Synthesis and characterization of fluoroalkyldistannoxanes

Article abstract of DOI:10.1016/S0022-328X(01)01398-5

1,3-Disubstituted tetrakis(fluoroalkyl)distannoxanes (XRf₂SnOSnRf₂Y)₂ (Rf=C₆F₁₃C₂H₄; X, Y = Cl, Br, NCS) were synthesized from readily available dibenzyltin dibromide. The dimeri

Full text of DOI:10.1016/S0022-328X(01)01398-5

Journal of Organometallic Chemistry 648 (2002) 246–250
www.elsevier.com/locate/jorganchem
Synthesis and characterization of fluoroalkyldistannoxanes
Jiannan Xiang, Akihiro Orita, Junzo Otera *
Department of Applied Chemistry, Okayama Uni6ersity of Science, Ridai-cho, Okayama 700-0005, Japan
Received 27 September 2001; accepted 12 October 2001
Abstract
1,3-Disubstituted tetrakis(fluoroalkyl)distannoxanes (XRf2SnOSnRf2Y)2 (Rf=C6F13C2H4, C4F9C2H4; X, Y=Cl, Br, NCS)
were synthesized from readily available dibenzyltin dibromide. The dimeric formulation of these compounds that was confirmed
by 119Sn-NMR spectra gave rise to a structure in which the metalloxane core is covered by the surface fluorophilic alkyl groups.
Thus, these compounds exhibited high solubility in fluorocarbon solvents and large partition coefficients for FC-72 against
common organic solvent. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Fluoroalkyldistannoxanes; Partition coefficients; Alkyl groups
1. Introduction
highly soluble in fluorocarbons and served as an excel-
lent catalyst for fluorous biphasic transesterification
(Fig. 1) [8]. Accordingly, further exploitation of rele-
vant compounds in this category is expected to expand
the synthetic scope of this technology. Herein, is de-
scribed the full account on the synthesis and character-
ization of 1,3-disubstituted tetrakis(fluoroalkyl)-
distannoxanes.
Fluorous biphase technology has received extensive
attention from the viewpoint of environmentally-benign
chemical process [1]. A variety of reagents and catalysts
workable under fluorous biphasic conditions have been
developed. In this context, Curran and his coworkers
proved fluoroalkyltin hydrides [2], aryls [3], allyl [4],
and oxides [5] to be highly useful.
1,3-Disubsituted tetraalkyldistannoxanes (1) (R=al-
kyl) are unique in that they are soluble in most organic
solvents despite involving a large metalloxane core [6].
Such high solubility is attributable to a ladder structure
resulting from dimerization as shown below. The inor-
ganic core is surrounded by eight alkyl groups which
render the molecule hydrophobic [7]. This led us to
postulate that the compound would become soluble in
fluorocarbon solvents if the surface alkyl groups were
replaced by fluoroalkyl groups. Endowment of
fluorophilic character to the distannoxanes seemed to
us of great promise for exploring novel Lewis acid
catalysts useful in the fluorous biphase technology. In
fact, we disclosed preliminarily that [Cl(C6F13C2H4)2-
SnOSn(C2H4C6F13)2Cl]2 (1a, R=C6F13C2H4) was
* Corresponding author. Fax: +81-86-2564292.
E-mail address: otera@high.ous.ac.jp (J. Otera).
Fig. 1. Fluorous biphasic transesterification with fluoroalkyldistan-
noxaenes.
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01398-5

J. Xiang et al. / Journal of Organometallic Chemistry 648 (2002) 246–250
247
2. Results and discussion
dichlorodistannoxanes [10], did not work in the present
cases. The use of aqueous HBr in stead of HCl afforded
the 1,3-dibromo derivatives 1ab and 1bb in 78–84%
yields.
The synthetic route for the fluoroalkyldistannoxanes
is shown in Scheme 1. Treatment of dibenzyltin dibro-
mide that can be readily obtained from benzyl bromide
and tin powder [9] with RfMgX (Rf=C6F13C2H4 or
C4F9C2H4) furnished tetraalkyltins 2 in 80–99% yield.
Bromination of 2 (94–95% yield) followed by alkaline
hydrolysis (92–93% yield) provided oxides 4. These
compounds were amorphous solids like other organotin
oxides and difficult to obtain in analytically pure form.
Previously, 4a had been prepared by Curran et al.
according to Eq. (1)[5]. They suggested this
An FC-72 (perfluorohexanes, 3 M) solution of 1aa
was combined with aqueous solution of NaSCN, and
the mixture was stirred at room temperature for 20 h.
Only the terminal chlorine atoms were replaced to give
1ac (Eq. (2)). The structure of this compound is appar-
ent from IR spectrum. Appearance of w(NꢀC) at 2065
cm−1 indicates the presence of a terminal NCS group
since this group at the bridging position should give the
NꢀC stretching band at around 1960 cm−1 [11]. The
bridging chlorine never underwent substitution even by
exposing 1aa to a large excess amount of NaSCN, a
quite different outcome from conventional tetraalkyld-
istannoxanes which usually give 1,3-diisothiocyanato
derivatives upon treatment with two equivalents of
NaSCN [10]. In 1,3-dichlorotetraalkyldistannoxanes,
the bonds between tins and bridging chlorine are rather
weak as is evident from ionic bonding mode on the
basis of X-ray analysis [12]. On the hand, it is assumed
that the dimeric association in 1aa is tight because the
surface fluoroalkyl groups induce contraction of the
dimerized structure due to incompatibility of these
groups with organic surroundings (vide infra).
(C6F13C2H4)2SnPh2“(C6F13C2H4)2Sn(OCOCH2Cl)2“4a
(1)
compound to be oligomeric, yet a single 119Sn reso-
nance (l −59.1 in CDCl3) was observed. Our com-
pound, on the other hand, exhibited many (ca. 15)
signals in the region between −168 and −233 ppm.
Probably, the different preparative methods had re-
sulted in different degree and mode of oligomerization.
The 119Sn-NMR of 4b exhibited a similar pattern as 4a.
With the assumption that the desired oxides had been
formed, we treated 4 with a slightly excess of aqueous
HCl in acetone. 1,3-Dichlorodistanoxanes 1aa and 1ba
were obtained in 85 and 84% yields, respectively. Treat-
ment of dialkyltin oxide and dialkyltin dihalide in a 1:1
ratio, a very common procedure to arrive at 1,3-
(2)
All fluoroalkyldistannoxanes thus prepared were iso-
lated as crystals, yet they were not obtained in a
suitable form for X-ray analysis. However, 119Sn-NMR
spectra gave rise to two distinct singlets diagnostic of
characteristic dimeric distannoxane formulation [13].
Moreover, broadening of one of the 119Sn signals ob-
served for 1ac (Section 3) confirms the bonding of the
NCS group to tin [13].
Scheme 1.
As expected, these compounds are sparingly soluble
in common organic solvents except acetone and ethyl
acetate. The solubility of 1aa (g l−1) at room tempera-
ture is as follows: toluene, benzene, ꢀ1; hexane, B1;
CH2Cl2, ca. 1; methanol, 2; acetonitrile, 9; acetone, 40;
ethyl acetate, 48. On the other hand, this compound is
well soluble in fluorocarbon solvents such as FC-72,
FC-40, and octafluorocyclopentene: for example, solu-
bility in FC-72 is 41 g l−1 at room temperature. Next,
we determined the partition coefficients of this com-
pound between FC-72/organic solvent as given in Table
1 [14].
Table 1
Partition coefficients (PC) of 1aa in the binary FC-72/organic solvent
system at room temperature
Solvent
Distribution
FC-72
PC
Organic solvent
C6H5CH3
C6H6
CH2Cl2
CH3OH
C3H6O
THF
100
100
99
98
97
0
0
1
2
3
4
\100
\100
99
49
32
24
The perfect bias into the FC-72 phase against toluene
and benzene was revealed consistent with the previous
96

248
J. Xiang et al. / Journal of Organometallic Chemistry 648 (2002) 246–250
dimerization than normal distannoxanes and possess
unique solubility in fluorocarbon solvents. The applica-
tions of these compounds as Lewis acid catalysts in
fluorous biphase system are in progress.
3. Experimental
THF and Et2O were distilled from Na–benzophe-
none. CH3CN, CHCl3, CH2Cl2 and CH3COCH3 were
distilled from CaH2. FC-72 (perfluorohexane, 3 M) was
used without purification. Silica gel (Daiso gel IR-60)
was used for column chromatography. NMR spectra
were recorded at 25 °C on Brucker ARX-400, JEOL
Lambda 300 and JEOL Lambda 500 instruments and
calibrated with Me4Si, trifluoromethylbenzene or
Me4Sn as an internal standard. Mass spectra were
recorded on JEOL MStation JMS-700, Shimadzu/
Kratos MALDI 4 and Platform II single quadrupole
mass spectrometers (Micromass, Altrinchan, UK). Ele-
mental analyses were performed by the Perkin–Elmer
PE 2400.
Fig. 2. Double layered structure of fluoroalkyldistannoxane.
results where quantitative recovery of the catalyst was
attained in the fluorous biphasic transesterification us-
ing the FC-72/toluene binary system [8]. The high
partition coefficients were also found with CH2Cl2,
CH3OH, and THF. The value for acetone (32) is rather
surprising because the solubility of 1aa in pure FC-72
and acetone is comparable. Apparently, the fluorophilic
character of 1aa is responsible for the highly biased
distribution. Further, unique solubility is highlighted by
comparison with (C6F13C2H4)2SnO (4a). According to
Curran et al., partition coefficients of this compound
are as follows: toluene, 1.9; CH2Cl2, 1.7; CH3CN, 0.28
[5]. On account of this relatively low partition coeffi-
cients, repeated washings were necessary for recovery of
the oxide from the reaction mixture in fluorous biphasic
bezoylation of diols. By contrast, 1aa was recovered in
100% without any sign of decomposition from the 1:1
FC-72/toluene binary system in our transesterification
[8]. It follows therefore, that the double layered struc-
ture composed of the surface fluoroalkyl groups and
the stannoxane core renders 1aa completely fluorophilic
(Fig. 2) while the wrapping of the inorganic moiety by
the fluoroalkyl groups may be insufficient in 4a. It
should be noted that 1ab exhibited the similar solubility
to that of 1aa.
3.1. Preparation of (PhCH2)2SnBr2 [15]
In a 300 ml two neck-flask, a mixture of tin powder
(17.8 g, 0.15 mol), water (1 ml) and C6H5CH3 (150 ml)
was heated to reflux with stirring, and BnBr (26.6 g,
0.15 mol) was added slowly with syringe. After the
reaction mixture had been heated under reflux for 3 h,
the reaction mixture was cooled and filtered. The ob-
tained solid was dissolved in CH3COCH3 and filtered to
remove tin powder. The filtrate was evaporated, and
the residue was recrystallized from EtOAc to afford
(PhCH2)2SnBr2 (60.7 g, 88%,). M.p. 135–136 °C.
The partition coefficients of 1ba and 1bb are given in
Table 2. These compounds are also virtually
fluorophilic, yet the degree is somewhat lower than that
of 1aa. This is quite reasonable in terms of the shorter
fluoroalkyl chain length and clearly demonstrates the
crucial role of the fluoroalkyl groups for the
fluorophilicity.
In summary, a variety of 1,3-disubstituted tetrak-
is(fluoroalkyl)distannoxanes were synthesized. These
compounds are more tightly associated leading to
3.2. Preparation of 2a and 2b
Under Ar, C6F13C2H4I (14.22 g, 30 mmol) in dry
Et2O (20 ml) was added dropwise to a stirring suspen-
sion of Mg turnings (0.826 g, 34 mmol) with stirring in
dry Et2O (40 ml) at 0 °C. The reaction mixture was
stirred for 3 h at room temperature (r.t.) and, then, was
diluted with Et2O (30 ml). Dibenzyltin dibromide (4.6
g, 10 mmol) in THF (15 ml) was added at 0 °C. After
being stirred for 24 h at r.t., the reaction mixture was
Table 2
Partition coefficients (PC) of 1ba and 1bb in the binary FC-72/organic solvent system at room temperature
Solvent
1ba (distribution)
1bb (distribution)
FC-72
Organic solvent
PC
FC-72
Organic solvent
PC
C6H5CH3
C6H6
CH2Cl2
97
99
98
3
1
2
32
99
49
94
99
98
4
1
2
24
99
49

J. Xiang et al. / Journal of Organometallic Chemistry 648 (2002) 246–250
249
diluted with C6H14 (60 ml) and filtered through a celite
pad. The filtrate was evaporated and the residue was
subjected to column chromatography (C6H14) on silica
gel to afford pure 2a as a colorless oil (8.06 g, 81%).
1H-NMR (300 MHz, CDCl3): l 0.82–1.05 (m, 4H),
1.80–1.99 (m, 4H), 2.46 (s, 2J(1Hꢁ119Sn)=60.4 Hz,
4H), 6.90–7.24 (m, 10H); 119Sn-NMR (112 MHz,
CDCl3): l −19.1.
(75 MHz, C3H6O-d6): l 10.0–13.0 (m, 2C), 25.0–27.0
(m, 2C), 106.0–122.0 (m, 8C); 119Sn-NMR (112 MHz,
C3H6O-d6): l −174– −210 (complex pattern).
3.5. Preparation of 1aa and 1ba
To 4a (4.18 g, 4.95 mmol) in CH3COCH3 (50 ml) was
added 4 M HCl (1.63 ml, 6.50 mmol) at r.t. After
reaction mixture had been stirred at this temperature
for 24 h, CH2Cl2 (150 ml) was added. The organic layer
was washed with water (3×50 ml), dried (Na2SO4),
and evaporated. To the residual solids was added FC-
72 (30 ml), and the solution was washed with a 1:1
mixture of CH2Cl2 and water (2×10 ml). The FC-72
layer was evaporated, and the residue was recrystallized
from hot CH2Cl2 to afford 1aa in pure form (3.62 g,
85%). M.p. 71–72 °C; 1H-NMR (300 MHz, FC-72
with CDCl3 as external lock): l 1.87–2.35 (m, 16H),
2.65–3.05 (m, 16H); 13C-NMR (75 MHz, C3H6O-d6): l
13.7 (4C), 15.2 (4C), 25.8 (2J(13Cꢁ19F)=23.2 Hz, 4C),
26.0 (2J(13Cꢁ19F)=23.2 Hz, 4C), 106.3–122.3 (complex
pattern, 48C); 119Sn-NMR (112 MHz, C3H6O-d6): l
−178.3, −202.5; Anal. Calc. for C64H32Cl4F104O2Sn4:
C, 22.44; H, 0.94. Found: C, 22.58; H, 0.54.
An analogous procedure using C4F9C2H4Br afforded
1
2b in 99% yield. H-NMR (300 MHz, CDCl3): l 0.80–
1.06 (m, 4H), 1.80–2.00 (m, 4H), 2.45 (s,
2J(1Hꢁ119Sn)=60.2 Hz, 4H), 6.90–7.25 (m, 10H); 13C-
NMR (125 MHz, CDCl3): l −1.4 (1J(13Cꢁ117/119Sn)=
308 Hz, 2C), 18.5 (1J(13Cꢁ117/119Sn)=274/287 Hz, 2C),
27.2 (2J(13Cꢁ19F)=46 Hz, 2C), 106.0–121.5 (complex
pattern, 8C), 124.2 (2C), 127.0 (4C), 128.9 (4C), 140.9
(2C); 119Sn-NMR (112 MHz, CDCl3): l −19.2.
3.3. Preparation of 3a and 3b
Under Ar, Br2 (1.74 g, 10.8 mmol) was added to a
solution of 2a (5.20 g, 5.40 mmol) in CCl4 (70 ml) at r.t.
After 3 h, the reaction mixture was evaporated, and the
residue was subjected to column chromatography
(C6H14 followed by EtOAc) to provide 3a in a pure
form. A white solid was obtained by recrystallization
An analogous procedure using 4b afforded 1ba in
84% yield. M.p. 82–84 °C; 1H-NMR (500 MHz,
CDCl3): l 1.91–2.34 (m, 16H), 2.51–3.05 (m, 16H);
1
from C6H14 (5.03 g, 96%). M.p. 56–58 °C; H-NMR
(300 MHz, CDCl3):
l
2.04 (t, J=7.7 Hz,
13C-NMR (125 MHz, C3H6O-d6):
l
13.7 (1J-
2J(1Hꢁ117/119Sn)=60.0 Hz, 4H), 2.30–2.85 (m, 4H);
13C-NMR (75 MHz, CDCl3): l 14.9 (1J(13Cꢁ117/119Sn)
=457 Hz, 2C), 27.1 (2J(13Cꢁ19F)=23 Hz, 2C), 106.6–
123.1 (complex pattern, 12C); 119Sn-NMR (112 MHz,
CDCl3): l 54.8.
(13Cꢁ117/119Sn)=699/725 Hz, 4C), 15.2 (1J(13Cꢁ117/119Sn)
=717/750 Hz, 4C), 25.8 (2J(13Cꢁ19F)=23.3 Hz, 4C),
26.0 (2J(13Cꢁ19F)=23.3 Hz, 4C), 105.0–120.5 (32C);
119Sn-NMR (112 MHz, C3H6O-d6): l −178.0, −201.9.
Anal. Calc. for C48H32Cl4F72O2Sn4: C, 21.96; H, 1.23.
Found: C, 22.13; H, 1.25%.
An analogous procedure using 2b afforded 3b as a
1
pale yellow solid (2.90 g, 94%). M.p. 30–31 °C; H-
NMR (300 MHz, CDCl3): l 1.80–2.00 (m, 4H), 2.45–
2.75 (m, 4H); 119Sn-NMR (112 MHz, CDCl3): l 53.3,
(C3H6O-d6) l −57.0.
3.6. Preparation of 1ab and 1bb
To 4a (2.00 g, 2.37 mmol) in CH3COCH3 (50 ml) was
added 4 M HBr (0.76 ml, 3.08 mmol) at r.t. After the
reaction mixture had been stirred for 24 h, CH2Cl2 (150
ml) was added. The organic layer was washed with
water (3×50 ml), dried (Na2SO4), and evaporated. To
the residual solids was added FC-72 (30 ml) and the
solution was washed with a 1:1 mixture of CH2Cl2 and
water (2×10 ml). The FC-72 layer was evaporated,
and the residue was recrystallized from hot C6H5CH3 to
afford 1ab in a pure form as a white solid (1.65 g, 78%).
M.p. 68–70 °C; 1H-NMR (500 MHz, FC-72 with
CDCl3 as external lock): l 1.75–2.35 (m, 16H), 2.45–
3.25 (m, 16H); 13C-NMR (75 MHz, C3H6O-d6): l 14.9
(4C), 16.9 (4C), 25.9 (2J(13Cꢁ19F)=23.0 Hz, 4C), 26.5
(2J(13Cꢁ19F)=23.0 Hz, 4C), 105.8–122.3 (complex pat-
tern, 48C); 119Sn-NMR (112 MHz, C3H6O-d6): l
−182.9, −205.0. Anal. Calc. for C64H32Br4F104O2Sn4:
C, 21.33; H, 0.90. Found: C, 22.13; H, 1.25%.
3.4. Preparation of 4a and 4b
To a solution of 3a (5.03 g, 5.17 mmol) in THF (80
ml) was added dropwise 4 M NaOH aq. solution (3.9
ml, 15.5 mmol) at r.t. The mixture was stirred for 2 h
and, then concentrated. The residual solids were
washed with a 1:1 mixture of CH2Cl2 and water (2×10
ml). The remaining solids were dried by pumping to
1
give 4a as a white solid (4.07 g, 93%). H-NMR (300
MHz, FC-72 with C3H6O-d6 as external lock): l 1.30–
1.95 (br, 4H), 2.41–2.95 (br, 4H); 13C-NMR (75 MHz,
C3H6O-d6): l 10.0–14.0 (br, 2C), 25.0–27.0 (br, 2C);
104.0–123.0 (12C); 119Sn-NMR (112 MHz, C3H6O-d6):
l −168– −233 (complex pattern).
An analogous procedure using 3b afforded 4b as
1
white solid in 92% yield. H-NMR (300 MHz, C3H6O-
d6): l 1.10–2.00 (m, 4H), 2.40–3.25 (m, 4H); 13C-NMR

250
J. Xiang et al. / Journal of Organometallic Chemistry 648 (2002) 246–250
An analogous procedure using 4b afforded 1bb in
This mixture was stirred or shaken at r.t. for 30 min
and kept still until both organic and FC-72 layers
become clear. After separation, the organic and FC-72
layers were evaporated, respectively, and 1aa recovered
was weighed.
84% yield. M.p. 120–122 °C; 1H-NMR (500 MHz,
C3H6O-d6): l 1.93–2.38 (m, 16H), 2.60–3.14 (m, 16H);
13C-NMR (125 MHz, C3H6O-d6): l 14.9 (4C), 16.9
(4C), 25.6 (2J(13Cꢁ19F)=23.2 Hz, 4C), 26.2
(2J(13Cꢁ19F)=23.2 Hz, 4C), 104.0–122.0 (32C); 119Sn-
NMR (112 MHz, C3H6O-d6): l −205.2, −183.8.
Anal. Calc. for C48H32Br4F72O2Sn4: C, 20.57; H, 1.15.
Found: C, 20.96; H, 1.14%.
References
[1] (a) T. Horva´th, Acc. Chem. Res. 31 (1998) 641;
(b) D.P. Curran, Angew. Chem. Int. Ed. Engl. 37 (1998) 1174;
(c) E.G. Hope, A.M. Stuart, J. Flourine Chem. 100 (1999) 75.
[2] D.P. Curran, S. Hadida, S.-Y. Kim, Z. Luo, J. Am. Chem. Soc.
121 (1999) 6607.
3.7. Preparation of 1ac
To 1aa (172 mg, 0.1 mmol, calculated as a monomer)
in FC-72 (10 ml) was added NaSCN (5.5 g, 67.8 mmol)
in water (5 ml) at r.t. The reaction mixture was stirred
at r.t. for 20 h. After separation, the FC-72 layer was
washed with water (2×5 ml) and evaporated. The
residue was recrystallized from MeOH–THF to afford
1ac in pure form (165 mg, 95%). M.p. 143–145 °C;
1H-NMR (500 MHz, FC-72 with CDCl3 as external
lock): l 1.65–2.30 (m, 16H), 2.35–3.00 (m, 16H); 13C-
NMR (75 MHz, C3H6O-d6): l 13.0 (4C), 13.9 (4C), 25.8
(2J(13Cꢁ19F)=23.0 Hz, 8C), 106.0–123.0 (complex pat-
tern, 48C), 140.4 (2C); 119Sn-NMR (112 MHz, C3H6O-
d6): l −244.0, −191.4. IR (Nujol mull): 2900 (s),
2065, 1140, 1060, 890, 730, 540 cm−1; Anal. Calc. for
C66H32Cl2F104N2O2S2Sn4: C, 22.84; H, 0.93; N, 0.81.
Found: C, 22.97; H, 0.93; N, 0.75%.
[3] M. Larhed, M. Hoshino, S. Hadida, D.P. Curran, A. Hallberg,
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[9] (PhCH2)2SnBr2 was prepared in a way analogous to the corre-
sponding dichloride. K. Sisido, Y. Takeda, Z. Kinugawa, J. Am.
Chem. Soc. 83 (1961) 538.
[10] A. Orita, K. Sakamoto, Y. Hamada, A. Mitsutome, J. Otera,
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[14] FC-72 was solely used in this study since this is cheaper than the
other perfluorocarbons.
3.8. Determination of partition coefficient
A sample of 1aa (86 mg, 0.05 mmol, calculated as a
monomer) was dissolved in FC-72 (5 ml) to afford a
clear solution, and an organic solvent (5 ml) was added.
[15] T.A. Smith, F.S. Kipping, J. Chem. Soc. 101 (1912) 1553.