Lewis acidity of group 14 elements toward intramolecular sulfur in ortho-aryl-thioanisoles

Article abstract of DOI:10.1139/v03-163

The series of compounds (o-CH₃SC₆H ₄)CH₂EPh₃ (E = Si (1), Ge (2), Sn (3), and Pb (4)) have been synthesized and characterized by NMR spectroscopy and by single crystal X-ray diffraction. Compounds 1 a

Full text of DOI:10.1139/v03-163

1388
Lewis acidity of group 14 elements toward
intramolecular sulfur in ortho-aryl-thioanisoles1
Teresita Munguia, Ioana S. Pavel, Ramesh N. Kapoor, Francisco Cervantes-Lee,
László Párkányi, and Keith H. Pannell
Abstract: The series of compounds (o-CH3SC6H4)CH2EPh3 (E = Si (1), Ge (2), Sn (3), and Pb (4)) have been synthe-
sized and characterized by NMR spectroscopy and by single crystal X-ray diffraction. Compounds 1 and 2 are
isostructural with a triclinic crystal system and P-1 space group; however, morphotropic steps occur between Ge and
Sn, and Sn and Pb. While the E-S distances in 1 and 2 are 3.985 and 3.974 Å, respectively, ~100% of the sum of the
respective van der Waals (vdW) radii, there is a notable distortion from tetrahedral geometry about E. Compound 3 is
also triclinic with P-1 symmetry, but has two molecules in the unit cell that demonstrate a distorted tetrahedral geome-
try and intramolecular Sn-S distances of 3.699 and 3.829 Å, 88% and 91% of the sum of the vdW radii. Compound 4
has a Pb-S distance of 3.953 Å (91% of Σ vdW radii). The structure of the Grignard coupling product [o-
(SCH3)C6H4CH2]2 is also reported.
Key words: intramolecular self-assembly, silicon, germanium, tin, lead, sulfur.
Résumé : On a réalisé la synthèse d’une série de composés de formule (o-CH3SC6H4)CH2EPh3 dans lesquels E = Si
(1), Ge (2), Sn (3) et Pb (4) et on les a caractérisés par spectroscopie RMN et par diffraction des rayons X par un
cristal unique. Les composés 1 et 2 sont isostructuraux avec un système cristallin triclinique et un groupe d’espace P-
1; toutefois, on notre des différences morphotropes entre le Ge et le Sn ainsi qu’entre le Sn et le Pb. Alors que les dis-
tances E-S dans les composés 1 et 2 sont respectivement de 3,985 et 3,974 Å, environ 100 % de la somme des rayons
respectifs de van der Waals, on note une distorsion notable par rapport à la géométrie tétraédrique autour de E. Le
composé 3 est aussi triclinique avec une symétrie P-1, mais la maille cristalline comporte deux molécules ce qui dé-
montre la présence d’une géométrie tétraédrique déformée alors que les distances intramoléculaires Sn-S de 3,699 et
3,829 Å correspondent respectivement à 88 % et 91 % de la somme des rayons de van der Waals. Dans le composé 4,
la distance Pb-S est de 3,593 Å (91 % de la somme des rayons de van der Waals). On a aussi déterminé la structure
du produit de couplage de Grignard [o-(SCH3)C6H4CH2]2.
Mots clés : auto-assemblage intramoléculaire, silicium, germanium, étain, plomb, soufre.
[Traduit par la Rédaction] Munguia et al. 1397
Introduction
valency could impact the potential morphotropic steps as
originally described by Kitaigorodskii (1), and observed for
simpler group 14 systems where only tetrahedral structures
were possible. For example, the system Ph4E (E = Si (2), Ge
(3), Sn (4), Pb (5)) has been analyzed with respect to such
structural variations, and more recent studies by Párkányi et
al. (6) illustrated a morphotropic step occurring in the
heteronuclear intra(inter)-group 14 bonding organometallic
compounds (R3EE′R′R2). In these systems the packing coef-
ficient, defined as:
The system (o-CH3SC6H4)CH2EPh3 (E = Si (1), Ge (2),
Sn (3), and Pb (4)) offers the capacity to examine intra-
molecular sulfur–metal interactions via a five-membered
ring involving the ortho- thiomethyl group S atom (Fig. 1),
such that the varying Lewis acidities of the elements toward
sulfur may be evaluated. Furthermore, this possible hyper-
Received 12 March 2003. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 5 November 2003.
ZVm
η =
John: It has been one of my pleasures to get together with
you periodically to talk, drink, and generally enjoy your
company as well as your chemistry. Cheers, Keith.
V
where Z is the number of molecules in the unit cell, Vm is
the volume of the molecule, and V is the unit cell volume,
must be significantly decreased to change the packing motif
and create a morphotropic step (6). Thus, 1–4 present an ap-
pealing series with which to study whether the size changes
of the group 14 element would be sufficient to change the
packing coefficient. Furthermore, would the potential
intramolecular metal–sulfur interaction be adequate to dis-
tort the tetrahedral geometry about the metal center and fur-
ther aid, or impede, the potential for a morphotropic step.
T. Munguia, I.S. Pavel, R.N. Kapoor, F. Cervantes-Lee,
and K.H. Pannell.2 Department of Chemistry, University of
Texas at El Paso, El Paso, Texas 79968-0513, U.S.A.
L. Párkányi. Central Research Institute of Chemistry,
Hungarian Academy of Sciences, H-1525 Budapest, P.O.
Box 17, Hungary.
1This article is part of a Special Issue dedicated to Professor
John Harrod.
2Corresponding author (e-mail: kpannell@utep.edu).
Can. J. Chem. 81: 1388–1397 (2003)
doi: 10.1139/V03-163
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Munguia et al.
1389
Fig. 1. Triphenyl group 14 derivatives of o-aryl thioanisol.
Synthesis of o-(methylthio)benzyl triphenylsilane (1)
To a suspension of Li metal (0.55 g, 79 mmol) in THF
(20 mL) was added dropwise a solution of Ph3SiCl (1.7 g,
5.8 mmol) in THF (15 mL) at 0 °C. The reaction mixture
was allowed to warm to room temperature and stirred for
16 h resulting in a dark brown-black color. The solution was
transferred via cannula to a dropping funnel and then added
dropwise at –78 °C to a solution of o-(methylthio)benzyl
chloride (o-(SCH3C6H4)CH2Cl, 1.0 g, 5.8 mmol) in THF
(20 mL). This mixture was allowed to warm to room tem-
perature and stirred for 16 h. The solvent was removed un-
der reduced pressure, and the product was extracted with a
solution of 80 mL of hexanes and 5 mL dichloromethane
and subsequently filtered to remove LiCl. The crude material
was recrystallized from a hot hexanes:dichloromethane solu-
tion (10:1).
o-(SCH3C6H4)CH2SiPh3 (1) yield: 0.79 g (35%); mp 110–
Compounds in which systematic evaluations of the intra-
molecular interactions among group 14 organometallic com-
pounds have been previously reported but were limited to
investigations between tin and sulfur, as demonstrated by
Wardell and co-workers (7), Tzschach and co-workers (8),
and Dräger and co-workers (9) (Fig. 2).
1
112 °C. H NMR (CDCl3) δ: 2.1 (3H, s, S-CH3), 3.2 (2H, s,
CH2-Si), 7.5–6.9 (19H, m, Ph). 13C NMR (CDCl3) δ: 16.6
(S-CH3), 21.2 (CH2-Si), 125.1, 125.4, 127.3, 127.6, 129.0,
129.4, 134.4 (Cipso), 135.9, 137.1 (Cipso), 137.8 (Cipso). 29Si
NMR (CDCl3) δ: –11.9 Anal. calcd. for C26H24SSi: C 78.74,
H 6.10; found: C 77.86, H 6.08.
o-(SCH3C6H4)CH2GePh3 (2) yield: 0.93 g (37%); mp
Experimental section
1
104 °C. H NMR (CDCl3) δ: 2.1 (3H, s, S-CH3), 3.2 (2H, s,
CH2-Ge), 7.7–6.9 (19H, m, Ph). 13C NMR (CDCl3) δ: 16.2
(S-CH3), 22.2 (CH2-Ge), 125.1, 125.4, 126.9, 127.9, 128.5,
128.8, 134.4 (Cipso), 135.1, 136.6 (Cipso), 138.2 (Cipso). Anal.
calcd. for C26H24GeS: C 70.79, H 5.48; found: C 70.01, H
5.46.
General techniques
All syntheses were performed under a nitrogen atmo-
sphere using standard Schlenk line techniques. Reagent grade
tetrahydrofuran (THF) and hexanes were dried and distilled
under nitrogen from a sodium benzophenone ketyl solution;
benzene was dried and distilled from Na ribbon. Thionyl
chloride was purchased from Fisher Scientific and purified
by distillation; pyridine was purchased from E M Science
and dried and distilled over KOH; Ph3SiCl and Ph3GeCl
were purchased from Gelest; Ph3SnCl, Ph3PbCl, thiosalicylic
acid, and dimethyl sulfate were purchased from Aldrich and
were used as received. NMR spectra of all compounds were
recorded on a Bruker 300 MHz spectrometer in CDCl3. Ele-
mental analyses were performed by Galbraith Laboratories.
Syntheses of o-(methylthio)benzoic acid (10), o-(methyl-
thio)benzyl alcohol (10, 11), and o-(methylthio)benzyl chlo-
ride (12) followed literature procedures. o-(Methylthio)benzoic
acid, mp 165 °C (lit. (10) value 167–169 °C). 1H NMR
(CDCl3) δ: 2.5 (3H, s, S-CH3), 7.2–7.5 (4H, m, Ph), 8.1 (1H,
d, COOH). 13C NMR (CDCl3) δ: 15.6 (SCH3), 123.5, 124.4,
125.5, 132.5, 133.3 (Cipso), 144.4 (Cipso), 171.5 (COOH). o-
(Methylthio)benzyl alcohol, bp 156 °C/17 mmHg
(1 mmHg = 133.322 Pa) (lit. (10) value 88 °C/0.001 mmHg
o-(SCH3C6H4)CH2SnPh3 (3) yield: 2.0 g (71%); mp 106–
1
108 °C. H NMR (CDCl3) δ: 2.1 (3H, s, S-CH3), 3.1 (2H, s,
CH2-Sn, JH-117Sn = 64.3 Hz, JH-119Sn = 66.7 Hz), 7.6–7.0
(19H, m, Ph). 13C NMR (CDCl3) δ: 15.4 (S-CH3), 20.5 (CH2-Sn),
124.8, 125.0, 125.5, 127.6, 128.1 (Ph-Sn, JC-117/119 = 180 Hz),
Sn
128.6 (Ph-Sn, JC-117/119 = 75 Hz), 135.3 (Cipso), 136.8
Sn
(Ph-Sn, JC-117/119 = 150 Hz), 139.1 (Cipso), 139.2 (Cipso).
Sn
119Sn NMR (CDCl3) δ: –115.5. Anal. calcd. for C26H24SSn:
C 64.09, H 4.96; found: C 64.00, H 5.10.
o-(SCH3C6H4)CH2PbPh3 (4) yield: 0.93 g (30%); mp
1
110–114 °C. H NMR (CDCl3) δ: 2.1 (3H, s, S-CH3), 3.4
(2H, s, CH2-Pb, JH-Pb = 75.53 Hz), 7.6–6.9 (19H, m, Ph).
13C NMR (CDCl3) δ: 15.4 (S-CH3), 31.3 (CH2-Pb, JC-Pb
286.8 Hz), 124.7, 124.9, 125.1, 127.9, 128.1 (Ph-Pb, JC-Pb
=
=
17.6 Hz), 129.0 (Ph-Pb, JC-Pb = 72.6 Hz), 135.4 (Cipso),
137.2 (Ph-Pb, JC-Pb = 64.1 Hz), 139.7 (Cipso),152.2 (Ph-Pb,
JC-Pb = 359.2 Hz). 207Pb NMR (CDCl3) δ: –146.2. Anal.
calcd. for C26H24PbS: C 54.24, H 4.20; found: C 53.88, H
4.44.
1
(1 mmHg = 133.322 Pa)). H NMR (CDCl3) δ: 2.4 (3H, s, s-
CH3), 3.3 (1H, s, OH), 4.7 (2H, s, CH2-OH), 7.2–7.4
(4H, m, Ph). 13C NMR (CDCl3) δ: 16.3 (S-CH3), 63.2 (CH2-
OH), 125.7, 126.5, 128.0, 128.5, 136.8 (Cipso),139.3 (Cipso).
o-(Methylthio)benzyl chloride, bp 123 °C/9 mmHg
(1 mmHg = 133.322 Pa) (lit. (12) value 75 to 76 °C/1 ×
Alternative synthesis of o-(methylthio)benzyl
triphenyllead (4)
o-(Methylthio)benzyl chloride (1.0 g, 5.9 mmol) was
added dropwise to a mixture of Ph3PbCl (2.8 g, 5.9 mmol)
and Mg turnings (0.15 g, 6.2 mmol) in THF (10 mL) at
0 °C. The reaction mixture was kept at 0 °C and allowed to
stir until all the Mg had been consumed (16 h). The solution
was transferred via cannula to another flask where the sol-
vent was removed under reduced pressure and the product
was extracted with 80 mL hexanes and 5 mL of dichloro-
methane and the solution filtered. The crude material was
1
10–2 mmHg (1 mmHg = 133.322 Pa)). H NMR (CDCl3) δ:
2.5 (3H, s, S-CH3), 4.8 (2H, s, CH2-Cl), 7.2–7.4 (4H, m,
Ph). 13C NMR (CDCl3) δ: 16.7 (S-CH3), 45.1 (CH2-Cl),
126.0, 127.3, 129.9, 130.6, 136.0 (Cipso), 139.1 (Cipso).
The syntheses of the group 14 derivatives of o-(methyl-
thio)benzyl chloride were accomplished as illustrated below
for the silicon derivative in similar yields.
© 2003 NRC Canada

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Can. J. Chem. Vol. 81, 2003
Fig. 2. Summary of intramolecular interactions between tin and sulfur.
recrystallized from
a
hexane:dichloromethane solution
on glass fibers in a random orientation. Intensity data were
collected at room temperature for 1, 2, 5 and –85°C for 3 us-
(10:1) and cooled to –20 °C to yield 4, 1.2 g (70%). This
method was also used for the synthesis of 3 in a similar
yield.
ing
a Siemens/Bruker four-circle diffractometer with
graphite-monochromated Mo Kα radiation. Unit cell param-
eters and standard deviations were obtained by least-squares
fit of 25 reflections randomly distributed in reciprocal space
in the 2θ range of 15°–30°. The ω-scan technique was used
for intensity measurements in all cases. A range of 1.2° in ω
and variable speed of 4.00–20.00 °/min was used for com-
X-ray structural analysis
Crystals suitable for X-ray diffraction were obtained for
compounds 1–4, and 5 from hexane–dichloromethane solu-
tions. Five colorless crystals 1, 2, 3, 4, and 5 were mounted
© 2003 NRC Canada

Munguia et al.
1391
Fig. 3. Molecular diagram of 1.
pounds 1, 2, 3, and 5. Background counts were taken with a
stationary crystal and total background time to scan time ra-
tio of 0.5. Three standard reflections were monitored in all
cases every 97 reflections and showed no significant decay.
The data were corrected for Lorentz and polarization effects
and a semiempirical absorption correction was also applied
to the data set of 2 giving a min/max transmission ratio of
0.090:0.153. No absorption correction was applied to the
data sets of 1, 3, and 5.
Intensity data for compound 4 were collected at room
temperature on a Bruker SMART system with an APEX
CCD detector. All structures were solved by direct methods
and refined using the PC version of the SHELEXTL PLUS
crystallographic software by Siemens.3 Full-matrix least-
squares refinement of F2 against all reflections was carried
out with anisotropic thermal parameters for non-hydrogen
atoms. Hydrogen atoms for 1, 2, 3, and 5 were placed at cal-
culated positions (C-H = 0.96 Å; UH = 0.08) during refine-
ments, whereas those in compound 4 were located on a
difference map. The weighing scheme has the form w–1
=
2
2
2
σ2(Fo ) + (aP)2 + bP, where P is [2Fc + max(Fo ,0)]/3 and
Fig. 4. Molecular diagram of 2.
the final R factors have the form R12=2Σ |Fo – Fc| / Σ Fo and
2
2 2
Rw2 = {Σ [w(Fo – Fc ) / Σ [w(Fo ) ]}1/2; these and some
other relevant crystallographic parameters are summarized in
Table 1 and selected bond lengths and angles are presented
in Tables 2 and 3.
Compounds 1–3 (Figs. 3–5, respectively) crystallize in the
triclinic form with space group P-1. The latter compound
has two independent molecules in the asymmetric unit (3a
and 3b). Compound 4, in contrast, crystallized in the
monoclinic crystal structure with a space group of P2(1)/c
(Fig. 6).
Results and discussion
Synthesis and characterization
We have used two salt-elimination reactions to attach the
o-(methylthio)benzyl chloride ligand to the group 14 atom
(eqs. [1] and [2]).
presence of the halide reduced the extent of this problem
and resulted in the desired product in good yields (75%).
The reaction pathway involving the use of organometallic
lithium salt was equally successful. However, we think the
greater flexibility of the chemistry in eq. [1] makes this a
more general and useful route to such compounds, where the
organometallic lithium salts are less readily available. The
spectroscopic and elemental analytical data for the com-
pounds 1–4 are in total accord with their proposed struc-
tures, as is the data for 5.
Both routes are successful; however, when using the Grig-
nard route we observed the significant production of the
coupling product ([CH2(o-C6H4SMe)]2 (5)). This is formed
during the initial attempts to make the Grignard reagent
prior to subsequent addition of the group 14 halide. Modifi-
cation of the procedure to form the Grignard in situ in the
Periodic trends in the structural data for compounds 1–4
The E-S intramolecular distance in compounds 1–4 is an
essential structural feature for analysis of the progressive
change E = Si, Ge, Sn, and Pb. Not only is it an indirect
3 Supplementary data may be purchased from the Directory of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC
205424–205428 contain the crystallographic data for this manuscript. These data can be obtained, free of charge, via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
U.K.; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
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Munguia et al.
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Table 2. Selected interatomic bond distances (Å) and angles (°) for the compounds 1–4.
E = Si (1)
E = Ge (2)
E = Sn a (3)
E = Sn b (3)
E = Pb (4)
Bond distances (Å)
S—E
3.985
3.974
3.699
3.829
3.953
S—C(3)
S—C(8)
E—C(1)
E—C(9)
E—C(15)
E—C(21)
C(1)—C(2)
1.753(3)
1.776(4)
1.896(3)
1.873(3)
1.876(3)
1.876(3)
1.497(4)
1.766(5)
1.786(6)
1.976(5)
1.945(4)
1.957(4)
1.961(4)
1.491(6)
1.766(11)
1.812(12)
2.174(8)
2.143(9)
2.145(9)
2.156(9)
1.522(12)
1.777(10)
1.798(13)
2.174(11)
2.163(10)
2.170(11)
2.123(11)
1.462(15)
1.754(5)
1.786(6)
2.244(5)
2.204(5)
2.192(5)
2.200(5)
1.479(7)
Bond angles (°)
C(9)-E-C(1)
104.57(12)
110.07(12)
109.87(11)
114.57(12)
107.48(11)
110.24(13)
118.27(19)
117.1(2)
104.84(18)
110.17(17)
110.40(17)
115.20(19)
107.12(17)
109.1(2)
116.2(3)
116.7(3)
123.6(4)
107.7(3)
122.4(3)
119.6(3)
120.0(3)
122.0(3)
120.8(3)
120.9(3)
122.5(4)
112.6(4)
108.3(3)
108.0(3)
106.0(4)
109.0(3)
112.8(3)
112.2(6)
118.2(7)
122.6(9)
102.7(6)
118.8(7)
124.1(7)
121.5(7)
122.3(8)
118.6(7)
123.6(7)
120.1(9)
109.9(4)
109.0(4)
106.9(4)
110.1(5)
112.0(4)
108.9(4)
111.5(7)
117.6(8)
122.0(9)
102.7(6)
122.1(8)
122.6(7)
120.0(8)
121.4(9)
119.6(9)
120.9(9)
121.2(10)
103.35(18)
110.50(18)
109.21(18)
114.0(2)
107.00(19)
112.71(18)
114.1(3)
117.4(4)
123.1(4)
103.3(3)
119.7(4)
121.7(4)
122.0(4)
119.5(4)
121.4(4)
120.0(4)
121.9(4)
C(9)-E-C(15)
C(9)-E-C(21)
C(15)-E-C(1)
C(15)-E-C(21)
C(21)-E-C(1)
C(2)-C(1)-E
C(2)-C(3)-S
C(4)-C(3)-S
C(3)-S-C(8)
C(10)-C(9)-E
C(14)-C(9)-E
C(16)-C(15)-E
C(20)-C(15)-E
C(22)-C(21)-E
C(26)-C(21)-E
C(1)-C(2)-C(3)
123.1(2)
104.99(18)
123.40(19)
119.94(19)
121.17(19)
121.7(2)
121.81(19)
121.2(2)
122.1(2)
Table 3. Selected interatomic bond distances
(Å) and angles (°) for compound 5.
Both the ipso phenyl C—E bond lengths in compounds 1–
4 vary as expected because of the greater atomic radius of
the group 14 elements in the order Si < Ge < Sn < Pb and
are similar to those reported in the series Ph4E (2–5). Bonds
between E and benzyl groups are not well represented in the
literature, with the exception of that in Ph3PbCH2C6H5 (15).
The present examples also exhibit the expected increase in
bond lengths from C—Si to C—Pb, C1—E (E = Si, Ge, Sn,
Pb) = 1.896, 1.976, 2.174, and 2.244 Å, respectively.
5
Bond distances (Å)
S—C(1)
S—C(8)
C(6)—C(7)
1.768(4)
1.770(5)
1.510(5)
Bond angles (°)
C(6)-C(1)-S
C(2)-C(1)-S
C(1)-S-C(8)
C(1)-C(6)-C(7)
C(6)-C(7)-C(7a)
117.9(3)
122.5(3)
104.9(2)
121.9(4)
112.3(4)
Consequences of E–S interaction on tetrahedral geometry
In a perfect tetrahedral geometry, each angle is 109.5° and
the sum of three threefold symmetry angles will equal
328.5°. Group 14 organometallic compounds do not neces-
sarily exhibit perfect tetrahedral geometry and the amount of
distortion varies from system to system. In the Ph4E system,
all the molecules are spherical, crystallizing in the tetragonal
space group P¯421c (2–5). Despite the spherical nature and
symmetry of these molecules, the C-E-C dihedral angles
have a range of 108.1–111.2 (2–5). The wide range of angles
creates difficulty when comparing systems; as a result, all
angles of compounds 1–4 are compared with perfect tetrahe-
dral geometry. The “base” of the tetrahedral in this series is
comprised of the bond angles that would be pushed up as the
sulfur atom approaches the metal center trans to the “axial”
phenyl group. The numbering schemes for compounds 1 and
2 are identical; however, the numbering is slightly different
in the phenyl region for 3 and 4. For compounds 1 and 2, an-
gle C1-E-C9 is smaller than 109.5°, ranging from 104.57°
method of testing the Lewis acidity toward S of the central
metal atom, but it also lends a conformational degree of
freedom that may effect any potential morphotropic transi-
tion. Table 4 is a summary of covalent radii (13), van der
Waals (vdW) radii (13, 14), their sums, and their compari-
son to experimental E-S distances. Both 1 and 2 exhibit E-S
distances that are ~100% of the sum of the vdW radii indi-
cating that there are no significant intramolecular interac-
tions between the metal center and sulfur. The Sn-S
interactions in compound 3 are 3.699 Å (3a) and 3.829 Å
(3b), an average distance of ~90% of the sum of the vdW ra-
dii, similar to that in the lead compound 4, Pb-S = 3.953 Å,
91% of the vdW radii.
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Can. J. Chem. Vol. 81, 2003
Fig. 5. Molecular diagram of 3.
Fig. 6. Molecular diagram of 4.
for 1 to 104.84° for 2 with corresponding increases in C1-E-
C15. As we would expect for compounds with no E–S inter-
actions, the third angle (C9-E-C15) would also be close to
109.5°. The compounds 3a and 4 (with E–S interactions of
88% and 91% of the sum of the vdW radii, respectively)
have analogous angles that are smaller than 109.5° (108.0°
and 107.0°, respectively). However, the other two angles in
the base do not adjust to preserve the sum of 328.5°, as in
compounds 1 and 2. When all three angles in the base plane
are added together, 3a and 4 have the largest differences
from 328.5°, 333.4°, and 333.71° in that order, indicating
that the C-E-C plane is being pushed up slightly by the E–S
interactions. Table 5 summarizes the bond angles and their
sums for compounds 1–4.
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Munguia et al.
1395
Table 4. Comparison of sulfur – group 14 interactions.
Covalent
van der Waals
radii (Å)a,b
ΣCovalent
(Å)
Σvan der Waals
(Å)
S—E
(Å)
S—E as %
vdW radii
E
radii (Å)a
Si
Ge
Sn
1.17
1.22
1.40
2.10
2.15
2.40
2.20
2.25
2.43
3.90
3.95
4.20
3.985
3.974
3.699 (a)
3.829 (b)
3.764 (avg.)
3.953
102.2
100.6
88.1
91.2
89.6
91.0
Pb
S
1.44
1.03
2.53
1.80
2.47
4.33
aSee ref. 13.
bSee ref. 14.
Table 5. List of base and axial angles and their sums for compounds 1–4.
Base angles
Sum of base angles (°)
Axial angles
Sum of axial angles (°)
1
2
1
2
C(15)-E-C(1)
C(9)-E-C(15)
C(9)-E-C(1)
329.21
330.21
C(9)-E-C(21)
C(1)-E-C(21)
C(15)-E-C(21)
327.59
326.62
3a
3b
3a
3b
C(21)-E-C(1)
C(9)-E-C(21)
C(9)-E-C(1)
333.4
325.7
C(1)-E-C(15)
C(21)-E-C(15)
C(9)-E-C(15)
323.3
331.10
4
4
C(21)-E-C(1)
C(15)-E-C(21)
C(15)-E-C(1)
333.71
C(15)-E-C(9)
C(1)-E-C(9)
C(21)-E-C(9)
323.06
Further indications of the distortion about the central
metal atom are the axial angles. The sum of these angles un-
der normal geometry would also be 328.5°. Once the base
plane is pushed up by increasing E–S interactions, the sum
of these three angles mentioned above should be less than
328.5°. Indeed after analysis, the two compounds with the
smallest sums are 3a (323.3°) and 4 (323.06°), precisely
the compounds with the shortest E-S distances in terms of
% Σ vdW radii.
Fig. 7. Superposed structures of 3a and 3b.
Another trend that illustrates how the E–S interaction dis-
torts the molecule is that as the E-S distance decreases, the
C(2)-C(1)-E bond angle decreases as well. This makes sense
because angle C(1)-C(2)-C(3) will not change much because
of the rigid angle system dictated by the aromatic ring. As a
result, the only angle within the “arm” substructure that
gives flexibility is the C(2)-C(1)-E angle, which contains the
methylene moiety. Shortening of the E-S distance would be
facilitated by a contraction of the C(2)-C(1)-E angle. Indeed
this angle does contract when comparing 1 and 2 with com-
pounds 3 and 4, with the minimum occurring at compound
3.
Isostructural considerations
We have investigated the possible isostrucutural relation-
ships of 1–4. From their respective structural data 1 and 2
seem to be isostructural. However, due to the high degree of
freedom of assigning a triclinic unit cell and putting the
molecule in that cell with respect to the eight centers of
symmetry, the observation is not truly a proof. We computed
a least-squares fit of these two molecules including all non-
© 2003 NRC Canada

1396
Can. J. Chem. Vol. 81, 2003
Fig. 8. Solid-state conformational analysis of 3. (a) View down Sna(1)-Ca(1), (b) view down Snb(1)-Cb(1).
Table 6. Molecular volumes and packing coefficients for 1–4.
Fig. 9. Molecular diagram of 5.
Molecule
Volume (Å3)
Packing coefficient
Si
Ge
Sn 1
Sn 2
Pb
371.1
374.6
386.1
385.9
388.3
0.68
0.68
0.69
0.69
0.71
hydrogen atoms and the mean distance is 0.100 Å; RMS =
0.0823, a rather good fit. To prove absolutely we refined the
Si structure with the coordinates of the Ge compound and in
this manner proved that 1 and 2 are isostructural (R =
0.0476). The Sn and Pb derivatives do not belong (in the
sense of isostructurality) to a homologous series.
A superpositioning of the two forms of the tin compound
(3a and 3b) is illustrated in Fig. 7 and their two distinct con-
formations are presented in Fig. 8. The two independent
molecules are not superimposible, except to a high degree
the Sn–S interaction grouping, despite their differing Sn-S
distances. The two forms have fully staggered (3b) and par-
tially eclipsed forms (3a), which is similar to other
organometallic group 14 compounds (16). Thus, despite be-
ing relatively weak, the intramolecular Sn-S interactions
have a significant effect upon the conformational character
of the two molecules.
We have computed molecular volumes and packing coeffi-
cients for 1–4 (Table 6). These data illustrate a significant
jump in the molecular volume between Ge and Sn, where
the morphotropic step occurs. Overall, the packing coeffi-
cients are very similar, and the slight increase in the value
for lead could be the driving force for the change in its crys-
tal form.
Compound 5 (Fig. 9) crystallized in the monoclinic crys-
tal group with a space group of P2(1)/n. In total its structure
is unremarkable, however, the various bond lengths and an-
gles about the S atom serve as a baseline to note any varia-
tions in 1–4 by virtue of the intramolecular E–S interactions
(Table 5).
Magnesium-induced dimerization of o-(SCH3)C6H4CH2Cl
The capacity of Grignard reagents to produce dimers of
their parent organic halides is well established, thus the for-
mation of 5 from such attempted reactions is not surprising.
In 1980 an attempt by Zheltov et al. (17) to study the conju-
gation of aromatic disulfides by UV, mentions the prepara-
tion of compound 5, however, studies were limited, hence
we have performed a single crystal structural analysis.
Acknowledgments
Support for this research was provided by the R.A. Welch
Foundation, Houston, Texas (Grant AH-0546) and SCORE
NIH (Grant No. S06-GM-08012). L.P. wishes to thank the
Hungarian Academy of Sciences for the leave of absence.
© 2003 NRC Canada

Munguia et al.
1397
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