, 1221, 837 cm–1.
Anal. Calcd for C9H14TeNCl: C, 36.12; H, 4.72; N, 4.68. Found: C,
35.62; H, 4.82; N, 4.71.
Anal. Calcd for C4H12SeNCl: C, 25.48; H, 6.41; N, 7.43. Found: C,
25.30; H, 6.50; N, 7.49.
2-(Methylsulfanyl)ethylamine (5)
Yield: 43.6%; bp 50–53 °C (25 Torr); nD22 1.4910.
IR (neat): 3356, 3291, 2916, 1592, 1429, 1273, 860 cm–1.
3-(Phenylselanyl)propylamine Hydrochloride (3b)
Yield: 99.7%; mp 141–143 °C (EtOH).
IR (KBr): 2927 (br), 1613, 1578, 1512, 1228 cm–1.
EI–MS: m/z = 91 [M]+, 75 [MeSCH2CH2]+, 61 [MeSCH2]+, 48
[MeSH]+, 45 [NH2CH2CH3]+, 31 [NH2CH3]+.
Anal. Calcd for C9H14SeNCl: C, 43.13; H, 5.63; N, 5.59. Found: C,
42.30; H, 5.74; N, 5.06.
2-(Phenylselanyl)ethylamine (6b)
PhSe(CH2)2NH2·HCl (1b; 1.55 g, 6.55 mmol) was treated with a
50% aq solution of KOH (10.00 g KOH) and extracted with Et2O
Synthesis 2005, No. 10, 1641–1648 © Thieme Stuttgart · New York

1646
S. V. Amosova et al.
PAPER
(3 × 20 mL). The Et2O extract was dried over MgSO4 for 3 h. Re-
moval of the solvent afforded PhSe(CH2)2NH2 [6b; 0.59 g (45.0%)]
as a yellow liquid; nD22 1.6131.
EI–MS: m/z = 153 [M]+, 124 [EtSeCH3]+, 122 [CH2=CHSeCH3]+,
109 [EtSe]+, 107 [CH2=CHSe]+, 96 [MeSeH]+, 80 [Se]+, 42
[NH2CH=CH]+, 31 [NH2CH3]+.
IR (neat): 3348, 3256, 2930, 1578, 1477, 1248, 893 cm–1.
2-(Methyltellanyl)ethylamine (7a)
EI–MS: m/z = 201 [M]+, 183 [PhSeCH=CH]+, 157 [PhSe]+, 106
Yield: 21.3%; nD20 1.6074.
[PhCH2CH3]+, 77 [Ph]+, 44 [NH2CH2CH2]+, 31 [NH2CH3]+.
IR (neat): 3352, 3283, 2921, 1575, 1419, 1219, 832 cm–1.
Free ethylamines 6, 7 and propylamines 8, 9 were generated analo-
gously.
EI–MS: m/z = 189 [M]+, 172 [MeTeCH = CH2]+, 160 [MeTeMe]+,
145 [MeTe]+, 130 [Te]+, 44 [NH2CH2CH2]+, 31 [NH2CH3]+.
2-(Methylselanyl)ethylamine (6a)
2-(Phenyltellanyl)ethylamine (7b)
Yield: 42.0%; nD20 1.5863.
Yield: 24.9%; nD20 1.6496.
IR (neat): 3355, 3283, 2923, 1587, 1424, 1249, 850 cm–1.
IR (neat): 3364, 3287, 2926, 1596, 1474, 1226, 841 cm–1.
EI–MS: m/z = 139 [M]+, 122 [MeSeCH=CH2]+, 110 [MeSeMe]+, 95
EI–MS: m/z = 251 [M]+, 222 [PhTeCH3]+, 207 [PhTe]+, 130 [Te]+,
[MeSe]+, 80 [Se]+, 42 [NH2CH=CH]+, 31 [NH2CH3]+.
93 [PhNH2]+, 77 [Ph]+, 44 [NH2CH2CH2]+, 31 [NH2CH3]+.
2-(Ethylselanyl)ethylamine (6c)
3-(Methylselanyl)propylamine (8a)
Yield: 57.9%; nD22 1.5191.
Yield: 18.9%; nD20 1.6373.
IR (neat): 3356, 3283, 2922, 1588, 1450, 1231, 846 cm–1.
EI–MS: m/z
=
153 [M]+, 138 [MeSe(CH2)2CH3]+, 123
[MeSeCH2CH2]+, 109 [MeSeCH2]+, 95 [MeSe]+, 80 [Se]+, 57
[NH2CH=CHCH3]+, 42 [NH2CH=CH]+, 31 [NH2CH3]+.
Table 3 1H NMR Data for Schiff Bases 10 and 11
1H NMR data, δ, ppm (multiplicity, JHH, Hz)
Schiff
Base
RX
R
C6H3
R'
N=CH
NCH2
CH2
–
CH2X
OH
10a
MeS
2.17 (s)
6.81–7.36
(m)
1.47 (s)
8.39
(t, 1.21)
3.81
(dt, 6.71, 1.22)
2.86
(t, 7.02)
13.89 (s)
10b
10c
10d
10e
10f
MeSe
PhSe
MeTe
PhTe
MeSe
MeS
2.04 (s)
6.84–7.34
(m)
1.48 (s)
1.45 (s)
1.46 (s)
1.49 (s)
1.46 (s)
8.37
(t, 1.22)
3.87
(dt, 6.41, 1.22)
–
–
–
–
2.86
(t, 6.71)
13.91 (s)
13.77 (s)
13.88 (s)
13.81 (s)
14.00 (s)
13.53 (s)
7.25–7.52
(m)
6.81–7.32
(m)
8.30
(t, 1.16)
3.87
(dt, 7.63, 1.22)
3.21
(t, 7.02)
1.94 (s)
6.83–7.33
(m)
8.37
(t, 1.24)
3.96
(dt, 7.63, 1.22)
2.93
(t, 7.02)
7.22–7.77
(m)
6.83–7.32
(m)
8.31 (s)
3.99 (t, 6.71)
3.19
(t, 7.32)
2.01 (s)
6.83–7.32
(m)
8.37 (s)
3.69 (t, 6.41)
2.08 (quint, 2.64
6.69)
(t, 7.32)
11a
2.14 (s)
6.87–7.17
(m)
3.04 (m),
1.68 (m),
8.37
(t, 1.22)
3.79
(dt, 6.71, 1.22)
–
2.83
(t, 6.71)
0.83 (t, 7.32)
11b
11c
11d
11e
11f
MeSe
PhSe
MeTe
PhTe
MeSe
2.01 (s)
6.86–7.17
(m)
3.03 (m),
1.67 (m),
0.80 (t, 7.32)
8.36 (s)
8.31 (s)
3.86 (t, 7.02)
3.87 (t, 7.02)
–
–
–
–
2.84
(t, 7.02)
13.51 (s)
13.45 (s)
13.49 (s)
13.41 (s)
13.62 (s)
7.25–7.53
(m)
6.86–7.18
(m)
3.04 (m),
1.69 (m),
0.84 (t, 7.32)
3.21
(t, 7.02)
1.91 (s)
6.85–7.17
(m)
3.02 (m),
1.66 (m),
0.81 (t, 7.63)
8.36
(t, 1.24)
3.95
(dt, 6.71, 1.24)
2.91
(t, 7.02)
7.20–7.75
(m)
6.86–7.26
(m)
3.03 (m),
1.68 (m),
0.83 (t, 7.32)
8.31 (s)
3.98 (t, 7.32)
3.17
(t, 7.32)
1.99 (s)
6.84–7.15
(m)
3.00 (m),
1.66 (m),
8.36
(t, 1.22)
3.68
2.06 (quint, 2.63
(t, 7.32)
(dt, 6.74, 1.22) 7.32)
0.81 (t, 7.61)
Synthesis 2005, No. 10, 1641–1648 © Thieme Stuttgart · New York

PAPER
Terminal Organylchalcogenoethyl- and -propylamines
1647
3-(Phenylselanyl)propylamine (8b)
in MeOH (10 mL) and the resulting mixture was refluxed for 30
min. After removal of MeOH the residue was diluted with water and
extracted with CH2Cl2. This extract was dried over Na2SO4 for 3 h.
Removal of the solvent afforded the product 10a [2.50 g (99.6%)]
as a yellow liquid.
Yield: 53.5%; nD18 1.6371.
IR (neat): 3367, 3290, 2928, 1578, 1477, 1232, 816 cm–1.
EI–MS: m/z = 215 [M]+, 198 [PhSeCH=CHCH3]+, 183 [Ph-
SeCH=CH]+, 157 [PhSe]+, 117 [PhCH=CHCH2]+, 106
[PhCH2CH3]+, 91 [PhCH2]+, 57 [NH2CH=CHCH3]+, 31
[NH2CH3]+.
Anal. Calcd for C14H21NOS: C, 66.89; H, 8.42; N, 5.57. Found: C,
67.12; H, 8.15; N, 5.27.
2-(tert-Butyl)-6-{([2-(methylselanyl)ethyl]imino)methyl}ben-
zenol (10b)
3-(Methyltellanyl)propylamine (9a)
Yield: 31.0%; nD22 1.6369.
A solution of MeONa, prepared by dissolution of Na (0.12 g, 5.0
mmol) in MeOH (5.22 mL), was added to MeSe(CH2)2NH2·HCl
(1a; 0.88 g, 5.0 mmol). After stirring for 10 min 3-(tert-butyl)-2-hy-
droxybenzenecarbaldehyde (0.89 g, 5.0 mmol) was added to the re-
sulting mixture and refluxed for 30 min. After removal of MeOH,
the residue was diluted with water and extracted with CH2Cl2. The
extract was dried over Na2SO4 for 3 h. Removal of the solvent af-
forded the product 10b [1.42 g (94.7%)] as a yellow liquid.
IR (neat): 3356, 3284, 2922, 1595, 1457, 1205, 832 cm–1.
EI–MS: m/z = 203 [M]+, 188 [MeTe(CH2)2CH3]+, 171 [Me-
TeCH=CH]+, 145 [MeTe]+, 130 [Te]+, 56 [NH2CH=CHCH2]+, 42
[NH2CH=CH]+.
3-(Phenyltellanyl)propylamine (9b)
Yield: 37.5%; nD17 1.6371.
IR (neat): 3362, 3288, 2926, 1573, 1474, 1205, 850 cm–1.
Anal. Calcd for C14H21NOSe: C, 56.37; H, 7.10; N, 4.70. Found: C,
56.65; H, 7.38; N, 4.39.
EI–MS: m/z = 265 [M]+, 235 [PhTe(CH2)2]+, 207 [PhTe]+, 130
[Te]+, 77 [Ph]+, 58 [NH2(CH2)3]+, 42 [NH2CH=CH]+.
Schiff bases 10c–f, 11a–f were prepared by analogous procedures.
2-(tert-Butyl)-6-{([2-(phenylselanyl)ethyl]imino)methyl}ben-
zenol (10c)
Yield: 94.4%.
2-(tert-Butyl)-6-{([2-(methylsulfanyl)ethyl]imino)methyl}ben-
zenol (10a)
3-(tert-Butyl)-2-hydroxybenzenecarbaldehyde (1.78 g, 10.0 mmol)
was added to a solution of MeS(CH2)2NH2 (5; 0.91 g, 10.0 mmol)
Table 4 13C NMR Data for Schiff Bases 10 and 11
13C NMR data, δ, ppm
Schiff
Base
RX
R
C6H3
R'
N=CH
166.4
NCH2
58.8
CH2
–
CH2X
35.0
10a
MeS
15.9
160.3, 137.3, 129.6,
129.4, 118.4, 117.8
29.3, 34.7
10b
10c
10d
10e
10f
MeSe
PhSe
MeTe
PhTe
MeSe
MeS
4.4
160.3, 137.2, 129.7,
129.4, 118.4, 117.8
29.3, 34.4
29.3, 34.8
29.5, 34.7
29.3, 34.7
29.3, 34.7
166.2
166.4
165.6
165.8
165.9
166.2
166.0
166.2
165.4
165.6
165.8
59.6
59.4
61.3
60.9
58.8
58.7
59.7
59.3
61.3
61.0
58.8
–
25.8
28.2
4.1
133.0, 129.1,
127.1, 117.9
160.3, 137.4, 129.7,
129.4, 118.5, 117.8
–
–21.8
160.3, 137.3, 129.6,
129.4, 118.4, 117.8
–
138.6, 129.2,
127.8, 111.0
160.3, 137.3, 129.7,
129.4, 118.4, 117.8
–
9.1
3.9
160.3, 137.3, 129.5,
129.5, 118.5, 117.7,
22.6
30.8
35.0
25.9
28.1
4.2
11a
11b
11c
11d
11e
11f
15.8
4.5
159.3, 133.1, 130.3,
128.9, 118.1, 117.9
11.9, 27.6,
40.4
–
MeSe
PhSe
MeTe
PhTe
MeSe
159.4, 133.3, 130.5,
128.9, 118.1, 117.9
11.9, 27.6,
40.4
–
132.8, 129.4,
127.0
159.3, 133.2, 130.5,
129.1, 118.1, 118.0
12.0, 27.6,
40.5
–
–21.9
159.3, 133.2, 130.4,
129.0, 118.1, 118.0
11.9, 27.6,
40.4
–
138.6, 129.2,
127.8, 111.1
159.4, 133.2, 130.5,
129.0, 118.2, 118.0,
12.0, 27.6,
40.5
–
9.1
3.9
159.4, 133.2, 130.3,
128.8, 118.1
11.9, 27.6,
40.4
22.6
30.8
Synthesis 2005, No. 10, 1641–1648 © Thieme Stuttgart · New York

1648
S. V. Amosova et al.
PAPER
Anal. Calcd for C19H23NOSe: C, 63.33; H, 6.43; N, 3.89. Found: C,
63.14; H, 6.53; N, 3.59.
References
(1) Garnovskii, A. D.; Vasil’chenko, I. S. Usp. Khim. 2002, 71,
1064.
(2) (a) Panova, G. V.; Vikulova, N. K.; Potapov, V. M. Usp.
Khim. 1980, 49, 1234. (b) Garnovskii, A. D.; Vasil’chenko,
I. S.; Garnovskii, D. A. Modern Aspects of Synthesis of
Metallocomplexes; LaPo: Rostov, 2000.
(3) Labisbal, E.; Garcia-Vasquez, J. A.; Romero, J.; Sousa, A.;
Castineiras, A.; Maihle-Mossmer, C.; Russo, U. Inorg.
Chim. Acta 1994, 223, 87.
(4) Tripathi, S. K.; Khandelwal, B. L.; Gupta, S. K. Phosphorus,
Sulfur Silicon Relat. Elem. 2002, 177, 2285.
2-(tert-Butyl)-6-{([2-(methyltellanyl)ethyl]imino)methyl}ben-
zenol (10d)
Yield: 86.2%.
Anal. Calcd for C14H21NOTe: C, 48.47; H, 6.10; N, 4.04. Found: C,
48.19; H, 6.32; N, 3.86.
2-(tert-Butyl)-6-{([2-(phenyltellanyl)ethyl]imino)methyl}ben-
zenol (10e)
Yield: 82.9%.
(5) Bermejo, M. R.; Sousa, A.; Garcia-Deibe, A.; Maneiro, M.;
Sanmartin, J.; Fondo, M. Polyhedron 1999, 18, 511.
(6) Bastida, R.; Deblas, A.; Fenton, D. E.; Rodriguez, T.
Polyhedron 1992, 11, 2739.
Anal. Calcd for C19H23NOTe: C, 55.80; H, 5.67; N, 3.42. Found: C,
56.05; H, 5.81; N, 3.20.
2-(tert-Butyl)-6-{([2-(methylselanyl)propyl]imino)methyl}ben-
(7) (a) Singh, A. K.; Kumar, J. S.; Butcher, R. J. Inorg. Chim.
Acta 2001, 312, 163. (b) Singh, A. K.; Sooriyakumar, J.;
Husebye, S.; Tonroos, K. W. J. Organomet. Chem. 2000,
612, 46.
(8) Khanna, A.; Bala, A.; Khandelwal, B. L. J. Organomet.
Chem. 1995, 494, 199.
(9) (a) Root, M. J.; Deutsch, E. Inorg. Chem. 1981, 20, 4375.
(b) Roecker, L.; Dickman, M. H.; Nosco, D. L.; Doedens, R.
J.; Deutsch, E. Inorg. Chem. 1983, 22, 2022. (c) Konno, T.;
Okamoto, K.; Hidaka, J. Chem. Lett. 1982, 5354.
(d) Nakajima, K.; Kojima, M.; Fujita, J. Chem. Lett. 1982,
925.
(10) (a) Fache, F.; Gamez, P.; Nour, F.; Lemaire, M. J. Mol.
Catal. 1993, 85, 131. (b) Cran, G. A.; Gibson, C. L.; Handa,
S.; Kennedy, A. R. Tetrahedron: Asymmetry 1996, 7, 2511.
(11) (a) Crane, C. W.; Rydon, H. N. J. Chem. Soc. 1947, 766.
(b) Tsatsas, G.; Sandris, G.; Kontonassios, D. Bull. Soc.
Chim. Fr. 1964, 3100. (c) Brighton, K. W.; Reid, E. E. J.
Am. Chem. Soc. 1943, 65, 458. (d) McIntyre, G. H.; Block,
B. P.; Fernelius, W. C. J. Am. Chem. Soc. 1959, 81, 529.
(e) Burfield, D. R.; Gan, S. N.; Smithers, R. H. J. Chem.
Soc., Perkin Trans. 1 1977, 666. (f) Okuda, J.; Eberle, T.;
Spaniol, T.; Piquet-Fauré, V. J. Organomet. Chem. 1999,
591, 127. (g) Clark, R. J. H.; McAlees, A. J. Inorg. Chem.
1972, 11, 342. (h) Davis, R. E.; Molnar, S. P.; Nehring, R. J.
Am. Chem. Soc. 1969, 91, 97. (i) Jinachitra, S.; MacLeod,
A. J. Tetrahedron 1979, 35, 1315. (j) Heart, R. T.; Lambert,
A. J. Chem. Soc. 1947, 1477.
zenol (10f)
Yield: 95.5%.
Anal. Calcd for C15H23NOSe: C, 57.69; H, 7.42; N, 4.48. Found: C,
57.91; H, 7.27; N, 4.37.
2-(1-Ethylpropyl)-6-{([2-(methylsulfanyl)ethyl]imino)meth-
yl}benzenol (11a)
Yield: 99.2%.
Anal. Calcd for C15H23NOS: C, 67.88; H, 8.73; N, 5.28. Found: C,
67.47; H, 8.65; N, 5.07.
2-(1-Ethylpropyl)-6-{([2-(methylselanyl)ethyl]imino)meth-
yl}benzenol (11b)
Yield: 96.8%.
Anal. Calcd for C15H23NOSe: C, 57.69; H, 7.42; N, 4.48. Found: C,
57.83; H, 7.35; N, 4.29.
2-(1-Ethylpropyl)-6-{([2-(phenylselanyl)ethyl]imino)meth-
yl}benzenol (11c)
Yield: 94.1%.
Anal. Calcd for C20H25NOSe: C, 64.16; H, 6.73; N, 3.74. Found: C,
64.01; H, 6.89; N, 3.60.
2-(1-Ethylpropyl)-6-{([2-(methyltellanyl)ethyl]imino)meth-
yl}benzenol (11d)
Yield: 88.4%.
Anal. Calcd for C15H23NOTe: C, 49.91; H, 6.42; N, 3.88. Found: C,
49.70; H, 6.25; N, 3.64.
(12) (a) Klayman, D. L. J. Org. Chem. 1965, 30, 2454.
(b) Odom, J. D.; Dawson, W. H.; Ellis, P. D. J. Am. Chem.
Soc. 1979, 101, 5815. (c) Tanaka, H.; Sakurai, H.;
Yokoyama, A. Chem. Pharm. Bull. 1970, 18, 1015.
(13) Heck, J. V.; Christensen, B. G. Tetrahedron Lett. 1981, 22,
5027.
2-(1-Ethylpropyl)-6-{([2-(phenyltellanyl)ethyl]imino)meth-
yl}benzenol (11e)
Yield: 63.7%.
(14) Percy, G. C.; Thornton, D. A. J. Inorg. Nucl. Chem. 1972,
34, 3369.
Anal. Calcd for C20H25NOTe: C, 56.79; H, 5.96; N, 3.31. Found: C,
56.65; H, 5.79; N, 3.19.
(15) Initial investigations have been carried out with Schiff bases
11a and 11b which readily form stable complexes on
reaction with Li2PdCl4. These complexes are now being
investigated as catalysts for cross-coupling reactions and
encouraging preliminary results have so far been obtained
for the Suzuki reaction. This work is now being actively
pursued and will be reported in due course.
2-(1-Ethylpropyl)-6-{([2-(methylselanyl)propyl]imino)meth-
yl}benzenol (11f)
Yield: 94.5%.
Anal. Calcd for C16H25NOSe: C, 58.89; H, 7.72; N, 4.29. Found: C,
59.18; H, 7.49; N, 4.46.
(16) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.;
Matsukawa, N.; Takagi, Y.; Tsuri, K.; Nitabaru, M.;
Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am.
Chem. Soc. 2001, 123, 6847.
(17) (a) Syper, J.; Mlochowski, J. Synthesis 1984, 439. (b) De
Filippo, D.; Momicchioli, F. Tetrahedron 1969, 25, 5735.
(c) Chen, M. T.; George, J. W. J. Organomet. Chem. 1968,
12, 401. (d) Haller, W. S.; Irgolic, K. J. J. Organomet.
Chem. 1972, 38, 97.
Acknowledgment
Financial support of this work by the Russian Academy of Sciences
and the Greek General Secretariat for Research and Technology is
gratefully acknowledged.
Synthesis 2005, No. 10, 1641–1648 © Thieme Stuttgart · New York