Selective Preparation of Sterically Encumbered Diaryltin Dihalides from Grignard Reagents via Salt Metathesis and Halide Exchange

Article abstract of DOI:10.1002/ejic.201900180

A general route for the selective preparation of diaryltin dichlorides, dibromides, and diiodides from readily accessible but sterically demanding, 2,6-disubstituted or 2,4,6-trisubstituted aryl Grignard reagents ArylMgBr and tin tetrachloride was developed. During work-up, the initially obtained mixture of halides is converted into a single species. The thus obtained diaryltin dichlorides were reacted to yield the dihydrides Aryl₂SnH₂. These exhibit high thermal stability and moderate oxygen tolerance.

Full text of DOI:10.1002/ejic.201900180

A Journal of
Accepted Article
Title: Selective Preparation of Sterically Encumbered Diaryltin
Dihalides From Grignard Reagents via Salt Metathesis and
Halide Exchange
Authors: Beate Gabriele Steller and Roland C. Fischer
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10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
Selective Preparation of Sterically Encumbered Diaryltin
Dihalides From Grignard Reagents via Salt Metathesis and Halide
Exchange
Beate G. Steller,[a] and Roland C. Fischer*[a]
Abstract: A general route for the selective preparation of diaryltin
dichlorides, dibromides and diiodides from readily accessible but
sterically demanding, 2,6-disubstituted or 2,4,6-trisubstituted aryl
Grignard reagents ArylMgBr and tin tetrachloride was developed.
During work-up, the initially obtained mixture of halides is converted
into a single species. The thus obtained diaryltin dichlorides were
reacted to yield the dihydrides Aryl2SnH2. These exhibit high thermal
stability and moderate oxygen tolerance.
Examples of oligostannanes stabilized by bulky aryl ligands are
small cyclic compounds like cyclotri- or tetrastannanes (Aryl2Sn)2,
n=3, 4,[9–11] polyhedral compounds such as the [1.1.1]propellanes
Aryl6Sn5,[12,13] and the di- or tricoordinate tin species Aryl2Sn or
[Aryl2Sn]2.[14]
Introduction
Diaryltin dihalides Aryl2SnX2 (X= Cl, Br, I) and the corresponding
hydrides Aryl2SnH2 are prominent starting materials for the
preparation of transition metal and main group compounds
including oligo- and polystannanes.[1] Due to their difunctional
nature, electrophilic character and high reactivity in reduction
reactions, the heavier diaryltin dihalides Aryl2SnX2 (X= Cl, Br, I)
find widespread synthetic application, while the typically only
sparingly soluble diorganotin difluorides are less commonly
used.[2] The reductive coupling of diaryltin dihalides with alkali or
alkaline metals in polar aprotic solvents or e.g. liquid ammonia
has been investigated as a route towards polystannanes and
linear X-(Aryl2Sn)n-X or cyclic oligostannanes (Aryl2Sn)n.[3] In this
context it was shown that not only stoichiometry and the aromatic
substituent determine the reaction pathway, but that also the
nature of the halide and hence the reduction potential of the
diorganotin species influences the product distribution.[4] An
alternative method for the preparation of oligo- and polystannanes,
the (catalytic) dehydrogenative coupling of diorganotin dihydrides
was employed in the synthesis of oligostannanes.[5] For both
routes an increase in the steric demand of the organic
substituents results in the preferred formation of small rings or
short, linear oligomers like di-, tri-, or tetrastannanes. Among the
extensive group of possible aromatic substituents, especially 2,6-
di- and 2,4,6-tri -substituted phenyl rings gained considerable
interest in the past as these provide sufficient steric shielding to
kinetically stabilize organotin compounds with intriguing structural
and spectroscopic properties and chemical reactivity.[6–8]
Scheme 1. Selection of commonly employed synthetic methods for the
preparation of diaryltin dihalides Aryl2SnX2. (X = Cl, Br, I)
In the past, several synthetic methods for the preparation of
diaryltin dichlorides have been investigated. An overview of the
most prominent synthetic methods is provided in Scheme 1.
Unfortunately the most obvious approach, the salt metathesis
reaction of two equivalents of an aryl lithium or aryl Grignard
species, where the aryl group is of small to moderate steric
demand, with one equivalent of tin tetrahalide does not provide
direct access to diaryltin dihalides but typically leads to complex
product mixtures.[15,16] Nevertheless, diaryltin dihalides with
aromatic substituents of limited steric hindrance are accessible
via the Kozeshkov equilibrium (I) by reacting stoichiometric
amounts of either tetraaryltin Aryl4Sn or the respective triaryltin
halide Aryl3SnX and the respective tin tetrahalide SnX4 (X = Cl,
Br, I). Since selective access to a selected tin halide derivative is
granted and the formation of complex halide mixtures is excluded,
this strategy is a convenient method for the synthesis of diaryltin
dihalides with aryl groups of moderate steric demand.[17] Due to a
rapidly decreasing migration tendency when sterically more
demanding ligands are used, more specialized preparations
methods were applied for the preparation of diaryl dihalides with
bulky substituents. Different approaches (II-VII) with more
specified reaction conditions were used for the synthesis of aryltin
chlorides with substituents like Mes (=2,4,6-trimethylphenyl),
Tripp (=2,4,6-triisopropylphenyl) and Dep (=2,6-diethylphenyl).
These include the isolation of cyclotristannoxanes (R2SnO)3 and
[a]
BG Steller, MSc and Dr. RC Fischer
Institute of Inorganic Chemistry
Graz University of Technology
Stremayrgasse 9/V, 8010 Graz, Austria
E-mail: roland.fischer@tugraz.at
Homepage: https://www.ac.tugraz.at/
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
their subsequent conversion into the dichlorides (II)[9,10,18] or via
halodearylation using strong anhydrous acids, e.g. ethereal
HCl[19]. Aryl4-nSnCln derivatives are also obtained from the
cleavage of Sn-Aryl bonds with e.g. mercury dichloride (VIII).[20]
Alternatively, diorganomercurials undergo oxidative addition to
SnCl2 (III).[21,22] In a similar fashion Wesemann and coworkers
utilized ArylSnCl3 from the reaction of ArylSn(II) chloride and
HgCl2.[23] The toxicity of diorgano mercury compounds is a
significant disadvantage of this method. It was also shown that
exchange reactions between e.g. ArylGaCl and organotin halides
can provide access to Aryl2SnCl2 (VII).[24] A major obstacle of the
use of Grignard reagents in the preparation mono-, di- or
triorganotin compounds with only one sort of halide in the
molecule is the extensive halogen-halogen exchange. This
inevitably results in the formation of product mixtures unless the
organic reagent used in the preparation of the Grignard reagent
and the tin species carry the same halide (IV). The use of aryl
lithiums as nucleophiles as in V is often hampered by metal
halogen exchange reactions which result in tin-tin bond formation
reactions as demonstrated by Molloy and coworkers. Here the
reaction of TrippLi with SnCl4 or SnBr4 led to the isolation of the
distannane (XTripp2Sn)2 (X=Cl/Br). In stark contrast, the reaction
of MesLi with tin tetrachloride under identical conditions allowed
for the isolation of Mes2SnCl2 as did the use of MesMgBr.[15]
Moreover, the reaction of Mes*Li with SnCl4 yielded the CH
activation product Mes*SnCl2(CH2CMe2)C6H2-3,5-tBu as the
major product.[16] The compared to organolithium or -Grignard
species lower tendency of organocuprates to undergo
transmetallation reactions was successfully demonstrated in the
synthesis of Tripp2SnCl2.[25] These examples show that the
outcome of seemingly simple salt metathesis reactions between
metallated aryl reagents and tin tetrahalides are by no means
straight forward to predict. A detailed overview of synthetic
strategies for Organotin(IV) halides is given by van Koten.[26]
Halide-halide interconversions (IX) were conducted for alkyltin
halides and phenyltin halides either in the fashion of a Finkelstein
reaction in dry acetone[27,28] using e.g. sodium iodide for the
conversion of triphenyltinchloride into the respective iodide or
adjustment of reactions condition, i.e. stoichiometric ratio,
reaction temperature, addition rate and solvents employed,
allowed the preparation of mononuclear, disubstituted organotin
compounds as a roughly 1:2:1 mixture of the diaryltin dichloride,
bromide-chloride and dibromide Aryl2SnX2 (X=Cl2, ClBr, Br2).
Aqueous workup of this product mixture with diluted HCl under
phase transfer conditions results in halide exchange reactions
and yields the dichloride species Aryl2SnCl2 as the sole product.
(Figure 1)
Scheme 2. Preparation of Diaryltin dihalides 1, 3, 5 and 7.
In addition to the already literature-known diaryltin dichlorides
[15]
[9]
[10]
Mes2SnCl2
,
Dep2SnCl2
and Tripp2SnCl2
which were
prepared in good to high yields, this approach was used to
prepare the novel compound Dipp2SnCl2. Furthermore and in
order to demonstrate the synthetic potential of the halide/halide
exchange, Tripp2SnCl2 was readily converted into Tripp2SnBr2
and Tripp2SnI2 by treatment with aqueous MgBr2 and ZnI2
solutions, respectively. Finally, the diaryltin dihalides were
converted into the diaryltin dihydrides Aryl2SnH2 via hydride
transfer utilizing LiAlH4. Compounds 1-8 were characterized by
heteronuclear NMR and IR spectroscopy. Single crystal X-ray
crystallographic investigations confirm the identity of these
compounds and provide insight into the solid state structure of
these compounds.
utilizing ammonium halides in Et2O/THF and H2O[29,30]
.
Alternatively, a halide-halide exchange reaction with alkyl or
silicon halides is possible and are particularly important in the
recovery of organotin fluorides from organic synthesis.[31]
Nevertheless, none of the strategies outlined in Scheme 1 is
universally applicable, since byproduct formation via
transmetallation reactions or the isolation of product mixtures are
frequently encountered, especially when more sterically
demanding carbanions are used. Once the diaryltin dichlorides
are at hand the corresponding hydrides are readily accessed as
a number of synthetic strategies for their preparation have been
developed. These include the use of lithium aluminum hydride,
LiAlH4, DIBAL-H or other hydride sources.[32]
Considering the high synthetic potential of diaryltin dihalides and
the corresponding dihydrides featuring sterically demanding aryl
ligands, we started out to develop a straight forward, readily
applicable synthetic protocol for the selective synthesis of
sterically encumbered diaryl tin dichlorides, -bromides or iodides.
Starting from Grignard reagents ArylMgBr and SnCl4, careful
Results and Discussion
Synthesis and NMR spectroscopy
Following standard Grignard reaction protocols, the aryl bromides
ArylBr, (Aryl = Mes, Dep, Dipp, Tripp), were reacted with a slight
excess of magnesium in THF and refluxed for about 2 h. Prior to
the addition to tin tetrachloride, unreacted magnesium was
removed by filtration using a filter cannula. The solution of the
Grignard reagent in THF was slowly added to a 0.5 eq. solution
of SnCl4 in toluene (for Aryl = Mes) or in n-heptane in the case of
Aryl = Dep, Dipp and Tripp, which was maintained at -50°C during
addition. The use of mixtures of tetrahydrofurane and aromatic or
aliphatic hydrocarbon solvents rather than neat THF prevents to
formation of di- and oligostannanes. Under these conditions, only
the formation of the disubstituted product is observed in the crude
reaction mixture. However, chloride-bromide exchange leads to
the formation of a mixture of Aryl2SnCl2, Aryl2SnBrCl and
Aryl2SnBr2 in a roughly 1:2:1 ratio in the crude product. (c.f. SI)
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10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
Scheme 3. Hydrogenation of Aryl2SnCl2 leads to the corresponding Aryl2SnH2.
In comparison to diphenyltin dichloride ( = -26.4 ppm)[17] the
sterically more shielded species 1a (-51.1 ppm), 3a (-65.5 ppm),
5a (-70.1 ppm) and 7a (-65.5 ppm) display a significant upfield
119Sn NMR shift of roughly 40 ppm. Interestingly, the shifts of the
dichlorides 1a, 3a, 5a and 7a are largely independent on the
substituent pattern of the aryl groups once both ortho position are
occupied by alkyl groups, but show a much stronger dependence
on the nature of the halide substituents. Hence, substitution of a
chloride by a bromide group at tin results in two successive upfield
shifts of ca 45-55 ppm for the resonances of Aryl2SnBrCl and
Aryl2SnBr2, respectively. Similarly, chloride/iodide exchange in
7a/7d/7e results in ca. 200 ppm upfield shifted resonances
at -246.1 (7d) and -462.2 ppm (7e). The upfield shift of 119Sn NMR
resonances upon descending group 17 has previously been
studied by computational methods by Bagno and coworkers.[33]
Using the two-component zeroth order regular approximation
(ZORA) as implemented in the ADF program package,[34–37] it was
shown that relativistic effects account for the upfield chemical
shifts in bromides and particularly iodides as compared to the
lighter halogens.[38] The upfield shift was attributed to an
increasing extent of spin-orbit coupling for atoms of higher atomic
number and is also apparent in the 1H shifts of hydrogen halides
and 13C NMR shifts of organic halides.[39,40] A summary of the
119Sn NMR resonances for compounds 1a-c, 3a-c, 5a-c and 7a-d
is provided in Table 1. (For spectra see SI) The diaryltin
dihydrides 2, 4, 6 and 8 were accessed via the widely applied
hydride transfer with LiAlH4 in Et2O of the corresponding chlorides
1a, 3a, 5a, 7a. (Scheme 3) Previous investigations of the
conversion of diphenyltin dichloride into the dihydrides show a
detrimental effect on the isolated yield of the respective dihydride
when ratios of LiAlH4 to Aryl2SnCl2 larger 0.8 to 1.0 are used.
With excess LiAlH4, dehydrogenative coupling, aryl group
migration to aluminum and organostannide formation are
observed as a side reactions.[41] In our hands, best results were
obtained with the above mentioned stoichiometric ratio, resulting
in isolated yields of the dihydrides between 40 and 84% with
respect to diaryltin dichloride. No additional purification steps
were necessary for the dihydrides 2, 4 and 6 while Tripp2SnH2, 8,
was recrystallised from n-pentane. NMR and IR spectroscopic
data for 2, 4, 6, and 8 are summarised in Table 2. While diaryltin
dihydrides are stable against moisture, the sterically unprotected
diorganotin dihydrides are thermolabile and rapidly react with
oxygen to form the corresponding hydroxides or oxides and
oligomerize following a radical pathway.[32] Yet, thermal stability
and oxygen tolerance of diaryltin dihydrides is greatly enhanced
with appropriate steric protection as in compounds 2, 4, 6 and 8
for which the solids can be manipulated in air for short periods of
Figure 1. Exemplary depiction of the crude product Dep2SnX2 showing 119Sn
NMR resonances for 3a, b and c before aqueous workup (above) and after the
wash with aqueous hydrochloric acid showing only one resonance for 3a.
The extent of halide exchange varies between repeated
experiments and strongly depends on the solubility of resulting
magnesium halides, concentration of the reactions mixture,
temperature, reaction time and addition rate of the Grignard
reagent. The crude products were investigated NMR
spectroscopically after aqueous work up of an aliquot. Due to the
1
complexity of their NMR spectra, H and 13C resonances of the
3c
crude product mixture were not assigned with certainty. However,
in all cases the 119Sn NMR spectra of the crude products show
three signals. (Figure 1) In agreement with literature data and
corroborated by the selective preparation of 1a[15], 3a, 5a and
7a[10], in all cases the resonances at lowest field were attributed
to Aryl2SnCl2. In contrast to Molloy and coworkers, who found
solely the formation of the distannane XTripp2SnSnTripp2X, X =
Cl, Br, in the reaction of the more sterically demanding carbanion
2,4,6-triisopropylphenyl lithium with SnX4, X = Cl, Br, in THF,[15]
we did not observe the formation of a coupling product under the
herein reported reaction conditions.
In order to convert the halide mixtures into neat dichlorides, the
dry, crude products were redissolved in
a
mixture of
dichloromethane (DCM/THF = 4/1) and were vigorously stirred
with the same volume of 1.0 M aqueous hydrochloric acid. After
two consecutive washes with dilute HCl, complete
bromide-chloride exchange was observed, hence leading to pure
diaryltin chlorides 1a, 3a, 5a and 7a in moderate to good overall
yields of 30-90%. Using small amounts of THF to ensure phase
transfer of the halide ions proofs critical, as no halide exchange
occurs when neat DCM is used as solvent. Treatment of the
organic phases with saturated brine and standard work-up yielded
crude products which were further purified by recrystallization
from DCM/n-heptane to give spectroscopically pure samples.
Similarly, treatment of a DCM/THF solution of Tripp2SnCl2 with
0.8 M aqueous solutions of MgBr2 and ZnI2 led to a halogen
exchange and the formation of Tripp2SnBr2 and Tripp2SnI2
respectively. The chloride-iodide exchange reactions were
followed NMR spectroscopically. For spectra see SI. Noteworthy,
halogen exchange is more efficient when using 0.8 M ZnI2
solution than 1.6 M KI solution. (See SI)
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10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
Table 1. 119Sn NMR Shifts [ppm] of Aryl2SnCl2, Aryl2SnXCl and Aryl2SnX2 (X = Br, I) in the crude product in CDCl3.
Aryl =
Mes[a]
X =
Aryl2SnCl2
-51.1
Δδ
45.1
47.3
50.3
50.1
180.6
Aryl2SnXCl
-96.2
Δδ
50.0
52.1
55.4
55.3
216.1
Aryl2SnBr2
-146.2
1a-c
3a-c
5a-c
7a-c
7a,d,c
Br
Br
Br
Br
I
Dep
Dipp
Tripp
Tripp
-65.4[b]
-70.1
-112.8
-164.9
-120.4
-175.8
-64.8[c]
-65.5
-115.6
-170.9[c]
-462.2
-246.1
[a] All values correspond nicely to the data given in literature.[15] [b] No literature value given.[9] [c] Values are in accordance to literature value.[10,18]
time and for which decomposition temperatures of up to 115°C
were observed.
Mes*2SnCl2 (95.5(1)°).[16] The C-Sn-C angles decrease when the
chlorine atoms are replaced by bromine or iodine as exemplified
in the series 7a/7c/7e (Tripp2SnCl2: 120.4(2)°, Tripp2SnBr2:
114.98(7)°, Tripp2SnI2: 106.64(9)°). This trend is accompanied by
the expected elongation of the Sn-X distances (2.353(2) in 7a,
2.5067(5) in 7c and 2.7260(8) in 7e). A comparable behaviour is
Solid state structures
Although diaryltin dichlorides and dihydrides are a widely known
class of compounds, no structural data on the dichlorides 3a and
5a, the dibromide 7c and the diiodide 7e as well as the dihydrides
4, 6 and 8 has been reported. The number of diaryltin dihydrides
which were structurally authenticated by single crystal X-ray
structure analysis is currently limited to the structures of 2[42] and
diphenyltin dihydride[43]. An overview of selected bond distances
and angles for the dihalides 1a, 3a, 5a, 7a, 7c and 7e is provided
in Table 3. Irrespective of the aromatic substituent, the tin atom is
found in a distorted tetrahedral environment, covalently bonded to
two halogens and two aryl substituents. (Figure 2) The C-Sn-C
angles in the dichlorides 1a[24], 3a, 5a, 7a[44] are widened and
significantly deviate from the ideal tetrahedral geometry
(119.4(1)° for 5a and 125.0(1)° for 3a). Consequently, the
Cl-Sn-Cl angels in 5a (94.40(3)°), 3a (97.86(3)°) and 7a 98.0(1)°
are more acute than the respective angles in the previously
reported compounds Ph2SnCl2 (101.7(1)°) and 1a Mes2SnCl2
(100.3(2)°) but are in good agreement with the value for
[45]
met for the C-Sn-C angles in the diphenyltindihalides Ph2SnCl2
(123.85°/126.95°, two independent molecules in the asymmetric
[46]
[27]
unit), Ph2SnBr2
123.54(7)° and Ph2SnI2
(116.72(4)°). The
decrease in the C-Sn-C angle upon descending group 17 is hence
probably a consequence of a then reduced electronic repulsion
between aryl groups and the heavier halogens. The sterically
most encumbered dichlorides 3a, 5a and 7a reported herein
display slightly elongated average Sn–C bonds (between
2.145(1) and 2.160(8) Å), compared to compounds with no or less
sterically demanding ortho-alkyl groups of the aryl substituent as
[45]
[24]
e.g. in Ph2SnCl2
(2.112(5) Å) and 1a, Mes2SnCl2
,
(2.117(2) Å). Overall, structural properties as Sn-C bond lengths
as well as C-Sn-C and Cl-Sn-Cl angles are in agreement with
values for other diaryltin dichlorides featuring aryl groups with
bulky ortho-substituents, c.f the supermesityl derivative
Table 3. Selected bond lengths (Å) and angles (°) of Aryl2SnX2 (Aryl = Mes
(1a, X = Cl), Dep (3a, X = Cl), Tripp (X = Cl (7a), Br (7c), I (7e)).
Table 2 Overview of 119Sn NMR shifts [ppm] and 1J (1H, 119/117Sn) [Hz] of
-1
̃
isolated diaryltin dihydrides in C6D6 as well as 흊 (Sn-H) [cm ].
Sn–C
Sn–X
C–Sn–C
X–Sn–X
119Sn Shift
[ppm]
1J (1H, 117/119Sn)
AT-IR
Ref
[Å] (avg.)
[Å] (avg.)
[°]
[°]
̃
[Hz]
흊 (Sn-H)
[cm-1]
[24]
1a
3a
5a
7a
7c
7e
2.117(7)
2.157(3)
2.145(1)
2.147(4)
2.149(2)
2.160(8)
2.414(2)
2.361(7)
2.359(5)
2.353(2)
2.5067(5)
2.7260(8)
119.7(3)
125.0(1)
119.4(1)
120.4(2)
114.98(7)
106.64(9)
100.29(7)
97.86(3)
94.40(3)
98.0(1)
[43]
Ph2SnH2
-233.7
-352.82[47]
-352.20
-355.41
-352.29
1841/1939
1764.8/1846.3
1762.7/1843.8
1753.3/1835.0
1736.8/1820.0
1862
1846
1852
1860
2
4
6
8
[44]
99.51(1)
97.59(1)
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10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
observed (Ph2SnH2: 114.4(7)°; Mes2SnH2: 111.07(4)°). The
isolated diaryltin dihydrides 4 (107(1)°), 6 (103(1)°) and 8
(105.0(9)°) show similar H–Sn–H angles like Ph2SnH2 (105.0(2)°).
The Sn-C bond distances in 4 (2.163(2) Å), 6 (2.169(7) Å) and 8
(2.16(1) Å) are again slightly elongated in comparison to Ph2SnH2
(2.134(19) Å) and Mes2SnH2 (2.154(1) Å). In comparison to the
diaryltin dichlorides 3a, 5a and 7a, the Sn-C bond distances in the
respective dihydrides 4, 6 and 8 are moderately elongated.
Substitution of the chlorine atoms by hydrogens also strongly
effects the C-Sn-C angle as seen in 3a with an C–Sn–C angle of
125.0(1)° in comparison to the corresponding hydride 4 with a
C-Sn-C angle of 111.24(6)°. A similar situation is observed for
Table 4 Selected bond lengths (Å) and angles (°) of presented Aryl2SnH2
(Aryl = Dep (4), Dipp (6), Tripp (8)) compared to those of literature known
structures of Ph2SnH2 and Mes2SnH2.
Sn–C
Sn–H
[Å] (avg.)
1.65(6)
1.669(2)
1.60(8)
1.70(8)
1.62(2)
C–Sn–C
[°]
H–Sn–H
[°]
Ref
[Å] (avg.)
2.134(19)
2.154(1)
2.163(2)
2.169(7)
2.166(1)
[43]
[42]
Ph2SnH2
114.4(7)
111.07(4)
111.24(6)
108.19(8)
116.19(5)
105.0(2)
103.1(1)
107(1)
103(1)
105.0(9)
2
4
6
8
[44]
Tripp2SnCl2 7a (120.4(2)°) and Tripp2SnH2 8 (116.19(5)°) but
also for 5a Dipp2SnCl2 (119.4(1)°) and Dipp2SnH2 6 (108.19(8)°).
Conclusions
[16]
Mes*2SnCl2
(Mes* = 2,4,6-tri-tert-butylphenyl, 2.198(4) Å and
95.5(1)°).. Notably, there is a total absence of intermolecular
X∙∙∙Sn interactions in the structures of compounds 1a, 3a, 5a, 7a,
7c and 7e, possibly because of the high steric demand of the aryl
ligand.
Conversion of sterically demanding Aryl magnesium bromides
with SnCl4 in a 2:1 stoichiometric ratio at low temperatures and
mixtures of hydrocarbon solvents and THF gave a mixture of
dihalides Aryl2SnX2 (X=Cl,Br). By treating the thus obtained crude
products with aqueous HCl or MX2 (=MgBr2 or ZnI2) solutions,
these mixtures are selectively converted into the dichlorides,
dibromides or diiodides. The isolated diaryltin dichlorides wre
converted into the corresponding tin hydrides by hydrogenation
using LiAlH4. All isolated compounds were spectroscopically
characterized by multinuclear (1H, 13C, 119Sn) NMR and IR. In
addition the solid state structures of 3a, 4, 5a, 6, 7c and 7e and 8
are reported.
Experimental Section
General considerations: All manipulations involving air or
moisture sensitive compounds were either performed under a
nitrogen atmosphere using standard Schlenk tube techniques or
drybox techniques. Further details including analytical techniques
and data (spectra, etc.) can be found in the supporting information
(SI).
Figure 2. Solid State Structure of diaryltin dichloride 3a and the corresponding
dihydride compound 4. All non-hydrogen atoms shown as 30% shaded
ellipsoids. Hydrogen atoms except for those bonded to Sn are omitted for clarity.
Selected bond lengths [Å] and angles [°] see Table 3 and Table 4.
General Procedure for the preparation of Aryl2SnCl2
Due to high reactivity towards oxygen, there is only limited
number of crystallographic data for tin hydrides available in
literature and only two structures of diaryltin dihydrides, namely
Ph2SnH2 (crystallised from an in situ technique in a capillary)[43]
In a 3-necked round bottom flask tin tetrachloride was dissolved
in ca. 200 mL toluene (for Aryl = Mes) or ca. 150 ml n-heptane
(Aryl = Dep, Dipp, Tripp) and cooled to -50°C. To this vigorously
stirred reaction mixture, a freshly prepared solution of the
Grignard reagent ArylMgBr, which was obtained by reacting
ArylBr with Mg in THF, was added dropwise over a period of ca.
2 hours. After complete addition, the yellowish suspension was
allowed to warm up to rt overnight followed by heating to reflux for
2 h. Afterwards, the solvents were removed under reduced
pressure to yield an off-white solid. 119Sn NMR of the crude
product in CDCl3 revealed three species, Aryl2SnCl2, Aryl2SnClBr
and Aryl2SnBr2. For workup, the solid residues was dissolved in
200 mL DCM and 50 mL THF after which 200 mL aqueous HCl
[42]
and Mes2SnH2 are known. Similar to the halides, the tin atom
in the novel diaryltin dihydrides 4, 6 and 8, is found in a distorted
tetrahedral environment. (Figure 2) In Table 4 selected bond
distances and angles of 4, 6 and 8 and previously reported
examples 2 and Ph2SnH2 are summarised. All hydrogen atoms
bonded to tin were located in the difference map. The Sn–H bond
lengths of presented structures nicely compare to distances
observed in Ph2SnH2 (1.65(6) Å avg.) and Mes2SnH2 (1.67(2) Å
avg.). Similar to the corresponding dichlorides, no trend between
sterical demand of the aryl moiety and the C-Sn-C angle is
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10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
(1.0 M) were added and the two phase mixture was stirred for 1 h.
After separation of the organic and aqueous layer, this procedure
was repeated a second time with additional 200 ml of aqueous
HCl (1.0 M). The combined aqueous layers were reextracted with
DCM (2x100 mL). Combined organic layers were treated with
brine (1x200 mL), dried over Na2SO4 and filtered. The solvent was
removed under reduced pressure to give an off-white solid which
was recrystallized hereafter.
Synthesis of Mes2SnCl2 (1a): Starting from 4.25 mL SnCl4
(9.48 g, 36.4 mmol, 1.0 eq), 15.95 g MesBr (80.1 mmol, 2.2 eq)
and 2.16 g Mg turnings (88.8 mmol, 2.44 eq) and following the
general procedure, a crude product was obtained which exhibited
119Sn NMR resonances at -51.08 ppm (Mes2SnCl2), -96.17 ppm
(Mes2SnClBr) and -146.22 ppm (Mes2SnBr2). The crude product
was purified by recrystallization from DCM/n-heptane.
Spectroscopic data is in accordance with literature.[15]
6.7 Hz, 4 H; 4xCH), 1.21 (d, 3JH,H = 6.7 Hz, 24 H; 8xCH3) ppm. 13
C
NMR (75.5 MHz, CDCl3) δ 154.19 (CAryl), 142.71 (CAryl), 131.66
(CAryl), 124.89 (3JC,Sn = 74.8 Hz; CAryl), 37.58 (3JC,Sn = 51.0 Hz; CH),
24.81 (CH3) ppm. 119Sn NMR (111.92 MHz, CDCl3) δ -70.07 ppm.
Synthesis of Tripp2SnCl2 (7a): Starting from 4.25 mL SnCl4
(9.48 g, 36.4 mmol, 1.0 eq), 15.95 g MesBr (80.1 mmol, 2.2 eq)
and 2.16 g Mg turnings (88.8 mmol, 2.44 eq) and following the
general procedure, a crude product was obtained which exhibited
119Sn NMR resonances at -65.62 ppm (Tripp2SnCl2), -115.64 ppm
(Tripp2SnClBr) and -170.87 ppm (Tripp2SnBr2). The crude
product was purified by recrystallisation from n-heptane. Crystals
suitable for X-Ray crystallography were obtained by
recrystallisation from n-pentane. Crystals suitable for X-Ray
crystallography were obtained by recrystallisation from n-pentane.
1H and 119Sn spectroscopic data is in accordance with
literature.[10]
Yield: 4.01 g (26 %), colourless solid. m.p.exp 181-183°C (m.p.lit
185°C[22]) Anal. Calcd. for C18H22Cl2Sn: C, 50.52; H, 5.18. Found:
Yield: 19.30 g (90%), colourless solid. m.p.exp 142-144 °C (m.p.lit
155-157[10]). Anal. Calcd. for C30H46Cl2Sn: C, 60.43; H, 7.78.
Found: C, 59.94; H, 7.49. 1H NMR (300.22 MHz, CDCl3) δ 7.05
1
C, 50.19; H, 5.13. H NMR (300.22 MHz, CDCl3) δ 6.93 (s, 4 H;
4xHAryl), 2.55 (s, 12 H; 4xo-CH3), 2.30 (s, 6 H; 2xp-CH3) ppm. 13
C
(s, JH,Sn = 38.0 Hz, 4 H; 4xHAryl), 3.27 (qu, JH,H =6.7 Hz, 4 H;
4
3
NMR (75.5 MHz, CDCl3) δ 143.69 (CAryl), 141.54 (CAryl), 139.28
(CAryl), 129.70 (CAryl), 24.86 (CH3), 21.26 (CH3) ppm. 119Sn NMR
(111.92 MHz, CDCl3) δ -50.91 ppm.
4xCH), 2.88 (qu, 3JH,H = 7.0 Hz, 2 H; 2xCH), 1.43 – 0.99 (m, 36 H;
12xCH3) ppm. 13C NMR (75.5 MHz, CDCl3) δ 154.19 (2JC,Sn
66.0 Hz; CAryl), 152.33 (CAryl), 139.99 (CAryl), 123.00 (3JC,Sn
=
=
Synthesis of Dep2SnCl2 (3a): Starting from 4.25 mL SnCl4
(9.48 g, 36.4 mmol, 1.0 eq), 15.95 g MesBr (80.1 mmol, 2.2 eq)
and 2.16 g Mg turnings (88.8 mmol, 2.44 eq) and following the
general procedure, a crude product was obtained which exhibited
119Sn NMR resonances at -65.38 ppm (Dep2SnCl2), -112.81 ppm
(Dep2SnClBr) and -164.90 ppm (Dep2SnBr2). The solvent was
removed under reduced pressure to give a brownish solid. The
crude product was purified by recrystallisation from a mixture of
DCM/n-heptane. Crystals suitable for single crystal X-Ray
diffractometry were obtained by recrystallisation from n-pentane.
1H spectroscopic data is in accordance with literature.[9]
Yield: 10.88 g (66%), colourless solid. m.p.exp 69-70°C (m.p.lit
67.5-68.5°C[9]). Anal. Calcd. for C20H26Cl2Sn: C, 52.68; H, 5.75.
Found: C, 52.44; H, 5.75. 1H NMR (300.22 MHz, CDCl3) δ 7.38 (t,
3JH,H = 7.5 Hz, 2 H; 2xHAryl), 7.18 (d, 3JH,H = 7.5 Hz, 4 H; 4xHAryl),
2.91 (q, 3JH,H = 7.2 Hz, 8 H; 2xCH2), 1.23 (t, 3JH,H = 7.2 Hz, 12 H;
4xCH3) ppm. 13C NMR (75.5 MHz, CDCl3) δ 149.90 (CAryl), 142.73
(CAryl), 131.54 (CAryl), 127.47 (3JC,Sn = 74.5 Hz; CAryl), 31.70 (3JC,Sn
= 48.8 Hz; CH2), 16.77 (CH3) ppm. 119Sn NMR (111.92 MHz,
CDCl3) δ -65.36 ppm.
Synthesis of Dipp2SnCl2 (5a): Starting from 4.25 mL SnCl4
(9.48 g, 36.4 mmol, 1.0 eq), 15.95 g MesBr (80.1 mmol, 2.2 eq)
and 2.16 g Mg turnings (88.8 mmol, 2.44 eq) and following the
general procedure, a crude product was obtained which exhibited
119Sn NMR resonances at -70.06 ppm (Dipp2SnCl2), -120.35 ppm
(Dipp2SnClBr) and -175.75 ppm (Dipp2SnBr2). The crude product
was purified by recrystallisation from n-heptane. Crystals suitable
for X-Ray crystallography were obtained by recrystallisation from
n-pentane.
77.6 Hz; CAryl), 37.46 (3JC,Sn = 49.7 Hz; CH), 34.42 (CH), 24.91
(CH3), 23.96 (CH3) ppm. 119Sn NMR (111.92 MHz, CDCl3)
δ -64.76 ppm.
Synthesis of Tripp2SnBr2 (7c)
2.00 g Tripp2SnCl2 (3.35mmol) dissolved in 8 mL DCM and 2 mL
THF was stirred with 8 mL aqueous MgBr2 solution (0.8 M) for 1 h.
The phases were separated, after which the organic phase was
treated two more times with 8 mL aqueous MgBr2 solution (0.8 M).
The combined aqueous layers were reextracted with DCM
(2x10 mL). The combined organic layers were dried over Na2SO4,
filtered and the solvent was removed under reduced pressure.
Crystals suitable for X-Ray crystallography were obtained by
recrystallisation from DCM. Spectroscopic data is in accordance
with literature.[18]
Yield: 1.88 g (82%), colourless solid. m.p.exp 139-143°C (m.p.lit
65°C[18]). Anal. Calcd. for C30H46Br2Sn: C, 52.59; H, 6.77. Found:
C, 52.35; H, 6.61. 1H NMR (300.22 MHz, CDCl3) δ 7.01(s, 4JH,Sn
3
= 38.2 Hz, 4 H; 4xHAryl), 3.37 (sept, JH,H = 6.6 Hz, 4 H; 4xCH),
3
3
2.86 (sept, JH,H = 6.7 Hz, 2 H; 2xCH), 1.22 (d, JH,H = 6.7 Hz,
12 H; 4xCH3), 1.15 (d, JH,H = 6.6 Hz, 24 H; 8xCH3) ppm. 13C
3
NMR (75.5 MHz, CDCl3) δ 153.57 (CAryl), 152.08 (CAryl), 139.82
(CAryl), 122.91 (3JC,Sn = 74.3 Hz; CAryl), 37.31 (3JC,Sn = 51.2 Hz; CH),
34.39 (CH), 24.55 (CH3), 23.99 (CH3) ppm. 119Sn NMR
(111.92 MHz, CDCl3) δ -167.72 ppm.
Synthesis of Tripp2SnI2 (7e)
Yield: 5.78 g (31%), colourless solid. m.p.exp 196-198°C. Anal.
Calcd. for C24H34Cl2Sn: C, 56.29; H, 6.69. Found: C, 56.26; H,
6.69. 1H NMR (300.22 MHz, CDCl3) δ 7.42 (t, 3JH,H = 7.6 Hz, 2 H;
2.00 g Tripp2SnCl2 (3.35mmol) dissolved in 8 mL DCM and 2 mL
THF was stirred with 8 mL aqueous ZnI2 solution (0.8 M) for 1 h.
The phases were separated and the organic phase was treated a
second time with 8 mL aqueous ZnI2 solution (0.8 M). The
3
3
2xHAryl), 7.23 (d, JH,H = 7.6 Hz, 4 H; 4xHAryl), 3.29 (qu, JH,H
=
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10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
combined aqueous layers were reextracted with DCM (2x10 mL).
The combined organic layers were dried over Na2SO4, filtered and
the solvent was removed under reduced pressure. Crystals
suitable for X-Ray crystallography were obtained by
recrystallisation from n-pentane.
(CAryl), 126.15 (3JC,Sn = 43.7 Hz; CAryl), 33.26 (3JC,Sn = 40.2 Hz;
CH2), 16.76 (CH3) ppm. 119Sn NMR (111.92 MHz, C6D6) δ -352.20
(1JSn,H = 1844 Hz) ppm. MS (DI-EI): calcd for [M+]: 387.1138;
found: 387.1162. ATR-FTIR 휐̃ 1846 (s; νs SnH) cm-1.
Synthesis of Dipp2SnH2 (6): 1.20 g LiAlH4 (31.6 mmol, 0.81 eq)
and 20.00 g Dipp2SnCl2 (39.1 mmol, 1.0 eq) were reacted
according to the general procedure to yield a brownish oil after
removal of the solvent which crystallizes upon cooling to -30°C.
The crude product was recrystallized from alkanes. Crystals
suitable for single crystal X-Ray diffraction were obtained by
recrystallisation from n-pentane.
Yield: 2.37 g (91%), colourless solid. m.p.exp 145-148°C. Anal.
Calcd. for C30H46I2Sn: C, 46.24; H, 5.95. Found: C, 45.93; H, 5.78.
4
1H NMR (300.22 MHz, CDCl3) δ 6.93 (s, JH,Sn = 37.1 Hz, 4 H;
4xHAryl), 3.50 (sept, 3JH,H = 6.7 Hz, 4 H; 4xCH), 2.84 (sept, 3JH,H
=
6.9 Hz, 2 H; 2xCH), 1.20 (d, 3JH,H = 6.9 Hz, 12 H; 4xCH3), 1.10 (d,
3JH,H = 6.7 Hz, 24 H; 8xCH3) ppm. 13C NMR (75.5 MHz, CDCl3) δ
152.70 (2JC,Sn = 60.8 Hz; CAryl), 151.54 (4JC,Sn = 14.2 Hz; CAryl),
Yield: 14.15 g (82%), off-white solid. m.p.: 41-43°C. Anal. Calcd.
for C24H36Sn: C, 65.03; H, 8.19. Found: C, 64.73; H, 7.73. 1H NMR
(300.22 MHz, C6D6) δ 7.26-7.21 (m, 2 H; 2xHAryl), 7.15-7.05 (m,
137.45 (CAryl), 122.65 (3JC,Sn = 68.7 Hz; CAryl), 37.10 (3JC,Sn
=
51.8 Hz; CH), 34.18 (CH), 24.27 (CH3), 23.88 (CH3) ppm. 119Sn
NMR (111.92 MHz, CDCl3) δ -462.19 ppm.
4 H; 4xHAryl), 6.22 (s, JH,119Sn = 1835 Hz, JH,117Sn = 1753 Hz, 2 H;
3
SnH2), 3.27 (septett, JH,H = 6.7 Hz, 4 H; 4xCH), 1.15 (d, JH,H
=
6.7 Hz, 24 H; 8xCH3) ppm. 13C NMR (75.5 MHz, C6D6) δ 155.56
(CAryl), 138.77 (CAryl), 130.09 (CAryl), 123.51 (3JC,Sn = 44.0 Hz; CAryl),
38.27 (3JC,Sn = 41.0 Hz; CH), 24.65 (CH3) ppm. 119Sn NMR
(111.92 MHz, C6D6) δ -355.41 (JSn,H = 1835 Hz) ppm MS (DI-EI):
calcd for [M+]: 443.1765; found: 443.1792. ATR-FTIR 휐̃ 1852 (s;
νs SnH) cm-1.
General Procedure for Aryl2SnH2
In a 250 mL round-bottom Schlenk flask LiAlH4 was suspended in
Et2O and cooled down to 0°C. At 0°C diaryltin dichloride was
added in portions. After 1 h of stirring at 0°C the reaction mixture
was transferred via a canula onto 35 ml of degassed H2SO4
(0.5 M, cooled to 0°C), while anaerobic conditions were
maintained. After separation of the layers and still under exclusion
of oxygen, the organic phase was extracted twice with degassed,
saturated potassium tartrate solution (75 ml each) to remove
aluminum salts. The organic layer dried over Na2SO4 and filtered.
The solvent was removed to give colourless to brownish crude
reactions products which was recrystallized n-pentane.
Synthesis of Tripp2SnH2 (8): 0.98 g LiAlH4 (25.8 mmol, 0.86 eq)
and 18.00 g Tripp2SnCl2 (30.2 mmol, 1.0 eq) were reacted
according to the general procedure to yield a brownish solid. The
resulting brownish solid was purified by recrystallisation from
n-pentane. Crystals suitable for single crystal X-Ray diffraction
were also obtained by recrystallization also from n-pentane.
Spectroscopic data is in accordance with literature.[48]
Yield: 7.15 g (45%), colourless solid. m.p.: 55-57°C. Anal. Calcd.
Synthesis of Mes2SnH2 (2): 0.37 g LiAlH4 (0.95 mmol, 0.81 eq)
and 5.00 g Mes2SnCl2 (11.7 mmol, 1.0 eq) were reacted
according to the general procedure to yield a colourless solid after
removal of the solvent which was used without further purification.
Yield: 2.26 g (54%), colourless solid. m.p.exp 140-143°C (m.p.lit
133-135°C [47]). Anal. Calcd. for C18H24Sn: C, 60.21; H, 6.74.
Found: C, 59.73; H, 6.55. 1H NMR (300.22 MHz, C6D6) δ 6.75 (s,
for C30H48Sn: C, 68.32; H, 9.17. Found: C, 67.78; H, 8.85. 1H NMR
1
(300.22 MHz, C6D6) δ 7.14 (s, 4 H; 4xHAryl), 6.23 (s, JH,119Sn
=
1
1820 Hz, JH,117Sn = 1737 Hz, 2 H; SnH2), 3.40-3.29 (m, 4 H;
4xCH), 2.78 (qu, 3JH,H = 7.0 Hz, 2 H; 2xCH), 1.22 (t, 3JH,H = 6.5 Hz,
36 H; 12xCH3) ppm. 13C NMR (75.5 MHz, C6D6) δ 155.72 (CAryl),
150.39 (CAryl), 135.94 (CAryl), 121.62 (JC,Sn = 45.6 Hz; CAryl), 38.22
(CH), 34.72 (CH), 24.77 (CH3), 24.24 (CH3) ppm. 119Sn NMR
(111.92 MHz, C6D6) δ -352.29 (1JSn,H = 1820 Hz) ppm. ATR-FTIR
휐̃ 1860 (s; νs SnH) cm-1.
1
4JH,Sn = 18.28 Hz, 4 H; 4xHAryl), 5.94 (s, JH,119Sn = 1846 Hz,
1JH,117Sn = 1765 Hz, 2 H; SnH2), 2.36 (s, 12 H; 4xo-CH3) 2.11 (s,
6 H; 2xp-CH3) ppm. 13C NMR (75.5 MHz, C6D6) δ 144.87 (CAryl),
138.67 (CAryl), 135.13 (CAryl), 129.16 (CAryl), 25.99 (3JC,Sn = 43.6 Hz,
o-CH3), 21.0 (p-CH3) ppm. 119Sn NMR (111.92 MHz, C6D6)
δ -352.82 (1JSn,H = 1846 Hz) ppm (Lit δ -352.82 ppm.[47]). ATR-
FTIR 휐̃ 1862 (s; νs SnH) cm-1.
CCDC 1897146 (for 5a), 1897147 (for 7c), 1897148 (for 3a),
1897149 (for 7e), 1897150 (for 4), 1897151 (for 8) and 1897152
(for 6) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
Synthesis of Dep2SnH2 (4): 0.81 g LiAlH4 (21.1 mmol, 0.81 eq)
and 12.00 g Dep2SnCl2 (26.3 mmol, 1.0 eq) were reacted
according to the general procedure to yield a colourless solid after
removal of the solvent which was used without further purification.
Crystals suitable for single crystal X-Ray diffraction were obtained
by recrystallisation from n-pentane.
Acknowledgments
Yield: 4.12 g (40%), colourless solid at -30°C. m.p.: about rt. Anal.
Calcd. for C20H28Sn: C, 62.05; H, 7.29. Found: C, 61.62; H, 7.10.
1H NMR (300.22 MHz, C6D6) δ 7.11 (t, 3JH,H = 7.4 Hz, 2 H; 2xHAryl),
We wish to acknowledge the European COST Network for Smart
Inorganic Polymers for providing funding. BGS thanks the
Austrian Academy of Sciences for supporting this work with the
DOC fellowship.
3
6.94 (d, JH,H = 7.7 Hz, 4 H; 4xHAryl), 6.03 (s, JH,119Sn = 1844 Hz,
JH,117Sn = 1763 Hz, 2 H; SnH2), 2.70 (q, 3JH,H = 7.3 Hz, 8 H; 4xCH2),
3
1.06 (t, JH,H = 7.3 Hz, 12 H; 4xCH3) ppm. 13C NMR (75.5 MHz,
Keywords: NMR spectroscopy • IR spectroscopy • X-Ray
diffraction • Grignard reaction • Tin • Main group elements
C6D6) δ 151.41 (2JC,Sn = 32.1 Hz; CAryl), 138.27 (CAryl), 129.81
This article is protected by copyright. All rights reserved.

10.1002/ejic.201900180
European Journal of Inorganic Chemistry
FULL PAPER
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10.1002/ejic.201900180
European Journal of Inorganic Chemistry
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