Synthesis and structural characterization of two-coordinate low-valent 14-group metal complexes bearing bulky bis(amido)silane ligands

Article abstract of DOI:10.1039/c1dt11774b

A series of germylene, stannylene and plumbylene complexes [η²(N,N)-Me₂Si(DippN)₂Ge:] (3a), [η²(N,N)-Ph₂Si(DippN)₂Ge:] (3b), [η²(N,N)-Me₂Si(DippN)₂Sn:] (4), [η²(N,N)-Me₂Si(DippN)₂Pb:]₂ (5a), and [η²(N,N)-Ph₂Si(DippN)₂Pb:] (5b) (Dipp = 2,6-iPr₂C₆H₃) bearing bulky bis(amido)silane ligands were readily prepared either by the transamination of M[N(SiMe₃)₂]₂ (M = Sn, Pb) and [Me ₂Si(DippNH)₂] or by the metathesis reaction of bislithium bis(amido)silane [η¹(N),η¹(N)-R ₂Si(DippNLi)₂] (R = Me, Ph) with the corresponding metal halides GeCl₂(dioxane), SnCl₂, and PbCl₂, respectively. Preliminary atom-transfer chemistry involving [η ²(N,N)-Me₂Si(DippN)₂Ge:] (3a) with oxygen yielded a dimeric oxo-bridged germanium complex [η²(N,N)-Me ₂Si(DippN)₂Ge(μ-O)]₂ (6). All complexes were characterized by ¹H, ¹³C, ¹¹⁹Sn NMR, IR, and elemental analysis. X-ray single crystal diffraction analysis revealed that the metal centres in 3b, 4, and 5b are sterically protected to prevent interaction between the metal centre and the nitrogen donors of adjacent molecules while complex 5a shows a dimeric feature with a strong intermolecular Pb...N interaction.

Full text of DOI:10.1039/c1dt11774b

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PAPER
Synthesis and structural characterization of two-coordinate low-valent
14-group metal complexes bearing bulky bis(amido)silane ligands†
Dongming Yang,a Jianmei Guo,a Haishun Wu,b Yuqiang Dingc and Wenjun Zheng*a,b
Received 19th September 2011, Accepted 17th November 2011
DOI: 10.1039/c1dt11774b
2
A series of germylene, stannylene and plumbylene complexes [h (N,N)-Me2Si(DippN)2Ge:] (3a),
2
2
2
[h (N,N)-Ph2Si(DippN)2Ge:] (3b), [h (N,N)-Me2Si(DippN)2Sn:] (4), [h (N,N)-Me2Si(DippN)2Pb:]2
2
(5a), and [h (N,N)-Ph2Si(DippN)2Pb:] (5b) (Dipp = 2,6-iPr2C6H3) bearing bulky bis(amido)silane
ligands were readily prepared either by the transamination of M[N(SiMe3)2]2 (M = Sn, Pb) and
1
1
[Me2Si(DippNH)2] or by the metathesis reaction of bislithium bis(amido)silane [h (N),h (N)-
R2Si(DippNLi)2] (R = Me, Ph) with the corresponding metal halides GeCl2(dioxane), SnCl2, and PbCl2,
2
respectively. Preliminary atom-transfer chemistry involving [h (N,N)-Me2Si(DippN)2Ge:] (3a) with
2
oxygen yielded a dimeric oxo-bridged germanium complex [h (N,N)-Me2Si(DippN)2Ge(m-O)]2 (6). All
complexes were characterized by 1H, 13C, 119Sn NMR, IR, and elemental analysis. X-ray single crystal
diffraction analysis revealed that the metal centres in 3b, 4, and 5b are sterically protected to prevent
interaction between the metal centre and the nitrogen donors of adjacent molecules while complex 5a
shows a dimeric feature with a strong intermolecular Pb ◊ ◊ ◊ N interaction.
(M = Ge, Sn, Pb).4 One of our recent interests, the use and
Introduction
implementation of rigid chelating ligands with bulky substituent
groups, led us to choose the bis(amido)silane ligand that yielded
a four-membered metalloheterocycle system when coordinated
to a metal centre such as alkaline earth metals.5 We noted that
In past decades, it has been recognized that carbenes play
important roles as transient intermediates. Since the chemistry of
divalent 14-group compounds present carbene-like properties,1,2
much attention has been recently paid to the heavier analogues
of silylenes, germylenes, stannylenes, and plumbylenes. Although
M(II) compounds (M = Ge(II), Sn(II), Pb(II)) are generally reactive
and tend to oligomerize or polymerize, they can be stabilized kinet-
ically by sterically demanding ligands and/or thermodynamically
by inter- and intramolecular coordination, representing potential
building blocks for further synthetic chemistry.3 For example,
a few of heavier analogues of carbenes such as germylenes,
stannylenes, plumbylenes proved to be preparable on a sufficient
scale to enable their reactivity, in particular regarding their use
as ligands towards transition metals.3 Nitrogen-based ligands,
presumably due to the s-inductive effect of the electronegative
nitrogen atom, have played a pivotal role in the successful
isolation of these species with the archetype being M[N(SiMe3)2]2
2
two bis(amido)silane germylenes [h (N,N)-iPr2Si(DippN)2Ge:],6a
2
[h (N,N)-iPr2Si(SiPh3N)2Ge:],6a and three bis(amido)silane stan-
2
nylenes [h (N,N)-Ph2Si(DippN)2Sn:],6b [(iPr)2Si(DippN)2Sn],6a
2
[h (N,N)-iPr2Si(SiPh3N)2Sn:]6a have been described in the liter-
ature very recently, but we anticipated that the tunable steric
impact exerted by the nitrogen and silicon substituents of this
ligand would be significant for the stabilization and isolability
of the low-valent 14-group metal compounds.7 In this contri-
2
bution we describe the synthesis of a few germylenes [h (N,N)-
2
Me2Si(DippN)2Ge:] (3a), [h (N,N)-Ph2Si(DippN)2Ge:] (3b),
2
stannylene [h (N,N)-Me2Si(DippN)2Sn:] (4), and plumbylenes
2
2
[h (N,N)-Me2Si(DippN)2Pb:]2 (5a), [h (N,N)-Ph2Si(DippN)2Pb:]
(5b) with sterically demanding bis(amido)silane ligands, as
2
well as
a
dimeric germanium oxo complex [h (N,N)-
Me2Si(DippN)2Ge(m-O)]2 (6) that arises from the oxygen-transfer
reaction of the germylene (3a) and dry oxygen.
aInstitute of Organic Chemistry, Shanxi Normal University, Gongyuan
Street 1, Linfen, Shanxi Province 041004, People’s Republic of China.
E-mail: wjzheng@sxnu.edu.cn
bCollege of Chemical and Materials Science, Shanxi Normal University,
Gongyuan Street 1, Linfen, Shanxi Province 041004, People’s Republic of
China
Results and discussion
Preparation of complex [g2(N,N)-Ph2Si(DippNLi)2] (2b)
cSchool of Chemical and Material Engineering, Jiangnan University, 1800
Lihu Road, Wuxi, Jiangsu Province 214122, People’s Republic of China
† Electronic supplementary information (ESI) details X-ray crystallo-
graphic files for 3b, 4, 5a, 5b and 6. CCDC reference numbers 823608–
823610, 838183 and 838184. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt11774b
The silanediamine [Me2Si(DippNH)2] (1a), [Ph2Si(DippNH)2]
(1b), and bislithium bis(diamido)silane [Me2Si(DippNLi)2]2 (2a)
were prepared according to published protocol (Scheme 1).7
Compound [Ph2Si(DippNLi)2] (2b) can be readily deprotonated
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at d = 1.41, 3.56 ppm in 1H NMR spectrum are assigned to the sol-
vated tetrahydrofuran molecule in 3b, supporting determination of
the ratio of tetrahydrofuran molecules to bis(amido)silane ligands.
No signals were observed at about 2.5 ppm for N–H resonance in
1
the H NMR spectra,7 excluding the existence of the free ligand
(1a, 1b) in the samples.
Preparation of complex [g2(N,N)-Me2Si(DippN)2Sn:] (4)
By slightly altering the reaction conditions for the preparation
of 3a, 3b, such as the use of n-hexane as solvent at 0 ◦C, we
were able to cleanly prepare in good purity bis(amido)silane
2
stannylene [h (N,N)-Me2Si(DippN)2Sn:] (4) as air- and moisture-
Scheme 1 Synthesis of bis(diamido)silane complexes 2b, 3a, 3b, 4, 5a
and 5b.
sensitive yellow crystals in 80.0% isolated yield (Scheme 1). Alter-
natively, complex 4 could be readily prepared by transamination
of Sn[N(SiMe3)2]2 and Me2Si(DippNH)2 in n-hexane at room
temperature in high yield (90.0%) (Scheme 1). The second pathway
was preferable for isolation of the product. Complex 4 has good
solubility in common organic solvents, such as n-hexane, benzene,
and toluene, exhibits a sharp, reversible melting point at 190 ◦C.
The formation of 4 is confirmed by H NMR spectroscopy, as
evident from only one sharp resonance for the –SiCH3 groups (d =
0.28 ppm), one set of coupled doublets for –CH(CH3)2 groups (d =
by the reaction of n-BuLi and 1b in a molar ratio of 2 : 1 at
1
room temperature as a white precipitate in n-hexane (95%). H
NMR spectroscopy revealed two sets of resonances for the non-
equivalent –CH(CH3)2 substituents, suggesting that the molecular
asymmetry of dimer in the solution, similar to the observation for
2a.7 No signals were observed at about 2.5 ppm for the N–H
resonance, excluding the existence of the free ligand (1b). In the
7Li NMR spectrum, only one sharp resonance at d = -0.98 ppm
was assigned to the equivalent coordinated lithium ions in the
solution, supporting the formation of 2b. However, the 7Li NMR
resonance at d = -0.98 ppm for 2b is drastically shifted upfield
relative to the signal of 2a (7Li d = 1.97 ppm), suggesting lower
electrophilicity of lithium atoms in 2b. This arises from the phenyl
substitutes of 2b.
1
1
1.27 ppm, JH-H = 7.4 Hz), and one set of septet for –CH(CH3)2
groups (d = 3.76 ppm), these suggest that the solid structure of 4
is maintained in solution i.e. no dimerization occurs in solution.
No 117/119Sn satellites were discerned in the 1H NMR spectrum of
4, presumably as a result of interaction through the quadrupolar
amide nitrogen centres.
In the 119Sn NMR spectrum of 4, only one sharp resonance
was shown at d = 514 ppm. The chemical shift is consistent
with a two-coordinate tin centre and is similar to those recently
observed for complexes [Ph2Si(DippN)2Sn:] (d = 499 ppm)6b and
[(iPr)2Si(DippN)2Sn:] (d = 536 ppm).6a
Preparation of complexes [g2(N,N)-Me2Si(DippN)2Ge:] (3a) and
[g2(N,N)-Ph2Si(DippN)2Ge:] (3b)
The metathetical reaction between an equimolar ratio of 2a
2
and GeCl2(dioxane) in n-hexane successfully gave [h (N,N)-
Me2Si(DippN)2Ge:] (3a) as air- and moisture-sensitive pale-
Preparation of complexes [g2(N,N)-Me2Si(DippN)2Pb:]2 (5a) and
[g2(N,N)-Ph2Si(DippN)2Pb:] (5b)
yellow needles in 53.0% isolated yield (Scheme 1). In a fash-
2
ion similar to the preparation of 3a, compound [h (N,N)-
Ph2Si(DippN)2Ge:] (3b) was obtained by the metathesis reaction of
2b and GeCl2(dioxane) in n-hexane as air- and moisture-sensitive
pale-yellow crystals in 80.0% isolated yield.
In searching for heavier analogues of silylenes, germylenes,
stannylenes, and plumbylenes, most attention has focused on the
lighter elements Si and Ge,1 and no structurally characterized
examples of plumbylenes have been reported containing the
bis(diamido)silane ligand. The plumbylenes 5a and 5b were thus
synthesized by the reaction of dilithium salt of the appropriate
bis(amido)silane 2a, 2b with PbCl2 in ether at room tempera-
ture (Scheme 1). These produced deep red-coloured solutions
from which the solvents were partially removed in vacuo after
24 h. The solids were re-crystallized in the mother liquor at
-30 ◦C and yielded dark red crystals of the pure plumbylenes
5a and 5b,respectively. Plumbylene 5a was also obtained eas-
ily in a transamination reaction between Pb[N(SiMe3)2]2 and
Me2Si(DippNH)2 in ether at ambient temperature. It could also
be re-crystallized from ether to give red crystals. Both of 5a and 5b
are well soluble in most common organic solvents such as ether,
tetrahydrofuran, exhibit sharp, reversible melting points at 148 ◦C
(for 5a) and 215 ◦C (for 5b), and were characterized by NMR
spectroscopy, elemental analysis, and X-ray diffraction.
Both compounds 3a and 3b are soluble in a variety of organic
solvents, exhibit sharp, reversible melting points at 128 ◦C (for 3a)
and 178 ◦C (for 3b), and were characterized by NMR spectroscopy,
elemental analysis, and for 3b only X-ray diffraction. 1H and 13
C
NMR spectroscopy indicated a symmetrical solution structure
both for 3a and 3b with a single set of resonances for the iPr
substituents and symmetrical phenyl skeletons. This suggested
that complexes 3a and 3b, which have less steric congestion
as a result of the smaller central four membered GeN2Si ring,
exhibit magnetically equivalent isopropyl groups, presumably
because of relatively fast rotation (on a 1H NMR time scale)
about the C–N bond. This difference in only one single set
of resonances for the iPr groups contrasts sharply with those
observed in the analogous alkaline earth metal–bis(amido)silane
complexes, in which two sets of resonances for the iPr groups
were observed.5 The asymmetrical conformation of alkaline earth
metal–bis(amido)silane complexes in solution probably arises
from solvated tetrahdrofuran molecules.5 Two multiple resonances
1H NMR spectra (C6D6, 23 ◦C) of both 5a and 5b show
only one doublet for the isopropyl –CH(CH3)3 groups and one
2188 | Dalton Trans., 2012, 41, 2187–2194
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septet signal for the –CH(CH3)3 groups as encountered for the
diisopropylphenyl ligand owing to the molecular symmetry in the
solution, demonstrating the formation of 5a and 5b in solution,
indicating that 5a undergoes dissociation into monomeric species
in solution. This is, however, in contrast to the observation in the
analogous system of a neutral dimeric magnesium complex, where
two doublets for the isopropyl –CH3 groups and two signals for
isopropyl –CH groups were observed.5a
Preparation of complex [g2(N,N)-Me2Si(DippN)2Ge(l-O)]2 (6)
Divalent germylene 3a, 3b, 4, 5a, and 5b were expected to exhibit
diverse reaction chemistry due to their dual donor/acceptor nature
and proclivity for oxidative bond forming reactions.1a,8,9,10,11 This
may lead to the isolation of heavy analogues of ketones similar
to stable divalent 14-group derivative R2M = E (M = Si, Ge,
Sn, Pb; E = O, S, Se, Te).11,12 In our case, the products from
chalcogen atom-transfer may enable confirmation of germerylene
3a formation. We preliminarily explored chalcogen atom-transfer
chemistry involving 3a with the goal of isolating hitherto rare
examples of Ge O multiple bond. The further reaction of 3a
with dry O2 was therefore carried out. After workup, only a
dimeric germanium oxo-bridged complex [Me2Si(DippN)2Ge(m-
O)]2 (6) was isolated in good yield (70%), rather than the expected
corresponding heavy analogues of ketone (Scheme 2).13 Complex
6 is air-, and moisture-stable and well soluble in ether, THF, and
DMSO. The 1H NMR spectrum of compound 6 in C6D6 displays
two sets of coupled doublets for –CH(CH3)2 groups (d = 1.08
ppm, 1JH–H = 6.6 Hz; d = 1.23 ppm, 1JH–H = 6.6 Hz). The two sets of
resonances for the nonequivalent –C(CH3)2 groups in complex 6
reveal molecular asymmetry and a hindered rotation about the C–
N bond in solution, similar to that observed in neutral dimeric
Fig. 1 Molecular structure of 3b with thermal ellipsoids at 30%
probability level. Hydrogen atoms are omitted for clarity. Selected
˚
bond lengths (A) and bond angles (deg): Ge(1)–N(2) 1.887(3),
Ge(1)–N(1) 1.888(3), Ge(1)–Si(1) 2.6616(10), N(1)–Si(1) 1.724(3),
N(2)–Si(1) 1.726(3), C(25)–Si(1) 1.870(3), C(31)–Si(1) 1.859(4),
C(9)–N(2), 1.421(4), C(21)–N(1) 1.433(4); N(2)–Ge(1)–N(1) 80.47(11),
C(21)–N(1)–Si(1) 137.7(2), C(21)–N(1)–Ge(1) 125.0(2), Si(1)–N(1)–Ge(1)
94.83(12), C(9)–N(2)–Si(1) 132.8(2), C(9)–N(2)–Ge(1) 128.7(2),
Si(1)–N(2)–Ge(1) 94.79(12), N(1)–Si(1)–N(2) 89.91(13), N(1)–Si(1)–C(31)
116.71(14), N(2)–Si(1)–C(31) 115.45(15), N(1)–Si(1)–C(25) 114.22(14),
N(2)–Si(1)–C(25) 115.06(15), C(31)–Si(1)–C(25) 105.50(15).
1
1
magnesium complex [h ,h -Me2Si(DippN)2Mg)].5a Notably, the
1
resonances of the –C(CH3)2 groups in the H NMR spectrum
were slightly overlapped by the signals of the lattice ether.
Fig.
2
Molecular structure of 4 with thermal ellipsoids at 30%
probability level, only one of the two independent molecules is shown.
˚
Hydrogen atoms are omitted for clarity. Selected bond lengths (A)
and bond angles (deg): Sn(1)–N(1) 2.064(14), Sn(1)–N(2) 2.045(9),
N(1)–C(3) 1.443(15), N(2)–C(15) 1.411(18), Si(1)–N(1) 1.719(11),
Si(1)–N(2) 1.726(12); N(1)–Sn(1)–N(2) 73.6(4), N(1)–Si(1)–N(2) 91.2(5),
Si(1)–N(2)–Sn(1) 97.7(4), Si(1)–N(1)–Sn(1) 97.3(6), C(1)–Si(1)–C(2)
107.5(9), C(15)–N(2)–Sn(1) 130.6(9), C(3)–N(1)–Sn(1) 129.3(8),
C(2)–Si(1)–Sn(1) 124.6(8), C(1)–Si(1)–Sn(1) 127.9(5).
Scheme 2 The formation of complex 6.
Single crystal and molecular structures
Single crystal X-ray diffraction experiments were carried out on
3b–6. Thermal ellipsoid plots of the molecular structures are
shown in Fig. 1–5 and selected structural parameters are presented
in the legend of each figure; the crystallographic data of complexes
are given in Table 1.
space group P2(1)/c. Subsequent solution and refinement of
the structure confirmed this choice. The crystals were sealed
in capillary and mounted nearly equidimensional. In spite of
air- and moisture-sensitivity, the diffraction properties of the
sample were excellent. The structure elucidation of 3b revealed
a monomeric complex in which the central germanium(ii) atom
[g2(N,N)-Ph2Si(DippN)2Ge:] (3b)
2
A systematic search of a limited hemisphere of reciprocal
space located a set of diffraction maxima with symmetry and
systematic absences uniquely corresponding to the monoclinic
is h (N,N)-coordinated by one bis(amido)silane ligands (Fig. 1),
showing a geometry with planar four-membered NSiNGe ring
and trigonal planar coordination involving the chelating nitrogen
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Fig. 3 Molecular structure of 5a with thermal ellipsoids at 30% prob-
ability level. Hydrogen atoms and isopropyl groups are omitted for
Fig.
5
Molecular structure of
6
with thermal ellipsoids at 30%
˚
clarity. Selected bond lengths (A) and bond angles (deg): Pb(1)–N(1)
probability level. Hydrogen atoms are omitted for clarity. Se-
2.218(3), Pb(1)–N(2) 2.417(3), N(1)–C(1) 1.438(5), N(2)–C(15) 1.468(5),
Si(1)–N(1) 1.711(3), Si(1)–N(2) 1.766(3); N(1)–Pb(1)–N(2) 68.62(11),
N(1)–Si(1)–N(2) 97.68(16), Si(1)–N(2)–Pb(1) 92.13(13), Si(1)–N(1)–Pb(1)
100.86(15), C(13)–Si(1)–C(14) 104.3(2), C(15)–N(2)–Pb(1) 128.5(2),
C(1)–Si(1)–Pb(1) 124.6(2). Symbol A ∫ the symmetry code (2-x, -y, 2-z).
˚
lected bond lengths (A) and bond angles (deg): Ge(1)–N(2)
1.812(4), Ge(1)–N(1) 1.816(4), Ge(1)–Si(1) 2.5816(19), N(1)–Si(1)
1.735(4), Ge(1)–O(1) 1.799(8), Ge(1)–O(2) 1.875(6), Ge(1)–Ge(1A)
2.5972(14); N(2)–Ge(1)–N(1) 84.54(19), O(1)–Ge(1)–N(2) 135.8(2),
O(1)–Ge (1)–N(1) 116.3(2), O(1)–Ge(1)–O(2) 90.0(3), N(1)–Ge(1)–O(2)
127.02(18), O(1)–Ge(1A)–O(2) 90.0(3), C(15)–N(1)–Ge(1) 131.8(3),
Ge(1A)–O(1)–Ge(1) 92.4(6). Symbol A ∫ the symmetry code (1/2–x, y,
1/2–z).
[g2(N,N)-Me2Si(DippN)2Sn:] (4), [g2(N,N)-Me2Si(DippN)2Pb:]2
(5a), and [g2(N,N)-Ph2Si(DippN)2Pb:] (5b)
The structures of complexes 4, 5a, and 5b were determined by
single-crystal X-ray diffraction analyses. The molecular struc-
ture of 4 is monomeric in the solid state and has a pla-
nar trigonal geometry about the metal centre with consider-
ation of the lone-pair electron. The tin atom exhibits two-
coordination, being bonded to two planar N-centres and form-
ing a planar four-membered heterocyclic ring with only one
bis(diamido)silane [Me2Si(DippN)2]2- ligand (Fig. 2). The tin–
˚
˚
nitrogen bond lengths are 2.064(14) A and 2.045(9) A, respectively,
which are comparable with those found in [Ph2Si(DippN)2Sn:]
(2.100(3), 2.071(2) A),6b and in [(iPr)2Si(DippN)2Sn:] (2.0709(12),
˚
2.0631(12)).6a The molecular structure of 5a is, however, re-
vealed as a dimer in solid state, exhibiting strong intermolec-
ular Pb ◊ ◊ ◊ N interactions (Fig. 3). This mode of dimerization
has been reported previously for several plumbylenes with
the lead-containing heterocycles, such as in [PhB(ButN)2Pb]2,14
[(C3H6)Si(ButN)2Pb]2,15 and in [DippN(CH2)3N(Dipp)Pb].16a The
Fig. 4 Molecular structure of 5b with thermal ellipsoids at 30%
probability level. Hydrogen atoms are omitted for clarity. Selected
˚
bond lengths (A) and bond angles (deg): Pb(1)–N(2) 2.267(7),
Pb(1)–N(1) 2.206(8), Pb(1)–Si(1) 2.950(3), N(1)–Si(1) 1.712(8),
N(2)–Si(1) 1.711(8), C(25)–Si(1) 1.883(10), C(31)–Si(1) 1.881(10),
C(9)–N(1), 1.423(11), C(21)–N(2) 1.398(11); N(2)–Pb(1)–N(1) 70.4(3),
C(21)–N(2)–Si(1) 141.6(7), C(21)–N(1)–Pb(1) 122.6(6), Si(1)–N(2)–Pb(1)
˚
˚
lead–nitrogen bond lengths are 2.218(3) A and 2.417(3) A,
94.7(3),
C(9)–N(1)–Si(1)
129.9(7),
C(9)–N(1)–Pb(1)
126.0(6),
respectively, which are within the range of those found in {[{N(2,6-
Si(1)–N(2)–Pb(1) 96.9(3), N(1)–Si(1)–N(2) 97.8(4), N(2)–Si(1)–C(31)
114.7(4), N(1)–Si(1)–C(31) 113.4(4), N(2)–Si(1)–C(25) 114.5(4),
N(1)–Si(1)–C(25) 110.4(4), C(31)–Si(1)–C(25) 106.1(5).
i
16b
˚
Pr2C6H3)C(Me)}2CH]Pb}{B(C6F5)4} (2.242(4), 2.228(4) A),
and in [DippN(CH2)3N(Dipp)Pb] (2.125(4), 2.136(5)).16a The
length of the intermolecular Pb(1) ◊ ◊ ◊ N(2A) separation (2.587(3)
˚
A) is only slightly longer than the values of Pb–N bond lengths
atoms. The Ge–N bond lengths were Ge(1)–N(2) 1.887(3), Ge(1)–
found in 5a, indicative of the strengths of the interaction. In
addition, the dimerization via strong intermolecular Pb ◊ ◊ ◊ N
interaction obviously has a strong impact on the geometric
parameters of N-heterocyclic plumbylene, namely the Pb cen-
tre is asymmetrically bound to the nitrogen atoms within the
˚
N(1) 1.888(3) A, respectively, slightly longer than those found
6a
˚
in [iPr2Si(DippN)2Ge:] (1.8627(10) A (av.)). Compound 3b
represents a rare uncomplexed germylene heterocycle featuring an
NSiNGe core to be structurally authenticated by crystallography.6a
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Table 1 Crystal and Data Collection Parameters of Complexes 3b, 4, 5a, 5b, and 6
Compounds
3b
4
5a
5b
6
Formula
Fw
C40H52SiN2OGe
677.52
0.35 ¥ 0.27 ¥ 0.08
Monoclinic
P21/n
10.8195(15)
18.818(3)
19.240(3)
90
103.039(2)
90
C26H40N2SiSn
527.38
0.18 ¥ 0.16 ¥0.13
Orthorhombic
Pna21
17.83(4)
8.55(2)
36.69(8)
90
90
90
5595(22)
8
1.252
C52H80N4Si2Pb2
1231.78
0.15 ¥ 0.18 ¥ 0.20
Monoclinic
P21/n
12.444(4)
18.724(6)
12.638(4)
90
116.420(4)
90
2637.3(16)
2
C36H44N2SiPb
740.01
0.42 ¥ 0.48 ¥ 0.31
Tetragonal
P43212
12.4575(10)
12.4575(10)
43.426(7)
90
C56H90Ge2N4O3Si2
1068.68
0.15 ¥ 0.14 ¥ 0.25
Monoclinic
P2/n
13.449(4)
10.478(4)
21.692(7)
90
90.705(5)
90
3056.5(18)
2
Cryst. size (mm)
Cryst. syst.
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (◦)
b (◦)
g (◦)
90
90
3
˚
V (A )
3816.1(9)
4
1.179
6739.2(13)
8
1.459
Z
Dc (g cm-3)
e (mm-1)
1.551
6.457
1.157
1.064
0.865
0.970
5.068
F (000)
1440
298(2)
1.99–25.50
19903
7076
25.50
0.0437
2192
293
2.22–25.01
18142
7707
25.01
0.0626
1224
293
1.91–26.01
11715
5195
26.01
0.0350
2960
298(2)
1.88–27.00
38768
7339
27.00
0.1244
1132
293(2)
1.77–25.01
11715
5382
25.01
0.0605
T (K)
Range (◦)
Reflns measured
Unique reflns
qmax (◦)
Rint
Min and max transmn
R1, wR2 [I > 2s(I)]a
R1, wR2 (all data)b
GOF
0.7516 and 0.9340
0.0543, 0.1317
0.0888, 0.1495
1.026
—
0.532
0.8448 and 0.8843
0.0760, 0.1899
0.1122, 0.2075
1.037
0.00(17)
1.032
0.3583 and 0.4442
0.0259, 0.0563
0.0403, 0.0593
0.944
—
1.168
0.1947 and 0.3026
0.0618, 0.1129
0.0946, 0.1233
1.063
0.032(12)
1.432
0.7769 and 0.8654
0.0739, 0.1946
0.1385, 0.2312
0.871
—
1.207
Flack parameter
-3
˚
˚
Dr (max) (e¥A )
-3
Dr (min) (e¥A )
-0.330
-0.863
-0.775
-1.313
-0.084
a R1 = R|Fo| -|Fc|/R|Fo|. b wR2 = [Rw(Fo2- Fc2)2/Rw(Fo2)2]0.5
.
˚
four-membered ring (Pb(1)–N(1) 2.218(3) A, Pb(1)–N(2) 2.417(3)
˚
To compare the steric and electronic effects of bis-
(diamido)silane ligands, crystal and physical data for a few of
bis(diamido)silane germylenes, stannylenes and plumbylenes are
collected in Table 2. The corresponding values shown that metal–
nitrogen bond lengths varied slightly with ligands but the melting
points, crystal systems, bond angles in addition to space groups
are mainly related to the substituents of ligands. For example, the
metal–nitrogen bond lengths found in four stannylenes are almost
comparable while the melting points, crystal systems as well as
chemical shifts in 119Sn NMR spectra are significantly distinct. In
addition, the presence of more encumbered groups on silicon of
ligands will result in the substituents on nitrogen of the ligands
being pushed further toward the metal centre, leading to wider
angles, e.g. 5a and 5b.
A). However, the molecular structure of 5b is rigorously
monomeric with no close-range intermolecular interactions in the
solid state and actually isostructual to 5a without considering the
intermolecular Pb ◊ ◊ ◊ N interactions. This difference in solid-state
packing is likely a consequence of added intra-ligand repulsion
in 5b. The presence of encumbered Ph2Si– group within the same
heterocycle results in the aryl rings in 5b being pushed even further
toward the Pb centre, leading to greater steric coverage. The lead–
nitrogen bond lengths are 2.267(7) A and 2.206(8) A, respectively,
which are significantly shorter than those found in 5a, obviously
due to the lack of the intermolecular Pb ◊ ◊ ◊ N interactions.
˚
˚
[g2(N,N)-Me2Si(DippN)2Ge(l-O)]2 (6)
The crystallographic data quality of 3a is not warranted for
publication in this case because of the poor crystal nature,
but it could be further confirmed by the elucidated structure of
germanium oxo complex 6. The molecular structure of 6 is dimeric
in solid state and contains planar NSiNGe and Ge2O2 arrays that
are mutually rotated by 49.3 and 63.0◦, with average endocyclic
Conclusions
This work has demonstrated that a series of low coordinate group
14 compounds featuring sterically encumbered bis(diamido)silane
ligand have been readily prepared. The ligands employed are hin-
dered enough to facilitate the isolation of rigorously monomeric,
two-coordinate germylenes 3a, 3b, stannylene 4, and plumbylenes
5a (dimeric), 5b but the formation of a dimeric arrangement of
6 suggests the difficulty associated with isolating a monomeric
germanone (R2Ge O) under ambient conditions, probably due
to the highly polar nature of the Ge O p-bond that makes this
unit prone to dimerization/oligomerization to yield thermody-
namically more stable s-lingages.18 Complexes 3–5 are highly
˚
˚
Ge–O and Ge–N bond lengths of 1.837(7) A and 1.814(4) A
(Fig. 5). The dimeric structure of 6 lies about a twofold axis
with the twofold axis passing through O(1) and O(2). A related
amide-substituted 1,3-cyclodigermoxane, [Ge{N(SiMe3)2}2(m-
O)]2, was previously prepared through the direct reaction of
Ge{N(SiMe3)2}2 and oxygen.17 The germanium–oxygen bond
˚
˚
lengths in 6 are 1.799(8) A and 1.875(6) A, respectively, which
are comparable with those found in [(iPr)2Si(DippN)2Ge((m-O)]2
6a
˚
(1.8045(18), 1.8063(19) A).
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2187–2194 | 2191
©

View Article Online
Table 2 Crystal and physical data collection of bis(diamido)silane germylenes, stannylenes and plumbylenes
Mp (◦C)
119Sn (d ppm)
Ref.
˚
Compounds
Crystal system
M–N Bond lengths (A)
N–M–N (deg)
2
[h (N,N)-Ph2Si(DippN)2Ge:]
Monoclinic
Monoclinic
Monoclinic
Orthorhombic
Orthorhombic
Monoclinic
Monoclinic
Tetragonal
1.888(3)
1.887(3)
80.47(11)
83.31(6)
81.26(6)
74.62(10)
73.6(4)
74.60(5)
76.28(6)
70.4(3)
178
197
172
190–195
190
130
114
215
148
—
—
—
499
514
536
527
—
[a]
2
[h (N,N)-iPr2Si(SiPh3N)2Ge:]
1.8834(14)
1.8627(10)
2.1000(3)
2.064(14)
2.0709(12)
2.0888(15)
2.267(7)
1.8829(14)
1.8627(10)
2.071(2)
[6a]
[6a]
[6b]
[a]
2
[h (N,N)-iPr2Si(DippN)2Ge:]
2
[h (N,N)-Ph2Si(DippN)2Sn:]
2
[h (N,N)-Me2Si(DippN)2Sn:]
2.045(9)
2
[h (N,N)-iPr2Si(DippN)2Sn:]
2.0631(12)
2.0882(15)
2.206(8)
[6a]
[6a]
[a]
2
[h (N,N)-iPr2Si(SiPh3N)2Sn:]
2
[h (N,N)-Ph2Si(DippN)2Pb:]
2
[h (N,N)-Me2Si(DippN)2Pb:]2
Monoclinic
2.218(3)
2.417(3)
68.62(11)
—
[a]
a This work.
potential as precursors in catalysis and materials chemistry. Work
is proceeding along these lines.
1H NMR (C6D6, 23 ◦C): d = 0.29 (s, 6 H, Si-CH3), 1.27 (d, 28 H,
1J = 7.2 Hz, (CH3)2C), 3.85 (sept, ◦8 H, Me2CH), 7.03–7.22 (m, 6
1
H, Ph); 13C{ H} NMR (C6D6, 23 C): d = 5.3 (s, (CH3)2Si), 26.5
(s, (CH3)2C), 27.3 (s, (CH3)2C), 123.3, 142.9, 143.8, 148.5 (4 s, C
Experimental
-1
˜
for [Ph]); IR(Nujol Mull, cm ): n = 2919(s), 2852(s), 2725(w),
All manipulations were carried out in an argon atmosphere
under anaerobic conditions using standard Schlenk, vacuum line
and glove box techniques. The solvents were thoroughly dried,
deoxygenated and distilled in an argon atmosphere prior to use.
DMSO-d6 was degassed and dried over molecular sieves for
24 h before use. C6D6 was dried with metallic sodium before
use. The 1H NMR, 13C NMR, and 119Sn NMR spectra were
recorded with a Bruker DRX-600 spectrometer. IR measurements
were carried out on a NICOLET 360 FT-IR spectrometer
from Nujol mulls prepared in a dry box. Melt points were
measured in sealed argon-filled capillaries without temperature
correction with an apparatus XT4-100A (Electronic and Optical
Instruments, Beijing). GeCl2·Dioxane, SnCl2, and PbCl2 were
purchased from Aldrich. Me2Si(DippNH)2,7 Me2Si(DippNLi)2,7
Ph2Si(DippNH)2,7 and M[N(SiMe3)2]2 (M = Ge, Sn, Pb)19 were
prepared according to the literature.
2031(w), 1460(w), 1376(s), 1311(w), 1250(s), 1202(s), 1155(m),
916(s), 776(s), 722(s). Anal. Calcd. for C26H40N2SiGe: C 64.83,
H 8.33, N 5.90; Found: C 64.70, H 8.19, N 5.77.
Synthesis of complex [g2(N,N)-Ph2Si(DippN)2Ge:] (3b)
To a mixture of 2b (0.546 g, 1.00 mmol) and GeCl2·dioxane (0.232
g, 1.0 mmol) in a Schlenk flask (100 mL), n-hexane (50 mL) was
◦
added via a syringe at 0 C. After the suspension was stirred for
about 5 h, tetrahydrofuran (15 mL) was added. The clear solution
was stirred for further 48 h at room temperature and then filtered
through Celite. The filtrate was concentrated to about 35 mL to
afford 3b as colorless solid at ◦room temperature for several days
(0.542 g, 58.0%). Mp = 178 C. H NMR (C6D6, 23 ◦C): d =
1
1.05, 1.06 (d, 24 H, (CH3)2C), 1.41 (m, 4 H, THF), 3.56 (m, 4
H, THF), 3.75 (sept, 4 ◦H, Me2CH), 6.96–7.44 (m 16 H, Ph);
1
13C{ H}NMR (C6D6, 23 C): d = 144.3, 141.0, 135.7, 134.8, 129.9,
124.1, 123.6 (7 s, C for [Ph]), 67.5, 25.4 (2 s, C for THF), 25.0 (s,
C for (CH3)2C), 28.6 (s, C for (CH3)2C); IR (Nujol Mull, cm-1):
Synthesis of complex [g2(N,N)-Ph2Si(DippNLi)2] (2b)
˜
To a solution of Ph2Si(DippNH)2 (1.1 g, 2.0 mmol) in n-hexane
(50 mL), 1.6 mL n-BuLi (2.5 M, 4.0 mmol) was added via a
syringe at 0 ◦C. After the suspension was stirred for 3 h at
room temperature and then filtered. The collected precipitate was
washed with n-hexane (3 ¥ 10◦mL) to afford 2b as pure white solid
(0.54 g, 87.8%). Mp > 300 C, decomp.1H NMR (DMSO-d6,
n = 3085(s), 3028(s), 2948(s), 2873(w), 1942(w), 1460(w), 1376(s),
1311(w), 1210(s), 1107(m), 895(s), 786(s), 678(s). Anal. Calcd. for
C40H52SiN2OGe: C 70.90, H 7.74, N 4.13; Found: C 70.52, H 7.33,
N 4.01. Single crystals suitable for X-ray diffraction analysis were
obtained from re-crystallization at room temperature in a mixed
solvent of n-hexane and tetrahydrofuran (2 : 1).
◦
1
23 C): d = 0.86 (d, 24 H, J = 6.6 Hz, (CH3)2C), 3.57 (sept, 2
H, Me2CH), 3.83 (sept, 2 H, Me2CH), 5.91–7.66 (m, 16 H, Ph);
Synthesis of complex [g2(N,N)-Me2Si(DippN)2Sn:] (4)
◦
1
13C{ H} NMR (DMSO-d6, 23 C): d = 24.0, 24.6 (2 s, (CH3)2C),
To a mixture of 2a (0.422 g, 1.00 mmol) and SnCl2 (0.19 g,
1.0 mmol), n-hexane (30 mL) was added at 0 ◦C via a syringe.
After the solution was stirred for 2 days at room temperature the
orange solution was filtered through Celite. The solvent of the
filtrate was concentrated to about 5 mL under reduced pressure
and then kept at -30 ◦C to afford 4 as yellow crystals (0.42 g,
80.0%). Alternatively, to a mixture of 1a (0.410 g, 1.00 mmol)
and Sn[N(SiMe3)2]2 (0.439 g, 1.0 mmol), n-hexane (20 mL) was
added via a syringe. After the solution was stirred for 18 h at room
temperature the volatile components were removed under reduced
pressure. The resulting residue was extracted with n-hexane (3 ¥
10 mL). The solvent of the solution was concentrated to about
5 mL and then kept at -30 ◦C to afford 4 as yellow crystals
27.2, 28.4 (2 s, (CH3)2C), 107.6, 118.0, 121.2, 122.8, 126.6, 135.2,
137.6, 138.3, 144.5, 146.4, 154.6 (12 s, C for [Ph]); 7Li{ H} NMR
1
(DMSO-d6, 23 ◦C): d = -0.98; Anal. Calcd. for C36H44N2SiLi: C
79.09%, H 8.11%, N 5.12%; Found: C 78.67%, H 8.26%, N 5.03%.
Synthesis of complex [g2(N,N)-Me2Si(DippN)2Ge:] (3a)
To a mixture of 2a (0.422 g, 1.00 mmol) and GeCl2·dioxane (0.232
g, 1.0 mmol), n-hexane (30 mL) was added at 0 ◦C via a syringe.
After the solution was stirred for 2 days at room temperature the
light yellow solution was filtered through Celite. The solvent of the
filtrate was concentrated to about 5 mL under reduced pressure
to afford 3a as colorless needles (0.26 g, 53.0%). Mp = 128 ◦C.
2192 | Dalton Trans., 2012, 41, 2187–2194
This journal is
The Royal Society of Chemistry 2012
©

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◦
(0.47 g, 90.0%). Mp = 190 C. H NMR (CDCl3, 23 ◦C): d =
solvent of the solution was concentrated to about 5 mL under
1
0.23 (s, 6 H, Si-CH3), 1.29 (d, 28 H, (CH3)2C), 3.77 (sept, 8 H,
reduced pressure and then kept at -30 ◦C to afford 6 as light
◦
◦
1
1
Me2CH), 6.96–7.25 (m, 6 H, Ph); 13C{ H} NMR (CDCl3, 23 C):
yellow crystals (0.75 g, 70.0%). Mp >250 C decomp. H NMR
(C6D6, 23 ◦C): d = 0.21 (s, 6 H, Si-CH3), 6.84–7.30 (m, 6 H, Ph),
3.75 (sept, 4 H, Me2CH), 1.08 (d, 12◦H, (CH3)2C), 1.23 (d, 12 H,
d = 5.2 (s, (CH3)2Si), 25.4 (br, (CH3)2C), 27.5 (s, (CH3)2C), 122.5,
122.8, 142.7, 143.8 (4 s, C for [Ph]); 119Sn{ H} NMR (CDCl3,
1
◦
23 C): d = 514 (s); IR (Nujol Mull, cm ): n = 2919(s), 2853(s),
(CH3)2C); 13C{ H} NMR (C6D6, 23 C): d = 123.5 (s. C for [Ph]),
-1
1
˜
2725(w), 2031(w), 1461(w), 1376(s), 1312(w), 1250(s), 1203(s),
1155(m), 916(s), 776(s), 722(s). Anal. Calcd. for C26H40N2SiSn:
C 59.22, H 7.63, N 5.30; Found: C 59.04, H 7.55, N 5.20. Single
crystals suitable for X-ray diffraction analysis were obtained from
re-crystallization at room temperature in n-hexane.
125.4 (s, C for [Ph]), 135.4 (s, C for [Ph]), 146.9 (s, C for [Ph]),
27.9 (s, (CH3)2C), 24.3, 24.9 (2 s, (CH3)2C), 1.65 (s, (CH3)2Si);
-1
˜
IR (Nujol Mull, cm ): n = 2921(s), 2852(s), 2725(w), 2031(w),
1461(w), 1376(s), 1312(w), 1250(s), 1153(m), 1083(w), 1019(w),
966(w), 800(w), 722(s). Anal. Calcd. for C56H90Ge2N4O3Si2: C
62.93, H 8.49, N 5.24; Found: C 62.61, H 8.27, N 5.15. Single
crystals suitable for X-ray diffraction analysis were obtained from
re-crystallization at room temperature in ether.
Synthesis of complex [g2(N,N)-Me2Si(DippN)2Pb:]2 (5a). To a
mixture of 2a (0.422 g, 1.00 mmol) and PbCl2 (0.28 g, 1.0 mmol),
n-hexane (30 mL) was added at 0 ◦C via a syringe. After the
solution was stirred for 2 days at room temperature the deep-red
solution was filtered through Celite. The solvent of the filtrate was
concentrated to about 5 mL under reduced pressure and then kept
at -30 ◦C to afford 5a as red crystals (0.52 g, 85.0%). Alternatively,
to a mixture of 1a (0.410 g, 1.00 mmol) and Pb[N(SiMe3)2]2 (0.53
g, 1.0 mmol), ether (20 mL) was added via a syringe. After the
solution was stirred for 18 h at room temperature the volatile
components were removed under reduced pressure. The resulting
residue was extracted with ether (3 ¥ 10 mL). The solvent of the
solution was concentrated to about 5 mL and then kept at ◦-30 ◦C
X-ray structure determination
Suitable single crystals were sealed under argon in thin-walled
glass capillaries. X-ray diffraction data were collected on a
SMART APEX CCD diffractometer (graphite-monochromated
˚
Mo-Ka radiation, j-w-scan technique, l = 0.71073 A). The
intensity data were integrated by means of the SAINT program.20
SADABS21 was used to perform area-detector scaling and absorp-
tion corrections. The structures were solved by direct methods
and were refined against F2 using all reflections with the aid
of the SHELXTL package.22 All non-hydrogen atoms in 3b–
6 were refined anisotropically. Crystallographic parameters for
compounds 3b, 4, 5a, 5b and 6, along with details of the data
collection and refinement, are collected in Table 1.
1
to afford 5a as red crystals (0.51 g, 82.0%). Mp = 148 C. H
NMR (C6D6, 23 ◦C): d = 0.24 (s, 6 H, Si-CH3), 6.65–7.22 (br., 6 H,
Ph), 3.80 (sept, 4 H, Me2CH), 1.21 (d, 24 H, (CH3)2C); 13C{ H}
1
NMR (C6D6, 23 ◦C): d = 121.9 (s. C for [Ph]), 123.4 (s, C for
[Ph]), 142.4 (s, C for [Ph]), 145.4 (s, C for [Ph]), 26.28 (s, (CH3)2C),
-1
˜
9.97 (s, (CH3)2C), 1.03 (s, (CH3)2Si); IR (Nujol Mull, cm ): n =
Acknowledgements
2918(s), 2852(s), 2721(w), 2032(w), 1460(w), 1374(s), 1310(w),
1247(s), 1200(s), 916(s), 842(s), 776(s), 722(s). Anal. Calcd. for
C26H40N2SiPb: C 50.72, H 6.50, N 4.53; Found: C 50.60, H 6.43,
N 4.44. Single crystals suitable for X-ray diffraction analysis were
obtained from re-crystallization at room temperature in ether.
We acknowledge support from the National Natural Science
Foundation of China (NSFC; Grant 20872017) and Shanxi
Normal University.
References
Synthesis of complex [g2(N,N)-Ph2Si(DippN)2Pb:] (5b)
1 (a) Y. Mizuhata, T. Sasamori and N Tokitoh, Chem. Rev., 2009, 109,
3479; (b) P. A. Chase and D. W. Stephan, Angew. Chem., Int. Ed., 2008,
47, 7433; (c) S. Nagendran and H. W. Roesky, Organometallics, 2008,
27, 457; (d) M. F. Lappert and R. S. Rowe, Coord. Chem. Rev., 1990,
100, 267.
2 (a) S.-H. Zhang and C.-W. So, Organometallics, 2011, 30, 2059; (b) N.
Tokitoh and R. Okazaki, Coord. Chem. Rev., 2000, 210, 251; (c) M.
Veith, Angew. Chem., Int. Ed. Engl., 1987, 26, 1.
3 (a) P. Bazinet, G. P. A. Yap and D. Richeson, J. Am. Chem. Soc.,
2001, 123, 11162; (b) A. Jana, H. W. Roesky and C. Schulzke, Dalton
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Organometallics, 2009, 28, 4909; (d) S. S. Sen, D. Kratzert, D. Stern,
H. W. Roesky and D. Stalke, Inorg. Chem., 2010, 49, 5786; (e) S. M. I.
Al-Rafia, A. C. Malcolm, S. K. Liew, M. J. Ferguson and E. Rivard,
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C. Mu¨ck-Lichtenfeld, S. Grimme and F. E. Hahn, J. Am. Chem. Soc.,
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2011, 30, 3353; (h) S. Inoue and M. Driess, Organometallics, 2009, 28,
5032.
4 (a) R. W. Chorley, P. B. Hitchcock, M. F. Lappert, W. Leung, P. P. Power
and M. M. Olmstead, Inorg. Chim. Acta, 1992, 198–200, 203; (b) M. J.
S. Gynane, D. H. Harris, M. F. Lappert, P. P. Power, P. Rivie´re and M.
Rivie´re-Baudet, J. Chem. Soc., Dalton Trans., 1977, 2004.
5 (a) C.-F. Pi, L. Wan, H.-Y. Wu, C.-X. Wang, W. Zheng, L.-H. Weng, Z.-
X. Chen, X.-D. Yang and L.-M. Wu, Organometallics, 2009, 28, 5281;
(b) D.-M. Yang, Y.-Q. Ding, H.-S. Wu and W. Zheng, Inorg. Chem.,
2011, 50, 7698.
To a mixture of 2b (0.546 g, 1.0 mmol) and PbCl2 (0.278 g,
1.0 mmol) in 100 mL Schlenk flask, ether (30 mL) was added via a
syringe. The suspension was stirred at ambient temperature for 48
h, and then filtered through Celite. The filtrate was concentrated
to about 5 mL under reduced pressure to afford 5b as air- and
◦
moisture-sensitive red crystals at -30 C (0.54 g, 80.0 %). Mp =
178 ◦C. 1H NMR (C6D6, 23 ◦C): d = 1.03,1.04 (d, 24 H, (CH3)2C),
1
3.88 (sept, 4 H, Me2CH), 6.81–7.46 (m, 16 H, Ph); 13C{ H} NMR
(C6D6, 23 ◦C): d = 26.3, (s, (CH3)2C), 26.9 (s, (CH3)2C), 122.1,
123.6, 127.0, 128.5, 134.3, 142.4, 145.4, 145.9 (8 s, C for [Ph]); IR
-1
˜
(Nujol Mull, cm ): n = 3080(s), 3028(s), 2948(s), 2850(w), 2023(w),
1944(w), 1467(w), 1371(s), 1210(s), 1105(m), 897(s), 780(s), 674(s).
Anal. Calcd. for C36H44N2PbSi: C 58.43, H 5.99, N 3.79; Found: C
58.31, H 5.81, N 3.69. Single crystals suitable for X-ray diffraction
analysis were obtained from re-crystallization at -30 ◦C in a mixed
solvent of n-hexane and tetrahydrofuran (2 : 1).
Synthesis of complex [g2(N,N)-Me2Si(DippN)2Ge(l-O)]2 (6)
A solution of 3a (0.481 g, 1.00 mmol) in ether (30 mL) was stirred
2 h in the presence of dry oxygen (11.2 mL, 0.5 mmol). The
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