Synthesis, characterization and catalytic properties of diorganotin derivatives. Crystal and molecular structure of the first complex of 2-(2-methyl-3-nitroanilino)benzoic acid of 1,2:3,4-di-μ2-2-(2-methyl-3-nitroanilino)benzoato-O,O-1,3-bis-2-(2-methyl-3-nitroanilino)benzoato-O-1,2,4:2,3,4-di-μ3-oxo-tetrakis[di-methyltin(IV)]

Article abstract of DOI:10.1016/j.jorganchem.2008.07.011

The complexes [Me₂(MNAB)SnOSn(MNAB)Me₂]₂ (2) and [Me₂Sn(MNAB)₂] (3), where HMNAB is 2-(2-methyl-3-nitroanilino)benzoic acid, (1), have been prepared and structurally characterized by means of vibrational, ¹H and ¹³C NMR spectroscopies. The crystal structure of [Me₂(MNAB)SnOSn(MNAB)Me₂]₂ has been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric tetraorganodistannoxane of planar ladder arrangement. The structure is centro-symmetric and features a central rhombus Sn₂O₂ unit with two additional tin atoms linked at the O atoms. Six-coordinated tin centers are present in the dimmer distannoxane. This structure is self-assembled in one dimensional infinite chain via intermolecular hydrogen bonds, π → π and C-H → π stacking interactions. The polar imino hydrogen atom participates in intramolecular hydrogen bonds. The catalytic activity of the prepared complexes in transesterification reactions has been studied. The diorganotin complexes efficiently catalyze the transesterification reaction of 2-phenylethanol without addition of free ligand or any promoting additive.

Full text of DOI:10.1016/j.jorganchem.2008.07.011

Journal of Organometallic Chemistry 693 (2008) 3587–3592
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and catalytic properties of diorganotin derivatives.
Crystal and molecular structure of the first complex
of 2-(2-methyl-3-nitroanilino)benzoic acid of 1,2:3,4-di-
l2-2-(2-
methyl-3-nitroanilino)benzoato-O,O-1,3-bis-2-(2-methyl-3-nitroanilino)-
benzoato-O-1,2,4:2,3,4-di-
l3-oxo-tetrakis[di-methyltin(IV)]
a
b
a
Vaso N. Dokorou a, Dimitra Kovala-Demertzi a, , Maria Louloudi , Anca Silvestru , Mavroudis A. Demertzis
*
a Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
b Faculty of Chemistry and Chemical Engineering, ‘‘Babes-Bolyai” University, RO-400028 Cluj-Napoca, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
The complexes [Me2(MNAB)SnOSn(MNAB)Me2]2 (2) and [Me2Sn(MNAB)2] (3), where HMNAB is
2-(2-methyl-3-nitroanilino)benzoic acid, (1), have been prepared and structurally characterized by
means of vibrational, 1H and 13C NMR spectroscopies. The crystal structure of [Me2(MNAB)SnOSn-
(MNAB)Me2]2 has been determined by X-ray crystallography. Three distannoxane rings are present to
the dimeric tetraorganodistannoxane of planar ladder arrangement. The structure is centro-symmetric
and features a central rhombus Sn2O2 unit with two additional tin atoms linked at the O atoms. Six-coor-
dinated tin centers are present in the dimmer distannoxane. This structure is self-assembled in one
Received 6 March 2008
Received in revised form 10 July 2008
Accepted 14 July 2008
Available online 19 July 2008
Keywords:
2-(2-Methyl-3-nitroanilino)benzoic acid
Diorganotin adducts
Crystal structure
Spectroscopic studies
Catalytical activity
dimensional infinite chain via intermolecular hydrogen bonds,
p ? p and C–H ? p stacking interactions.
The polar imino hydrogen atom participates in intramolecular hydrogen bonds. The catalytic activity of
the prepared complexes in transesterification reactions has been studied. The diorganotin complexes effi-
ciently catalyze the transesterification reaction of 2-phenylethanol without addition of free ligand or any
promoting additive.
Transesterification reactions
Ó 2008 Published by Elsevier B.V.
1. Introduction
another important and versatile means. The acetyl ester plays an
important role for protection of the hydroxyl group in organic syn-
Diorganotin carboxylates derived from carboxylic acids are
among the most extensively studied class of compounds owing
to their rich structural chemistry. The diverse structural motifs
known in this family of compounds are attributed to the ambiden-
tate character of the carboxylate ligands. Steric and electronic attri-
butes of organic substituents on tin and/or the carboxylate moiety
impart significant influence on the structural characteristics in tin
carboxylates. Information on the structures of organotin carboxyl-
ates continues to accumulate, and at the same time new applica-
tions of such compounds are being discovered in industry,
ecology and medicine. Recently, much attention has also been fo-
cused on their use as metal-based drugs [1–3].
thesis. Consequently, numerous methodologies have so far been
put forth for the acetylation of alcohols [4].
Dimeric organotin cations [5] and neutral dimeric tetraorganod-
istannoxanes of the type [R2XSnOSnXR2]2 (X = Cl, OH, R0COO, NCS;
R, R0 = alkyl, aryl) have been found to be efficient catalysts for
transesterifications and for the highly selective acylation of alco-
hols [6,7]. The catalytic activity of distannoxanes in this type of
reaction was reported to be the result of their dimeric structure
[7] in solution. 2-(2-Methyl-3-nitroanilino)benzoic acid (Scheme
1), HMNAB (1), resembles mefenamic, tolfenamic, flufenamic acids
and other fenamates in clinical use, it was thought of interest to ex-
plore the chemistry of organotin/anilinobenzoic acid compounds,
as a continuation of our studies on organotin chemistry [8–10]
and to study the catalytical activity of the prepared diorganotin
derivatives.
Tin derivatives are used as homogeneous catalysts in esterifica-
tion and transesterification reactions [4]. Acylation of alcohols is
one of the most important manipulations in organic synthesis
and transestrification by using of esters as acylating reagents is
2-(2-Methyl-3-nitroanilino)benzoic acid (1), and the novel
complexes [Me2(MNAB)SnOSn(MNAB)Bu2]2 (2) and [Me2Sn-
(MNAB)2] (3), where HMNAB is 2-(2-methyl-3-nitroanilino)ben-
zoic acid (1), have been prepared and structurally characterized
* Corresponding author. Tel.: +30 2651098425; fax: +30 2651098786.
E-mail address: dkovala@cc.uoi.gr (D. Kovala-Demertzi).
0022-328X/$ - see front matter Ó 2008 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2008.07.011

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orated under vacuum to a small volume (2 ml), chilled and tritu-
rated with acetone to give a yellow solid. The yellow powder
was recrystallized from CH2Cl2 and was dried in vacuo over silica
gel. M.p. 219–221 °C; yield 26%. IR (KBr, cmꢀ1): 3324, 3290
m
(NY), 1614, 1590
m
as(COO), 1373, 1457
m
sym(COO); 569, 522
m(Sn–C); 440, 411
m(Sn–O)2; 281, 225, 218 m
(Sn–O); 1H NMR
Scheme 1.
(CDCl3): d 9.57 (s, 1H, NH), 7.89 (d, H3), 6.89 (d, H4), 7.57 (t, H5),
6.77 (t, H6), 7.65 (dt, H40), 7.37 (t, H50), 7.34 (d H60), 3.31/2.45(s,
CH3), 13C NMR: d 175.7 (COOH), 152.4 (C1), 114.4 (C2), 132.9
(C3), 118.3 (C4), 134.6 (C5), 115.5 (C6), 148.0 (C10), 120.0 (C20),
142.0 (C30), 127.6 (C50) 127.3 (C60) 14.5 (CH3) 10.4/7.80 (ꢀR–Sn)
Anal. Calc.: C, 44.90; H, 4.00; N, 6.15. Found: C, 44.50; H, 4.14; N,
5.90%. Crystals of 2 suitable for X-ray analysis were obtained by
slow evaporation of a CHCl3/CH3CN solution.
by means of vibrational, 1H and 13C NMR. The crystal and molecu-
lar structure of 2 is described. Also, the transesterification reactions
of 2 and 3 are described.
[Me2Sn(MNAB)2] (3). Dimethyl tin(IV) oxide (0.1649 g,
1.0 mmol), HMNAB (0.5989 g, 2.20 mmol) and 30 ml of benzene
were refluxed for 24 h with azeotropic removal of water via a
Dean-Stark trap. The resulting clear solution was rotary evaporated
under vacuum to a small volume (2 ml), chilled and triturated with
acetone to give a bright yellow solid. The yellow powder was
recrystallized from CH2Cl2 and dried in vacuo over silica gel. M.p.
2. Experimental
2.1. General and instrumental
2.1.1. General
The reagents (Aldrich, Merck) were used as supplied while the
solvents were purified according to standard procedures [11c].
Elemental analyses (C, H and N) were carried out by the microan-
alytical service of the University of Ioannina. Melting points were
determined in open capillaries and are uncorrected. Infrared and
far-infrared spectra were recorded on a Perkin–Elmer Spectrum
GX Fourier transform spectrophotometer using KBr pallets
(4000–400 cmꢀ1) and nujol mulls dispersed between polyethyl-
ene disks (400–40 cmꢀ1). The 1H (250.13 MHz), 13C (62.90 MHz)
NMR spectra were recorded on a Bruker AC-250 and on a Bruker
AMX-400 spectrometers. Samples were dissolved in CDCl3 and
spectra were obtained at room temperature with the signal of
the free CDCl3 at 7.24 ppm. GC analysis was performed using a
Shimadzu GC-17A gas chromatograph coupled with a GCMS-
QP5000 mass spectrometer with the following temperature pro-
gram: initial temperature, 80 °C (starting time 5 min); heating
rate, 10 °C/min; final temperature, 150 °C (final time 5 min);
injector temperature, 230 °C. The yields of products were esti-
mated from the peak areas based on the internal standard tech-
nique [11d].
165–166 °C; yield 77%. IR (KBr): 3318
m
(NY), 1666
mas(COO), 1404
m
sym(COO); 569, 545 (Sn–C); 280, 217 m
m
(Sn–O). 1H NMR (CDCl3):
d 9.29 (s, 1H, NH), 8.15 (dd, H3), 6.92 (d, H4), 7.60 (t, H5), 6.85
(t, H6), 7.60 (t, H40), 7.31 (t, H50), 7.35 (d, H60); 3.49/2.17(s, CH3),
13C NMR: d 177.6 (COOH), 151.9 (C1), 112.3 (C2), 133.4 (C3),
118.2 (C4), 135.0 (C5), 113.9 (C6), 147.7 (C10), 119.7 (C20), 141.4
(C30), 121.2 (C40), 127.3 (C50), 126.7 (C60) 13.6 (CH3). Anal. Calc.
for C30H28SnN4O8 (691.2 g molꢀ1): C, 52.10; H, 4.10; N, 8.10.
Found: C, 52.10; H, 4.07; N, 8.26%.
2.3. Catalytic reactions
2-Phenylethanol (1 mM) was slowly added to a solution of eth-
ylacetate (5 ml). As an internal standard acetophenone was used.
Catalytic reaction was started by adding 10 lM of 2 or 3. The ratio
of catalyst: 2-phenylethanol was 1:100. The reaction mixture was
refluxed at 77 °C and the progress of the reaction was monitored
by GC–MS, by removing small samples of the reaction mixture.
To establish the identity of the products unequivocally, the
retention times and spectral data were compared to those of com-
mercially available compounds. Thus, 2-phenylethanol, 2-phenyl-
ethyl acetate and acetophenone were purchased in their highest
commercial purity, stored at 5 °C and purified by passage through
a column of basic alumina prior to use.
2.2. Synthesis
2-(2-Methyl-3-nitroanilino)benzoic acid (HMNAB) (1), was syn-
thesized according to published procedure, the Ullmann–Goldberg
condensation [11a,b]. 2-Methyl-3-nitro-benzenamine (11.26 g,
0.074 mol), potassium 2-bromobenzoate (18.17 g, 0.076 mol), 4-
ethylmorpholine (9.5 ml, 0.076 mol) and 0.8 g of anhydrous copper
acetate in 30 ml of distilled N,N-dimethylformamide under nitro-
gen atmosphere were refluxed at 145 °C for 4 h. In the resulting
solution 20 ml of distilled N,N-dimethylformamide was added,
and 30 ml of 12% hydrochloric acid. The aqueous layer was dec-
anted and methanol was added. The solid was collected and recrys-
tallized three times from acetone. M.p. 222–223 °C. Yield 24.35%
2.4. X-ray crystallography
Slow evaporation of a dilute 1:1 by volume CH3CN/CHCl3 solu-
tion provided a yellow prismatic crystal of 2, which was mounted
on a sealed tube and used for data collection. Cell constants and an
orientation matrix for data collection were obtained by least-
squares refinement of the diffraction data from 25 reflections in
the range 1.34 < h < 26.30° on a Bruker Smart Apex diffractometer.
(2.70 g). IR (KBr): 3323sh m(NY), 1597 mas(COO), 1425 msym(COO);
1H NMR (CDCl3): d 9.30 (s, 1H, NH), 8.07 (dd, H3), 6.83 (t, H4),
7.65 (d, H5), 6.81 (t, H6), 7.57 (d, H40), 7.37 (t, H50), 7.35 (d, H60)
3.49/2.17 (s, CH3), 13C NMR: d 174.1 (COOH), 147,7 (C1), 111.4
(C2), 131.6 (C3), 114.2 (C4), 135.8 (C5), 118.8 (C6), 135.5 (C10),
132.2 (C20), 141.4 (C30), 120.2 (C40), 130.4 (C50). Anal. Calc. for
C14H13N2O4 (272.3 g molꢀ1): C, 61.77; H, 4.44; N, 10.29. Found: C,
61.25; H, 4.10; N, 10.05%.
[Me2(MNAB)SnOSn(MNAB)Me2]2 (2). Dimethyl-tin(IV) oxide
(0.1977 g, 1.2 mmol), HMNAB (0.2723 g, 1.0 mmol) and 30 ml of
benzene were refluxed overnight with azeotropic removal of water
via a Dean-Stark trap. The resulting clear solution was rotary evap-
Data were collected at 293 K using Mo K
and the -scan technique, and corrected for Lorentz and polariza-
tion effects [12]. A semi-empirical absorption correction ( -scans)
a radiation (k = 0.71073 Å)
x
W
was made. The structure was solved by direct methods (program
SHELXS97) and refined by the full-matrix least-squares method on
all F2 data using the WinGX version of SHELXL97 programs [13]. All
hydrogen atoms were located in their calculated positions (C–H
0.93–0.97 Å) and refined using a riding model. Molecular graphics
were performed using PLATON2001 [14]. A summary of the crystal
data, experimental details and refinement results are listed in
Table 1.

V.N. Dokorou et al. / Journal of Organometallic Chemistry 693 (2008) 3587–3592
3589
Table 1
nated by an anisobidentate chelating carboxylate ligand (Sn(2)–
O(4) 2.177(5) Å and Sn(2)–O(5) 2.865 (6) Å). The distance
Sn(1)–O(4) is 2.781(5) Å. The Sn–O distances 2.865 and 2.781 Å
are considered long to indicate strong bonding interactions, how-
ever, the range of distances Sn–O of 2.61–3.02 Å, has been confi-
dently reported for intramolecular bonds [15]. In this case the
O(5) acts as monoatomic bridge and connects the endocyclic and
exocyclic tin centers.
The phenyl rings are planar. The dihedral angles between the
planes of the phenyl rings for 2 are 59.5(4) and 56.5(5)° for the
bidentate bridging and the anisobidentae chelating ligands, respec-
tively. The aminobenzoate portion of each carboxylato ligand is
effectively planar which presumably facilitates the formation of
intramolecular N(18)–H00ꢁ ꢁ ꢁO(3) and N(38)–Hꢁ ꢁ ꢁO(5) interactions
of 2.660(9) and 2.675(10) Å, respectively. The monomers of 2 form
hydrogen-bonded dimers linked by two hydrogen bonds involving
the C(28)H hydrogen atom and the adjacent O(25) atom, and vice
versa, of centro-symmetrically related pairs of molecules. The ob-
served hydrogen-bonding pattern is of the DA = AD type, Fig. 2.
The crystal structure of 2 shows ring stacking interactions. The
Crystal data and structure refinement
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C64H72N8O20Sn4
1748.04
293(2)
Mo Ka 0.71073
Triclinic
P1
8.504(2)
14.760(3)
16.761(3)
65.786(3)
83.109(4)
85.074(4)
1903.4(7)
ꢀ
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
4
Dc (mg mꢀ3
)
1.525
1.367
872
Absorption coefficient,
F(000)
Crystal size (mm)
h range for data collection (°)
Ranges of h, k, l
l
(mmꢀ1
)
0.30 ꢃ 0.40 ꢃ 0.50
1.34, 26.37
ꢀ10 6 h 6 10, ꢀ18 6 k 6 18, ꢀ20 6 l 6 20
15429/7686 [0.0505]
7686/0/434
Reflections collected/unique [R(int)
Data/parameters
]
monomers are stacked by a strong
p
?
p
interaction and weaker
interactions. The monomers are stacked to a chain by a
interaction, the phenyl rings C(39)–C(40)–C(41)–
distance of 3.579(6) (symmetry
operation; 1 ꢀ x, 1 ꢀ y, ꢀz). In this case 2 is self-assembled via in-
ter-molecular hydrogen bonds, C–H ? and stacking inter-
actions. C–H ? stacking, intra- and inter-molecular
C–H ?
strong
p
p
Goodness-of-fit (F2)
1.001
? p
Final R1/wR2 indices (I > 2rI
)
R1 = 0.0613, wR2 = 0.1504
1.334 and ꢀ0.765
Largest diff. peak/hole (e Åꢀ3
)
C(42)–C(43)–C(47) are at
a
p
p ? p
p, p ? p
3. Results and discussion
hydrogen interactions stabilize this structure, Table 3. The struc-
tures of dimeric distannoxane of anthranilic acid, [Me2(NH2-o-
H46CO2)SnOSn(NH2-o-H4C6CO2)Me2]2 [16] and of [Bu2(DMPA)
SnOSn(DMPA)Bu2]2 HDMPA is 2-[bis(2,6-dimethylphenyl)amino]-
benzoic acid [10b] have solid state structure closely resembling 2
both in the geometry of the central core (Sn2O2)2, the coordination
mode of anthranilic acid and the presence of weaker interactions
2.736(9)–2.918(6) Å.
3.1. Synthetic aspects
Compound 1 was synthesized according to Ullmann–Goldberg
condensation from 2-methyl-3-nitro-benzenamine (11.26 g,
0.074 mol), potassium 2-bromobenzoate in the presence of 4-eth-
ylmorpholine and Cu(OAc)2, scheme 2. Adducts 2 and 3 were ob-
tained by azeotropic removal of H2O from the reaction (in
benzene) between the dimethylorganotin oxide and HMNAB in a
molar ratio of 1:1 and 1:2 for 2 and 3, respectively, scheme 3.
3.3. Spectroscopy
3.3.1. Infrared spectroscopy
3.2. Crystal structure of 2
As the carboxylic hydrogen is more acidic than the imino
hydrogen the deprotonation occurs in the carboxylic group. This
is confirmed by the IR spectra of the complexes, showing the char-
acteristic bands for the secondary amino groups and for the coor-
dinated carboxylate group [17]. The band at ꢂ3300 cmꢀ1, which
appears in the IR spectra of the ligand, is assigned to the NH
stretching motion and the broad band at ꢂ3000–2900 cmꢀ1 is ta-
ken to represent the v(NHꢁ ꢁ ꢁO) mode, due to intramolecular hydro-
gen bonding [3,8–10,17]. The absence of large systematic shifts of
the v(NH) and d(NH) bands in the spectra of the complexes com-
pared with those of the ligand indicates that there is no interaction
between the NH group and the metal ions, which is also confirmed
The molecular structure of 2 is shown in Fig. 1 and selected
interatomic parameters are collected in Table 2. Compound 2 is a
centrosymmetric dimmer distannoxane built up around the planar
cyclic Sn2O2 unit. The two oxygen atoms of this unit are tridentate
as they link three Sn centres, two endo-cyclic and one exo-cyclic.
The distance between the endocyclic and exocyclic tin atoms is
3.6306(10) and the distance between the two endocyclic tin cen-
ters is 3.2660(11). The additional links between the endo- and
exo-cyclic Sn atoms are provided by bidentate carboxylate ligands
that form nearly symmetrical bridges (Sn(1)–O(2) 2.242(6) Å and
Sn(2a)–O(3) 2.294(5) Å). Each exocyclic Sn atom is also coordi-
Scheme 2. The reaction scheme for synthesis of 1.

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V.N. Dokorou et al. / Journal of Organometallic Chemistry 693 (2008) 3587–3592
Scheme 3. The reaction scheme for synthesis of 2 and 3.
Fig. 1. Perspective view of 2 showing the atomic numbering scheme.
by X-ray analysis. The
m
m
as(COO) bands appear at 1614 and 1590 and
nance in the 1H NMR spectra of complexes indicates that the nitro-
sym(COO) at 1373 and 1459 cmꢀ1 for 2. The difference,
D
[mas
-
gen atom remain protonated and the downfield chemical shift for
this group indicates that this proton is involved in an intramolec-
ular hydrogen bond between the HN group and the carbonyl oxy-
gen of the carboxylato group. Deshielding of protons H(3) and H(4)
is observed in complexes, which should be related to the electro-
(COO)–
m
sym(COO)] between these frequencies for
2
(241,
133 cmꢀ1) is close to that found for anisobidentate chelate mode
(241 cmꢀ1
(133 cmꢀ1). This is totally consistent with the X-ray structure of
2. The asym(COO) and sym(COO) bands appear at 1666 and
)
and bridging bidentate carboxylato groups
m
m
philicity of the tin. A r-charge donation from the COO-donor to
1404 cmꢀ1 for 3. The difference
D
[
masym(COO)–msym(COO)] between
the tin center removes electron density from the ligand and pro-
duces this deshielding which will attenuate at positions remote
from the metal. All shifts are downfield except for that due to
H(5) which is shifted upfield. The upfield shift observed for H(5)
and its corresponding carbon atom C5, para to the tin center, could
be due to the flow of charge from the tin into the aromatic ring. The
13C NMR spectra of 2 and 3 reveal resonance assignable to the CO2
nucleus and coordination is confirmed by the fact that this reso-
nance exhibits a downfield shift. Involvement of the carboxyl
group in bonding to tin is confirmed by the resonance ascribed
these frequencies is 262 cmꢀ1, which is close to that found for the
anisobidentate chelate carboxylato group [7–10,17]. Two bands at
440–410 for 2, are assigned to mas,sym(SnO)2, indicating non-linear
O–Sn–O moieties, while the bands at 280–210 cmꢀ1 are assigned
to the tin-oxygen (COO) stretching modes [8–10,17].
3.3.2. NMR spectra
1H and 13C NMR chemical shifts of ligand and its complexes
were recorded in CDCl3 solution. The existence of the HN reso-

V.N. Dokorou et al. / Journal of Organometallic Chemistry 693 (2008) 3587–3592
3591
Table 2
Table 3
Bond lengths [Å] and angles [°] for 2
Distances (Å) and angles (°) of C–H–
p,
p
–p
interactions and intramolecular hydrogen
bonds for 2 and
Sn(1)–O(1)a
Sn(1)–C(1)
Sn(1)–C(2)
Sn(1)–O(1)
Sn(1)–O(2)a
Sn(1)–Sn(1)a
Sn(2)–O(1)
Sn(2)–C(3)
Sn(2)–C(4)
Sn(2)–O(4)
Sn(2)–O(3)
2.023(4)
2.078(9)
2.089(8)
2.145(4)
2.242(6)
3.2661(11)
2.011(4)
2.080(8)
2.090(7)
2.177(5)
2.294(5)
C
H
Cg
Hꢁ ꢁ ꢁCg
Cꢁ ꢁ ꢁCg
\(C–Hꢁ ꢁ ꢁCg)
C–H/
p
C(2)i
Y(2A)
H(2A)
Cg(2)
2.967
3.088
3.680(9)
3.657(9)
132.13
121.09
a
C(2)ii
Cg(2)a
Cg–Cgb
3.579(6)
bc
3.98
CgI-Perpd
3.570
CgJ-Perpd
3.570
Cg(8)iv
Cg(8)
H-bonds
N(18)
H(18)
H(38)
H(28A)
O(3)
O(5)
O(5)
2.01
2.12
2.42
2.660(9)
2.675(10)
3.175(13)
131
122
135
N(38)
C(28)iv
O(2)–Sn(1)a
2.242(6)
O(1)a–Sn(1)–C(1)
O(1)a–Sn(1)–C(2)
C(1)–Sn(1)–C(2)
O(1)a–Sn(1)–O(1)
C(1)–Sn(1)–O(1)
C(2)–Sn(1)–O(1)
O(1)a–Sn(1)–O(2)
C(1)–Sn(1)–O(2)a
C(2)–Sn(1)–O(2)a
O(1)–Sn(1)–O(2)a
O(1)a–Sn(1)–Sn(1)
C(1)–Sn(1)–Sn(1)a
C(2)–Sn(1)–Sn(1)a
O(1)–Sn(1)–Sn(1)a
O(2)a–Sn(1)–Sn(1)
O(1)–Sn(2)–C(3)
O(1)–Sn(2)–C(4)
C(3)–Sn(2)–C(4)
O(1)–Sn(2)–O(4)
C(3)–Sn(2)–O(4)
C(4)–Sn(2)–O(4)
O(1)–Sn(2)–O(3)
C(3)–Sn(2)–O(3)
C(4)–Sn(2)–O(3)
O(4)–Sn(2)–O(3)
Sn(2)–O(1)–Sn(1)a
Sn(2)–O(1)–Sn(1)
Sn(1)a–O(1)–Sn(1)
107.2(3)
a
Cg(8) and Cg(2) refer to the centroids C(39)ꢁ ꢁ ꢁC(47), and Sn(1)–O(1)–Sn(1a)–
103.4(3)
148.5(4)
76.86(17)
99.9(3)
93.9(3)
91.5(2)
O(1a).
b
Cg–Cg is the distance between ring centroids; symmetry transformations, (i) x,
y, z; (ii) ꢀx, ꢀy, 1 ꢀ z; (iii) 1 ꢀ x, 1 ꢀ y, ꢀz; (iv) ꢀ1 ꢀ x, ꢀy, 2 ꢀ z.
c
Where b is the angle Cg(I) ? Cg(J).
d
CgI-Perp or CgJ-Perp is the perpendicular distance of Cg(I) on ring J.
87.4(4)
84.7(3)
167.6(2)
39.76(12)
107.2(3)
100.9(3)
37.11(11)
131.11(16)
104.4(3)
107.7(3)
147.2(3)
79.97(17)
97.1(3)
The reaction mixture was refluxed at 77 °C under aerobic condi-
tions and the progress of the reaction was monitored by GC–MS,
by removing small samples of the reaction mixture. Under these
conditions, the transesterification catalysed by 2 was normally
progressed and quantitative yields were obtained after 6 h. When
the monomeric catalyst 3 was used, low yields of 25% were ob-
tained within 6 h. However, after 22 h, 3 was able to give quantita-
tive yields as well. In all cases, the only reaction product which has
been detected was 2-phenylethylacetate.
To identify the active catalytic species involved in the present
reaction, small liquots of the reaction mixture were studied by
LC–MS method and the analysis was performed in the negative
ion mode. For reactions catalysed by 2, after 0, 2, 4 and 22 h, LC–
MS spectroscopy always revealed one major product, with a very
intense anion at m/z 853.5 tentatively assigned to a dianion of 2.
When the catalyst 3 was used, sample analysis after 0, 2, 4 and
6 h reaction time, exhibited characteristic ions at m/z 565.4, which
is the major one, and one less intense at m/z 853.5. The first anion
assigned to 3 after the cleavage of the peripheral CHꢀ3 and NO2ꢀ
groups of the organic ligand. The analysis of an aliquot of the reac-
tion mixture after 22 h, interestingly, showed a very intense anion
at m/z 853.5 and only a small one at m/z 565.4. The appearance of
the peak at m/z 853.5 clearly indicates the formation of a dimeric
species analogous to 2. This was possibly generated after several
hours into the refluxed catalytic reaction, it seems to be the active
catalyst and it is directly correlated to the quantitative yields ob-
tained after 22 h.
95.1(3)
92.36(18)
87.8(3)
84.1(3)
171.70(18)
134.9(2)
121.7(2)
103.14(17)
Symmetry transformations used to generate equivalent atoms.
a
ꢀx + 2, ꢀy + 2, ꢀz+.
to C(2) and C(3), which exhibit the greatest shift upon coordination
[3,8–10].
3.4. Catalysis
The catalytic activity of 2 and 3 were assessed for acetylation of
2-phenylethanol by ethylacetate (Table 4). Ethylacetate was used
as solvent, while the molar ratio of catalyst: substarte was 1:100.
Fig. 2. Inter- and intra molecular hydrogen bonding pattern of 2.

3592
V.N. Dokorou et al. / Journal of Organometallic Chemistry 693 (2008) 3587–3592
Table 4
Acetylation of 2-phenylethyl alcohol catalyzed by 2 and 3a
O
OH
O
H3C
CH3
C2H5
Ethylacetate
2 or 3
O
+
C2H5OH
Ethanol
+
O
770
Reflux
2-
Phenylethanol
2-Phenylethylacetate
Cat (conc./mol%)
Reaction time (h)
Yieldb (%)
2 (0.01)
2 (0.01)
2 (0.01)
2 (0.01)
3 (0.01)
3 (0.01)
3 (0.01)
3 (0.01)
1
4
6
22
1
4
38.8
88.5
100
100
21.3
25.1
25.7
100
6
22
a
Reaction conditions: ROH (1 mmol); ethylacetate (5 ml); catalyst (10
Yields were based on alcohol and determined by GC–MS.
lmol).
b
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The present findings are in accordance and further support pre-
viously proposed mechanism, whereas the fundamental aspects is
the existence of an active core which involves a dimeric distannox-
ane [4]. In this context, transesterification catalysed by 2, which
bears such distannoxane centre, evolved progressively, and re-
sulted in a 100% yield within 6 h. The reaction catalysed by mono-
meric 3 slowed down, however, when active distannoxane core
formed, it was able to function as an efficient catalyst leading final-
ly to quantitatively yields too.
In conclusion, the present air and moisture stable diorganotin
complexes efficiently catalyze the transesterification reaction of
2-phenylethanol without addition of free ligand or any promoting
additive. Moreover, we have demonstrated that for the develop-
ment of efficient catalytic systems, a distannoxane core should
be involved into the catalyst molecule.
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Supplementary material
CCDC 671218 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[b] A. Galani, D. Kovala-Demertzi, N. Kourkoumelis, A. Koutsodimou, V.
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Acknowledgements
This research was funded by the program ‘‘Heraklitos” of the
Operational Program for Education and Initial Vocational Training
of the Hellenic Ministry of Education under the 3rd Community
Support Framework and the European Social Fund. We thank the
NMR center of the University of Ioannina. Dr. R. Vargas is kindly
acknowledged for recording the X-ray data at the X-ray crystallog-
raphy center of the University of Babes-Bolyai University, Cluj-
Napoca, Romania.
[d] R.L. Grob, E.F. Barry, Modern Practice of Gas Chromatography, fourth ed.,
Wiley Interscience, New York, 2004.
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University of Göttingen, 1997.;
[b] G.M. Sheldrick, Acta Crystallogr. A 46 (1990) 467.
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