Synthesis and crystal structures of the compounds [Sn{C(SiMe2Ph)3}Cl]2, [Pb{C(SiMe3)3}Cl]3, and [M{C(SiMe3)2(SiMe2OMe)}Cl]2 (M = Sn or Pb)

Article abstract of DOI:10.1021/om9707580

The title compounds have been made by treatment of SnCl₂or PbCl₂ in tetrahydrofuran with the appropriate reagent LiR, where R = (PhMe₂Si)₃C, (Me₃Si)₃C, or (MeOMe₂Si)(Me₃-Si)₂C, and their crystal structures determined. In all four compounds, as in the previously reported [Pb{C(SiMe₂Ph)₃}Cl]₂, the metal atoms are linked by bridging Cl atoms, unsymmetrically except in the case of the trimeric [Pb{C(SiMe₃)₃}Cl]₃ (in which the six-membered ring has a distorted boat form). In [M{C(SiMe₃)₂(SiMe₂OMe)}Cl]₂, M = Sn or Pb, which are isomorphous, there are (relatively weak) intramolecular MeO?M interactions in addition. The compounds [Pb{C(SiMe₂Ph)₃}Cl]₂ and [Pb{C(SiMe₃)₃}Cl]₃ are the only known σ-bonded mono(organo)lead(II) compounds to have been structurally characterized, and [Sn{C(SiMe₂-Ph)₃}Cl]₂ is only the second solvent-free mono(alkyl)tin(II) compound. All of the compounds are yellow and air-sensitive in the solid and in solution, and the lead compounds are readily decomposed in solution by exposure to daylight.

Full text of DOI:10.1021/om9707580

Organometallics 1997, 16, 5653-5658
5653
Syn th esis a n d Cr ysta l Str u ctu r es of th e Com p ou n d s
[Sn {C(SiMe2P h )3}Cl]2, [P b{C(SiMe3)3}Cl]3, a n d
[M{C(SiMe3)2(SiMe2OMe)}Cl]2 (M ) Sn or P b)
Colin Eaborn,* Peter B. Hitchcock, J . David Smith,* and Sebnem E. So¨zerli
School of Chemistry, Physics and Environmental Science, University of Sussex,
Brighton BN1 9QJ , U.K.
Received August 25, 1997X
The title compounds have been made by treatment of SnCl2 or PbCl2 in tetrahydrofuran
with the appropriate reagent LiR, where R ) (PhMe2Si)3C, (Me3Si)3C, or (MeOMe2Si)(Me3-
Si)2C, and their crystal structures determined. In all four compounds, as in the previously
reported [Pb{C(SiMe2Ph)3}Cl]2, the metal atoms are linked by bridging Cl atoms, unsym-
metrically except in the case of the trimeric [Pb{C(SiMe3)3}Cl]3 (in which the six-membered
ring has a distorted boat form). In [M{C(SiMe3)2(SiMe2OMe)}Cl]2, M ) Sn or Pb, which are
isomorphous, there are (relatively weak) intramolecular MeO‚‚‚M interactions in addition.
The compounds [Pb{C(SiMe2Ph)3}Cl]2 and [Pb{C(SiMe3)3}Cl]3 are the only known σ-bonded
mono(organo)lead(II) compounds to have been structurally characterized, and [Sn{C(SiMe2-
Ph)3}Cl]2 is only the second solvent-free mono(alkyl)tin(II) compound. All of the compounds
are yellow and air-sensitive in the solid and in solution, and the lead compounds are readily
decomposed in solution by exposure to daylight.
In tr od u ction
pound PbArCl.2 (In their review of relevant literature,
the authors appear to have overlooked our report of
(PbR*Cl)2.1)
We previously reported the first preparation of a
σ-bonded heteroleptic organolead(II) compound of the
type PbRX, namely PbR*Cl, where R* denotes the bulky
group (PhMe2Si)3C.1 In the crystal, the compound is
present as the dimer 1, which has a form fairly similar
to that shown for the corresponding tin compound in
Figure 2, with one longer and one shorter metal-Cl
bond in each of the Cl bridges.
An analog of 5, viz. Sn{C(SiMe3)2(NC5H4-2)}Cl, is
known; in this analog there is intramolecular coordina-
tion of the pyridyl N to tin, but the compound is
monomeric, and the tin is, thus, only three-coordinate.3
Resu lts a n d Discu ssion
Com p ou n d 1. The structure of compound 1 that we
described previously was that of a monoclinic crystal
obtained by crystallization from methylcyclohexane
after preparation in tetrahydrofuran (THF).1 We later
obtained an orthorhombic form of the same compound
from the reaction between R*Li and PbCl2 in THF and
subsequent crystallization from heptane. The X-ray
data from the orthorhombic form were of poorer quality
than those from the monoclinic form, but the molecular
structure was unambiguous and revealed that the
centrosymmetrical dimeric molecules differ from those
in the monoclinic form only in the conformations of the
C(SiMe2Ph)3 groups. (The dimer of the orthorhombic
form is, in fact, isomorphous with the tin compound 2,
and so its structure is essentially the same as that
shown in Figure 1.)
(PbR*Cl)2 1 (SnR*Cl)2 2 (PbR†Cl)3 3 (PbR′Cl)2 4
(SnR′Cl)2 5
R* ) (PhMe2Si)3C R† ) (Me3Si)3C
R′ ) (MeOMe2Si)(Me3Si)2C
We now describe the preparation and structural
characterization of (a) an orthorhombic form of 1; (b)
the analogous tin compound 2; (c) the related lead
compound PbR†Cl, where R† ) (Me3Si)3C, which crys-
tallizes as a trimer, 3; and (d) the compounds MR′Cl,
where R′ ) (MeOMe2Si)(Me3Si)2C and M ) Pb or Sn,
which crystallize from light petroleum as dimers 4 and
5, respectively, in which there is intramolecular coor-
dination of the MeO group to the metal.
We previously4 showed that C(SiMe2Ph)3 groups can
adopt one of several configurations depending on how
each PhMe2Si group is oriented with respect to the
substituents at the adjacent central carbon, which in
the present case are one Pb and two Si atoms. The
Since this work was completed, Power and colleagues
have reported the preparation and characterization of
the aryltin(II) compound (SnArCl)2, where Ar ) 2,6-
{2,4,6-Me3C6H2}2C6H3); they also made the (structurally
very different) germanium compound (GeArCl)2 but
were unable to obtain the corresponding lead(II) com-
(2) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organo-
metallics 1997, 16, 1920.
(3) Engelhardt, L. M.; J olly, B. S.; Lappert, M. F.; Raston, C. L.;
White, A. H. J . Chem. Soc., Chem. Commun. 1988, 336.
(4) Al-J uaid, S. S.; Eaborn, C.; Habtemariam, A.; Hitchcock, P. B.;
Smith, J . D.; Tavakkoli, K.; Webb, A. D. J . Organomet. Chem. 1993,
462, 45.
X Abstract published in Advance ACS Abstracts, November 15, 1997.
(1) Eaborn, C.; Izod, K.; Hitchcock, P. B.; So¨zerli, S. E.; Smith, J . D.
J . Chem. Soc., Chem. Commun. 1995, 1829.
S0276-7333(97)00758-9 CCC: $14.00 © 1997 American Chemical Society

5654 Organometallics, Vol. 16, No. 26, 1997
Eaborn et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [{(P h Me2Si)3CMCl}2]
M ) Pb (1)a
M ) Sn (2)
M-C(1)
2.435(10)
2.729(3)
2.962(3)
1.89(1)
2.296(10)
2.596(3)
2.779(3)
1.90(1)
M-Cl
M-Cl′
C(1)-Si (mean)
M-Cl-M′
92.92(8)
87.08(8)
98.5(2)
112.0(2)
116.7(5)
118.7(5)
108.8(5)b
115.4(5)c
109.9(5)
97.2(4)
101.63(9)
78.37(9)
99.1(3)
111.1(2)
113.9(5)
111.2(5)
110.1(5)
113.7(5)
112.7(4)
99.2(4)
Cl-M-Cl′
Cl-M-C(1)
Cl′-M-C(1)
Si1-C(1)-Si2
Si1-C(1)-Si3
Si2-C(1)-Si3
C(1)-Si-Me (mean)
C(1)-Si-Ph (mean)
M-C(1)-Si1
M-C(1)-Si2
M-C(1)-Si3
M-C(1)-Si (mean)
Me-Si-Me,Ph (mean)
101.5(4)
111.9(4)
103.5d
100.6(4)
121.3(4)
(107.0)e
105(1)
105(1)
F igu r e 1. Molecular structure of [Sn{C(SiMe2Ph)3}Cl]2,
2. (The orthorhombic form of compound 1 has a similar
form.)
a
Monoclinic form. The numbers of the atoms Si2 and Si3, as
shown in ref 1, have here been interchanged to match those for 2.
Incorrectly reported previously as 118.7(5)°.1 c Values ranged
b
d
from 108.0(4)° to 117.8(5)°. Values ranged from 97.2° to 111.9°.
e Values ranged from 99.2° to 121.3°.
angles, 114.7° and 111.7°, are not very different. That
the Si-C bond lengths and Si-C-Si angles in the two
compounds are similar is as expected in view of the
similar electronegativities of the two metals.5
The Sn-C bond in 2, 2.296(10) Å, is significantly
longer than that in the aryltin chloride (SnArCl)2 with
Ar ) 2,6-{2,4,6-Me3C6H2}2C6H3), 2.222(5) Å.2 The
lengths of the (stronger) Sn-Cl bonds are effectively the
same in the two compounds, but those of the (weaker)
Sn-Cl′ bond are significantly different, that in the aryl
derivative being only 0.085 Å longer than the Sn-Cl
bond, so that the bridge is much more symmetrical than
in 2. The Sn-Cl-Sn′ and Cl-Sn-Cl′ angles do not
differ much between the compounds, but the C(1)-Sn-
Cl′ angle in the aryl derivative, 92.35(14)°, is markedly
smaller than that in 2, 111.1(2)°, which means that the
Sn-C(1) bond lies closer to the plane of the four-
membered ring in the latter.
Our attempts to make the compound SnR†Cl have so
far been unsuccessful (There are strong indications that
the reactions of LiR , R ) R* or R†, with SnCl2 both
initially give a salt Li[SnRCl2], which then breaks down
to RSnCl, but the latter has been isolated only for R )
R*.)
Com p ou n d 3. This compound was made by treat-
ment of PbCl2 with 1 mol equiv of LiR† in THF, and
after removal of the solvent, it was extracted into
toluene from which it separated in 85% yield as yellow-
orange crystals. (The same compound was formed when
2 mol equiv of LiR* was used.) Like 1, it is very air
sensitive and readily decomposed by light in solution
(but more slowly in the solid).
An X-ray diffraction study revealed the trimeric
structure shown in Figure 3, and selected bond lengths
and angles are shown in Table 2. The trimer has its
six-membered ring in a distorted boat form, as shown
in Figure 4, in which the prow of the boat, represented
by the Pb1-Cl3-Pb3 triangle, lies almost at right
angles to the base, Pb1-Cl1-Cl2-Pb3. The R† groups
F igu r e 2. Projections along C-M bonds in (MR*Cl)2: (a)
The monoclinic form of 1 (M ) Pb). (b) The orthorhombic
form of 1 (M ) Pb) or 2 (M ) Sn).
monoclinic form of 1 has two PhMe2Si fragments with
methyl groups anti to Pb and the third PhMe2Si with
the phenyl group anti to Pb, whereas in the more
symmetrical orthorhombic form all three PhMe2Si frag-
ments are oriented so that methyl groups are anti to
Pb; the difference can be seen from Figure 2.
Com p ou n d 2. This compound was made by treat-
ment of SnCl2 with 1 mol equiv of LiR* in THF, and
after removal of the solvent, it was extracted into light
petroleum and isolated as yellow air-sensitive crystals.
The structure of 2 is shown in Figure 1, and selected
geometrical data are listed in Table 1 alongside those
for the monoclinic form of 1. As will be evident from
the discussion of the two forms of 1 above, the structure
of 2 and that of the monoclinic form of 1 differ mainly
in the configurations of one of the SiMe2Ph groups, but
in addition the geometries of the four-membered bridg-
ing rings in the two compounds differ in that the M-Cl-
M′ angles and Cl-M-Cl′ angles in the monoclinic form
of 1 are, respectively, 7-9° narrower and 7-9° wider
than those in the orthorhombic form and than those in
2. The lower symmetry of the R* group in the mono-
clinic form also affects the mismatch between the Pb-
Cl and Pb-Cl′ bonds, which is ca. 0.11 Å in the
orthorhombic and 0.223 Å in the monoclinic form (cf.
0.183 Å in 2). The mean lengths of the C(1)-Si bonds
are identical within experimental uncertainty. Because
of the differing configurations of the C(SiMe2Ph)3 groups,
the Si-C(1)-Si angles range more widely in 1, from
108.8(5) to 116.7(5)° to 118.7(5)°, than in 2, from 110.1(5)
to 111.2(5)° to 113.9(5)°, although the means of these
(5) Eaborn, C.; Izod, K.; Smith, J . D. J . Organomet. Chem. 1995,
500, 89.

Synthesis of Sn and Pb Compounds
Organometallics, Vol. 16, No. 26, 1997 5655
Figu r e 5. Molecular structure of M{C(SiMe3)2(SiMe2OMe)}-
Cl]2, M ) Pb (4) or Sn (5).
1.88(4)) Å) and the C-SiMe2Ph bond lengths (mean
1.889(10) Å) in 1.
F igu r e 3. Molecular structure of [Pb{C(SiMe3)3}Cl)3], 3.
It is of interest to consider why PbR*Cl forms a dimer
in the solid and PbR†Cl a trimer. The electronic effects
of the R* (i.e., (PhMe2Si)3C) and R† (i.e., Me3Si)3C)
groups must be very similar, and so the differences
between the two compounds are presumably to be
attributed to the difference in the sizes of R* and R†.
When the smaller R† is present, a six-membered ring,
which would be disfavored on entropy grounds, is
evidently more stable and so this must be the form with
the lowest free energy when the ring strain (determined
largely by the intra-ring bond angles and lengths) and
the steric interactions between the R groups and
between these and the neighboring Cl atoms are taken
into account. In the four-membered ring species, not
only will the steric interaction with the neighboring Cl
atoms be lower (compare the R*-Pb-Cl angles of 98.5°
and 112.0° in 1 and R†-Pb-Cl angles between 99.5° and
103° in 3) but also, probably more importantly, that
between the R* groups, which are far apart in their
trans disposition in the dimer. The shortest C‚‚‚C
distances between the R† groups in 3 are 4.08 Å between
C7 and C22 and 4.19 Å between C10 and C12, values
only slightly larger than twice the van der Waals radius
(2.0 Å7) of the Me group. It, thus, seems likely that
replacement of some Me by Ph groups would lead to
significant steric repulsion between the R* ligands if
PbR*Cl were to form trimers rather than dimers. A
comparable relation was observed previously for the
compounds CdR†Cl and CdR*Cl; the former crystallizing
as a tetramer8 and the latter as a dimer.4
Com p ou n d 4. Reaction of LiR′ with PbCl2 in a 1:1
mol ratio gave the product RPb′Cl, which crystallized
as the Cl-bridged dimer 4, having the structure shown
in Figure 5 and selected bond lengths and angles as
given in Table 3. In the dimer, each MeO group is
intramolecularly coordinated to its adjacent Pb atom,
so that the Pb(II) atoms are four-coordinate, but in
terms of the dispositions of the Cl, Cl′, Pb, and C(1)
atoms, the skeleton of 4 is rather similar to that in the
dimer 1 in which the Pb atoms are three-coordinate. All
of the atoms bound to lead lie on one side. The
coordination may be described as distorted trigonal
bipyramidal with the electronegative ligands Cl and O
in the axial positions and the stereochemically active
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [{(Me3Si)3CP bCl}3], 3
Pb1-C(1)
Pb3-C(21)
Pb1-Cl3
Pb2-Cl2
Pb3-Cl3
2.37(4)
2.27(6)
2.73(1)
2.71(2)
2.74(1)
Pb2-C(11)
2.41(6)
2.71(1)
2.74(2)
2.71(2)
1.88(6)
1.87(6)
Pb1-Cl1
Pb2-Cl1
Pb3-Cl2
Si-C(1,11,21) (mean)
Si-Me (mean)
C(1)-Pb1-Cl1
C(1)-Pb1-Cl3
C(11)-Pb2-Cl1
C(11)-Pb2-Cl2
102.7(10) Cl2-Pb3-Cl3
100.7(10) Pb1-Cl1-Pb2
99.6(13) Pb1-Cl3-Pb3
99.5(14) Pb2-Cl2-Pb3
91.2(4)
115.7(5)
90.9(4)
112.0(6)
C(21)-Pb3-Cl2 103(2)
C(21)-Pb3-Cl3 101(2)
Pb-C-Si (mean)
106(3)a
Si-C(1,11,21)-Si (mean) 113(3)
Cl1-Pb1-Cl3
Cl1-Pb2-Cl2
87.7(4) Me-Si-Me (mean)
106(2)
92.6(5)
a
Values ranged from 99(2)° to 116(3)°.
F igu r e 4. Structure of [Pb{C(SiMe3)3}Cl)3], 3, showing the
form of the six-membered ring.
linked to Pb1 and Pb3 point up and away from the base
of the boat, with Cl2-Pb3-C21 and Cl1-Pb1-C(1)
angles of ca. 103°, whereas the R† group linked to Pb2
points downward with Cl1-Pb2-C(11) and Cl2-Pb-
C(11) angles of ca. 99.5°. These orientations allow the
bulky groups R† to point outward from the ring; they
have been found previously, e.g., in the boat form of
(Me2AlNHMe)3.6
The six Pb-Cl bonds in 3 have lengths which differ
insignificantly from the mean, 2.72 Å, which is similar
to that of the shorter Pb-Cl bonds in 1. If the atoms
within the R† groups are ignored, the molecule is
roughly symmetrical about the plane through C11, Pb2,
and Cl3; the C-Pb-Cl angles range between 99° and
103° and the Cl-Pb-Cl angles between 88° and 93°.
The Pb-C bond lengths in 3 (mean 2.35(6) Å) and 1
(mean 2.435(10) Å) are not significantly different, and
neither are the C-SiMe3 bond lengths in 3 (mean
(6) McLaughlin, G. M.; Sim, G. A.; Smith, J . D. J . Chem. Soc., Dalton
Trans. 1972, 2197. Alford, K. J .; Gosling, K.; Smith, J . D. J . Chem.
Soc., Dalton Trans. 1972, 2203.
(7) Bondi, A. J . Phys. Chem. 1964, 68, 441.
(8) Al-J uaid, S. S.; Buttrus, N. H.; Eaborn, C.; Hitchcock, P. B.;
Smith, J . D.; Tavakkoli, K. J . Chem. Soc., Chem. Commun. 1988, 1389.

5656 Organometallics, Vol. 16, No. 26, 1997
Eaborn et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
phous with the lead analog 4, so that a single diagram,
Figure 5, serves for both compounds. Selected bond
lengths and angles are given in Table 3 alongside those
for 4.
(d eg) in [M{C(SiMe3)2(SiMe2OMe)}Cl]2
M ) Pb (4)a
M ) Sn (5)a
M-C(1)
M-Cl
2.37(2)
2.294(5)
2.538(2)
2.952(3)
2.416(4)
1.872(5)
1.686(4)
1.445(7)
As in 4, the metal-O bond, 2.416(4) Å, is rather long
(compare the sum, 2.06 Å, of the covalent radii, the
lengths of the Sn-O bonds in SnO, 2.224(8) Å,16 and
SnCl2‚2H2O, 2.325(5)°,17 and that of 1.999(6) Å in the
monomeric Sn(IV) hydroxide (2,4,6-Me3C6H2)3SnOH.18
The Si-O bond length is the same as that in 4. The
sum of the angles at O is 353.8°. The presence of the
stereochemically active lone pair between the O-M and
M-Cl′ bonds leads to an O-Sn-Cl′ angle of 158.8(1)°.
The shape of the four-membered O-Sn-C-Si ring is
closely similar to that of the corresponding ring in 4,
but the O-Sn-C angle, 69.1(2)°, not quite as narrow
as the O-Pb-C angle, 65.9(5)°, in 4. As in 4, there is
a large asymmetry in the locations of the Si2 and Si3
atoms (larger than in 2), the Sn-C(1)-Si2 and Sn-
C(1)-Si3 angles being 98.1(2)° and 123.2(2)°, respec-
tively, but again the CSi3 system is undistorted, all three
Si-C(1)-Si angles remaining at ca. 113°.
2.680(5)
2.868(5)
2.598(12)
1.87(2)
1.684(14)
1.45(3)
M-Cl’
M-O
C(1)-Si (mean)
Si(1)-O
O-C2
M-Cl-M′
97.67(14)
82.33(14)
103.4(4)
100.9(4)
83.2(3)
157.4(3)
96.7(8)
97.7(8)
99.57(7)
80.43(7)
103.12(13)
99.45(13)
84.85(11)
158.79(10)
94.6(2)
98.1(2)
123.2(2)
94.9(2)
Cl-M-Cl′
C(1)-M-Cl
C(1)-M-Cl′
O-M-Cl
O-M-Cl′
M-C(1)-Si1
M-C(1)-Si2
M-C(1)-Si3
M-O-Si1
120.8(8)
93.2(5)
Si-C(1)-Si (mean)
C(1)-Si1-C3
C(1)-Si1-C4
C(1)-Si(2,3)-Me (mean)
113.4(9)
116.4(9)
117.8(9)
112.6(9)
113.0(2)
117.0(3)
119.4(3)
112.5(3)
a
The dimer lies on a crystallographic inversion center. Sym-
Comparison of 1 with 4 and of 2 with 5 reveals that
the introduction of the chelate ring has surprisingly
little effect on the rest of the molecule. The internal
coordination increases the difference between the lengths
of the Sn-Cl and Sn-Cl′ bonds from 0.183 Å in 2 to
0.414 Å in 5 and the difference between the lengths of
the Pb-Cl and Pb-Cl′ bonds from 0.11 Å in the
orthorhombic form of 1 to 0.188 Å in 4. The observa-
tions are consistent with the generalization that the
effect of the lone pair is much more evident in the
chemistry of Sn(II) than in that of Pb(II).19 Put in
another way, tin is more reluctant than lead to increase
its coordination number beyond three. The difference
in length between the third and fourth longest bond to
the metal is 0.28 Å in SnCl220 but only 0.13 Å in PbCl2.21
The M-Cl bonds in 4 and 5 show a similar pattern.
NMR Da ta . The NMR data were mainly recorded
for solutions, and we cannot be sure that they refer to
the dimers or trimers present in the solids, although
we observed no indication that dissociation occurred.
Attempts to resolve the uncertainty for the tin com-
pounds by determination of solid state 119Sn and 207Pb
spectra failed because no signal could be obtained for
either nucleus, probably because of severe chemical shift
anisotropy. With one exception for the compounds
examined, there was no significant difference between
the positions of the solution and solid state 29Si reso-
nances. The exception was provided by the chelated tin
compound 5, for which chemical shifts of δ 33 and 39.5,
respectively, were observed for the Si of the SiMe2OMe
group in the solid and in a C6D6 solution but a shift only
δ 18 for a solution in C4D8O. Since this last value is in
the region found, for example, for the parent molecule
R′H, viz., 15.9,22 the related iodide R′I (15.2) (in CDCl3),14
metry operation: -x, -y, -z.
lone pair equatorial. The small C-Pb-O angle, 65.9-
(5)°, is noteworthy.
The Pb-O bond length, 2.598(12) Å, is significantly
larger than the sum, 2.20 Å, of the covalent radii of Pb
and O, than the Pb-O bond lengths of 2.221(2), 2.249-
(2), and 2.481(1) Å in the orthorhombic form of PbO or
2.30 Å in the tetragonal form,9 and than those of 2.37(2)
and 2.44(2) Å in the Pb(IV) compound Ph3PbOH.10
However, Pb(II) often achieves coordination numbers
higher than 2 or 3 by forming secondary bonds of 2.4-
2.8 Å in length,11 and so in this context the Pb-O
interaction in 4 is not unusual, but not particularly
strong. The Si-O bond, 1.684(14) Å, is markedly longer
than the great majority of Si-OR bonds, which com-
monly fall within the range 1.63-1.66 Å,12 and is
essentially the same as that in [YbR′I‚OEt2]2,13 but
perhaps a little shorter than that in MgR′2, viz. 1.705(6)
Å.14 (In But SiOH2+, in which a lone pair of the O atom
3
is fully engaged in interaction with the proton, the Si-O
bond is lengthened to 1.779(9) Å.15) The geometry at
the O atom in 4 is not quite planar, the sum of the
angles being 351.3°.
The coordination to lead of the oxygen atom on Si(1)
results in a small Pb-C-Si1 angle of 96.7(8)°. The Pb-
C-Si2 angle is similar (97.7(8)°), but Pb-C-Si3 is
120.8(8)°. However, the CSi3 system as a whole is not
distorted, the three Si-C(1)-Si angles all remaining at
ca. 113°, as in the case of 2 and 3.
Com p ou n d 5. Reaction of LiR′ with SnCl2 readily
gave the product 5, which proved to be closely isomor-
(9) Hill, R. J . Acta Crystallogr., Sect. C 1985, 41, 1281. Leciejewicz,
J . Acta Crystallogr. 1961, 14, 66 and 1304.
(10) Glidewell, C.; Liles, D. C. Acta Crystallogr., Sect. B 1978, 34,
129.
(11) Harrison, P. G.; Steel, A. T. J . Organomet. Chem. 1982, 239,
105.
(12) Lukevics, E.; Pudova, O.; Sturkovich, R. Molecular Structure
of Organosilicon Compounds; Horwood: Chichester, U.K., 1989; p 180.
(13) Eaborn, C.; Hitchcock, P. B.; Izod, K.; Lu, Z.-R.; Smith, J . D.
Organometallics 1996, 15, 4783.
(14) Eaborn, C.; Hitchcock, P. B.; Kowalewska, A.; Lu, Z.-R.; Smith,
J . D.; Stanczyk, W. A. J . Organomet. Chem. 1996, 521, 113.
(15) Xie, Z.; Bau, R.; Reed, C. A. J . Chem. Soc., Chem. Commun.
1994, 2519.
(16) Pannetier, J .; Denes, G. Acta Crystallogr., Sect. B 1980, 36,
2763.
(17) Kiriyama, H.; Kitahama, K.; Nakamura, O.; Kiriyama, R. Bull.
Chem. Soc. J pn. 1973, 46, 1389.
(18) Reuter, H.; Puff, H. J . Organomet. Chem. 1989, 379, 223.
(19) Wells, A. F. Stuctural Inorganic Chemistry, 5th ed.; Oxford
University Press: New York, 1984; pp 1182-1189.
(20) Van den Berg, J . M. Acta Crystallogr. 1961, 14, 1002; 1962,
15, 1051.
(21) Sass, R. L.; Brackett, E. B.; Brackett, T. E. J . Phys. Chem. 1963,
67, 2863.

Synthesis of Sn and Pb Compounds
Organometallics, Vol. 16, No. 26, 1997 5657
Ta ble 4. Su m m a r y of Cr ysta llogr a p h ic Da ta for 2, 3, a n d 4
2a
3
4a
5a
empirical formula
fw
C50H66Cl2Si6Sn2
1143.9
C30H81Cl3Pb3Si9
1422.7
C20H54Cl2O2Pb2Si6
980.5
C20H54Cl2O2Si6Sn2
803.5
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.30 × 0.15 × 0.05
orthorhombic
Pbca (No. 61)
16.146(13)
13.793(5)
24.027(9)
90
90
90
5351(5)
4
1.42
2336
1.20
2-22
0 < h < 17
0 < k < 14
0 < l < 25
3262
3262
2173
0.3 × 0.3 × 0.3
monoclinic
P2/c (No. 13)
13.772((9)
8.835(4)
44.35(2)
90
90.62(4)
90
5397(5)
0.4 × 0.4 × 0.1
triclinic
P1h (No. 2)
9.070(4)
9.212(3)
12.781(7)
84.51(3)
77.76(4)
60.90(3)
911.8(7)
1
1.79
472
9.58
2-25
0 < h < 10
-9 < k < 10
-14 < l < 15
3195
3195
2873
0.4 × 0.4 × 0.2
triclinic
P1h (No. 2)
9.049(6)
9.214(6)
12.805(5)
82.99(4)
76.81(4)
60.88(5)
908.0(9)
1
1.47
408
1.74
2-25
0 < h < 10
-9 < k < 10
-14 < l < 15
3182
3182
3004
0.038; 0.129
0.040; 0.138
3178/0/145
1.132
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
4
1.75
2736
9.70
dc (Mg m-3
F(000)
)
µ (mm-1
)
θ range (deg)
index range
2-18
0 < h < 11
0 < k < 7
-38 < l < 38
3917
no. of rflns collected
no. of unique reflns
no. of rflns with I > 2(σ)I
R1; wR2 (I > 2σ(I)
R1; wR2 (all data)
no. of data/restraints/parameters
GOF on F2
3708 (Rint ) 0.2768)
2338
0.098; 0.246
0.155; 0.318
3688/0/256
1.034
0.061; 0.137
0.105; 0.165
3261/0/271
1.029
0.073; 0.224
0.081; 0.242
3191/0/145
1.128
max shift/error
0.001
1.09, -1.8 (near Sn)
1.00; 0.70
0.005
2.16, -2.19
0.99; 0.64
0.002
4.1, -6.4 (near Pb)
1.00; 0.22
0.001
largest diff peak/hole (e Å-3
)
1.68, -1.51 (near Sn)
1.00; 0.84
abs corr Tmax; Tmin
a
The molecule lies on a crystallographic inversion center.
(MeOMe2Si)3CSiMe2H (14.0),23 ZnR′2 (17.1),24 and even
Me3SiOMe (17.2),25 it seems reasonable to conclude that
in THF, coordination of the solvent to tin replaces the
internal coordination of OMe. Comparison of the shifts
of ca. 33 and 39.5 observed for 5 in the solid and in
benzene solution, respectively, with those of 19.6 (in
C6D6) and 18.8 (in toluene-d8) observed for solutions of
which may be compared with that of δ 3870 for PbAr2
with Ar ) 2,6-{2,4,6-Me3C6H2}2C6H3).2 A 119Sn shift of
777 was observed for 2 in C6D6 and one of δ 469 for 5 in
C6D6 and 267 in C4D8O; the substantial change in the
position of the signal from 5 is consistent with a change
in the nature of the compound on going from benzene
to the donor solvent. Shifts of δ 635 and 562, respec-
tively, were reported for the aryltin compounds SnAr2
and (SnArCl)2, Ar ) 2,6-{2,4,6-Me3C6H2}C6H3), in C6D6.2
The other NMR solution data are unexceptional, but
the small variation in the chemical shift for the 13C atom
of the OMe group over a range of compounds is
noteworthy, the values (for solutions in C6D6 or toluene-
d8) all lying between δ 49.5 and 51.5 for 4, 5, R′H,22 R′I,14
LiR′‚2THF,14 MgR′2,14 and YbR′2.13 (A shift of δ 55 was
observed for 4 in the solid.)
In the solid state NMR spectra of 4, in the Me3Si
region, there are two 29Si signals at δ -2.7 and -8.4
and four 13C signals at 5.6, 7.6, 11.5, and 14.0. Likewise,
for 5 there are two 29Si signals at δ -1.0 and -3.0; the
13C spectrum was not recorded. These effects can be
attributed to inhibition of rotation about the M-C or
Si-C bonds; it is such restriction of rotation about Si-C
bonds that gives rise to the polymorphism of com-
pound 1.
F a ilu r e To Ma k e Dia lk ylm eta l Com p ou n d s. In
the reactions of PbCl2 with LiR* or LiR†, use of 2 mol
equiv of the lithium reagent did not change the outcome,
only the monoalkyl compounds 1 and 3 being obtained.
Our failure to obtain the dialkyllead compounds, even
though the diaryl compounds MAr2 with M ) Sn or Pb
and Ar ) 2,6-{2,4,6-Me3C6H2}2C6H3) were readily made
by Power and colleagues,2 is probably to be attributed
to a greater effective bulk of the alkyl than of the aryl
ligands. We attempted to convert 1 into R*PbPh by
treatment with LiPh in Et2O, but a complex mixture
13
LiR′‚2THF14 and [YbR′I‚OEt2]2 suggests that in both
of these latter cases the MeO‚‚‚M coordination observed
in the solid is absent for solutions even in hydrocarbons,
probably because of the presence of ether molecules in
the compounds. (We previously14 reported a shift of 0.7
for LiR′‚2THF in C6D6, but reinvestigation in light of
the results discussed in the present paper showed this
to be in error.) The shift of δ 17.7 observed for 4 in
solution in C6D6 likewise suggests that there is no MeO
coordination even in this solvent, but the value for the
solid in this case is puzzlingly close, at 21, even though
the X-ray diffraction study reveals an unambiguous
(though weak) O‚‚‚Pb interaction. We do not, of course,
know whether or not 4 and 5 remain dimeric in solution;
in 5, in particular, the length of the Sn-Cl′ bond in the
solid suggests that dissociation in solution might be a
real possibility.
We failed in many attempts to detect 207Pb signals
from 1 and 3 either in the solid or in solution and also
observed no coupling between Pb and the attached
(quaternary) carbon nucleus in the 13C NMR spectra of
solutions. However, for 4, a 207Pb NMR signal was
observed, at δ 4249, from a solution in C6D6, a value
(22) This paper.
(23) Aigbirhio, F. I.; Buttrus, N. H.; Eaborn, C.; Gupta, S. H.;
Hitchcock, P. B.; Smith, J . D.; Sullivan, A. C. J . Chem. Soc., Dalton
Trans. 1992, 1015.
(24) Al-J uaid, S. S.; Eaborn, C.; Habtemariam, A.; Hitchcock, P. B.;
Smith, J . D. J . Organomet. Chem. 1992, 437, 41.
(25) Radeglia, R. Z. Phys. Chem. (Leipzig) 1975, 256, 453.

5658 Organometallics, Vol. 16, No. 26, 1997
Eaborn et al.
temperature, the solvent removed under vacuum, and the
residue extracted with light petroleum (bp 40-60 °C;
25 cm3 ). The bright yellow extract was concentrated to 5 cm3,
then kept at 5 °C to deposit yellow crystals of (PbR′Cl)2, 4 (0.74
g, 60%), mp 160 °C (with onset of decomposition at ca. 165
°C). Anal. Calcd for C20H54Cl2O2Pb2Si6: C, 24.5; H, 5.6.
Found: C, 24.2; H, 5.7. 1H NMR: δ 0.41 (s, 6H, SiMe2), 0.42
(s, 18H, SiMe3), 3.12 (s, 3H, OMe). 13C NMR: δ 6.77(SiMe3),
6.42 (SiMe2), 50.35 (OMe), 83.0 (CSi3); and for the solid (at
100.6 MHz) 5.55, 7.61, 11.5, 14.00 (all four from Me3Si and
Me2Si), 54.9 (OMe). 29Si NMR: δ -8.1 (SiMe3), 17.7 (SiOMe);
for the solid (at 79.5 MHz) -2.7 and -8.4 (both Me3Si), 20.8
(SiOMe). 207Pb NMR: δ 4249. MS: m/z 490 (5, R′PbCl), 475
(40, R′PbCl - Me), 455 (25, R′Pb), 247 (15, R), 233 (60, RH -
Me), 217 (100), 187 (35), 129 (35, Me2SiCHdSiMe2), 73 (70,
Me3Si).
was formed, from which the only species isolated was
the dilead compound Ph3PbPbPh3, which was identified
by a single-crystal X-ray diffraction study.
Exp er im en ta l Section
All operations were carried out under argon in Schlenk
tubes. For reactions involving lead compounds, the Schlenk
tubes were made of amber-colored glass.
The organolithium reagents LiR†‚2THF,26 LiR*‚THF,27 and
LiR′‚2THF14 were prepared as solids as previously described,
except that LiR′‚2THF was recrystallized from light petroleum
(bp 40-60 °C) rather than heptane-THF.
NMR Sp ectr a . Unless otherwise stated, the NMR spectra
were determined for solutions in C6D6. The frequencies (MHz)
used for the various nuclei were 1H, 300.1; 13C, 125.8 ; 29Si,
99.4; 119Sn, 186.6; 207Pb, 104.3. Chemical shifts are relative
to SiMe4 for H, C, and Si, SnMe4 for Sn, and PbMe4 for Pb.
Mass spectra were obtained by EI at 70 eV; m/z values refer
to 35Cl, 120Sn, and 208Pb. Additional spectra recorded for
previously reported compounds were as follows: (a) (Me3Si)2-
(MeOMe2Si)CH 13C NMR δ 1.4 (SiMe2), 3.2 (SiMe3), 6.4 (CH),
49.5 (OMe); 29Si NMR δ -1.3 (SiMe3), 15.9 (SiOMe). (b) (Me3-
P r ep a r a tion of (Sn R′Cl)2, 5. A solution of LiR′‚2THF
(0.73 g, 1.83 mmol) in THF (20 cm3) was added dropwise under
argon to a stirred solution of SnCl2 (0.35 g, 1.83 mmol) in THF
(15 cm3) at -10 °C. The stirred mixture was allowed to warm
to room temperature during 14 h, and the solvent was then
removed under vacuum. The residue was extracted with light
petroleum (bp 40-60 °C; 30 cm3), the pale yellow extract
filtered, and the filtrate concentrated to 10 cm3 then cooled to
5 °C to give yellow crystals of 5 (0.68 g, 93%). Anal. Calcd
for C20H54Cl2O2Si6Sn2: C, 29.9; H, 6.8. Found: C, 28.5; H, 6.4.
1H NMR: δ 0.25 (s, 6H, SiMe2), 0.28 (s, 18H, SiMe3 ), 2.84 (s,
3H, OMe).13C NMR: δ 5.4 (SiMe3), 5.5 (SiMe2), 51.8 (OMe),
1
Si)2(MeOMe2Si)CLi‚2THF H NMR δ 0.43 (SiMe3), 0.45 (SiMe2),
3.11 (OMe), 1.28 (THF), and 3.40 (THF); 13C NMR δ 3.35
(SiMe2), 7.9 (SiMe3), 7.1 (CLi), 49.7 (OMe), 25.3 (THF), and
68.1 (THF).
Or th or h om bic F or m of (P bR*C1)2, 1. This was prepared
in the manner described for the monoclinic form,1 but the
recrystallization was from heptane as yellow-orange plates.
P r ep a r a tion of (P bR†Cl)3, 3. A solution of LiR†‚2THF
(3.50 g, 9.15 mmol) in THF (35 cm3) was added dropwise to a
stirred suspension of PbCl2 (2.54 g, 9.15 mmol) in THF (25
cm3), and the mixture was stirred overnight at room temper-
ature. The solvent was removed under vacuum, the residue
extracted with toluene (20 cm3), and the extract filtered
through Celite, concentrated to 10 cm3, and then kept at -6
°C to deposit yellow-orange crystals of (R†PbCl)3, 3 (3.7 g, 85%),
mp 148 °C (with onset of decomposition). 1H NMR: δ 0.36.
13C NMR: δ 6.7 (SiMe3), 97.5 (CSi3). 29Si NMR: δ -8.4. MS:
m/z 439 (18, R†Pb), 231 (35, R†), 201 (100, Me2SiC(SiMe2-
OMe)dSiMe2). Because of the instability of the compound, a
satisfactory elemental analysis could not be obtained.
P r ep a r a tion of (Sn R*Cl)2, 2. A solution of LiR*‚THF
(1.00 g, 2.0 mmol) in THF (20 cm3) was added to a stirred
solution of SnCl2 (0.38 g, 2.0 mmol) in THF (15 cm3), and the
mixture was stirred at room temperature overnight. The
solvent was removed under vacuum, and the residue was
extracted with light petroleum (bp 40-60 °C; 30 cm3). The
extract was filtered and concentrated to 10 cm3, then kept at
10 °C to deposit a fine yellow powder. Two recrystallizations
from light petroleum gave good quality yellow crystals.
Yield: 0.80 g (70%). (The crystals became orange at 80 °C
and melted at 145-148 °C to give an orange liquid, which
turned black with decomposition at ca. 154 °C.) Anal. Calcd
for C50H66Cl2Si6Sn2: C, 52.5; H, 5.8. Found: C, 52.3; H, 5.8.
1
32.7 (1J (C-Si) ) 36.3 and 46.1 Hz; J (CSn) ) 348 Hz, CSi3).
29Si NMR: δ -4.8 (SiMe3), 39.5 (SiOMe); and in the solid δ
-1.0 and -3.0 (both SiMe3), 33.0. 119Sn NMR: δ 469. MS
m/z 402 (5, R′SnCl), 387 (25, R′SnCl - Me), 367 (5, R′Sn), 233
(10, R′H - Me), 217 (100), 187 (25), 129 (20), 73 (35).
Cr ysta l Str u ctu r e Deter m in a tion s. Data were collected
on an Enraf-Nonius CAD4 diffractometer and corrected for
Lorentz and polarization effects and for absorption; details are
given in Table 4. The structures were determined by direct
methods, with SHELXS-86 and SHELXL-93 programs used
for structure solution and refinement on F2 using all reflec-
tions. The H atoms were refined in riding mode with Uiso(H)
) 1.5Ueq(C). Non-hydrogen atoms were normally anisotropic,
but in the case of 3, only Pb, Cl, and Si atoms were. For 3,
the diffraction was weak and was complicated by overlap
arising from the extremely long c axis of the unit cell. For 2,
4, and 5, the dimers lie on crystallographic inversion centers.
Crystal data for the orthorhombic form of (PbR*Cl)2: C50H66
-
Cl2Pb2Si6, M ) 1320.8, a ) 16.067(8) Å, b ) 13.861(6) Å, c )
24.012(13) Å, V ) 5348 Å3, space group Pbca (No. 61), Mo KR
radiation, λ ) 0.710 73 Å, Z ) 4, F(000) 2592, T ) 173(2) K,
2° < θ < 15°. Direct methods. R1 ) 0.054 (I > 2σ(I)), wR2 )
0.141 (all data) for 1073 independent reflections from a crystal
0.20 × 0.10 × 0.05 mm. Because of the small size of the crystal
and the limited data, the only aspects of the structure referred
to in the discussion are the conformation and the Pb-Cl and
Pb-Cl′ distances within the ring of 2.834(9) and 2.724(9) Å.
1
H NMR: δ 0.60 (s, 18H, Me2Si), 7.1-7.5 (m, 15H, Ph). 13C
Ack n ow led gm en t. We thank the Engineering and
Physical Sciences Research Council for financial sup-
port, the Turkish Government for the award of a
Research Scholarship to S.E.S., and Dr. A. G. Avent,
Mr. C. Dadswell, and Mr. J . Keates for valuable help
with NMR spectra.
NMR: δ 5.4 (Me), 37.1 (1J (SiC) ) 34 Hz, 1J (119SnC) ) 420 Hz,
CSi3), 129.9-138.5 (Ph). 29Si NMR: δ -9.5. 119Sn NMR: δ
777. MS: m/z 572 (10, SnR*Cl), 495 (50, SnR*Cl - Ph), 417
(5, R*), 402 (60, R* - Me), 135 (100, PhMe2Si), 73 (45, Me3Si).
P r ep a r a tion of (P bR′Cl)2, 4. A solution of LiR′‚2THF (1.0
g, 2.50 mmol) in THF (20 cm3) was added to a stirred
suspension of PbCl2 (0.70 g, 2.50 mmol) in THF (15 cm3) at
-10 °C. The stirred mixture was allowed to warm to room
Su p p or tin g In for m a tion Ava ila ble: Tables of atom
coordinates, bond lengths and angles, and anistropic displace-
ment parameters for 2-5 and the orthorhombic form of 1 (17
pages). Ordering information is given on any current mast-
head page.
(26) Eaborn, C.; Hitchcock, P. B.; Smith, J . D.; Sullivan, A. C. J .
Chem. Soc., Chem. Commun. 1983, 827.
(27) Eaborn, C.; Hitchcock, P. B.; Smith, J . D.; Sullivan, A. C. J .
Chem. Soc., Chem. Commun. 1983, 1390.
OM9707580