Aryltin chlorides and hydrides: Preparation, detailed NMR studies and DFT calculations

Article abstract of DOI:10.1016/j.jorganchem.2013.03.012

A series of novel tin chlorides R_nSnCl_4-n and respective hydrides R_nSnH_4-n were synthesized displaying a range of substituted phenyl residues, as well as naphthyl moieties (R = Ph, o-tolyl, 2,4-xylyl, 2,6-xylyl, p-biphenyl, 1-naphthyl, 2-naphthyl). These compounds were characterized using 1H, 13C and 119Sn NMR spectroscopy. In addition, X-ray diffraction was employed to elucidate the molecular structure of all solid aryltin chlorides (8e10, 14, 15). In each case, the tin is in a distorted tetrahedral environment. All naphthyl containing derivatives exhibit displaced π-π stacking. DFT calculations were carried out to compare experimental NMR data with calculated ¹³C and ¹¹⁹Sn shifts, as well as ¹³C-¹¹⁹Sn coupling constants.

Full text of DOI:10.1016/j.jorganchem.2013.03.012

Accepted Manuscript
Aryltin Chlorides and Hydrides: Preparation, Detailed NMR Studies and DFT
Calculations
Cathrin Zeppek, Johann Pichler, Ana Torvisco, Michaela Flock, Frank Uhlig
PII:
S0022-328X(13)00197-6
10.1016/j.jorganchem.2013.03.012
JOM 17922
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 24 January 2013
Revised Date: 26 February 2013
Accepted Date: 7 March 2013
Please cite this article as: C. Zeppek, J. Pichler, A. Torvisco, M. Flock, F. Uhlig, Aryltin Chlorides
and Hydrides: Preparation, Detailed NMR Studies and DFT Calculations, Journal of Organometallic
Chemistry (2013), doi: 10.1016/j.jorganchem.2013.03.012.
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ACCEPTED MANUSCRIPT
Hydrogen coupled 119Sn-NMR
H
Sn H
H
Sn H
H
Sn
H
Sn

ACCEPTED MANUSCRIPT
The graphical abstract depicts a hydrogen coupled 119Sn-NMR of four phenyl substituted
organostannanes (Ph4Sn, Ph3SnH, Ph2SnH2, PhSnH3). In accordance to the number of
hydrogen atoms bond to the tin the multiplicity of the signal increases.

ACCEPTED MANUSCRIPT
Aryltin Chlorides and Hydrides: Preparation, Detailed NMR Studies and DFT
Calculations
Cathrin Zeppek, Johann Pichler, Ana Torvisco, Michaela Flock, Frank Uhlig*
Graz, Austria
*Corresponding author: TU Graz, 6330 Institut für Anorganische Chemie, 8010 Graz,
Stremayrgasse 9/IV, Room CE04502, Austria
Telephone : +43-316-873 32101; Fax : +43-316-873 32102
Email : frank.uhlig@tugraz.at
Keywords: diaryltin dichlorides, aryltin trichlorides, diaryltin dihydrides, aryltin trihydrides,
119Sn- and 13C-NMR, DFT calculations
1 Abstract
A series of novel tin chlorides RnSnCl4-n and respective hydrides RnSnH4-n were synthesized
displaying a range of substituted phenyl residues, as well as naphthyl moieties (R= Ph, o-
tolyl, 2,4-xylyl, 2,6-xylyl, p-biphenyl, 1-naphthyl, 2-naphthyl). These compounds were
1
characterized using H-, 13C- and 119Sn-NMR spectroscopy. In addition, X-ray diffraction
was employed to elucidate the molecular structure of all solid aryltin chlorides (8-10, 14,
15). In each case, the tin is in a distorted tetrahedral environment. All naphthyl containing
derivatives exhibit displaced π-π stacking. DFT calculations were carried out to compare
experimental NMR data with calculated 13C- and 119Sn- shifts, as well as 13C-119Sn coupling
constants.
1

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2 Introduction
Group 14 metal hydrides become increasingly sensitive towards oxygen or temperature the
heavier the homologue according to the dissociation energy of the M-H bond [1]. Stannane
(SnH4) itself is highly labile and undergoes rapid decomposition at room temperature under the
formation of elementary tin and hydrogen [2]. This sensitivity towards elevated temperatures can
be lowered by the substitution of a hydrogen atom with an alkyl or aryl moiety. Furthermore, the
reactivity towards atmospheric oxygen increases with the number of hydride functionalities
leading to poorly soluble precipitates [3].
Initial preparation methods of organotin hydrides involved treating organotin sodium with
ammonium chloride or bromide in liquid ammonia [4]. In this manner, Kraus and Greer were the
first to successfully synthesize trimethyltin hydride and triphenyltin hydride. Further
investigations concerning the preparation, characteristics and reaction behaviour of organotin
hydrides were quite neglected due to their instability. This lasted until 1947, when Finholt and
co-workers developed a novel and more convenient route, generating hydrides of Group 14
elements and their organic derivatives using LiAlH4 (lithium aluminum hydride) starting with the
corresponding chloride [2]. They were able to generate stannane, methyltin trihydride,
dimethyltin dihydride, and trimethyltin hydride. Afterwards, Ziegler and Gellert reported the
formation of organotin hydrides using DIBAL (diisobutylaluminum hydride) as reducing agent
[5]. However, using LiAlH4 as a straight forward synthetic procedure has been applied as general
approach for the successful formation of mono-, di- and trihydrido organotin compounds (R3SnH,
R2SnH2, and RSnH3) in high yields and purity (Scheme 1) [2].
2

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Scheme 1: Formation of organotin mono-, di- and trihydrides via hydrogenation of the corresponding chloride.
Synthetic applications for triorgano tin hydrides (R3SnH) are a well investigated field in
organometallic and organic synthesis, especially in mediating radical additions, rearrangement
and elimination reactions. Specifically, Bu3SnH (TBTH, tributyltin hydride) is widely used to
bring about hydrostannolysis or hydrostannation by radical chain mechanisms [6]. Furthermore,
in the last decade, organotin dihydrides have been studied as precursors in the formation of
polymeric materials exhibiting a linear backbone of covalently bonded tin atoms. Organotin
hydrides can also undergo a catalytic dehydropolymerization using metal complexes based on
palladium, zirconium, rhodium, lanthanides, or platinum [7,8,9]. Moreover, a solvent and catalyst
free dehydrogenation reaction was described as a successful route towards polystannanes [10].
More recently, amine bases such as TMEDA (N,N,N’,N’-tetramethylethylenediamine) have been
reported to efficiently catalyze the polymerization reaction of organotin dihydrides leading to
poly(diarylstannane)s [ 11 ]. Linear polystannanes harboring a covalently linked metal (tin)
backbone, which can be seen as a molecular metal wire embedded in an organic jacket, feature an
increased degree of electron delocalization by catenation leading to promising materials in
charge-transfer devices [12,13].
In comparison to the use of organotin monohydrides (R3SnH) as a versatile synthetic tool,
less is known about the synthesis, properties, as well as applications of dihydrides (R2SnH2)
[2,14,15]. In case of trihydrides (RSnH3), mainly alkyl substituted species have been reported, but
3

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have not been fully characterized [16]. In most cases, 119Sn- and 13C-NMR spectroscopy was not
performed and only 1H-NMR shifts or elemental analysis were reported. In addition, all reported
trihydrides are liquids leading to a lack of structural information. Even less is known on tin
hydride derivatives containing aromatic substituents. Apart from the published compounds
PhSnH3 and tripSnH3 (trip= 2,4,6-triisopropylphenyl), all other known trihydrides exhibit alkyl
moieties [17,18]. TerphenylSnH3 has only been mentioned as a calculated intermediate in the
activation of hydrogen by distannanes leading to a tin (II) hydride product [19].
The limited number of investigations on the synthesis and spectral data of dihydrides and
especially trihydrides and their potential use as polymerization educts provided motivation for the
synthesis and full characterization of a series of novel aryltin di- and trihydrides and to provide
1
extensive H-, 13C- and 119Sn-NMR studies. Furthermore, theoretical DFT calculations were
carried out to supplement the experimental NMR data.
3 Experimental
3.1 Materials and methods
See Supplementary material for detailed information on general experimental details for synthesis
and characterization of compounds 1-25.
All reactions, unless otherwise stated, were carried out using standard Schlenk line techniques
under nitrogen atmosphere. All dried and deoxygenated solvents were obtained from a solvent
drying system (Innovative Technology, inc). Tin tetrachloride anhydrous (98% v/v) was
purchased at Alfa Aesar, distilled and stored under nitrogen. C6D6 was distilled over sodium and
4

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stored under nitrogen. All other chemicals from commercial sources (arylbromides, Ph3SnCl and
Ph4Sn) were utilized without further purification. All starting compounds, tetraaryl stannanes
(Ar4Sn), were obtained according to published procedures [20]. All aryltin dichlorides and
trichlorides were synthesized following the literature procedure via a Kozeshkov redistribution
reaction [21-24]. Aryltin dihydrides and trihydrides were generated according to the preparation
method of Finholt, Bond and Schlesinger in Et2O using lithium aluminum hydride (LiAlH4) as
reducing agent [2]. For already published compounds, only 1H-, 13C- and 119Sn-NMR is provided.
Elemental analysis was performed with an Elementar Vario EL III. Melting point measurements
were carried out by threefold determination with a Stuart Scientific SMP 10 (up to 300°C).
3.2 NMR- Spectroscopy
13
1H (300.22 MHz), C (75.5 MHz) and 119Sn (111.92 MHz) NMR spectra were recorded on a
Mercury 300 MHz spectrometer from Varian at 25°C. Chemical shifts are given in parts per
million (ppm) relative to TMS (δ= 0 ppm) regarding 13C and 1H and relative to SnMe4 in the case
of 119Sn. Coupling constants (J) are reported in Hertz (Hz). All NMRs were taken in C6D6.
Reactions were monitored via 119Sn-NMR using a D2O capillary as external lock signal. For
complete peak assignment, multinuclear NMR experiments were also carried out (H,H-COSY
and C,H-HETCOR) as well as shift comparisons to already known and similar compounds in
literature were made [25,26].
5

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3.3 Crystal structure determination
XRD data collection was performed on a Bruker Apex II diffractometer with use of Mo Kα
radiation (λ= 0.71073 Å) and a CCD area detector. Empirical absorption corrections were applied
using SADABS [27,28]. The structures were solved with use of either direct methods or the
Patterson option in SHELXS and refined by the full-matrix least-squares procedures in SHELXL
[29,30]. Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were located in
calculated positions corresponding to standard bond lengths and angles.
3.4 Theoretical calculations
Density functional calculations were performed using the Gaussian03 software package [31]. For
geometry optimizations and analytical frequencies the MPW1PW91 [32] functional was applied
in basis set combination denoted SDD consisting of a Stuttgart-Dresden relativistic
pseudopotential on tin and D95V double-zeta all electron basis sets on the remaining atoms.
Magnetic shieldings and nuclear spin-spin coupling constants were obtained with the same
functional using Iglo-II basis sets for all atoms. The NMR chemical shifts were calculated by
referencing to the magnetic shieldings of SiMe4 (σC= 186.5 ppm) and SnMe4 (σSn= 2552.5 ppm).
6

ACCEPTED MANUSCRIPT
4 Results and Discussion
4.1 Synthesis
The tin containing starting compound for all further conversions discussed herein is the
corresponding tetraaryl stannane (2-5). In the case of already published and spectroscopically
well described tetraaryl stannanes, no further information is provided. All aryltin di- and
trichlorides (7-15) as well as di- and trihydrides (17-25) were synthesized according to Scheme 2.
A wide range of substituted phenyl residues was chosen in order to provide information on the
influence of steric pressure as well as electronic factors, structural and spectroscopic parameters.
Ar= phenyl (2,6,7,11,16,17,21), o-tolyl (12,22), 2,4-xylyl (13,23), 2,6-xylyl (14,24), 1-naphthyl (3,8,15,18,25),
2-naphthyl (4,9,19) p-biphenyl (5,10,20).
Scheme 2: General synthetic scheme towards aryltin dihydrides and trihydrides.
In each case, the commercially available arylbromide was converted into the Grignard
reagent in THF or Et2O, respectively and subsequently treated with SnCl4 in order to generate the
corresponding tetraaryl stannane (Ar4Sn) [20,33]. For the ortho- substituted species (o-tolyl4Sn,
2,4-xylyl4Sn and 2,6-xylyl4Sn) the formation of product mixtures was observed. Ar4Sn was
detected in the presence of Ar3SnX and Ar2SnX2 via 119Sn-NMR. The formation of 2,6-xylyl4Sn
7

ACCEPTED MANUSCRIPT
was not observed, however the existence of not fully arylated species was confirmed via NMR.
Moreover, a halogen interchange could be detected leading to bromine species. This interchange
has also been described for the preparation of mesityl (2,4,6-methylphenyl) tin compounds,
which are considered to be sterically encumbered species as well [34]. In accordance to the steric
demand of the ortho substituent, the ratio of the desired Ar4Sn product was observed to decrease,
giving rise to a higher amount of the Ar3SnX species. Isolation of the different aryltin species as
well as optimization of the reaction conditions was not necessary because the mixtures were
treated with excess SnCl4 to generate the desired aryltin trichloride according to the Kozeshkov
equilibrium (Scheme 3) [22,23].
Scheme 3: Stoichiometry of the Kozeshkov redistribution reaction.
Nevertheless, product distribution could probably be influenced by the stoichiometry of the
Grignard reagent, solvent and reaction time. Moreover, it was reported that for the generation of
organosilicon halides, Grignard reagents permit a better control of product composition but are
sensitive towards sterically demanding organic groups which limit their reactivity [ 35 ].
Therefore, organolithium compounds could alter the ratio of the formed products. In addition, the
use of more reactive tin educts could be considered, such as replacing SnCl4 by SnI4 or SnBr4,
which would also lead to a facilitated salt formation.
8

ACCEPTED MANUSCRIPT
In contrast to the formation of aryltin trichlorides, the stoichiometric ratio of SnCl4 reacted
with tetraaryl stannane in the preparation of the dichlorides has to be regulated 2:1 to avoid
product mixtures. This pathway is illustrated in Scheme 2 as A. Route B (Scheme 2) employing
the Kocheskov equilibrium depicted in Scheme 3, is a more convenient method towards diaryltin
dichlorides. Herein, the aryltin trichloride is formed as an intermediate and subsequently treated
with 0.5 eq. of the respective tetraorgano stannane (R4Sn). Tetraorgano stannanes have the
advantage of being solid and more stable at atmospheric conditions than SnCl4 and therefore the
stoichiometry can be adjusted easily. The reaction progress for aryltin trichlorides and diaryltin
dichlorides was monitored via 119Sn-NMR in CDCl3 comparing the shifts to known literature data
[33,36,37].
Diaryltin dichlorides were isolated in high purity employing a standard work-up procedure.
In this manner residual aryltin trichlorides present were also removed. Di-1-naphthyltin
dichlorides (8) as well as di-2-naphthyltin dichloride (9) were recrystallized from ethyl acetate at
room temperature. Di-p-biphenyltin dichloride (10) was recrystallized from benzene at room
temperature. Aryltin trichlorides with less sterically demanding substituents on the aromatic ring
(11,12,13) could be purified by distillation, whereas twofold ortho substitution in 2,6-position of
the aromatic ring (14) leads to a change from the liquid to the solid state at room temperature.
Therefore, 2,6-xylyltin trichloride (14) was able to be recrystallized as well as 1-naphthyltin
trichloride (15) from pentane to afford colorless crystals.
In order to obtain the hydride species (Ar2SnH2, ArSnH3), the respective aryltin di- and
trichlorides were subjected to a hydrogenation reaction in Et2O with an excess of LiAlH4 as
described in literature [2]. Synthesis of diaryltin dihydrides was carried out at 0°C, whereas
aryltin trihydrides were generated at -30°C. For the trihydrides, the ether was removed gently at
approximately 200 mbar to avoid loss of product. In the case of di-p-biphenyltin dihydride (20)
9

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the reaction was performed in a mixture of Et2O and THF, due to the poor solubility of the educt
(10) and therefore the workup procedures differ. With the exception of Ph2SnH2 (17) the
presented dihydrides (18-20) are solid at room temperature, whereas the aryltin trihydrides are
liquids. Thermal stability of organotin hydrides was reported to decrease with replacement of
each organic group by a hydrogen atom as evidenced by trihydrides being the least stable [3].
However, all liquid aryltin trihydrides were able to be purified by distillation. The distillation was
carried out at the lowest temperature possible according to their boiling point. All dihydrides and
trihydrides were stored at -80°C under inert conditions due to their reported instability towards
oxygen and their disposition to radical reaction even at room temperature [38].
4.2 NMR- Spectroscopy and Theoretical Calculations
Herein, an extensive spectroscopic study on the synthesized, tetraaryl stannanes (Ar4Sn), di-
and trichlorides (Ar2SnCl2, ArSnCl3) as well as di- and trihydrides (Ar2SnH2, ArSnH3) is
presented. For each presented stannane, theoretical DFT calculations were carried out to
supplement the experimental 119Sn- and 13C-NMR data. For comparison purposes, phenyl
substituted monochlorides and hydrides were also included in the study.
Spectral parameters such as coupling constants and shifts are dependent on the solvent used
[39]. Therefore, C6D6 was chosen as a non-coordinating, non-reacting and comparable solvent
system. Although the synthesis of tetraorganostannanes, organotin dichlorides and organotin
trichlorides exhibiting a phenyl residue (1,5,9,14,18) is already well described in literature [20-
24,33] either no detailed NMR data is available or compounds were measured in solvents other
than C6D6 [15,20,33,34,36,40-44].
10

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The experimental data is supplemented by DFT calculations for the phenyl compound series
(PhnSnY4-n, Y= Cl, H), for methyl substituted aryltin trichlorides (o-tolylSnCl3, 2,4-xylylSnCl3,
2,6-xylylSnCl3, p-tolylSnCl3), as well as for 1-naphthylSnCl3 (Table 1). 119Sn- and 13C-NMR
shifts, 1J(13C-119Sn), as well as Sn-Cipso bond lengths and partial charges (q) at the tin and the ipso
carbon were calculated. As depicted in Figure 1, coupling constants are correctly reproduced and
results permit a qualitative interpretation. However, a certain deviation between measured and
calculated values can be observed, especially for compounds containing chlorines and their
calculated shifts. The neglect of relativistic effects of the heavy atoms (Cl and Sn) account for
part of the deviations. Moreover, molecules were regarded in the gas phase and not in solution.
Table 1: Sn-C
bond lengths (Å), partial charges of Sn and C , δ 119Sn (ppm), δ 13
C
ipso
(ppm) and 1J(13C-119Sn)
ipso
ipso
(Hz) for PhnSnY4-n, methyl substituted aryltin trichlorides and 1-naphthylSnCl3 obtained by DFT calculations.
Measured values are shown in parenthesis.
Ph₃SnH Ph₂SnH₂ PhSnH₃ Ph₃SnCl Ph₂SnCl₂ PhSnCl₃ o-tolylSnCl₃
2,4-xylylSnCl₃
2,6-xylylSnCl₃ p-tolylSnCl₃ 1-naphthylSnCl₃
(16)
(17)
(21)
(6)
(7)
(11)
(12)
(13)
(14)
(15)
Sn-Cipso
q(Sn)
2.1508
2.1494
2.1506
2.1359
2.1244
2.1153
2.1206
2.1161
2.1419
2.1108
1.67
2.1127
1.55
-0.45
1.3
1.04
-0.43
1.81
-0.49
1.77
-0.51
1.67
-0.51
1.66
-0.5
1.67
-0.52
1.65
-0.49
1.67
-0.51
q(Cipso
)
-0.44
-0.52
-27.1
δ 119Sn
-192.4
(-163)
143.5
(137.3)
-490.6
(534)
-251.0
(-233)
142.9
(135.5)
-494.5
(544)
-367.5
(-345)
141.0
(132.7)
-506.5
(562)
-46.7
-14.2
-30.0
-28.2
-25.9
-43.5
-28.1
(-44.4)
142.4
(137.6)
-567.8
(614)
(-26.4)
140.2
(137.1)
-693.6
(785)
(-61.0)
140.6
(135.8)
-932.4
(1120)
(-60.7)
141.5
(136.7)
-904.9
(1085)
(-56.5)
137.7
(133.4)
-921.1
(1098)
(-90.5)
143.3
(138.5)
-886.1
(1064)
(-62.3)
137.0
(136.1)
-942.3
(1098)
δ 13Cipso
136.9
1J(119Sn -13C)
-950.5
11

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Figure 1: Correlation between measured and calculated 1J(13C-119Sn) coupling constants (Hz).
The experimental 13C-NMR data as well as a detailed summary of 13C-119Sn coupling
constants are listed in Table 2. For comparison, coupling constants of p-biphenyl4Sn in CDCl3
were taken from literature due to its poor solubility in C6D6. Therefore p-biphenyl4Sn is not
included in Table 2 [45] and excluded in shift comparisons. In order to assign 13C and 1H peaks,
2D-NMR experiments were carried out as well (H,H-COSY and H,C-HETCOR). For the
substituted phenyl derivatives, the size of long range coupling constants provides sufficient
information about the position in the aromatic ring system according to the following sequence
Jipso>Jmeta>Jortho>Jpara. It should be noted that the 3J coupling constant is bigger than the 2J (Table
2). This trend is also observed for 13C-X- couplings for the heavier homologues of the fourth
group, such as X= Sn or Pb. In the case of sterically encumbered compounds, a dihedral angle
relationship according to the Karplus type exists [46]. However, for X= Si long range coupling
12

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constants are rarely detected, because of their small size [47]. This coupling constants sequence
can be explained by negative hyperconjugation effects. Natural bonding analyses show that the
σSn-Cipso orbital donates additional electron density into the σ*C2-C3 and σ*C5-C6, while there is no
comparable interaction between σSn-Cipso and any other antibonding σ* orbital in the phenyl ring.
A higher electron density leads to higher coupling constants [48].
13

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Table 2: 13C-NMR data and J(13C-119Sn) coupling constants for compounds 2-4, 6-25.
8
8
7
6
Sn
8
8
4
1
4
8a
4a
1
8a
4a
4
Sn
3
2
3
2
2
3
3
2
5
5
6
7
7
6
5
6
2
3
4
1
6
3
2
5
7
7
1
1
1
5
4
5
4
Sn
Sn
Sn
Sn
C(1)
δ
C(2)
δ
C(3)
δ
C(4)
δ
C(4a)
C(5)
C(6)
C(7)
C(8)
C(8a)
compound
Ph4Sn 2
J(13C-119Sn)
530
J(13C-119Sn)
37.0
38.1
529
J(13C-119Sn)
50.7
43.8
40.3
64.5
86.3
95.6
67.5
88.8
126.3
119
J(13C-119Sn)
11.1
32.2
50.6
13.0
17.5
13.21
84.3
17.9
121
δ
J(13C-119Sn)
δ
J(13C-119Sn)
δ
J(13C-119Sn)
δ
J(13C-119Sn)
δ
J(13C-119Sn)
δ
J(13C-119Sn)
138.3
140.7
138.7
137.6
137.1
138.1
137.0
137.7
137.6
135.9
136.5
135.2
135.8
134.5
135.7
133.9
142.9
142.8
143.6
134.8
137.7
137.8
134.3
133.0
138.3
138.1
144.8
144.6
144.9
138.2
129.0
129.4
130.6
128.6
130.6
131.7
132.4
129.6
144.9
132.9
133.3
144.0
132.9
133.3
129.3
129.2
130.1
128.2
142.4
129.1
129.8
139.3
129.4
123.0
1-naphthyl4Sn 3
2-naphthyl4Sn 4
Ph3SnCl 6
520
126.80
133.67
129.4
134.5
134.5
37.7
10.0
129.3
128.3
6.7
4.6
126.1
126.8
n.r.
n.r.
126.4
126.4
n.r.
4.3
130.3
11.7
139.4
34.7
57.8
36.9
614
128.2 under C6D6
50.7
64.7
54.37
788
Ph2SnCl2 7
785
129.78
126.15
130.04
128.51
130.25
131.57
132.52
129.32
125.78
129.0
1-naphthyl2SnCl2 8
2-naphthyl2SnCl2 9
771
134.8
135.0
66.2
16.2
129.5
128.7
140.4
13.8
3.1
126.9
128.0
127.5
n.r.
3.69
n.r.
128.0
127.0
129.2
24.4
7.4
128.4
128.2
128.3
52.4
6.8
136.8
133.8
67.1
96.8
64.1
795
p-biphenyl2SnCl2 10 135.7
67.1
78.79
75.18
79.45
75.5
63.4
41.4
41.34
36.3
542
7.7
n.r.
n.r.
PhSnCl3 11
o-tolylSnCl3 12
2,4-xylylSnCl3 13
2,6-xylylSnCl3 14
1-naphthylSnCl3 15
Ph3SnH 16
135.8
136.7
133.4
138.5
136.1
137.3
135.5
136.7
138.7
134.2
132.7
134.4
130.4
135.4
134.4
1120
1085
1098
1064
1098
534
24.0
24.3
23.4
27.5
11.4
11.9
12.4
52.5
11.8
14.0
11.4
11.6
8.8
127.2
128.0
24.9
128
132
134.4
134.2
77.8
82.2
24.3
24.2
55.3
54.8
124
21.4
14.3
58.3
121
57.5
20.8
141
134.8
103
129.4
127.3
n.r.
128.7
6.9
127.5
135.1
139.2
85.5
53.0
54.4
62.7
44.3
55.7
57
Ph2SnH2 17
544
128.91
126.09
133.8
1-naphthyl2SnH2 18
2-naphthyl2SnH2 19
p-biphenyl2SnH2 20
PhSnH3 21
544
137.4
134.2
39.2
9.8
129.3
128.2
141.4
7.3
5.2
5.5
126.7
126.6
127.5
n.r.
n.r.
n.r.
126.1
126.3
129.1
5.8
4.40
n.r.
130.6
41.2
36.3
63.9
40.0
546
128.1 under C6D6 134.1
42.8
44
127.70
128.8
127.7
n.r.
562
o-tolylSnH3 22
569
32.4
34.4
30.4
39.2
129.34
130.43
126.95
125.92
43.0
44.5
43.5
64.5
126.0
126.8
26.7
57.8
59.5
47.3
7.2
139.0
139.0
44.4
n.r.
25.8
25.7
40.3
40.8
2,4-xylylSnH3 23
2,6-xylylSnH3 24
1-naphthylSnH3 25
579
21.5
n.r.
582
534
12.6
134.1
37.6
129.2
126.6
n.r.
126.0
10.9
130.7
42.5
139.1
35.8
n.r.= not resolved
14

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Table 3 demonstrates 119Sn-NMR shifts for all included compounds. The signals lie in a
range of -9.0 to -418 ppm. Figure 2 illustrates the relationship between the number of chlorine
atoms and the 119Sn-NMR shift in ppm. For the aryltin chloride species (ArnSnCl4-n), an increase
in number of chlorines results in a lower shielding of the 119Sn nucleus, thus in a high field shift
in 119Sn-NMR, which can be graphically depicted as a U-shaped curve (Figure 2). For
comparison, SnCl4, Ph3SnCl and Ph4Sn were included in the graph. Wrackmeyer reported the
modified shielding of the Sn as a dependency of the number (n) of groups X bonded in Me4-
nSnXn. If X= Cl an almost linear relationship is observed. The graph becomes more U-shaped if
X is a heavier halogen like Br and I [16]. Thus, the aromatic residue reveals great influence on
the shape of the 119Sn shift dependency graph. Major changes in the shielding and therefore the
shift are reported if tetrahedral symmetry is lowered to e.g. C3v or C2v, as can be observed for
Ar2SnCl2 [16].
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Table 3: 119Sn-NMR shifts (C6D6) of included compounds.
chlorides
119Sn-NMR shift (ppm)
hydrides
119Sn-NMR shift (ppm)
compound
compound
SnCl4 1
Ph4Sn 2
-149
-127
-119
-118
-125a
-44.4
-26.4
-9.0
1-naphthyl4Sn 3
2-naphthyl4Sn 4
p-biphenyl4Sn 5
Ph3SnCl 6
Ph3SnH 16
Ph2SnH2 17
-163
-233
-250
-230
-233
-345
-358
-352
-418
-354
Ph2SnCl2 7
1-naphthyl2SnCl2 8
2-naphthyl2SnCl2 9
p-biphenyl2SnCl2 10
1-naphthyl2SnH2 18
2-naphthyl2SnH2 19
p-biphenyl2SnH2 20
PhSnH3 21
-23.9
-22.0
-61.0
-60.7
-56.5
-90.5
-62.3
PhSnCl3 11
o-tolylSnCl3 12
o-tolylSnH3 22
2,4-xylylSnCl3 13
2,6-xylylSnCl3 14
1-naphthylSnCl3 15
a = measured in CDCl3
2,4-xylylSnH3 23
2,6-xylylSnH3 24
1-naphthylSnH3 25
Figure 2: Correlation between number of chlorine atoms and 119Sn-NMR shift (ppm).
16

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A change of the shielding of the tin nucleus and therefore the 119Sn-NMR signal is also
observed for ArnSnH4-n, leading to a significant high field shift of the central tin atom as the
number of bonded hydrogens increases. The effect is similar to the one observed for chlorinated
organotin compounds, showing a nonlinear relationship, however it is less pronounced. This has
also been described for silicon hydrides and is supported by theoretical calculations [49].
Both, 2,6-xylyltin trichloride and trihydride follow the 119Sn shift trend, but show a deviation
in comparison to the other trichlorides and hydrides (Figure 2). DFT calculations support that
methyl substitution in both ortho positions alters the electronic environment on the tin leading to
a high field shift of 119Sn-NMR shifts (Table 1). The neighboring methyl groups make the ipso
carbon less negative causing a slightly higher electron density on the tin (Table 1). All measured
13
C
signals lie in a small range of 7 ppm (135.8-140.7 ppm). A decrease of Cipso shifts
ipso
progressing from Ar4Sn to ArSnCl3 or ArSnH3, respectively. This trend was also observed for
13
PhnSnCl4-n [42]. However, these findings are in contrast to Cipso chemical shifts of the methyl
series MenSnCl4-n where an increase of 13C shifts was reported.
Table 2 summarizes 13C-119Sn coupling constants illustrating a significant increase of ipso
coupling with rising number of chlorines attached to the tin. The ipso coupling constant of the
previously reported o-tolyl4Sn was included [36]. This effect was previously described for a
series of compounds RnSnCl4-n, (R= Me, nBu, Ph) [42]. Concerning the compound family
ArnSnH4-n, the changes in 1J(13C-119Sn) constants by increasing the number of hydrogens are not
significant. These trends are confirmed by DFT calculations (Figure 1).
Conversely, a replacement of an aryl group by a chlorine leads to a ꢀ((1J(13C-119Sn)) of
about 80-90 Hz. Further chlorine substitution augments the ipso coupling by ꢀ≈170 Hz. The
difference between Ar2SnCl2 and ArSnCl3 is about 330 Hz. In addition, DFT calculations support
that with every aryl replacement by a chlorine atom, the increment for the ipso coupling
17

ACCEPTED MANUSCRIPT
increases. This effect can be explained by the high electronegativity (EN(Cl)= 3.16) and therefore
electron withdrawing properties of the chlorine leading to a shortening of the Sn-Cipso bond and
thus an increase in (1J(13C-119Sn) coupling constants as already reported by Bent [48]. As the
electronegativity of hydrogen is smaller (EN(H)= 2.2) changes in coupling constants are not
significant.
Figure 3: Correlation between number of chlorine atoms and 1J(13C-119Sn) (Hz).
These observations are in accordance with calculated bond lengths, which decrease with the
substitution of an organic residue by an electronegative chlorine, and remain similar regarding
organotin hydrides. Bond lengths acquired by X-ray analysis are comparable to DFT calculated
ones (1-naphthylSnCl3: measured: 2.114 (10) Å, calculated: 2.1206 Å; 2,6-xylylSnCl3: measured:
2.123(2) Å, calculated: 2.1419 Å) and therefore calculated values allow a reliable comparison.
Calculations show that a high number of chlorine substituents shortens the Sn-Cipso bond lengths,
18

ACCEPTED MANUSCRIPT
which can be explained by the back donation of electron density of the chlorine’s free electron
pairs in the Sn-Cipso antibonding orbital, which is also considered as the +M effect.
4.3 X-Ray Crystallography
This section summarizes the crystallographic data of compounds 8, 9, 10, 14 and 15 and
compares it to already published compounds. Despite several attempts to crystallize the aryltin
dihydride species, their poor solubility and high reactivity did not allow for X-ray diffraction
studies and were characterized using other methods (NMR spectroscopy and theoretical
calculations).
4.3.1 Di-1-naphthyltin dichloride (8), di-2-naphthyltin dichloride (9) and di-p-
biphenyltin dichloride (10)
Di-1-naphthyltin dichloride (8) (Figure 4), di-2-naphthyltin dichloride (9), and di-p-
biphenyltin dichloride (10) crystallize at room temperature from ethyl acetate. In each case the tin
is found in a distorted tetrahedral environment bound to two chlorines and two aryl substituents.
Table 4 summarizes average bond lengths and angles of 8, 9, 10 and of comparable aryltin
dichlorides (Ar= Ph, biphenylyl, mesityl, supermesityl or Mes*, Trip). The average Sn-C bond
for compound 8 (2.118(2) Å) compares nicely with Ph2SnCl2 (2.112(5) Å) and Mes2SnCl2
(2.117(2) Å), while for compound 9 (2.106(8) Å) and 10 (2.102(3) Å), the bond is slightly
shorter. The average C-Sn-C angles for all three compounds do not show a significant deviation
in comparison to published species. Only compound 8 shows deviations concerning the average
Cl-Sn-Cl angle. The average Cl-Sn-Cl angle of 8 is 114.6(6)° which is wider than for the other
19

ACCEPTED MANUSCRIPT
species presented. The two phenyl rings of the substituents in compound (10) show a twisting of
38.05° with respect to each other.
Figure 4: Crystal structure of di-1-naphthyltin dichloride (8). All non-carbon atoms shown as 30% shaded ellipsoids.
Hydrogen atoms removed for clarity.
Table 4: Selected bond lengths and angles of di-1-naphthyltin dichloride (8), di-2-naphthyltin dichloride (9), di-p-
biphenyltin dichloride (10) and similar compounds known in literature.
space group
bond length avg. [Å]
angle avg. [°]
compound
Sn-C
Sn-Cl
C-Sn-Cl Cl-Sn-Cl C-Sn-C
Ph2SnCl2 [50]
P-1
2.112(5)
2.118(2)
2.106(8)
2.102(3)
2.130(9)
2.117 (2)
2.345(2) 107.3(2) 101.7(1) 123.9(2)
2.359 (1) 105.2(5) 114.6(6) 116.6(11)
2.354(19) 108.7(2) 101.4(8) 119.1(3)
2.337(9) 108.0(9) 104.4(5) 119.3(17)
2.386(3) 105.6(2) 99.71(9) 130.8(3)
2.414(2) 115.4(2) 100.3(2) 119.7(2)
102.4(2)
1-naphthyl2SnCl2 (8)
2-naphthyl2SnCl2 (9)
p-biphenyl2SnCl2 (10)
(biphenylyl)2SnCl2 [51]
Mes2SnCl2 [52]
P2/n
P21/n
C2/c
P21/n
Pbcn
Mes*2SnCl2 [53]
Trip2SnCl2 [54]
P21/c
C2/c
2.198(4)
2.147(4)
2.371(1) 118.2(1) 95.5(1) 116.9(1)
103.7(1)
2.353(2) 100.1(1) 98.0(1) 120.4(2)
118.5(1)
Mes= (2,4,6-Me)Ph, Mes*= Supermes or (2,4,6-tBu)Ph, Trip= (2,4,6-iPr)Ph
20

ACCEPTED MANUSCRIPT
4.3.2 2,6-xylyltin trichloride (14) and 1-naphthyltin trichloride (15)
2,6-xylyltin trichloride (14) and 1-naphthyltin trichloride (15) (Figure 5) crystallize from
pentane at room temperature. In each case, the tin can be found in a distorted tetrahedral
environment bonded to three chlorides and one aryl substituent. Table 5 gives an overview of
structural parameters of (14) and other aryltin trichlorides published in literature (Ar= (2,6-
Mes)Ph, Ph*). The average Sn-C bond length in 15 (2.114(10) Å) is the shortest one to be found
among the listed compounds, while average Sn-Cl bond lengths for 14 (2.332(1) Å) and 15
(2.312 (3) Å) lie in the expected range. Due to the higher steric demand of the 2,6-methyl
substituted phenyl group, the average C-Sn-Cl angle (116.3(1)°) is wider than the average Cl-Sn-
Cl (102.0(1)°) angle.
Figure 5: Crystal structure of 1-naphthyltin trichloride (15). All non-carbon atoms shown as 30% shaded ellipsoids. Hydrogen
atoms removed for clarity.
21

ACCEPTED MANUSCRIPT
Table 5: Selected bond lengths and angles of 2,6-xylyltin trichloride (14), 1-naphthyltin trichloride (15) and similar
compounds known in literature.
space group
bond length avg. [Å]
angle avg. [°]
compound
Sn-C
Sn-Cl
C-Sn-Cl
Cl-Sn-Cl
102.0(1)
100.8(3)
100.9(8)
103.3(13)
2,6-xylylSnCl3 (14)
(2,6-Mes)PhSnCl3 [55]
Ph*SnCl3 [56]
Pbcn
P21/c
P1-n
P21/c
2.123(2)
2.128(6)
2.155(5)
2.114(10)
2.332(1)
2.315(2)
2.324(3)
2.312 (3)
116.3(1)
117.3(2)
117.1(14)
122.7(3)
107.3(3)
115.2(3)
1-naphthylSnCl3 (15)
Ph*= (2,6-Trip)Ph, Trip= (2,4,6-iPr)Ph, Mes= (2,4,6-Me)Ph
All three naphthyl containing compounds di-1-naphthyltin dichloride (8), di-2-naphthyltin
dichloride (9), and 1-napthyltin trichloride (15) show a pi-stacking conformation in the solid
state, where the adjacent naphthyl ring systems align parallel to each other with a specific
distance between the ring centers (d). They are also found to be parallel-displaced to each other
with a certain off-set (R). This is a very well described phenomenon for aromatic rings (Figure
6). Herein, the T-shaped conformation is the most favored one, followed by the found parallel-
displaced stacking. The least favored one, because of electron density repulsion is the sandwich
geometry, where the aromatic moieties are arranged in a parallel way. It was reported that smaller
aromatic hydrocarbons such as naphthalene or pyrene are more likely to crystallize in a T-shape
geometry in accordance to benzene, whereas larger aromatic molecules (coronene, kekulene or
hexabenzocurene) exhibit parallel-stacked arrangement [57]. This is in contrast to the packing of
the naphthyl containing compounds 8 and 9. Figure 6 illustrates the three different types of π-π
interactions.
22

ACCEPTED MANUSCRIPT
Figure 6: Types of π-π interactions.
1-naphthyltin dichloride (8) shows an interplanar distance (d) of 3.597 Å, 1-naphthyltin
trichloride (15) a distance (d) of 3.556 Å, whereas the 2-naphthyltin dichloride (9) is slightly
tighter packed with a distance of 3.402 Å. These findings are in accordance to a reported range of
3.4-3.6 Å for benzene or 3.354 Å in graphite. The displacement (R) for 8 can be calculated as
1.42 Å, 1.57 Å for 14 and 1.67 Å for 7. Offset distances for other benzyl systems are found in a
range of 1.6-1.8 Å [57].
5 Conclusion
In summary, we were able to synthesize and fully characterize a series of novel aryltin
dichlorides, dihydrides as well as aryltin trichlorides and trihydrides featuring at least one ortho-
substituent on the phenyl ring, a naphthyl or a p-biphenyl group as organic residue. Organotin
chlorides were generated according to the Kozeshkov equilibrium and subsequently
hydrogenated to the corresponding organotin hydride using LiAlH4. Apart from solid dihydrides,
structural information by X-ray crystallography was gained for all investigated solid compounds
1-naphthyl2SnCl2 (8), 2-naphthyl2SnCl2 (9), p-biphenyl2SnCl2 (10), 2,6-xylylSnCl3 (14) and 1-
naphthylSnCl3 (15). As it was already observed for other aromatic carbon based systems like
benzene, graphite or aromatic amino acids in biological systems, adjacent aromatic rings from
23

ACCEPTED MANUSCRIPT
two molecules interact with each other leading to specific three dimensional structures. In the
case of compounds containing a 1-naphtyl or 2-naphthyl group, respectively, the solid state
structure shows a three dimensional stabilization via a parallel displaced stacking with a certain
distance and offset. In contrast to the herein reported aryltin dihydrides, 1-naphthyl2SnH2 (18), 2-
naphthyl2SnH2 (19) and p-biphenyl2SnH2 (20), all published aryltin trihydrides as well as those
presented in this work are liquids. While reported to easily decompose at room temperature, they
could be purified by distillation. All reported organotin compounds were subjected to an
13
1
extensive 119Sn-, C- and H-NMR study in the appropriate solvent C6D6. Shifts and coupling
constants were compared to already published aryltin compounds. Experimental NMR data of 13C
and 119Sn shifts as well as 13C-119Sn coupling constants is supplemented by DFT calculations and
confirms that an increased number of chlorines attached to the tin leads to an U-shaped 119Sn-
shift dependency, as well as augmentation of 1J(13C-119Sn) coupling constants is observed. These
effects are less pronounced regarding an increased number of bonded hydrogens to the tin,
because of its smaller electronegativity in contrast to chlorine. A detailed long range coupling
constants overview reveals, as reported in literature, that Jipso>Jmeta>Jortho>Jpara. This is supported
by NBO analyses showing a negative hyperconjugation from the σSn-Cipso orbital into the C2-C3
and C5-C6 antibonding sigma orbital.
Acknowledgements
This work was supported by the NAWI Graz project, a collaboration between the Graz University
of Technology and the Graz University.
Appendix A. Supplementary Material
Supplementary data related to this article can be found at:
24

ACCEPTED MANUSCRIPT
Appendix B. Supplementary Data
Crystallographic data (excluding structure factors) for the structures reported herein
(supplementary information) have been deposited in the Cambridge Crystallographic Data Center
(CCDC deposition numbers 918396 – 918400 for compounds 8, 9, 10, 14 and 15). CIF files can
be obtained from the CCDC free of charge via http://www.ccdc.cam.ac.uk/data_request/cif.
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