A base-stabilized 2-silaallene

Article abstract of DOI:10.1021/om301175p

The reaction of [CH₂(PPh₂S)₂] (1) with 2 equiv of MeLi in Et₂O followed by addition of 0.5 equiv of SiCl ₄ afforded the base-stabilized 2-silaallene [(PPh₂S) ₂CSiC(PPh₂S)₂] (2). It has been characterized by X-ray crystallography, NMR spectroscopy, and theoretical studies. The results show that compound 2 comprises a C-Si²⁺-C ylidic skeleton with a negative charge at the C _methanediide atoms and two positive charges at the Si atom. The reaction of 2 with excess PrⁱNCNPrⁱ in refluxing toluene gave the thiophosphinoyl-stabilized silene [(PPh₂S)₂C ^- - Si⁺(NPrⁱ)₂CC(PPh ₂S)₂] (3).

Full text of DOI:10.1021/om301175p

Note
pubs.acs.org/Organometallics
A Base-Stabilized 2‑Silaallene
Yi-Fan Yang,† Cechao Foo,† Hong-Wei Xi,‡ Yongxin Li,† Kok Hwa Lim,‡ and Cheuk-Wai So*,†
†Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University,
637371 Singapore
‡Division of Chemical and Biomolecular Engineering, School of Chemical and Biomedical Engineering, Nanyang Technological
University, 637459 Singapore
S
* Supporting Information
ABSTRACT: The reaction of [CH2(PPh2S)2] (1) with 2
equiv of MeLi in Et2O followed by addition of 0.5 equiv of
SiCl4 afforded the base-stabilized 2-silaallene [(PPh2S)2CSiC-
(PPh2S)2] (2). It has been characterized by X-ray crystallog-
raphy, NMR spectroscopy, and theoretical studies. The results
show that compound 2 comprises a C¯−Si2+−C¯ ylidic skeleton with a negative charge at the Cmethanediide atoms and two positive
charges at the Si atom. The reaction of 2 with excess PriNCNPri in refluxing toluene gave the thiophosphinoyl-stabilized
silene [(PPh2S)2C−Si+(NPri)2CC(PPh2S)2] (3).
n the past two decades, the concepts of thermodynamic
stabilized 2-silaallene [(PPh2S)2CSiC(PPh2S)2]. Its reactivity
Iand/or kinetic stabilization have been applied successfully in toward PriNCNPri is also described.
the isolation of stable multiple bonded group 14 compounds.
One of the well-studied examples is a compound containing a
double bond between carbon and heavier group 14 elements.
RESULTS AND DISCUSSION
■
For example, stable silenes (>SiC<),1 germenes (>Ge
C<),2 and stannenes (>SnC<)3 were isolated by incorporat-
ing sterically hindered substituents at both carbon and heavier
group 14 elements. They have been the focus of several reviews
in the past 20 years.4,11 Moreover, 1-silaallenes and 1-
germaallenes of the composition R2ECCR′2 (R, R′ =
supporting ligand, E = Si, Ge), which contain an EC double
The reaction of [CH2(PPh2S)2] (1) with 2 equiv of MeLi in
Et2O followed by addition of 0.5 equiv of SiCl4 afforded
[(PPh2S)2CSiC(PPh2S)2] (2; Scheme 1). Compound 2 was
isolated as a colorless crystalline solid in 71% yield, which is
soluble only in CH2Cl2, THF, and DME. It has been
1
characterized by NMR spectroscopic analysis. The H and
13C NMR spectra display resonances for the phenyl protons.
The 13C NMR spectrum shows a triplet at δ 42.3 ppm (1JP−C
=
bond, have also been investigated.5 Furthermore, Escudie
́
et al.
67.1 Hz) for the Cmethanediide atoms. The result is in contrast to
the 13C NMR spectra of the heavier analogues [(PPh2S)2C
MC(PPh2S)2] (M = Ge, Sn), in which no signal was
observed for the Cmethanediide atoms.9,10 In addition, the 31P
NMR spectrum at room temperature shows one signal at δ 27.8
ppm, which is comparable with those of [(PPh2S)2CSn
C(PPh2S)2] (δ 28.1 ppm)9 and [(PPh2S)2CGeC-
(PPh2S)2] (δ 33.7 ppm).10 However, the 31P NMR spectrum
is inconsistent with the solid-state structure. In this regard, 31P
NMR spectroscopy was performed at −100 °C, which shows
two singlets at δ 20.6 and 29.4 ppm for two nonequivalent P
nuclei. The results indicate that the thiophosphinoyl sub-
stituents are fluxional in solution at room temperature.
Furthermore, the 29Si NMR spectrum at room temperature
displays a quintet at δ −28.9 ppm (2JSi−P = 7.6 Hz), which
shows an upfield shift in comparison with those of the 1-
silaallenes (δ 13.1−58.6 ppm).5b The results indicate that the
Si−C bonds in compound 2 do not have multiple-bond
character, which has also been confirmed by X-ray crystallog-
raphy and theoretical studies (see below). The 29Si NMR
reported the synthesis and reactivity of stable allene analogues
which contain heavier group 14 and 15 elements at the 1,3-
positions of the skeleton.6 It is noteworthy that the heavier
group 14 elements in these aforementioned examples are at the
1-position of an allene skeleton, which is protected kinetically
by two sterically hindered substituents. When a heavier group
14 element is incorporated at the 2-position of an allene, which
is known as a 2-metallaallene, theoretical studies show that it is
highly unstable due to the presence of two reactive EC
double bonds.7 Moreover, decreased kinetic stabilization at the
heavier group 14 element will lead to oligomerization easily.
Recently, several research groups reported that 2-metallaallenes
containing transition metals, lanthanides, and actinides can be
derived from bis(thiophosphinoyl)- and bis-
(iminophosphoranyl)methanediide ligands.8 Hence, we utilized
this strategy to synthesize the base-stabilized 2-germaallene
derivative [(PPh2S)2CGeC(PPh2S)2], in which the C
GeC skeleton is stabilized by sterically hindered substituents
at the carbon atoms and two donor moieties at the germanium
atom.9 Very recently, the heavier congener [(PPh2S)2CSn
C(PPh2S)2] was reported and structurally characterized.10 In
contrast, a 2-silaallene derivative is still unknown. In this paper,
we report the synthesis and theoretical studies of the base-
Received: December 4, 2012
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om301175p | Organometallics XXXX, XXX, XXX−XXX

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Note
Scheme 1. Synthesis of 2 and 3
spectrum at −100 °C shows a multiplet at δ −25.1 ppm due to
coupling to two nonequivalent P environments that are also
evidenced from the low-temperature 31P NMR spectrum.
Compound 2 has been characterized by X-ray crystallog-
raphy (Figure 1). There are two independent molecules in the
shortened and the P−S bonds (1.967(5)−2.085(8) Å) are
lengthened in comparison with those in [CH2(PPh2S)2] (C−P
= 1.827(3), 1.831(3) Å; P−S = 1.941(1), 1.948(1) Å).12
To understand the bonding nature in compound 2, it was
investigated by means of quantum chemical calculations.13 The
optimized geometry (UB3PW91/6-31+G(d) level; Figure S1,
Supporting Information) is in good agreement with the X-ray
crystallographic data. The HOMO (Figure S2, Supporting
Information) comprises a lone pair orbital on the Cmethanediide
and sulfur atoms. In addition, the natural bond orbital14 analysis
of the Lewis structure of compound 2 (Table S2, Supporting
Information) shows that the Si(1)−Cmethanediide bonds comprise
a lone pair orbital (LP) on each Cmethanediide atom and a Si−C
occupied σ orbital. The LPs at the Cmethanediide atoms are p
orbitals, which are stabilized by forming p−σ* negative
hyperconjugation with the σ*(P−CPh) and σ*(Si−S) orbitals
(stabilizing energy: for LP(C(1)), 52.9 kcal mol−1; for
LP(C(2)), 57.8 kcal mol−1). The negative hyperconjugation
leads to shorter P−Cmethanediide bonds. The Si(1)−Cmethanediide
bonds are highly polarized toward the Cmethanediide atoms (75.3%
polarization). Moreover, the Wiberg bond index (WBI)15
shows that the Si(1)−Cmethanediide bonds are single bonds (WBI:
0.80, 0.81). Furthermore, the NPA charges of the Cmethanediide
atoms are −1.68 and −1.66, while that of the Si(1) atom is 1.53
(Table S3, Supporting Information). The results show that
compound 2 comprises a C¯−Si2+−C¯ ylidic skeleton with a
negative charge at the Cmethanediide atoms and two positive
charges at the Si atom.
Figure 1. ORTEP drawing of compound 2 (50% thermal ellipsoids).
One of two independent molecules in the asymmetric unit is shown.
Disordered 2 atoms, hydrogen atoms, and DME molecules are omitted
for clarity. Selected bond lengths (Å) and angles (deg): Si(1)−C(1) =
1.810(8), Si(1)−C(2) = 1.810(9), Si(1)−S(1) = 2.204(8), Si(1)−S(3)
= 2.178(8), C(1)−P(1) = 1.726(11), C(1)−P(2) = 1.750(8), P(1)−
S(1) = 2.076(10), P(2)−S(2) = 1.972(5), C(2)−P(3) = 1.723(9),
C(2)−P(4) = 1.754(9), P(3)−S(3) = 2.085(8), P(4)−S(4) =
1.967(5); C(1)−Si(1)−C(2) = 134.9(8), C(1)−Si(1)−S(1) =
89.0(5), C(1)−Si(1)−S(3) = 117.4(7), C(2)−Si(1)−S(1) =
115.3(7), C(2)−Si(1)−S(3) = 89.6(4), P(1)−C(1)−P(2) =
123.6(6), P(1)−C(1)−Si(1) = 98.1(5), P(2)−C(1)−Si(1) =
137.8(7), P(3)−C(2)−P(4) = 121.8(6), P(3)−C(2)−Si(1) =
97.7(5), P(4)−C(2)−Si(1) = 137.6(6).
In addition, the WBI shows that the P−C and P−S bonds are
single bonds (WBI: P−C, 0.90−1.08; P−S, 0.96−1.33).
Together with the NPA charges of the Cmethanediide, P(1−4),
and S(1−4) atoms (Table S3), the bis(thiophosphinoyl)-
methanediide ligands are best described as the resonance
structure A (Scheme 2). Accordingly, the S(1) and S(3) atoms
Scheme 2. Resonance Structure A of the Methanediide
Ligand
asymmetric unit with slightly different bond lengths and angles.
The molecules are disordered because the crystal selected for
analysis was a twin crystal. The disorder was treated with the
appropriate restraints and constraints (see the Supporting
Information). Moreover, only one independent molecule is
discussed here for clarity. It consists of two bidentate
bis(thiophosphinoyl)methanediide ligands bound to the silicon
center in a spirocyclic fashion. One thiophosphinoyl group of
each ligand is uncoordinated. The Cmethanediide atoms (sum of
bond angles: 357.1, 359.5°) and Si(1) atom adopt a trigonal-
planar and tetrahedral geometry, respectively. The C(1)−Si(1)
and C(2)−Si(1) bond lengths (average 1.810 Å) are
comparable with normal C−Si single-bond lengths (1.87−
1.91 Å).11 The P−C bonds (1.723(9)−1.754(9) Å) are
donate one of the LPs to the Si(1) atom. As a result, there are
two LPs remaining on the S(1,3) atoms (sp0.47, p) and three
LPs remaining on the S(2,4) atoms (sp0.20, p, p, Table S2).
The reactivity of 2 was studied. Treatment of 2 with excess
PriNCNPri in refluxing toluene afforded the base-
stabilized silene [(PPh2S)2C−Si+(NPri)2CC(PPh2S)2]
(3). The reaction appears to proceed through an insertion
reaction of the C−Si2+ bond with the NC bond of PriN
CNPri to form intermediate B (Scheme 3). The Cmethanide−Si
B
dx.doi.org/10.1021/om301175p | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Note
Scheme 3. Proposed Mechanism for the Formation of 3
bond is then cleaved and the CN bond attacks the silicon
center to form 3.
Compound 3 was isolated as a colorless crystalline solid in
23% yield. It has been characterized by NMR spectroscopy.
1
The H and 13C NMR spectra display resonances for the
isopropyl and phenyl protons. The 13C NMR spectrum also
shows a triplet at δ 173.6 ppm for the NCN atom, but no
signals were observed for the PCP atoms. In addition, the 31P
NMR spectrum at room temperature exhibits two sharp singlets
(δ 27.0, 40.5 ppm) for the P nuclei, while that at −100 °C
shows one broad signal (δ 26.6 ppm) and one singlet (δ 39.8
ppm). The results indicate that the thiophosphinoyl sub-
stituents at the Cmethanediide atom are still fluxional in solution at
low temperature. Moreover, the 29Si NMR spectra at room
temperature (δ −30.7 ppm) and at −100 °C (δ −29.9 ppm)
display a triplet, which indicate the fluxional behavior of the
thiophosphinoyl substituents at the Cmethanediide atom. The
signals are shifted upfield in comparison with that of the amine-
stabilized silenes (δ 33.4−39.4 ppm) and the oxophosphine-
stabilized silene (δ −18.7 ppm).16
The results of the X-ray crystallographic data confirm that
compound 3 is a thiophosphinoyl-stabilized silene comprising a
four-coordinate silicon atom (Figure 2). The C(1)P(1)S(1)-
Si(1) least-squares plane is orthogonal to the Si(1)N(1)C(32)-
N(2) least-squares plane. The C(1)−Si(1) bond (1.788(4) Å)
is comparable with those in 2 and amine-stabilized silenes such
as [{2,6-(CH2NMe2)2C6H3}PhSiC(SiMe3)2] (1.744(2) Å)17
and [(Me2EtN)Me2SiC(SiMe2Ph)2] (1.761(4) Å).18 The
Si(1)−N bonds (1.753(3), 1.752(3) Å) are similar to the Si−
Namide bonds in [SiCl2{N(But)C(Ph)C(Ph)N(But)}] (average
1.701 Å).19 The C(32)−C(33) bond (1.388(5) Å) is a typical
CC double bond. The C(33)−P bonds are lengthened and
the P(4)−S(4) and P(3)−S(3) bonds are shortened in
comparison with the C(1)−P, P(1)−S(1), and P(2)−S(2)
bonds, respectively.
Figure 2. ORTEP drawing of compound 3 (50% thermal ellipsoids).
Disordered Pri and Ph substituents, CH2Cl2 molecules, and hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Si(1)−S(1) = 2.1961(13), Si(1)−C(1) = 1.788(4), Si(1)−
N(1) = 1.735(3), Si(1)−N(2) = 1.752(3), C(1)−P(1) = 1.725(4),
C(1)−P(2) = 1.751(4), P(1)−S(1) = 2.0722(13), P(2)−S(2) =
1.9612(15), C(32)−N(2) = 1.392(4), C(32)−N(1) = 1.400(4),
C(32)−C(33) = 1.388(5), C(33)−P(3) = 1.799(4), C(33)−P(4) =
1.818(4), P(3)−S(3) = 1.9674(13), P(4)−S(4) = 1.9643(17); C(1)−
Si(1)−S(1) = 89.91(13), C(1)−Si(1)−N(1) = 130.64(16), C(1)−
Si(1)−N(2) = 134.44(16), N(1)−Si(1)−N(2) = 76.23(14), P(1)−
C(1)−P(2) = 137.2(2), P(1)−C(1)−Si(1) = 97.60(18), P(2)−C(1)−
Si(1) = 125.0(2), P(3)−C(33)−C(32) = 123.2(3), P(4)−C(33)−
C(32) = 119.4(3), P(3)−C(33)−P(4) = 117.14(19).
Biological Chemistry, Nanyang Technological University. Melting
points were measured in sealed glass tubes and were not corrected.
Synthesis of 2. Methyllithium (1.3 mL, 1.6 M in Et2O, 2.1 mmol)
was added to a solution of 1 (0.45 g, 1.0 mmol) in Et2O (10 mL) at
−78 °C. The resulting mixture was warmed to room temperature and
stirred for 3 h. SiCl4 (0.5 mL, 1.0 M in toluene, 0.5 mmol) was added
dropwise to the reaction mixture at −78 °C. The resulting yellow
solution was warmed to room temperature and stirred overnight to
form a white suspension. Volatiles in the reaction mixture were
removed under reduced pressure, and the residue was extracted with
DME. After filtration and concentration of the filtrate, 2 was afforded
as colorless crystals. Yield: 0.35 g (71%). Mp: 245 °C. Anal. Calcd for
In conclusion, the base-stabilized 2-silaallene
[(PPh2S)2CSiC(PPh2S)2] (2) was synthesized by a simple
procedure. X-ray structural, spectroscopic, and theoretical
studies show conclusively that compound 2 has a C¯−Si2+−C¯
ylidic skeleton. The formation of the base-stabilized silene
[(PPh2S)2C−Si+(NPri)2CC(PPh2S)2] (3) by the reaction
of 2 with excess PriNCNPri is consistent with the presence
of the ylidic skeleton in 2.
1
C50H40P4S4Si: C, 65.21; H, 4.38. Found: C, 64.87; H, 4.13. H NMR
(399.5 MHz, C6D6, 23 °C): δ 6.85−6.90 (m, 16H, Ph), 6.95−6.98 (m,
8H, Ph), 7.94−7.99 ppm (m, 16H, Ph). 13C{1H} NMR (100.5 MHz,
C6D6, 23 °C): δ 42.33 (t, JP−C = 67.1 Hz, PCP), 128.16 (s, Cmeta of
Ph), 131.08 (s, Cpara of Ph), 132.98 (d, 2JP−C = 11.5 Hz, Cortho of Ph),
135.2 (d, JP−C = 85.3 Hz, Cipso of Ph). 31P{1H} NMR (161.7 MHz,
C6D6, 23 °C): δ 27.83 ppm. 29Si{1H} NMR (79.4 MHz, CDCl3, 23
EXPERIMENTAL SECTION
■
All manipulations were carried out under an inert atmosphere of
nitrogen gas using standard Schlenk techniques. Et2O and DME were
dried over and distilled over Na/K alloy prior to use. CH2Cl2 was
dried over and distilled over CaH2 prior to use. 1 was prepared as
2
°C): δ −28.87 ppm (quintet, JSi−P = 7.6 Hz). 31P{1H} NMR (161.7
MHz, C6D6, −100 °C): δ 20.61, 29.43 ppm. 29Si{1H} NMR (79.4
MHz, CDCl3, −100 °C): δ −25.10 (m) ppm.
described in the literature.20 The H, 13C, 31P, and 29Si NMR spectra
1
were recorded on a JEOL ECA 400 spectrometer. The chemical shifts
Synthesis of 3. Toluene (15 mL) was added to a mixture of
PriNCNPri (0.13 g, 1.0 mmol) and 2 (0.48 g, 0.5 mmol) at room
temperature. The resulting mixture was refluxed at 140 °C overnight
1
δ are relative to SiMe4 for H, 13C, and 29Si and 85% H3PO4 for 31P.
Elemental analyses were performed by the Division of Chemistry and
C
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Organometallics
Note
to form a yellow solution. Volatiles in the reaction mixture were
removed under reduced pressure, and the residue was extracted with
CH2Cl2/Et2O (1/1). After filtration and concentration of the filtrate, 3
was obtained as colorless crystals. Yield: 0.14 g (23%). Mp: 229 °C
dec. Anal. Calcd for C57H54N2P4S4Si: C, 65.38; H, 5.20; N, 2.68.
1998, 178−180, 565. (c) Chaubon, M. A.; Ranaivonjatovo, H.;
Escudie, J.; Satge, J. Main Group Met. Chem. 1996, 19, 145. (d) Baines,
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K. M.; Stibbs, W. G. Adv. Organomet. Chem. 1996, 39, 275. (e) Barrau,
J.; Escudie, J.; Satge, J. Chem. Rev. 1990, 90, 283. (f) Lee, V. Y.;
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Sekiguchi, A. Organometallics 2004, 23, 2822.
1
Found: C, 65.12; H, 5.15; N, 2.55. H NMR (399.5 MHz, CDCl3, 23
(5) (a) Miracle, G. E.; Ball, J. L.; Powell, D. R.; West, R. J. Am. Chem.
Soc. 1993, 115, 11598. (b) Eichler, B. E.; Miracle, G. E.; Powell, D. R.;
West, R. Main Group Met. Chem. 1999, 22, 147. (c) Trommer, M.;
Miracle, G. E.; Eichler, B. E.; Powell, D. R.; West, R. Organometallics
1997, 16, 5737. (d) Spirk, S.; Belaj, F.; Albering, J. H.; Pietschnig, R.
Organometallics 2010, 29, 2981. (e) Tokitoh, N.; Kishikawa, K.;
Okazaki, R. Chem. Lett. 1998, 811. (f) Eichler, B. E.; Powell, D. R.;
West, R. Organometallics 1998, 17, 2147. (g) Tokitoh, N.; Kishikawa,
K.; Okazaki, R. Phosphorus, Sulfur Silicon Relat. Elem. 1999, 150−151,
°C): δ 1.06 (d, 3JH−H = 6.0 Hz, 12H, CH(CH3)2), 5.14 (sept, 3JH−H
=
6.4 Hz, 2H, CH(CH3)2), 7.29−7.39 (m, 20H, Ph), 7.48−7.51 (m, 4H,
Ph), 7.61−7.66 (m, 8H, Ph), 8.03−8.08 ppm (m, 8H, Ph). 13C{1H}
NMR (100.5 MHz, CDCl3, 23 °C): δ 23.44 (s, CH(CH3)2), 47.52 (s,
3
3
CH(CH3)2), 127.61 (d, JP−C = 6.7 Hz, Cmeta of Ph), 128.47 (d, JP−C
= 13.3 Hz, Cmeta of Ph), 130.51 (s, Cpara of Ph), 131.91 (s, Cpara of Ph),
132.36−133.29 (m, Cortho and Cipso of Ph), 173.56 ppm (t, 2JP−C = 4.29
Hz, NCN). 31P{1H} NMR (161.7 MHz, CDCl3, 23 °C): δ 26.96,
40.45 ppm. 29Si{1H} NMR (79.4 MHz, CDCl3, 23 °C): −30.65 ppm
137. For a recent review, see: (h) Escudie,
Organometallics 2007, 26, 1542.
(6) (a) Couret, C.; Satge, J.; Escudie,
́
J.; Ranaivonjatovo, H.
2
(t, JSi−P = 7.5 Hz). 31P{1H} NMR (161.7 MHz, C6D6, −100 °C): δ
26.56 (br s), 39.76 (s) ppm. 29Si{1H} NMR (79.4 MHz, CDCl3, −100
°C): δ −29.90 ppm (t).
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X-ray Data Collection and Structural Refinement. Intensity
data for compounds 2 and 3 were collected using a Bruker APEX II
diffractometer. The crystals of 2 and 3 were measured at 103(2) K.
The structures were solved by a direct phase determination (SHELXS-
97) and refined for all data by full-matrix least-squares methods on
F2.21 All non-hydrogen atoms were subjected to anisotropic refine-
ment. The hydrogen atoms were generated geometrically and allowed
to ride on their respective parent atoms; they were assigned
appropriate isotopic thermal parameters and included in the
structure-factor calculations. The X-ray crystallographic data of 2
and 3 are summarized in Table S1 (see the Supporting Information).
́
́
́
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Miqueu, K.; Matioszek, D.; Ladeira, S.; Saffon-Merceron, N.
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ASSOCIATED CONTENT
* Supporting Information
A table giving crystallographic data for 2 and 3, figures and
tables giving selected calculation results for 2, and CIF files
giving X-ray data for 2 and 3. This material is available free of
charge via the Internet at http://pubs.acs.org.
■
Nief, F.; Ricard, L.; Mez
5178. (c) Cantat, T.; Jaroschik, F.; Ricard, L.; Le Floch, P.; Nief, F.;
Mezailles, N. Organometallics 2006, 25, 1329. (d) Tourneux, J.-C.;
Berthet, J.-C.; Thuery, P.; Mezailles, N.; Le Floch, P.; Ephritikhine, M.
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ailles, N.; Le Floch, P. Chem. Commun. 2005,
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Dalton Trans. 2010, 39, 2494. (e) Cooper, O. J.; McMaster, J.; Lewis,
W.; Blake, A. J.; Liddle, S. T. Dalton Trans. 2010, 39, 5074.
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(f) Tourneux, J.-C.; Berthet, J.-C.; Cantat, T.; Thuery, P.; Mezailles,
AUTHOR INFORMATION
Corresponding Author
*E-mail for C.-W.S.: CWSo@ntu.edu.sg.
Notes
N.; Le Floch, P.; Ephritikhine, M. Organometallics 2011, 30, 2957.
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(10) Leung, W.-P.; Chan, Y.-C.; Mak, T. C. W. Inorg. Chem. 2011, 50,
10517.
The authors declare no competing financial interest.
(11) Lee, V. Y.; Sekiguchi, A. Organometallic Compounds of Low-
Coordinated Si, Ge, Sn, and Pb: From Phantom Species to Stable
Compounds; Wiley: Chichester, U.K., 2010; p 248.
(12) Carmalt, C. J.; Cowley, A. H.; Decken, A.; Lawson, Y. G.;
Norman, N. C. Acta Crystallogr. 1996, C52, 931.
(13) For details of the theoretical studies and references, see the
Supporting Information.
(14) Weinhold, F.; Landis, C. R. In Valency and Bonding: A Natural
Bond Orbital Donor-Acceptor Perspective; Cambridge University Press:
Cambridge, U.K., 2005.
ACKNOWLEDGMENTS
This work was supported by the Academic Research Fund Tier
1 (RG 57/11).
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dx.doi.org/10.1021/om301175p | Organometallics XXXX, XXX, XXX−XXX