Heteroleptic tin (II) dialkoxides stabilized by intramolecular coordination Sn(OCH2CH2NMe2)(OR) (R = Me, Et, iPr, tBu, Ph). Synthesis, structure and catalytic activity in polyurethane synthesis

Article abstract of DOI:10.1016/j.jorganchem.2009.05.014

A straightforward method of synthesis of heteroleptic tin (II) alkoxides stabilized by one intramolecular coordination bond was developed. Addition of one equivalent of dimethylamino ethanol to diamide Sn(N(SiMe₃)₂)₂ (5) y

Full text of DOI:10.1016/j.jorganchem.2009.05.014

Journal of Organometallic Chemistry 694 (2009) 3184–3189
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Heteroleptic tin (II) dialkoxides stabilized by intramolecular coordination
i
t
Sn(OCH2CH2NMe2)(OR) (R = Me, Et, Pr, Bu, Ph). Synthesis, structure and
catalytic activity in polyurethane synthesis
Oleg V. Chernov a,b, Aleksandr Yu. Smirnov a, Ivan A. Portnyagin a,b, Victor N. Khrustalev c,
Mikhail S. Nechaev a,b,
*
a Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russian Federation
b A.V. Topchiev Institute of Petrochemical Synthesis, RAS, Leninsky Prosp., 29, Moscow 119991, Russian Federation
c A.N. Nesmeyanov Institute of Organoelement Compounds, RAS, Vavilov Str., 28, Moscow 119991, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
A straightforward method of synthesis of heteroleptic tin (II) alkoxides stabilized by one intramolecular
coordination bond was developed. Addition of one equivalent of dimethylamino ethanol to diamide
Sn(N(SiMe3)2)2 (5) yields alkoxy-amido derivative Sn(OCH2CH2NMe2)(N(SiMe3)2) (2). Further addition
of alcohol leads to corresponding heteroleptic dialkoxides Sn(OCH2CH2NMe2)(OR) (R = Me (6), Et (7),
Received 10 April 2009
Received in revised form 6 May 2009
Accepted 8 May 2009
Available online 18 May 2009
t
iPr (8), Bu (9), Ph (10)). Catalytic activity of tin (II) compounds in polyurethane formation was tested.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Tin (II)
Intramolecular coordination
Homogeneous catalysis
Polyurethane synthesis
Me3Si
SiMe3
1. Introduction
Ar*
Ar*
ArF
ArF
R
R
Sn
Sn
Sn
Stannylenes R2Sn are divalent tin compounds. Those bearing
simple alkyl and aryl groups are reactive compounds that could
not be isolated. They undergo rapid oligomerization and/or inser-
tion in C–H, C–X and multiple bonds [1–3].
SiMe3
Me3Si
A
B
C
There are two approaches of stabilization of stannylenes in
solution and in solid state. First is introduction of steric bulk – ki-
netic stabilization (types A [4–13] and B [14–21]). The alternative
approach – thermodynamic stabilization stems from electronic ef-
fects: (i) introduction of acceptor substituents X to tin (type C
[22–24]), (ii) formation of intramolecular coordination bonds
Y ? Sn (Y – heteroatom bearing a lone electron pair, N, P, O, S; type
D [25–32]), (iii) conjugation and delocalization (types E [33–47]
and F [48–54]). In 2003 Zemlyansky et al. reported on the synthesis
and solid state structure of stannylene Sn(OCH2CH2NMe2)2 (1),
stabilized by a combination of factors (i) and (ii) without the
introduction of sterically bulky groups [55].
R'
Y
N
R'
R'
Sn
Sn
Sn
N
R'
Y
D
F
E
Ar* - bulky aryl ligand
ArF = 2,4,6 -tri fl uoromethylp henyl
R = H, Alk, SiMe3; R' = Alk, Ar, SiMe3
Y = donor group
The key features of stannylene Sn(OCH2CH2NMe2)2 (1) are: (i) lone
electron pair, as well as (ii) partially occupied pz-orbital on metal
atom M, and (iii) labile strongly polarized M–O bonds (Scheme 1).
This leads to unique chemical properties of stannylene 1: addition
of Lewis acids–transition metals [56], addition of strong Lewis bases
* Corresponding author. Address: Department of Chemistry, M.V. Lomonosov
Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russian Federation.
Tel./fax: +7 495 9392677.
E-mail address: nechaev@nmr.chem.msu.ru (M.S. Nechaev).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.05.014

O.V. Chernov et al. / Journal of Organometallic Chemistry 694 (2009) 3184–3189
3185
soluble in hexane. Methyl, ethyl and isopropyl derivatives 6–8 are
powders that decompose in air in several seconds. Compounds 9
and 10 bearing more bulky tert-butyl and phenyl substituents form
large crystals that remain in air for several hours.
N
N
Sn
N
O
O
O
O
Sn TM
N
Y
Compounds 6–10 were characterized by 1H, 13C and elemental
analysis. In NMR spectra the signals of OCH2CH2N groups are
broaden due to fast opening–closing of Me2N ? Sn coordination
bonds in solution [55,60,70]. Solid state structures of 9 and 10 were
established by X-ray analysis.
d
N
a
O
Sn
O
c
b
N
N
1
2.2. X-ray
[Sn (OCH2CH2NMe2)3Li]2
O
Sn
X
Crystals of 9 and 10 suitable for X-ray diffraction analysis were
obtained from THF solution. The molecular structures of 9 and 10
are shown in Fig. 1. Selected bond lengths and angles are presented
in Table 1.
;
a: TM*THF b: LiOCH2CH2NMe2; c: SnX2; d: S8 or N3R
TM = Fe(CO)4, Cr(CO)5; X = Cl, N3, N(SiMe3)2; Y = S, NR
Scheme 1.
Compounds 9 and 10 were found to be centrosymmetric dimers
via two intermolecular dative Sn O bonds. They consist of two
Sn(OCH2CH2NMe2)(OR) units, sharing a Sn2O2 four-membered
ring. Molecular inversion center lies at the center of this ring relat-
ing the unprimed to primed atoms.
Tin atoms have a distorted trigonal bipyramidal configuration
with a lone electron pair in the equatorial position. Stereochemi-
cally active lone pairs at Sn atoms push the atoms at the axial posi-
tions towards the equatorial bonded atoms. The resulting
distortions towards a tetragonal pyramid are evident in the
[57,58], facile substituent redistribution reactions to form
Sn(OCH2CH2NMe2)X (X = N(SiMe3)2 (2), Cl, F, N3) [59–61]. Due to
efficient thermodynamic stabilization of stannylene 1 it is reluctant
to form doubly bonded species [62].
Dibutyltin derivatives are known to catalyze different polycon-
densation reactions such as polyurethane synthesis, synthesis of
polyesters, polylactides and organic polycarbonates [63]. Dialkyltin
derivatives have toxicity issues [64,65] and the search for less toxic
or non-toxic catalysts is an important task. A possible solution is
utilization of inorganic tin derivatives that do not contain car-
bon–tin bonds and are virtually non-toxic. It was recently reported
that sterically hindered phenoxide 3 [66] and divalent derivative,
stabilized by intramolecular coordination, 4 [67] are active cata-
lysts in polyurethane formation.
N(1) ? Sn O(1A) bond angles of 140.79(4)° for
9
and
140.36(3)° for 10 (Table 1).
Sn–O bond lengths in the four-membered rings in both 9 and 10
(2.126(1) and 2.286(1) Å in 9, and 2.118(1) and 2.245(1) Å in 10,
Table 1) are significantly different. In 10 they are more equalized
than in 9. We suppose that this is due to smaller steric effects of
phenyl substituents in 10 in comparison with tert-butyl substitu-
ents in 9.In contrast, Sn(1) N(1) coordination bond lengths in 9
(2.503(1) Å) and 10 (2.470(1) Å) are only slightly different and very
close to those in Sn(OCH2CH2NMe2)2 (2.458(2) Å) [55] and
[Sn(OCH2CH2NMe2)(N(SiMe3)2)]2 (2.505(5) Å [60]. Bridging oxygen
atoms are practically planar (angles at O sum to 357.3° and 358.8°
for 9 and 10, respectively). Obtuse Sn–O–Sn angles together with
the large Sn(1)ꢀ ꢀ ꢀSn(2) separation (3.6162(2) and 3.5918(2) Å)
indicate there are no attractive interactions between the metal
atoms. Apparently, the combination of electronic effects of the che-
lating b-dimethylaminoethoxy group and sterics of the terminal
tert-butoxy- or phenoxy-groups is not enough to stabilize the
monomeric species 9 and 10.
It is interesting to note that the X-ray crystal structure of 9 re-
veals tert-butyl substituents turned away from the Sn2O2 ring
plane (torsion angle O(1)–Sn(1)–O(2)–C(5) is 133.0(1)°) while
structural data for 10 show that phenyl groups occupy sites above
the Sn2O2 ring plane (the torsion angle O(1)–Sn(1)–O(2)–C(5) is
72.3(1)°, Fig. 2). The same disposition above the Sn2O2 ring plane
was observed for the azido-groups in the dimer [Sn(OCH2CH2N-
Me2)N3]2 (torsion angle O(1)–Sn(1)–N(2)–N(3) is 49.0(5)° [59]).
Such arrangement of the phenyl and azido moieties is presumably
explained by the weak attractive interactions Snꢀ ꢀ ꢀC@C
(Sn1ꢀ ꢀ ꢀC(5A) 3.960(1) and Sn(1)ꢀ ꢀ ꢀC(10A) 3.634(1) Å) in 10 and
Snꢀ ꢀ ꢀN„N (Sn(1)ꢀ ꢀ ꢀN(3A) 3.653(5) and Sn(1)ꢀ ꢀ ꢀN(4A) 3.532(5) Å)
in [Sn(OCH2CH2NMe2)N3]2.
tBu
tBu
tBu
tBu
tBu
tBu
P
Sn
P
F3C
F3C
t
Bu
O
Sn
O
tBu
O
O
CF3
CF3
tBu
tBu
3
4
In this contribution we report on the stepwise synthesis of het-
eroleptic tin dialkoxides Sn(OCH2CH2NMe2)(OR) (R = Me, Et, iPr,
tBu, Ph) via intermediate formation of alkoxy-amide Sn(OCH2CH2N-
Me2)(N(SiMe3)2) (2) and their application as catalysts for the forma-
tion of polyurethanes.
2. Results and discussion
2.1. Synthesis
A convenient way of preparation of alkoxy tin compounds is
interaction of tin amides with alcohols. Interaction of halogenated
tin derivatives with alcoholates of alkali metals is frequently ham-
pered by formation of heterometallic alkoxides [68,69].
For synthesis of heteroleptic tin (II) dialkoxides we used the
consecutive substitution of amido groups in stannylene 5. Treat-
ment of 5 with one equivalent of dimethylaminoethanol in THF
yields alkoxy-amido derivative 2. Reactions of 2 with a slight ex-
cess of alcohols give a series of heteroleptic tin (II) dialkoxides
6–10 (Scheme 2).
It is important to point out that the molecules of 9 and 10 could
form the dimers via
l-bridging O atoms of the terminal tert-but-
oxy- or phenoxy-groups. To our best knowledge, the X-ray crystal
structures of the divalent tin compounds containing terminal tert-
butoxy- or phenoxy- ligands are unknown to date. The dimeric
structures observed are obviously determined by the space-geo-
metrical properties of the chelate b-dimethylaminoethoxy-ligand
which facilitate the more favorable trigonal bipyramidal configura-
Compounds 6–10 are white crystalline solids sensitive to air
and moisture. They are soluble in THF and benzene and moderately

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O.V. Chernov et al. / Journal of Organometallic Chemistry 694 (2009) 3184–3189
N
N
Me3Si
Me3Si
SiMe3
SiMe3
SiMe3
Me2NCH2CH2OH
- HN(SiMe3)2
ROH
N
Sn
N
O
Sn
N
O
Sn OR
- HN(SiMe3)2
SiMe3
5
2
R = Me (6), Et (7), iPr (8), tBu (9), Ph (10)
Scheme 2.
Fig. 1. Molecular structure of compounds 9 and 10 (50% probability ellipsoids; labeling A denotes symmetrically equivalent atom relative to the inversion center; hydrogen
atoms are omitted for clarity; coordination bonds are shown by double lines).
tion of the tin atoms with the two axial coordination bonds
(N ? Sn and Sn O(CH2CH2NMe2)).
longer observed in polyol-diisocyanate mixture [72]. The results
of catalytic tests are presented in Table 2, Figs. 3 and 4.
It was found that under argon compounds 1, 2, 9 and 10 are
effective catalysts of polyurethane formation (Fig. 3). As it was ex-
pected, ‘‘gel time” decrease upon increase of catalyst concentration.
In the region of low concentrations below 0.2 mol% the most active
is alkoxy-amide 2. In the region of higher concentrations the most
active is DBTDL, although divalent tin compounds 1, 2, 9 and 10 ex-
hibit relatively high activity. Compounds 1 and 10 are less active at
high concentrations than amido derivative 2 and tert-butoxy deriv-
2.3. Catalytic activity in polyurethane formation
Polyurethanes are usually produced via cross-linking of polyols
and diisocyanates [71]. Catalytic activity of the compounds 1, 2, 9
and 10 in polyurethane formation was compared to industry stan-
dard catalyst – dibutyltin dilaurate (DBTDL). The test system was
equimolar mixture of polyethylene glycol of average molecular
weight 600 (PEG-600, Acros) and hexamethylene diisocyanate
(HDI). ‘‘Gel time” was measured under argon (TAr) and under air
(Tair). The ‘‘gel time” corresponds to the time at which flow is no
Table 1
Selected bond lengths [Å] and angles [°] for 9 and 10.
9
10
Sn(1)?O(1)
Sn(1)?O(2)
2.126(1)
2.030(1)
2.503(1)
2.286(1)
2.118(1)
2.089(1)
2.470(1)
2.245(1)
Sn(1) N(1)
Sn(1) O(1A)*
O(1)?Sn(1)?O(2)
91.79(4)
69.93(4)
91.62(4)
72.23(4)
79.59(4)
140.79(4)
110.07(4)
93.03(4)
69.19(4)
88.39(3)
73.14(3)
81.60(4)
140.36(3)
110.81(4)
O(1)?Sn(1) O(1A)
O(2)?Sn(1) O(1A)
O(1)?Sn(1) N(1)
O(2)?Sn(1) N(1)
N(1) ? Sn(1) O(1A)
Sn(1)?O(1) ? Sn(1A)
*
The labeling A denotes symmetrically equivalent atom relative to the inversion
Fig. 2. A fragment of crystal structure 10 indicating disposition of phenyl groups
center.
relative to Sn2O2 ring plane.

O.V. Chernov et al. / Journal of Organometallic Chemistry 694 (2009) 3184–3189
3187
Table 2
ative 9. We suppose that this is due to chelating effect of dimethyl-
amino alkoxy group in 1 and lower basicity (comparing to amido
and tert-butoxy groups) of phenoxy group in 10.
In case of diamide 5 we were unable to reliably determine ‘‘gel
times” because the spread of results was too high. We suppose that
in absence of supporting dimethylamino ethoxy ligand 5 interacts
with mixture components giving associates of low catalytic activ-
ity. As a result, the ‘‘gel time” is dependent on small deviations
in experiment conditions and rates of addition and mixing of the
reagents.
Under aerobic conditions the activity of DBTDL is the same to
anaerobic conditions (Fig. 4). The activity of divalent compounds
1, 2, and 9 at 1 mol% concentration slightly decreases, although re-
mains high. The decrease of activity of 10 is more pronounced. At
lower concentrations the activity of divalent derivatives decrease
more rapidly than for anaerobic conditions. At concentrations be-
low 0.2 mol% ‘‘gel times” were not reached (>180 min). We sup-
pose that this is due to oxidation and hydrolysis of divalent
derivatives under moist air.
Gel times under argon (TAr) and under air (Tair) for compounds 1, 2, 9, 10 and DBTDL
(min).
Entry
Compound
Catalyst (mol%)
TAr
Tair
1
2
3
4
5
6
7
8
1
1
1
1
1
2
2
2
2
2
9
9
9
9
9
10
1.00
0.50
0.20
0.10
0.05
1.00
0.50
0.20
0.10
0.05
1.00
0.50
0.20
0.10
0.05
1.00
0.50
0.20
0.10
0.05
1.00
0.50
0.20
0.10
0.05
N/A
8.1
10.3
20.1
60.3
–
5.7
7.7
10
11.2
16.2
3.7
6.8
15
8.2
17.8
90.7
–
–
8.8
23.3
–
–
–
4.8
13.5
–
–
–
22.3
–
–
–
–
2.1
2.5
4.5
30.1
65.4
–
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
70.1
–
9.8
10.1
45.2
90.5
–
2.0
2.6
4.5
31.8
66.9
–
10
10
10
10
3. Conclusions
DBTDL
DBTDL
DBTDL
DBTDL
DBTDL
No catalyst
A straightforward method of synthesis of heteroleptic tin (II)
dialkoxides (6–10) stabilized by one intramolecular coordination
bond was developed. Dialkoxides 9 and 10 are surprisingly stable
(at least for several hours) in solid state under aerobic conditions.
Compounds 1, 2, 9 and 10 are active catalysts in polyurethane for-
mation under anaerobic conditions.
4. Experimental
4.1. General procedures
All manipulations with air and moisture sensitive compounds
were carried out under purified argon using standard Schlenk
and high-vacuum-line techniques. The commercially available sol-
vents were purified by conventional methods and distilled imme-
diately prior to use [73]. Sn(N(SiMe3)2)2 (5) was synthesized
using published procedure [74]. NMR spectra were recorded on
an AVANCE-400 NMR spectrometer at 400.13 MHz (1H) and
100.62 MHz (13C) in THF-d8 or C6D6. Chemical shifts are indirectly
referenced to tetramethylsilane (SiMe4) via the solvent signals. The
accuracy of chemical shift measurements is 0.01 ppm (1H) and
0.05 ppm (13C). Elemental analyses were performed on a Carlo
Erba EA1108 CHNS-O elemental analyzer.
Fig. 3. Gel time for 1, 2, 9 and 10 and DBTDL under argon (TAr, min).
4.2. X-ray structure determination
Data were collected on a Bruker SMART APEX II CCD diffractom-
eter (k(Mo Ka)-radiation, graphite monochromator, x and u scan
mode) and corrected for absorption [75]. For details, see Table 3.
The structures were determined by direct methods and refined by
full-matrix least squares technique with anisotropic thermal
parameters for non-hydrogen atoms. The hydrogen atoms were
placed in calculated positions and refined in riding model with fixed
thermal parameters (Uiso(H) = 1.5Ueq(C) for the CH3-groups and Ui-
so(H) = 1.2Ueq(C) for the other groups). All calculations were carried
out by use of the SHELXTL PLUS (Version 6.12) program package [76].
4.3. Sn(OCH2CH2NMe2)(N(SiMe3)2) (2)
To a solution of Sn(N(SiMe3)2)2 (45.7 g, 0.104 mol) in 50 ml THF
9,28 g (0.104 mol) of N,N-dimethylaminoethanol was added. After
stirring for 30 min the solvent was removed in vacuo at 0.1 mm
Hg, and the residue was recrystallized from hexane. Yield of
Fig. 4. Gel time for 1, 2, 9 and 10 and DBTDL in air (Tair, min).

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O.V. Chernov et al. / Journal of Organometallic Chemistry 694 (2009) 3184–3189
Table 3
0.242 g (4.03 mmol) of i-propanol to give 0.685 g (67%) of white so-
Crystallographic data for 9 and 10.
lid. Anal. Calc. for C7H17NO2Sn (mol wt 265.93): C, 31.62; H, 6.44;
N, 5.27. Found: 31.55; H, 6.56; N, 5.20%. 1H NMR (THF-d8): d 1.09
(d, JHH = 5.9 Hz, 6H, Me2CH), 2.28 (s, 6H, Me2N), 2.59 (br. s, 2H,
CH2N), 3.83 (t, JHH = 5.2 Hz, 3H, CH2O), 4.27 (sept., JHH = 5.9 Hz,
1H, CH). 13C NMR (THF-d8): d 29.6 (Me2CH), 43.5 (Me2N), 59.8
(CH2N), 61.0 (CH2O), 64.0 (CH).
9
10
Empirical formula
Formula weight
Temperature (K)
Crystal size (mm)
Crystal system
Space group
a (Å)
C16H38N2O4Sn2
559.86
100(2)
0.25 ꢁ 0.25 ꢁ 0.20
Monoclinic
P21/c
10.9437(4)
9.0826(4)
11.9307(5)
90
106.907(1)
90
1134.62(8)
2
1.639
560
C20H30N2O4Sn2
599.84
100(2)
0.20 ꢁ 0.15 ꢁ 0.12
Orthorhombic
Pbca
13.0745(4)
12.9669(7)
13.6824(7)
90
4.7. Sn(OCH2CH2NMe2)(OtBu) (9)
b (Å)
c (Å)
The compound was prepared according to the procedure for 6
from 1.390 g (3.79 mmol) of Sn(OCH2CH2NMe2)(N(SiMe3)2) and
0.296 g (4.00 mmol) of tert-butanol to give 0.764 g (72%) of white
solid. The structure was proven by X-ray analysis. Anal. Calc. for
C8H19NO2Sn (mol wt 279.95): C, 34.32; H, 6.84; N, 5.00. Found: C,
34.25; H, 6.90; N, 5.14%. 1H NMR (THF-d8): d 1.24 (s, 9H, Me3C),
2.28 (s, 6H, Me2N), 2.50 (br. t, JHH = 5.2 Hz, 2H, CH2N), 3.85 (br. t,
JHH = 5.2 Hz, 2H, CH2O). 13C NMR (THF-d8): 31.8 (Me3C), 35.7
(Me2N), 43.7 (CH2N), 61.3 (CH2O).
a
(°)
b (°)
(°)
90
90
c
Volume (Å3)
Z
2319.66(19)
4
1.718
1184
2.179
Dcalc (g/cm3)
F(0 0 0)
l
(1/mm)
2.220
60
2hmax (°)
Index range
60
ꢂ15 6 h 6 15
ꢂ12 6 k 6 12
ꢂ16 6 l 6 16
14 327 (Rint = 0.0250)
3285
ꢂ18 6 h 6 18
ꢂ18 6 k 6 18
ꢂ19 6 l 6 19
77 220 (Rint = 0.0312)
3341
4.8. Sn(OCH2CH2NMe2)(OPh) (10)
No. of reflections collected
No. of unique reflections
No. of reflections with I > 2
Data/restraints/parameters
The compound was prepared according to the procedure for 6
from 1.850 g (5.05 mmol) of Sn(OCH2CH2NMe2)(N(SiMe3)2) and
0.498 g (5.30 mmol) of phenol. The product was recrystallized
from THF to give 1.12 g (74%) of white solid. The structure was pro-
ven by X-ray analysis. Anal. Calc. for C8H19NO2Sn (mol wt 299.94):
C, 40.04; H, 5.04; N, 4.67. Found: C, 39.95; H, 5.07; N, 4.58%. 1H
NMR (THF-d8): d 2.20 (s, 6H, Me2N), 2.55 (t, JHH = 5.3 Hz, 2H,
CH2O), 3.62 (t, JHH = 5.3 Hz, 2H, CH2N), 6.54 (t, JHH = 7.1 Hz, 1H, p-
Ph), 6.66 (d, JHH = 8.1 Hz, 2H o-Ph,), 7.01 (t, JHH = 8.1 Hz, 2H, m-
Ph). 13C NMR (THF-d8): d 43.2 (Me2N), 59.0 (CH2N), 60.4 (CH2O),
117.1 (o-Ph), 121.3 (p-Ph), 129.6 (m-Ph).
r(I)
2968
2807
3285/0/114
0.0162; 0.0196
0.0363; 0.0375
1.002
3341/0/129
0.0147; 0.0201
0.0341; 0.0372
1.016
R1; wR2 (I > 2r(I))
R1; wR2 (all data)
Goodness-of-fit (GOF) on F2
Tmin; Tmax
0.586; 0.646
0.666; 0.777
Sn(OCH2CH2NMe2)(N(SiMe3)2) was 25.8 g (67%) as a white solid.
Anal. Calc. for C10H28N2OSi2Sn (mol wt 367.22): C, 32.71; H, 7.69;
N, 7.63. Found: C, 32.94; H, 7.87; N, 7.46%. 1H NMR (C6D6): d
2
0.43 (s, JSiH = 5.8 Hz, 18H, Me3Si), 1.98 (s, 6H, Me2N), 2.23 (br. t,
3JHH = 5.3 Hz, 2H, CH2N), 3.71 (t, JHH = 5.3 Hz, 2H, CH2O). 13C
3
3
NMR (C6D6):
d
7.41 (1JSiC = 54.6, JSnNSiC = 37.3, Me3Si), 44.3
4.9. Standard polymerization procedure
(Me2N), 57.88 (CH2N), 61.1 (CH2O).
All test samples were prepared under an argon atmosphere.
Samples were prepared by taking a known mass of the precatalyst
and diluting it with THF until it reached the desired percent con-
centration. The starting materials for the gel time were measured
with 1.68 g (10 mmol) of hexamethylene diisocyanate (HMDI)
and 6.00 g (10 mmol) of polyethyleneglycol (PEG-600). To this
mixture was added 0.25 ml of stock solution to produce the desired
concentration of the precatalyst, and the contents were mixed.
From this, two samples are produced: one is left stirring under
an argon atmosphere and the other is left stirring exposed to air.
The samples were checked frequently, and the time it took for
the samples to gel is recorded for both.
4.4. Sn(OCH2CH2NMe2)(OMe) (6)
To
a
solution of 1.36 g Sn(OCH2CH2NMe2)(N(SiMe3)2)
(3.71 mmol) in 10 ml of THF 0.130 g (4.07 mmol) of methanol
was added. After stirring for 30 min the solvent was removed in va-
cuo at 0.1 mmHg, and the residue was recrystallized from hexane.
Yield of Sn(OCH2CH2NMe2)(OMe) was 0.710 g (81%) as a white so-
lid. Anal. Calc. for C5H13NO2Sn (mol wt 237.87): C, 25.25; H, 5.51;
N, 5.89. Found: C, 25.12; H, 5.57; N, 5.73%. 1H NMR (THF-d8): d 2.27
(s, 6H, Me2N), 2.49 (t, JHH = 5.3 Hz, 2H, CH2N), 3.58 (br. s, 3H, MeO),
3.87 (t, JHH = 5.3 Hz, 2H, CH2O). 13C NMR (THF-d8): d 43.7 (Me2N),
50.8 (MeO), 58.6 (CH2N), 61.0 (CH2O).
5. Supplementary material
4.5. Sn(OCH2CH2NMe2)(OEt) (7)
CCDC 709480 and 709481 contain the supplementary crystallo-
graphic data for 9 and 10. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
The compound was prepared according to the procedure for 6
from 1.727 g (4.71 mmol) of Sn(OCH2CH2NMe2)(N(SiMe3)2) and
0.232 g (4.95 mmol) of ethanol to give 0.890 g (75%) of white solid.
Anal. Calc. for C6H15NO2Sn (mol wt 251.90): C, 28.61; H, 6.00; N,
5.56. Found: C, 28.52; H, 6.07; N, 5.48%. 1H NMR (THF-d8): d 1.13
(t, JHH = 5.4 Hz, 3H, CH3CH2O), 2.27 (s, 6H, Me2N), 2.53 (t,
JHH = 5.4 Hz, 2H, CH2N), 3.83 (t, JHH = 5.4 Hz, 2H, OCH2CH2N), 3.88
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