Triphenylphosphine oxide adducts of diphenylantimony(V) and diorganotin(IV) Lewis acids: Structures of SnPh2Cl2·OPPh3, SnPh2Cl2·2OPPh3, SnPh2Br2·OPPh3 and SbPh2Cl3·OPPh3

Article abstract of DOI:10.1016/S0022-328X(00)00383-1

1:1 and 1:2 adducts of diphenyltin dichloride with triphenylphosphine oxide can be isolated in the solid state but the preparative conditions necessary to isolate an adduct of specific stoichiometry are difficult to define; none of acid: base ratio, choice of solvent or reaction temperature are significant factors. Adventitious crystal seeding probably has a dominant role. Both the 1:1 and 1:2 adducts of SnPh₂Cl₂, but only the 1:1 adduct of SnPh₂Br₂, were isolated. 1:1 and 1:2 adducts of both SnMe₂Cl₂ and SnBuⁿ₂Cl₂ were readily isolated whereas only 1:2 adducts were obtained with SnPh₂(NCS)₂ and SnBuⁿ₂(NCS)₂. SbPh₂Cl₃ readily forms a 1:1 adduct with triphenylphosphine oxide and the same adduct is obtained from the reaction of the phosphine oxide with SbPhCl₂. Crystallographic data are reported for SnPh₂Cl₂·OPPh₃, SnPh₂Cl₂·2OPPh₃, SnPh₂Br₂·OPPh₃ and SbPh₂Cl₃·OPPh₃. Both SnPh₂Cl₂·OPPh₃ and SnPh₂Br₂·OPPh₃ have tin in trigonal bipyramidal environments. ¹¹⁹Sn Mo?ssbauer quadrupole splitting data are consistent with the same trigonal bipyramidal geometry for tin in SnMe₂Cl₂·OPPh₃ whereas the data for the butyl analogue suggest the presence of six-coordinated tin as a result of intermolecular Sn-Cl interactions. A notable feature of all of the adducts subjected to crystallographic studies is the presence of intramolecular π-interactions involving phenyl groups of the phosphine oxide and phenyl groups bonded to the metal.

Full text of DOI:10.1016/S0022-328X(00)00383-1

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 612 (2000) 53–60
Triphenylphosphine oxide adducts of diphenylantimony(V) and
diorganotin(IV) Lewis acids: structures of SnPh2Cl2·OPPh3,
SnPh2Cl2·2OPPh3, SnPh2Br2·OPPh3 and SbPh2Cl3·OPPh3
D. Cunningham *, E.M. Landers, P. McArdle, N. N´ı Chonchubhair
Department of Chemistry, NUI, Galway, Ireland
Received 20 April 2000; accepted 8 June 2000
Abstract
1:1 and 1:2 adducts of diphenyltin dichloride with triphenylphosphine oxide can be isolated in the solid state but the preparative
conditions necessary to isolate an adduct of specific stoichiometry are difficult to define; none of acid: base ratio, choice of solvent
or reaction temperature are significant factors. Adventitious crystal seeding probably has a dominant role. Both the 1:1 and 1:2
adducts of SnPh2Cl2, but only the 1:1 adduct of SnPh2Br2, were isolated. 1:1 and 1:2 adducts of both SnMe2Cl2 and SnBun2Cl2
were readily isolated whereas only 1:2 adducts were obtained with SnPh2(NCS)2 and SnBun2(NCS)2. SbPh2Cl3 readily forms a 1:1
adduct with triphenylphosphine oxide and the same adduct is obtained from the reaction of the phosphine oxide with SbPhCl2.
Crystallographic data are reported for SnPh2Cl2·OPPh3, SnPh2Cl2·2OPPh3, SnPh2Br2·OPPh3 and SbPh2Cl3·OPPh3. Both
SnPh2Cl2·OPPh3 and SnPh2Br2·OPPh3 have tin in trigonal bipyramidal environments. 119Sn Mo¨ssbauer quadrupole splitting data
are consistent with the same trigonal bipyramidal geometry for tin in SnMe2Cl2·OPPh3 whereas the data for the butyl analogue
suggest the presence of six-coordinated tin as a result of intermolecular Sn–Cl interactions. A notable feature of all of the adducts
subjected to crystallographic studies is the presence of intramolecular p-interactions involving phenyl groups of the phosphine
oxide and phenyl groups bonded to the metal. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Organotin; Organoantimony; Adduct; Mo¨ssbauer
Triphenylphosphine oxide is an interesting ligand in
organotin chemistry insofar as it is one of the few
1. Introduction
donor ligands which apparently facilitates the isolation
of both 1:1 and 1:2 adducts of diorganotin(IV) di-
halides. However, in this respect there is a degree of
controversy. Although the 1:1 adducts are the predomi-
nant solution species, it was the 1:2 adduct of diphenyl-
tin(IV) dichloride with triphenylphosphine oxide which
was initially reported in the solid state [1]. Later groups
however failed to isolate this adduct, the 1:1 adduct
being the product of all preparative attempts [2,3]. On
the other hand, 1:2 adduct formation is apparently
favoured by SnMe2Cl2, SnBun2Cl2 and SnPhMeCl2 in
the solid state even though in these instances also it is
the 1:1 adduct which dominates in solution [3,4]. An
objective of the present work was to establish the
precise conditions that are necessary to isolate 1:1 and
1:2 adducts of diphenyltin dichloride with triphenyl-
phosphine oxide and if possible to determine the struc-
Triphenylphosphine oxide has been extensively em-
ployed as a ligand for many p-, d-, and f-block metals.
Its use has extended to organotin(IV) chemistry where
the structures of its adducts have been investigated by
Mo¨ssbauer, NMR and IR spectroscopy, dipole mea-
surements, and X-ray crystallography [1–11]. Equi-
librium studies between diorganotin dihalides and
triphenylphosphine oxide in various solvents have been
investigated by NMR spectroscopy and calorimetry
[6–9]. Crystallographic data are available for
SnPh2Cl2·OPPh3
[12]
SnPh3(NO3)·OPPh3
[10],
SnPh2(NO3)2·OPPh3 [11] and for the diphosphine oxide
adducts SnPh3Cl·(OPPh2)CH2CH2(OPPh2) [13] and
(SnPh3Cl)2·(OPPh2)CH2CH2(OPPh2) [14].
* Corresponding author. Fax: +353-91-525700.
E-mail address: des.cunningham@nuigalway.ie (D. Cunningham).
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00383-1

54
D. Cunningham et al. / Journal of Organometallic Chemistry 612 (2000) 53–60
ture of the 1:2 adduct. With structural data already
available for the 1:1 adduct [12], crystallographic data
would then be available, for the first time, for both a
five- and six-coordinated diorganotin dihalide adduct
containing the same acid–base pair. Furthermore, we
were interested in comparing structural parameters for
these adducts with those for the adduct SbPh2Cl3·
OPPh3 for the following reason: The crystal structure
determination of SbPh2Cl3·H2O [15] revealed a surpris-
ingly weak antimony–water interaction compared to
the tin–water interactions in aqua adducts of
dimethyltin dichloride, which would tend to suggest
that dimethyltin dichloride is a stronger Lewis acid
than diphenylantimony trichloride. This would indeed
be a surprising result. However, in apparent contradic-
tion with the above crystallographic observations for
aqua adducts, a comparison of the w(PꢀO) stretching
frequency data for SbPh2Cl3·OPPh3 and SnPh2Cl2·
2OPPh3 suggests that the former contains the stronger
acid–base interaction.
1000 Infrared spectrometer. X-ray diffraction data were
collected at room temperature on an Enraf Nonius
CAD4 diffractometer. 119Sn Mo¨ssbauer spectra were
recorded on a constant acceleration spectrometer sup-
plied by J&P Engineering (Reading). The spectra were
recorded with the sample at liquid nitrogen temperature
and a 119CaSnO3 source at room temperature. Spectra
were fitted using the program PEAKFIT from Jandel
Scientific. Chemical shifts are quoted relative to
BaSnO3.
2.2. Starting materials
Tin starting materials were purchased from Aldrich
Chemical Company. Triphenylphosphine oxide and
diphenyltin dichloride were used without further purifi-
cation. Dimethyltin dichloride was sublimed before use.
Dibutyltin dichloride was recrystallized from 60:80
petroleum ether. Diphenyltin dibromide, diphenyltin
diisothiocyanate, dibutyltin diisothiocyanate, diphenyl-
antimony trichloride and phenylantimony dichloride
were prepared by literature methods [16–19].
2. Experimental
2.3. Synthesis of SnPh2Cl2·OPPh3, SnPh2Cl2·2OPPh3
and SnPh2Br2·OPPh3
2.1. Instrumentation
Preparations of these adducts were undertaken dur-
ing two phases of the study which were separated by
approximately 6 months. During the first phase, only
the 1:2 adduct of diphenyltin dichloride could be pre-
pared whereas during the second phase only the 1:1
adduct could be isolated.
Elemental carbon, hydrogen and nitrogen analyses
were determined using a Perkin–Elmer 2400 elemental
analyser. Infrared spectra were recorded as Nujol mulls
between cesium iodide plates on a Perkin–Elmer FT
Table 1
The 1:2 adduct of diphenyltin dichloride was typi-
cally prepared as follows: An ethanolic solution of
diphenyltin dichloride (1 mmol in 50 cm3) was added
dropwise to an ethanolic solution of triphenylphosphine
oxide (2 mmol in 50 cm3) at room temperature. A
microcrystalline complex precipitated rapidly from so-
lution and was isolated by filtration and dried under
vacuum. Analytical data are in Table 1. Using the same
procedure but employing chloroform, toluene or tetra-
hydrofuran as solvent invariably resulted in the forma-
tion of an identical adduct. The same 1:2 adduct was
also obtained from refluxing solvents. Good quality
crystals, one of which was selected for the crystallo-
graphic study, were obtained from a hot toluene solu-
tion of the adduct.
During this same phase of the work, attempts were
made to isolate the 1:1 adduct of diphenyltin dichlo-
ride. Typically, a solution of the phosphine oxide was
added dropwise to a solution of the tin Lewis acid. A
wide range of solvents was employed, both dried and
undried, and reactions were carried out at room tem-
perature, approximately −8°C, and under refluxing
conditions. Reactions were also carried out both in the
open atmosphere and under nitrogen. All reactions
Analytical data for SnR2X2·nOPPh3 and SbR2X3·nOPPh3
a
R
M
X
n
Analyses
%C
%H
4.16
(4.22)
4.78
(4.64)
5.20
(5.67)
6.01
(5.58)
3.80
(4.02)
4.32
(4.44)
4.68
(5.30)
3.72
%N
Me
Me
Bun
Bun
Ph
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sb
Cl
1
2
1
2
1
2
2
2
1
1
48.25
(48.19)
58.96
(58.74)
53.49
(53.61)
60.93
(61.38)
57.89
(57.88)
63.87
(63.98)
60.82
(60.98)
62.79
(63.47)
50.58
–
–
–
–
–
–
–
–
–
–
–
–
Cl
Cl
Cl
Cl
Ph
Cl
Bun
Ph
NCS
NCS
Br
2.93
(3.09)
2.87
(2.96)
–
–
–
–
(4.23)
3.80
(3.52)
3.83
Ph
(50.65)
54.12
Ph
Cl
(54.50)
(3.78)
a Found (Calc.).

D. Cunningham et al. / Journal of Organometallic Chemistry 612 (2000) 53–60
55
resulted in the precipitation of the 1:2 adduct exclu-
sively. In a further bid to obtain the 1:1 adduct, as
much as a ten-fold excess of the Lewis acid was em-
ployed in preparative reactions but not even then was
the desired adduct obtained.
When the second phase of the work began, renewed
emphasis was placed on the isolation of the 1:1 adduct
of diphenyltin dichloride. The first preparative effort
resulted in the successful isolation of the 1:1 adduct
adducts. Hot ethanol was the solvent employed in the
preparation of the 1:1 adduct while cold ethanol was
employed for the preparation of the 1:2 adduct. Analyt-
ical data are in Table 1.
2.6. Synthesis of SnBun2(NCS)2·2OPPh3 and
SnPh2(NCS)2·2OPPh3
These adducts were prepared using the procedure
outlined for the preparation of SnMe2Cl2·2OPPh3 using
acetonitrile and toluene as solvents for the preparation
of the dibutyl- and diphenyltin adducts, respectively.
Analytical data are in Table 1. All efforts at synthesis-
ing 1:1 adducts were unsuccessful.
using the following procedure:
A
solution of
triphenylphosphine oxide in methanol (1 mmol in ca.
30 cm3) was added to a solution of diphenyltin dichlo-
ride in methanol (1 mmol in ca. 20 cm3). A white
powder precipitated from solution which was isolated
by filtration and dried under vacuum. Analytical data
are in Table 1. Good quality crystals of the 1:1 adduct
were obtained from the filtrate after approximately
twelve hours and one of these was selected for a
crystallographic study.
Following the successful isolation of the 1:1 adduct,
all efforts to isolate the 1:2 adduct met with failure, the
sole product of reaction invariably being the 1:1 ad-
duct. Furthermore, a sample of the 1:2 adduct, ob-
tained from the earlier phase of the work was
crystallised from toluene (as had been done in the
earlier phase to obtain suitable crystals for crystallogra-
phy) but now it was the 1:1 adduct which crystallised
from solution.
2.7. Synthesis of SbPh2Cl3·OPPh3
A toluene solution of triphenylphosphine oxide (1
mmol in ca. 30 cm3) was added to a toluene solution of
SbPh2Cl3 (1 mmol in ca. 30 cm3). After approximately
30 min, a white precipitate had formed which was
isolated by filtration and dried under vacuum. Analyti-
cal data are in Table 1.
Although crystals of reasonable quality were ob-
tained from the toluene filtrate, better quality crystals
of the diphenylantimony adduct were obtained from a
preparation starting with SbPhCl2. 1 mmol solid
SbPhCl2 was added to a toluene solution of the phos-
phine oxide (1 mmol in ca. 40 cm3). A white precipitate
formed immediately. This solid, which was isolated by
filtration, contained chlorine and antimony but almost
no carbon. The filtrate, on standing for several days,
yielded good quality crystals of SbPh2Cl3·OPPh3. One
such crystal was selected for a crystallographic study.
SnPh2Br2·OPPh3 was prepared using the method de-
scribed for the preparation of SnPh2Cl2·OPPh3. Analyt-
ical data are in Table 1. All efforts at obtaining a 1:2
adduct were unsuccessful. A crystal of the 1:1 adduct,
grown from methanol, was selected for a crystallo-
graphic study.
2.4. Synthesis of SnMe2Cl2·OPPh3 and
SnMe2Cl2·2OPPh3
2.8. X-ray crystallography
Crystal data are in Table 2. The structures were
solved by direct methods, SHELXS-97 [20], and refined
by full matrix least squares using SHELXL-97 [21].
SHELX operations were rendered paperless using OSCAIL
which was also used to obtain the drawings [22]. Data
were corrected for Lorentz and polarization effects but
not for absorption. Hydrogen atoms were included in
calculated positions with thermal parameters 30%
larger than the atom to which they were attached. The
non-hydrogen atoms were refined anisotropically. All
calculations were performed on a Pentium PC.
The 1:1 adduct was prepared by slowly adding a
dichloromethane solution of the phosphine oxide (1
mmol in ca. 30 cm3) to a dichloromethane solution of
SnMe2Cl2 (1 mmol in ca. 30 cm3). The resulting white
precipitate was isolated by filtration and dried under
vacuum. Analytical data are in Table 1.
The 1:2 adduct was prepared by adding
a
dichloromethane solution of SnMe2Cl2 (1 mmol in ca.
30 cm3) to a dichloromethane solution of the phosphine
oxide (2 mmol in ca. 30 cm3). The resulting white
precipitate was isolated by filtration and dried under
vacuum. Analytical data are in Table 1.
3. Discussion
2.5. Synthesis of SnBun2Cl2·OPPh3 and
SnBun2Cl2·2OPPh3
The first objective of the present work was to resolve
the controversy regarding the stoichiometry of the
triphenylphosphine oxide adduct of diphenyltin dichlo-
ride. It is clear that the conditions employed in the first
The general procedures were as outlined for the
preparation of the dimethyltin dichloride 1:1 and 1:2

56
D. Cunningham et al. / Journal of Organometallic Chemistry 612 (2000) 53–60
Table 2
Crystallographic data
SnPh2Cl2·OPPh3
SnPh2Cl2·2OPPh3
SnPh2Br2·OPPh3
SbPh2Cl3·OPPh3
Empirical formula
Formula weight
Temperature (K)
C30H25Cl2OPSn
622.06
293(2)
C48H40Cl2O2P2Sn
450.17
293(2)
C30H25Br2OPSn
710.98
293(2)
C30H25Cl3OPSb
660.57
293(2)
,
Wavelength (A)
0.71069
Triclinic
0.71069
Monoclinic
P21/n
0.71069
Triclinic
0.71069
Monoclinic
P21/n
Crystal system
Space group
(
(
P1
P1
Unit cell dimensions
,
a (A)
8.9264(7)
10.590(2)
15.475(2)
96.240(10)
99.870(10)
105.870(10)
1367.5(3)
2
11.7160(10)
12.1450(10)
17.3740(9)
90
104.540(10)
90
2393.0(3)
2
1.250
8.9911(11)
10.7393(13)
15.5943(18)
96.852(10)
99.759(10)
105.240(10)
1410.4(3)
2
10.981(2)
20.352(5)
12.991(2)
90
101.01(2)
90
2849.9(10)
4
1.540
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
Volume (A )
Z
Dcalc (Mg m−3
)
1.511
1.209
624
1.674
3.816
696
Absorption coefficient (mm−1
F(000)
)
0.746
916
1.327
1320
Crystal size (mm)
Theta range for data collection 2.03–27.97
(°)
0.25×0.3×0.25
0.3×0.41×0.21
2.07–31.96
0.2×0.15×0.25
2.21–25.97
0.52×0.45×0.42
2.00–27.98
Index ranges
05h511; −135k513;
−205l520
7227
05h57; 05k518;
−255l525
5201
05h511; −135k512;
−195l518
6069
05h514; 05k526;
−175l516
7475
Reflections collected
Independent reflections
Reflections observed (\2|)
Refinement method
6591 [Rint=0.0197]
5719
4738 [Rint=0.0130]
4152
5520 [Rint=0.0204]
3437
6871 [Rint=0.0359]
5332
Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares
on F2
on F2
on F2
on F2
Data/restraints/parameters
Goodness-of-fit on F2
6591/0/316
1.108
4738/0/250
1.344
5520/0/316
0.952
6871/0/325
1.027
a
Final R indices [I\2|(I)]
R1=0.0316, wR2=0.1004 R1=0.0687, wR2=0.2765 R1=0.0500, wR2=0.1173 R1=0.0644, wR2=0.1534
R1=0.0397, wR2=0.1165 R1=0.0726, wR2=0.2827 R1=0.0922, wR2=0.1306 R1=0.0779, wR2=0.1610
a
R
indices (all data)
Largest difference peak and
1.140 and −0.816
3.015 and −0.359
1.107 and −2.127
2.869 and −2.635
−3
,
hole (e A
)
a R1=(SꢀꢀFoꢀ−ꢀFcꢀꢀ)/SꢀFoꢀ. wR2=[Sw(ꢀF2o−F2cꢀ)2/Sw(ꢀF2oꢀ)2].1/2 w=1/[(|(Fo)2+(aP)2]; the value of aP was obtained from structure refinement.
report [1] of the diphenyltin dichloride adduct favoured
1:2 stoichiometry (analytical data clearly establish the
stoichiometry). However, later efforts apparently using
the same conditions invariably led to the exclusive
isolation of the 1:1 adduct [2,3]. In the initial studies in
this laboratory, reactions were carried out using 1:2
acid:base ratios in the hope of isolating the 1:2 adduct.
A range of solvents was employed, including chloro-
form, which was the solvent employed in the earlier
work that yielded the 1:2 adduct [1]. Elemental analyti-
cal data for products of these reactions were always
consistent with 1:2 adduct formation. Identical 1:2 ad-
ducts were obtained from all solvents. Slow cooling of
either a hot toluene or a hot ethanolic solution contain-
ing the acid–base reactants in a 1:2 molar ratio resulted
in the formation of the crystalline 1:2 adduct. Best
quality crystals were obtained from toluene, one of
which was selected for a crystallographic study. The
study confirmed the 1:2 stoichiometry of the adduct.
Having successfully established the existence of the
1:2 adduct, further work was directed towards the
isolation of the 1:1 adduct. At that time all efforts at
isolating a 1:1 adduct failed, the 1:2 adduct invariably
being the isolated product (see Section 2). However,
after an intervening six month period, further work was
commenced and quite remarkably, it was no longer
possible to reproduce the 1:2 adduct (for this reason
Mo¨ssbauer data were not obtained for the 1:2 adduct),
which was the sole product of the earlier work. All
efforts now resulted in the formation of the 1:1 adduct.
It proved possible to grow crystals of this adduct, even
employing the conditions that were previously em-
ployed to grow crystals of the 1:2 adduct. A crystallo-
graphic study confirmed the 1:1 stoichiometry.
It is frequently the case that, while a 1:1 adduct is
predominately, or indeed solely, the adduct which exists
in solution, the 1:2 adduct is invariably the one which is
isolated in the solid state. This is often attributed to the

D. Cunningham et al. / Journal of Organometallic Chemistry 612 (2000) 53–60
57
1:2 adduct having the more favourable lattice energy. It
would appear that very similar lattice energies for
SnPh2Cl2·OPPh3 and SnPh2Cl2·2OPPh3 contributes to
the uncertainty of isolating an adduct with a specific
stoichiometry. The situation is highly reminiscent of the
problem that is frequently encountered in the synthesis
of polymorphic materials. Difficulty in isolating a spe-
cific polymorph when a compound is known to exist in
two or more solid state modifications is frequently
encountered. The persistence of a modification first
encountered in a particular laboratory is well docu-
mented. This phenomenon, which is clearly applicable
to the 1:1 and 1:2 adducts as indicated above, is not
well understood but it is speculated that particles in the
environment at the time of synthesis preferentially seed
the growth of a specific phase.
During the second phase of the present work, when
only the 1:1 adduct of diphenyltin dichloride could be
isolated, reactions of several other diorganotin dihalides
and diisothiocyanates with the phosphine oxide were
investigated. Reactions with SnPh2Br2 failed to yield
anything other than the 1:1 adduct; the crystal structure
of this adduct was determined. On the other hand, it
did prove possible to isolate both 1:1 and 1:2 adducts
for both SnMe2Cl2 and SnBun2Cl2. Only the 1:2 adducts
were previously reported [1–5]. Only 1:2 adducts were
isolated for the thiocyanate containing Lewis acids.
The trigonal bipyramidal geometry about tin in
SnPh2Cl2·OPPh3 (see Fig. 1) is similar to that previ-
ously reported for the pyrazine and benzthiazole ad-
ducts of diphenyltin dichloride [23,24]. SnꢁCl bond
lengths for the latter adducts compare favourably with
those for SnPh2Cl2·OPPh3 and the CꢁSnꢁC bond angles
of 133.1(2) and 132.5(7)° for the pyrazine and benzthia-
zole adducts, respectively compare with a correspond-
ing angle of 131.05(13)° for SnPh2Cl2·OPPh3.
SnPh2Cl2·OPPh3 and SnPh2Br2·OPPh3 are isostructural
and replacement of chloride by bromide has remark-
ably little effect on angles about tin (see Table 3), the
biggest change been registered in the OꢁSnꢁX (X=Cl
or Br) bond angle which increases by 1.64°. The
CꢁSnꢁC bond angles of 131.05(13)° for the chloride
compares with 132.0(3)° for the bromide. The bonding
of the phosphine oxide to SnPh2Cl2 and SnPh2Br2
(monitored by the SnꢁOꢁP bond angles, the SnꢁO bond
lengths and, in particular, the PꢁO bond lengths) is
remarkably constant despite the difference in Lewis
acidity of the organotin species. Thus, the crystallo-
graphic data account for the very similar w(PꢀO)
stretching frequencies for the two adducts (see Table 6).
The addition of the second mole of triphenylphos-
phine oxide to SnPh2Cl2·OPPh3 gives the centrosym-
metric six-coordinated tin adduct (see Fig. 2). This
appears to be the only occasion where crystallographic
data have been made available for both a five-coordi-
nated (1:1) and six-coordinated (1:2) diorganotin di-
halide adduct with the same donor ligand. Notable
changes in bond lengths occur as a result of the addi-
tion of the second mole of ligand (compare data in
Tables 3 and 4). A detectable increase in SnꢁC bond
lengths is observed along with a decisive increase in
SnꢁCl bond lengths. By contrast, the SnꢁO bond length
Fig. 1. The atomic labelling scheme for the asymmetric unit of
SnPh2X2·OPPh3 Dashed line connects aromatic rings involved in
p-interactions. Close ring contacts are as follows, for X=Cl (Br):
C(7)ꢁC(25), 3.71 (3.73); C(8)ꢁC(26), 3.73 (4.06); C(9)ꢁC(27), 4.02
,
(4.29); C(11)ꢁC(29), 4.28 (3.99); C(12)ꢁC(30) 4.01 (3.71) A.
Table 3
,
Selected bond lengths (A) and bond angles (°) for SnPh2X2·OPPh3
(X=Cl, Br)
SnPh2Cl2·OPPh3
SnPh2Br2·OPPh3
Sn(1)ꢁO(1)
Sn(1)ꢁX(1)
Sn(1)ꢁX(2)
Sn(1)ꢁC(7)
Sn(1)ꢁC(1)
P(1)ꢁO(1)
2.278(2)
2.3543(8)
2.4703(9)
2.119(3)
2.126(3)
1.501(2)
2.287(4)
2.5000(9)
2.6325(9)
2.101(6)
2.131(6)
1.504(4)
P(1)ꢁO(1)ꢁSn(1)
C(7)ꢁSn(1)ꢁC(1)
C(7)ꢁSn(1)ꢁO(1)
C(1)ꢁSn(1)ꢁO(1)
C(7)ꢁSn(1)ꢁX(1)
C(1)ꢁSn(1)ꢁX(1)
O(1)ꢁSn(1)ꢁX(1)
C(7)ꢁSn(1)ꢁX(2)
C(1)ꢁSn(1)ꢁX(2)
O(1)ꢁSn(1)ꢁX(2)
X(1)ꢁSn(1)ꢁX(2)
148.04(13)
131.05(13)
86.35(10)
84.35(10)
113.51(9)
113.53(9)
85.72(6)
96.88(9)
94.89(9)
176.25(6)
91.23(3)
148.3(3)
132.0(3)
86.0(2)
84.1(2)
,
decreases from the value of 2.278(2) A in the 1:1 adduct
113.06(19)
113.16(19)
87.11(11)
96.05(18)
94.76(18)
177.89(12)
91.67(3)
,
to a value of 2.214 A in the 1:2 adduct. The decrease in
SnꢁO donor bond length can be attributed to increased
Snd+ꢁCld− character on formation of the 1:2 adduct.
Despite this decrease in SnꢁO bond length, the PꢁO
bond length remains unchanged and this accounts for
the fact that the w(PꢀO) stretching frequency remains

58
D. Cunningham et al. / Journal of Organometallic Chemistry 612 (2000) 53–60
,
this paper [2.214(4)–2.287(4), 1.501(2)–1.504(4) A, and
1138–1140 cm−1, respectively) suggest greater Lewis
acidity for SbPh2Cl3 than for SnPh2Cl2. This is contrary
to the weak Lewis acidity of SbPh2Cl3 that is suggested
by the long SbꢁOH2 donor bond in SbPh2Cl3·H2O [14].
The anomalous nature of this latter donor bond will be
discussed in a later paper. The longer PꢁO bond length
for the antimony adduct compared to those for the tin
adducts accounts for the w(PꢀO) stretching frequency
Fig. 2. The atomic labelling scheme for SnPh2Cl2·2OPPh3. Dashed
lines connect aromatic rings involved in p-interactions. Close ring
,
contacts (A) are as follows: C(1)ꢁC(19), 3.82; C(2)ꢁC(20), 3.89;
C(6)ꢁC(24), 3.89.
Table 4
,
Selected bond lengths (A) and angles (°) for SnPh2Cl2·2OPPh3
Sn(1)ꢁC(1)
Sn(1)ꢁO(1)
Sn(1)ꢁCl(1)
P(1)ꢁO(1)
2.140(5)
2.214(4)
2.5537(10)
1.503(3)
Fig. 3. The atomic labelling scheme for SbPh2Cl3·OPPh3. Dashed line
connects aromatic rings involved in p-interactions. Close ring con-
C(1)ꢁSn(1)ꢁO(1%)
C(1%)ꢁSn(1)ꢁO(1%)
P(1)ꢁO(1)ꢁSn(1)
C(1)ꢁSn(1)ꢁCl(1)
O(1%)ꢁSn(1)ꢁCl(1)
O(1)ꢁSn(1)ꢁCl(1)
C(1)ꢁSn(1)ꢁCl(1%)
O(1%)ꢁSn(1)ꢁCl(1%)
O(1)ꢁSn(1)ꢁCl(1%)
91.61(17)
88.39(17)
145.66(18)
90.20(11)
87.08(8)
92.92(8)
89.80(11)
92.92(8)
,
tacts (A) are as follows: C(7)ꢁC(25), 3.74; C(8)ꢁC(30), 3.66;
C(9)ꢁC(29), 3.86; C(12)ꢁC(26), 4.02.
Table 5
,
Selected bond lengths (A) and angles (°) for SbPh2Cl3·OPPh3
Sb(1)ꢁC(25)
Sb(1)ꢁC(19)
Sb(1)ꢁO(1)
Sb(1)ꢁCl(1)
Sb(1)ꢁCl(2)
Sb(1)ꢁCl(3)
P(1)ꢁO(1)
2.133(4)
2.138(4)
2.148(3)
2.4071(12)
2.4224(12)
2.4787(12)
1.514(3)
87.08(8)
essentially unchanged on addition of the second mole
of triphenylphosphine oxide to diphenyltin dichloride
(see Table 6).
C(25)ꢁSb(1)ꢁC(19)
C(25)ꢁSb(1)ꢁO(1)
C(19)ꢁSb(1)ꢁO(1)
O(1)ꢁSb(1)ꢁCl(2)
Cl(1)ꢁSb(1)ꢁCl(3)
P(1)ꢁO(1)ꢁSb(1)
C(25)ꢁSb(1)ꢁCl(1)
C(19)ꢁSb(1)ꢁCl(1)
O(1)ꢁSb(1)ꢁCl(1)
C(25)ꢁSb(1)ꢁCl(2)
C(19)ꢁSb(1)ꢁCl(2)
Cl(1)ꢁSb(1)ꢁCl(2)
C(25)ꢁSb(1)ꢁCl(3)
C(19)ꢁSb(1)ꢁCl(3)
O(1)ꢁSb(1)ꢁCl(3)
Cl(2)ꢁSb(1)ꢁCl(3)
172.80(15)
88.74(15)
84.89(13)
177.47(8)
176.03(5)
152.71(18)
91.11(13)
92.18(13)
89.42(9)
93.73(13)
92.62(11)
91.05(5)
87.14(13)
89.17(13)
86.98(9)
Addition of triphenylphosphine oxide to SbPh2Cl3
produces the expected octahedral 1:1 adduct (see Fig.
3). The SbꢁC bond lengths (see Table 5) are similar to
the Sn-C bond lengths in SnPh2Cl2·2OPPh3 but the
SbꢁCl bond lengths are, on average, shorter than the
SnꢁCl bond lengths. In actual fact, there is a disparity
in the SbꢁCl bond lengths that is difficult to rationalise,
since the unique SbꢁCl bond (trans to the donor bond)
has a length that falls between the lengths of the trans
SbꢁCl bonds. Comparison of the MꢁO and PꢁO bond
lengths and the w(PꢁO) stretching frequency for
−1
,
SbPh2Cl3·OPPh3 [2.148(3), 1.514(3) A and 1126 cm
,
respectively) with those for the organotin halide phos-
phine oxide adducts whose structures are described in
92.62(5)

D. Cunningham et al. / Journal of Organometallic Chemistry 612 (2000) 53–60
59
pole splitting of 3.48 mm s−1 for the mono aqua
adduct of dimethyltin dichloride in SnMe2Cl2·H2O/
Ni(MeOsal - 1,2pn) [H2MeOsal - 1,2pn=N,N% - bis(3-
methoxysalicylidene)propane-1,2-diamine] reflected the
presence of the intermolecular SnꢁCl interactions [26].
The large Mo¨ssbauer quadrupole splittings ranging
from 3.94–4.32 mm s−1 for the 1:2 adducts clearly
point to trans organo-octahedral tin complexes. The
point should also be made that the large increases
in quadrupole splitting associated with the addition
of the second phosphine oxide ligand to both
SnMe2Cl2·OPPh3 and SnBun2Cl2·OPPh3 clearly establish
that the extra phosphine oxide is coordinated to tin
rather than having merely a lattice role.
Table 6
Selected IR and 119Sn Mo¨ssbauer data for adducts of triphenylphos-
phine oxide
a
a
l
Z
w(PꢀO)
(mm s−1
)
(mm s−1
)
(cm−1
)
SnPh2Cl2·OPPh3
SnPh2Cl2·2OPPh3
SnPh2Br2·OPPh3
SnMe2Cl2·OPPh3
SnMe2Cl2·2OPPh3
SnBun2Cl2·OPPh3
SnBun2Cl2·2OPPh3
SnPh2(NCS)2·2OPPh3
SnBun2(NCS)2·2OPPh3
SbPh2Cl3·OPPh3
1.25
3.04
1140
1139
1138
1153
1139
1156
1150
1140
1138
1126
1.35
1.39
1.44
1.16
1.60
1.26
1.59
3.08
3.14
4.14
3.46
4.09
3.94
4.32
a
90.03 mm s−1
.
4. Supplementary material
data in Table 6, e.g. for the antimony adduct w(PꢀO) is
Crystallographic data for the structure analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 143186 (SbPh2Cl3·OPPh3),
143187 (SnPh2Cl2·2OPPh3), 143188 (SnPh2Cl2·OPPh3),
143189 (SnPh2Br2·OPPh3). Copies of this information
may be obtained free of charge from: The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(Fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
observed at 1126 cm−1 while for SnPh2Cl2·2OPPh3 it is
observed at 1139 cm−1
.
There is an interesting structural feature common to
all of the adducts described above in that, in each, a
phenyl ring of the phosphine oxide is involved in p-aro-
matic interactions with a phenyl attached to the metal.
In the case of the tin 1:1 adducts and the antimony
adduct, only one of the phenyl groups attached to the
metal is involved in such interactions (with a phenyl of
the phosphine oxide) but in the case of the tin 1:2
adduct both phenyl groups attached to the metal are
involved (as a result of their symmetry relationship).
The presence of the interactions is strongly suggested
both by the short carbon–carbon contacts between the
rings and the relative positioning of the rings (see Figs.
1–3) [25].
Acknowledgements
Two of us, N.N.C. and E.M.L. are grateful to Enter-
prise Ireland for financial support.
The Mo¨ssbauer quadrupole splittings of 3.04 and
3.08 mm s−1 for SnPh2Cl2·OPPh3 and SnPh2Br2·
OPPh3, respectively are totally consistent with the their
trigonal bipyramidal structures and the lower chemical
shift of the chloride is consistent with the electronega-
tivity order Cl\Br. Unlike 1:1 adducts of SnPh2Cl2,
1:1 adducts of Sn(alkyl)2Cl2 tend to exhibit intermolec-
ular SnꢁCl contacts thus giving tin octahedral (or
pseudo octahedral) coordination geometry. However,
the quadrupole splitting of 3.14 mm s−1 for
SnMe2Cl2·OPPh3 is consistent with a trigonal bipyrami-
dal structure with no intermolecular Sn-Cl contacts.
For example, the true trigonal bipyramidal 1:1 aqua
adduct of dimethyltin dichloride in SnMe2Cl2·H2O/
Ni(MeOsalen) [H2MeOsalen=N,N%-bis(3-methoxysali-
cylidene)ethane-1,2-diamine] exhibits almost identical
Mo¨ssbauer parameters (Z=3.12 mm s−1 and l=1.35
mm s−1 [26]) to those of SnMe2Cl2·OPPh3. However,
the considerably greater quadrupole splitting of 3.46
mm s−1 for SnBu2nCl2·OPPh3 points to the presence of
intermolecular SnꢁCl bonds, just as a similar quadru-
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