Divalent tin and lead complexes of a bulky salen ligand: The syntheses and structures of [SalenBut,Me]Sn and [SalenBut,Me]Pb

Article abstract of DOI:10.1039/a905490a

The divalent tin and lead complexes, [Salen^But,Me]Sn and [Salen^But,Me]Pb, have been synthesized by the reactions of [(Me₃Si)₂N]₂M (M = Sn, Pb) with the substituted Salen compound, [Salen^But,Me

Full text of DOI:10.1039/a905490a

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Divalent tin and lead complexes of a bulky salen ligand: the
t
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syntheses and structures of [SalenBu ,Me]Sn and [SalenBu ,Me]Pb
Matthew C. Kuchta, Juliet M. Hahn and Gerard Parkin*
Department of Chemistry, Columbia University, New York, New York 10027, USA
Received 1st July 1999, Accepted 17th August 1999
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t
The divalent tin and lead complexes, [SalenBu ,Me]Sn and [SalenBu ,Me]Pb, have been synthesized by the reactions of
t
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[(Me3Si)2N]2M (M = Sn, Pb) with the substituted Salen compound, [SalenBu ,Me]H2. [SalenBu ,Me]Sn and [SalenBu ,Me]Pb
have been characterized by X-ray diffraction, which demonstrates that the complexes are structurally similar, with
the metal atom located above the [N2O2] plane. Despite their similar structures, however, 1H NMR spectroscopy
demonstrates that the barrier for the formal transfer of the metal from one face of the ligand to the other is
significantly greater for the tin derivative.
and Me substituents occupy the 4- and 6-positions of the aryl-
Introduction
ring, respectively.9 As a consequence of these substituents, the
t
We are presently interested in the chemistry of divalent
complexes of the Group 14 elements, germanium, tin and lead,
supported by tetradentate nitrogen and oxygen donor ligands.
For example, we have used the [N4] octamethyldibenzotetra-
[SalenBu ,Me] ligand provides both a greater steric bulk and a
simpler 1H NMR spectroscopic probe as compared to the
parent [Salen] ligand.
t
The divalent tin and lead complexes, [SalenBu ,Me]M (M =
aza[14]annulene dianion [η4-Me8taa]2Ϫ to prepare a series of
Sn, Pb), are readily prepared by the reaction of [(Me3Si)2N]2M
subvalent complexes, [η4-Me8taa]M (M = Ge, Sn, Pb), of which
the germanium and tin derivatives undergo oxidative addition
t
(M = Sn, Pb) with [SalenBu ,Me]H2 (Scheme 1). The tin com-
with the elemental chalcogens producing terminal chalcogenido
complexes [η4-Me8taa]ME (M = Ge, E = S, Se, Te; M = Sn,
E = S, Se).1–3 In addition, the X-ray diffraction data for the lead
complex [η4-Me8taa]Pb were found to be capable of being
refined into a well-behaved false minimum, the result of which
is the generation of a non-macrocyclic structure for a com-
pound that is actually macrocyclic.4 More recently, we have
used the [O4] donor calix[4]arene ligand system to synthesize
related subvalent complexes of germanium and tin, namely
5
[Butcalix(TMS) ]M (M = Ge, Sn). To complement the above
2
studies using [N4] and [O4] donor ligands, we have started to
explore the subvalent chemistry of these elements using hybrid
[N2O2] donor ligands, and in this paper we describe the
syntheses and structures of divalent tin and lead complexes
t
supported by a bulky Salen ligand, namely [SalenBu ,Me]M
(M = Sn, Pb).
Results and discussion
The [SalenR,RЈ] ligand system (Fig. 1), obtained by condensation
Scheme 1
of a salicylaldehyde derivative with 1,2-ethylenediamine, has
t
plex, [SalenBu ,Me]Sn, may also be prepared by the reaction of
proved to be very useful in coordination chemistry. Historically,
t
SnCl2 with [SalenBu ,Me]H2 in the presence of Et3N.10 Divalent
however, the vast majority of studies using [SalenRRЈ] ligands
tin and lead complexes of [Salen] and its derivatives are rare,11
has focussed on transition metal chemistry,6 with the interest in
with only one structurally characterized example, [Saldph]-
main group [SalenRRЈ] complexes being more recent. Further-
Sn,10,12 being listed in the Cambridge Structural Database.13,14
more, to date, most applications in main group chemistry have
Other reports of [SalenR,RЈ] tin15 and lead16 complexes have
been concerned with the Group 13 elements.7,8 The specific
been made, but these deal almost exclusively with tetravalent
ligand that we chose to use for studying divalent compounds
complexes, e.g. [SalenR,RЈ]MR2.17
t
of the heavy Group 14 elements is [SalenBu ,Me], in which But
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The molecular structures of [SalenBu ,Me]Sn and [SalenBu ,Me]-
Pb have been determined by X-ray diffraction, as illustrated
in Fig. 2 and 3; selected metrical data are listed in Table 1.
As would be expected, their structures are very similar.
t
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Thus, the metal atoms in [SalenBu ,Me]Sn and [SalenBu ,Me]Pb
are located above the “[N2O2] coordination plane” (vide infra),
with the only significant difference being that the Sn–X (X = O,
N) distances are ca. 0.1 Å shorter than the corresponding Pb–X
lengths, a difference which is comparable to the variation in
covalent radii of Sn (1.40 Å) and Pb (1.54 Å).18 For comparison
Fig. 1 The [SalenR,RЈ]H2 system.
J. Chem. Soc., Dalton Trans., 1999, 3559–3563
This journal is © The Royal Society of Chemistry 1999
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Table 1 Selected bond lengths (Å) and angles (Њ) for [SalenBu ,Me]M
Table 2 Comparison of [SalenBu ,Me]M (M = Sn, Pb) and [Saldph]Sn
(M = Sn, Pb)
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t
[SalenBu ,Me]Sn
[SalenBu ,Me]Pb
[Saldph]Sna
t
t
[SalenBu ,Me]Sn
[SalenBu ,Me]Pb
d(M–O)/Å
2.11
2.35
1.11
2.23
2.45
1.22
2.14
2.38
1.13
M–O1
M–O2
M–N1
M–N2
2.137(3)
2.091(2)
2.347(3)
2.351(3)
2.255(7)
2.206(5)
2.455(7)
2.443(7)
d(M–N)/Å
d(M–N2O2)/Åb
O–M–O/Њ
N–M–N/Њ
80.6
68.5
81.0
66.5
78.1
68.0
O1–M–O2
N1–M–N2
O1–M–N1
O1–M–N2
O2–M–N1
O2–M–N2
80.6(1)
68.5(1)
77.6(1)
130.7(1)
107.7(1)
77.1(1)
81.0(2)
66.5(3)
75.2(2)
126.6(2)
104.4(2)
74.3(2)
(O–M–N)cis/Њ
(O–M–N)trans/Њ
77.4
107.7 & 130.7
74.8
104.4 & 126.6
77.7
119.4
a Data taken from ref. 10. b d(M–N2O2) is the distance of the metal
from the mean plane defined by the coordinating oxygen and nitrogen
atoms.
Table 3 1H, 13C and 119Sn NMR spectroscopic data
δ (ppm) and
coupling (Hz)
δ (ppm) and
coupling (Hz)
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Assignment
1H(CDCl3)
[SalenBu ,Me]Sn
[SalenBu ,Me]Pb
C(CH3)3
CH3
CH2CH2
1.48, s
2.24, s
3.72, m (2H)
3.87, m (2H)
6.73, d, 2
1.49, s
2.27, s
3.87, s, JPb–H = 14
CH
CH
6.73, d, 2
7.18, d, 2
7.23, d, 2
HC᎐N
8.05, s, 3JSn–H = 21
7.98, s, 3JPb–H = 46
᎐
13C(CDCl3)
2C(CH3)3
2CH3
2C(CH3)3
NCH2CH2N
2C
20.5, q, JC–H = 125
29.8, q, JC–H = 126
35.1, s
55.7, t, JC–H = 141
120.3, s
20.5, q, JC–H = 126
29.9, q, JC–H = 126
35.1, s
57.9, t, JC–H = 139
122.1, s
2C
123.7, s
122.7, s
2CH
2CH
2C
131.4, d, JC–H = 153
133.0, d, JC–H = 151
142.7, s
131.2, d, JC–H = 154
132.3, d, JC–H = 151
143.1, s
t
Fig. 2 Two views of the molecular structure of [SalenBu ,Me]Sn.
2C
163.4, s
164.7, s
2(H)C᎐N
167.2, d, JC–H = 158
167.1, d, JC–H = 159
᎐
119Sn(CDCl3)
Ϫ518, s
t
A notable feature of the structures of [SalenBu ,Me]Sn and
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[SalenBu ,Me]Pb is that the [SalenBu ,Me] ligand is not flat but
adopts a slightly twisted conformation, such that the four
coordinating atoms of the [N2O2] core are not coplanar but
deviate significantly from their mean-plane (Fig. 2 and 3).20
A
further manifestation of the twisting is the observation that the
t
two (O–M–N)trans angles in [SalenBu ,Me]M (M = Sn, Pb) differ
by more than 20Њ. In contrast, the [N2O2] atoms in [Saldph]Sn
are coplanar with identical (O–M–N)trans angles (119.4Њ), as
t
compared to the two distinct values for [SalenBu ,Me]Sn (107.7
and 130.7Њ).
t
t
[SalenBu ,Me]Sn and [SalenBu ,Me]Pb have also been charac-
terized by multinuclear NMR spectroscopy (Table 3). For
example, the tin complex is characterized by a 119Sn signal at
δ Ϫ518, a value which is comparable to those of the related
divalent derivatives, [Salen]Sn (δ Ϫ564), [Saldph]Sn (δ Ϫ543),
[Salph]Sn (δ Ϫ559), [SaleanH2]Sn (δ Ϫ524), and [SalpanH2]Sn
(δ Ϫ521).10,14 The most interesting spectroscopic features, how-
ever, are concerned with the 1H NMR spectroscopic signals for
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Fig. 3 Two views of the molecular structure of [SalenBu ,Me]Pb.
the [CH᎐N] and [NCH CH N] moieties of [SalenBu ,Me]Sn and
᎐
2
2
t
[SalenBu ,Me]Pb. In particular, the signals for the [NCH2CH2N]
t
purposes, salient average metrical data are presented in Table 2,
which also includes the data for [Saldph]Sn.12 There are,
however, no structurally characterized divalent [SalenR,RЈ]Pb
groups are substantially different for [SalenBu ,Me]Sn and
t
[SalenBu ,Me]Pb, as shown in Fig. 4. Thus, the [NCH2CH2N]
t
moiety of [SalenBu ,Me]Pb is observed as a singlet with 207Pb21
t
complexes listed in the Cambridge Structural Database for
satellites [3J(207Pb–H) = 14 Hz], whereas that for [SalenBu ,Me]Sn
t
comparison with [SalenBu ,Me]Pb.19
is observed as two complex multiplets. The complex nature
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J. Chem. Soc., Dalton Trans., 1999, 3559–3563

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Fig. 4 1H NMR signals (300 MHz) for the [CH᎐N] (upper) and
᎐
t
t
[NCH2CH2N] (lower) moieties of [SalenBu ,Me]Sn and [SalenBu ,Me]Pb
in CDCl3.
t
of the spectrum for [SalenBu ,Me]Sn is that which would be
Fig. 5 Variable temperature 1H NMR spectra (500 MHz) of the
t
[NCH2CH2N] moiety of [SalenBu ,Me]Pb in C6D5CD3.
expected for the solid state structure which has only C1 sym-
metry.22 In view of the chemical inequivalence of the [NCH2-
t
CH2N] protons in [SalenBu ,Me]Sn, the observation of a singlet
t
IR spectra were recorded as KBr pellets on a Perkin-Elmer
for the lead complex [SalenBu ,Me]Pb may be explained by the
formal translation of the lead atom from one side of the ligand
to the other, thereby resulting in all of the [NCH2CH2N]
hydrogen atoms becoming equivalent on the NMR timescale.23
Paragon 1000 FT-IR spectrometer and are reported in cmϪ1
.
Carbon, hydrogen and nitrogen elemental analyses (CHN) were
performed on a Perkin-Elmer 2400 CHN Elemental Analyzer.
1H NMR spectra were recorded on Varian VXR-300 and VXR-
400 spectrometers operating at 299.924 and 399.95 MHz,
respectively, and Bruker DMX-500 and DPX-300 spectro-
1
Variable temperature H NMR spectroscopic studies confirm
this suggestion, with decoalescence of the [NCH2CH2N] proton
t
signals for [SalenBu ,Me]Pb being observed at 260 K (Fig. 5).24
meters operating at 500.133 and 300.132 MHz, respectively. 13
C
The tin complex, however, is still static at 353 K, so that the
t
and 119Sn spectra were recorded on the Varian VXR-300 operat-
ing at 75.429 and 111.800 MHz, respectively. 1H and 13C NMR
spectra are reported in ppm relative to SiMe4 and were
referenced internally to the residual protio solvent (δ 7.15 for
C6D5H and δ 7.26 for CHCl3) and the 13C resonances of the
solvents (δ 128 for C6D6 and δ 77 for CDCl3). 119Sn spectra were
referenced externally to a CDCl3 solution of SnMe4.31
barrier for exchange within [SalenBu ,Me]Sn is considerably
t
greater than that within [SalenBu ,Me]Pb. Since Pb is slightly
larger than Sn, the latter observation is interesting because it
suggests that the exchange mechanism for lead does not involve
a simple passage of the metal through the [N2O2] plane, since
the barrier for Sn would be expected to be lower than that for
Pb.
t
t
Finally, both [SalenBu ,Me]Sn and [SalenBu ,Me]Pb exhibit
coupling, in the form of satellites (119/117Sn25 and 207Pb21),
between the central metal atom and the hydrogen of the
t
Synthesis of [SalenBu ,Me]H2
Ethylenediamine (0.77 mL, 11.43 mmol) was added to a solu-
tion of 4-methyl-6-tert-butylsalicylaldehyde (4.42 g, 22.9 mmol)
in ethanol (ca. 50 mL) and the mixture was heated at ca. 85–
90 ЊC in an ampoule for 1 hour, thereby depositing a yellow
[CH᎐N] moiety, as illustrated in Fig. 4: J(119/117Sn–H) = 21 Hz
᎐
and J(207Pb–H) = 46 Hz. The J(119/117Sn–H) coupling constant
is similar in magnitude to that reported for the tetravalent tin
complex, [Salen]SnCl2, J(119/117Sn–H) = 36 Hz.26
solid. The mixture was cooled to room temperature and filtered
t
giving [SalenBu ,Me]H2 as a yellow solid (2.5 g, 53%).
t
Experimental
Synthesis of [SalenBu ,Me]Sn
General considerations: techniques and reagents
Method A. Benzene (ca. 5 mL) was added to a mixture of
t
All manipulations were performed using a combination of
glovebox, high vacuum or Schlenk techniques.27 Solvents were
purified and degassed by standard procedures and all com-
mercially available reagents were used as received. [(Me3-
[(Me3Si)2N]2Sn (0.39 g, 0.89 mmol) and [SalenBu ,Me]H2 (0.30
g, 0.73 mmol). The resulting mixture was stirred for ca. 4 hours
at room temperature to give a yellow precipitate. The mixture
was filtered and the yellow solid was washed with benzene (ca. 3
Si)2N]2Sn and [(Me3Si)2N]2Pb were prepared by the literature
mL) and pentane (ca. 10 mL) and dried under vacuum giving
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t
method.28 [SalenBu ,Me]H2 was prepared by condensation of
ethylenediamine with 4-methyl-6-tert-butylsalicylaldehyde29
using a procedure analogous to that for other Salen ligands.30
[SalenBu ,Me]Sn (0.30 g, 78%). Analysis calcd. for C26H34N2-
O2Sn: C, 59.5; H, 6.5; N, 5.3. Found: C, 59.5; H, 6.3; N, 4.7%.
IR data: 2937(s), 2862(s), 1650(vs), 1621(vs), 1545(vs), 1460(m),
J. Chem. Soc., Dalton Trans., 1999, 3559–3563
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Table 4 Crystal, intensity collection and refinement data
sole pair of divalent Group 14 [Salen] complexes to have
been structurally characterized. The molecular structures of
t
t
t
t
[SalenBu ,Me]Sn
[SalenBu ,Me]Pb
[SalenBu ,Me]Sn and [SalenBu ,Me]Pb are very similar, both
1
featuring non-planar geometries, but H NMR spectroscopy
Lattice
Formula
Formula weight
Triclinic
C26H34N2O2Sn
525.2
Triclinic
C26H34N2O2Pb
613.7
demonstrates that the barrier for the formal transfer of the
metal from one face of the ligand to the other is significantly
greater for the tin derivative.
¯
¯
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
P1 (no. 2)
P1 (no. 2)
7.765(2)
12.812(3)
14.187(3)
110.12(2)
97.67(2)
97.45(2)
1269.7(6)
2
7.720(2)
12.880(3)
14.316(4)
111.05(2)
97.02(2)
98.52(2)
1297.0(7)
2
Acknowledgements
We thank the National Science Foundation (CHE 96-10497) for
support of this research.
γ/Њ
V/Å3
Z
T/K
296
0.71073
1.374
1.029
22.5
3346, 3119 [F > 2σ(F)]
281
0.0247
0.0360
1.09
296
0.71073
1.571
6.526
22.5
3396, 3018 [F > 2σ(F)]
281
0.0345
0.0448
1.20
References
Radiation (λ/Å)
ρ (calcd.)/g cmϪ3
µ(Mo-Kα)/mmϪ1
θ max/Њ
No. of data
No. of parameters
R
1 (a) M. C. Kuchta and G. Parkin, J. Chem. Soc., Chem. Commun.,
1994, 1351; (b) M. C. Kuchta and G. Parkin, J. Am. Chem. Soc.,
1994, 116, 8372; (c) M. C. Kuchta and G. Parkin, Chem. Commun.,
1996, 1669.
2 For further oxidative addition chemistry of [η4-Me8taa]Sn see:
M. C. Kuchta and G. Parkin, Polyhedron, 1996, 15, 4599.
3 For a review of terminal chalcogenido complexes, see: M. C. Kuchta
and G. Parkin, Coord. Chem. Rev., 1998, 176, 323.
Rw
GOF
4 M. C. Kuchta and G. Parkin, New J. Chem., 1998, 22, 523.
5 T. Hascall, A. L. Rheingold, I. Guzei and G. Parkin, Chem.
Commun., 1998, 101.
6 For reviews of transition metal Salen complexes see: (a) M. D.
Hobday and T. D. Smith, Coord. Chem. Rev., 1972–1973, 9, 311; (b)
R. H. Holm, G. W. Everett, Jr. and A. Chakravorty, Prog. Inorg.
Chem., 1966, 7, 83.
1410(s), 1380(s), 1351(m), 1334(m), 1282(s), 1262(vs), 1237(s),
1203(s), 1164(s), 1097(s), 1027(s), 970(m), 927(w), 868(m),
796(s), 689(w), 599(w), 497(m).
Method B. Ethanol (ca. 10 mL) was added to a mixture of
t
[SalenBu ,Me]H2 (0.20 g, 0.49 mmol) and SnCl2 (0.09 g, 0.49
mmol) in a glass ampoule. Et3N (0.15 mL, 0.99 mmol) was
added and the mixture was heated at ca. 80 ЊC for 3 hours after
which time it was cooled to room temperature giving a yellow
precipitate. The mixture was filtered, and the yellow solid was
7 (a) D. A. Atwood, M. S. Hill, J. A. Jegier and D. Rutherford, Organo-
metallics, 1997, 16, 2659; (b) D. A. Atwood and D. Rutherford,
Organometallics, 1996, 15, 4417 and refs. therein; (c) D. A. Atwood,
J. A. Jegier and D. Rutherford, Inorg. Chem., 1996, 35, 63;
(d) M. G. Davidson, C. Lambert, I. Lopez-Solera, P. R. Raithby and
R. Snaith, Inorg. Chem., 1995, 34, 3765; (e) J. T. Leman, J.
Braddock-Wilking, A. J. Coolong and A. R. Barron, Inorg. Chem.,
1993, 32, 4324; ( f ) D. A. Atwood, J. A. Jegier and D. Rutherford,
Bull. Chem. Soc. Jpn., 1997, 70, 2093; (g) M. S. Hill, P. R. Wei and
D. A. Atwood, Polyhedron, 1998, 17, 811.
washed with ethanol (2 × 7 mL) and dried in vacuo giving
t
[SalenBu ,Me]Sn (0.15 g, 57%).
t
Synthesis of [SalenBu ,Me]Pb
8 The related [SalanH2] ligand system, which differs from the [Salen]
system in the sense that the imine, [HC᎐N], moiety is formally
Benzene (ca. 10 mL) was added to a mixture of [(Me3Si)2N]2Pb
᎐
t
(1.00 g, 1.89 mmol) and [SalenBu ,Me]H2 (0.70 g, 1.71 mmol).
The resulting mixture was stirred for ca. 3 days at room tem-
perature to give a yellow precipitate. The mixture was filtered
hydrogenated to give a CH2NH group, has also been studied
recently. For a review of Salan complexes of the Group 12, 13, and
14 elements, see: D. A. Atwood, Coord. Chem. Rev., 1997, 165,
267.
t
9 Aluminium complexes of this ligand, namely, [SalenBu ,Me]AlCl and
and the yellow solid was washed with benzene (2 × 2 mL) and
t
t
dried in vacuo giving [SalenBu ,Me]Pb (0.80 g, 76%). Analysis
calcd. for C26H34N2O2Pb: C, 50.9; H, 5.6; N, 4.6. Found: C,
49.9; H, 5.3; N, 4.3%. IR data: 2940(s), 2903(s), 2864(s),
1643(vs), 1615(vs), 1542(s), 1472(m), 1460(m), 1408(s), 1376(s),
1348(m), 1308(m), 1285(s), 1262(s), 1237(s), 1201(m), 1161(m),
1095(m), 1027(w), 969(w), 927(vw), 869(w), 840(w), 793(m),
597(vw), 569(vw), 531(vw), 490(m).
[SalenBu ,Me]AlR (R = Me, Et), have been prepared. See: I. Taden,
H.-C. Kang, W. Massa and J. Okuda, J. Organomet. Chem., 1997,
540, 189.
10 This method has previously been used for the synthesis of [Salen]Sn
and related complexes. See: A. M. van den Bergen, J. D. Cashion,
G. D. Fallon and B. O. West, Aust. J. Chem., 1990, 43, 1559.
11 For a recent review of the coordination chemistry of PbII, see:
J. Parr, Polyhedron, 1997, 16, 551.
12 [Saldph] differs from [Salen] in being derived from 4,5-dimethyl-
phenylene-1,2-diamine rather than ethylenediamine.
13 CSD Version 5.17. 3D Search and Research Using the Cambridge
Structural Database, F. H. Allen and O. Kennard, Chem. Des.
Automat. News, 1993, 8 (1), pp. 1, 31–37.
14 There is one related divalent tin complex listed in the Cambridge
Structural Database, namely [Salean]Sn. See: D. A. Atwood, J. A.
Jegier, K. J. Martin and D. Rutherford, J. Organomet. Chem., 1995,
503, C4.
15 (a) W. D. Honnick and J. Zuckerman, Inorg. Chem., 1979, 18,
1437 and refs. therein; (b) D. K. Dey, M. K. Das and H. Nöth,
Z. Naturforsch., Teil B, 1999, 54, 145.
16 F. Di Bianca, E. Rivarola, G. C. Stocco and R. Barbieri, Z. Anorg.
Allg. Chem., 1972, 387, 126.
Crystal structure determinations
t
t
Crystallographic data for [SalenBu ,Me]Sn and [SalenBu ,Me]Pb
were collected on a Siemens P4 diffractometer using graphite
monochromated Mo-Kα X-radiation (λ = 0.71073 Å). The unit
cells were determined by the automatic indexing of 25 centered
reflections and confirmed by examination of the axial photo-
graphs. Check reflections were measured every 100 reflections,
and the data were scaled accordingly and corrected for Lorentz,
polarization and absorption effects. The structures were solved
using direct methods and standard difference map techniques,
and were refined by full-matrix least-squares procedures using
SHELXTL.32 Hydrogen atoms attached to carbon were
included in calculated positions. Crystal data, data collection
and refinement parameters are summarized in Table 4.
17 For a review of organotin Schiff base complexes, which include
Salen derivatives, see: M. Nath and S. Goyal, Main Group Met.
Chem., 1996, 19, 75.
18 L. Pauling, The Nature of the Chemical Bond, Cornell University
Press, Ithaca, New York, 3rd edn., 1960, p. 256.
CCDC reference number 186/1620.
19 Some PbII complexes of protonated [SalenR,R]H2 are, however,
known. See, for example: (a) J. Parr, A. T. Ross and A. M. Z. Slawin,
J. Chem. Soc., Dalton Trans., 1996, 1509; (b) J. Parr, A. T. Ross and
A. M. Z. Slawin, Polyhedron, 1997, 16, 2765.
Conclusion
t
t
In conclusion, [SalenBu ,Me]Sn and [SalenBu ,Me]Pb are the
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J. Chem. Soc., Dalton Trans., 1999, 3559–3563

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20 [Salen]Ni provides an example in which the [N2O2] coordination
core is planar and the ligand adopts an approximately planar
geometry, see: A. G. Manfredotti and C. Guastini, Acta Crystallogr.,
Sect. C, 1983, 39, 863.
J(117Sn) = 1.05, due to the ratio of the respective magnetogyric
ratios. See ref. 21.
26 A. van den Bergen, R. J. Cozens and K. S. Murray, J. Chem. Soc. A,
1970, 3060.
27 (a) J. P. McNally, V. S. Leong and N. J. Cooper, A. C. S. Symp. Ser.,
1987, 357, 6; (b) B. J. Burger and J. E. Bercaw, A. C. S. Symp. Ser.,
1987, 357, 79.
28 (a) D. H. Harris and M. F. Lappert, J. Chem. Soc., Chem. Commun.,
1974, 895; (b) M. J. S. Gynane, D. H. Harris, M. F. Lappert,
P. P. Power, P. Rivière and M. Rivière-Baudet, J. Chem. Soc., Dalton
Trans., 1977, 2004.
21 207Pb (I = 1/2, 22.1%). See: J. Emsley, The Elements, Clarendon
Press, Oxford, 2nd edn., 1991.
t
22 The protons of a static [CH2CH2] bridge in [SalenBu ,Me]M belong to
an ABCD spin system since the carbon atoms are not coplanar with
the approximate [N2O2] mirror plane (see Fig. 2 and 3). If the bridge
is sufficiently flexible that a planar arrangement may be obtained,
the spin system simplifies to AAЈBBЈ.
23 Although the precise mechanism of the exchange process is un-
29 G. Casiraghi, G. Casnati, G. Puglia, G. Sartori and G. Terenghi,
J. Chem. Soc., Perkin Trans. 1, 1980, 1862.
known, the observation that the [HC᎐N] group exhibits 3J(207Pb–H)
᎐
coupling at high temperatures suggests that dissociation of lead is
not involved and that the exchange is intramolecular.
30 See, for example: W. Zhang and E. N. Jacobsen, J. Org. Chem., 1991,
56, 2296.
31 Multinuclear NMR, ed. J. Mason, Plenum Press, New York, 1987.
32 G. M. Sheldrick, SHELXTL, An Integrated System for Solving,
Refining and Displaying Crystal Structures from Diffraction Data,
University of Göttingen, 1981.
24 Due to the complex nature of the ABCD pattern of the
stereochemically rigid structure, a detailed analysis of the dynamics
was not performed. Nevertheless, an upper limit for the exchange
barrier at 270 K can be estimated as 13 kcal molϪ1
.
25 The coupling to tin is an unresolved composite of coupling to both
117Sn (I = 1/2, 7.68%) and 119Sn (I = 1/2, 8.58%) where J(119Sn)/
Paper 9/05490A
J. Chem. Soc., Dalton Trans., 1999, 3559–3563
3563