Synthesis and properties of the alkyl/aryl germanium dioximates containing Ge-O bond: Stability factors-A theoretical approach

Article abstract of DOI:10.1002/hc.21048

The reactions of R₂GeCl₂ and R₃GeCl with 9,10-phenanthrenequinone dioxime in 1:1 and 1:2 molar ratios to form a series of organogermanium complexes of the general formula R₂GeL and (R ₃Ge)₂

Full text of DOI:10.1002/hc.21048

Heteroatom Chemistry
Volume 23, Number 6, 2012
Synthesis and Properties of the Alkyl/Aryl
Germanium Dioximates Containing Ge O
Bond: Stability Factors–A Theoretical Approach
Raji Thomas,1 Nelson Joseph P.,1 Pushpa Pardasani,1
and T. Mukherjee2
1Department of Chemistry, University of Rajasthan, Jaipur 302 055, India
2Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
Received 16 June 2012; revised 12 August 2012
much explored and merited a detailed investigation.
ABSTRACT: The reactions of R2GeCl2 and R3GeCl
The organometallic and coordination chemistries
with 9,10-phenanthrenequinone dioxime in 1:1 and
of oximes constitute an active area of research, in
1:2 molar ratios to form a series of organogermanium
which the oxime function (>C N O ) acts as a
complexes of the general formula R2GeL and (R3Ge)2L
binucleating bridging unit to yield homo- and het-
[R=Me, Et, Ph] have been investigated. The physical
erometallic complexes [8–11], which can be poten-
and spectral properties of all derivatives are described.
tially useful for the development of new materi-
In addition, the nature of Ge O bond has been studied
als. Thus, in continuation to our interest in metal
ꢀC
by using the DFT/B3LYP method. 2012 Wiley Pe-
chelates of group IV elements [12–14], we have syn-
thesized a series of tetravalent germanium deriva-
tives and examined the nature of Ge O bond by
using the DFT/B3LYP method. The results are pre-
sented herein.
riodicals, Inc. Heteroatom Chem 23:545–550, 2012;
View this article online at wileyonlinelibrary.com.
DOI 10.1002/hc.21048
INTRODUCTION
RESULTS AND DISCUSSION
In the past two decades, the chemistry of diva-
lent derivatives of germanium has developed into
an active area of research [1–4]. Organogermanium
compounds have many applications in the field of
medicines [5,6], optics, and so on. Germanium com-
pounds are also very attractive as potential precur-
sors for obtaining the films by Metal Organic Chem-
ical Vapor Deposition processes [7]. However, to
the best of our knowledge, tetravalent germanium
complexes containing Ge O bonds have not been
The selected ligand, 9,10-phenanthrenequinone
dioxime (H2L), was prepared by the reaction of
hydroxylamine hydrochloride with corresponding
diketone in a 2:1 molar ratio in dry ethanol. It was
then converted to its sodium salt by refluxing with
sodium methoxide in methanol. The stoichiometric
amount of sodium salt of 9,10-phenanthrenequinone
dioxime was reacted with alkyl/aryl-germanium(IV)
chloride in 1:1 and 1:2 molar ratios, respectively, to
produce organogermanium complexes of the general
formula R2GeL and (R3Ge)2L in 48–72% yield. The
reactions are depicted in Scheme 1.
Correspondence to: Pushpa Pardasani; e-mail: pushpa
.pardasani@gmail.com.
Contract grant sponsor: Department of Atomic Energy/Board of
Research in Nuclear Sciences.
All the newly synthesized oxime complexes
are crystalline solids, soluble in common organic
solvents such as C6H6, CHCl3, CH2Cl2, and DMSO
and characterized by spectroscopic techniques.
Contract grant number: 2009/37/31/BRNS/2099.
2012 Wiley Periodicals, Inc.
ꢀC
545

546 Thomas et al.
HON
NOH
O
O
EtOH
+ NH2OH.HCl
CH3COONa
R
O
N
R
Ge
R
R
R
R
O
Ge
O
R
Ge
NaON
NONa
R
N
O
N
N
C6H6
C6H6
4: R=Me; 5: R=Et; 6: R=Ph
1: R=Me; 2: R=Et; 3: R=Ph
!
SCHEME 1 Preparation of complexes.
The IR spectra of all compounds were inter-
preted by comparing with those of the free ligand
and related derivatives. A medium intensity band
at 3140–3122 cm−1 in the free ligand due to ν(OH)
was absent in the spectra of complexes, confirming
the deprotonation of oxime and synchronous for-
mation of the Ge O bond. There was no signifi-
cant shifting for ν(C=N) in the complexes that was
observed at 1600 cm−1 in the ligand, clearly indi-
cating that the imino group is not involved in co-
ordination with germanium. In all complexes, new
peaks were observed in the region 880–845 cm−1
assignable to Ge O stretching [15] and in the re-
gion 689–630 cm−1 on account of different Ge C
stretchings for alkyl/aryl-germanium compounds [
16]. The NMR spectra for complexes 1–6 did not
show a characteristic signal for the =NOH protons
observed at 12.24 ppm in the parent oxime. The aro-
matic protons of the phenanthrene moiety appeared
in the region 8.68–7.27 ppm. For 1:1 complexes (1–
3), the resonance due to methyl, ethyl, and phenyl
protons were observed at 0.678 (s, CH3), 0.97 (t,
CH2CH3), 1.14 (q, CH2CH3), and 8.53–7.32 (m, Ar-H)
ppm, whereas in the case of 1:2 complexes (4–6) the
corresponding resonances were observed at 0.63 (s,
CH3), 0.91 (t, CH2CH3), 1.17 (q, CH2CH3), and 8.49–
7.32 (m, Ar-H), respectively. In the 13C NMR spectra
of complexes, no significant shifting was observed
for the C N signal, suggesting no chelate formation
through the imine nitrogen atom. For methyl deriva-
tives 1 and 4, methyl carbons resonated at 4.51 and
5.14 ppm [17] whereas for ethyl derivatives 2 and
5, characteristic signals appeared at 7.18 (CH2CH3),
9.02 (CH2CH3), and 7.03 (CH2CH3), 8.70 (CH2CH3)
respectively. Spectral characteristics of germanium
oximates are presented in Table 1.
TABLE 1 Spectral Characteristics of Germanium Oximates
NMR (ppm)
Compound
IR(cm−1
)
1H
13C
1
ν(C=N) (1588), ν(NO) (950)
ν(Ge–O) (879), ν(Ge–C) (630)
8.66–7.36 (m, 8H, ArH),
0.678 (s, 6H, Ge-Me)
147.90 (C N),
143.95–123.15 (C C),
4.51 (Ge Me)
2
ν(C=N) (1596), ν(NO) (948)
ν(Ge–O) (848), ν(Ge–C) (648)
8.58–7.29(m, 8H, ArH),
1.14(q, 4H, Ge CH2CH3),
0.97(t, 6H, Ge CH2CH3)
148.10 (C N),
136.21–123.29 (C C),
9.02 (Ge CH2CH3),
7.18 (Ge CH2CH3)
156.17 (C N),
134.6–121.2(C C)
145.58 (C N)
3
4
ν(C=N) (1598), ν(NO) (945)
ν(Ge–O) (845), ν(Ge–C)(682)
ν(C = N) (1594), ν(NO) (942)
ν(Ge–O) (855), ν(Ge–C) (644)
8.53–7.32 (m, 18H,
8ArH + 10PhH)
8.68–7.37 (m, 8H, ArH)
0.63 (s, 18H, Ge Me)
142.12–123.13 (C C)
5.14(Ge Me)
5
6
ν(C=N) (1593), ν(NO) (940)
ν(Ge–O) (860), ν (Ge–C)(640)
8.25–7.27 (m, 8H, ArH)
1.17 (q, 12H, Ge CH2CH3),
0.91 (t, 18H, Ge CH2CH3)
148.48 (C N),
133.00–123.05 (C C)
8.70 (Ge–CH2CH3),
7.03 (Ge CH2CH3)
144.28 (C N)
ν(C=N) (1597), ν(NO) (942)
ν(Ge–O) (880), ν (Ge–C)(689)
8.49–7.32 (m, 23H,
8ArH + 15PhH)
136.98–123.67 (C C)
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Properties of the Alkyl/Aryl Germanium Dioximates Containing Ge O Bond 547
TABLE 2 Optimized Parameters of Compound 1–6
Compound
R (Ge O1)
R (Ge O2)
R (Ge C)
R (N O)
θ (C Ge C)
θ (O Ge O)
1
2
3
4
5
6
1.83
1.75
1.82
1.86
1.88
1.85
1.83
1.81
1.82
1.86
1.85
1.85
1.93
1.86
1.90
1.95
1.96
1.93
1.44
1.44
1.44
1.43
1.43
1.43
119.69
118.82
116.44
117.17
108.97
113.34
96.63
99.55
95.91
–
–
–
TABLE 3 BE of Complexes
Compound
Characteristics
1
2
3
4
5
6
BE (anti) (Kcal/mol)
BE (syn) (Kcal/mol)
−27.76
−1.30
−19.58
−6.87
−28.58
−2.12
−31.40
−4.94
−28.47
−2.02
−39.20
−12.75
TABLE 4 Thermodynamic Stability Data of the Complexes
Theoretical Calculations
Compound
ꢀH (kJ/mol)
ꢀG (kJ/mol)
ln K
Geometry Optimizations. To understand the na-
ture of the Ge O bond, the structures of ligand
as well as the complexes were optimized at the
DFT/B3LYP level. The ligand may exist in syn
(−704447.765 kcal/mol) and anti (−704474.220
kcal/mol) conformations and the anti isomer ap-
peared to be the most stable. The N O bond length
in all the complexes increased compared to lig-
1
2
3
4
5
6
− 96.41
− 83.12
− 131.70
− 117.85
− 144.25
− 104.33
− 84.60
10.01
8.96
10.96
7.93
6.43
8.35
− 116.28
− 125.36
− 108.85
− 111.356
− 109.83
´
˚
and (1.40 A), whereas the C N bond length de-
´
˚
creased from 1.32 to 1.30–1.31 A. All other optimized
parameters of the complexes are summarized in
Table 2.
Binding Energy. Binding energy of complexes is
an important factor to account their stabilization.
Greater the negative value of binding energy, the
stronger the binding capacity, resulting in forma-
tion of the most stable complexes. The details are
presented in Table 3, and it is evident that 1:2 mo-
lar complexes have greater binding capacity than 1:1
molar complexes.
FIGURE 1 Variation of NPA charges on Ge atom in reactants
and products.
Thermodynamic Stability. The frequency calcu-
lations on optimized structures gave a zero imagi-
nary frequency, and it was used to calculate ther-
modynamic stability constants by the equation
ꢀG = −RT ln K. The results are summarized in
Table 4, and it was observed that the stability con-
stants of 1:1 complexes (1–3) are larger than that of
1:2 (4–6).
were obtained using the natural population analysis
(NPA) method within the NBO approach.
The positive charge on the germanium atom in
the reactant changes due to delocalization of elec-
trons upon complex formation is shown in Fig. 1. In
the case of 1:1 complexes (1–3), there is a decrease
in the positive charge on germanium upon substi-
tution of halide with two oxygen atoms. However,
in 1:2 complexes (4–6) there is not much variation
because of unavailability of interaction of lone pairs
from both the oxygen. Nearly 97.79% of the elec-
trons are located in the Lewis orbitals. Remaining
Natural Bond Orbital Calculations. Among the-
oretical methods, natural bond orbital (NBO) anal-
ysis is a unique approach to evaluate the delocaliza-
tion effects [18]. Atomic charges in all the structures
Heteroatom Chemistry DOI 10.1002/hc

548 Thomas et al.
TABLE 5 Possible Interactions in Dimethylgermanium Diox-
imate
TABLE 6 Important Delocalization Effects in 1:1 Molar
Complexes
Donor
Acceptor
E(2) (Kcal/mol)
Compound
Donor
Acceptor
E(2) (Kcal/mol)
σ(O25–Ge27
)
ꢁ*(C7–N24
σ* (N23–O26)
)
4.97
6.37
7.16
3.60
3.22
3.84
3.23
4.20
7.46
6.75
4.77
3.53
4.24
3.25
3.01
24.49
3.55
10.75
7.11
1
LP O25
LP O26
σ (Ge27–C28
σ (Ge27–C28
σ (Ge27–C32
σ (Ge27–C32
LP O25
σ* (O26–Ge27
σ* (O25–Ge27
σ* (O25–Ge27
σ* (O26–Ge27
σ* (O25–Ge27
σ* (O26–Ge27
σ* (O26–Ge27
σ* (O25–Ge27
σ* (O25–Ge27
σ* (O26–Ge27
σ* (O25–Ge27
σ* (O26–Ge27
σ* (O26–Ge27
σ* (O25–Ge27
σ* (O25–Ge49
σ* (O26–Ge49
σ* (O25–Ge49
σ* (O25–Ge49
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
24.49
7.11
7.46
6.75
4.77
3.53
25.05
5.14
7.98
6.53
4.92
3.53
14.50
14.50
4.59
7.22
7.22
4.59
σ (O26–Ge27
σ (O25–Ge27
σ (O26–Ge27
σ (O25–Ge27
σ (O25–Ge27
σ (O26–Ge27
σ (O26–Ge27
σ (Ge27–C28
σ (Ge27–C28
σ (Ge27–C32
σ (Ge27–C32
σ (Ge27–C32
LP N23
)
)
)
)
)
)
)
)
)
)
)
)
σ* (O26–Ge27
σ* (O25–Ge27
σ* (Ge27–C28
σ* (Ge27–C32
σ* (Ge27–C28
σ* (Ge27–C32
σ* (O25–Ge27
σ* (O26–Ge27
σ* (O25–Ge27
σ* (O26–Ge27
σ* (Ge27–C28
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
2
3
LP O26
σ (Ge27–C28
σ (Ge27–C28
σ (Ge27–C32
σ (Ge27–C32
LP O25
)
)
)
)
σ* (O26 –Ge27
LP O26
LP O25
LP O25
LP O25
LP O26
σ* (Ge27–C32
σ* (O26–Ge27
σ* (Ge27–C28
σ* (Ge27–C28
σ* (O25–Ge27
σ (Ge49–C27
σ (Ge49–C27
σ (Ge49–C38
σ (Ge49–C38
)
)
)
)
LP O26
listed in Table 6. In the case of the diphenyl complex
(3), the lone pairs of both the oxygen atoms are sym-
metrically oriented, hence it gave same magnitude
of interaction with both the Ge O bonds as com-
pared to other complexes where these interactions
are different.
The bond pair electrons of Ge C also inter-
act with σ* orbitals of the Ge O bond. These
interactions are also same and slightly larger for the
diphenyl complex. In the case of dimethyl- and di-
ethylgermanium complexes, these interactions are
different leading to the fact that there are stere-
oelectronic and structural differences between the
complexes.
2.201% of electrons are delocalized, leading to slight
departures from a localized Lewis structure model.
The donor–acceptor interactions in the NBO provide
qualitative information about the delocalization of
electron leading to the hyperconjugative effect. Pos-
sible hyperconjugative interactions in dimethylger-
manium dioximate are presented in Table 5.
The highest interaction takes place between the
lone pair of oxygen with antibonding orbital (σ*) of
the other Ge O bond, which is visualized in Fig. 2.
In all the complexes, the value of these interactions
varied depending upon the nature of the substituent.
The main interactions involved in 1:1 complexes are
FIGURE 2 (a) Atomic labeling and (b) lone pair interaction with Ge O bond for 1.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Properties of the Alkyl/Aryl Germanium Dioximates Containing Ge O Bond 549
TABLE 7 Physical and Analytical Data of Organogermanium(1V) Complexes
Elemental Analysis
Compound
Physical Appearance
Yield (%)
mp (◦C)
C
H
N
Ge
1
2
3
4
5
6
Brown, solid
Brown, solid
Green, solid
57
72
55
48
63
58
170(d)
139
120
182
212(d)
235(d)
56.07 (56.21)
58.91 (58.11)
67.44 (67.84)
50.93 (50.21)
56.18 (56.02)
71.15 (71.03)
4.16 (4.55)
4.94 (4.61)
3.92 (3.89)
5.56 (5.45)
6.89 (6.18)
4.54 (3.98)
8.27 (8.22)
7.63 (7.05)
6.05 (6.55)
5.94 (5.14)
5.04 (5.42)
3.32 (3.13)
21.42 (21.03)
19.79 (19.01)
15.68 (15.18)
30.79 (30.13)
26.13 (26.71)
17.20 (17.11)
Yellowish green, solid
Dark green, solid
Yellow, solid
Values given without parenthesis refer to elemental analysis found (%) and within parenthesis refer to elemental analysis calculated (%). d =
decomposed.
CONCLUSIONS
jugative effects, NBO analysis was carried out and
each compound was modeled with a Gauss View
visualizer.
A convenient synthesis of novel germanium com-
plexes of the general formula R2GeL and (R3Ge)2L
(R Me, Et, Ph) has been accomplished. The stability
of complexes has been evaluated by different com-
putational parameters.
General Procedure for Synthesis
Preparation of Ligand. The desired ligand 9,10-
phenathrenequinone dioxime was prepared by the
reaction of 9,10-phenanthrenequinone (0.8328 g,
4 mmol) and hydroxylamine hydrochloride (1.042 g,
15 mmol) in ethanol (25 mL) with sodium acetate
(0.8203 g, 10 mmol). The shining yellowish green
compound was crystallized from methanol (83%);
mp 197–202◦C (lit mp 202◦C) [22].
EXPERIMENTAL
General Procedures
All the chemicals were purchased from Merck (In-
dia) and Aldrich (Germany) and used without fur-
ther purification. All the reactions were carried out
in the presence of nitrogen atmosphere. Solvents
were dried by standard methods [19]. The melting
points are recorded on a Perfit apparatus and are
uncorrected. The IR spectra from 4000–400 cm−1
were recorded on Nicolet Shimandzu spectrometer
(Japan) in KBr pellets and CCl4 solution. The 1H
(CDCl3, DMSO, 300 MHz) and 13C (CDCl3, DMSO,
75.5 MHz) NMR spectra of complexes were recorded
at room temperature on a JEOL 300 ALFT NMR
(Japan) spectrometer using TMS as an internal stan-
dard. Germanium was estimated as germanium ox-
ide using platinum crucible, and nitrogen was esti-
mated as reported in the literature method [20].
Preparation of Dimethylgermanium(IV)-9,10-
Phenanthrenequinone Dioximate. To the freshly
prepared methanolic solution (5 mL) of sodium
methoxide [prepared in situ by taking sodium
(0.1279 g, 5.1 mmol) in methanol], a solution of
phenanthrenequinone dioxime (0.5955 g, 2.5 mmol)
in benzene (15 mL) was added dropwise. The yel-
lowish green color of the solution changed to dark
brown during the addition. Subsequently, the mix-
ture was refluxed for 5 h. To the methanolic–benzene
solution (10 mL) of the sodium salt of ligand H2L,
the benzene solution of dimethylgermanium dichlo-
ride (0.4339 g, 2.5 mmol) was added slowly through
a dropping funnel at room temperature under the ni-
trogen atmosphere. The color of the reaction mixture
changed to brown, and a precipitate of NaCl started
to form. It was then refluxed for 6 h to ensure com-
pletion of the reaction. The precipitated NaCl was
filtered off, and the solvent was dried in vacuum.
A brown-colored compound obtained was washed
with hexane and dried (0.481 g, 57%).
Computational Details
To reveal the local minimum on the Potential Energy
Surface of each germanium derivatives, we carried
out geometry optimization using restricted density
functional calculations in Gaussian 03 suite of pro-
grams [21], with using the B3LYP hybrid method
that employs the Becke three parameters exchange
functional and the Lee–Yang–Parr correlation func-
tional and 6-31G level of theory. The normal mode
analysis on the preferred structure yielded no imag-
inary frequency on vibrational study using the same
level of theory, which is used for optimization. To
study the intramolecular interactions and hypercon-
Diethyl- and diphenylgermanium derivatives of
the type R2GeL were also prepared using the above
procedure. For the preparation of complexes 4–6,
to the sodium salt of ligand, trialkyl/triaryl germa-
nium halides were added in a 1:2 molar ratio to form
corresponding products without changing the above
Heteroatom Chemistry DOI 10.1002/hc

550 Thomas et al.
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Heteroatom Chemistry DOI 10.1002/hc