Structure of dialkyltin diaryloxides and their reactivity toward carbon dioxide and isocyanate

Article abstract of DOI:10.1016/S0022-328X(02)01719-9

The synthesis, structure, and reactivity of dialkyltin diaryloxides, R₂Sn(OAr)₂ (R = Me, Bu; Ar=Ph, p-F-C₆H₄, p-t-Bu-C₆H₄), were investigated focusing on the differences between aryloxides

Full text of DOI:10.1016/S0022-328X(02)01719-9

Journal of Organometallic Chemistry 659 (2002) 133Á141
/
www.elsevier.com/locate/jorganchem
Structure of dialkyltin diaryloxides and their reactivity toward carbon
dioxide and isocyanate
Hiroyuki Yasuda, Jun-Chul Choi, Sang-Chul Lee, Toshiyasu Sakakura *
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, Tsukuba 305-8565, Japan
Received 16 May 2002; received in revised form 3 June 2002; accepted 9 July 2002
Abstract
The synthesis, structure, and reactivity of dialkyltin diaryloxides, R2Sn(OAr)2 (Rꢀ
/
Me, Bu; ArꢀPh, p-F-C6H4, p-t-Bu-C6H4),
/
were investigated focusing on the differences between aryloxides and methoxides. Me2Sn(OAr)2 in the solid state formed a dimer.
The aryloxo-bridged structure was confirmed by single crystal X-ray analysis. On the other hand, R2Sn(OAr)2 in solution easily
dissociated upon dilution. The 119Sn-NMR spectra, especially for Me2Sn(OAr)2, exhibited two distinctly resolved signals assignable
to the presence of isomeric five-coordinate environments. The reactivity of R2Sn(OAr)2 was much lower than that of R2Sn(OMe)2.
Thus, R2Sn(OAr)2 did not react with carbon dioxide even at high pressure and excess amount of carbon disulfide. On the other
hand, the reaction with p-methoxyphenyl isocyanate led to the corresponding aryl carbamates, suggesting the occurrence of an
isocyanate insertion into the tinÁoxygen bond of R2Sn(OAr)2. # 2002 Elsevier Science B.V. All rights reserved.
/
Keywords: Dialkyltin diaryloxides; Carbon dioxide; Isocyanate
1. Introduction
reactivity of dialkyltin aryloxides with carbon dioxide,
and even the structure of dialkyltin diaryloxides is not
fully elucidated [4]. In this paper, we report the synthesis
and structure of the dialkyltin diaryloxides, R2Sn(OAr)2
We have recently discovered an efficient catalysis
using dialkyltin dimethoxides, R2Sn(OMe)2 (RꢀBu,
/
(Rꢀ
/
Me, Bu; ArꢀPh, C6H4-p-F, C6H4-p-t-Bu), and
/
Me), for the dimethyl carbonate (DMC) synthesis via
the reaction of dehydrated derivatives of methanol (e.g.
ortho esters and acetals) with carbon dioxide under
supercritical conditions [1]. We have also elucidated the
X-ray structure of Me2Sn(OMe)2 and its carbon dioxide
insertion product, Me2Sn(OMe)(OCO2Me), which pro-
duced DMC upon thermolysis [2]. These findings
prompted us to investigate the diphenyl carbonate
(DPC) synthesis catalyzed by dialkyltin diphenoxides,
R2Sn(OPh)2. DPC has attracted considerable attention
as a starting material of the polycarbonate synthesis by
transesterification, an environmentally benign synthetic
route to polycarbonates without using toxic and corro-
sive phosgene [3]. If dialkyltin diphenoxides catalyze the
DPC formation, a key step in the catalytic cycle would
their reactivities toward cumulenes such as carbon
dioxide, carbon disulfide, and isocyanate, especially
focusing on the differences between the aryloxides and
methoxides.
2. Results and discussion
2.1. Synthesis and solid state structure of dialkyltin
diaryloxides
Reaction of dimethyltin dimethoxide, Me2Sn(OMe)2,
with two equivalents of phenols (PhOH, p-F-C6H4OH,
and p-t-Bu-C6H4OH) at room temperature afforded the
corresponding dimethyltin diaryloxide complexes
(Me2Sn(OPh)2 (1), Me2Sn(OC6H4-p-F)2 (2), and Me2S-
be the insertion of carbon dioxide into the tinÁ
/oxygen
bond. However, there have been no reports on the
n(OC6H4-p-t-Bu)2 (3)) as white solids (Eq. (1)) [5].
1
Complexes 1Á
/
3 were characterized by H-, 13C{1H}-,
and 119Sn{1H}-NMR spectroscopies, as well as elemen-
tal analysis. The 119Sn-NMR spectra of 1Á
3 at 0.1 M in
* Corresponding author. Tel./fax: ꢁ
/
81-298-61-4719
E-mail address: t-sakakura@aist.go.jp (T. Sakakura).
/
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 7 1 9 - 9

134
H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á141
/
CDCl3 contained two sharp singlets around d ꢂ
/
140
ppm as well as one broad signal around d ꢂ80 ppm.
/
This indicates that several species with coordination
numbers around the tin atoms of four and five coexist in
a dilute solution; the detailed solution structures of the
dialkyltin diaryloxides are discussed in the next section.
ð1Þ
X-ray quality crystals of 1 and 2 were obtained from a
CH2Cl2Áether solution at room temperature. The mo-
/
lecular structures of 1 and 2, as determined by X-ray
crystallography, are shown in Figs. 1 and 2, respectively;
selected bond distances and angles are provided in Table
1. Note that this is the first X-ray structure of dialkyltin
diaryloxides. Both complexes have a centrosymmetric
aryloxo-bridged dinuclear structure. The geometry
around the tin center is regarded as distorted trigonal-
bipyramidal, with one of the three aryloxy groups and
the two methyl groups lying on the equatorial plane and
the other two aryloxy groups occupying the apical
Fig. 2. ORTEP drawing of Me2Sn(OC6H4-p-F)2 (2). Ellipsoids repre-
sent 50% probability.
Table 1
˚
Selected bond distances (A) and angles (8) for 1 and 2
Complex 1; Me2 Sn(OPh)2
Bond distances
Sn(1)ÃO(1)
Sn(1)ÃO(2)
Sn(1)ÃC(2)
O(2)ÃC(9)
2.437(2)
2.035(2)
2.095(4)
1.343(4)
Sn(1)ÃO(1*)
Sn(1)ÃC(1)
O(1)ÃC(3)
2.052(2)
2.114(4)
1.382(4)
positions (e.g. O(1)Ã
/
Sn(1)Ã/O(2) bond angle for 1 of
169.95(9)8). This configuration is similar to those
reported for the alkoxo- or hydroxo-bridged dinuclear
trigonal-bipyramidal organotin(IV) complexes, such as
Me2Sn(OMe)2 [2], i-PrSn(O-i-Pr)3 [6], Me2Sn(OH)NO3
Bond angles
O(1)ÃSn(1)ÃO(1*)
O(1)ÃSn(1)ÃC(1)
O(1*)ÃSn(1)ÃO(2)
O(1*)ÃSn(1)ÃC(2)
O(2)ÃSn(1)ÃC(2)
Sn(1)ÃO(1)ÃSn(1*)
Sn(1*)ÃO(1)ÃC(3)
70.4(1)
86.7(1)
95.7(1)
107.3(1)
96.2(1)
109.6(1)
125.8(2)
O(1)ÃSn(1)ÃO(2)
O(1)ÃSn(1)ÃC(2)
O(1*)ÃSn(1)ÃC(1)
O(2)ÃSn(1)ÃC(1)
C(1)ÃSn(1)ÃC(2)
Sn(1)ÃO(1)ÃC(3)
Sn(1)ÃO(2)ÃC(9)
165.95(9)
86.8(1)
109.6(1)
100.1(1)
137.6(2)
119.9(2)
127.0(2)
[7], t-Bu2Sn(OH)X (XꢀF, Cl, or Br) [8], and t-
/
Bu2Sn(O2CMe)(OH) [9]. It has been suggested, based
on 119Sn-NMR studies, that dibutyltin diphenoxide is
associated into a dimer in its saturated solution in CCl4
or benzene [4a] or in the neat liquid [4b]. The X-ray
structures of the dimethyltin diaryloxides obtained here
are in accord with the dimeric structure predicted for
dibutyltin diphenoxide in a concentrated solution.
Complex 2; Me2 Sn(OC6 H4 -p-F)2
Bond distances
Sn(1)ÃO(1)
Sn(1)ÃO(2)
Sn(1)ÃC(2)
O(2)ÃC(9)
2.409(2)
2.024(2)
2.103(4)
1.361(4)
Sn(1)ÃO(1*)
Sn(1)ÃC(1)
O(1)ÃC(3)
2.061(2)
2.121(4)
1.379(4)
Bond angles
O(1)ÃSn(1)ÃO(1*)
O(1)ÃSn(1)ÃC(1)
O(1*)ÃSn(1)ÃO(2)
O(1*)ÃSn(1)ÃC(2)
O(2)ÃSn(1)ÃC(2)
Sn(1)ÃO(1)ÃSn(1*)
Sn(1*)ÃO(1)ÃC(3)
69.3(1)
86.8(1)
O(1)ÃSn(1)ÃO(2)
O(1)ÃSn(1)ÃC(2)
163.93(9)
87.2(1)
94.72(9) O(1*)ÃSn(1)ÃC(1)
107.6(1)
96.5(1)
110.3(2)
100.9(1)
136.5(2)
121.7(2)
127.1(2)
O(2)ÃSn(1)ÃC(1)
C(1)ÃSn(1)ÃC(2)
Sn(1)ÃO(1)ÃC(3)
Sn(1)ÃO(2)ÃC(9)
110.7(1)
124.8(2)
A notable structural feature of the dimethyltin
diaryloxides concerns the definite asymmetry in the
aryloxide bridging. For example, the Sn(1)Ã
/
O(1) dis-
tance of 1 (2.437(2) A) is longer than the Sn(1)ÃO(1*)
and Sn(1)ÃO(2) distances (2.052(2) and 2.035(2) A,
˚
/
˚
/
respectively). This can be accounted for by the alternat-
ing covalent/coordinate bonds in the Sn2O2 ring. The
SnÃ
/
O covalent bond distances (Sn(1)Ã
/
O(1*) and Sn(1)Ã
/
Fig. 1. ORTEP drawing of Me2Sn(OPh)2 (1). Ellipsoids represent 50%
probability.
O(2) for both 1 and 2) are close to the ordinary covalent

H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á
/
141
135
˚
bond of 2.06 A [10], and lie in the range of 1.99(1)Ã
/
˚
2.097(4) A reported for tinÃ
SnÃO covalent bond distances in 1 and 2 are also close
to those for dimethyltin dimethoxide [2]. On the con-
trary, slightly longer distances of Sn(1)ÃO(1) in 1
(2.437(2) A) and 2 (2.409(2) A) than the Sn(1)ÃO(1*)
distance (2.324(6) A) in the dimethyltin dimethoxide [2]
suggest that the oxygen atoms of the aryloxides co-
ordinate more weakly to the tin atom than the oxygen
atom of the methoxide. This is probably due to the
difference in the nucleophilicity of the oxygen between
the aryloxy and methoxy groups. It is likely that this
difference is reflected in the difference in the solution
structure as well as in the reactivity toward carbon
dioxide, as described in a later section.
/
aryloxide distances [11]. The
/
/
˚
˚
/
˚
2.2. Solution structure of dialkyltin diaryloxides
It has been revealed that dimethyltin diaryloxides
have a dimeric structure in the solid state. Thus, we
further investigated in detail the association of dialkyltin
diaryloxides in solution. The monomers of the dialkyltin
diaryloxides are distinguishable from their dimers by
119Sn-NMR spectroscopy. It is known that four-coordi-
nate dialkyltin compounds give a 119Sn chemical shift
(d) ranging from about ꢁ
of the five-coordinate compounds ranges from ꢂ
190 ppm [12]. For instance, dibutyltin dimethoxide,
di-n-propoxide, and di-n-butoxide, which are suggested
to be associated into a dimer (five-coordinate tin atom)
based on the molecular weight and IR measurements,
/
200 to ꢂ
/
60 ppm, whereas d
/90 to
Fig. 3. 119Sn{1H}-NMR spectra of (a) Bu2Sn(OPh)2 (4) at 0.25 M, (b)
4 at 3.3 M, and (c) Me2Sn(OPh)2 (1) at 0.25 M in CDCl3 at room
temperature.
ꢂ
/
show d values ranging from ꢂ
/
159 to ꢂ165 ppm as neat
/
liquids, whereas the neat liquid dibutyltin di-t-butoxide,
which is fully dissociated into a monomer (four-coordi-
nate tin atom) based on the IR, gives a low-field signal
at d ꢂ34 ppm [4a]. For the neat dibutyltin diphenoxide,
/
Bu2Sn(OPh)2 (4), the changes in enthalpy (DH) and
entropy (DS) for the equilibrium between [Bu2S-
n(OPh)2]2 and Bu2Sn(OPh)2 have been estimated to be
789
based on the temperature dependence (0Á
d values assuming d for the dimer of ꢂ148 ppm and d
for the monomer of ꢂ48 ppm [4b].
/
2 kJ molꢂ1 and 2389
/
7 J molꢂ1 Kꢂ1, respectively,
/
150 8C) of the
/
/
In this study, we examined the variation with
concentration in the 119Sn{1H}-NMR for 4. The
119Sn{1H}-NMR spectrum at 0.25 M in CDCl3 at
room temperature showed one broad signal at d
ꢂ
/
65.5 ppm (Fig. 3(a)). The broad signal remarkably
Fig. 4. Changes in the 119Sn chemical shifts (d) of Bu2Sn(OPh)2 (4) in
shifted upfield to d ꢂ139.0 ppm with an increase in the
concentration to 3.3 M (Fig. 3(b)). Fig. 4 shows the
changes in the d values in the concentration range of
/
the concentration range of 0.25Á3.3 M in CDCl3 at room temperature.
/
judged by 119Sn-NMR [4a]; A dimer of 4 dissociates
more easily than that of dibutyltin dimethoxide does. It
is noted that the 119Sn{1H}-NMR spectra of 4, espe-
cially at high concentrations, contained two very small
0.25Á3.3 M. The d shift clearly demonstrates that an
/
equilibrium between four- and five-coordinate tin atoms
exists in 4 in solution. It has been shown that dibutyltin
dimethoxide is almost fully associated into a dimer in
peaks around d ꢂ180 ppm besides the above-stated
/
CCl4 within the temperature range of ca. 20Á180 8C as
/

136
H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á141
/
large broad signal, as shown in Fig. 3(b). Therefore, the
structural change of 4 in solution is not so simple as was
explained in the previous papers [4] based on the simple
equilibrium between the dimer and the monomer.
The 119Sn-NMR of Me2Sn(OPh)2 (1) is significantly
different from that of Bu2Sn(OPh)2 (4). Fig. 3(c) shows
the 119Sn{1H}-NMR spectrum of 1 at 0.25 M in CDCl3
at room temperature. The spectrum exhibited two sharp
ppm). The tin atoms in the dimers are roughly classified
into two different five-coordinate magnetic environ-
ments. Thus, the rather slow equilibrium of process B
would produce two distinctly resolved signals with d
values corresponding to the five coordination (ca. ꢂ140
/
ppm). In contrast, the two high-field signals for 4 were,
if any, very small (Fig. 3(b)). This suggests that the
equilibrium of process B for 4 lies further to the left
compared with that for 1Á3. In other words, the
/
singlets around d ꢂ
/
140 ppm and one broad signal at d
dissociation of the dimer in solution for 4 would be
easier than for the dimethyltin diaryloxides. The d
ꢂ
/
88.5 ppm. Similarly, three signals were observed for 2
and 3. The lower concentration caused the increase of
the low-field broad signal relative to the two sharp high-
field peaks. The broad signal in the intermediate region
between four- and five-coordinate alkyltin compounds,
are assumed to be a weighted average for more than two
different species with four- or five-coordinate tin atoms,
as a result of a fast equilibrium on the NMR time scale.
In addition, compared with 4 more distinct appearance
of two sharp singlets with the d values in the region
typical of five-coordinate alkyltin compounds suggests
the presence of two kinds of magnetic environments
concerning the five-coordinate tin atoms for each
dimethyltin diaryloxide.
values for the dimers of 4 (ca. ꢂ
than those for the dimers of 1Á
/
180 ppm) were higher
3 (ca. ꢂ140 ppm),
/
/
possibly due to the larger electron-donating property of
the butyl group than the methyl group.
The results of the structural studies on 1Á4 are
/
summarized as follows: dialkyltin diaryloxides exist as
a dimer in the solid state, while they easily dissociate
into a monomer in solution. This behavior of the
dialkyltin diaryloxides is in contrast to dialkyltin
dimethoxide, which forms a stable dimer even in a
dilute solution [2,4a]. The instability of the dialkyltin
diaryloxide dimers in solution would be related to the
lower nucleophilicity of the aryloxide compared with the
methoxide. The reactivity of the aryloxide and methox-
ide toward carbon dioxide is compared in the next
section.
Scheme 1 depicts a plausible structural change in the
dialkyltin diaryloxides to account for the 119Sn-NMR
results. If we assume that the bridged oxygen atoms
occupy one of the two axial positions in a trigonal-
bipyramid as seen in the X-ray structures (Figs. 1 and 2),
three kinds of isomeric dimers ((III)Á(V)) are possible.
/
2.3. Reactivity of dialkyltin diaryloxides with carbon
dioxide and carbon disulfide
In solution, the dialkyltin diaryloxide dimer dissociates
into a four-coordinate tetrahedral monomer (I), which is
then in a dynamic equilibrium with each of the three
dimers, (III), (IV), and (V), via the intermediate (II). For
The reaction of 4 with carbon dioxide was attempted
and followed by NMR spectroscopy. As mentioned in
the preceding section, one broad 119Sn-NMR signal was
1Á
broad signal with the d value belonging in the middle
range of the four- and five- coordinations (ca. ꢂ80
/3, the fast equilibrium of process A would give a
observed in the d range from ꢂ
/
60 to ꢂ140 ppm in the
/
/
absence of carbon dioxide. When excess carbon dioxide
Scheme 1.

H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á
/
141
137
d values of the two high-field singlets becomes small
with increasing the temperature. Two different magnetic
environments around the tin atoms in the dimers get
closer at higher temperatures.
The reaction of 1 with carbon dioxide was also carried
out under higher carbon dioxide pressures (80Á150
/
atm), and followed by high-pressure IR spectroscopy.
However, we could not observe the formation of the
carbonate complex derived from 1 even at 150 atm; no
absorption peaks assignable to n(CO) appeared in the
range of 1650Á
/
1750 cmꢂ1. In the case of dimethyltin
dimethoxide, carbon dioxide insertion into the tinÁ
/
oxygen bond readily occurs at one of the two methoxy
groups [2]. Therefore, it is clear that the reactivity of the
dialkyltin diaryloxides with carbon dioxide is much
lower than that of dimethyltin dimethoxide. Tributyltin
phenoxide is also less reactive toward carbon dioxide
than the alkoxide [13,14].
The reaction of 1Á3 with carbon disulfide (four
/
equivalents) was further examined at room temperature.
However, no evidence for the carbon disulfide insertion
into the tinÁoxygen bond was obtained by NMR. The
/
lower reactivity of the dialkyltin diaryloxides toward
carbon dioxide and carbon disulfide compared with the
dialkyltin dimethoxides is presumably due to the lower
nucleophilicity of the aryloxy groups due to the smaller
electron-donating property of the aryl groups compared
with the methyl group. On the other hand, an increase in
the coordination number around tin atoms by the
methoxide (or aryloxide) bridging causes an increase in
the electron density of the tin atoms, as evidenced by an
upfield shift in the 119Sn{1H}-NMR signals for the
dialkyltin diaryloxides. Since the electron-donating
property of the methoxy group is higher than that of
the aryloxy group, the five-coordinate dimer in solution
is more stable for R2Sn(OMe)2 than for R2Sn(OAr)2 as
discussed earlier. Moreover, the nucleophilicity of
[R2Sn(OMe)2]2 is higher than that of [R2Sn(OAr)2]2
even when compared between the dimers. The higher
nucleophilicity of the dimeric methoxide compared with
the corresponding phenoxide is shown in the chemical
Fig. 5. 119Sn{1H}-NMR spectra of Bu2Sn(OPh)2 (4) at 0.25 M in
CDCl3 in the presence of carbon dioxide (four equivalents) at (a)
0
8C, (b) 25 8C and (c) 60 8C.
(four equivalents) was introduced at room temperature,
the two high-field singlets clearly appeared around
ꢂ180 ppm while the low-field broad signal significantly
/
decreased (Fig. 5(b)). The broad signal further decreased
with decreasing the temperature (Fig. 5(a)), and com-
pletely disappeared at ꢂ50 8C. The chemical shift of
/
the broad signal was also shifted to the higher magnetic
field by lowering the temperature. However, no evidence
for the insertion of carbon dioxide into the tinÁoxygen
/
bond in 4 was obtained by 13C{1H}-NMR and IR.
These results suggest that the addition of carbon dioxide
merely shifted the equilibrium of process B toward the
five-coordinate dimers (Scheme 1). It is possible that
carbon dioxide lowered the polarity of the solvent
resulting in the association to the dimers, especially at
lower temperatures. On the other hand, when the
reaction mixture was heated to 60 8C, the low-field
shift of 119Sn{1H}-NMR: [Me2Sn(OMe)2]2 (d ꢂ
ppm) [2] and [Me2Sn(OPh)2]2 (d ꢂ141 ppm). Conse-
quently, the carbon dioxide insertion into the tinÁ
/
162
/
/
oxygen bond might become easier in methoxides than
in aryloxides.
Dialkyltin dimethoxides, R2Sn(OMe)2 (RꢀBu, Me),
/
can efficiently catalyze the reaction of the dehydrated
derivatives of methanol (e.g. ortho esters and acetals)
with carbon dioxide to produce DMC under super-
critical conditions [1]. This fact interested us in examin-
ing the catalytic efficiency of 4 for the analogous
reaction of dehydrated derivatives of phenol (tetraphe-
noxy methane and triphenoxy methane) with carbon
dioxide to produce DPC. For both reactions, however,
an appreciable amount of DPC was not formed,
broad peak became sharp, showing the d value (ꢂ33.9
/
ppm) assignable to the monomer (Fig. 5(c)), whereas the
carbon dioxide insertion was not evidenced again by
13C{1H}-NMR. This indicates that the shift of process
A to the left, that is, dissociation to the four-coordinate
monomer, becomes more favorable and faster at higher
temperatures. It is noteworthy that the difference in the

138
H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á141
/
possibly due to no carbon dioxide insertion into the tinÁ
oxygen bond of 4.
/
Table 2
˚
Selected bond distances (A) and angles (8) for 6
Compound 6; p-MeOC6 H4 NHCO2 C6 H4 -p-F
Bond distances
2.4. Reactivity of dialkyltin diaryloxides with isocyanate
F(1)ÃC(1)
O(1)ÃC(7)
O(3)ÃC(11)
N(1)ÃC(7)
1.364(4) O(1)ÃC(4)
1.375(4) O(2)ÃC(7)
1.372(4) O(3)ÃC(14)
1.341(4) N(1)ÃC(8)
1.398(4)
1.192(4)
1.421(4)
1.421(4)
The fact that dialkyltin diaryloxides did not react with
carbon dioxide and carbon disulfide induced us to
further examine the reactivity of dialkyltin diaryloxides
with isocyanate, which has a higher reactivity than
carbon dioxide or carbon disulfide. The reaction of 4
with two equivalents of p-methoxyphenyl isocyanate at
room temperature gave p-MeOC6H4NHCO2Ph (5) in
63% yield. The structure of the carbamate 5 was
Bond angles
C(4)ÃO(1)ÃC(7)
C(7)ÃN(1)ÃC(8)
F(1)ÃC(1)ÃC(6)
O(1)ÃC(4)ÃC(5)
O(1)ÃC(7)ÃN(1)
N(1)ÃC(8)ÃC(9)
O(3)ÃC(11)ÃC(10)
118.0(3) C(11)ÃO(3)ÃC(14)
126.8(3) F(1)ÃC(1)ÃC(2)
119.1(4) O(1)ÃC(4)ÃC(3)
120.5(4) O(1)ÃC(7)ÃO(2)
107.7(3) O(2)ÃC(7)ÃN(1)
124.6(3) N(1)ÃC(8)ÃC(13)
117.4(3) O(3)ÃC(11)ÃC(12)
117.6(3)
118.3(4)
117.6(4)
123.1(3)
129.1(3)
117.1(3)
124.8(3)
1
confirmed by H- and 13C{1H}-NMR, IR, mass spec-
trum, and elemental analysis. Similarly, the reaction of 2
with p-methoxyphenyl isocyanate, followed by recrys-
tallization from an etherÁ
/
hexane solution afforded a
isocyanate in the absence of tributyltin phenoxide has
also been pointed out [15].
If these results are taken into account, it is very
probable that isocyanates such as p-methoxyphenyl
single crystal of p-MeOC6H4NHCO2C6H4-p-F (6),
which was characterized by X-ray crystallography
(Fig. 6 and Table 2). The unit cell contains two
molecules of 6, and the H(23) and H(24) atoms are
bound to the O(5) and O(2) atoms, respectively, through
a hydrogen-bond.
isocyanate can insert into the tinÁoxygen bond of the
/
dialkyltin diaryloxides (Scheme 2). The formation of
alkylstannylcarbamates by the insertion of isocyanates
There is the possibility that 5 and 6 were formed via
the reaction of p-methoxyphenyl isocyanate with ArOH
into the tinÁoxygen bond of tributyltin phenoxide [15]
/
as well as alkyltin alkoxides, such as tributyltin methox-
ide [15] and dibutyltin dimethoxide [16], has been
assumed mainly based on IR and elemental analyses.
Such alkylstannylcarbamates are readily converted into
the corresponding carbamates by hydrolysis or proto-
lysis. Thus, carbamates 5 and 6 were probably formed
(ArꢀPh, p-F-C6H4), which could be produced by the
/
hydrolysis of 4 and 2. Thus, the reaction of p-methox-
yphenyl isocyanate with phenol was carried out in the
absence of 4. However, no formation of 5 was observed
in this reaction, indicating tin phenoxide plays an
important role in the carbamate formation. No occur-
rence of the reaction between phenol and phenyl
through hydrolysis of the tinÁnitrogen bond. On the
/
other hand, the reaction of p-F-C6H4OH with p-
methoxyphenyl isocyanate in the presence of catalytic
amount of 2 at 60 8C did not yield 6, indicating that
dialkyltin diaryloxides are not regenerated by phenolysis
of alkylstannylcarbamates.
In summary, we elucidated the structure and the
reactivity of the dialkyltin diaryloxides toward carbon
dioxide, carbon disulfide, and isocyanate. The structure
of the dimethyltin diaryloxides in the solid state
determined by X-ray crystallography was aryloxo-
bridged dinuclear, while the 119Sn-NMR spectroscopic
study revealed that dialkyltin diaryloxides are easily
Fig. 6. ORTEP drawing of p-MeOC6H4NHCO2C6H4-p-F (6). Ellip-
soids represent 50% probability.
Scheme 2.

H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á
/
141
139
dissociated into a monomer when in solution. Neither
carbon dioxide nor carbon disulfide reacted with the
dialkyltin diaryloxides, whereas isocyanate readily re-
acted to produce aryl carbamates. These results clearly
demonstrate that the reactivity of the dialkyltin diaryl-
oxides is quite different from that of the dialkyltin
dimethoxides.
1H-NMR (400 MHz in CDCl3 at 25 8C) d 0.92 (s,
6H, CH3, J(SnÃCÃH)ꢀ70.7 Hz), 6.55Á6.81 (m, 8H,
aromatic). 13C{1H}-NMR (100 MHz in CDCl3 at
25 8C) d 1.98 (s, SnÃCH3), 116.10 (J(CÃF)ꢀ23.2
Hz), 121.36, 154.98, 157.40 (J(CÃF)ꢀ239 Hz) (aro-
matic). 119Sn{1H}-NMR (149 MHz, CDCl3 at 25 8C) d
140.51 (s), ꢂ140.30 (s), ꢂ67.30 (br). M.p.: 234Á
/
/
/
/
/
/
/
/
/
ꢂ
/
/
/
/
237 8C. Anal. Calc. for C14H14F2O2Sn: C, 45.33; H,
3.80. Found: C, 44.88; H, 3.98%.
3. Experimental
3.3. Synthesis of Me2Sn(OC6H4-p-t-Bu)2 (3)
All manipulations were carried out under purified
argon with use of standard Schlenk and glovebox
techniques. Solvents were distilled from sodium or
calcium chloride. Carbon dioxide (Showa Tansan Co.,
Kawasaki, purity: over 99.9%, water content: less than
0.01%) was used without further purification. Carbon
disulfide and p-methoxyphenyl isocyanate was pur-
chased from Tokyo Kasei Co. Dimethyltin dimethoxide
[17] and dibutyltin diphenoxide (4) [18] were synthesized
according to the literature method. Melting points
(m.p.) were measured on a Yanaco Model MP-S3
melting point apparatus and are uncorrected. Elemental
analyses were carried out by using a CE-EA 1110
automatic elemental analyzer. 1H-, 13C{1H}-, and
119Sn{1H}-NMR spectra were recorded on a JEOL-
LA400WB superconducting high-resolution spectro-
meter (400 MHz for 1H). 119Sn-NMR spectra were
referenced to external tetramethyltin. IR spectra were
measured on a JASCO FTIR-5300 spectrometer. IR
spectra under high pressure carbon dioxide were col-
lected by using an IR cell with zinc sulfide windows.
Complex 3 was prepared analogously by reacting
dimethyltin dimethoxide with two equivalents of p-t-
1
Bu-C6H4OH in 76% yield as a white powder. H-NMR
(400 MHz in CDCl3 at 25 8C) d 0.93 (s, 6H, CH3,
J(SnÃ
7.10 (m, 8H, aromatic). 13C{1H}-NMR (100 MHz in
CH3), 31.89 (s,
/
CÃ
/
H)ꢀ
/
71.9 Hz), 1.25 (s, 18H, C(CH3)3), 6.52Á
/
CDCl3 at 25 8C) d 2.24 (s, SnÃ
/
C(CH3)3), 34.29 (s, C(CH3)3), 120.18, 126.33, 143.06,
156.66 (s, aromatic). 119Sn{1H}-NMR (149 MHz,
CDCl3 at 25 8C) d ꢂ
/
144.79 (s), ꢂ
/
141.65 (s), ꢂ
/
75.96
(br). M.p.: 172Á175 8C. Anal. Calc. for C22H32O2Sn: C,
/
59.09; H, 7.21. Found: C, 58.47; H, 7.38%.
3.4. Reaction of 4 and 1 with carbon dioxide
In an NMR tube (5 mm in diameter), four equivalents
of carbon dioxide (0.42 mmol) was vacuum-transferred
into a CDCl3 (0.4 ml) solution of 4 (42 mg, 0.10 mmol as
1
a monomer). The H-, 13C{1H}-, and 119Sn{1H}-NMR
spectra of the reaction mixture were recorded in the
temperature range from ꢂ50 to 60 8C.
/
3.1. Synthesis of Me2Sn(OPh)2 (1)
A CH2Cl2 (4.0 ml) solution of 1 (33 mg, 0.099 mmol
as a monomer) was placed in a high-pressure IR cell
under argon atmosphere, followed by the introduction
To a toluene (25 ml) solution of dimethyltin dimeth-
oxide (3.3 g, 0.016 mol) was added phenol (3.0 g, 0.032
mol). After stirring the reaction mixture for 16 h at
room temperature (r.t.), the solvent was evaporated. The
resulting product was washed repeatedly with hexane to
of carbon dioxide (1Á150 atm). IR spectra from 1 were
/
obtained by subtracting the spectrum of CH2Cl2 alone
from the spectrum obtained for 1 in CH2Cl2 at each
pressure.
give a white solid. Recrystallization from a CH2Cl2Á
/
ether solution gave colorless crystals of 1 (4.2 g, 79%
1
yield). H-NMR (400 MHz in CDCl3 at 25 8C) d 0.96
3.5. Reaction of 1Á3 with carbon disulfide
/
(s, 6H, CH3, J(SnÃ
10H, aromatic). 13C{1H}-NMR (100 MHz in CDCl3 at
25 8C) d 2.06 (s, SnÃCH3), 117.48, 120.59, 129.69,
158.50 (s, aromatic). 119Sn{1H}-NMR (149 MHz,
CDCl3 at 25 8C) d ꢂ141.87 (s), ꢂ140.11 (s), ꢂ88.53
(br). M.p.: 166Á169 8C. Anal. Calc. for C14H16O2Sn: C,
/
CÃ
/
H)ꢀ
/
72.4 Hz), 6.61ꢂ
/
7.14 (m,
To a CH2Cl2 (5 ml) solution of 1 (0.23 g, 0.70 mmol as
a monomer) was added four equivalents of carbon
disulfide (0.17 ml, 2.8 mmol). After stirring the reaction
mixture for 24 h at r.t., the solvent was evaporated. The
resulting product was washed repeatedly with hexane to
/
/
/
/
/
1
50.20; H, 4.81. Found: C, 49.52; H, 5.06%.
give a white solid. H-, 13C{1H}-, and 119Sn{1H}-NMR
data of the solid were consistent with 1. The same result
was obtained for the reaction in an NMR tube.
Reactions of 2 and 3 with carbon disulfide were
analogously carried out. 1H-, 13C{1H}-, and
119Sn{1H}-NMR data of each product were consistent
with those of each complex.
3.2. Synthesis of Me2Sn(OC6H4-p-F)2 (2)
Complex 2 was synthesized analogously in 82% yield
as a white powder via the reaction of dimethyltin
dimethoxide with two equivalents of p-F-C6H4OH.

140
H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á141
/
Table 3
Data collection and refinement parameters for 1, 2 and 6
1
2
6
Formula
C14H16O2Sn
334.97
C14H14F2O2Sn
370.95
C28H24F2N2O6
522.50
Formula weight
Crystal size (mm)
Crystal system
Space group
0.30ꢃ0.30ꢃ0.40
Monoclinic
P21/n (No. 14)
10.354(3)
0.30ꢃ0.30ꢃ0.40
Monoclinic
P21/n (No. 14)
10.341(3)
0.30ꢃ0.30ꢃ0.40
Triclinic
¯
P1 (No. 2)
/
˚
a (A)
10.491(1)
13.664(2)
9.852(1)
98.89(1)
105.010(10)
68.80(1)
1268.9(3)
2
˚
b (A)
12.260(4)
11.348(3)
13.045(4)
11.080(4)
˚
c (A)
a (8)
b (8)
111.29(2)
110.53(2)
g (8)
3
V (A )
˚
1342.2(7)
4
296
1399.9(7)
4
296
Z
T (K)
˚
296
l (A)
0.71069
1.66
0.71069
1.76
0.71069
1.37
1.06
Dcalc (g cmꢂ3
)
m (cmꢂ1
F(000)
R
)
18.91
664
18.42
728
544
0.049
0.030
0.041
155
0.035
0.053
173
a
Rw
0.069
344
2247
Number of variables
Number of observations (I ꢀ3s(I))
2430
2827
a
wꢀ[s(Fo)]ꢂ2
.
3.6. Reaction of 4 and 2 with p-methoxyphenyl
isocyanate
3.6.2. Compound 6
1H-NMR (CDCl3, 400 MHz): d 3.77 (s, 3H, OCH3),
7.33Á
6.84 (m, 9H, aromatic and NH). 13C-NMR
(CDCl3, 100 MHz): d 55.80 (OCH3), 114.67, 116.28
(J(CÃF)ꢀ23.1 Hz), 121.05, 123.38 (J(CÃF)ꢀ8.2 Hz),
130.53, 146.81 (J(CÃF)ꢀ1.6 Hz), 152.21, 160.43 (J(CÃ
F)ꢀ243 Hz) (aromatic), 156.64 (CO). Anal. Calc. for
/
To a solution of 4 (0.21 g, 0.50 mmol) in ether (5 ml)
was added two equivalents of p-methoxyphenyl isocya-
nate (0.13 ml, 0.99 mmol). When the reaction mixture
was stirred at r.t., it turned into a pale yellow homo-
geneous solution. After 1 h, the addition of two
equivalents of water (0.018 ml, 0.99 mmol) to the
solution caused the instant formation of white precipi-
tates. The precipitates were filtered, washed repeatedly
with hexane, and dried in vacuo. Recrystallization from
/
/
/
/
/
/
/
/
C14H12FNO3: C, 64.36; H, 4.63; N, 5.36. Found: C,
64.76; H, 4.52; N, 5.28%.
3.7. X-ray crystallographic study
an etherÁhexane solution gave 76 mg (63% yield) of
/
Data collection and refinement parameters for 1, 2,
and 6 are summarized in Table 3. The data were
collected on a Rigaku AFC 7R diffractometer at
colorless crystals of p-MeOC6H4NHCO2Ph (5). A
similar procedure employed for the reaction of 2 (0.17
g, 0.45 mmol) with p-methoxyphenyl isocyanate (0.12
ml, 0.93 mmol) gave p-MeOC6H4NHCO2C6H4-p-F (6)
(67 mg, 58% yield).
ambient temperature using graphite-monochromated
˚
MoÁ
/
Ka radiation (0.71069 A) and the v scan mode
(2u 5
/
558). Correction for the Lorentz and polarization
effects, and an empirical absorption correction (C-scan)
were applied. The full-matrix least-squares refinement
was carried out by applying anisotropic thermal factors
to all the non-hydrogen atoms. The hydrogen atoms
were located by assuming an ideal geometry.
3.6.1. Compound 5
1H-NMR (CDCl3, 400 MHz): d 3.77 (s, 3H, OCH3),
7.39Á
6.84 (m, 10H, aromatic and NH). 13C-NMR
/
(CDCl3, 100 MHz): d 55.52 (OCH3), 114.37, 120.70,
121.65, 125.60, 129.38, 130.43, 150.70, 151.95 (aro-
matic), 156.29 (CO). Mass spectrum (EI, 70 eV): eight
most intense m/e peaks at 44, 66, 78, 94, 106, 121, 149,
243. IR (KBr, cmꢂ1): 1711 (nCO), 3341 (nNH). Anal.
Calc. for C14H13NO3: C, 69.12; H, 5.39; N, 5.76. Found:
C, 69.63; H, 4.55; N, 5.51%.
4. Supplementary material
Crystallographic data for the structural analysis of
complexes 1 and 2 and compound 6 have been deposited
with the Cambridge Crystallographic Data Centre

H. Yasuda et al. / Journal of Organometallic Chemistry 659 (2002) 133Á
/
141
141
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