Synthesis and structural characterisation of low-valent Group 14 metal complexes containing tridentate 2,6-pyridyl-bridged bis(1-azaallyl) ligands

Article abstract of DOI:10.1039/b211305h

Treatment of GeCl₂(dioxane), SnCl₂ and PbCl ₂ with appropriate alkali-metal compounds containing 2,6-pyridyl-bridged bis(1-azaallyl) dianionic ligands afforded bivalent Group 14 metal compounds [M{{N(SiMe₃)C(R)CH}₂-C₅H ₃N-2,6}] [R = Ph, M = Ge (1), Sn (2) and Pb (3); R = Bu^t, M = Sn (4) and Pb (5)]. The structures of the monomeric complexes 1, 2, 3 and 5 have been confirmed by single-crystal X-ray structure determination; it has been shown that the 2,6-pyridyl-bridged bis(1-azaallyl) ligand is bonded to the metal centre in a N,N,N′-chelate fashion. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b211305h

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Synthesis and structural characterisation of low-valent Group 14
metal complexes containing tridentate 2,6-pyridyl-bridged
bis(1-azaallyl) ligands
Wing-Por Leung,* Henry L. Hou, Hui Cheng, Qing-Chuan Yang, Hung-Wing Li and
Thomas C. W. Mak
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong
Received 20th November 2002, Accepted 3rd March 2003
First published as an Advance Article on the web 13th March 2003
Treatment of GeCl2(dioxane), SnCl2 and PbCl2 with appropriate alkali-metal compounds containing 2,6-pyridyl-
bridged bis(1-azaallyl) dianionic ligands afforded bivalent Group 14 metal compounds [M{{N(SiMe3)C(R)CH}2-
C5H3N-2,6}] [R = Ph, M = Ge (1), Sn (2) and Pb (3); R = But, M = Sn (4) and Pb (5)]. The structures of the
monomeric complexes 1, 2, 3 and 5 have been confirmed by single-crystal X-ray structure determination; it has been
shown that the 2,6-pyridyl-bridged bis(1-azaallyl) ligand is bonded to the metal centre in a N,N,NЈ-chelate fashion.
Introduction
The chemistry of low-valent Group 14 metal amides M(NR2)2
(R = alkyl or phenyl) has attracted much attention in the
past two decades. It has been realised that incorporating
sterically hindered substituents at the metal center can stabilize
these carbene analogues. Lappert and coworkers reported the
first examples of stable metal diamides [M{N(SiMe3)2}2]
(M = Ge,1a–c Sn1b,c or Pb1c). These diamagnetic compounds
exhibit V-shaped geometry as expected for a singlet electronic
ground state, in which the metal atom possesses a stereo-
chemically active lone pair of electrons. Among these Group
14 heavier metals, only a few thermally stable organolead()
compounds are structurally characterised. For examples,
monomeric Group 14 metal amides such as M[NC(Me)2-
(CH2)3CMe2]2 (M = Ge1b,2a or Sn1a,2b), Ge[1,2-{N(SiMe3)}2-
C6H4],3 Sn[1,2-{N(SiMe3)}2C6H4(µ-tmen)],4 meta-bis(stannyl-
amino)cyclophane,5 1,4-[N(SiMe3)Sn(NSiMe3)]2C6H4,6 Sn[N-
(But)SiMe2NBut]n,7 and M[RC6H4C(NSiMe3)2]2 (R = H, Me,
Ph or CF3; M = Sn or Pb) have been reported.8 We reported the
synthesis of a series of thermally stable alkali-metal com-
pounds containing the bis(1-azaallyl) ligands.9 By using these
alkali-metal compounds as transfer reagents, we here report
the preparation and structural characterisation of a series
of Group 14 metal compounds containing the tridentate bis(1-
azaallyl) ligands [{N(SiMe3)C(R)CH}2C5H3N-2,6]2Ϫ [R = Ph or
But].
Scheme 1
the reaction of Li2L(tmen)2 with PbCl2 and isolated as red
crystalline solids. These Pb() compounds are only soluble in
THF or toluene. Among these Group 14 compounds the Pb()
compounds 3 and 5 are less stable, as they decompose slowly in
solution at room temperature to lead metal.
These compounds have been characterised by elemental
analysis, spectroscopic methods and single-crystal X-ray struc-
ture analysis. As shown by the structural data, these com-
pounds are more appropriately classified as dienamides rather
than the π-bonded bis-azaallyl compounds. The enamido nitro-
gens are σ-bonded to the metal centre along with the coordin-
ation from the pyridyl nitrogen from the N,N,NЈ-tridentate
chelate complex. The π-bonded bis-azaallyl complex is not
formed; probably due to the π electrons at the ligands remain-
ing in nonbonding orbitals.
The 1H NMR spectrum of 1 displayed sharp signals at δ 6.65
and δ 5.15 ppm which were assigned to the non-equivalent
methine protons and signals at δ 0.27 and δ 0.09 ppm were
assigned to the non-equivalent SiMe3 groups. The 13C spectrum
of 1 was also consistent with non-equivalent CH and SiMe3
groups. The non-equivalence could be due to the restricted
rotation about the germanium–nitrogen bond. A similar phen-
omenon has been reported for some Group 13 compounds, but
only a few examples have been observed for Group 14 com-
Results and discussion
Group 14 metal compounds [M{{N(SiMe3)C(R)C(H)}2-
C5H3N-2,6}] [R = Ph, M = Ge (1), Sn (2) and Pb (3); R = But,
M = Sn (4) and Pb (5)] were prepared by the reaction of 2
equivalents of the corresponding alkali-metal compounds
[M2L(tmen)2] [M = Li, Na or K; L = {N(SiMe3)C(R)C(H)}2-
C5H3N-2,6}2Ϫ R = Ph or But; tmen = Me2NCH2CH2NMe2] with
a slight excess (except for 2) of GeCl2(1,4-dioxane), SnCl2 or
PbCl2 in diethyl ether solution (Scheme 1).
The Ge() compound [Ge{{N(SiMe3)C(Ph) C(H)}2C5H3N-
2,6}] (1) was isolated as a red crystalline solid with good solubil-
ity in solvents such as diethyl ether, toluene and THF. The Sn()
compounds [Sn{{N(SiMe3)C(Ph)C(H)}2C5H3N-2,6}] (2) and
[Sn{{N(SiMe3)C(But)C(H)}2C5H3N-2,6}] (4) were isolated as
orange crystalline solids in moderate yields. Compounds 2 and
4 are soluble in diethyl ether, THF or toluene. The Pb()
compounds [Pb{{N(SiMe3)C(Ph)C(H)}2-C5H3N-2,6}] (3) and
[Pb{{N(SiMe3)C(But)C(H)}2C5H3N-2,6}] (5) were prepared by
1
pounds.10,11 In contrast, the H and 13C spectra of compounds
2–5 displayed only one set of signals for the ligands, suggesting
that the compounds are centro-symmetric with the azaallyl
arms positioned in the same chemical environment.
The 119Sn NMR chemical shift of δ 5.37 ppm for 3 is signifi-
cantly different from the chemical shifts of the three-coordinate
tin() compounds [Sn{CH(SiMe3)C9H6N-8}X] (X = Cl, δ 327
ppm; Br, δ 353 ppm; I, δ 386 ppm).12 It is also lower than those
for the tin() amide Sn{N(SiMe3)2}2 (δ 776 ppm) and the amide
[Sn(µ-Cl){N(SiMe3)2}2 (δ 138 ppm).5 The 207Pb NMR spectra
of the three-coordinate Pb() compounds 3 and 5 showed
peaks at δ 1577.36 and δ 994.11 ppm, respectively, which are
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 1 5 0 5 – 1 5 0 8
1505

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Table 1 Selected bond distances (Å) and angles (Њ) for compounds 1–3
and 5
In 1, the Ge–N(2) and Ge–N(3) distances of 1.992(2) Å and
1.979(8) Å are comparatively longer than those found for
related Ge–N(amido) distances, such as 1.87(1) Å and 1.90(1) Å
in Ge[NCMe2(CH2)3CMe2]2,2a and 1.878(5) Å and 1.873(5) Å in
Ge[N(SiMe3)2]2.1a The Ge–N(1) distance of 2.019(6) Å is
shorter than the distance of 2.0814(16) Å in [Ge{Si(Me2)-
C(SiMe3)2C5H4N-2}].15
1
2
3
5
M–N(1)
M–N(2)
M–N(3)
2.0196(14)
1.9922(16)
1.9798(15)
1.7719(14)
1.7327(17)
1.379(2)
1.384(2)
1.441(3)
1.425(3)
1.364(2)
2.224(3)
2.171(3)
2.204(3)
1.727(4)
1.753(4)
1.398(5)
1.382(5)
1.426(6)
1.453(6)
1.372(6)
1.359(6)
2.323(3)
2.264(3)
2.300(3)
1.726(3)
1.751(3)
1.382(4)
1.350(4)
1.435(5)
1.465(5)
1.357(5)
1.377(5)
2.330(3)
2.316(4)
2.298(4)
1.734(4)
1.720(4)
1.383(5)
1.421(7)
1.419(6)
1.401(7)
1.393(6)
1.339(6)
In 2, the Sn–N(2) and Sn–N(3) distances of 2.204(3) Å
and 2.171(3) Å fall in the range of normal Sn–N(amido) bond
distances, and are comparable with the Sn–N distances of
2.153(4) and 2.288(4) Å in [Sn{C(SiMe3)2C(Ph)N(SiMe3)}2].16
The Sn–N(1) distance is marginally shorter than that found
for related Sn–N(pyridyl) distances, e.g. 2.26(2) Å and 2.27(2) Å
in [Sn{2-C(SiMe3)2C5H4N}Cl],17 2.288(2)Å in [Sn{2-C(SiMe3)2-
N(2)–Si(1)
N(3)–Si(2)
N(2)–C(7)
N(3)–C(15)
C(1)–C(14)
C(5)–C(6)
C(6)–C(7)
C(14)–C(15)
1.368(3)
C5H4N}{Sn(SiMe3)3}],18 2.449(7)
Å
in [Sn{2-C(SiMe3)2-
N(1)–M–N(2)
N(1)–M–N(3)
N(2)–M–N(3)
M–N(2)–C(7)
M–N(3)–C(15)
92.97(6)
86.62(6)
108.31(7)
121.67(12)
103.20(12)
81.8(1)
87.7(1)
107.1(1)
102.8(3)
116.9(3)
79.81(10)
85.62(10)
108.04(10)
102.4(2)
85.81(12)
78.63(12)
110.38(14)
114.5(3)
C5H4N}2], and 2.300(6)
Å in [Sn{2-C(SiMe3)2C5H4N}-
{CH(PPh2)2}].19
¯
Compound 3 crystallized in a triclinic space group P1 and
exhibits a molecular geometry similar to compound 5. Plumb-
ylenes are regarded as carbene-analogues, the energetically
most favourable electronic state is the singlet 1σ2 found by
experiment and calculation.20 The structure of the singlet
plumbylenes as well as other carbene analogues can be
described by the following two geometries. (A) The non-bond-
ing electron pair occupies an s-orbital, the bonding electrons
occupy p-orbitals, while the third p-orbital remains empty with
a bond angle of exactly 90Њ.(B) Both non-bonding and bonding
electron pairs occupy sp2-hybrid orbitals while a p-orbital is
unoccupied with a bond angle of 120Њ. As the bond angle of
N(2)–Pb–N(3) is 110.4Њ, compound 5 is expected to be of
geometry B. However, as mentioned before, the lone pair on the
Pb() atom involved may lead to sp3 hybridization. The Pb–N
distances of 2.330(3) Å, 2.316(4) Å and 2.298(4) Å in
compound 5 are almost the same as those in compound 3,
indicating both Ph and But subsituents make no significant
difference to the stability of the compound.
117.5(2)
95.3(3)
significantly lower than those of δ 1981 ppm in the four-
coordinate [Pb{CH(SiMe3)(C9H6N-8)}2]13 and δ 3919 ppm in
the two-coordinate [Pb{C6H3(NMe2)2-2,6}].14
Molecular structures
The single-crystal X-ray structures of 1, 2, 3 and 5 have been
determined. They are isostructural and only the molecular
structure of 3 is shown in Fig. 1. Selected bond distances and
angles for 1, 2, 3 and 5 are shown in Table 1. All the compounds
are monomeric with the dianionic ligand [{N(SiMe3)-
C(R)CH}2C5H3N-2,6]2Ϫ bonded in a [N,N,N]-chelate fashion to
the metal centre. The geometry at the metal centre is trigonal
pyramidal with a stereo-active lone pair at the metal. The dis-
tance between the metal and the centre of the trigonal plane
described by the three nitrogens is 1.030 Å (for 1), 1.223 Å (for
2), 1.302 Å (for 3 and 5). In each case, for the two azaallyl
moieties the bonding is delocalised along the C(6)C(7)N(2)
and C(14)C(15)N(3) backbones. The sum of the bond
angles around atoms N(2) and N(3) suggests that they are sp2
hybridized. Within a homologous series, the metal–nitrogen
distance of the divalent Group 14 metal compounds varies
according to the size of the metal atoms. The sum of bite angles
subtended at the metal centres in 1, 2, 3 and 5 are 287.9, 276.7,
273.5 and 274.8Њ, respectively. Suitable crystals of the tin()
analogue 4 could not be obtained, but the spectral data are
similar to those of 2 and 5. It is proposed that 4 has a structure
similar to its analogues. The structures of the analogous
dilithium, dipotassium, and lithium–potassium 2,6-pyridyl-
bridged bis-azaallyl complexes showed that one of the metals
is bonded to the ligand in a tridentate-chelate fashion, while
the other metal interacts with the π-orbitals of the azaallyl
arm.9
In conclusion, the dianionic bis(1-azaallyl) ligands
[{N(SiMe3)C(R)CH}2C5H3N-2,6]2Ϫ [R = Ph or But] are capable
of forming thermally stable bivalent Group 14 metal dien-
amides through the coordination of the pyridyl nitrogen.
Experimental
General procedures
All manipulations were carried out either in a nitrogen-filled
dry-box or under nitrogen using standard Schlenk techniques.
Solvents were dried over and distilled from sodium/benzphen-
one (diethyl ether and tetrahydrofuran) or sodium/potassium
alloy (pentane). n-Butyllithium, potassium tert-butoxide, tin()
chloride and lead() chloride were purchased from Aldrich and
used without further purification. Benzonitrile and N,N,NЈ,NЈ-
tetramethylethylenediamine (tmen) were purchased from
Aldrich and distilled from KOH prior to use. GeCl2(dioxane)
was prepared according to the literature.1 2,6-Bis(trimethyl-
silylmethyl)-pyridine was prepared as described in the liter-
ature.21 1H and 13C NMR spectra were recorded at 300 and 75.5
MHz, respectively, using a Bruker DPX-300 spectrometer in
1
sealed tubes at ambient probe temperature. The H chemical
shifts were referenced to internal C6D5H (δ 7.15 ppm), 13C
chemical shifts were referenced to C6D6 (δ 128.0 ppm), 119Sn
chemical shifts to SnMe4 and 207Pb chemical shifts to PbCl2 in
D2O. Mass spectral data were recorded on a 5989-In mass spec-
trometer. Elemental analyses were preformed at MEDAC Ltd.,
Department of Chemistry, Brunel University, Uxbridge, UK.
Preparation of compounds
[Ge{N(SiMe3)C(Ph)CH}2C5H3N-2,6] (1). To a stirred sus-
pension of GeCl2(dioxane) (0.311 g, 1.34 mmol) in diethyl ether
(20 ml) was added a solution of [{N(SiMe3)C(Ph)CH}2-
Fig. 1 Molecular structure of 3; hydrogen atoms are omitted for
clarity. The therrmal ellipsoids are shown at 30%.
D a l t o n T r a n s . , 2 0 0 3 , 1 5 0 5 – 1 5 0 8
1506

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Table 2 Selected structural data for compounds 1, 2, 3 and 5
1
2
3
5
Empirical formula
M
C27GeH33N3Si2
528.33
C27H33N3Si2Sn
574.43
C27H33N3PbSi2
662.93
C23H41N3PbSi2
622.96
Colour, shape
T /K
Red, block
293(2)
Orange, prism
293(2)
Red, block
293(2)
Red, block
294(2)
Crystal size/mm
Crystal system
Space group
0.67 × 0.65 × 0.66
Monoclinic
P21/n
0.50 × 0.50 × 0.26
Triclinic
P1
0.53 × 0.48 × 0.45
Triclinic
P1
0.26 × 0.25 × 0.22
Triclinic
P1
¯
¯
¯
a/Å
b/Å
c/Å
α/Њ
β/Њ
13.876 (2)
13.739 (2)
14.587 (2)
90
95.110 (3)
90
2770.0 (6)
4
1.267
8.6497 (17)
11.619 (2)
13.869 (3)
84.69 (3)
83.38 (3)
88.21 (3)
1378.3 (5)
2
8.569 (1)
11.720 (2)
13.850 (2)
84.487 (2)
83.495 (3)
87.398 (3)
1375.0 (3)
2
9.7518 (2)
12.115 (3)
12.609 (3)
103.360 (8)
100.73 (1)
100.66 (1)
1382.8 (5)
2
γ/Њ
V/Å3
Z
ρ/Mg mϪ3
1.384
1.033
1.601
6.242
1.496
6.200
µ/mmϪ1
)
1.212
No. of reflns collected
No. of indept reflns (Rint
No. of obsd reflns [I>2σ(I )]
R1, wR2 [I>2σ(I )]
R1, wR2 (all data)
18346
6692 (0.0234)
6672
0.0305, 0.0708
0.0483, 0.0827
4629
4629 (0.0000)
4507
0.0501, 0.1484
0.0509, 0.1497
9250
6468 (0.0161)
6280
0.0251, 0.0595
0.0297, 0.0605
4104
4104 (0.0000)
3456
0.0616, 0.1651
0.0677, 0.1746
)
(C5H3N-2,6){Li(Et2O)}2] (0.810 g, 1.31 mmol) in diethyl ether
(30 ml) at Ϫ78 ЊC. The mixture was warmed to ambient tem-
perature and then stirred for 17 h to give a red slurry. The white
precipitate formed was filtered off and the filtrate was concen-
trated to ca. 10 ml. Red crystals of 1 were obtained, yield 0.410
g (59.2%, 0.78 mmol). Anal. Calcd for C27GeH33N3Si2: C, 61.38;
H, 6.30; N, 7.95. Found: C, 60.57; H, 6.59; N, 8.11%. 1H NMR
(300 MHz, C6D6 : C5D5N (2 : 1)) : δ 0.09 (s, 9H, SiMe3), 0.27
(s, 9H, SiMe3), 5.15 (s, 1H, CH ), 6.41 (t, J = 8.4 Hz, 2H,
m-C5H3N), 6.56 (s, 1H, CH ), 7.00 (t, J = 7.8 Hz, 1H, p-C5H3N),
7.18 (m, 6H, p-C6H5 and m-C6H5), 7.41 (dd, 2H, o-C6H5), 7.67
(dd, 2H, o-C6H5). 13C NMR (75.5 MHz, C6D6 : C5D5N (2 : 1)):
δ 3.41, 4.44, 103.07, 107.92, 115.26, 119.62, 128.90, 129.22,
136.16, 138.10, 142.07, 144.24, 144.77, 148.83, 150.84, 153.14,
157.45, 158.97, 161.64. MS (EI, 70 eV): m/z 528 (29, [M]ϩ), 455
(83, [M Ϫ SiMe3]ϩ), 382 (45, [M Ϫ 2 SiMe3]ϩ).
1H, p-C5H3N), 7.07 (m, 6H, p-C6H5 and m-C6H5), 7.51 (br, 2H,
o-C6H5). 13C NMR (75.5 MHz, C7D8): δ 4.81, 45.83, 58.16,
98.13, 112.63, 125.55, 126.54, 127.44, 129.03, 135.53, 152.82,
159.28, 158.97, 166.95. MS (EI, 70 eV): m/z 663 (30, [M]ϩ), 591
(44, [M Ϫ SiMe3 ϩ 1]ϩ).
[Sn{{N(SiMe3)C(But)C(H)}2C5H3N-2,6}] (4). To a suspen-
sion of SnCl2 (0.250 g, 1.32 mmol) in THF (10 ml) was added
a solution of [Na{{N(SiMe3)C(But)C(H)}2C5H3N-2,6}{Na-
(tmen)}]2 (1.10 g, 0.950 mmol) in THF (40 ml) at Ϫ78 ЊC. The
mixture was warmed to ambient temperature and then stirred
for an additional 20 h. The solvent was removed under reduced
pressure and Et2O (40 ml) was added for extraction. Filtration
and concentration (ca. 10 ml) of the resulting reddish orange
solution afforded 4 as orange microcrystals, yield 0.121 g
(23.6%, 0.221 mmol). mp 117–120 ЊC. Anal. Calcd for
C23H41N3Si2Sn: C, 54.82; H, 9.60; N, 12.79. Found: C, 54.52;
1
H, 9.53; N, 11.26%. H NMR (300 MHz, C7D8): δ 0.15 (s,
[Sn{{N(SiMe3)C(Ph)C(H)}2C5H3N-2,6}] (2). To a suspension
of SnCl2 (0.240 g, 1.27 mmol) in THF was added a solution of
[{N(SiMe3)C(Ph)CH}2(C5H3N-2,6){Li(Et2O)}2] (0.891 g, 1.27
mmol) in THF (20 ml) at Ϫ78 ЊC. After the mixture was
warmed to 21 ЊC and stirred for 16 h, the solvent was removed
under vacuum and the residue was extracted with n-hexane
(20 ml). Concentration to ca. 5 ml and cooling to Ϫ30 ЊC gave
orange crystals of 2, yield 0.362 g (53.1%, 0.221 mmol). Anal.
Calcd for C27H33N3Si2Sn: C, 56.45; H, 5.79; N, 7.31. Found: C,
18H, SiMe3), 1.17 (s, 18H, CMe3), 5.66 (s, 2H, CH ), 6.95 (d,
J = 7.8 Hz, 2H, m-C5H3N), 7.17 (t, J = 7.8 Hz, 1H, p-C5H3N).
13C NMR (75.5 MHz, C7D8): δ 2.24, 29.68, 45.89, 101.97,
118.93, 135.41, 157.99, 158.53. MS (EI, 70 eV): m/z 535 (21, [M
ϩ 1]ϩ), 416 (50, [M Ϫ Sn]ϩ).
[Pb{{N(SiMe3)C(But)C(H)}2C5H3N-2,6}] (5). To a suspen-
sion of PbCl2 (0.701 g, 2.53 mmol) in THF (40 ml) was added
an orange solution of [Li{{N(SiMe3)C(But)C(H)}2C5H3N-
2,6}][Li(tmen)2] (1.63 g, 2.46 mmol) in THF (40 ml) at Ϫ78 ЊC.
The mixture was warmed to ambient temperature and then
stirred for a further 16 h. The solvent was removed under
reduced pressure and Et2O (30 ml) was added for extraction.
Filtration and concentration (ca. 10 ml) of the resulting red
solution and storage at Ϫ30 ЊC afforded 5 as red crystals, yield
1.17 g (76.4%, 1.88 mmol). mp 117–120 ЊC. Anal. Calcd for
C23H41N3PbSi2: C, 44.34; H, 6.63; N, 6.74. Found: C, 44.34; H,
1
56.73; H, 5.72; N, 7.27%. H NMR (300 MHz, C6D6 : C5D4N
(4 : 1)): δ 0.11 (s, 18H, SiMe3), 5.65 (s, 2H, CH ), 6.63 (d, J = 7.8
Hz, 2H, p-C5H3N), 7.12 (m, 7H, m-C5H3N and C6H5), 7.62 (dd,
4H, C6H5). 13C NMR (75.5 MHz, C6D6 : C5D4N (4 : 1)): δ 1.64,
102.28, 118.29, 128.53, 128.94, 136.11, 142.13, 153.13, 157.46.
[Pb{{N(SiMe3)C(Ph)C(H)}2C5H3N-2,6}] (3). To a suspension
of PbCl2 (0.801 g, 2.88 mmol) in THF (40 ml) was added a red
solution of [{{N(SiMe3)C(Ph)C(H)}2C5H3N-2,6}{K(tmen)}2]
(1.88 g, 2.45 mmol) in THF (40 ml) at Ϫ78 ЊC. The mixture
was warmed to room temperature and then stirred for 24 h.
The solvent was removed under reduced pressure and Et2O
(30 ml) was added for extraction. Filtration and concentration
(ca. 10 ml) of the resulting red solution afforded 3 as yellow
crystals, yield 0.450 g (27.7%, 0.680 mmol). Some black solid
precipitate was formed due to the decomposition of the product
at room temperature. Anal. Calcd for C27H33N3PbSi2: C, 48.92;
H, 5.02; N, 6.34. Found: C, 48.97; H, 5.10; N, 6.62%. 1H
NMR (300 MHz, C7D8): δ 0.24 (s, 18H, SiMe3), 5.38 (d, 2H,
J = 2.1 Hz, CH ), 6.29 (d, J = 7.5 Hz, 2H, m-C5H3N), 6.92 (m,
1
6.51; N, 6.96%. H NMR (300 MHz, C6D6 : C5D5N (4 : 1)):
δ 0.35 (s, 18H, SiMe3), 1.21 (s, 18H, CMe3), 5.90 (s, 2H, CH ),
6.35 (d, J = 7.8 Hz, 2H, m-C5H3N), 6.94 (t, J = 7.8 Hz, 1H,
p-C5H3N). 13C NMR (75.5 MHz, C6D6 : C5D5N (4 : 1)): δ 5.53,
30.57, 40.50, 107.83, 118.30, 138.22, 154.33, 167.34. MS (EI,
70 eV): m/z 623 (65, [M]ϩ), 550 (40, [M Ϫ SiMe3]ϩ), 495 (37,
[M Ϫ SiMe3 Ϫ CMe3 ϩ 2]ϩ).
X-Ray crystallography
Crystals of compounds 3 and 5 were grown from diethyl ether
while those of compounds 1 and 2 were grown from diethyl
D a l t o n T r a n s . , 2 0 0 3 , 1 5 0 5 – 1 5 0 8
1507

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M. F. Lappert and A. J. Thorne, J. Chem. Soc., Chem. Commun.,
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6 (a) H. Braunschweig, P. B. Hitchcock, M. F. Lappert and
L. J.-M. Pierssens, Angew. Chem., Int. Ed. Engl., 1994, 104, 1243;
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ether–hexane and hexane respectively. X-Ray data were
collected using single crystals sealed in capillaries under di-
nitrogen, and raw intensities were collected on a Bruker
SMART CCD diffractometer at 294 K for 1 and 3, while the
raw intensities of 2 and 5 were collected on Rigaku RAXIS IIc
and IIIIIP Rigaku diffractometers at 294 K, respectively. The
structures were solved by direct phase determination, and all
non-hydrogen atoms were subjected to anisotropic refinement.
The hydrogen atoms were generated geometrically (C–H bonds
fixed at 0.96 Å) and allowed to ride on their respective parent
atoms; they were assigned appropriate isotropic thermal
parameters and included in the structure-factor calculations.
Computations were performed using the Siemens SHELXTL
PC program package22 on a PC 486 computer, and anomalous
dispersion corrections were incorporated. The crystallographic
data for 1, 2, 3 and 5 are shown in Table 2.
10 O. T. Beachley, Jr., D. B. Rosenblum and D. J. MacRae,
Organometallics, 2001, 20, 945.
11 W.-P. Leung, C. M. Y. Chan, B.-M. Wu and T. C. W. Mak,
Organometallics, 1996, 15, 5179.
12 W.-P. Leung, W.-H. Kwok, F. Xue and T. C. W. Mak, J. Am. Chem.
Soc., 1997, 119, 1145.
CCDC reference numbers 198206–198209.
See http://www.rsc.org/suppdata/dt/b2/b211305h/ for crystal-
lographic data in CIF or other electronic format.
13 W.-P. Leung, W.-H. Kwok, L.-H. Weng, L. T. C. Law, Z.-Y. Zhou
and T. C. W. Mak, J. Chem. Soc., Dalton Trans., 1997, 4301.
14 C. Drost, P. B. Hitchcock, M. F. Lappert and L. J.-M Pierssens,
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16 P. B. Hitchcock, J. Hu, M. F. Lappert, M. Layh and J. Servern,
Chem. Commun., 1997, 1189.
Acknowledgements
This work was supported by Research Grants Council of the
Hong Kong Special Administrative Region (Project No.
CUHK 4265/00P). We also thank the UGC Central Allocation
for partial funding of a 400 MHz NMR spectrometer.
17 B. S. Jolly, M. F. Lappert, L. M. Engelhardt, A. H. White and
C. L. Raston, J. Chem. Soc., Dalton Trans., 1993, 2653.
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20 O. M. Nefedov, S. P. Kolesnikov and A. I. Ioffe, J. Organomet.
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