Synergistic effects of alkali metals in the alkylation of naphthalene and toluene with ethene in the ArH-alkali metal systems in THF (ArH - naphthalene, phenanthrene)

Article abstract of DOI:10.1016/j.jorganchem.2008.12.052

The use of mixtures of metallic lithium and sodium in the naphthalene-alkali metal systems in THF leads to a synergistic acceleration of the naphthalene alkylation with ethene at room temperature and atmospheric pressure. The greatest synergistic effect is observed at a Li:Na molar ratio of 2:1. Under these conditions, the overall conversion of naphthalene into alkylation products (linear 1-alkylnaphthalenes and their dihydro derivatives) attains 88% after 24 h (a (Li + Na):C₁₀H₈ ratio is 2:1). The use of mixtures of metallic lithium and potassium in such systems results, however, in a synergistic retardation of the alkylation process. The strongest retarding effect is observed at a Li:K molar ratio of 1:1. The efficiency of the toluene alkylation with ethene in the naphthalene-alkali metal systems in THF is also increased on the replacement of lithium or sodium by their mixtures. The best results are obtained at a Li:Na molar ratio of 1:3. With this Li:Na ratio, toluene is almost quantitatively converted into linear and α-branched higher monoalkylbenzenes (24 h, (Li + Na):C₁₀H₈ = 2:1). The rate of the naphthalene alkylation with ethene in the presence of toluene is enhanced as well on an introduction of mixtures of lithium and sodium into the system. However the maximum of the activity is shifted here towards higher lithium content (Li:Na = 1:1). A similar synergistic effect of lithium and sodium was found on studying the toluene alkylation with ethene in the phenanthrene-Li-Na systems in THF (a (Li + Na):phenanthrene ratio is 3:1). An addition of potassium to sodium also considerably increases the efficiency of the toluene and naphthalene alkylation with ethene in the naphthalene-based systems. The possible mechanism of the alkali metal synergism in the above-mentioned alkylation reactions is discussed.

Full text of DOI:10.1016/j.jorganchem.2008.12.052

Journal of Organometallic Chemistry 694 (2009) 1467–1472
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synergistic effects of alkali metals in the alkylation of naphthalene and toluene
with ethene in the ArH–alkali metal systems in THF (ArH – naphthalene,
phenanthrene)
a
b
b
b,*
S. Rummel , S.M. Yunusov , E.S. Kalyuzhnaya , V.B. Shur
a
Leibniz-Institut für Oberflächenmodifizierung e.V., Permoserstr. 15, D-04318 Leipzig, Germany
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov St. 28, Moscow 119991, Russia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 June 2008
Received in revised form 28 November 2008
Accepted 17 December 2008
Available online 30 December 2008
The use of mixtures of metallic lithium and sodium in the naphthalene–alkali metal systems in THF leads
to a synergistic acceleration of the naphthalene alkylation with ethene at room temperature and atmo-
spheric pressure. The greatest synergistic effect is observed at a Li:Na molar ratio of 2:1. Under these con-
ditions, the overall conversion of naphthalene into alkylation products (linear 1-alkylnaphthalenes and
8
their dihydro derivatives) attains 88% after 24 h (a (Li + Na):C10H ratio is 2:1). The use of mixtures of
metallic lithium and potassium in such systems results, however, in a synergistic retardation of the alkyl-
ation process. The strongest retarding effect is observed at a Li:K molar ratio of 1:1. The efficiency of the
toluene alkylation with ethene in the naphthalene–alkali metal systems in THF is also increased on the
replacement of lithium or sodium by their mixtures. The best results are obtained at a Li:Na molar ratio
Keywords:
Activation of C–H bonds
Alkali metals
Alkylation
Aromatic hydrocarbons
Ethene
of 1:3. With this Li:Na ratio, toluene is almost quantitatively converted into linear and
a-branched higher
monoalkylbenzenes (24 h, (Li + Na):C10 = 2:1). The rate of the naphthalene alkylation with ethene in
H
8
Synergism
the presence of toluene is enhanced as well on an introduction of mixtures of lithium and sodium into
the system. However the maximum of the activity is shifted here towards higher lithium content
(Li:Na = 1:1). A similar synergistic effect of lithium and sodium was found on studying the toluene alkyl-
ation with ethene in the phenanthrene–Li–Na systems in THF (a (Li + Na):phenanthrene ratio is 3:1). An
addition of potassium to sodium also considerably increases the efficiency of the toluene and naphtha-
lene alkylation with ethene in the naphthalene-based systems. The possible mechanism of the alkali
metal synergism in the above-mentioned alkylation reactions is discussed.
Ó 2008 Elsevier B.V. All rights reserved.
1
. Introduction
Adducts of aromatic hydrocarbons with alkali metals play an
novel reaction has shown that the rate of the H/D exchange is
strongly increased in the presence of the solid phase of the alkali
metal in a mixture and drops practically to zero on the replace-
ment of THF by 1,2-dimethoxyethane (DME) as well as on an addi-
tion of [15]crown-5 to the system. Subsequently, it has been
established that similar systems based on naphthalene and alkali
metals (Li, Na, K) in THF are able to introduce naphthalene and tol-
uene into the alkylation reactions with ethene under ambient con-
ditions yielding linear 1-alkylnaphthalenes (together with small
important role in chemistry. They are excellent reagents for elec-
tron transfer to various organic and inorganic substrates, which
is used successfully in organic and organometallic synthesis and
catalysis (for reviews, see, e.g. [1–5]). One of the outstanding
achievements in this area was the discovery of a remarkable ability
of radical-anion adducts of alkali metals with naphthalene and
other arenes to induce the ‘‘living” polymerization of 1,3-dienes
and some monoenes.
As part of our ongoing research into CꢀH bond activation by
non-transition metal compounds [6–11], we have previously re-
ported on a high catalytic activity of systems, derived from naph-
thalene and metallic sodium in THF, in the hydrogen–deuterium
exchange of hydrocarbons (naphthalene, benzene, toluene, ethene,
methane) at room temperature [8]. A detailed examination of this
quantities of their dihydro derivatives) and linear and a-branched
higher monoalkylbenzenes, respectively [10,11]. Here too, the pro-
cess was strongly accelerated when the solid phase of the alkali
metal was present in a mixture, whereas the use of DME instead
of THF as well as an addition of [15]crown-5 led again to a sharp
decrease in the reaction rate, thus indicating on the possible simi-
larity of mechanisms of the H/D exchange and the alkylation. Sys-
tems formed on the treatment of a number of other aromatic
hydrocarbons (biphenyl, phenanthrene, trans-stilbene, pyrene,
anthracene) with alkali metals in THF proved also to be active in
the toluene alkylation with ethene at 22 °C [11].
*
Corresponding author.
E-mail address: vbshur@ineos.ac.ru (V.B. Shur).
0
022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.12.052

1
468
S. Rummel et al. / Journal of Organometallic Chemistry 694 (2009) 1467–1472
8
the C10H –Li system in THF is used, the interaction of toluene with
In the present article, we report on unusual synergistic effects of
alkali metals in the above-mentioned alkylation reactions with
ethene in the ArH–alkali metal systems (ArH – naphthalene, phen-
anthrene) in THF. The discovery of these synergistic effects not
only allows one to increase substantially the efficiency of the alkyl-
ation but is also of great importance for elucidation of the mecha-
nism of activation of C–H bonds in hydrocarbons by systems of
such a type.
ethene results in the formation of n-propylbenzene (12) (30%), n-
pentylbenzene (13) (5%), 3-phenylpentane (14) (8%) and 3-phenyl-
heptane (15) (5%) in a total yield of 48% based on toluene. How-
ever, if metallic sodium is introduced into this system, the rate of
the toluene alkylation increases, and at a Li:Na molar ratio of 1:3
the toluene conversion into the alkylation products reaches 97%
(12 – 46%, 13 – 3%, 14 – 44%, 15 – 4%). Still further enhancement
in the sodium content lowers the reaction rate, and with sodium
alone the toluene conversion amounts to only 18% (12 – 15%,
For a short preliminary account of a part of this study, see
[
12,13].
1
4 – 3%). On carrying out the reaction at a Li:Na ratios of 2:1, 1:1
and 1:2, small quantities of 5-phenylnonane (16) are formed along
with 12–15. Importantly, when 12 instead of toluene is introduced
2
. Results and discussion
into the alkylation reaction with ethene in the C10
in THF (Li:Na = 1:3), exclusively -branched higher monoalkyl-
benzenes, viz., 14 and 15, are produced in an overall yield of 70%
(14 – 68%, 15 – 2%). This means that only more acidic -C–H bonds
of the side alkyl chain in monoalkylbenzenes are able to be acti-
vated by alkali metal-based systems of such a type.
8
H –Li–Na system
The reactions were carried out at room temperature and atmo-
a
spheric pressure for 24 h by the standard procedure. In all experi-
ments with the naphthalene-containing systems, the amount of
naphthalene (3 mmol) and its initial concentration in THF (2 M)
was maintained constant. The relative amounts of alkali metals
a
in a mixture were varied but overall (Li + Na):C10
H
8
, (Na + K):C10
H
8
The naphthalene alkylation with ethene in the presence of tol-
uene is accelerated as well on the use of mixtures of lithium with
sodium (Table 3). The greatest acceleration is observed here at a
Li:Na ratio of 1:1. Under such conditions, naphthalene is converted
into 1–8 in a total yield of 84% (1 – 45%, 2 + 3 – 9%, 4 – 16%, 5 – 3%,
6 – 6%, 7 + 8 – 5%). If the reaction is conducted in the absence of
sodium the naphthalene conversion decreases to 55% (1 – 34%,
2 + 3 – 2%, 4 – 13%, 5 – 3%, 7 + 8 – 3%) and in the absence of lithium
it does not exceed 35% (1 – 33%, 2 + 3 – 2%). On using a Li:Na ratio
of 1:3, small amounts of two dihydro derivatives (17 and 18) of 4
are produced together with 1–5, 7 and 8. As in all of the above-de-
scribed reactions, the quantity of absorbed ethene is considerably
larger than its overall consumption for the alkylation (Table 4).
A similar lithium–sodium synergism is observed in systems
based on phenanthrene (Table 5). For example, when a Li:Na molar
ratio is 1:2, the yield of products of the toluene alkylation under
the action of the phenathrene-containing system reaches 91% of
the theoretical value with respect to toluene (12 – 43%, 14 – 45%,
15 – 3%). Both an increase and a decrease in this ratio diminish
the rate of the process. In the absence of sodium, the toluene
conversion into higher monoalkylbenzenes drops to 36% (12 –
27%, 13 – 4%, 14 – 3%, 15 – 2%), and without lithium it is only
11% (12 – 10%, 14 – 1%). If the reaction is carried out at a Li:Na ratio
of 5:1, n-heptylbenzene (19) is formed in a small quantity along
with 12–15. According to GLC/MS, phenanthrene is also alkylated
with ethene in such systems but the exact nature of resulting prod-
ucts could not be established here.
In contrast to lithium–sodium mixtures, an introduction of a
mixture of lithium with potassium into the naphthalene-contain-
ing system in THF leads to a synergistic retardation of the naphtha-
lene alkylation with ethene (Table 6). The strongest retarding effect
is observed at a Li:K molar ratio of 1:1. On using such a ratio, the
reaction gives 1, 4 and 5 in a total yield of 19% based on naphtha-
lene. In the absence of potassium, the naphthalene conversion into
the alkylation products increases to 60% (see above) while in the
absence of lithium it reaches 85% (1 – 83%, 2 + 3 – 2%). The rate
of ethene uptake also passes through a minimum on changing
the Li:K ratio but the position of this minimum is shifted here to-
wards higher potassium contents in the system (K:Li = 2–3:1). In
all experiments, the amount of absorbed ethene is again noticeably
greater than the ethene quantity consumed for the alkylation. It
should be noted that when the reaction of ethene with the
and (Li + K):C10 molar ratios were kept equal to 2:1. On using
H
8
such a ratio of the reagents, a part of the taken quantity of the al-
kali metals remained undissolved and thus was present in the sys-
tems in the form of the solid state. In the case of phenanthrene,
mixtures of lithium with sodium were tested in the alkylation with
ethene. The content of phenanthrene in these experiments was
3
(
mmol whereas its initial concentration in THF was 2.67 M. A
Li + Na):phenanathrene molar ratio was maintained equal to 3:1.
The experiments on the toluene alkylation with ethene were con-
3
ducted at an equimolar PhCH :ArH ratio. The products were ana-
lyzed by GLC and GLC/MS.
In Table 1, data on the naphthalene alkylation with ethene in
the C10 –Li–Na systems in THF are presented. As it has been
shown previously [11], the interaction of ethene with the
–Na system in THF affords 1-ethylnaphthalene (1) (35%) to-
H
8
10 8
C H
gether with small quantities (2%) of its two dihydro derivatives (2
and 3) in a total yield of 37% based on naphthalene. It turned out,
however, that if metallic lithium is added to this system the rate
of ethene uptake and the efficiency of the naphthalene alkylation
are strongly enhanced, reaching a maximum at a Li:Na molar ratio
of 2:1 (Table 1). Under these conditions, a mixture of 1–3 (23% of
1, 3% of 2 and 3) together with 1-n-butylnaphthalene (4) (28%), 1-
n-hexylnaphthalene (5) (17%), 1-n-octylnaphthalene (6) (7%), two
dihydro derivatives (7 and 8) of 5 (4%), two dihydro derivatives (9
and 10) of 6 (3%) and 1-n-decylnaphthalene (11) (3%) are pro-
duced in a total yield of 88%. Further increase in the lithium con-
tent leads, however, to a decrease in the rates of ethene uptake
and the naphthalene alkylation, and when lithium alone is used
the naphthalene conversion into the alkylation products dimin-
ishes to 60% (1 – 26%, 4 – 15%, 5 – 9%, 6 – 5%, 7 + 8 – 3%,
9
+ 10 – 2%). Thus, the presence of Li and Na in the system results
in a synergistic acceleration of the alkylation of naphthalene with
ethene.
It is of interest that at all tested Li:Na ratios, the amount of ab-
sorbed ethene in these experiments noticeably exceeds its con-
sumption for the formation of alkylation products (Table 1), thus
suggesting the involvement of ethene in some other reactions,
for example, with the alkali metal(s) (activated by naphthalene)
to give aliphatic organolithium and/or organosodium compounds
[
14] and also (in the case of lithium) with the corresponding naph-
thalene dianion to afford products of the ethene carbolithiation
15,16].
The efficiency of the toluene alkylation with ethene is also shar-
ply enhanced in the presence of lithium–sodium mixtures. As a re-
sult of these reactions, linear and
-branched higher
monoalkylbenzenes are produced. As seen from Table 2, when
[
C10H –Li–K system is carried out in the presence of toluene, no
8
lithium–potassium synergism is observed in both the naphthalene
and toluene alkylation.
The behavior of sodium–potassium mixtures in the toluene
alkylation with ethene is analogous to that of lithium–sodium ones
a

S. Rummel et al. / Journal of Organometallic Chemistry 694 (2009) 1467–1472
1469
Table 1
Alkylation of naphthalene with ethene in the C10
H
8
–Li–Na systems in THF.a
Alkali metal (mmol)
Absorbed C
2
H
4
Yield of alkylation products (%)b
C
2
H
4
consumption for alkylation
Naphthalene conversion (%)
Li
6
Na
(mmol)
(mol/mol C10
H
8
)
1
2 + 3
4
5
6
7 + 8
9 + 10
11 (mmol)
8
(mol/mol C10H )
0
1.5
2
3
4
5.40
6.72
6.95
6.15
4.20
2.53
2.19
1.80
2.24
2.32
2.05
1.40
0.84
0.73
26
24
23
20
41
41
35
–
–
3
3
4
8
2
15
21
28
25
18
9
9
5
7
7
5
2
–
–
3
5
4
3
3
–
–
2
4
3
8
2
–
–
–
3
3
–
–
–
–
3.60
5.37
6.00
5.19
3.72
2.37
1.11
1.20
1.79
2.00
1.73
1.24
0.79
0.37
60
77
88
77
76
62
37
4
4
3
2
1
0
.5
13
17
13
6
4
–
.5
4.5
6
–
a
2
2 °C, 1 atm, 24 h, 3 mmol of naphthalene, (Li + Na):C10
H
8
= 2:1, [C10
8
H ]
o
= 2M.
b
Based on naphthalene.
Table 2
Alkylation of toluene with ethene in the C10
H
8
–Li–Na systems in THF.a
Yield of alkylation products (%)b
Alkali metal (mmol)
Toluene conversion (%)
Li
6
Na
12
13
14
15
16
0
1.5
2
3
4
4.5
5
6
30
35
37
43
47
46
38
15
5
8
6
8
9
19
44
43
3
5
8
10
10
8
4
5
–
–
–
2
4
3
–
–
–
48
59
67
74
82
97
86
18
4
4
3
2
1
1
0
.5
10
10
8
5
3
.5
–
–
a
2
2 °C, 1 atm, 24 h, 3 mmol of naphthalene, (Li + Na):C10
H
8
8 o 8
= 2:1, [C10H ] = 2M, a C10H :PhMe molar ratio is 1.06:1.
b
Based on toluene.
Table 3
Alkylation of naphthalene with ethene in the C10H
8
–Li–Na systems in THF in the presence of toluene.a
Alkali metal (mmol)
Yield of alkylation products (%)b
Naphthalene conversion (%)
Li
6
Na
1
2 + 3
4
5
6
17 + 18
7 + 8
9 + 10
0
1.5
2
3
4
4.5
5
6
34
43
43
45
43
38
52
33
2
1
3
9
8
15
7
13
20
20
16
15
9
3
4
2
3
5
9
3
–
–
4
3
6
2
–
2
–
–
–
–
–
–
2
–
–
3
3
4
5
5
3
2
–
–
–
3
–
–
–
–
–
55
75
79
84
78
76
74
35
4
4
3
2
1
1
0
.5
.5
8
–
2
a
2
2 °C, 1 atm, 24 h, 3 mmol of naphthalene, (Li + Na):C10
H
8
= 2:1, [C10
8
H ]
o
8
= 2M, a C10H :PhMe molar ratio is 1.06:1.
b
Based on naphthalene.
Table 4
Comparison of the amount of absorbed ethene with its consumption for the formation of products of toluene and naphthalene alkylation in the C10
H
8
–Li–Na systems in THF.a
Alkali metal (mmol)
Absorbed C
2
H
4
(mmol)
Ethene consumption for alkylation
Toluene
Naphthalene
(mmol)
Total (mmol)
Li
6
Na
(mmol)
(mol/mol PhMe)
8
(mol/mol C10H )
0
1.5
2
3
4
4.5
5
6
7.25
9.42
8.81
9.05
8.48
8.80
7.03
2.77
2.01
2.58
3.14
3.48
3.71
4.30
3.93
0.59
0.71
0.91
1.11
1.23
1.31
1.52
1.39
0.21
2.40
3.63
3.84
4.02
3.57
3.33
2.94
1.05
0.80
1.21
1.28
1.34
1.19
1.11
0.98
0.35
4.41
6.21
6.98
7.50
7.28
7.63
6.87
1.64
4
4
3
2
1
1
0
.5
.5
a
2
8 8 o 8
2 °C, 1 atm, 24 h, 3 mmol of naphthalene, (Li + Na):C10H = 2:1, [C10H ] = 2M, a C10H :PhMe molar ratio is 1.06:1.
(
Table 7). It was found that when potassium metal is added to the
the yield of the reaction products does not exceed 9% (12 – 8%, 14 –
1%).
10 8
C H
–Na system in THF the conversion of toluene into 12 and 14
first increases from 18% to 43% (12 – 26%, 14 – 17%) at a Na:K ratio
of 1:1 but then starts to decrease. If sodium is absent in a mixture
To elucidate the possible role of the sodium–potassium alloy in
the observed synergism, we carried out special control experi-

1
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S. Rummel et al. / Journal of Organometallic Chemistry 694 (2009) 1467–1472
Table 5
Alkylation of toluene with ethene in the phenanthrene–Li–Na systems in THF.
a
Alkali metal (mmol)
Absorbed C
2
H
4
(mmol)
Yield of alkylation products (%)b
C
2
H
4
consumption for toluene alkylation
Toluene conversion (%)
Li
9
Na
12
13
19
14
15
(mmol)
(mol/mol PhMe)
0
1.5
3
4.5
6
7.5
9
5.41
9.63
8.38
8.20
9.34
8.32
5.29
27
38
47
51
43
49
10
4
6
5
4
–
–
–
–
2
–
–
–
–
–
3
7
2
5
5
–
3
–
–
1.33
2.41
2.72
2.69
4.02
2.41
0.34
0.47
0.85
0.96
0.95
1.42
0.85
0.12
36
58
69
73
91
67
11
7
6
4
3
1
0
.5
12
18
45
18
1
.5
.5
a
2
2 °C, 1 atm, 24 h, 3 mmol of phenanthrene, (Li + Na):phenanthrene = 3:1, [phenanthrene]
o
= 1.67 M, a phenanthrene:PhMe molar ratio is 1.06:1.
b
Based on toluene.
Table 6
Alkylation of naphthalene with ethene in the C10
H
8
–Li–K systems in THF.a
Yield of alkylation products (%)b
Alkali metal (mmol)
Absorbed C
2
H
4
C
2
H
4
consumption for alkylation
Naphthalene conversion (%)
Li
6
K
(mmol)
(mol/mol C10
H
8
)
1
2 + 3
4
5
6
7 + 8
9 + 10
(mmol)
8
(mol/mol C10H )
0
1.5
2
3
4
5.40
4.09
3.28
2.08
1.60
1.61
2.70
1.80
1.36
1.09
0.69
0.53
0.54
0.90
26
25
16
9
18
38
83
–
–
–
–
–
–
2
15
16
12
8
6
–
9
7
5
2
–
–
–
5
4
3
–
–
–
–
3
–
–
–
–
2
–
–
–
–
–
–
3.60
2.82
2.01
0.93
0.90
1.14
2.55
1.20
0.94
0.67
0.31
0.30
0.38
0.85
60
52
36
19
24
38
85
4
4
3
2
1
0
.5
.5
4.5
6
–-
–
–
a
2
2 °C, 1 atm, 24 h, 3 mmol of naphthalene, (Li + K):C10
H
8
= 2:1, [C10
H ]
8 o
= 2M.
b
Based on naphthalene.
ments on the interaction of toluene with ethene in THF at 22 °C in
the presence of an authentic sodium–potassium alloy
Table 7
Alkylation of toluene and naphthalene with ethene in the C10
8
H –Na–K systems in
(
K:Na = 1.77:1). It turned out, however, that no alkyaltion occurs
THF.a
under such conditions. Thus, for the sodium–potassium synergism
to be manifested in the toluene alkylation, naphthalene must be
present in the system.
Alkali metal (mmol)
Yield of alkylation products (%)
Tolueneb Napnthalenec
The rate of the naphthalene alkylation in the presence of tolu-
ene also increases on the use of sodium–potassium mixtures but
the synergistic effect observed in this case is noticeably less pro-
nounced than that in the toluene alkylation (Table 7). The highest
activity in the alkylation of naphthalene is exhibited here by the
system with a Na:K molar ratio of 5.1:0.9. The reaction of ethene
with naphthalene in this system gives rise to 1–3 in a total yield
of 50% (1 – 42%, 2 + 3 – 8%). When sodium alone is present in the
mixture, the yield of 1–3 lowers to 36%, and with potassium alone
only 1 is formed in a very low yield (7%). The amount of ethene ab-
Na
6
K
12
14
12 + 14
1
2 + 3
1 + 2 + 3
0
15
24
26
25
26
21
16
9
3
8
18
32
37
40
43
32
25
12
9
33
42
37
38
35
27
19
8
3
8
4
–
–
–
–
–
–
36
50
41
38
35
27
19
8
5
4
4
3
2
2
1
0
.1
.5
0.9
1.5
2
3
3.5
4
11
15
17
11
9
.5
5
6
3
1
8
7
7
a
2
2 °C, 1 atm, 24 h, 3 mmol of naphthalene, (Na + K):C10
H :PhMe molar ratio is 1.06:1.
Based on toluene.
Based on naphthalene.
H
8
8 o
= 2:1, [C10H ] = 2M,
8
sorbed by these toluene-containing C10H –Na–K systems passes
through a maximum at a Na:K ratio of 3:1 (Table 8). At all ratios
used, the quantity of absorbed ethene significantly exceeds its con-
a C10
8
b
c
Table 8
Comparison of the amount of absorbed ethene with its consumption for the formation of products of toluene and naphthalene alkylation in the C10
H
8
–Na–K systems in THF.a
Alkali metal (mmol)
Absorbed C
2
H
4
(mmol)
Ethene consumption for alkylation
Toluene
Naphthalene
(mmol)
Total (mmol)
Na
6
K
(mmol)
(mol/mol PhMe)
8
(mol/mol C10H )
0
2.77
3.25
4.44
4.22
3.66
2.55
2.38
1.41
1.21
0.59
1.13
1.36
1.56
1.70
1.22
0.96
0.42
0.28
0.21
0.40
0.48
0.55
0.60
0.43
0.34
0.15
0.10
1.05
1.50
1.23
1.14
1.05
0.81
0.57
0.24
0.21
0.35
0.50
0.41
0.38
0.35
0.27
0.19
0.08
0.07
1.64
2.63
2.59
2.70
2.75
2.03
1.53
0.66
0.49
5
4
4
3
2
2
1
0
.1
.5
0.9
1.5
2
3
3.5
4
.5
5
6
a
2
8 8 o 8
2 °C, 1 atm, 24 h, 3 mmol of naphthalene, (Na + K):C10H = 2:1, [C10H ] = 2M, a C10H :PhMe molar ratio is 1.06:1.

S. Rummel et al. / Journal of Organometallic Chemistry 694 (2009) 1467–1472
1471
sumption for the toluene and naphthalene alkylation. Interestingly,
no sodium–potassium synergism is observed in the case of the
naphthalene alkylation with ethene in the absence of toluene.
the active species was also discussed [11]. Within the framework
of this mechanism, the observed alkali metal synergism could be
due to the formation of the mixed lithium–sodium, sodium–potas-
sium and lithium–potassium salts of the naphthalene dianion dif-
fering in their stability and reactivity from the corresponding
homonuclear dilithium, disodium and dipotassium derivatives.
Note, however, that the use of the above dianionic mechanism
for an explanation of the alkylation reactions found meets with
considerable difficulties because metallic sodium, in contrast to
lithium, does not form the dianion with naphthalene in THF at
room temperature in any detectable amounts [18], and for potas-
sium metal no unambiguous evidences for the formation of the
naphthalene dianion in THF at 22 °C are available as well.
Further studies are required for the elucidation of the nature of
these synergistic effects of alkali metals.
3
. Conclusion
The results of this study revealed the remarkable synergistic ef-
fects of alkali metals in the alkylation of toluene and naphthalene
with ethene in the ArH–alkali metal systems (ArH – naphthalene,
phenanthrene) in THF. In the case of the naphthalene-containing
systems, the use of mixtures of lithium and sodium or sodium
and potassium leads, as a rule, to a synergistic acceleration of the
process. The only exception is the naphthalene alkylation in the
10 8
C H –Na–K systems in the absence of toluene, wherein no so-
dium–potassium synergism is observed. The use of mixtures of
lithium and potassium in the naphthalene-based systems, not con-
taining toluene, results in a synergistic retardation of the naphtha-
lene alkylation, but when toluene is present no lithium–potassium
synergism occurs in both the naphthalene and toluene alkylation.
Earlier, for interpreting experimental data on the hydrogen–
deuterium exchange of hydrocarbons under the action of the naph-
thalene–sodium system in THF, it has been suggested that this pro-
cess proceeds via the following main steps [8]:
4. Experimental
The experiments were carried out in an Ar atmosphere with
careful exclusion of air oxygen and moisture using standard Shlenk
techniques. THF and toluene were purified in the usual manner and
freshly distilled prior to use from sodium/benzophenone (THF) or
over sodium (toluene) under Ar. Commercial naphthalene and
phenanthrene were used without further purification. Metallic
lithium, sodium and potassium were introduced into the reactions
in the form of the particles of the size: ca. 3 ꢂ 2 ꢂ 0.3 mm in the
case of lithium and ca. 4 ꢂ 3 ꢂ 0.5 mm in the case of sodium and
potassium. The reaction products were analysed by GLC with tem-
perature programming (160 °C, 10 min; 160–300 °C, 10 °C/min;
300 °C, 40 min) on a Crompack CP 9001 chromatograph equipped
with a flame ionization detector and a DB5 MS (30 m ꢂ 0.25 mm)
capillary column (the internal standard – dodecane). The GLC/MS
analyses were performed on a Trio 1000, FISONS instrument. The
most part of the experiments was duplicated or triplicated
showing reasonably good reproducibility. On using the naphtha-
lene–potassium system in THF for the naphthalene alkylation in
the absence of toluene, the reproducibility was somewhat worse
and here the results obtained were averaged for five runs
(
1) Generation of atomic sodium in the C10
the reactions (a), (b), (c):
8
H –Na system due to
g
þ
þ
g
Namet þ ArH Na ¢ Na ArH þ Naat
ðaÞ
ðbÞ
ðcÞ
g
þ
g
þ
þ
g
ArH Na þ ArH Na ¢ ArH þ Na ArH þ Naat
ArH Na ¢ ArH þ Naat
ArH — naphthalene
g
þ
(
(
n
2) Agglomeration of atomic sodium into sodium clusters [Na ]
stabilized by the formation of surface complexes with
naphthalene.
3) Reversible cleavage of C–H and C–D bonds of hydrocarbons
on the surface of sodium clusters, resulting in the hydro-
gen–deuterium exchange.
(
1 – 83 ± 6%), 2 + 3 – 2 ± 1%).
A similar ‘‘cluster” mechanism has been proposed [11] for the
reactions of the naphthalene and toluene alkylation with ethene
in the ArH–alkali metal systems (ArH – naphthalene, biphenyl,
phenanthrene, trans-stilbene, pyrene, anthracene) in THF. Accord-
ing to this mechanism, the formation of the alkylation products oc-
curs here through the step of the ethene insertion into the alkali
metal–carbon bonds [M]–R, arising on the surface of clusters as a
result of the above-mentioned reversible cleavage of the reactive
C–H bonds of a hydrocarbon substrate (RH).
4.1. Product identification
Compounds 1, 4, 5, 12, 13 and 19 were identified by GLC and
GLC/MS using authentic samples of these compounds. Products
14 and 15 were identified on the basis of coincidence of their mass
spectra with the corresponding literature data [19]. The conclusion
on the nature of other products is based on the analysis of their
mass spectra. The most important characteristics of the mass spec-
tra recorded for these products are given below. Compound 2, m/z:
2
½Mꢁ þ RH ¢ ½Mꢁ ꢀ R þ ½Mꢁ ꢀ H
M ¼ Li; Na; K
+
+
+
1
58 ([M] , 53%), 129 ([MꢀEt] , 100%), 128 ([C10
8
H ] , 65%). Com-
+
+
From the proposed mechanism, it follows that the correspond-
pound 3, m/z: 158 ([M] , 63%), 129 ([MꢀEt] , 100%), 128
+
+
ing heteronuclear lithium–sodium, sodium–potassium and lith-
ium–potassium clusters could form in the bimetallic ArH–Li–Na,
ArH–Na–K and ArH–Li–K systems, respectively, in THF. Such heter-
onuclear clusters might be responsible for the observed synergism
of alkali metals in the above-described alkylation reactions.
Similar synergistic effects have previously been observed in the
reactions of catalytic olefin oligomerization induced by dispersions
of alkali metals in the absence of aromatic promoters (see review
8
([C10H ] , 92%). Compound 6, m/z: 240 ([M] , 12%), 142
+
+
+
([MꢀC H ] , 28%), 141 ([MꢀC H ] , 100%), 128 ([C H ] , 14%),
7
14
7
15
10
8
+
+
115 ([MꢀC H ꢀC H ] , 79%). Compound 7, m/z: 214 ([M] , 12%),
7
15
+
2
2
+
+
185 ([MꢀEt] , 30%), 157 ([MꢀBu] , 22%), 129 ([MꢀHex] , 100%),
+
+
128 ([C H ] , 80%). Compound 8, m/z: 214 ([M] , 8%), 185
1
+
0
8
+
+
([MꢀEt] , 14%), 157 ([MꢀBu] , 16%), 129 ([MꢀHex] , 100%), 128
+
+
+
([C H ] , 86%). Compound 9, m/z: 242 ([M] , 10%), 213 ([MꢀEt] ,
1
0
8
+
+
+
35%), 185 ([MꢀBu] , 11%), 157 ([MꢀHex] , 31%), 129 ([MꢀOct] ,
+
+
[
17]). One may assume that the active species ensuring the syner-
10 8
100%), 128 ([C H ] , 93%). Compound 10, m/z: 242 ([M] , 13%),
+
+
+
gistic acceleration of these reactions (occurring at elevated tem-
peratures) are also heteronuclear clusters, present in the
dispersions.
For the naphthalene and toluene alkylation, an alternative
mechanism with the participation of the naphthalene dianion as
213 ([MꢀEt] , 44%), 185 ([MꢀBu] , 15%), 157 ([MꢀHex] , 42%),
+
+
129 ([MꢀOct] , 84%), 128 ([C H ] , 100%). Compound 11, m/z:
1
0
8
+
+
+
268 ([M] , 13%), 142 ([MꢀC H ] , 31%), 141 ([MꢀC H ] , 100%),
9
18
9
19
+
+
128 ([C H ] , 22%), 115 ([MꢀC H ꢀC H ] , 69%). Compound 16,
1
0
8
9
19
2
2
+ + +
m/z: 204 ([M] , 8%), 147 ([MꢀBu] , 9%), 91 ([C H ] , 100%). Com-
7
7

1
472
S. Rummel et al. / Journal of Organometallic Chemistry 694 (2009) 1467–1472
+
+
+
pound 17, m/z: 186 ([M] , 23%), 157 ([MꢀEt] , 34%), 129 ([MꢀBu] ,
is 76% (38% of 1, 15% of 2 and 3, 9% of 4, 9% of 5, 2% of 17 and 18,
and 3% of 7 and 8); the toluene conversion is 97% (46% of 12, 3% of
13, 44% of 14, 4% of 15).
Other experiments on the toluene and naphthalene alkylation
were carried out by similar procedures. The results are summa-
rized in Tables 1–8.
+
+
9
8
8%), 128 ([C10H ] , 100%). Compound 18, m/z: 186 ([M] , 21%), 157
[MꢀEt] , 23%), 129 ([MꢀBu] , 100%), 128 ([C10
+
+
+
(
8
H ] , 89%).
4
.2. Alkylation of naphthalene in the C10 –Li–Na system
H
8
Naphthalene (0.384 g, 3 mmol), THF (1.5 ml), metallic lithium
0.028 g, 4 mmol), metallic sodium (0.046 g, 2 mmol) and dode-
(
References
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(
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