New organogermanium cations [RGe(OCH2CH2NME 2)2]+ with intramolecular N→Ge coordination bonds

Article abstract of DOI:10.1007/s11172-007-0141-x

New organohalogermanes RGe(OCH₂CH₂NMe ₂)₂X (R = Ph, X = I (5); R = Me, X = Cl (6) or I (7)) with an intramolecular N→Ge coordination bond were synthesized. According to the ¹H and ¹³C NMR spectroscopic data, iodides 5 and 7 exist in solution as ionic compounds with the pentacoordinated germanium atom. In solution of compound 4 (R = Ph, X = Cl), there is an equilibrium between the ionic and covalent forms. The equilibrium shifts toward the ionic form with increasing solvent polarity or temperature. In solution, chloride 6 is a covalent compound. The structures and relative stabilities of different isomers of compounds 4-7 were studied by quantum chemical calculations at the density functional level of theory.

Full text of DOI:10.1007/s11172-007-0141-x

Russian Chemical Bulletin, International Edition, Vol. 56, No. 5, pp. 926—934, May, 2007
926
New organogermanium cations [RGe(OCH2CH2NMe2)2]+
with intramolecular N→Ge coordination bonds
I. A. Portnyagin, V. V. Lunin, and M. S. Nechaevꢀ
Department of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 939 2677. Eꢀmail: nechaev@nmr.chem.msu.ru
New organohalogermanes RGe(OCH2CH2NMe2)2X (R = Ph, X = I (5); R = Me, X =
Cl (6) or I (7)) with an intramolecular N→Ge coordination bond were synthesized. According
1
to the H and 13C NMR spectroscopic data, iodides 5 and 7 exist in solution as ionic comꢀ
pounds with the pentacoordinated germanium atom. In solution of compound 4 (R = Ph,
X = Cl), there is an equilibrium between the ionic and covalent forms. The equilibrium shifts
toward the ionic form with increasing solvent polarity or temperature. In solution, chloride 6 is
a covalent compound. The structures and relative stabilities of different isomers of compounds
4—7 were studied by quantum chemical calculations at the density functional level of theory.
Key words: organogermanium compounds, hypercoordinated compounds, germyl cations,
intramolecular coordination bonds, 1H and 13C NMR spectroscopy, density functional method.
The synthesis, structures, and properties of cations of
Group 14 organometallics R3E+ (E = Si, Ge, or Sn) have
been extensively studied in recent years.1—4 In addition to
fundamental interest associated with elucidation of the
similarity and difference between these compounds and
the carbenium ions R3C+, they have received increasing
interest in applied research as efficient catalysts for polyꢀ
merization5 and hydrosilylation6—9 of alkenes, acylation
of alcohols,10,11 and the Diels—Alder reaction.12,13
The R3E+ cations exhibit high electrophilicity and
readily coordinate various nucleophiles, including donor
solvent molecules and counterions. Stability of such catꢀ
ions can be increased by (1) introducing bulky substituꢀ
ents at Group 14 element atoms, (2) using nucleofugic
counterions, and (3) forming intramolecular Y→E coorꢀ
dination bonds (Y is an atom with lone electron pairs
(N or O)).14—19 Pentacoordinated tin complexes with pinꢀ
cer ligands 1 20—22 and 2 23—25 serve as examples of stable
cations of this element. Trigermacyclopropenyl cation 3 26
isoelectronic with the aromatic cyclopropenyl cation is
also stable.
1: R, R´ = Alk, Ar, Cl; 2: Y = OAlk, NAlk2; X = CF3COO, PF6, HgI3
nium and tin derivatives (Me2NCH2CH2O)EX (X =
OCH2CH2NMe2 and E = Ge or Sn (see Ref. 30); X = Cl
or OAc and E = Ge (see Ref. 31)) through electronꢀ
withdrawing substituents (O or Cl) at the Group 14 eleꢀ
ment atom and the formation of one or two stable inꢀ
tramolecular N→E coordination bonds. The use of such
substituents made it possible to isolate, for the first time,
the germyl cation in the condensed phase in the presꢀ
ence of the nucleophilic chloride anion, viz., the salt
[PhGe(OCH2CH2NMe2)2]+Cl–•2CHCl3 (4•2CHCl3),
without introduction of steric substituents.32
In all cases, germyl cations were stabilized in the conꢀ
densed phase with the use of bulky substituents.19,26—29
An approach developed30—32 for the stabilization of R2E
compounds (E = GeII or SnII) and R3Ge+ cations is
based on the use of the electronic factors of stabilization
(electronꢀwithdrawing substituents at Group 14 element
atoms and intramolecular coordination bonds) without
introduction of bulky substituents.
The latest investigations33,34 concerned with R3E+ catꢀ
ions have demonstrated that the character of the E—anꢀ
ion bond substantially varies depending on the nature of
substituents at the E atom, as well as on the nature of
The βꢀ(N,Nꢀdimethylamino)ethoxy ligand was
demonstrated to stabilize the monomeric divalent germaꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 892—900, May, 2007.
1066ꢀ5285/07/5605ꢀ0926 © 2007 Springer Science+Business Media, Inc.

New organogermanium cations
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
927
Scheme 2
anions, donor groups (NR2 or OR), and the solvent. In
the present study, we investigated the influence of these
factors on the character of Ge—anion bonding in the
presence of two βꢀ(N,Nꢀdimethylamino)ethoxy ligands.
We report the synthesis of the organogermanium comꢀ
pounds RGe(OCH2CH2NMe2)2X (R = Ph and X = I (5);
R = Me and X = Cl (6) or I (7)). The structures of the
resulting compounds were investigated by NMR specꢀ
1
troscopy. Compound 4 was characterized by H and
13C NMR spectra in CDCl3 and tolueneꢀd8 at different
temperatures. The structures and relative stabilities of difꢀ
ferent isomers of compounds 4—7 were also studied by
quantum chemistry calculations at the density functional
level of theory.
in THF and toluene. All compounds are readily soluble in
CH2Cl21and CHCl3 and are insoluble in hexane.
The H and 13C NMR spectra of all compounds were
recorded in CDCl3. The spectra of compound 4 were also
measured in tolueneꢀd8 at different temperatures. Princiꢀ
pal spectroscopic characteristics are given in Table 1. The
spectra of the chlorides are substantially different from
those of the iodides.
The Xꢀray diffraction analysis showed that the crystalꢀ
line [PhGe(OCH2CH2NMe2)2]+Cl–•2CHCl3 complex
(4•2CHCl3) is chiral and has C2 symmetry (Fig. 1).32 The
geometry of the complex can be described as a distorted
trigonal bipyramid. Two oxygen atoms and one carbon
atom are in equatorial positions, and two nitrogen atoms
occupy axial positions. The chiral environment of the
germanium atom results in the diastereotopicity of the
CH2 and NMe2 groups in the coordination cycle. The
aboveꢀmentioned structural features of the ionic forms
are manifested in the NMR spectra of solutions of comꢀ
pounds 4, 5, and 7.
Results and Discussion
Compounds 5 and 6 were synthesized analogously
to compound 4 by the reaction of RGeX3 with
Et3GeOCH2CH2NMe2 in THF using a reagent ratio
of 1 : 2 (Scheme 1).32
Scheme 1
5: R = Ph, X = I (90%); 6: R = Me, X = Cl (92%)
The MeGe(OCH2CH2NMe2)2I compound (7) was
synthesized by the oxidative coupling reaction of MeI
with Ge(OCH2CH2NMe2)2 (Scheme 2). Earlier, this apꢀ
proach has been applied27,28 to the synthesis of sterically
hindered germyl cations.
Compounds 5—7 are white crystalline compounds,
which are very sensitive to atmospheric moisture. Unlike
iodides 5 and 7, chlorides 4 and 6 are moderately soluble
The 1H NMR spectra of iodides 5 and 7 in chloroform
show two singlets of the NMe2 groups with equal intensity
Table 1. Chemical shifts of the signals of the βꢀ(dimethylamino)ethoxy group in the 1H and
13C spectra of compounds 4—7
Comꢀ
pound
Solvent
δ
δ
H
C
NMe2
CH2N
CH2O
NMe2
CH2N CH2O
4a
4b
4a
4b
5
CDCl3
CDCl3
Tolueneꢀd8
2.47
2.00, 2.57
1.95
2.95
2.75, 3.02
2.49
2.23, 2.60
2.76, 3.00
2.87
3.80
3.97
4.09
4.13
4.03
3.77
3.89
41.78
43.37, 44.15
45.82
45.42, 45.51
44.89, 45.45
44.70
54.80
56.09
62.28
61.62
57.50
57.71
58.06
58.05
57.84
62.92
62.62
59.05
58.98
59.19
Tolueneꢀd8 1.83, 2.04
CDCl3
CDCl3
CDCl3
2.01, 2.59
2.45
2.52, 2.57
6
7
2.95
44.79, 45.46

928
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
Portnyagin et al.
Cl(2SA)
C(6A)
an AA´XX´ multiplet of the diastereotopic protons of the
CH2N (δ 2.75 and 3.02) and CH2O groups (δ 3.97).
The 13C NMR spectrum of form 4b has singlets of the
diastereotopic Me groups of the NMe2 fragment at δ 43.37
and 44.15 and singlets at δ 56.0 (CH2N) and 57.84
(CH2O). Covalent structure 4a is characterized by signals
at δ 2.47 (NMe2), 2.95 (CH2N), and 3.80 (CH2O) in the
1H NMR spectrum and signals at δ 41.78 (NMe2), 54.80
(CH2N), and 58.05 (CH2O) in the 13C NMR spectrum.
In the 1H and 13C NMR spectra of form 4a, all signals are
substantially broadened. This is evidence that the NMe2
groups in covalent structure 4a are in fast exchange
C(5A)
C(8A)
C(7A)
C(1SA)
N(1A)
C(2A)
C(3A)
C(4)
O(1A)
Ge(1)
O(1)
Cl(1SA)
Cl(1)
Cl(1S)
C(1)
Cl(3SA)
Cl(3S)
N(1)
C(2)
C(3)
C(7)
C(1S)
C(8)
C(5)
C(6)
Crystal
Cl(2S)
the salt
Fig.
1.
structure
of
(4a
4a´) on the NMR time scale, whereas the
Ph(Me2NCH2CH2O)2Ge+Cl–•2CHCl3 (4•2CHCl3).32
interconversion of 4a and 4b under these conditions is
slow on the NMR time scale (see Scheme 3).
and AA´XX´ multiplets of the diastereotopic protons of
the CH2O and CH2N groups. The carbon atoms of the
Me groups at the N atom are also nonequivalent in the
13C NMR spectrum. This spectral pattern unambiguously
indicates that the rigid ionic structures of both compounds
are retained in solution. These structures are analogous to
the structure of compound 4 in the crystalline state
(see Fig. 1).32
Thermodynamically more favorable covalent strucꢀ
ture 4a predominates in less polar tolueneꢀd8 at 291 K.
The molar ratio 4a : 4b is ~3 : 1. Structure 4a is characterꢀ
ized by a singlet at δ 1.95 (NMe2) and broadened triplets
(3JH,H = 6.0 Hz) at δ 2.49 (CH2N) and 4.09 (CH2O). The
ionic form is characterized by singlets of the diastereotopic
NMe2 groups at δ 1.83 and 2.04 and multiplets at δ 2.23,
3
2.60 (CH2N, JH,H = 5.8 Hz), and 4.13 (CH2O). The
1
The H NMR spectrum of chloride 6 shows a broadꢀ
13C NMR spectrum of structure 4a shows singlets at
δ 45.82 (NMe2), 62.28 (CH2N), and 62.92 (CH2O). Strucꢀ
ture 4b is characterized by singlets of the diastereotopic
Me groups of the NMe2 fragments at δ 45.42 and 45.51
and singlets at δ 61.62 (CH2N) and 62.62 (CH2O). The
percentage of thermodynamically less favorable ionic
structure 4b in toluene gradually increases as the temꢀ
perature is raised to 373 К. This is accompanied by broadꢀ
ening of all signals in the spectrum, which is evidence that
ened singlet of the NMe2 groups and triplets (A2X2 sysꢀ
tem) of the protons of the CH2O and CH2N groups. This
spectral pattern is indicative of the covalent structure. In
our opinion, two forms with pentaꢀ and hexacoordinated
germanium atoms exist in equilibrium in solution. In soꢀ
lution, the NMe2 groups are in fast exchange due to the
relatively easy closure and cleavage of the N→Ge coordiꢀ
nation bonds. As a result of this process, the signals of the
NMe2 groups are averaged in the 13C NMR spectrum.
The 1H and 13C NMR spectra of compound 4
in CDCl3 at room temperature and in tolueneꢀd8 at
291—373 К provide evidence that, in solution, the neuꢀ
tral form PhGe(OCH2CH2NMe2)2Cl (4a) is in equilibꢀ
rium with the ionic form [PhGe(OCH2CH2NMe2)2]+Cl–
(4b), in which the germanium atom has the coordination
number 5 (Scheme 3). Ionic form 4b predominates in
solution in CDCl3 (molar ratio 4b : 4a = 6.5 : 1). Like the
1H NMR spectra of ionic compounds 5 and 7, the
1H NMR spectrum of form 4b shows two singlets of the
NMe2 groups with equal intensity (δ 2.00 and 2.57) and
the exchange 4a
4b becomes more fast. At 373 К,
the molar ratio 4a : 4b is ~1 : 1. The temperature changes
in the spectrum are reversible. The character of the temꢀ
perature dependence of the NMR spectra of compound 4
is, on the whole, analogous to that described earlier29 for
ionic pentacoordinated germanium compounds containꢀ
ing the pincer sterically crowded C,N,N´ꢀ[2,6ꢀbis(diꢀ
methylaminomethyl)ꢀ4ꢀtertꢀbutyl]phenyl ligand.
The molecular structures of compounds 4—7 were
studied by quantum chemical calculations at the density
functional level of theory. The molecular geometry was
optimized using the generalized gradientꢀcorrected funcꢀ
Scheme 3

New organogermanium cations
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
929
tional PBE,35 which has been earlier tested35,36 for differꢀ
ent classes of molecules. In the calculations, the TZ2P
(triple zeta plus polarization functions) basis set was
used.37 The innerꢀshell electrons of the Ge, C, N, and
O atoms were described by the effectiveꢀcore potentials
ECPꢀSBKJC.38,39
The energies E, E°, and H° were calculated for all
stationary states. All calculations were carried out with
the use of the PRIRODA program.40 Earlier, we have
successfully used this approach and the PRIRODA proꢀ
gram in studies of the structures and reactivity of comꢀ
pounds with double bonds E=X (E = Si, Ge, or Sn;
X = CR2 (R = Alk or Ar), O, S, or N),41 germanium(II)
and tin(II) compounds,42 and the structures and
thermodynamic parameters of the ionic compound
[Ge(OCH2CH2NMe2)2]+Cl–•2CHCl3.32
The Xꢀray diffraction data were obtained for
[PhGe(OCH2CH2NMe2)2]+Cl–•2CHCl3.32 The concluꢀ
sions about the molecular structures of compounds 4—7
were made based on the NMR spectra in CDCl3. Hence,
we used the RGe(OCH2CH2NMe2)2X•2CHCl3 comꢀ
plexes (R = Me or Ph; X = Cl or I) containing two
chloroform molecules as model compounds in theoretical
calculations. Isomers of these molecules containing one
or two N→Ge coordination bonds and the isomer, in
which this bond is absent, were considered. For an adꢀ
equate comparison of the relative energies of the ionic
and covalent structures of 4—7, we considered systems,
in which the chloroform molecules are coordinated only
to halogen atoms through hydrogen bonds.
The isomers under consideration are denoted as folꢀ
lows: A is the covalent structure with two N→Ge coordiꢀ
nation bonds, B is the ionic structure with two N→Ge
coordination bonds, C is the covalent structure with one
N→Ge coordination bond, D is the ionic structure with
one N→Ge coordination bond, and E is the covalent
structure without coordination bonds.
of 5—7 are analogous. The principal geometric paramꢀ
eters are listed in Table 2. The calculations adequately
reproduced the structure of molecular complex 4 in the
crystal.32 For chlorides 4 and 6 containing two N→Ge
coordination bonds, minima on the potential energy surꢀ
face were found. These minima correspond to both covaꢀ
lent forms 4A and 6A and ionic forms 4B and 6B. For
iodides 5 and 7, the potential energy surface has minima
corresponding only to ionic forms 5B and 7B. In both
cases, two minima were found for the ionic forms, which
differ only in the position of the iodide ion with respect to
the cationic center.
For all derivatives with one N→Ge coordination bond,
both types of structures, viz., covalent C and ionic D,
exist. For molecules, in which coordination bonds are
absent, minima corresponding only to covalent strucꢀ
tures E were found. These results seem to be reasonable
because the cationic center is not stabilized by coordinaꢀ
tion bonds and there are no factors facilitating the formaꢀ
tion of ionic structures.
Some changes in the geometric parameters of the calꢀ
culated structures on varying the number of N→Ge coorꢀ
dination bonds as well as on going from covalent to ionic
structures are worthy of notice. The Ge—Cl interatomic
distances in chlorides 4A and 6A are abnormally long.
The cleavage of one coordination bond (transitions
4A → 4C and 6A → 6C) leads to a substantial shortening
of the Ge—Cl bond (by ~0.4 Å). It is noteworthy that no
minima were found for structures 5A and 7A on the poꢀ
tential energy surface of the iodides. This is apparently
due to the bulkiness of the iodide ion.
It is noteworthy that one of the N→Ge coordination
bonds in ionic structures B is shorter than those in the
corresponding covalent derivatives A (by 0.08 Å). For
structures D and C, the differences in the bond lengths are
even larger (~1.3 Å). This is attributed to a stronger interꢀ
action between the donor NMe2 group and the metal
atom in ionic forms B and D compared to covalent comꢀ
pounds A and C.
The calculated structures of different isomers of comꢀ
pound 4 are presented in Fig. 2; the molecular structures

930
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
Portnyagin et al.
N(1)
Ge
N(1)
Cl
Cl
O(1)
O(2)
O(2)
Ge
O(1)
N(2)
N(2)
4A
4B
N(1)
Cl
N(2)
Cl
O(2)
O(1)
Ge
Ge
O(1)
N(1)
O(2)
N(2)
4C
4D
Cl
N(2)
O(2)
O(1)
Ge
N(1)
4E
Fig. 2. Calculated structures of isomers of compound 4•2CHCl3.
1
According to the results of calculations for iodides 5
and 7, ionic forms 5B´ and 7B have the lowest energies
(Table 3). The next in energy (∆H°298) covalent structures
the H and 13C NMR spectra of compounds 5 and 7,
which show signals of only the ionic forms of the molꢀ
ecules. For chloride 6, covalent structure 6A containing
two coordination bonds is most stable. For the next in
energy structure 6C, ∆H°298 = 0.9 kcal mol–1. In the case
of chloride 4, ionic structure 4B corresponds to the miniꢀ
5C and 7C have energies higher by 4.0 and 3.5 kcal mol–1
,
respectively. The energy difference between the ionic and
covalent structures is rather large. This is manifested in

New organogermanium cations
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
931
Table 2. Selected calculated bond lengths (d) in isomers of compounds 4—7
Comꢀ
pound
Isomer
d/Å
Ge—O(1)
Ge—O(2)
Ge—N(1)
Ge—N(2)
Ge—X
4
A
1.846
1.795
1.773
1.763
1.769
1.867
1.795
1.779
1.742
1.753
2.283
2.207
3.151
2.060
5.261
2.213
2.207
5.254
5.269
5.253
2.646
3.983
2.223
4.715
2.233
B
C
D
E
5*
6
B
B´
C
D
E
1.783
1.793
1.776
1.763
1.786
1.809
1.793
1.782
1.742
1.757
2.203
2.207
3.234
2.058
5.215
2.211
2.208
5.259
5.274
5.261
4.575
4.524
2.598
5.200
2.588
A
1.837
1.794
1.770
1.763
1.767
1.865
1.794
1.763
1.741
1.752
2.297
2.214
3.286
2.052
5.265
2.211
2.224
5.325
5.278
5.255
2.654
4.051
2.251
4.719
2.240
B
C
D
E
7*
B
B´
C
D
E
1.795
1.793
1.774
1.763
1.772
1.818
1.793
1.766
1.742
1.757
2.267
2.213
3.385
2.050
5.276
2.195
2.222
5.333
5.271
5.260
3.793
4.581
2.623
5.218
2.612
* Two minima, which differ only in the position of the iodide ion with respect to the cationic center, were found.
Table 3. Calculated energy parameters (E, E°, and H ) and relaꢀ
tive energies (∆E° and ∆H°298) of isomers of compounds 4—7
mum on the potential energy surface. According to the
NMR spectroscopic data, this structure predominates in
CDCl3. However, covalent forms 4A and 4C are higher in
energy (∆H°298) by only 0.7 and 0.3 kcal mol–1, respecꢀ
tively. The structure with one coordination bond (4C)
is more favorable than that with two coordination
bonds (4A), which is consistent with the experimental
data. The small energy difference between isomers 4A—4C
Comꢀ
Isoꢀ
–E
–E°
H°
∆E° ∆H°
298
pound mer
a.u.
kcal mol–1
4
A
267.23090 266.81908
267.23236 266.82023
267.22873 266.82084
267.20399 266.79441
267.22447 266.81727
282.2 0.0 0.0
B
C
D
E
282.4 –0.7 –0.7
280.5 –1.1 –0.4
281.5 15.5 16.2
1
results in that the H and 13C NMR spectra of chloride 4
show signals of the ionic (4b) and covalent (4a) strucꢀ
tures, the signals of the latter being substantially broadꢀ
ened due to the mutual transformations of the hexaꢀ and
281.0
1.1
2.9
5*
6
B
B´
C
D
E
263.75553 263.34427
263.75843 263.34691
263.74971 263.34242
263.73019 263.32145
263.74656 263.34013
282.2
0.0
0.0
282.3 –1.7 –1.7
280.8 1.2 2.3
281.4 14.3 15.1
pentacoordinated species 4A
4C.
The electronic structures of ionic derivatives B with
two coordination bonds were analyzed by the AIM
method.43 The critical points in the electron density corꢀ
responding to the Ge—O, Ge—C, and N→Ge bonds were
found (Table 4). In all the molecules under study, no
critical points corresponding to the germanium—halogen
bond were found, which is typical of separated ions. The
bond critical points for the Ge—O and Ge—C interatomic
interactions are characterized by a rather high electron
density (ρ(rcr) > 0.1), positive Laplacians of the electron
density (∇2ρ(rcr)), and |λ1|/λ3 = 0.23 and 0.39, respecꢀ
tively. These values describe the Ge—O bonds as closedꢀ
shell interactions (ionic bonds). The Ge—C bonds can be
assigned to interactions intermediate between covalent
280.1
2.6
3.6
A
237.66873 237.30944
237.66424 237.30448
237.66548 237.30982
237.63957 237.28247
237.66306 237.30825
247.3
247.5
246.2 –0.2
246.6 16.9 17.6
246.1
0.0
3.1
0.0
3.0
0.9
B
C
D
E
0.7
2.3
7*
B
B´
C
D
E
234.19230 233.83342
234.19026 233.83113
234.18621 233.83164
234.16563 233.80933
234.18409 233.83005
246.3
247.4
245.9
246.5 15.1 16.9
245.8 2.1 4.7
0.0
1.4
1.1
0.0
2.4
3.5
* Two minima, which differ only in the position of the iodide
ion with respect to the cationic center, were found.

932
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
Portnyagin et al.
2
Table 4. Parameters of the bond critical points (ρ(rcr), ∇ ρ(rcr), and λ —λ ) at the Ge atom in molecules 4B—7B
1
3
2
Comꢀ
pound
Bond
ρ(rcp
)
∇ ρ(rcp
)
–λ
–λ
λ
|λ |/λ
ε
1
2
3
1
3
a.u.
4B
5B
6B
7B
Ge—O(1)
Ge—O(2)
Ge—C
Ge—N(2)
Ge—N(1)
0.140
0.140
0.127
0.070
0.070
0.525
0.525
0.099
0.102
0.102
0.215
0.215
0.162
0.080
0.080
0.201
0.201
0.152
0.076
0.076
0.940
0.940
0.413
0.258
0.258
0.23
0.23
0.39
0.31
0.31
0.07
0.07
0.06
0.05
0.05
Ge—O(1)
Ge—O(2)
Ge—C
Ge—N(1)
Ge—N(2)
0.140
0.140
0.127
0.070
0.070
0.528
0.528
0.098
0.102
0.102
0.216
0.216
0.162
0.080
0.080
0.201
0.201
0.153
0.076
0.076
0.946
0.946
0.413
0.258
0.258
0.23
0.23
0.39
0.31
0.31
0.07
0.07
0.06
0.06
0.06
Ge—O(1)
Ge—O(2)
Ge—C
Ge—N(2)
Ge—N(1)
0.140
0.140
0.124
0.069
0.068
0.527
0.527
0.083
0.103
0.100
0.216
0.216
0.150
0.079
0.077
0.201
0.201
0.147
0.075
0.073
0.944
0.944
0.381
0.257
0.250
0.23
0.23
0.39
0.31
0.31
0.07
0.07
0.02
0.05
0.05
Ge—O(1)
Ge—O(2)
Ge—C
Ge—N(1)
Ge—N(2)
0.140
0.140
0.124
0.069
0.068
0.530
0.531
0.083
0.103
0.100
0.217
0.217
0.150
0.079
0.077
0.202
0.202
0.147
0.075
0.074
0.949
0.950
0.380
0.258
0.251
0.23
0.23
0.40
0.31
0.31
0.08
0.07
0.02
0.05
0.05
bonds and closedꢀshell interactions. The parameters of
the N→Ge bonds (ρ(rcr) < 0.1, ∇2ρ(rcr) ≈ 0.1, and
|λ1|/λ3 = 0.31) are typical of donorꢀacceptor interactions.
The π component of the bond is characterized by the
ellipticity (ε). The ellipticity ε for the Ge—C bond in the
derivatives containing the Ph group (4B and 5B) is 0.06.
This is indicative of the π overlap between the 4pz orbital
of the germanium atom and the π system of the Ph ring.
To the contrary, ε for the Ge—C bond in Me derivatives
6B and 7B is substantially smaller (0.02). Apparently, the
π interaction between the Ph ring and the cationic center
additionally stabilizes the ionic form of chloride 4. As a
result, the ionic form is in equilibrium with the covalent
form in solution. By contrast, Me derivative 6, in which
this stabilization cannot occur, exists exclusively in the
covalent form.
The presence of electronꢀwithdrawing substituents at
the metal atom is known to destabilize ionic forms of
molecules. This is due to a higher positive charge on
the metal atom, which facilitates the formation of the
metal—nucleophile covalent bond. To the contrary, the
formation of intramolecular coordination bonds between
the central atom and the donor groups leads to a decrease
of the positive charge on the metal atom, resulting in
stabilization of the ionic form.
NMe2 group is possible. Our results showed that both
ionic and covalent forms of the organogermanium comꢀ
pounds RGe(OCH2CH2NMe2)2X can be prepared in the
presence of this substituent.
The structures of the compounds under consideration
in solution depend on the nature of the counterion X,
the organic substituent R, and the solvent. In the presꢀ
ence of the bulky iodide anion, the ionic structures
(RGe(OCH2CH2NMe2)2I, R = Ph (5) or Me (7)) are
formed regardless of the nature of the hydrocarbon
substituent. To the contrary, the covalent structures
(MeGe(OCH2CH2NMe2)2Cl (6)) are formed in the presꢀ
ence of chloride anions combined with an alkyl subꢀ
stituent. A combination of the nucleophilic anion favorꢀ
able for the formation of the covalent structure and
the aryl substituent stabilizing the ionic structure
(PhGe(OCH2CH2NMe2)2Cl (4)) is the limiting case. In
solution of compound 4, there is an equilibrium between
the ionic and covalent structures. The equilibrium shifts
toward the ionic structure with increasing solvent polarity
or temperature.
Experimental
All operations associated with the synthesis and isolation of
the reaction products were carried out under purified argon
using the standard Schlenk technique. Commercially available
solvents were purified according to standard procedures and
distilled immediately before use. The PhGeI3 compound was
The βꢀ(dimethylamino)ethoxy substituent is involved
in the covalent bond with the metal atom through the
electronegative oxygen atom. In this case, the formaꢀ
tion of the intramolecular coordination bond with the

New organogermanium cations
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
933
synthesized by the reaction of PhGeCl3 with NaI in dry acꢀ
etone followed by recrystallization from acetic acid. The
physical constants were consistent with the published data.44
The Ge(OCH2CH2NMe2)2,30 Et3GeOCH2CH2NMe2,30 and
PhGe(OCH2CH2NMe2)2Cl 32 compounds were prepared acꢀ
cording to known procedures. The NMR spectra were reꢀ
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 04ꢀ03ꢀ32662
and 04ꢀ03ꢀ32549) and the Russian Academy of Sciences
(Program "Theoretical and Experimental Studies of
Chemical Bonds and Mechanisms of Chemical Reacꢀ
tions and Processes").
1
corded on an Avance 400 instrument (400.13 MHz for H and
100.62 MHz for 13C) in CDCl3 and tolueneꢀd8. The concentraꢀ
tion of the samples was 0.2—0.3 mmol mL–1. The chemical
References
1
shifts in the H and 13C NMR spectra were recorded relative to
the signals of the solvent on the δ scale. The melting points were
determined in sealed tubes on a SANYO Gallenkamp PLC inꢀ
strument. The elemental analysis was carried out on a Carlo
Erba EA1108 CHNSꢀO instrument.
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THF (25 mL) was slowly added with stirring to a solution of
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1
C, 36.11; H, 7.74; N, 9.36. H NMR (CDCl3), δ: 0.96 (s, 3 H,
1
Me); 2.45 (br.s, 12 H, Me2N, JC,H = 138 Hz); 2.87 (t, 4 H,
3
3
CH2N, JH,H = 6.0 Hz); 3.77 (t, 4 H, CH2O, JH,H = 6.0 Hz).
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Received November 15, 2006;
in revised form February 28, 2007