Reactivity of a C,N-chelated stannoxane

Article abstract of DOI:10.1021/om801037b

The stannylene {2-[(CH3)2NCH2]2C6H4}2Sn (1) did not react with CO2 at room temperature and atmospheric pressure, but its oxidation product {{2-[(CH3)2NCH2]2C6H4}2Sn- (fi-O)}2 (2)is very reactive toward CO2 to give the cyclic compound {{2-[(CH3)2NCH2]2C6H4

Full text of DOI:10.1021/om801037b

Organometallics 2009, 28, 2629–2632
2629
Reactivity of a C,N-Chelated Stannoxane†
Zdenˇka Padeˇlkova´,‡ Hana Vanˇka´tova´,‡ Ivana C´ısaˇrova´,§ Mikhail S. Nechaev,|
Thomas A. Zevaco, Olaf Walter, and Alesˇ Ru˚zˇicˇka*,‡
Department of General and Inorganic Chemistry, Faculty of Chemical Technology,
ˇ
UniVersity of Pardubice, na´m. Cs. legi´ı 565, CZ-532 10 Pardubice, Czech Republic, Department of
Inorganic Chemistry, Faculty of Natural Science, Charles UniVersity in Prague, HlaVoVa 2030, 128 40
Praha 2, Czech Republic, Department of Chemistry, LomonosoV State UniVersity, 1 Leninskie Gory,
Moscow 119992, Russia, and Forschungszentrum Karlsruhe GmbH, Institut fu¨r Technische Chemie,
Bereich Chemisch-Physikalische Verfahren, Hermann-Von-Helmholtz-Platz 1,
76344 Eggenstein-Leopoldshafen, Germany
ReceiVed October 29, 2008
Summary: The stannylene {2-[(CH3)2NCH2]2C6H4}2Sn (1) did
not react with CO2 at room temperature and atmospheric
pressure, but its oxidation product {{2-[(CH3)2NCH2]2C6H4}2Sn-
(µ-O)}2 (2) is Very reactiVe toward CO2 to giVe the cyclic
compound {{2-[(CH3)2NCH2]2C6H4}2Sn}2(µ-O)(µ-CO3) (2b).
The product of reaction of 2 with silicon grease is also a cyclic
compound with an eight-membered ring, {{{2-[(CH3)2NCH2]2-
C6H4}2Sn}(Me2SiO)}2 (2c), as the structural characterization
reVealed (XRD). Triphenylsilanol condensates with 2 to form
{2-[(CH3)2NCH2]2C6H4}2Sn(OSiPh3)2 (2b). The reaction of 2
with ethylene glycol gaVe the cyclic compound {2-[(CH3)2-
NCH2]2C6H4}2Sn(OCH2CH2O) · 1/2(HOCH2CH2OH) (2e).
The reactivity of higher congeners of carbenes, e.g. silylenes,
germylenes, stannylenes, and plumbylenes, has been studied very
Figure 1. Reactivity of 1.
extensively over the last 20 years.1
The stannylene (LCN)2Sn2 (1), where LCN is the chelating ligand
affords the bridged carbonato species Bu3Sn-OCO2-SnBu34 and
was also observed in the case of C,N-chelated triorganotin(IV)
oxides and hydroxides.5
Similar compounds ((R2Sn)2OCO2) with 5-fold-coordinated tin
atoms were suggested to be products of the reaction of dialkyltin
dihalides with alkali-metal carbonates in water.6
Compound 2b is a cyclic oxo-carbonato-bridged dinuclear
species containing a six-membered, rather puckered ring (Figure
2). The O2 and O3 atoms lie above and below the plane defined
by Sn1, O1, Sn2, CdO(4), and all the nitrogen atoms coordinated
to the tin atoms. It seems that one of the tin atoms (Sn1) is six-
coordinated in a distorted-octahedron-like geometry with nitrogen
donor (N1 and N2) and oxygen bridging atoms in mutual cis
positions and carbon atoms of the ligands in a trans arrangement.
The second tin atom has only one nitrogen atom (N4) coordinated
with an Sn-N distance comparable to that of diorganotin dihalides
with the same ligand.7 The second nitrogen atom is on the border
of possible interaction. The carbonate fragment is bonded to both
tin atoms by oxygen atoms O2 and O3 with bond lengths
comparable to those of the tin-O1 bridge and to those in literature
data. On the other hand, O4 has no interaction to the adjacent
2-((dimethylamino)methyl)phenyl, can be oxidized with excess
oxygen, nitrous oxide, or the TEMPO free radical to give the
dimeric stannoxane [(LCN)2Sn]2(µ-O)2 (2), which is in dynamic
equilibrium with its monomeric form in benzene solution. In the
solid state, the tetraoxatetrastannacycle cyclo-[(LCN)2SnO]4 can be
crystallized from diethyl ether and the trioxatristannacyclic complex
of formula cyclo-[(LCN)2SnO]3 from hexane solution.3 In this paper,
we expand the reactivity studies of 2 toward other reagents.
Results and Discussion
When the oxidation product of 1, [(LCN)2Sn]2(µ-O)2 (2) (obtained
either with oxygen or N2O), was left in air, compound 2b ({{2-
[(CH3)2NCH2]2C6H4}2Sn}2(µ-O)(µ-CO3)) was isolated as the sole
product after a few minutes (Figure 1). This behavior is similar to
the well-known reaction of Bu3Sn-O-SnBu3 with CO2, which
* To whom correspondence should be addressed. Fax: +420-466037068.
E-mail: ales.ruzicka@upce.cz.
† First presented during the XVIth FECHEM Conference on Organo-
metallic Chemistry, Budapest, Hungary, Sept 3-8, 2005, Poster No. 166.
‡ University of Pardubice.
§ Charles University in Prague.
(4) (a) Bloodworth, A. J.; Davies, A. G.; Vasishtha, S. C. J. Chem. Soc.
C 1967, 1309. (b) Smith, P. J.; Hill, R.; Nicolaides, A.; Donaldson, J. D. J.
Organomet. Chem. 1983, 252, 149. (c) Blunden, S. J.; Hill, R.; Ruddick,
J. N. R. J. Organomet. Chem. 1984, 267, C5.
(5) Padeˇlkova´, Z.; Weidlich, T.; Kolarˇova, L.; Eisner, A.; C´ısarˇova´, I.;
Zevaco, T. A.; Ru˚zˇicˇka, A. J. Organomet. Chem. 2007, 692, 5633.
(6) Smith, P. J.; Hill, R.; Nicolaides, A.; Donaldson, J. D. J. Organomet.
Chem. 1983, 252, 149.
(7) (a) Nova´k, P.; Brus, J.; C´ısaˇrova´, I.; Ru˚zˇicˇka, A.; Holec`ek, J. J.
Fluorine Chem. 2005, 126, 1531. (b) Nova´k, P.; Padeˇlkova´, Z.; Kolarˇova,
L.; Brus, J.; Ru˚zˇicˇka, A.; Holecˇek, J. Appl. Organomet. Chem. 2005, 19,
1101.
| Lomonosov State University.
Forschungszentrum Karlsruhe GmbH, Institut fu¨r Technische Chemie.
(1) (a) Davies, A. G. Organotin Chemistry; VCH: Weinheim, Germany,
1997, 2004. (b) Driess, M.; Gru¨tzmacher, H. Angew. Chem., Int. Ed. Engl.
1996, 35, 828. (c) Weidenbruch, M. Eur. J. Inorg. Chem. 1999, 373. (d)
Weidenbruch, M. J. Organomet. Chem. 2002, 646, 39. (e) Jutzi, P.; Burford,
N. Chem. ReV. 1999, 99, 969.
(2) Angermund, K.; Jonas, K.; Kruger, C.; Latten, J. L.; Tsay, Y.-H. J.
Organomet. Chem. 1988, 353, 17.
ˇ
(3) Padeˇlkova´, Z.; Nechaev, M. S.; Cernosˇek, Z.; Brus, J.; Ru˚zˇicˇka, A.
Organometallics 2008, 27, 5303.
10.1021/om801037b CCC: $40.75
2009 American Chemical Society
Publication on Web 03/30/2009

2630 Organometallics, Vol. 28, No. 8, 2009
Notes
Figure 2. ORTEP presentation at the 50% probability level of the
molecular structure of 2b. Hydrogen atoms are omitted for clarity.
Selected interatomic distances (Å) and angles (deg): Sn(1)-O(1) )
1.988(3), Sn(1)-O(2) ) 2.079(4), Sn(2)-O(1) ) 1.966(4), Sn(2)-O(3)
) 2.080(4), Sn(1)-N(1) ) 2.653(5), Sn(1)-N(2) ) 2.614(4),
Sn(2)-N(3) ) 2.874(5), Sn(2)-N(4) ) 2.544(4), C(100)-O(2) )
1.312(2), C(100)-O(3) ) 1.322(2), C(100)-O(4) ) 1.215(8);
O(3)-Sn(2)-N(4) ) 164.23(14), Sn(2)-O(1)-Sn(1) ) 121.29(19),
O(4)-C(100)-O(2) ) 121.4(5).
Figure 3. ORTEP presentation at the 50% probability level of the
molecular structure of 2c. Hydrogen atoms are omitted for clarity.
Selected interatomic distances (Å) and angles (deg): Sn(1)-O(1) )
1.9951(19), Sn(1)-O(2) ) 1.9962(19), Sn(1)-C(21) ) 2.126(3),
Sn(1)-C(11) ) 2.131(3), Si(1)-O(2) ) 1.613(2), Si(1)-O(1) )
1.620(2),Sn(1)-N(1))2.717(2),Sn(1)-N(2))2.736(3);O(1)-Sn(1)-O(2)
) 98.98(8), O(2)-Si(1)-O(1) ) 112.53(11), Si(1)-O(1)-Sn(1) )
134.11(12), Si(1)-O(2)-Sn(1) ) 137.31(12).
acceptor atoms, and from C100-O4 bond shortening in comparison
with O2 and O3, the double-bond character is clearly seen.
In the 119Sn NMR spectra of 2b at various temperatures, there
is only a slight dependence of chemical shift observed (-309.2
ppm at 350 K and -315.8 ppm at 220 K) typical for six-coordinate
fortuitous results8 where silicone grease is incorporated into the
structure, but only the tricyclic ring system reported by Pannell
and co-workers is a tin-containing species.9 However in our case,
2c is more likely the product of a “transesterification” of (Me2SiO)n
with [(LCN)2Sn]2(µ-O)2 than a product of hydrolysis and self-
assembly as in Pannell’s case (t-Bu4Sn(Me2Si)O3 · t-Bu2Sn(OH)2).9
The same C,C-transoid geometry is concluded from two broad
1
species. On the other hand, in the H NMR spectra two sets of
signals appear for each nonequivalent NCH2 group as two AX
patterns. All signals coalesce as the temperature is increased to
very broad signals at 350 K. For the carbonate group in the 13C
NMR spectrum, over the whole temperature range there is only
one sharp signal at 161.9 ppm with tin satellites visible, which
corresponds to recently published bridging carbonates with no
interaction of the CdO group.5 Also in the IR spectrum, the
wavelength 1587 cm-1 similar to previous findings supports the
suggestion that the structure of 2b is the same in the solid and in
solution.
1
signals for NCH2 groups found in the H NMR spectrum of 2c.
The tin atoms in 2c are again six-coordinated, as seen from the
119Sn NMR spectrum and chemical shift value (- 359.9 ppm)
compared to similar compounds.
Similar systems10 revealed two main structural motifs, chair-
and boatlike, where n-butylferrocenylsilyl-10a and diphenylsilyl-
substituted10b systems are boatlike, tert-butylsilyl species10c oscillate
between both extremes, and isopropylsilyl-substituted10e systems
were found to be almost planar. The structure of 2c can be related
to the structure of compounds where two 3-(dimethylamino)propyl
groups are chelating ligands and the silicon atom is substituted by
two phenyl groups.10d 2c has a chairlike structure with both tin
atoms in a distorted -octahedral geometry, where the C,C-transoidal
arrangement is applied. The C1-Sn-C11 angle is 143.85(11)°,
in comparison to the compound described in ref 10d to be
154.5(2)°. Two intramolecular connections, Sn(1)-N(1) ) 2.717(2)
Å and Sn(1)-N(2) ) 2.736(3) Å, which complete the octahedral
coordination geometry, are medium strong and comparable to those
in 2b and previously reported bis-chelated dihalides.7
In view of this reactivity of complex 2 with carbon dioxide, the
stannoxane 2 was tested as a catalyst for the formation of cyclic
carbonates and aliphatic polycarbonates by reaction of epoxides
with CO2. Propylene oxide and cyclohexene oxide were used in
preliminary screening tests. Only the test involving propylene oxide
and complex 2 showed the formation of propylene carbonate in
measurable amounts (yield estimated to be under 5% molar),
without formation of the related aliphatic polycarbonate. The
reaction with cyclohexene oxide did not lead to the formation of
organic carbonates. Other catalytic tests carried out with ethanol,
carbon dioxide, and triethyl orthoacetate (as water-trapping agent)
in order to produce a carbonic acid hemiester (LSn-CO2-OEt)
or, better, diethyl carbonate were also unsuccessful.
(8) Haiduc, I. Organometallics 2004, 23, 3.
(9) Lee, F. C.; Sharma, H. K.; Haiduc, I; Pannell, K. H. J. Chem. Soc.,
Dalton Trans. 1998, 1.
A hypothetical mechanism for the formation of propylene
carbonate in the presence of compound 2 is proposed in Figure
S2 (Supporting Information).
(10) (a) Reyes-Garcia, E. A.; Cervantes-Lee, F.; Pannell, K. H. Orga-
nometallics 2001, 20, 4734. (b) Beckmann, J.; Mahieu, B.; Nigge, W.;
Schollmeyer, D.; Schurmann, M.; Jurkschat, K. Organometallics 1998, 17,
5697. (c) Beckmann, J.; Jurkschat, K.; Schurmann, M.; Dakternieks, D.;
Lim, A. E. K.; Lim, K. F. Organometallics 2001, 20, 5125. (d) Beckmann,
J.; Jurkschat, K.; Kaltenbrunner, U.; Pieper, N.; Schurmann, M. Organo-
metallics 1999, 18, 1586. (e) Englich, U.; Prass, I.; Ruhlandt-Senge, K.;
Schollmeier, T.; Uhlig, F. Monatsh. Chem. 2002, 133, 931.
An unusual product of the accidental “transesterification” of
silicone grease ({{{2-[(CH3)2NCH2]2C6H4}2Sn}(Μe2SiO)}2 (2c))
(Figure 3) could be also isolated as a minor product when 2a was
refluxed in toluene under an argon atmosphere in order to remove
water and prepare 2. 2c can be compared to various related

Notes
Organometallics, Vol. 28, No. 8, 2009 2631
Figure 4. ORTEP presentation at the 50% probability level of the
molecular structure of 2d. Hydrogen atoms and one of the independent
molecules are omitted for clarity. Selected interatomic distances (Å)
and angles (deg), with appropriate parameters for the geometrically
independent molecule given in parentheses: Sn(1)-O(1) ) 2.008(3)
(2.005(4)), Sn(1)-O(2) ) 1.997(3) (1.987(4)), Sn(1)-N(1) ) 2.605(4)
(2.663(5)), Sn(1)-N(2) ) 2.715(4) (2.675(15)), Si(1)-O(1) ) 1.590(3)
(1.590(4)), Si(2)-O(2) ) 1.592(3) (1.594(4)); O(1)-Sn(1)-O(2) )
95.19(14) (96.38(16)), Si(1)-O(1)-Sn(1) ) 172.9(2) (172.1(2)),
Si(2)-O(2)-Sn(1) ) 175.0(2) (177.5(3)), N(1)-Sn(1)-O(1) )
170.58(13) (168.46(14)), N(2)-Sn(1)-O(2) ) 169.67(13) (171.9(3)).
Figure 5. ORTEP presentation at the 50% probability level of the
molecular structure of 2e · 1/2HOCH2CH2OH. Hydrogen atoms and the
ethylene glycol molecule are omitted for clarity. Selected interatomic
distances (Å) and angles (deg): Sn(1)-O(1) ) 2.0360(19), Sn(1)-O(2)
) 2.058(2), Sn(1)-N(1) ) 2.519(2), Sn(1)-N(1) ) 2.640(2);
O(1)-Sn(1)-O(2) ) 83.36(8), O(2)-Sn(1)-N(1) ) 163.01(8).
the CO2 unit in 2b is quite labile. This could be the reason for the
high catalytic activity of 2b in the formation of carbonates.
Experimental Section
General Methods. NMR Spectroscopy. The NMR spectra were
recorded as solutions in toluene-d8 or benzene-d6 on a Bruker Avance
500 spectrometer (equipped with Z-gradient 5 mm probe) at 220-300
K for 1H (500.13 MHz) and 119Sn{1H} (186.50 MHz). The solutions
were obtained by dissolving 40 mg of each compound in 0.5 mL of
deuterated solvent. 13C{1H} NMR spectra were measured at 90.35
MHz in a 5 mm wide-zone tunable sampler. The values of 1H chemical
shifts were calibrated to the internal standard tetramethylsilane (δ(1H)
0.00 ppm) or to residual signals of benzene (δ(1H) 7.16 ppm), toluene
(δ(1H) 2.09 ppm). The values of 13C chemical shifts were calibrated
to signals of benzene (δ(13C) 128.3 ppm), and 119Sn chemical shifts to
external Me4Sn (0.0 ppm).
X-ray Crystallography. Data for crystals were collected on a
Nonius KappaCCD diffractometer using Mo KR radiation (λ )
0.710 73 Å), and a graphite monochromator. The structures were solved
by direct methods (SIR9211). All reflections were used in the structure
refinement based on F2 by full-matrix least-squares techniques
(SHELXL9712). Heavy atoms were refined anisotropically. Hydrogen
atoms were mostly localized on a difference Fourier map; however,
to ensure uniformity of the treatment of the crystal, all hydrogen atoms
were recalculated into idealized positions (riding model) and assigned
temperature factors Uiso(H) ) 1.2[Ueq(pivot atom)] or of 1.5Ueq for
the methyl moiety. Absorption corrections were carried out using
Gaussian integration from the crystal shape for 2b,d,13 by SORTAV
for 2e · 1/2HOCH2CH2OH,14 or by SADABS15 for 2c. The disorder
of one of the ligands in one of the two independent molecules in 2d
was solved by splitting appropriate atoms to two positions.
To evaluate this reactivity, the reaction of oxide 2 and 2 equiv
of triphenylsilanol was carried out. The hexane solution of the
reaction mixture became opalescent immediately, yielding 2d
essentially quantitatively. 2d is unstable in air and in moist
chloroform solution is converted to carbonate 2b and oxide
dihydroxide 2a. The 119Sn NMR shift value (-355.4 ppm) for 2d
in benzene solution is close to the shift found for 2c and is attributed
to the six-coordinate tin atom in solution. The 1H as well as 119Sn
NMR spectra reveal patterns similar to those found for 2c, where
these are due to the C,C-transoid geometry and mutual cis positions
for nitrogen donors (Figure 4) similarly as found for 2b,c and for
bis-chelated tin dihalides.7
The reaction of [(LCN)2Sn]2(µ-O)2 with an excess of ethylene
glycol also was examined. In refluxing toluene solution using a
Dean-Stark apparatus, the reaction gave after crystallization a
complex product of composition {2-[(CH3)2NCH2]2C6H4}2-
Sn(OCH2CH2O) · 1/2HOCH2CH2OH (2e · 1/2HOCH2CH2OH (Fig-
ure 5 and Figure S2 (Supporting Information)), whose excess
ethylene glycol could be removed by vacuum distillation to give
{2-[(CH3)2NCH2]2C6H4}2Sn(OCH2CH2O) (2e).
The structure of 2e · 1/2HOCH2CH2OH is comparable to the
structures of 2b-d, where the intramolecular Sn-N contacts in
this complex are a bit stronger, probably due to strain in the five-
membered ring. Each of the two molecules of 2e are interconnected
through one molecule of ethylene glycol via H bridges (Figure S2
(Supporting Information); the OH · · · O distance is 2.661(3) Å).
On the basis of the NMR parameters and the spectral patterns,
also the structure of 2e in solution seems to be very close to those
of the aforementioned structures 2b-d.
The activation of the aforementioned molecules was studied by
a theoretical approach as well (see the Supporting Information).
Thermodynamic parameters of reactions of 2 with CO2, silicon
grease, and ethylene glycol were calculated theoretically (Scheme
S1, Supporting Information). Addition of one molecule of CO2 to
2, yielding 2b, is exothermic (∆H° ) -12.2 kcal/mol), but the
Gibbs free energy is slightly positive (∆G° ) 0.4 kcal/mol). Thus,
A full list of crystallographic data and parameters, including
fractional coordinates, has been deposited at the Cambridge Crystal-
(11) Altomare, A.; Cascarone, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 1045.
(12) Sheldrick, G. M. SHELXL-97, A Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(13) Coppens, P. In Crystallographic Computing; Ahmed, F. R., Hall,
S. R., Huber, C. P., Eds.; Munksgaard: Copenhagen, 1970; pp.
255-270.
(14) Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421.
(15) SADABS is an empirical absorption correction program using the
method described by: Blessing, R. H. Acta Crystallogr. 1995, A51. Sheldrick,
G. M. SADABS; University of Go¨ttingen, Go¨ttingen, Germany, 1989.

2632 Organometallics, Vol. 28, No. 8, 2009
Notes
lographic Data Center, 12 Union Road, Cambridge CB2 1EZ, U.K.
(fax, int. code +44(1223)336-033; e-mail, deposit@ccdc.cam.ac.uk)
with CCDC deposition numbers 684119-684124.
2-[(CH3)2NCH2]2C6H4}2SnBr2 and 2c. (ii) 2 (1 g, 1.25 mmol) was
refluxed with hexamethyltrisiloxane (0.3 g, 1.25 mmol) or octameth-
ylcyclotrisiloxane (0.37 g, 1.25 mmol) in xylene for 12 h. The solvent
was removed by vacuum and the crude product washed twice with
warm hexane (30 mL). The solid was extracted with dichloromethane
to give after crystallization 0.15 g of 2c as a white solid (yield 13%).
1H NMR (500.13 MHz, C6D6, 300 K, ppm): 8.28 (broad, 4H, H(6));
Calculation Procedure. All calculations were done at the DFT
level of theory. Geometry optimizations were carried out using the
PBE generalized gradient functional.16,17 The triple-ꢀ valence basis
set including polarization functions TZ2P {3,1,1/3,1,1/1,1} for Sn, C,
N, and O atoms and {3,1,1/1) for H atoms was used. The innermost
electrons for Sn, C, N, and O atoms were treated using the ECP-SBKJC
relativistic effective core potentials.18 Total energies E, zero-point
vibration energies ZPE, E° ) E + ZPE, H°, and G° were calculated
for all stationary points. Vibration frequencies were used to characterize
stationary points as minima. All calculations were performed using
the PRIRODA program.19 The same approach and program were
previously used in studies of various types of germanium and tin
compounds.20
3
7.34 (m, 8H, H(4,5)); 6.85 (d, 4H, H(3), J(1H,1H) ) 7.0 Hz); 3.53
and 2.96 (two broad signals, 8H, NCH2); 1.81 (broad, 24H, N(CH3)2);
0.07 (s, 8H, SiMe2). 119Sn{1H} NMR (C6D6, 300 K, ppm): -359.9.
Anal. Found: C, 50.2; H, 6.2; N, 5.8. Calcd for C40H60N4O4Si2Sn2
(954.50): C, 50.33; H, 6.34; N, 5.87. Mp: 222-225 °C.
{2-[(CH3)2NCH2]2C6H4}2Sn(OSiPh3)2 (2d). This compound was
prepared by mixing 2 (1 g, 1.25 mmol) and 2 equiv of Ph3SiOH (2.04
g, 7.4 mmol) in benzene (20 mL). Immediate formation of opalescence
was observed and the solvent removed in vacuo. The remaining white
solid was crystallized from diethyl ether, giving 2.18 g of 2d (93%
yield). 1H NMR (500.13 MHz, C6D6, 300 K, ppm): 8.45 (d, 2H, H(6),
3J(1H,1H) ) 6.8 Hz, 3J(1H,119Sn) ) 78 Hz); 7.79 (d, 12H, H (ortho-
Synthetic Procedures. (LCN)2Sn (1)2 and {{2-[(CH3)2-
NCH2]2C6H4}2Sn(µ-O)}2 (2).3 These compounds were prepared
according to published procedures. All solvents and starting compounds
were obtained from commercial sources (Sigma-Aldrich). Stopcocks
were greased and additional experiments made using Dow Corning
high-vacuum grease. Toluene, THF, diethyl ether, benzene, n-hexane,
and n-pentane were dried over and distilled from sodium, degassed,
and stored over potassium mirror under argon. CO2 was absorbed from
air or used dry from a cylinder to give the same results. Standard
Schlenk techniques were used for all manipulations under an argon
atmosphere.
{{2-[(CH3)2NCH2]2C6H4}2Sn}2(µ-O)(µ-CO3) (2b). This com-
pound was prepared by bubbling dried CO2 into a Et2O solution (ca.
10% w/w) of 2 (2 g, 2.5 mmol) for 5 min. A white precipitate of 2b
was washed with pentane (10 mL) and crystallized from THF to give
1.77 g of white solid (yield 84%). 1H NMR (500.13 MHz, C6D6, 300
3
SiPh), J(1H,1H) ) 6.6 Hz); 7.34 (m, 4H, H(4,5)); 7.31 (m, 18H, H
(meta and para SiPh)); 7.01 (m, 2H, H(3)); 3.57 and 2.78 (AX spin
system, 4H, NCH2); 1.48 (s, 12H, N(CH3)2). 119Sn{1H} NMR (C6D6,
300 K, ppm): - 355.6. Anal. Found: C, 69.3; H, 6.0; N, 3.1. Calcd
for C54H54N2O2Si2Sn (937.91): C, 69.15; H, 5.8; N, 2.99. Mp: 237-240
°C.
{2-[(CH3)2NCH2]2C6H4}2Sn(OCH2CH2O) (2e). An excess of
ethylene glycol (5 mL, 71.6 mmol) and 2 (1 g, 1.25 mmol) were
refluxed in benzene (30 mL) in a Dean-Stark apparatus for 3 h, giving
a white solid after vacuum evaporation. The solid was washed with
1
hexane and crystallized from diethyl ether in 74% yield. H NMR
(500.13 MHz, C6D6, 300 K, ppm): 7.95 (broad, 2H, H(6), 3J(1H,119Sn)
) 86 Hz); 7.28 (broad, 4H, H(4,5)); 7.10 (broad, 2H, H(3)); 3.63
(broad, 4H, OCH2); 3.46 (s, 4H, NCH2); 2.06 (s, 12H, N(CH3)2).
119Sn{1H} NMR (C6D6, 300 K, ppm): -243.6. Anal. Found: C, 53.6;
H, 6.2; N, 6.2. Calcd for C20H28N2O2Sn (447.15): C, 53.72; H, 6.31;
N, 6.26. Mp: 230-232 °C. Single crystals of 2e · 1/2HOCH2CH2OH
were obtained by crystallization of the crude product from ethylene
glycol.
3
3
K, ppm): 7.95 (d, 2H, H(6), J(1H,1H) ) 6.8 Hz, J(1H,119Sn) ) 68
Hz); 7.56 (d, 2H, H(6), J(1H,1H) ) 6.6 Hz, J(1H,119Sn) ) 72 Hz);
7.36, 7.27, 7.21 (m, 8H, H(4,5)); 7.09, 6.85 (d and d of d, 4H, H(3));
3.80, 3.69, 3.49, 3.23 (four equivalent doublets, 8H, NCH2); 2.01 and
1.92 (broad singlets, 24H, N(CH3)2). 13C{1H} NMR (CDCl3, 300 K,
ppm): 161.9 (3J(13C,119Sn) ) 21.5 Hz), 142.9, 142.6, 142.1, 140.8,
137.6, 137.0, 130.2, 129.0, 128.7, 128.2, 127.8, 127.6, 127.2, 126.6,
126.4, 125.3, 124.8, 64.7, 64.4, 46.2. 119Sn{1H} NMR (C6D6, 300 K,
ppm): - 311.9, (3J(119Sn,117Sn) ) 286 Hz). IR (in KBr): 1587 cm-1
as ν3 of CO32-. Anal. Found: C, 52.3; H, 5.6; N, 6.5. Calcd for
C37H48N4O4Sn2 (850.20): C, 52.27; H, 5.69; N, 6.59. Mp: 226-230
°C with loss of CO2 (detected by DSC).
3
3
Catalytic Tests. The tests were performed in stainless steel
autoclaves with a separated loop to allow easy handling of the catalyst
under argon and its reaction with a definite epoxide/CO2 mixture (ca.
80 °C and 80 bar CO2) similar to the procedure reported in detail in
earlier contributions.21 IR and H and 13C NMR spectroscopy was
1
used to assess the nature of the carbonate (cyclic monomer or polymer)
and evaluate the efficiency of the CO2 insertion. The tests were carried
out using a 1:1000 catalyst to substrate molar ratio and a large excess
of carbon dioxide (a ca. 2- to 3-fold excess relative to the epoxide), in
agreement with standard procedures reported in the relevant CO2
literature.22
{{{2-[(CH3)2NCH2]2C6H4}2Sn}(Me2SiO)}2 (2c). This compound
was first observed as a minority product when 2a was refluxed in
toluene in a Dean-Stark apparatus, in order to prepare 2, as a product
of reaction with silicone grease used for greasing of apparatus joints.
2c can be prepared by two alternative pathways. (i) 2-[(CH3)2NCH2]2-
C6H4}2SnBr2 (1 g, 1.83 mmol), Me2SiCl2 (0.236 g, 1.83 mmol), and
4 equiv of NaOH (0.3 g) were stirred overnight in 20 mL of benzene
and 20 mL of water. After separation of layers, the organic phase was
dried with sodium sulfate and evaporated in vacuo. The crude product
Acknowledgment. The Pardubice group thanks the Grant
Agency of the Czech Republic (Grant No. 104/09/0829) and
the Ministry of Education of the Czech Republic (No. VZ
0021627501) for financial support.
was extracted with dichloromethane to give
a mixture of
Supporting Information Available: Text, figures, tables, and CIF
files giving the molecular structure of 2e · HOCH2CH2OH, calculated
energetic parameters, an IR spectrum of the catalytic test product, a
hypothetical mechanism of CO2 activation, and crystallographic
parameters. This material is available free of charge via the Internet
at http://pubs.acs.org.
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