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