Synthesis and characterization of a germanium bismethanediide complex

Article abstract of DOI:10.1039/b911384c

The reaction of [(PPh₂=S)₂CH₂] (1) with MeLi followed by a salt elimination reaction with GeCl₄ in toluene afforded a novel germanium bismethanediide complex, 2. The structure of compound 2 has been determined b

Full text of DOI:10.1039/b911384c

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Synthesis and characterization of a germanium bismethanediide
complexw
Cechao Foo,a Kai-Chung Lau,b Yi-Fan Yanga and Cheuk-Wai So*a
Received (in Cambridge, UK) 10th June 2009, Accepted 21st September 2009
First published as an Advance Article on the web 8th October 2009
DOI: 10.1039/b911384c
The reaction of [(PPh2QS)2CH2] (1) with MeLi followed by a
salt elimination reaction with GeCl4 in toluene afforded a novel
germanium bismethanediide complex, 2. The structure of
compound 2 has been determined by X-ray crystallography.
The topological analysis of the electron densities of compound
2 was performed.
Scheme 1 Synthesis of 2.
Compounds containing a double bond between carbon and
signal for the carbenic carbon. Similarly, there is no 13C NMR
heavier group 14 elements (4MQCo; M = Si, Ge, Sn) have
attracted much attention in the past 20 years, and have been
the focus of several reviews.1 It was found that the thermal
stability of the MQC bond is intrinsically low, and it can
undergo oligomerization readily. Nevertheless, stable silenes
(4SiQCo),2 germenes (4GeQCo)3 and stannenes
(4SnQCo)4 can be synthesized by incorporating sterically
hindered substituents at both carbon and heavier group 14
elements. In contrast, heavier allene analogues with 4MQCQCo
or 4CQMQCo skeletons are rare.5 Until now, only two
examples of 1-germaallenes have been synthesized by the
reaction of t-BuLi with a fluorogermylalkyne or by the
dechlorination of dichlorogermapropene with t-BuLi.6
On the other hand, 2-germaallene (4CQGeQCo) is still
unknown. Theoretical studies of heavier group 14 allene
analogues showed that 2-germaallene is highly unstable due
to the presence of two reactive GeQC double bonds.7
signal for the carbenic carbon in [(PPh2QS)2CQPd(PPh3)].12
The 31P NMR spectrum at room temperature or at ꢀ60 1C
shows one signal (d 33.7 ppm) which is inconsistent with the
solid-state structure. It is suggested that two thiophosphinoyl
substituents of each ligand could be coordinated with the
germanium center in the solution and the structure should
be similar to that of [(PPh2QS)2CQTmQC(PPh2QS)2]ꢀ.13
The solid-state 31P CP/MAS NMR spectrum displays two
signals (d 4.72, 6.05 ppm) due to two non-equivalent
phosphorus nuclei.
The molecular structure of compound 2 is shown in Fig. 1.14
It consists of two bidentate bis(thiophosphinoyl)methanediide
ligands bound to the germanium center in a spirocyclic
fashion. One of the thiophosphinoyl groups of the ligand remains
uncoordinated. The C(1)–Ge(1) bond distance (1.882(2) A) is
significantly longer than the theoretical calculations for
In this communication, we report the synthesis and
characterization of
a novel germanium bismethanediide
complex, 2, which is regarded as a spirocyclic derivative of
2-germaallene.
The reaction of 1 with two equivalents of MeLi in toluene
followed by addition of 0.5 equivalents of GeCl4 afforded
compound 2 (Scheme 1).8 Other examples consisting of
the 4CQMQCo skeleton derived from a bis(phosphinoyl)-
methanediide ligand are [(PMe2QNSiMe3)2CQZrQC(PMe2Q
NSiMe3)2]9 and Li(THF)4[(PPh2QS)2CQSmQC(PPh2QS)2].10
Compound 2 was isolated as a colorless crystalline solid
which is soluble in CH2Cl2 and THF only. It has been
characterized by NMR spectroscopy and elemental analysis.11
The 1H and 13C NMR spectra display resonances for the
phenyl protons. It is noteworthy that there is no 13C NMR
a Division of Chemistry and Biological Chemistry, School of Physical
and Mathematical Sciences, Nanyang Technological University,
Singapore 637371. E-mail: CWSo@ntu.edu.sg;
Fax: +65 6791 1961; Tel: +65 6513 2730
b Department of Biology and Chemistry, City University of Hong
Kong, Tat Chee Avenue, Kowloon, Hong Kong
w Electronic supplementary information (ESI) available: Selected
theoretical calculation data for 2. CCDC 735370. For ESI and
crystallographic data in CIF or other electronic format, see DOI:
10.1039/b911384c
Fig. 1 Molecular structure of 2. Hydrogen atoms are omitted for
clarity. Selected bond distances (A) and angles (deg): C(1)–Ge(1)
1.882(2), C(1)–P(1) 1.747(2), C(1)–P(2) 1.723(2), P(1)–S(1) 1.964(6),
P(2)–S(2) 2.060(6), Ge(1)–S(2) 2.325(4); C(1)–Ge(1)–C(1A) 142.6(1),
S(2)–Ge(1)–S(2A)
114.1(3),
C(1)–Ge(1)–S(2)
85.3(5),
C(1A)–Ge(1)–S(2) 115.5(5), Ge(1)–C(1)–P(2) 99.0(8), Ge(1)–C(1)–P(1)
131.3(9), P(2)–C(1)–P(1) 128.0(9).
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[H2CQGeQCH2]
GeQC(Bt-Bu)2C(SiMe3)2] (1.827(4) A)3a and [Mes2GeQCR2]
(Mes 2,4,6-trimethylphenyl, CR2 fluorenylidene)
(1.745–1.795
A),7a
[{(Me3Si)2N}2-
Table
1
Theoretical topological features at the BCP of 2,
[H2CQGeQCH2] and [H3C–GeH2–CH3]a
=
=
2
Bond
r
r r
H
G
7V7
(1.803 A),3b but it is shorter than that of bisgermavinylidene
[(PPh2QNSiMe3)2CQGe:]2 (1.908(7), 1.905(8) A) due to the
higher oxidation state of the germanium atom in 2.15
This demonstrates some double bond character in the
C(1)–Ge–C(1A) skeleton. The differences in the P–S and
C–P bond distances in 2 suggest the delocalization of
p-electrons resulted from the conjugation of PQS and CQGe
double bonds, which lengthens the CQGe double bond
distance. The C(1)–Ge(1)–C(1A) angle (142.6(1)1) is smaller
than the theoretical studies of [H2CQGeQCH2] (153–1731) as
two thiophosphinoyl substituents coordinate to Ge(1) at a
distance of 2.325(4) A.7 The sum of the angles at C(1) in 2 is
358.31 which is in good agreement with that of
[H2CQGeQCH2] (355.4–3601). The C(1)–P(1) (1.747(2) A)
and C(1)–P(2) (1.723(2) A) bonds in 2 are longer than
those in [(PPh2QS)2CQZrCp2] (1.670(2), 1.666(2) A),16
[(PPh2QS)2CQTm(THF)2(m-I)]2 (1.661(5), 1.653(5) A)13 and
[(PPh2QS)2CQPd(PPh3)] (1.689(2), 1.690(2) A)12 which
result from the negative hyperconjugation from carbon to
phosphorus s* orbitals.
2
Ge(1)–C(1)
C(1)–P(2)
P(2)–S(2)
Ge(1)–S(1)
C(1)–P(1)
[H2CQGeQCH2]
Ge–C
0.9
3.10
ꢀ0.52
ꢀ1.22
ꢀ0.60
ꢀ0.20
ꢀ1.11
0.74
1.16
0.24
0.29
1.11
1.26
2.38
0.84
0.49
2.21
1.21
0.93
0.51
1.14
ꢀ0.77
ꢀ5.25
1.28
ꢀ0.04
1.10
5.24
ꢀ0.70
ꢀ0.47
1.06
0.67
1.76
1.14
[H3C–GeH2–CH3]
Ge–C
0.84
2.85
a
2
Units: r: e Aꢀ3; r r: e Aꢀ5; H, G, 7V7: hartree Aꢀ3
.
The topological analysis of the electron densities of
compound 2, [H2CQGeQCH2] and [H3C–GeH2–CH3]
according to Bader’s quantum theory of atoms in molecules
(QTAIM) was performed.21 The Laplacian of electron density
2
r r and the total energy density H at the (3,ꢀ1) bond critical
Compound 2 was investigated by means of quantum
chemical calculations. The molecule was first fully optimized
with the DFT-variant B3LYP17 as implemented in the
Gaussian 03 program18 using the 6-31+G(d) basis set.19
The calculated structural parameters (Ge(1)–S(2): 2.379 A,
Ge(1)–C(1): 1.888 A, Ge(1)–P(2): 2.789 A, P(2)–S(2): 2.095 A,
C(1)–P(1): 1.749 A; C(1)–Ge(1)–C(1A): 142.01) are in good
agreement with the crystallographic data. The natural-
bond-orbital (NBO) analysis20 (Table S1, see ESIw) shows
that the Ge(1)–C(1) bond is formed by sp1.85 hybrids on the
germanium atom and sp2.22 hybrids on the carbon atom, with
the carbon atom contributing 71.8% of the electron density.
For simplification, 2A (Fig. 2) is applied as a model for the
theoretical calculations of compound 2. The calculated structural
parameters of optimized 2A (Ge–S: 2.371 A, Ge–C: 1.877 A,
Ge–P: 2.760 A, P–S: 2.094 A, C–P: 1.727 A; C–Ge–C: 133.61)
are also comparable with the crystallographic data of 2. When
the C–Ge–C angle is 180.01 and the P, C, S and Ge atoms are
constrained on the same plane, the resulting structure is more
unstable by 43.1 kJ/mol than 2A. When both sulfur donors are
not coordinated with the germanium atom, the optimized
structure 2B (Ge–C: 1.789 A, P–S: 1.959 A, C–P: 1.825 A;
C–Ge–C: 153.91) is higher in energy than 2A by 218.8 kJ/mol.
It is noteworthy that the Ge–C bond (1.789 A) in 2B is similar
to that in [H2CQGeQCH2] (1.745–1.795 A). The coordination
of the sulfur donors with the germanium atom in 2A leads to
the delocalization of p-electrons, which lengthens the GeQC
double bond distance (1.877 A).
2
Fig.
3
r r in the GeCH planes in (a) CH3–GeH2–CH3 and
2
(b) CH2QGeQCH2; (c) r r in the GeCS plane of compound 2.
2
Green lines indicate negative values in r r, black lines stand for
Fig. 2 Simple derivative of 2.
positive values.
ꢁc
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Chem. Commun., 2009, 6816–6818 | 6817

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point (BCP) show that the Ge–C bonds in compound 2,
[H2CQGeQCH2] and [H3C–GeH2–CH3] are polar and
covalent (Table 1). The bond nature of the Ge–C bonds in
compound 2 is in-between that of GeQC in [H2CQGeQCH2]
and that of Ge–C in [H3C–GeH2–CH3]. As there may be
substantive p-electron delocalization along the Ge–C bonds
in compound 2, it is unsurprising to find that the Ge–C bonds
in compound 2 may have little double bond character compared
with the GeQC bond in [H2CQGeQCH2]. Fig. 3(a)–(c)
depict the Laplacian distributions in the GeCH planes of
[CH3–GeH2–CH3] and [CH2QGeQCH2] and in the GeCS
plane of compound 2, respectively. It reveals that the bonding
nature of the GeQC bond in [CH2QGeQCH2] and in
compound 2 are similar.
5 For
a
Organometallics, 2007, 26, 1542.
review, see: J. Escudie
´
and H. Ranaivonjatovo,
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Chem. Lett., 1998, 811.
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(b) M. Alam Sk, H.-W. Xi and K. H. Lim, Organometallics,
2009, 28, 3678.
8 Methyllithium (2.05 mL, 1.6 M in diethyl ether, 3.28 mmol) was
added to a solution of 1 (0.699 g, 1.56 mmol) in toluene (10 mL) at
ꢀ78 1C. The resulting mixture was warmed to room temperature
and stirred for 3 h. GeCl4 (0.089 mL, 0.780 mmol) was added
dropwise to the reaction mixture at ꢀ78 1C. The resulting white
suspension was warmed to room temperature and stirred
overnight. Volatiles in the mixture were removed under reduced
pressure and the residue was extracted with CH2Cl2. The solution
was filtered off. CH2Cl2 was removed under reduced pressure
and the residue was extracted with THF. After filtration and
concentration of the filtrate, 2 was obtained as colorless crystals.
Yield: 1.07g (71%).
In conclusion, the first example of
a germanium
bismethanediide compound, 2, has been synthesized successfully
by the reaction of 1 with two equivalents of MeLi in toluene,
followed by reaction with 0.5 equivalents of GeCl4. X-Ray
crystallography shows that the Ge–C bonds in compound 2
have double bond character. DFT calculations show that the
coordination of the sulfur donors with the germanium atom in 2
leads to the delocalization of p-electrons, which lengthens the
GeQC double bond distance. Topological analysis of the electron
densities shows that the Ge–C bonds in 2 are polar and covalent
and their bond nature is between a single and double bond.
This work is supported by the Ministry of Education,
Singapore (AcRF Tier 1, RG 47/08) and by a Strategic
Research Grant from City University of Hong Kong
(Project No. 7002285).
9 K. Aparna, R. P. Kamalesh Babu, R. McDonald and R. G. Cavell,
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´
10 T. Cantat, F. Jaroschik, F. Nief, L. Ricard, N. Mezailles and
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11 Mp 245 1C. Elemental analysis found (%): C 62.06; H 4.07. Calcd.
for C50H40GeP4S4: C 62.19; H 4.18. 1H NMR (d8-THF, 25 1C):
d = 7.15–7.20 (m, 7H, Ph), 7.33–7.37 (m, 5H, Ph), 7.66–7.71 ppm
(m, 8H, Ph). 13C{1H} NMR (d8-THF, 25 1C): d = 128.6, 128.7,
128.8, 131.8, 133.2, 133.3, 133.4, 135.3, 136.2 ppm (Ph). 31P{1H}
NMR (d8-THF, 25 1C): d = 33.7 ppm. 31P CP/MAS NMR
(25 1C): d = 4.72 (br s), 6.05 ppm (br s).
´
12 T. Cantat, N. Mezailles, L. Ricard, Y. Jean and P. Le Floch,
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14 Crystal data for 2ꢂ(THF)2: [C58H56GeO2P4S4], M = 1109.74,
orthorhombic, space group Pccn, 23.5445(9),
11.4051(5), c = 19.7011(7) A, a = 90, b = 90, g = 901, V =
´
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a
=
b =
Notes and references
5290.3(4) A3, Z = 4, T = 173(2) K, Dc = 1.393 Mg mꢀ3
,
m = 0.901 mmꢀ1, 74 919 measured reflections, 10 186 independent
reflections, 358 refined parameters, R1 = 0.0379, wR2 = 0.0978
(I 4 2s(I)). CCDC 735370.
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6818 | Chem. Commun., 2009, 6816–6818