C,N-chelated organotin(IV) trifluoromethanesulfonates: Synthesis, characterization and preliminary studies of its catalytic activity in the direct synthesis of dimethyl carbonate from methanol and CO2

Article abstract of DOI:10.1016/j.jorganchem.2012.02.022

C,N-chelated tri- and diorganotin(IV) halides react with 1 or 2 mol equiv of silver trifluoromethanesulfonate (triflate, AgOTf, OTf = OSO ₂CF₃^-) to give corresponding C,N-chelated organotin(IV) triflates. The triorganotin(IV) triflates of general formula L^CNR₂SnOTf (R = n-Bu (1), Ph (2)) are presumably more stable towards hydrolysis than the diorganotin(IV) triflates L ^CNRSn(OTf)₂ (R = n-Bu (3), Ph (4)). All prepared organotin(IV) triflates bearing the L^CN ligand (where L^CN is 2-(N,N-dimethylaminomethyl)phenyl-) were characterized by multinuclear NMR spectroscopy and elemental analysis. In addition, the structure of 3 was determined by the X-ray diffraction analysis. The catalytic activity of 1, 2 and 3 in the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol was investigated showing promising yield of DMC in the case of reaction promoted by 1.

Full text of DOI:10.1016/j.jorganchem.2012.02.022

Journal of Organometallic Chemistry 708-709 (2012) 82e87
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
C,N-chelated organotin(IV) trifluoromethanesulfonates: Synthesis,
characterization and preliminary studies of its catalytic activity in the direct
synthesis of dimethyl carbonate from methanol and CO2
a
a
a
a
,
b
ꢀ
*
ꢀ
ꢀ
ꢀ ꢁꢀ ꢀ
Petr Svec , Roman Olejník , Zdenka Padelková , Ales Ruzicka , Laurent Plasseraud
a Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, CZ-532 10, Pardubice, Czech Republic
b Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), UMR CNRS 6302, UFR Sciences et Techniques, 9 allée A. Savary, BP 47870, F-21078 DIJON Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
C,N-chelated tri- and diorganotin(IV) halides react with
1
or 2 mol equiv of silver tri-
fluoromethanesulfonate (triflate, AgOTf, OTf ¼ OSO2CFꢀ3 ) to give corresponding C,N-chelated organo-
tin(IV) triflates. The triorganotin(IV) triflates of general formula LCNR2SnOTf (R ¼ n-Bu (1), Ph (2)) are
presumably more stable towards hydrolysis than the diorganotin(IV) triflates LCNRSn(OTf)2 (R ¼ n-Bu (3),
Ph (4)). All prepared organotin(IV) triflates bearing the LCN ligand (where LCN is 2-(N,N-dimethylami-
nomethyl)phenyl-) were characterized by multinuclear NMR spectroscopy and elemental analysis. In
addition, the structure of 3 was determined by the X-ray diffraction analysis. The catalytic activity of 1, 2
and 3 in the direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol was investigated
showing promising yield of DMC in the case of reaction promoted by 1.
Received 19 January 2012
Received in revised form
20 February 2012
Accepted 21 February 2012
Keywords:
Organotin(IV) compounds
C,N-chelating ligand
Trifluoromethanesulfonate
Catalysis
Ó 2012 Elsevier B.V. All rights reserved.
Carbon dioxide
1. Introduction
ligand described in the literature. There are only a few studies
briefly discussing the chemistry of O,C,O- and N,C,N-chelated
Organotin(IV) trifluoromethanesulfonate (abbreviated as tri-
flates or OTf) of general formula R3SnOTf and R2Sn(OTf)2 (R ¼ Me,
n-Bu, Ph) were first reported by Schmeisser et al. in 1970 [1]. During
the years a number of both di- and triorganotin(IV) triflates with
interesting structural motifs (such as double-ladder structures)
have been described [2]. These compounds are usually prepared by
the reactions of organotin(IV) oxides (R2SnO and (R3Sn)2O) with
HOTf [1e3] or treating the respective organotin(IV) halide with
AgOTf [1]. The most important aspects of chemistry of organo-
tin(IV) triflates have been reviewed by Beckmann [4].
organotin(IV) triflates [8,9]. The impulse to establish this field of
chemistry was the report of Sakakura who discovered that triflate
salts are very efficient catalysts in direct synthesis of dimethyl
carbonate [10].
We have recently synthesized and structurally characterized
novel C,N-chelated organotin(IV) trifluoroacetates [11]. The use of
these species bearing the C,N-chelating ligand(s) LCN (where LCN is
2-(N,N-dimethylaminomethyl)phenyl-) as potential catalysts in the
direct synthesis of dimethyl carbonate (DMC) from CO2 and
methanol was investigated, too.
Organotin(IV) triflates can serve as useful Lewis acid catalysts
for a variety of organic reactions. For example, it was found that (n-
Bu)2Sn(OTf)2 can catalyze the Mukaiyama aldol reaction, in which
aldehydes, ketones, and their acetals were completely discrimi-
nated [5]. The same compound also effectively mediates the Rob-
inson annulations [6]. Recently, Otera used structurally similar
organotin(IV) perfluorooctanesulfonates as catalysts for various
carbonecarbon bond-forming reactions [7]. To the best of our
knowledge, there are no organotin(IV) triflates bearing the LCN
Here we report on the preparation and structural investigation
of some novel C,N-chelated organotin(IV) triflates and the use of 1,
2 and 3 as catalyst precursors for the direct synthesis of DMC from
CO2 and methanol.
2. Results and discussion
2.1. General remarks
L
CN(n-Bu)2SnCl [12b], LCNPh2SnCl [12a], LCN(n-Bu)SnCl2 [12b,d]
and LCNPhSnCl2 [12c] reacted with 1 or 2 mol equiv of AgOTf in
* Corresponding author. Tel.: þ420 4 66037151; fax: þ420 466037068.
ꢁꢀ ꢀ
E-mail address: ales.ruzicka@upce.cz (A. Ruzicka).
THF to give corresponding organotin(IV) triflates 1e4 (for
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.02.022

ꢀ
P. Svec et al. / Journal of Organometallic Chemistry 708-709 (2012) 82e87
83
numbering of compounds and NMR numbering of organic
substituents bound to the central tin atom see Scheme 1) while
attempts to prepare mixed organotin(IV) halidesetriflates were not
carried out. Preparation of C,N-chelated organotin(IV) triflates
requires the use of anhydrous THF and strictly anaerobic conditions
due to the presumptive sensitivity of formed products to moisture.
All target products were prepared in satisfactory yields varying
from 56% (for compound 4) to 82% yield in the case of 2. In addition,
doubly C,N-chelated tin(IV) bis(triflate) and C,N-chelated tin(IV)
tris(triflate) were synthesized but all attempts to study the struc-
ture of these two compounds by multinuclear solution NMR
spectroscopy failed for two reasons: i) (LCN)2Sn(OTf)2 is almost
insoluble even in THF-d8 and the use of chlorinated solvents led to
the exchanging of triflate ligands, ii) due to unprecedented reac-
tivity of LCNSn(OTf)3 no solution NMR spectra were recorded since
this compound reacts readily at ambient temperature with the
solvent (THF-d8) to form unidentified polymeric products. Unfor-
tunately, however, both compounds failed to give suitable single
crystals for the X-ray diffraction analysis as well.
constant 1J(19F, 13C) z 319 Hz (CF3 moiety). The resonances of the
CF3 group(s) in the 19F{1H} NMR spectra were found as singlets at
ca. ꢀ77 ppm for all prepared compounds.
The most valuable data about the structure (i.e. the coordination
geometry of the tin atom) of 1e4 in solution always arose from the
119Sn{1H} NMR spectra. According to the 119Sn{1H} NMR spectrum
of 1 in benzene-d6 we suggest partial dissociation of 1 leading to
the formation of an ion pair with [4 þ1] coordinated tin atom. The
ionization is
a well-known feature of organotin(IV) triflates
[2,3,8,9]. The formation of the [LCN(n-Bu)2Sn]þ cation has already
been described for the [LCN(n-Bu)2Sn]þ[Ti2Cl9]ꢀ where the tin atom
resonates at 69 ppm in the 119Sn{1H} NMR spectrum [13]. The
assumption of some degree of ionization of 1 is supported by the
chemical shift value (
d
(
119Sn) ¼ ꢀ1.0 ppm) of the only resonance
found in the 119Sn{1H} NMR spectrum in benzene-d6. The value of
d(
119Sn) is consistent with a tin atom bearing three organic
substituents plus exhibiting the intramolecular N / Sn interaction
which increases the coordination number of the tin atom from 3 to
4. In other words, the resonance is shifted about 50 ppm downfield
relative to the 119Sn{1H} NMR chemical shift value of starting LCN(n-
Bu)2SnCl (
d
(
119Sn) z ꢀ50.0 ppm) where the tin atom is penta-
2.2. Solution NMR studies of 1e4
coordinated with a distorted trigonal-bipyramidal geometry [12b].
Similar results were deduced from the 119Sn{1H} NMR spectra of 1
recorded in methanol-d4 (broad resonance at ꢀ0.5 ppm) or THF-d8
(ꢀ6.7 ppm). On the other hand, the SneO bond cannot be of purely
ionic character and there should be a SneOTf interaction because
measured chemical shifts are nearly in the middle of the range
found for the covalent character in some carboxylates
(w ꢀ80 ppm) and ionic chlorotitanate [13].
Compounds 1e4 were primarily characterized by multinuclear
NMR spectroscopy in solution. Multinuclear NMR spectra of 2e4
compounds were recorded in THF-d8 because of their limited
solubility in other common organic solvents. Multinuclear NMR
spectra of 1 were recorded in benzene-d6 and, in addition, in
methanol-d4 in the air in order to check out the stability of 1
towards air moisture. Based on the data acquired from these
measurements it was found that compound 1 does not react with
air moisture at room temperature, because all the recorded spectral
patterns remained unchanged even when measured again after one
week.
Similarly, the only resonance in the 119Sn NMR spectrum of 2
found at ꢀ162.8 ppm in THF-d8 can be best attributed to the [4 þ1]
coordinate tin-containing species as it is very close to the 119Sn{1H}
NMR chemical shift value of starting LCNPh2SnCl (
d(
119Sn) z ꢀ
176.0 ppm) where the tin atom reveals a distorted trigonal-
bipyramidal geometry (e.g. coordination number being 5) [12a].
The 119Sn{1H} NMR chemical shifts in related diphenyltin(IV)
carboxylates found at wꢀ210 ppm indicate similar weakening of
the SneOTf bond. Despite the fact that the spectrum was recorded
in THF-d8 we did not observe any coordination of the solvent to the
central tin atom in the case of 2.
In contrast to 1 and 2, the coordination of the THF-d8 to the tin
atom in 3 and 4 was detected by the help of the 119Sn{1H} NMR
spectroscopy. Observed 119Sn{1H} NMR chemical shift values of
The chemical shift values, integral intensities and multiplicity of
each signal in the 1H NMR spectra of 1e4 correspond well to
proposed molecular structures with the respect to the number and
nature of organic substituents bound to the tin atom. The value of
the 3J(119Sn, 1H) coupling constant of satellites of the doublet of the
H(60) signal in the 1H NMR spectra is a very useful tool for char-
acterization of all C,N-chelated organotin(IV) compounds. Prepared
triorganotin(IV) triflates exhibit the coupling constant 3J(119Sn, 1H)
of 56.1 Hz in the case of 1 and 64.8 Hz in the case of 2. Corre-
sponding 1H NMR resonances of diorganotin(IV) bis(triflates) 3 and
4 reveal much higher values 3J(119Sn, 1H) of 101.5 Hz and 113.8 Hz,
respectively. This difference is in good agreement with previously
published results [11,12].
both 3 (
d
(
119Sn) ¼ ꢀ350.9 ppm) and 4 (
d
(
119Sn) ¼ ꢀ418.6 ppm) are
shifted about 250 ppm to lower frequencies relative to the starting
L
CN(n-Bu)SnCl2
(
(d(
119Sn) z ꢀ105 ppm) [12b,d] and LCNPhSnCl2
119Sn) z ꢀ167 ppm) [12c]. Based on these facts, and according to
The 13C{1H} and 19F{1H} NMR spectra of 1e4 were recorded in
order to elucidate the presence of the OTf substituent(s). All signals
in the 13C{1H} NMR spectra were in good agreement with expected
patterns for each particular compound (see Experimental for
detailed assignment of all resonances). There is one characteristic
quartet in each 13C{1H} NMR spectra at ca. 121 ppm with coupling
(d
the results of the X-ray diffraction analysis of 3 (vide Infra), it is
unambiguous that the tin atom is six-coordinated with more or less
distorted octahedral geometry in both 3 and 4 bearing the C,N-
chelating ligand, n-Bu/Ph substituent, two OTf moieties and finally
the coordinated THF molecule.
Compound
N(CH3)2
Sn
LCN(n-Bu)2SnOTf
LCNPh2SnOTf
3'
2''
1
2
3''
2'
1
3
1''
4''
4'
4
Sn
1'
2
Sn
6'
5'
LCN(n-Bu)Sn(OTf)2
LCNPhSn(OTf)2
3
4
LCN
n-Bu
Ph
Scheme 1. Table of prepared compounds and the NMR numbering of organic substituents.

ꢀ
84
P. Svec et al. / Journal of Organometallic Chemistry 708-709 (2012) 82e87
2.3. X-ray crystal structure of 3$THF
structure of LCNPhce:inf>)/ce:inf>)2$DMSO which was determined
by the X-ray crystallography in one of our previous papers [11].
Several attempts to crystallize all prepared compounds were
made yielding only single crystals of 3 suitable for the X-ray
diffraction analysis. Low-quality single crystals of 1 were obtained
from its diethyl ether solution but the data collected by X-ray
crystallography techniques enabled only partial determination and
refinement of its molecular structure with disordered ligand and
butyl groups. Nevertheless, it was found that the tin atom in 1 is
definitively five-coordinate in the solid state and reveals distorted
trigonal-bipyramidal geometry which is in contrast with its
behaviour in the solution as discussed above (for X-ray crystallog-
raphy details see Supplementary material).
2.4. Catalytic experiments
During the last decades and in the quest of efficient catalysts for
the direct synthesis of dimethyl carbonate (DMC) from carbon
dioxide and methanol, several reports highlighted the efficiency of
Ti-, Sn-, and Nb-based organometallic complexes as potential
soluble active species [16]. Despite a lower activity than hetero-
geneous materials, molecular organometallic precursors are
strongly more selective, and, in addition, they can also be consid-
ered as appropriate molecular models for calculation studies as
described in recent papers [16i,17]. To the best of our knowledge,
the dialkyldimethoxystannanes, [R2Sn(OCH3)2] (R ¼ Me, n-Bu, t-
Bu), are the best molecular candidates reported up to now in the
literature [18]. However, the recorded values of nDMC/ncat ratio
(where nDMC is the amount of formed DMC and ncat is the amount of
catalyst used in moles) which expresses their activity did not go
beyond the stoichiometry. Catalytic behaviour requires the pres-
ence of dehydrating agents, or the implementation of recyclings
[19]. In this context, Sakakura et al. published recently about the
promoting role of triflate salts which drastically enhanced the yield
of DMC [10]. In addition, Sakakura reviewed key issues of the
synthesis of organic carbonates from carbon dioxide in 2009 [20].
As foreshadowed in Introduction, we have already tested the
potential catalytic activity of some C,N-chelated organotin(IV) tri-
fluoroacetates in the direct synthesis of DMC with promising
results [11]. Therefore, it seemed promising to use the three orga-
notin(IV) triflate compounds 1, 2 and 3 described in this study as
catalyst precursors for the direct high-pressure carbonation of
methanol (see Table 1) because of two major reasons: i) the tri-
organotin(IV) triflates 1 and 3 can presumably form [LCNR2Sn]þ and
[OTf]ꢀ ions in the methanol solution at elevated temperatures
increasing thus its potential catalytic activity and ii) due to the high
Lewis acidity of the central tin atom in the diorganotin(IV) triflate 3
which might promote the formation of desired DMC. Interestingly,
2 and 3 appeared inefficient or very poorly active for the target
reaction. In the case of 2, the cleavage of the SnePh bond was in
particular observed leading to the release of benzene molecules
(detected by gas chromatography). In contrast, using 1 as the
catalyst precursor, an amount of DMC slightly higher than the
stoichiometry (nDMC/ncat ¼ 1.15) was detected (the detailed proce-
dure is described in Experimental). Such activity (presumably
caused by its relatively easy ionization in methanol at elevated
temperatures) positions the species 1 as one of the best organo-
metallic candidates reported so far, however we still do not fully
understand the actual mechanism of the reaction. Due to the poor
solubility of 4 and observed cleavage of the SnePh bond in 2 during
the DMC synthesis we did not employ compound 4 in the catalytic
activity studies.
Compound 3 was isolated in the form of its adduct with THF
(Fig. 1). The tin atom in 3$THF is six-coordinate with nearly octa-
hedral geometry having both carbon atoms mutually in trans
positions (C1eSn1eC10A 174.0(3)ꢁ). Oxygen atoms of OTf substit-
uents are mutually in trans position (O1eSn1eO4 174.73(8)ꢁ), too,
which means that the nitrogen atom is positioned trans to the
oxygen atom of the THF molecule (N1eSn1eO7 168.92(10)ꢁ). The
ꢁ
Sn1eN1 (2.346(2) A) interatomic distance reveals one of the
strongest intramolecular N / Sn interaction ever reported in the
solid state [for comparison see Refs. [8,9,11e14]]. All three SneO
ꢁ
interatomic distances fall within the range from 2.224(2) A
ꢁ
(Sn1eO1) to 2.281(2) A (Sn1eO4) which reveals a very strong
O / Sn coordination of THF molecule. Thus both OTf substituents
are covalently bound to the tin atom in strictly monodentate
fashion which underlines the tendency of 3$THF to retain its
monomeric covalent structure even in the solid state. The SneC
ꢁ
ꢁ
distances, being 2.102(3) A (Sn1eC1) and 2.124(8) A (Sn1eC10A),
respectively, are comparable with corresponding interatomic
distances previously published in the literature [11e14]. Another
comparison with structures of triflates [4,15] which adopt a higher
nuclearity or polymeric character is not relevant here.
From another point of view the molecular structure (e.g. the
geometry of the central tin atom) of 3$THF highly resembles the
Further work is in progress now to improve these results by
adding the water trapping agents or using other weakly
Table 1
Summary of results of direct synthesis of DMC from CO2 and methanol using
compounds 1, 2 and 3 as catalyst precursors (P(CO2) ¼ 200 bar, T ¼ 150 ꢁC, reaction
time 15 h).
Fig. 1. Molecular structure of 3$THF (ORTEP view, 30% probability level). Hydrogen
atoms as well as the disordered parts are omitted for charity. Selected interatomic
ꢁ
ꢁ
a
distances [A] and angles [ ]: Sn1eN1 2.346(2), Sn1eO1 2.224(2), Sn1eO4 2.281(2),
Sn1eO7 2.271(2), Sn1eC1 2.102(3), Sn1eC10A 2.124(8), S1eO1 1.480(2), S1eO2
1.425(3), S1eO3 1.415(3), S2eO5 1.417(3), S2eO6 1.418(3), N1eSn1eO7 168.92(10),
O1eSn1eO4 174.73(8), C1eSn1eC10A 174.0(3), N1eSn1eC1 78.92(12), N1eSn1eC10A
100.9(2), N1eSn1eO1 87.66(8), N1eSn1eO4 97.31(9), O1eSn1eO7 87.27(8),
O4eSn1eO7 87.53(8), C1eSn1eO1 88.71(10), C1eSn1eO4 90.52(10), C1eSn1eO7
91.12(12).
Complex
Solvent
CO2 used
(g)
nDMC
ncat
(mmol)
nDMC/ncat
(mmol)
1
2
3
MeOH (20 mL)
MeOH (20 mL)
MeOH (20 mL)
32.7
32.1
32.0
2.3
0.6
Traces
2.00
1.17
1.17
1.15
0.51
e
a
Determined by GC using diethyl carbonate (DEC) as external standard.

ꢀ
P. Svec et al. / Journal of Organometallic Chemistry 708-709 (2012) 82e87
85
coordinating anions. After the high-pressure reaction catalyzed by
1, it is evident from the 119Sn{1H} NMR spectrum that only
decomposition products are present in the residue when all
volatiles were evaporated in vacuo. Three different broad signals of
various integral intensities were detected in the 119Sn{1H} NMR
spectrum. One of the decomposition products could be probably
attributed to 1$HOTf. This presumption is derived from
similar pattern of the 1H NMR spectrum and 119Sn{1H} NMR
prepared according to published procedures. All solvents and
AgOTf (99%) were obtained from commercial sources
(SigmaeAldrich). Diethyl ether and THF were distilled from
sodiumepotassium alloy, degassed and stored over a potassium
mirror. All reactions were carried out under an argon atmosphere
using standard Schlenk techniques. Melting points are uncorrected.
3.3.1. Preparation of LCN(n-Bu)2SnOTf (1)
chemical shift value (
L
The identity of other species is still uncertain.
d
(
119Sn) z ꢀ138 ppm) which is close to
L
CN(n-Bu)2SnCl (2.013 g, 5.0 mmol) was dissolved in THF
CN(n-Bu)2Sn(OCOCF3)$CF3COOH (
d
(
119Sn) z ꢀ130.1 ppm) [21].
(30 mL) and solution of AgOTf (99%, 1.299 g, 5.0 mmol) in THF
(30 mL) was added. AgCl precipitated immediately. The reaction
mixture was filtered and the filtration cake was washed with 10 mL
of THF. Oily yellowish product was obtained after removing the
solvent in vacuo. The crude product was crystallized from saturated
diethyl ether solution in a freezing box (ꢀ35 ꢁC) to give colourless
crystals of 1. Overall yield 2.01 g (78%). M.p. 63e66 ꢁC. 1H NMR
3. Experimental
3.1. NMR spectroscopy
3
1
The NMR spectra were recorded from solutions of compounds in
benzene-d6, THF-d8 or methanol-d4 on a Bruker Avance 500 spec-
trometer (equipped with Z-gradient 5 mm probe) at frequencies 1H
(500.13 MHz), 13C{1H} (125.76 MHz), 19F{1H} (470.57 MHz) and
119Sn{1H} (186.50 MHz) at 295 K. The solutions were obtained by
dissolving of approximately 40 mg of each compound in 0.6 mL of
deuterated solvent. The values of 1H chemical shifts were calibrated
(C6D6, 295 K, ppm): 8.30 (d, 1H, H(60), J(1H(50), H(60)) ¼ 6.8 Hz,
3J(119Sn, H) ¼ 56.1 Hz); 7.15 (m, 2H, H(40, 50)); 6.96 (d, 1H, H(30),
1
3J(1H(40), 1H(30)) ¼ 7.3 Hz); 3.17 (s, 2H, CH2N); 1.81 (s, 6H, N(CH3)2);
1.63 (m, 4H, H(1)); 1.51e1.31 (m, 8H, H(2) and H(3)); 0.90 (t, 6H,
H(4)). 13C{1H} NMR (C6D6, 295 K, ppm): 142.7 (C(20), 2J(119Sn, 13C) ¼
36.2 Hz); 139.8 (C(10), 1J(119Sn, 13C) ¼ 624.5 Hz); 138.3 (C(60),
2J(119Sn, 13C) ¼ 40.7 Hz); 130.5 (C(40)); 129.2 (C(50), 3J(119Sn, 13C) ¼
65.6 Hz); 127.2 (C(30), 3J(119Sn, 13C) ¼ 52.5 Hz); 121.3 (q, CF3, 1J(19F,
13C) ¼ 315.0 Hz); 65.9 (CH2N); 45.8 (N(CH3)2); 28.5 (C(2), 2J(119Sn,
13C) ¼ 35.3 Hz); 27.7 (C(3), 3J(119Sn, 13C) ¼ 92.5 Hz); 18.2 (C(1),
1J(119Sn, 13C) ¼ 462.3 Hz); 14.0 (C(4)). 19F{1H} NMR (C6D6, 295 K,
ppm): ꢀ77.7. 119Sn{1H} NMR (C6D6, 295 K, ppm): ꢀ1.0. Elemental
analysis (%): found: C, 42.3; H, 6.6; N, 2.5; S, 5.5. Calcd. for
C18H30F3NO3SSn (516.19): C, 41.88; H, 5.86; N, 2.71; S, 6.21.
to residual signals of benzene-d6
(
d
(1H) ¼ 7.16 ppm), THF-d8
(
d
(1H) ¼ 3.57 ppm) or methanol-d4
(
d
(1H) ¼ 3.31 ppm). The values
of 13C{1H} chemical shifts were calibrated to signals of benzene-d6
(d
(
(
13C) ¼ 128.4 ppm), THF-d8
(d
(
13C) ¼ 67.4 ppm) or methanol-d4
(d
13C) ¼ 49.0 ppm). The values of 19F chemical shifts were cali-
brated to external standard CCl3F (
d
(
19F) ¼ 0.0 ppm). The 119Sn
chemical shift values are referred to external neat tetramethyl-
stannane
(
d
(
119Sn) ¼ 0.0 ppm). Positive chemical shift values
denote shifts to the higher frequencies relative to the standards. All
119Sn{1H} NMR spectra were measured using the inverse gated-
decoupling mode.
3.3.2. Preparation of LCNPh2SnOTf (2)
L
CNPh2SnCl (2.213 g, 5.0 mmol) was dissolved in THF (50 mL).
AgCl precipitated immediately upon addition of a solution of AgOTf
(99%, 1.299 g, 5.0 mmol) in THF (30 mL). The reaction mixture was
filtered and the filtration cake was washed with 25 mL of THF. The
filtrate was concentrated in vacuo until solid started to precipitate
from the solution. This saturated solution was then stored at ꢀ35 ꢁC
for several days to give pure 2 as a white crystalline solid. Overall
isolated yield 2.28 g (82%). M.p. 165e167 ꢁC. 1H NMR (C6D6, 295 K,
3.2. X-ray crystallography
Data for colourless crystal of 3$THF were collected on a Nonius
ꢁ
KappaCCD diffractometer using MoKa radiation (
l
¼ 0.71073 A),
and graphite monochromator at 150 K. The structures were solved
by direct methods (SIR92 [22]). All reflections were used in the
structure refinement based on F2 by full-matrix least-squares
technique (SHELXL97 [23]). Heavy atoms were refined anisotropi-
cally. Hydrogen atoms were mostly localized on a difference Fourier
map, however to ensure uniformity of treatment of crystal, all
hydrogens were recalculated into idealized positions (riding
model) and assigned temperature factors Hiso(H) ¼ 1.2Ueq(pivot
atom) or of 1.5Ueq for the methyl moiety. Absorption corrections
were carried on, using Gaussian integration from crystal shape [24].
The static positional disorder in 3$THF was treated by standard
SHELXL procedures, where disordered carbon atoms from THF and
n-butyl chain were split to two positions.
3
1
ppm): 8.74 (d, 1H, H(60), J(1H(50), H(60)) ¼ 6.8 Hz, 3J(119Sn, 1H) ¼
64.8 Hz); 7.60 (d, 4H, H(200), J(1H(300), H(200)) ¼ 5.2 Hz, 3J(119Sn,
3
1
1H) ¼ 66.9 Hz); 7.29 (t, 1H, H(50)); 7.16 (m, 7H, H(40) and H(300 and
3
1
400)); 6.80 (d, 1H, H(30), J(1H(40), H(30)) ¼ 7.6 Hz); 2.82 (s, 2H,
NCH2); 1.24 (s, 6H, N(CH3)2). 1H NMR (THF-d8, 295 K, ppm): 8.24
(br, 1H, H(60), 3J(119Sn, H) z 65 Hz); 7.73 (d, 4H, H(200), J(1H(300),
1H(200)) ¼ 7.3 Hz, 3J(119Sn, 1H) ¼ 65.6 Hz); 7.46 (m, 3H, LCN and Ph
groups); 7.42 (m, 5H, LCN and Ph groups); 7.34 (m, 1H, H(30)); 3.83
(s, 2H, NCH2); 2.07 (s, 6H, N(CH3)2). 13C{1H} NMR (THF-d8, 295 K,
ppm): 144.6 (C(20)); 138.8 (C(60), 2J(119Sn, 13C) ¼ 51.5 Hz); 137.2
(C(200), 2J(119Sn, 13C) ¼ 47.2 Hz); 136.3 (br, C(100)); 131.8 (C(40)); 131.4
1
3
(C(400)); 130.1 (C(300), 3J(119Sn, C) ¼ 69.9 Hz); 129.6 (C(50)); 128.6
13
Selected crystallographic parametersof 3$THF: C19H29F6NO7S2Sn,
(C(30), 3J(119Sn, 13C) ¼ 62.4 Hz); 121.9 (q, CF3, 1J(19F, 13C) ¼ 318.5 Hz);
65.5 (CH2N); 46.5 (N(CH3)2), signal of the C(10) was not found. 19F
{1H} NMR (THF-d8, 295 K, ppm): ꢀ77.0. 119Sn{1H} NMR (THF-d8,
295 K, ppm): ꢀ162.8. Elemental analysis (%): found: C, 48.1; H, 4.4;
N, 2.2; S, 5.2. Calcd. for C22H22F3NO3SSn (556.17): C, 47.51; H, 3.99;
N, 2.52; S, 5.77.
ꢁ
ꢁ
MW ¼ 680.24, triclinic, P-1, a ¼ 9.2150(5) A, b ¼ 11.5401(10) A,
ꢁ
c ¼ 13.1290(5) A,
a
¼ 86.527(4)ꢁ,
b
¼ 72.105(5)ꢁ,
g
¼ 82.766(5)ꢁ,
3
ꢁ
ꢀ3
Z ¼ 2, V ¼ 1317.68(14) A , Dc ¼ 1.714 g cm
,
m
¼ 1.209 mmꢀ1, Tmin
/
Tmax ¼ 0.9042, 20,941 reflections measured (qmax ¼ 26.37ꢁ), 5335
independent (Rint ¼ 0.0496), 4747 with I > 2
s(I), 351 parameters,
S ¼ 1.077, R1(obs. data) ¼ 0.0329, wR2(all data) ¼ 0.0684; max., min.
ꢁꢀ3
residual electron density ¼ 0.729, ꢀ0.608 e A
.
3.3.3. Preparation of LCN(n-Bu)Sn(OTf)2$THF (3$THF)
L
CN(n-Bu)SnCl2 (2.514 g, 6.6 mmol) was dissolved in THF (40 mL)
3.3. Synthesis
and solution of AgOTf (99%, 3.426 g, 13.2 mmol) in THF (30 mL) was
added. AgCl precipitated immediately. The reaction mixture was
filtered and the filtration cake was washed with THF (15 mL). The
filtrate was concentrated in vacuo and stored at ꢀ35 ꢁC. Crystals of
L
CN(n-Bu)2SnCl [12b], LCNPh2SnCl [12a], LCN(n-Bu)SnCl2 [12b,d],
CNPhSnCl2 [12c], (LCN)2SnBr2 [12c] and LCNSnBr3 [14i] were
L

ꢀ
86
P. Svec et al. / Journal of Organometallic Chemistry 708-709 (2012) 82e87
pure 3$THF grew in few days. Overall isolated yield 2.77 g (69%).
temperature was controlled by an internal thermocouple. After
a reaction time of 15 h the reactor was cooled down to 0 ꢁC, the
pressure was gently released and the liquid phase was transferred
to a Schlenk tube. Trap-to-trap distillation under vacuum at
ambient temperature allowed separation of volatiles compounds
that were quantitatively analyzed by GC (DEC external standard,
Thermo Scientific FOCUS GC, TR-Wax 30 m capillary column, FID
detector). The tin-based residue was studied by IR and multinuclear
NMR spectroscopy.
1
M.p. 88e90 ꢁC. H NMR (THF-d8, 295 K, ppm): 7.70 (d, 1H, H(60),
1
3J(1H(50), H(60)) ¼ 7.0 Hz, 3J(119Sn, 1H) ¼ 101.5 Hz); 7.42e7.34 (m,
3
2H, H(40) and H(50)); 7.27 (d, 1H, H(30), J(1H(40), 1H(30)) ¼ 7.3 Hz);
4.02 (s, 2H, NCH2); 2.65 (s, 6H, N(CH3)2); 2.17 (m, 2H, H(1)); 1.85 (m,
2H, H(2)); 1.45 (m, 2H, H(3)); 0.94 (t, 3H, H(4)). 13C{1H} NMR (THF-
d8, 295 K, ppm): 142.1 (C(20)); 140.9 (C(10)); 134.7 (C(60)); 132.0
(C(40)); 129.8 (C(50)); 128.6 (C(30)); 120.7 (q, CF3, 1J(19F, 13C) ¼
318.8 Hz); 64.0 (CH2N); 46.1 (N(CH3)2); 32.7 (br, C(1)); 28.2 (C(2));
26.7 (C(3)); 13.8 (C(4)); nJ(119Sn, 13C) were not observed. 19F{1H}
NMR (THF-d8, 295 K, ppm): ꢀ76.5. 119Sn{1H} NMR (THF-d8, 295 K,
ppm): ꢀ350.9. Elemental analysis (%): found: C, 33.6; H, 4.4 N, 2.0;
S, 9.5. Calcd. for C19H29F6NO7S2Sn (680.25): C, 33.55; H, 4.30; N,
2.06; S, 9.43.
4. Conclusions
Four novel organotin(IV) triflates bearing the C,N-chelating
ligand were synthesized and structurally characterized in the terms
of this work. It was found that triorganotin(IV) triflate 1 (which is
presumably stable towards air moisture at ambient temperature)
undergoes significant weakening of the SneOTf bond in solution
which makes it effective catalyst precursor for the direct synthesis
of DMC as demonstrated. On the other hand, compounds 2 and 3
did not seem to be applicable for this purpose due to reasons dis-
cussed above. Unfortunately, it was found that the catalyst
precursor 1 was not able to survive the harsh reaction conditions as
detected by the multinuclear NMR spectroscopy. The possibility of
using of some drying agent(s) as well as the influence of the reac-
tion time, temperature and pressure with respect to the yield of the
DMC promoted by 1 is now under close investigation. Careful effort
is devoted to the further identification of products of decomposi-
tion of 1 during the high-pressure synthesis of the DMC, too.
3.3.4. Preparation of LCNPhSn(OTf)2 (4)
L
CNPhSnCl2 (0.930 g, 2.32 mmol) was dissolved in THF (40 mL)
and solution of AgOTf (99%, 1.194 g, 4.64 mmol) in THF (15 mL) was
added. AgCl precipitated upon mixing these solutions. The reaction
mixture was filtered and the filtration cake was washed with THF
(15 mL). The saturated THF solution of 4 was left for a couple of days
in a freezing box (ꢀ35 ꢁC) to give nearly colourless crystals. Yield
0.816 g (56%). M.p. 145e147 ꢁC. 1H NMR (THF-d8, 295 K, ppm): 7.96
3
1
(d, 2H, H(200), J(1H(300), H(200)) ¼ 7.5 Hz, 3J(119Sn, 1H) ¼ 110.4 Hz);
7.83 (d, 1H, H(60), J(1H(50), H(60)) ¼ 7.2 Hz, 3J(119Sn, 1H) ¼
113.8 Hz); 7.55 (m, 2H, LCN and Ph moieties); 7.40 (m, 3H, LCN and Ph
moieties); 7.30 (d, 1H, H(30), 3J(1H(40), 1H(30)) ¼ 7.2 Hz); 3.58 (s, 2H,
NCH2); 2.47 (s, 6H, N(CH3)2). 13C{1H} NMR (THF-d8, 295 K, ppm):
141.2 (C(20)); 140.6 (C(10)); 135.7 (C(200)); 134.8 (C(60)); 132.4 (C(40));
132.2 (C(400)); 130.6 (C(300)); 130.0 (C(50)); 128.8 (C(30)); 120.8 (q,
CF3, 1J(19F, 13C) ¼ 319.7 Hz); 63.8 (CH2N); 46.2 (N(CH3)2); signal of
the C(100) was not found; nJ(119Sn, 13C) were not observed. 19F{1H}
NMR (THF-d8, 295 K, ppm): ꢀ76.9. 119Sn{1H} NMR (THF-d8, 295 K,
ppm): ꢀ418.6. Elemental analysis (%): found: C, 33.0; H, 3.0; N, 2.0;
S, 9.9. Calcd. for C17H17F6NO6S2Sn (628.14): C, 32.51; H, 2.73; N,
2.23; S, 10.21.
3
1
Acknowledgements
The Pardubice group would like to thank the Grant Agency of
the Czech Republic (grant no. 104/09/0829) for financial support.
The Barrande Bilateral Programme (contracts No. MEB021040 &
21880RL) is also greatly acknowledged by both French and Czech
sides (French Ministry of Foreign Affairs and Czech Ministry of
Education, Youth and Sports, respectively). The French side also
gratefully acknowledges the Centre National de la Recherche Sci-
entifique (CNRS-France) for the financial support of this work.
3.3.5. Attempt for the preparation and characterization of
(LCN)2Sn(OTf)2
The synthesis was carried out similarly to the preparation of 1e4
using (LCN)2SnBr2 (0.547 g, 1.00 mmol) and AgOTf (99%, 0.514 g,
2.00 mmol). Due to the unexpected limited solubility in common
organic solvents only 1H NMR spectrum could be recorded but this
gave us no relevant information about the structure of the title
compound. Unfortunately, however, the single crystals of this
species were not obtained.
Appendix A. Supplementary material
CCDC 863441 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Center via www.cccdc.cam.ac.uk/
data-request/cif. Supplementary data related to this article can be
found in the online version, at doi:10.1016/j.jorganchem.2012.02.
022.
3.3.6. Attempt for the preparation and characterization of
L
CNSn(OTf)3
The synthesis was carried out similarly to the preparation of 1e4
References
using LCNSnBr3 (0.493 g, 1.00 mmol) and AgOTf (99%, 0.771 g,
3.00 mmol). Due to the unprecedented reactivity of the title
compound formed, no NMR spectra could be recorded since it
reacts with the solvent (THF) even at room temperature to form
presumably polymeric species. Unfortunately, however, the single
crystals of this compound were not obtained.
[1] M. Schmeisser, P. Sartori, B. Lippsmeier, Chem. Ber. 103 (1970) 868e879.
[2] (a) H. Lee, J.Y. Bae, O.S. Kwon, S.J. Kim, S.D. Lee, H.S. Kim, J. Organomet. Chem.
689 (2004) 1816e1820;
(b) A. Orita, J. Xiang, K. Sakamoto, J. Otera, J. Organomet. Chem. 624 (2001)
287e293;
(c) J. Beckmann, D. Dakternieks, A. Duthie, F.S. Kuan, E.R.T. Tiekink, Organo-
metallics 22 (2003) 4399e4404.
[3] (a) K. Sakamoto, H. Ikeda, H. Akashi, T. Fukuyama, A. Orita, J. Otera, Organo-
metallics 19 (2000) 3242e3248;
3.4. Catalytic experiments
(b) K. Sakamoto, Y. Hamada, H. Akashi, A. Orita, J. Otera, Organometallics 18
(1999) 3555e3557.
[4] J. Beckmann, Appl. Organomet. Chem. 19 (2005) 494e499.
[5] (a) T. Sato, J. Otera, H. Nozaki, J. Am. Chem. Soc. 112 (1990) 901e902;
(b) T. Sato, Y. Wakahara, J. Otera, H. Nozaki, Tetrahedron 47 (1991)
9773e9782.
[6] T. Sato, Y. Wakahara, J. Otera, Tetrahedron Lett. 31 (1990) 1581e1584.
[7] D.L. An, Z. Peng, A. Orita, A. Kurita, S. Man-e, K. Ohkubo, X. Li, S. Fukuzumi,
J. Otera, Chem.dEur. J. 12 (2006) 1642e1647.
General procedure for reactions of methanol with carbon
dioxide: the reaction was carried out in a 125 mL stainless steel
reactor equipped with a magnetic stirrer. The reactor was purged
with argon and a 20 mL solution of the appropriate organotin(IV)
triflate (1, 2 and 3) in methanol was introduced by syringe. Then,
CO2 was admitted to the desired amount (see Table 1). The reaction

ꢀ
P. Svec et al. / Journal of Organometallic Chemistry 708-709 (2012) 82e87
87
ꢀ
ꢀ
ꢀ
ꢀ
[8] (a) B. Kasná, R. Jambor, L. Dostál, I. Císarová, J. Holecek, B. Stíbr, Organome-
[16] (a) J. Kizlink, I. Pastucha, Collect. Czech. Chem. Commun. 6 (1995) 687e692;
(b) N.S. Isaacs, B. O’Sullivan, C. Verhaelen, Tetrahedron 55 (1999)
11949e11956;
tallics 25 (2006) 5139e5144;
ꢀ
ꢀ
(b) B. Kasná, L. Dostál, R. Jirásko, I. Císarová, R. Jambor, Organometallics 27
(2008) 3743e3747.
[9] S.H.L. Thoonen, H. van Hoek, E. de Wolf, M. Lutz, A.L. Spek, B.-J. Deelman,
G. Van Koten, J. Organomet. Chem. 691 (2006) 1544e1553.
[10] J.-C. Choi, K. Kohno, Y. Ohshima, H. Yasuda, T. Sakakura, Catal. Commun. 9
(2008) 1630e1633.
(c) M. Aresta, A. Dibenedetto, C. Pastore, Inorg. Chem. 42 (2003) 3256e3261;
D. Ballivet-Tkatchenko, R. Ligabue, L. Plasseraud, Braz. J. Chem. Eng. 23 (2006)
111e116;
(d) D. Ballivet-Tkatchenko, H. Chermette, L. Plasseraud, O. Walter, Dalton
Trans. (2006) 5167e5175;
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
[11] P. Svec, Z. Padelková, A. Ruzicka, T. Weidlich, L. Dusek, L. Plasseraud,
(e) D. Ballivet-Tkatchenko, R. Burgat, S. Chambrey, L. Plasseraud, P. Richard,
J. Organomet. Chem. 691 (2006) 1498e1504;
J. Organomet. Chem. 696 (2011) 676e686.
ꢁꢀ ꢀ
ꢀ
ꢀ
[12] (a) A. Ruzicka, R. Jambor, J. Brus, I. Císarová, J. Holecek, Inorg. Chim. Acta 323
(f) D. Ballivet-Tkatchenko, F. Bernard, F. Demoisson, L. Plasseraud,
S.R. Sanapureddy, ChemSusChem 4 (2011) 1316e1322;
(g) K. Tomishige, K. Kunimori, Appl. Catal., A: Gen. 237 (2002) 103e109;
(h) M. Honda, S. Kuno, N. Begum, K. Fujimoto, K. Suzuki, Y. Nakagawa,
K. Tomishige, Appl. Catal., A: Gen. 384 (2010) 165e170;
(i) M.P. Kalhor, H. Chermette, S. Chambrey, D. Ballivet-Tkatchenko, Phys.
Chem. Chem. Phys. 13 (2011) 2401e2408.
(2001) 163e170;
ꢁꢀ ꢀ
ꢀ
ꢀ
(b) A. Ruzicka, V. Pejchal, J. Holecek, A. Lycka, K. Jacob, Collect. Czech. Chem.
Commun. 63 (1998) 977e989;
ꢀ
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
(c) P. Novák, Z. Padelková, L. Kolárová, I. Císarová, A. Ruzicka, J. Holecek, Appl.
Organomet. Chem. 19 (2005) 1101e1108;
ꢀ
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
(d) P. Svec, Z. Padelková, I. Císarová, A. Ruzicka, J. Holecek, Main Group Met.
Chem. 31 (2008) 305e309.
[13] J. Turek, Z. Padelková, Z. Cernosek, M. Erben, A. Lycka, M.S. Nechaev,
[17] (a) K. Wakamatsu, A. Orita, J. Otera, Organometallics 29 (2010) 1290e1295;
(b) M. Poor Kalhor, H. Chermette, D. Ballivet-Tkatchenko, Polyhedron 32
(2012) 73e77.
[18] (a) J.-C. Choi, T. Sakakura, T. Sako, J. Am. Chem. Soc. 121 (1999) 3793e3794;
(b) T. Sakakura, J.-C. Choi, Y. Saito, T. Masuda, T. Sako, T. Oriyama, J. Org. Chem.
64 (1999) 4506e4508;
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
I. Císarová, A. Ruzicka, J. Organomet. Chem. 694 (2009) 3000e3007.
ꢀ
ꢀ
ꢁꢀ ꢀ
[14] (a) P. Svec, Z. Padelková, Z. Cernosek, F. De Proft, A. Ruzicka, J. Organomet.
Chem. 693 (2008) 2937e2941;
ꢀ
ꢀ
ꢁꢀ ꢀ
(b) Z. Padelková, A. Havlík, P. Svec, M.S. Nechaev, A. Ruzicka, J. Organomet.
Chem. 695 (2010) 2651e2657;
(c) P. Svec, Z. Padelková, P. Stepnicka, A. Ruzicka, J. Holecek, J. Organomet.
(c) D. Ballivet-Tkatchenko, O. Douteau, S. Stutzmann, Organometallics 19
(2000) 4563e4567;
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
Chem. 696 (2011) 1809e1816;
(d) P. Svec, Z. Padelková, A. Ruzicka, J. Holecek, Main Group Met. Chem. 32
(2009) 217e218;
(e) R.A. Varga, M. Schuermann, C. Silvestru, J. Organomet. Chem. 623 (2001)
161e167;
(f) R.A. Varga, A. Rotar, M. Schuermann, K. Jurkschat, C. Silvestru, Eur. J. Inorg.
Chem. (2006) 1475e1486;
(d) D. Ballivet-Tkatchenko, T. Jerphagnon, R. Ligabue, L. Plasseraud, D. Poinsot,
Appl. Catal., A: Gen. 255 (2003) 93e99.
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
[19] D. Ballivet-Tkatchenko, S. Chambrey, R. Keiski, R. Ligabue, L. Plasseraud,
P. Richard, H. Turunen, Catal. Today 115 (2006) 80e87.
[20] T. Sakakura, K. Kohno, Chem. Commun. (2009) 1312e1330.
ꢀ
ꢀ
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
[21] P. Svec, E. Cernosková, Z. Padelková, A. Ruzicka, J. Holecek, J. Organomet.
Chem. 695 (2010) 2475e2485.
(g) R.A. Varga, K. Jurkschat, C. Silvestru, Eur. J. Inorg. Chem. (2008) 708e716;
(h) Z. Padelková, I. Císarová, A. Ruzicka, Acta Crystallogr. E61 (2005)
[22] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 26
(1993) 343e350.
ꢀ
ꢀ
ꢁꢀ ꢀ
m2691em2693;
[23] G.M. Sheldrick, SHELXL-97, A Program for Crystal Structure Refinement,
ꢀ
ꢀ
ꢀ
ꢁꢀ ꢀ
ꢀ
(i) P. Novák, Z. Padelková, I. Císarová, L. Kolárová, A. Ruzicka, J. Holecek, Appl.
University of Göttingen, Germany, 1997.
Organomet. Chem. 20 (2006) 226e232.
[15] L. Plasseraud, B. Therrien, A. Ruzicka, H. Cattey, Inorg. Chim. Acta 380 (2012) 50e56.
[24] P. Coppens, in: F.R. Ahmed, S.R. Hall, C.P. Huber (Eds.), Crystallographic
Computing, Munksgaard, Copenhagen, 1970, pp. 255e270.
ꢁꢀ ꢀ