Reaction of dibutyltin oxide with amides in presence of traces of water: Multinuclear NMR study and mechanism

Article abstract of DOI:10.1016/S0022-328X(98)01008-0

The product of the reaction of primary and secondary amides with dibutyltin oxide is shown to be a dimeric 1,3-diacyloxytetrabutyldistannoxane. The reaction was studied in bulk with model amides at 180°C, avoiding perfect anhydrous conditions, in view to be transposable to transamidification with reactive extrusion process. The formation of an intermediate compound of the type 1-acyloxy-3-alkylaminotetrabutyldistannoxane is pointed out. With an excess of amide, the presence of water leads to the dimeric 1,3-diacyloxytetrabutyldistannoxane. Without an excess of amide, the hydrolysis of this intermediate leads to a more complex tetrastannoxane structure associated in a more or less perfect ladder-like structure including partially hydrolyzed and condensed forms of the distannoxane. The dimeric 1-acyloxy-3-alkoxytetrabutyldistannoxanes resulting from the reaction of esters with dibutyltin oxide are shown to give a similar stannoxane structure after hydrolysis. All the products were characterized in solution by ¹H-, ¹³C- and ¹¹⁹Sn-NMR spectroscopy. On the basis of the spectroscopic analysis, a mechanism of the reaction is proposed and discussed.

Full text of DOI:10.1016/S0022-328X(98)01008-0

Journal of Organometallic Chemistry 575 (1999) 286–300
Reaction of dibutyltin oxide with amides in presence of traces of
water: multinuclear NMR study and mechanism
a
a,
b
b
J e´ r oˆ me Gimenez , Alain Michel *, Roger P e´ tiaud , Marie-France Llauro
a
Laboratoire d’Etudes des Mat e´ riaux Plastiques et des Biomat e´ riaux, CNRS, UMR 5627, Institut des Sciences et Techniques de l’Ing e´ nieur,
Uni6ersit e´ Claude Bernard Lyon I, 43 Boule6ard du 11 No6embre 1918, 69622 Villeurbanne, Cedex, France
b
Laboratoire des Mat e´ riaux Organiques a` Propri e´ t e´ s Sp e´ cifiques, CNRS, BP 24, 69390 Vernaison, France
Received 9 March 1998; received in revised form 23 September 1998
Abstract
The product of the reaction of primary and secondary amides with dibutyltin oxide is shown to be a dimeric 1,3-diacyloxyte-
trabutyldistannoxane. The reaction was studied in bulk with model amides at 180°C, avoiding perfect anhydrous conditions, in
view to be transposable to transamidification with reactive extrusion process. The formation of an intermediate compound of the
type 1-acyloxy-3-alkylaminotetrabutyldistannoxane is pointed out. With an excess of amide, the presence of water leads to the
dimeric 1,3-diacyloxytetrabutyldistannoxane. Without an excess of amide, the hydrolysis of this intermediate leads to a more
complex tetrastannoxane structure associated in a more or less perfect ladder-like structure including partially hydrolyzed and
condensed forms of the distannoxane. The dimeric 1-acyloxy-3-alkoxytetrabutyldistannoxanes resulting from the reaction of esters
with dibutyltin oxide are shown to give a similar stannoxane structure after hydrolysis. All the products were characterized in
1
13
119
solution by H-, C- and Sn-NMR spectroscopy. On the basis of the spectroscopic analysis, a mechanism of the reaction is
proposed and discussed. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Tin; Distannoxane; Amide and hydrolysis
1
. Introduction
polyamides using paratoluene sulfonic acid as catalyst
whereas this latter was known to be a good catalyst in
the ester–ester exchange reaction [9]. Inoshita et al.
reported that the heating of a mixture of poly(ethylene
terephthalate) and poly(amide-6,6) in the presence of
zinc acetate and antimony trioxide, at 230–280°C un-
der 0.01 Torr for 5 h results in the formation of a block
copolymer by ester–amide interchange reaction [10]. A
few other examples of catalyzed ester–amide inter-
change in a polyester/polyamide system are also re-
ported in the literature. Korshak et al. used PbO [11] or
PbO [12], whereas Frunze et al. applied isoBu Al as
Dibutyltin oxide and 1-alkoxy-3-acyloxytetrabutyl-
distannoxanes were shown to be at 200°C excellent
catalysts for transesterification reactions and excellent
crosslinking agents of ethylene-vinyl acetate copolymers
(
EVA) and ethylene-methyl acrylate copolymers (EMA)
[1,2]. The efficiency of these catalysts allows a direct
application to the crosslinking of the EVA–EMA dis-
persed in a polymer matrix by the reactive extrusion
process [3–5]. Furthermore a rheological characteriza-
tion of this crosslinking reaction was made [6,7].
Pillon and Utracki [8] have shown that block
polyester–polyamide copolymers can be obtained by
transamidification reactions of polyesters with
2
3
catalyst [13]
Some recent works in our laboratory have proved
that interchange reactions between amides and poly-
acrylic esters can be catalyzed by dibutyltin oxide and
1
-alkoxy-3-acyloxy-tetrabutyldistannoxanes at 180°C
*
Corresponding author.
[14]. In order to elucidate the exchange reaction mecha-
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 9 8 ) 0 1 0 0 8 - 0

J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
287
nism, this paper deals first with the reaction of
dibutyltin oxide with amides in the conditions of reac-
tive extrusion.
We have previously shown that dibultyltin oxide
reacts with esters leading to the dimeric form of 1-
alkoxy-3-acyloxytetrabutyldistannoxane (Eq. (1)).
[Et SnOCH ]
and
the
dimethoxydimethyltin
3
3
[Me
Sn(OCH ) )] are known to react easily with amides
2
3 2
[26–28]. The reaction requires primary or secondary
amides, cleaves the Sn–OR link and leads to a Sn–
NRCO bond. In the case of the dimethoxydibutyltin,
polyamides are claimed to be crosslinked. As for the
(
1)
This dimeric distannoxane has been fully characterized
by H-, C- and Sn-NMR [2,15]. The four tin atoms
are pentacoordinated in two different ways: endo or exo
bis-tributyltin oxide [(Bu Sn) O] which has a Sn–O–Sn
linking, it is indicated to cleave the Sn–O link and give
3
2
1
13
119
Bu Sn–NR%–CO–R and water [29] which seems to be
3
(
Scheme 1). Indeed two peaks of equal intensities are
contradictory. Indeed, it is worth pointing out that
Sn–N bonds are very sensitive to hydrolysis [30] and in
both cases, the Sn–NR%CO bond should be retained in
spite of the character of Sn–N bond to be easily
hydrolysed. At last, dibutyltin oxide which comprises a
1
19
observed in
Sn-NMR in the resonance region of
pentacoordinated tin atoms. By 2D/Sn–Sn COSY
NMR spectroscopy, each tin site (endo or exo) is shown
to be coupled to two tin atoms (site 1 is coupled with
site 2 and site 2%) with two different coupling constants
[Sn–O] backbone has been shown to react with imides
n
1
3
[
15,16]. In C-NMR, two butyl groups are evidenced by
(–CO–NH–CO–) via a CO–N bond cleavage followed
with an insertion of one O–Sn in the amide structure
[31]. This reaction should lead to the following structure
the presence of 2 peaks for each CH of the butyl groups
2
connected with the two different types of tin atoms.
More generally, difunctional Bu Sn XYO (tetraorgan-
–CO–O–Sn(Bu) –NH–CO–. These affirmations will
4
2
2
odistannoxanes) and monofunctional Bu Sn X O are
be discussed in the frame of the present work. Since
then, to our knowledge, nothing concerning the action
of organotin oxides on amides has been published. This
work proposes a reaction mechanism as a conclusion of
4
2
2
known to have a dimeric structure both in solution and
in the solid state, with two types of non-equivalent
1
19
pentacoordinated tin atoms [17] whereas
Sn M o¨ ss-
1
the results obtained by means of analysis by H-,
bauer spectroscopy showed only a single quadrupole
split resonance. Many reports published by different
authors using various techniques describe the structure
of distannoxanes in solution. In particular, Otera et al.
related the dimeric structure of distannoxanes, proposed
13
119
C- and Sn-NMR spectroscopy.
2
. Experimental details
119
by Okawara, to the general aspect of
Sn solution
2.1. Reagents
NMR spectra [18–20]. In certain conditions, monomer
exchanges between dimer entities or ligand exchanges
on tin atoms are observed [2,21,22]. Furthermore, X-ray
techniques [23] and sometimes both X-ray and NMR
techniques [24,25] were used in order to study the
distannoxanes inclined to yield monocrystals.
Dibutyltin oxide, propionamide, acetanilide, N,N-di-
Some tin compounds such as the methoxytriethyltin
Scheme 1.
Scheme 2.

288
J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
Fig. 1. NMR spectra (made at 25°C) of (1) the diacetoxytetrabutyldistannoxane and (2) the reaction product of dibutyltin oxide with
propionamide.
ethyldodecanamide and isobutylpropanoate were com-
mercial products (Aldrich). These amides were selected
for their high boiling points (213, 305 and 167°C, 2
mm).
dibutyltin diacetate. The latter was used here. A white
crystalline distannoxane was obtained. C H O Sn re-
quires C,40.04; H, 7.01; Sn, 39.60; found: C, 40.05, H,
7.09; Sn, 40.42%. All characteristic NMR chemical
shifts have yet been given [2].
20
42
5
2
2.2. Preparation of diacetoxytetrabutyldistannoxane
(model compound)
2.3. Reaction of dibutyltin oxide with isobutylpropanoate
(typical procedure)
Two methods are available [32], reaction of acetic
acid with dibutyltin oxide or partial hydrolysis of
Equimolar amounts of dibutyltin oxide and isobutyl-

J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
289
Scheme 3.
propanoate were mixed in a reactor equipped with
magnetic stirrer and a reflux condenser. The mixture
was heated at 200°C. After cooling, an oily colorless
and translucent liquid which is not crystallizable was
obtained. The NMR characterization ( H, C, Sn) of
the spectral features of the 1-propyloxy-3-isobutoxy-
tetrabutyldistannoxane formed was made.
chloroethylene to eliminate the excess of amide. A large
excess of water was then added leading to the forma-
tion of a white precipitate which was then treated as it
was previously shown below Section 2.5.
1
13
119
2.7. NMR spectroscopy
High resolution liquid NMR spectroscopy was car-
2
.4. Reaction of dibutyltin oxide with the model amide
ried out with a Bruker AC250 instrument working at
1
13
2
50 MHz for H and 62.9 MHz for C, and with a
The amide and 5% in mol of dibutyltin oxide were
Bruker AC200 instrument working at 74.6 MHz for
mixed in a reactor equipped with a magnetic stirrer and
a reflux condenser. The mixture was heated at 160 or
119
Sn. Tetrachloroethylene/deuterated benzene (TCE/
C D ) mixtures (2:1 by volume) were used as solvent.
6
6
180°C. After a few minutes the mixture of dibutyltin
Chemical shift values are in ppm with reference to
oxide in the molten amide became clear. After cooling,
because of a large excess of solid amide, the mixture
crystallized. In total 10% in mol of dibutyltin oxide can
be used, if fractional additions are carried out, but even
thus, no more than 10% in mol of dibutyltin oxide in
comparison with the amide amount reacts. Because of
the large excess of amide, an extraction with tetra-
chloroethylene is required to eliminate the excess of
amide which is not soluble at ambient temperature.
1
13
internal TMS for H and
C, and external te-
119
tramethyltin for Sn.
3
. Results and discussion
In view to conclude concerning the role of the –NH
6
–
in the reaction of amides with dibutyltin oxide, both
tertiary (N,N-diethyldodecanamide) and primary or
secondary amides (propionamide and acetanilide) have
been used.
2.5. Hydrolysis of the 1-propanoyloxy-3-isobutoxytetra-
butyldistannoxane
To the oily colorless and translucent liquid not crys-
tallizable obtained in the preparation of the distannox-
ane, a large excess of water was added at ambient
temperature. A white precipitate appeared. After filtra-
tion, tetrachloroethylene was added to the precipitate
which became soluble at 80°C. The NMR characteriza-
3.1. Preliminary obser6ations
When the reactions were performed with propi-
onamide and acetanilide, the opacity of the suspension
of dibutyltin oxide in the molten amide disappeared
completely after 10 min at 180°C. With N,N-diethyl-
dodecanamide, the dibutyl tin oxide remained in sus-
pension in the amide. It is well known that dibutyltin
oxide [33] is amorphous, insoluble in most organic
solvents even at high temperature and has a polymeric
structure with about 20 tin atoms in a chain (Scheme
1
13
119
tion ( H, C,
made.
Sn) of the compound formed was
2.6. Hydrolysis of the intermediate compound of the
reaction between dibutyltin oxide and propionamide
2
). This first observation, without being a real proof of
The product of the reaction between dibutyltin oxide
and propionamide, stopped before ammoniac was
evolved, was purified with an extraction with tetra-
reaction, shows in the two former cases that the
crosslinks in the dibutyltin oxide structure are disrupted
and a reaction may have happened (that will be confi-

290
J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
Fig. 2. 1H-NMR spectrum (made at 25°C) of the reaction product of dibutyltin oxide with propionamide.
rmed by NMR spectroscopy). In addition, it is worth
noticing that a great ammoniac release is observed
when propionamide is used as reagent.
sites and a single coupling between them could suggest
a monofunctional dimeric tetraorganodistannoxane of
formula Bu Sn X O. More precisely, because the two
4
2
2
In the light of this observation it seems tertiary
amides do not react with dibutyltin oxide and therefore
the reaction requires the presence of a hydrogen atom
only present in primary and secondary amides, as it is
generally claimed with other tin compounds.
initial reagents are propionamide and dibutyltin oxide
and ammoniac is evolved, this spectrum suggests it
could be the dimeric dipropanoyltetrabutyldistannox-
119
ane. Although the
Sn-NMR spectrum is not suffi-
cient to assert a result, it is worth noticing that in the
119
same way, the Sn-NMR spectrum of a diacetoxytetra-
butyldistannoxane resulting from the partial hydrolysis
of the dibutyltin diacetate, shows two resonances at l
−219.4 and −229.8 (Fig. 11) with a single doublet of
satellite peaks (J=12293 Hz).
3
3
.2. Characterization of the final reaction product
1
19
.2.1. Sn-NMR analysis
1
19
The
Sn-NMR spectrum of the product resulting
The unexpected single coupling between tin sites
observed by different authors on a monofunctional
tetraorganodistannoxane [15,20,34], compared to the
from the reaction of propionamide with dibutyltin ox-
ide at 170°C during 4 h presents two single resonances
at l −221.2 and −229.2 (Fig. 12). These chemical
shift values are typical of pentacoordinated tin atoms.
difunctional structures [Bu Sn XYO] where each tin site
2
2
119
119
A single doublet of satellite peaks
2493 Hz) is observed at the basis of each tin reso-
nance. Such a spectrum, with two equally populated tin
Sn– Sn (J=
shows two doublets with two different coupling con-
stant values [J1–2 and J1–2%], has been recently proved to
be the consequence of a rapid intradimeric rearrange-
1

J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
291
Fig. 3. 13C-NMR spectra (made at 25°C) of the product of the reaction of ditbutyltin oxide with propionamide.
ment (Scheme 3, [16]). The two expected satellite dou-
blets merge into a single one since this rearrangement
exchanges the covalent bond [Sn –O–Sn ] in the coor-
The quantitative analysis gives a relative proportion
of 1.9/12.8/2.9/6.2 for the areas S /S /S /S An estimate
1
2
3
4.
1
2
at 2/12/3/6 corresponds to the presence of one
propanoyl group for two butyl groups that is to say for
one tin atom if the dibutyltin structure is maintained.
Moreover the two different butyl groups indicated by
the two methylic protons (l=0.940 and 0.920) were
previously observed in all monofunctional or difunc-
dination bond [Sn –O“Sn ] and reversely the coordi-
1
2
nation bond [Sn –O“Sn ] in the covalent bond
1
2’
[
Sn –O“Sn ].
1 2%
1
3
.2.2. H-NMR analysis
1
tional
tetrabutyldistannoxane
(Bu Sn X O
and
4
2
2
H-NMR gives complementary information, particu-
Bu Sn XYO) investigated in our laboratory. This fea-
larly concerning the stoichiometry of the compound
obtained. The spectrum of the product resulting from
the reaction of dibutyltin oxide with propionamide
consists of four main resonance regions (Fig. 2). The
quartet S centered at l 2.170 and the triplet S at 1.075
4
2
ture is related to the dimeric structure of all these
Table 1
1
3C Chemical shifts (l in ppm) related to the propanoyl group in the
1
3
propionamide (P) and in its reaction product (P%) with dibutyltin
oxide
correspond, respectively to the CH and CH protons
2
3
of the propanoyl group. S and S should correspond to
2
4
Sample
CH3
CH2
CO
the protons of the butyl groups from a dibutyltin
compound. Actually, the pseudo quartet S4 is com-
posed of two overlapping triplets, respectively centered
at l 0.940 and 0.920, thus indicating an equal ratio of
P
P%
9.70
10.40
29.05
30.00
176.00
180.45
two types of butyl tin groups. The S region consists of
two large multiplet resonances at about l 1.730 and
2
Table 2
1
3
C Chemical shifts (l in ppm) of the two distinct butyl groups and
1
.400 assigned, respectively to the CH protons in h
2
1
3
coupling constants J(Sn–C*) and J(Sn–C–C–C*) (in Hz) in the
dibutyltin compound obtained by reaction of dibutyltin oxide with
propionamide
position and in i plus k position to the tin atom.
Carbone C1 (1J(Sn–C*))a C2
C3 (3J(Sn–C–C–C*)) C4
Shifts
28.00 (727–695) 27.50 27.30 (135)
9.80 (767–734) 28.00 27.90
14.05
2
a 1J(119Sn–C*)– J(117Sn–C*), values in parentheses.
1
Scheme 4.

292
J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
Fig. 4. 119Sn-NMR spectra (made at 25°C) of the product resulting from the reaction of propionamide with dibutyltin oxide stopped before
ammoniac being evolved.
compounds and it is associated to other typical features
observable in C-NMR [2,15,20].
onamide (Table 1) are deshielded, particularly the car-
1
3
bon of the carbonyl group (Dl=6.70). This deshielding
is consistent with the change RCONH “RCOOSn.
2
Such a deshielding has been previously observed with
the change RCOOR%“RCOOSn [15].
1
3
3
.2.3. C-NMR analysis
1
3
As shown on Fig. 3, the C-NMR spectrum of the
reaction product of propionamide with dibutyltin oxide
shows the different resonances easily assigned to C –C4
3.2.4. Interpretation and discussion
1
carbons of the butyltin groups (Scheme 4, Table 2).
Two different butyl groups are evidenced by a couple of
resonances for each methylenic carbon C –C –C
The elemental analysis provides C, 42.18; H, 7.39; O,
13.11; Sn, 36.38 and N, 0.94%. The residual N content
corresponds to a 4.9% rate of amide remaining in the
product of the reaction of propionamide with dibutyltin
oxide after the extraction. The percentage calculated for
the main product (95.1%) indicates C, 41.80; O, 12.82;
H, 7.22 and Sn, 37.9%. These values are in agreement
with the dipropanoyloxytetrabutyldistannoxane formu-
1
2
3
(
Table 2). Moreover the coupling Sn–C* and Sn–C–
C–C* can be observed and measured. The values of
1
3
J(Sn–C*) and J(Sn–C–C–C*) given in Table 2 are
typical of a pentacoordinated dibutyltin. All carbons of
the propanoyl group compared to those of pure propi-

J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
293
Scheme 5.
Scheme 6.
lae which requires C, 42.00; O, 12.70; H, 7.40 and Sn,
release of ammoniac, two weak singlets S1 and S
2
1
19
1
13
119
37.9%. The results of the
Sn-, H- and C-NMR
(l= −188.9 and −203.2) are observed in the
Sn-
spectroscopy and the elemental analysis allows to con-
clude that the reaction of dibutyltin oxide with a large
excess of proprionamide at 160°C leads to the forma-
tion of the dipropanoyloxytetrabutyldistannoxane with
ammoniac release. We notice that such a result implies
the presence of water and the reaction should be
globally given by Eq. (2).
NMR spectrum (Fig. 4). No peaks are detected in the
tetracoordinated tin resonance region (+200, −60).
At l −221.2 and −229.2 the two resonances with
their coupling correspond to the dipropanoyloxy-tetra-
butyldistannoxane. Therefore the formation of the
dipropanoyloxytetrabutyldistannoxane by hydrolysis
and condensation of a RCOO–SnBu –NH intermedi-
2
2
ate is precluded. On the contrary, a dimeric acyl-
oxyaminotetrabutyldistannoxane is very likely on the
basis of the Sn-NMR spectrum (Eq. (3)).
2
CH CH CO–NH +2 Bu SnO+H O
3 2 2 2 2
119
“
(CH CH CO–O–SnBu ) O+2 NH
3
2
2 2
3
(
2)
CH CH CO−NH +2 Bu SnO
3
2
2
2
In addition only primary and secondary amides react
with dibutyltin oxide, thus the presence of a –NH–
group is a prerequisite.
“
CH CH CO−O−SnBu −O−SnBu −NH
3 2 2 2 2
(
I)
(3)
Its low amount in the mixture and its disappearance
after a long time reveal that it would just be an
intermediate compound which should react with the
excess of amide to give the dipropanoyloxytetrabutyl-
distannoxane and ammoniac (Eqs. (4) and (5)).
3
.3. Tentati6e identification of the intermediate species
At this stage, without making any hypothesis on the
mechanistic path involving –NH– moiety, it is clear
from the final product that the CO–NH link is cleaved.
Whether one or two O–Sn moieties are inserted is an
outstanding question. With one [O–Sn] insertion
RCOO–SnBu –NH is expected whereas with [O–Sn]
C H COO−SnBu −O−SnBu −NH +H O
2
5
2
2
2
2
(
I)
“
C H COO−SnBu OSnBu −OH+NH
(4)
(5)
2
5
2
2
3
2
2
2
2
insertion RCOO–SnBu –O–SnBu –NH should be
C
2
H
5
COO–SnBu
2
–O–SnBu
2
–OH+CH
CH
3
CO
2
2
2
formed. The first should have a tetracoordinated
dibutyltin site in the region (+200, −60), whereas in
the last case two equally populated tin sites in the
pentacoordinated tin region, corresponding to a dimeric
distannoxane structure, are expected.
–
NH “(C H COO–SnBu ) O+NH
2 2 5 2 2 3
All attempts to separate this intermediate from the
mixture failed. Only a hydrolyzed form was obtained in
spite of the precautions we took. The hydrolysis done
with ammoniac release, occurred with a simple contact
with air (indeed Sn–N bonds are well known to be very
sensitive to hydrolysis [30]).
3.3.1. Distannoxane structure of the intermediate (I)
When the reaction is stopped before the complete

294
J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
Scheme 7.
3.3.2. Hydrolysis of the intermediate (I)
More than four tin sites, all of them probably
If a difunctional distannoxane, namely 1-propanoyl-
pentacoordinated.
oxy-3-aminotetrabutyldistannoxane [RCOO–SnBu2–
O–SnBu –NH ] is the intermediate (I) formed in the
reaction of dibutyltin oxide and propionamide, owing
The comparison between (I%) and (II%) as previously
1
13
119
defined is achieved by H-, C- and Sn-NMR spec-
troscopy. The obtained spectra show that I% and II% are
nearly identical (Figs. 5–7 and Tables 3–5). These three
analyses give complementary information concerning
the structure of these compounds.
2
2
to the high sensitivity of the Sn–NH bond to hydroly-
2
sis, then it is of interest to compare this hydrolyzed
intermediate (compound I%) to the hydrolysis product of
an acyloxyalcoxydistannoxane, since we have previ-
ously observed that the Sn–OR free ligand is highly
sensitive to hydrolysis. To our knowledge, the hydroly-
sis of acyloxyalcoxydistannoxanes has not been
previously investigated. The 1-propanoyloxy-3-isobutyl-
oxytetrabutyldistannoxane (II) has been hydrolyzed
1
The H spectra indicate nearly four butyl groups for
one propanoyl (3.5 and 4.5 for I% and II%, respectively).
It has been proved herein that, in the presence of an
excess of amide and water, the intermediate I gives
[
CH CH COOSnBu ] O with two butyl groups for one
3 2 2 2
propanoyl. On the contrary, the hydrolysis of the inter-
mediate I after cautious extraction of the excess of
amide, leads to I% which contains four butyl groups for
one propanoyl group. Moreover the two triplets corre-
sponding to an equal molar ratio of two types of butyl
groups in a distannoxane structure are no longer ob-
served (Fig. 5). So the dipropanoyltetrabutyldistannox-
ane of formula [CH CH COOSnBu ]O is excluded in
(
compound II%) and compared to the compound I%
1
19
1
13
through their
Sn-, H- and C-NMR spectra. In
both cases three types of products can be envis-
aged with the same global stoichiometry
CH CH COOSn(Bu) OSn(Bu) ] O (Eq. (6)): (1) a
[
3
2
2
2 2
monomeric 1-7-dipropanoyloxyoctabutyltetrastannox-
ane (Scheme 5) (2) a perfect ladder like dimeric struc-
ture with two tetrastannoxanes (Scheme 6) (3) an
associated form with more than two tetrastannoxanes
and a less perfectly ladder-like structure than the previ-
ous one (Scheme 7), somewhat similar to the pentaco-
ordinated network which is usually proposed [15] for
the dibutyltin oxide structure with a central square part
3
2
2
that case. 1
3
As for C spectra, the chemical shifts of the CO,
respectively l 180.05 for (I%) and 180.00 for (II’) com-
pared to the CO in the dipropanoyloxytetrabutyl-
distannoxane (180.45), show the structure CH –CH –
3
2
CO–O–Sn still remains. A set of unresolved peaks is
¸
¹¹¹¹¹¹¹¹¹º
observed for the CH butyl carbons (Fig. 6) which
2
[
Bu Sn–O–SnBu2–O –].
2
2
C H COO–SnBu OSnBu –(NH or OR%)+H O“(C H COO–SnBu OSnBu ) O+2 (NH or R%OH)
2
5
2
2
2
2
2
5
2
2 2
3
(6)
(
I)
(II)
(I%) and (II%)
1
19
1
Sn-NMR is a powerful tool in a view to conclude
supports the H-NMR results indicating a much more
complicated situation than in ladder-like 1-3-distannox-
ane structure where two different types of butyl groups
are always found.
between these three possibilities, since they will give,
respectively (1) two tetracoordinated tin sites equally
populated. (2) Four pentacoordinated tin sites equally
populated (a, b, c and d), two of them—the central
ones—(b and c) being very close to one other. (3)
119
The nearly identical Sn spectra (Fig. 7-1, 2) consist
of more than 97.5% pentacoordinated sites in the

J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
295
1
Fig. 5. H-NMR spectra (made at 80°C) of (1) the hydrolyzed intermediate (I%) of the reaction of dibutyltin oxide with propionamide and (2) the
hydrolyzed 1-propanoyl-3-isobutyloxytetrabutyldistannoxane (II%).
(
−150, −240) resonance region distributed into six
dimethoxytetrabutyldistannoxane. In that case the ex-
pected sites are Bu Sn[O] , Bu Sn[O] OH and
broad peaks. Then, both a monomeric 1,7-dipropanoyl-
oxytetrastannoxane (Scheme 5) and a perfect ladder-like
dimeric structure with two tetrastannoxanes (Scheme 6)
are precluded. The integral values are nearly 2/1/2.5/0.5
for peaks (1+2), 3, (4+5) and 6, respectively (Fig. 7-1),
the region (4+5) being more intense for the hydrolyzed
acyloxy alcoxydistannoxane (Fig. 7-2). The lower field
region (−157, −177) (peaks 1 and 2) corresponds to
the region already observed when nascent dibutyltin
oxide is formed by in situ hydrolysis of dimeric 1-3-
2
3
2
2
Bu Sn[O] OR corresponding to the unachieved hydroly-
2
2
sis and/or condensation. Endo tin sites of the type
Bu Sn[O] OR have already been observed at −174.1 in
2
2
1,3-dimethoxytetrabutyldistannoxane (Table 6). At
higher field (−177, −194), peak 3 is in a region where
exo tin sites in both dialcoxy and acyloxyalcoxydistan-
noxanes have been previously observed (Table 6) that is
to say Bu SnO(OR) (OCOR or OR). Moreover in the
2
1-propanoyloxy-3-aminodistannoxane (I) and in the 1-

296
J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
Fig. 6. 13C-NMR spectra (made at 80°C) of (1) the hydrolyzed intermediate (I%) of the reaction of dibutyltin oxide with propionamide and (2) the
hydrolyzed 1-propanoyl-3-isobutyloxytetrabutyldistannoxane (II%).
propanoyloxy-3-isobutoxydistannoxane (II), the exo tin
sites are assigned, respectively to l −188.9 for
Bu SnO(OCOR)(NH ) and −183.4 for Bu SnO(OCOR)
tetrastannoxane is not completely ruled out since all the
expected tin sites corresponding to this structure a/(b+
c)/d may be present, respectively under peaks 6/(1+2)/
(4+5). But the ratio 0.5/2/2.5 is far from the value 1/2/1
expected and SnO(OCOR)OH are also present (peak 3).
An irregular structure represented in Scheme 8 is highly
probable.
2
2
2
(
i-butoxy). In both cases hydrolysis will give (in I% and
II%) Bu SnO(OCOR)OH tin sites expected in the same
2
resonance region whereas after condensation
Bu SnO (OCOR) are expected at higher field. Peaks
2
2
4
+5 (−194, −225) are assigned to internal sites of
As for the resonance observed at 87.5 which represents
2.5% of tin sites, we have previously shown [15] that
tributyltin acetate is a by-product sometimes observed in
the formation of 1,3-acetoxyoctyloxydistannoxane by
reaction of octylacetate with dibutyltin oxide. This by-
product gives a single resonance at 84.4 in the region of
tetracoordinated tin. Then the resonance observed in the
present case could be attributed to the tributyltin propi-
onate. The presence of such a product would be explai-
ned with a second hydrolysis mechanism of the acyloxy
(alkoxy or amino) distannoxane by the way of Eq. (7).
type Bu Sn[O] (OCOR) both in diacyloxy and in acyl-
oxyalkoxydistannoxane as shown in Table 6. The same
chemical shift range is expected next to this internal tin
2
2
site when the alkoxy group of II or the NH group of
2
I becomes an OH group by hydrolysis and unachieved
condensation. Finally, peak 6 (−225, −240) is assigned
to Bu SnO(OCOR) sites.
2
2
This tentative assignment is in good agreement with
the global stoichiometry (one OCOCH CH group/ two
2
3
Sn atoms) since the ratio 1.92/2.08 corresponding to the
ratio (low field (1+2+3) regions/high field (4+5+6)
regions) shows 1.92 tin sites without any covalent bond
Sn–OCOR for 2.08 tin site with one covalent bond
Sn–OCOR. Indeed the global stoichiometry (one
OCOCH CH / two Sn) in the tetrastannoxane structure
C H COO–SnBu OSnBu –(NH or OR%)+H O
2
5
2
2
2
2
“Bu SnOCOC H +BuSnOOH
3
2
5
+
(NH or R%OH)
(7)
3
2
3
requires two tin sites without any Sn–OCOR covalent
bond (b+c) and two tin sites with one Sn–OCOR
covalent bond (a+d) (Scheme 6).
This mechanism supposes the presence of a single tin
resonance characterizing the butyltin hydroxide oxide
observed at l −230.5 for the Aldrich product, probably
included in peak 6.
As a conclusion the presence of the ladder-like dimeric

J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
297
Fig. 7. 119Sn-NMR spectra (made at 80°C) of (1) the hydrolyzed intermediate (I%) of the reaction of dibutyltin oxide with propionamide and (2)
the hydrolyzed 1-propanoyl-3-isobutyloxytetrabutyldistannoxane (II%).
3
.3.3. Nature of the intermediate species (I)
In view of the distannoxane structure observed by
Sn-NMR (Fig. 4) and the tetrastannoxane structure
drolysis leading to the tetrastannoxane structure sup-
port the 1-propanoyloxy-3-aminotetrabutyldistannox-
ane structure.
1
19
obtained after hydrolysis, the intermediate species (I) in
the reaction of propionamide with dibutyltin oxide can
reasonably be assigned to the 1-propanoyloxy-3-amino-
tetrabutyldistannoxane. The real nature of the amino
ligand has not been certainly identified. But the ammo-
niac release observed during the formation of the
dipropanoyloxytetrabutyldistannoxane and the easy hy-
3
.4. Reaction of acetanilide with dibutyltin oxide
An identical study was made with acetanilide. The
presence of two resonance peaks of equal intensities
was observed in Sn-NMR at l −187.8 and −200.6
before the appearance of the resonance of the diace-
toxytetrabutyldistannoxane. In the case of propi-
119

298
J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
Table 3
1
3C Chemical shifts (l in ppm) of (I%) and (II%) at 80°C
Sample
Propanoyl
CH3
Butyl
CH3
CH2
CO
CH2
Product (I%)
Product (II%)
10.25
10.20
29.70
29.75
180.05
180
13.70
13.60
24.45/27.10/28.00/28.60
24.50/27.10/27.90/28.60
(9)
The second step is an intramolecular rearrangement
obtained through a nucleophilic attack of the carbonyl
group by the oxygen of the hydroxyl end group SnOH
(Eq. (10)).
onamide two similar peaks were found at l −188.9
and −203.2 ppm. So, like propionamide, acetanilide
gives a 1-acyloxy-3-alkylaminotetrabutyldistannoxane
in presence of dibutyltin oxide.
3.5. Proposition of mechanisms for the reaction of amides
with dibutyltin oxide
Considering the highly probable formation of 1-acyl-
oxy-3-alkylaminotetrabutyldistannoxane as an interme-
diate in the reaction of amides with dibutyltin oxide,
one could reasonably propose a nitrogen–acyl bond
cleavage mechanism (Eq. (8)) similar to the O–CO
bond cleavage in the reaction with esters (Eq. (1)).
(
10)
When formed, the 1-acyloxy-3-alkylaminotetra-
butyldistannoxane reacts with the amide excess to give
the diacyloxytetrabutyldistannoxane (Eqs. (11) and
(
12)).
(
8)
But such a mechanism should not take into account
the fact that tertiary amides do not react. So we pro-
pose a mechanism in two steps involving the free hy-
drogen only present in primary and secondary amides.
The first step consists of the hydrogen–nitrogen bond
cleavage instead of the nitrogen–acyl one (Eq. (9)).
RCO–O–SnBu
SnBu –O–SnBu –OH+R%NH
2
2 2 2
–O–SnBu –NHR%+H O“RCO–O
–
(11)
(12)
2
2
RCO–O–SnBu –O–SnBu –OH+RCO–NHR%
2
2
“
{RCO–O–SnBu } O+R%NH
2 2 2
This reaction requires the presence of water possibly
supplied by the great hygroscopical character of
amides. When the amide excess is eliminated the hy-
drolysis of the acyloxyalkylaminodistannoxane with ad-
ditional water leads first of all to tetrastannoxanes (Eq.
Table 4
1
H Chemical shifts (l in ppm) of (I%) and (II%) at 80°C
Sample
Propanoyl
CH3 CH2
Butyl
CH3
(
13)) associated in a more or less perfect ladder-like
h CH2 i and k CH2
structure including partial hydrolysed forms of the dis-
tannoxane (Scheme 8). A secondary hydrolysis mecha-
nism (2.5% of tetracoordinared tin sites) involving a
butyl group transfer can be proposed releasing tri-
Product (I%)
Product (II%)
1.090 2.170 0.940 1.740
1.050 2.160 0.950 1.750
1.420
1.420

J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
299
Table 5
1
19Sn Chemical shifts (l in ppm) of (I%) and (II%) at 80°C
Sample
Peak 1
Peak 2
Peak 3
Peak 4
Peak 5
Peak 6
Product (I%)
Product (II%)
−163.6
−164.9
−170.5
−170.9
−183.9
−183.4
−208.5
−209.5
−214.5
−216.0
−230.0
−230.3
Table 6
1
19Sn Chemical shifts in some distannoxane compounds compared with Fig. 7 resonances
Tin site and integral regions
Tin site type
Bu SnO (OR)
Chemical shift value
Regiona
Reference
[2]
Internal site in dimeric
,3 Dimethoxy-TDSb
c
−174.1
1+2
1
2
2
External site in dimeric
c
1
1
1
1
1
,3-Dimethoxy-TDS
Bu SnO(OR)(OR)
−180.1
−181.4
−182.5
−183.4
−188.9
3
3
3
3
3
[2]
[2]
2
c
c
c
,3-Nonanoyloxy,methoxy-TDS
,3-Acetoxy, octyloxy-TDS
,3-Propanoyloxy, isobutoxy-TDS
,3-Propanoyloxy, amino-TDS
Bu SnO(OCOR)(OR)
Bu SnO(OCOR)(OR)
Bu SnO(OCOR)(OR)
Bu SnO(OCOR)(NH )
2
[2,15]
This work
This work
2
2
c
2
2
Internal site in dimeric
c
c
c
c
c
c
1
1
1
1
1
1
,3-Propanoyloxy, amino-TDS
,3-Propanoyloxy,isobutyl-TDS
,3-Acetoxy, octyloxy-TDS
,3-Nonanoyloxy, methoxy-TDS
,3-Diacetoxy-TDS
Bu SnO (OCOR)
−203.2
−209.5
−214.5
−218.2
−219.4
−221.2
4
5
5
5
5
5
This work
This work
[2,15]
[2]
[15]
2
2
Bu SnO (OCOR)
2
2
Bu SnO (OCOR)
2
2
Bu SnO (OCOR)
2
2
Bu SnO (OCOR)
2
2
,3-Propanoyloxy-TDS
Bu SnO (OCOR)
This work
2
2
External site in dimeric
c
c
1,3-Propanoyloxy-TDS
,3-Diacetoxy-TDS
Bu SnO (OCOR)(OCOR)
−229.2
−229.8
6
6
This work
[15]
2
2
1
Bu SnO (OCOR)(OCOR)
2
2
a
Corresponding region observed in Fig. 7.
TDS, tetrabutyldistannoxane.
Underlined group, group linked to the tin atom by covalent bond.
b
c
butyltin acyloxy and butyltin hydroxide oxide (Eq.
14)). Identical mechanisms are proposed for hydrolysis
of 1-acyloxy-3-alkoxytetrabutyldistannoxane (Eqs. (13)
and (14)).
contribution of dibutyltin oxide in the catalyst of ex-
change reaction between polyamides and polyesters in
extrusion reactive process.
(
In comparison with the reactivity with esters, the
reactivity of dibutyltin oxide with primary and sec-
ondary amides is found to be very low. In excess of
amide, a perfect ladder-like diacyloxytetrabutyldistan-
noxane is obtained if only a trace amount of water is
present in the mixture whereas in presence of water and
without excess of amide a less perfectly organized te-
trastannoxane structure is obtained. In the presence of
both amides and esters, dibutyl tin oxide reacts prefer-
entially with esters giving the 1-acyloxy-3-alcoxytetra-
butyldistannoxane. As shown by some recent works in
our laboratory [14] on model amide–ester and amide–
polyacrylic ester, this distannoxane is the predominant
catalytic entity of the exchange reaction between esters
and amides.
2
RCOOSnBu OSnBu (OR% or NHR%)+H O
2 2 2
“
{RCOOSnBu OSnBu } O+2 (R%OH or R%NH }
2 2 2 2
(
13)
RCOO–SnBu –O–SnBu –(NHR% or OR%)+H O
2
2
2
“
Bu Sn–OCOR+BuSnOOH
3
+
(R%NH or R%OH)
(14)
2
4. Conclusion
This paper deals with the reaction of dibutyltin oxide
with amides and consequently it sheds light on the
As for the very few examples of reaction of amides or
imides with organotin compounds presented in the

300
J. Gimenez et al. / Journal of Organometallic Chemistry 575 (1999) 286–300
Scheme 8.
Int. Polym. Process. XI 2 (1996) 139.
4] A. De Loor, P. Cassagnau, A. Michel, B. Vergnes, J. Appl.
Polym. Sci. 53 (1994) 1675.
5] A. De Loor, P. Cassagnau, A. Michel, B. Vergnes, J. Appl.
Polym. Sci. 63 (1997) 1385.
[6] I. Espinasse, P. Cassagnau, M. Bert, A. Michel, J. Appl. Polym.
Sci. 54 (1994) 2083.
literature [26–29] many years ago, we can make the
following comments in light of our results. In some
cases the Sn–O link is claimed to be cleaved and the
CONH link retained leading to the formation of Sn–
NHCO in presence of water (or ROH) which is a quite
questionable assertion owing to the highly hydrolyzable
character of Sn–N link. In other cases (dibutyltin oxide
with imides) the cleavage of CO–NHR% is claimed with
insertion of one [Sn–O] and the formation of COO–
[
[
[
7] P. Cassagnau, M. Bert, V. Verney, A. Michel, Polymer 34 (1)
1993) 124.
(
[
[
8] L.Z Pillon, L.A. Utracki, Polym. Eng. Sci. 24 (17) (1984) 1300.
9] M. Fieser, L. Fieser, Reagents for Organic Synthesis, vol. 1,
Wiley, New York, 1966.
SnBu –NHR%. From our results the cleavage of CO–
2
NHR% proceeds only in a second step, the first being the
insertion of two [Sn–O] giving a first distannoxane
HOSn(Bu) OSn(Bu) N(R%)COR. This latter quickly re-
[10] K. Inoshita, M. Terakowa, T. Yasuda, Japan patent, 7228.916
1972), CA, 76:114155d (1972).
(
[
11] V.V. Korshak, S.V. Vinogradova, M.M. Teplyakov, F.D. Fe-
dorova, G.Sh. Papava, Vysokomol. Soedin. 8 (1966) 2155.
2
2
arranges to give another one R%N(H)Sn(Bu)2-
[12] V.V. Korshak, S.V. Vinogradova, M.M. Teplyakov, A.D. Mak-
simov, Izv. Vyssh. Uchebn. Zaved. Khim. i Khim. Technol. 10
(1967) 688.
OSn(Bu) OCOR which reacts again in presence of
2
water with the excess of amide leading to a quite stable
diacyloxydistannoxane. The same mechanism but sup-
posing only one [Sn–O] insertion should give
[
13] T.M. Frunze, V.V. Kurashev, L.B. Danilevskayo, B.A. Rozen-
berg, V.V. Korshak, Vysokomol. Soedin. Ser. A 16 (1974) 1250.
14] E. Colomb, M. Gr e´ goire, J. Gimenez, R. P e´ tiaud, M.F. Llauro,
A. Michel, 12th European Symposium on Polymer Spec-
troscopy, Lyon, July 8–10, 1996.
[
RCOOSn(Bu) NHR% which—in presence of water—
2
should give the diacyloxytetrabutyldistannoxane by hy-
drolysis and condensation. But it is completely ruled
out by our NMR characterization of the distannoxane
intermediate.
[15] J. Bonetti, C. Gondard, R. P e´ tiaud, M-F. Llauro, A. Michel, J.
Organomet. Chem. 481 (1994) 7.
[
16] O. Primel, M.F. Llauro, R. P e´ tiaud, A. Michel, J. Organomet.
Chem. 558 (1998) 19.
[
[
[
17] R. Okawara, M. Wada, J. Organomet. Chem. 1 (1963) 81.
18] R. Okawara, M. Wada, J. Organomet. Chem. 8 (1967) 261.
19] J. Otera, T. Yano, K. Nakashima, R. Okawara, Chem. Lett.
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[
[
[
1] C. Gondard, A. Michel, Sotra Industries and CNRS, US patent,
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Anal. Charact. 1 (1995) 137.
[20] T. Yano, K. Nakashima, J. Otera, R. Okawara, Organometallics
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[21] D.C. Gross, Inorg. Chem. 28 (1989) 2355.
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3] A. De Loor, P. Cassagnau, A. Michel, L. Delamare, B. Vergnes,
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