Gas phase reaction of nucleogenic dimethylgermylium cations with benzene

Article abstract of DOI:10.1134/S1070363210090070

Reaction of nucleogenic dimethylgermylium cations with benzene in the gas phase was studied by the radiochemical method. The formation of the products of germylation of benzene, dimethylphenylgermane, and phenylgermane is indicative of the formation of dimethylgermylium cations by the β-decay of tritium in the molecule of dimethylditritium germane. Dimethylgermylium cations are shown to undergo a rearrangement in the course of the reaction with benzene, which is consistent with the earlier results of quantum-chemical calculations.

Full text of DOI:10.1134/S1070363210090070

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 9, pp. 1762–1766. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © D.L. Myalochkin, Т.А. Kochina, V.V. Avrorin, D.V. Vrazhnov, E.N. Sinotova, 2010, published in Zhurnal Obshchei Khimii, 2010,
Vol. 80, No. 9, pp. 1443–1447.
Gas Phase Reaction of Nucleogenic Dimethylgermylium Cations
with Benzene
D. L. Myalochkina, Т. А. Kochinab, V. V. Avrorina, D. V. Vrazhnovb, and E. N. Sinotovaa
a St. Petersburg State University, Universitetskii pr. 26, St. Petersburg, 198504 Russia
e-mail: radiochem@yandex.ru
b Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, Russia
Received February 15, 2010
Abstract―Reaction of nucleogenic dimethylgermylium cations with benzene in the gas phase was studied by
the radiochemical method. The formation of the products of germylation of benzene, dimethylphenylgermane,
and phenylgermane is indicative of the formation of dimethylgermylium cations by the β-decay of tritium in the
molecule of dimethylditritium germane. Dimethylgermylium cations are shown to undergo a rearrangement in
the course of the reaction with benzene, which is consistent with the earlier results of quantum-chemical
calculations.
DOI: 10.1134/S1070363210090070
Although the first indications on the formation of
the three-coordinate germylium cations in the gas
phase appeared about 50 years ago [1], up to now there
were few publications on the properties and reactivity
of these intermediates. Nevertheless, note the reviews
of Karni [2] and Zharov [3] devoted to three-
coordinate metal-centered cations R3M+ (M = Ge, Sn,
Pb).
tritium in the molecules of hydrocarbons was sug-
gested for generation and investigation of reactivity of
free carbenium ions [15]. However, the extension of
this strategy to the generation of silicenium [16, 17]
and, later, germenium analogs of carbenium ions has
acquired special importance. The problem consists in
the aforementioned ability of silicon and the elements
of its subgroup to expand the coordination sphere
leading to the formation of complexes of cations R3M+
with the nucleophiles of any type, including the
counter-ion and the solvent molecules.
In the last decades, the three-coordinate silicon
organic cations (silicenium ions) R3Si+ attracted much
attention from both the theoreticians [4–8] and
experimentalists [7, 9–12]. With this, special attention
was paid to the problem of preparation of “free”
silicenium ions in the liquid phase or in crystals, that
is, cations in which strong interaction with the solvent
or counter-ion is absent. This problem turned out to be
the most difficult because of the unique ability of
silicon to expand its coordination sphere. Only recently
these efforts led to success [7, 13, 14]. At present,
these studies were extended to other elements of the
silicon subgroup, Ge, Sn, Pb.
Theoretical background of the nuclear chemical
method [15] and experimental studies on the
carbenium [18–21] and silicenium ions [22–25] led to
the conclusion on the possibility and prospects of the
use of this strategy for generation and investigation of
reactivity of the three-coordinate cations of heavier
elements of the silicon subgroup both in the gas and
condensed phase.
The present work is devoted to investigation of the
gas phase reaction with benzene of dimethylgermylium
ions Me2TGe+ generated by the nuclear chemical
method.
In our studies, we used the absolutely original non-
traditional strategy for generation and investigation of
reactivity of cations R3M+, which was elaborated after
many years of studies of chemical consequences of
radioactive β-decay of tritium atoms in the molecules
of organic and organoelemental compounds [15–17].
First this strategy based on the processes of β-decay of
Benzene is a classical representative of π-electron-
donor compounds. The immense practical importance
of the reaction of carbenium ions with aromatic
hydrocarbons, under lying the industrial aromatic
1762

GAS PHASE REACTION OF NUCLEOGENIC DIMETHYLGERMYLIUM CATIONS
1763
alkylation is well known [26]. In contrast, the reaction
of electrophilic aromatic silylation for a long time was
not realized either in the gas or in the condensed phase.
The absence of silylation products was due to the fact
that the processes of desilylation proceeded under the
conditions of the experiments with much larger rates
than the deprotonation processes [27]. The electro-
philic silylation of benzene in the gas phase was
possible only in the presence of triethylamine as a
proton acceptor [28, 29].
with the formation of labeled benzene and a
germylium cation, or bimolecularly by proton transfer
to the molecules of the substrate with the formation of
phenylgermanes. The formation of labeled benzene is
due to isotope exchange in the σ-complex between
tritium of the dimethylgermylium cation and protium
in the ipso-position of the benzene ring.
The performed B3LYP/6-31G* quantum chemical
calculations of the stereoelectronic structure and
charge distribution in the model σ-complex suggest
that for the germylium as well as for silicenium ions
the processes of degermylation (desilylation) are more
preferable than the processes of deprotonation.
Our radiochemical studies of the reaction of
nucleogenic dimethyl- and diethylsilyl ions with
benzene in the absence of any additives in the gas and
condensed phase have shown that the yield of the
products of silylation (phenylsilanes) in both cases did
not exceed 8% [7, 22, 23]. The major product of these
reaction was labeled benzene.
The calculated angle between the Ge–C bond and
the plane of the benzene ring is 101.5°, that is, not
substantially different from that in the π-complex
(90°). With this, the main positive charge (+0.87) is
located on the Ge atom. It is well known that in the
course of alkylation of aromatic compounds the
covalently bonded σ-complex is formed in which the
angle between the alkyl group and the plane of the ring
is ~141°. The positive charge is shifted from the
carbenoid carbon atom to the hydrogen atoms of the
benzene ring and the highest positive charge (+0.36) is
located on the hydrogen atom in the ipso-position. The
structure and equilibrium geometry of σ-complexes of
the carbenium, silicenium and germylium ions with
benzene are shown in Fig. 2.
The observed difference in the reaction course for
the carbenium and silicenium ions corresponds to the
different structure of the intermediate complexes since
the silicenium ion in the σ-complex practically retains
its cationic nature.
Radiochemical investigation of the ion-molecular
reaction of dimethylgermylium cation Me2GeT+ with
C6H6 has shown that, as in the case of silicenium ions,
the main product of the reaction is labeled benzene
(92%). According to the adopted mechanism of the ion-
molecular reaction of carbenium ions with aromatic
compounds, the reaction of germylium cations
Me2GeT+ with benzene can be represented by the
following scheme (Fig. 1).
It is evident that this structure and charge
distribution in the complex are more appropriate for
the process of degermylation.
The approach of the ion to the molecule results in
the formation of the π-complex, which then is
transformed into the σ-complex. Decomposition of the
latter occurs either unimolecularly (degermylation)
The products of germylation, labeled phenyl-
germanes, are formed in a small amount of ~7%, and
their composition is 71% of Me2PhGeT to 29% of
PhH2TGe.
Me2TGe+
GeTMe2
Me2T+Ge
+C6H6
Me2TGe+ + C6H6
−C6H+7
5%
H
−Me2HGe+
−H3Ge+
C6H5T
93%
GeTH2
2%
H2T+Ge
H
+C6H6
−C6H+7
−C2H4
Fig. 1. Tentative mechanism of the reaction of dimethylgermylium cations with benzene.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 9 2010

1764
MYALOCHKIN et al.
+0.99
Si
H
–0.65
C
105.3°
141.0°
2.105 Å
C
–0.59
H
C
1.563 Å
–0.39
+0.36
+0.33
+0.87
Ge
H
101.5°
2.188 Å
–0.51
+0.33
C
Fig. 2. Electronic structure and equilibrium geometry of complexes of cations H3M+ (M = C, Si, Ge) with benzene (B3LYP/6-
31G*).
The former is the product of the reaction of benzene
with the major nucleogenic cation Me2GeT+, and the
latter is the product of its reaction with unsubstituted
germylium cation H2TGe+, which could be formed by
dissociation of the complex [H2TGe+·C2H4]. The
performed quantum chemical calculations (B3LYP/6-
31G* and aug-cc-pVDZ) [30] have shown that on the
potential energy surface (PES) of the system C2H7Ge+
the global minimum belongs to cation Me2GeH+.
However, the PES has also local minima close in
energy to the classical cation Me2GeH+ and belonging
to the donor–acceptor complexes [HGe+·C2H6],
[MeGe+·CH4], [H3Ge+·C2H4]. Dissociation of these
complexes may lead to the formation of germanium-
centered cations and the molecules of the
corresponding hydrocarbons.
Changing of the tetrahedral structure into the planar
structure characteristic of the three-coordinate cation,
is followed by the release of the energy of relaxation,
which may be consumed for excitation of this ion. For
the germylium cation Me2GeT+ we have estimated this
energy (B3LYP/6-31G*) as 24 kcal mol–1, that rules
out the isomerization of the free cation. An additional
energy can be acquired by association of this cation
with the molecule of the nucleophile.
For benzene, this energy is 36.5 kcal mol–1
(B3LYP/6-31G*). Therefore, the total energy is
enough to overcome the lowest isomerization barrier
of the cation (CH3)2GeH+ resulting in the formation of
the complex [H3Ge+·C2H4] and its further dissociation.
However, this energy is too small to overcome
other activation barriers, as shows the absence of
methane, ethane or other products of germylation
among the reaction products.
According to quantum chemical calculations, iso-
merization of the classical cation Me2HGe+ is
connected with high activation barriers (~75, 60,
52 kcal mol–1, respectively) [30]. Since the time of
emergence of the nucleogenic cation is very short
(10–14 s), it inherits the structure of the mother
molecule, that is, in our case, tetrahedral [17, 31].
It should be noted that earlier the possibility of
existence of complexes [HM+·H2] was theoretically
predicted for the unsubstituted cations H3M+ (M = Si,
Ge, Sn), but only the use of the nuclear chemical
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 9 2010

GAS PHASE REACTION OF NUCLEOGENIC DIMETHYLGERMYLIUM CATIONS
1765
strategy allowed for the first time to confirm
experimentally the predicted by us isomerization of
cation Me2GeT+.
Identification of the labeled products of the reaction
was performed by comparing their retention times with
those of the authentic compounds under the same
chromatographic conditions. The yield of the products
was determined as the ratio of activity of the given
compound to the total activity of all reaction products.
Therefore, the ionic germylation of aromatic
compounds (as well as the ionic silylation), unlike
electrophilic alkylation, practically does not occur due
to the structure of the arising intermediate complexes,
in which the germylium and silicenium ions retain
their cationic nature.
Dimethylphenylgermane was prepared by the
Grignard reaction from dimethylbromogermane and
bromobenzene with subsequent reduction of bromo-
dimethylphenylgermane with lithium hydride in hexane
at heating. Phenylgermane was prepared by reduction
of phenyltrichloro-germane with lithium hydride in
dioxane at heating. Phenyltrichlorogermane was
prepared by reflux of iodobenzene with germanium
tetrachloride in the presence of copper powder [33].
Dimethylphenylgermane and phenylgermane used as
authentic samples were identified by the method of
chromatomass spectrometry on a “Polaris 125”
instrument.
At the same time, the formation of a small amount
of the products of germylation of benzene both by the
principal cation Me2GeT+ and by the product of its
isomerization H2TGe+ may serve as an evidence of
formation of germylium cations as a result of β-decay
of tritium in the molecule of dimethylgermane
Me2GeT2.
EXPERIMENTAL
Free dimethylgermylium cations were generated by
nuclear chemical method [15–17].
ACKNOWLEDGMENTS
β−
This work was financially supported by Russian
Foundation for Basic Research (grant no. 09-03-00439)
and by the Department of Chemistry and Material Sciences
of Russian Academy of Sciences (Program no. 1).
(CH3)2Ge+T + 3He0.
(CH3)2GeT2
Dimethylditritiumgermane was synthesized by the
protocol described in [32].
Benzene of “chemically pure” grade was used as
substrate, which prior to filling the ampules was
thoroughly dried over sodium metal and distilled. The
purity was controlled by gas chromatography.
REFERENCES
1. Hobrock, B.G. and Kiser, R.W., J. Phys. Chem., 1962,
vol. 66, p. 155.
2. Karni, M., Apeloig, Y., Kapp, J., and Schleyer, P.v.R.,
in The Chemistry of Organic Silicon Compounds,
Rappoport, Z. and Apeloig, Y., Eds., New York: Wiley,
2001, vol. 3.
3. Zharov, I. and Michl, J., in The Chemistry of Organic
Germanium, Tin and Lead Compounds, Rappoport, Z.
and Apeloig, Y., Eds., New York: Wiley, 2003, vol. 2.
The reaction mixtures for investigation of the ion-
molecular reactions of dimethylgermylium cations
were placed into ampules of molybdenum glass of
spherical shape of ~20 ml capacity; the pressure of the
benzene vapors was 15 mm Hg, the activity of
dimethylditritium-germane was 0.001 Ci (3.7×107 Bq).
The accumulation of the products occurred at room
temperature in the dark for ~4 months.
4. Schleyer, P.v.R., Buzek, P., Muller, T., and Apeloig, Y.,
Angew. Chem. Int. Ed. Engl., 1993, vol. 32, no. 10,
p. 1471.
The analysis of the products of dimethylgermylium
cations with benzene was performed by the method of
gas radiochromatography on a Tsvet-500 chromato-
graph equipped with a flow-through proportional
counter as detector of β–-radiation of tritium. For
analysis, two chromatographic systems were used: the
stainless steel column 2000×2 mm packed with 5%
SE-30 on Inerton-AW, and the stainless steel column
3000×2 mm packed with Porapak R. The rate of the
gas carrier (helium) was 20 ml min–1, the rate of the
quenching gas [methane (5%)/argon] was 5 ml min–1.
5. Olsson, L. and Cremer, D., J. Chem. Phys. Lett., 1993,
vol. 215, no. 5, p. 433.
6. Ignatyev, I.S. and Sundius, T., Organometallics, 1996,
vol. 15, no. 26, p. 5674.
7. Kochina, T.A., Vrazhnov, D.V., and Ignatyev, I.S., J.
Organomet. Chem., 1999, vol. 586, nos. 1–2, p. 241.
8. Shchegolev, B.F. and Kochina, Т.А., Zh. Strukt. Khim.,
1992, vol. 33, no. 1, p. 156.
9. Lambert, J.B., Zhang, S., Stern, S.L. and Huffman, J.C.,
Science, 1993, vol. 260, p. 1917.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 9 2010

1766
MYALOCHKIN et al.
10. Lambert, J.B. and Zhang S., J. Chem. Soc. Chem.
Comm., 1993, no. 5, p. 383.
11. Kochina, Т.А., Nefedov, C.D., Sinotova, Е.N., and
Shchukin, E.V., Russ. J. Gen. Chem., 2001, vol. 71,
no. 2, p. 206.
12. Kochina, Т.А., Vrazhnov, D.V., Ignat’ev, I.S., and
Sinotova, Е.N., Russ. J. Gen. Chem., 2003, vol. 73,
no. 1, p. 61.
13. Lambert, J.B., Zhao, Y, Wu, H., Tse, W.C., and
Kuhlmann, B., J. Am. Chem. Soc., 1999, vol. 121,
no. 21, p. 5001.
14. Chuit, C.H., Corriu, R.J.P., Mehdi, A., and Reye, C.,
Angew Chem. Int. Ed. Engl., 1993, vol. 32, no. 9,
p. 1311.
15. Nefedov, V.D., Sinotova, Е.N., and Toropova, М.А.,
Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim., 1980, no. 3,
p. 35.
16. Nefedov, V.D., Kochina, Т.А., and Sinotova, Е.N.,
Russ. Chem. Rev. Engl. Transl., 1986, vol. 55, no. 5,
p. 426.
21. Gomzina, N.A., Kochina, Т.А., Nefedov, V.D.,
Sinotova, Е.N., and Vrazhnov, D.V., Zh. Obshch.
Khim., 1994, vol. 64, no. 3, p. 443
22. Kochina, Т.А., Nefedov, V.D., Sinotova, Е.N., and
Shchukin, E.V., Radiochemistry, 2000, vol. 42, no. 2,
p. 184.
23. Kochina, Т.А., Vrazhnov, D.V., Ignat’ev, I.S., Nefe-
dov, V.D., and Sinotova, Е.N., Russ. J. Gen. Chem.,
1999, vol. 69, no. 6, p. 905.
24. Kochina, Т.А., Vrazhnov, D.V., Ignat’ev, I.S., and
Sinotova, Е.N., Russ. J. Gen. Chem., 2005, vol. 75,
no. 1, p. 69.
25. Kochina, Т.А., Vrazhnov, D.V., Sinotova, Е.N., and
Ignat’ev, I.S., Russ. J. Gen. Chem., 2005, vol. 75, no. 5,
p. 708.
26. Olah, G.A., Friedel-Crafts and Related Reactions, New
York: Wiley, 1963.
27. Wojtinyak, A.C. and Stone, J., Int. J. Mass. Spectrom.
Ion Processes, 1986, vol. 74, no. 1, p. 59.
17. Kochina, T.A., Vrazhnov, D.V., Sinotova, E.N., and
Voronkov, M.G., Russ. Chem. Rev. Engl. Transl., 2006,
vol. 75, no. 2, p. 95-110.
18. Nefedov, V.D., Kochina, Т.А., Sinotova, Е.N., and
Kharitonov, N.P., Zh. Obshch. Khim., 1982, vol. 52,
no. 7, p. 1599.
28. Cacace, F., Crestoni, M., and Fornarini, S., J. Am.
Chem. Soc., 1992, vol. 114, no. 17, p. 6776.
29. Fornarini, S., J. Org. Chem., 1998, vol. 53, no. 6,
p. 1314.
30. Ignat’ev, I.S., Kochina, Т.А., and Vrazhnov, D.V., Russ.
J. Gen. Chem., 2007, vol. 77, no. 4, p. 575.
19. Kochina, T.A., Vrazhnov, D.V., and Ignatyev, I.S.,
31. Speransa, M., Chem. Rev., 1993, vol. 93, no. 8, p. 2933.
J. Organomet. Chem., 1999, vol. 589, no. 1, p. 45.
20. Kochina, Т.А., Vrazhnov, D.V., Sinotova, Е.N.,
Katsap, M.Yu., and Shchegolev, B.F., Russ. J. Gen.
Chem., 2001, vol. 71, no. 10, p. 1557.
32. Myalochkin, D.L., Kochina, Т.А., Vrazhnov, D.V.,
Avrorin, V.V., and Sinotova, Е.N., Russ. J. Gen. Chem.,
2007, vol. 77, no. 7, p. 1187.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 9 2010