Preparation of Organozinc and Organocadmium Compounds from the Metals and Alkyl Halides in the Presence of Stimulating Systems Based on a Derivative a Transition Metal and an Organometallic Compound

Article abstract of DOI:10.1023/A:1025684302325

Full and mixed alkyl derivatives of zinc and cadmium were prepared from these metals and organic halides in the presence of stimulating systems necessarily containing a transition metal derivative and an organometallic compound capable of reducing this derivative under the process conditions. Such stimulating systems make it possible to introduce selectively organic halides (iodides, bromides, chlorides) into the reaction with zinc and cadmium to obtain the corresponding mixed organometallic compounds.

Full text of DOI:10.1023/A:1025684302325

Russian Journal of General Chemistry, Vol. 73, No. 4, 2003, pp. 556 559. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 4, 2003,
pp. 589 592.
Original Russian Text Copyright
2003 by Eremeev, Danov, Skudin, Sakhipov.
Preparation of Organozinc and Organocadmium Compounds
from the Metals and Alkyl Halides in the Presence
of Stimulating Systems Based on a Derivative
a Transition Metal and an Organometallic Compound
I. V. Eremeev, S. M. Danov, A. G. Skudin, and V. R. Sakhipov
Nizhni Novgorod State Technical University, Dzerzhinsk Branch, Dzerzhinsk, Nizhni Novgorod oblast, Russia
Received March 20, 2001
Abstract Full and mixed alkyl derivatives of zinc and cadmium were prepared from these metals and
organic halides in the presence of stimulating systems necessarily containing a transition metal derivative and
an organometallic compound capable of reducing this derivative under the process conditions. Such stimulat-
ing systems make it possible to introduce selectively organic halides (iodides, bromides, chlorides) into the
reaction with zinc and cadmium to obtain the corresponding mixed organometallic compounds.
Alkyl compound of zinc and cadmium are widely
used in the preparative and industrial practice as
initial substances for inorganic, organic, and organo-
metallic syntheses and as catalysts for the polymeriza-
tion of unsaturated compounds [1 4]. The production
of materials for electronics is one of the most im-
portant applications of alkyl derivatives of these
elements [5 12]. However, simple and highly efficient
procedures of their synthesis are lacking. First of all,
this concerns the preparation of high-purity organo-
zinc and organocadmium compounds used in the
production of materials for electronics [9 11]. At
present, numerous methods for the synthesis of metal
alkyl derivative are known. They can be divided into
three groups: methods based on the direct alkylation
of elements and their derivatives, and also those
involving chemical transformations of full or mixed
organometallic compounds by rearrangement or trans-
formation of ligands under the action of various
agents. From the viewpoint of obtaining high-purity
organometallic compounds, the most promising is the
so-called direct synthesis based on the alkylation of
elements with organic halides. In particular, this is
confirmed by the experimental studies of the impurity
composition of alkyl compounds of nontransition
elements depending on the method of their synthesis:
the purest samples were obtained by the direct
synthesis [13 15]. However, only electropositive
alkali metals and magnesium readily react with alkyl
halides. Various procedures for stimulating the
process should be used to alkylate other elements, and
nevertheless in many cases it is impossible to combine
good results of the direct synthesis (high rate,
selectivity, possibility of using accessible and cheap
alkyl chlorides or alkyl bromides) with its simplicity
and efficiency. As a result, the most stimulation
procedures either have a limited application area or
are labor-consuming and uneconomical, or require
solvents or significant amounts of chemical additions.
As a result, the main potential advantage of direct
synthesis in the production of high-purity organo-
metallic compounds, namely, the possibility of using
minimal number of chemicals which are the main
source of impurities in the final product, is lost.
We have suggested a procedure for stimulating
direct synthesis of organometallic compounds using
systems whose necessary components are a derivative
of a transition metal and an organometallic compound
capable of reducing the transition metal derivative
under the process conditions. Such systems appeared
to be effective in the alkylation of a commercial zinc
powder with ethyl bromide [16] [schemes (1) and (2)].
Zn + EtBr
2EtZnBr
EtZnBr,
(1)
(2)
Et2Zn + ZnBr2.
Therefore, the aim of this work was to examine the
possibilities of this procedure for stimulating the
direct synthesis of organometallic compounds, using
the preparation of zinc and cadmium alkyl derivatives
as an example.
Our experiments have shown that, in the presence
of the above-mentioned stimulating systems, alkyl
halides (iodides, bromides, chlorides) readily react
1070-3632/03/7304-0556$25.00 2003 MAIK Nauka/Interperiodica

PREPARATION OF ORGANOZINC AND ORGANOCADMIUM COMPOUNDS
557
Synthesis of organozinc and organocadmium compounds by alkylation of zinc and cadmium with organic halides in the
presence of stimulating systems consisting of a transition metal compound and an organometallic compound
Parameters of the
Yield of
Composition of initial reaction mixture, mol
synthesis of
Yield of
isolated
com-
AlkMHlg
according
to the
AlkMHlg (M = Zn, Cd)
Synthesized
compound
di-
pound,
analysis
data, %
a
metal
organic halide
stimulating system
ethyl T, C
duration, h
%
ether
Me2Zn
Et2Zn
Pr2Zn
Bu2Zn
11.00 Zn 8.31 MeI
3.06 Zn 2.44 EtBr
0.77 Zn 0.66 PrBr
0.77 Zn 0.66 BuBr
0.226 CuI; 0.150 Me3Al2I3
0.080 CuI; 0.170 EtZnBr
0.046 CuI; 0.047 EtZnBr
0.046 CuI; 0.039 EtZnBr
42
38 40
50
12.0
4.5
7.0
90
82
81
78
61
84
68b
66b
45d
51d
42
50
8.0
C8H17ZnBrc 0.31 Zn 0.25 C8H17Br 0.021 CuI; 0.030 EtMgI
C10H21ZnBr 0.31 Zn 0.25 C10H21Br 0.021 CuI; 0.030 EtMgI
1.1
1.1
1.0
1.0
1.0
35
35
40
40
4
48.0
32.0
20.0
20.0
34.0
BuCdI
C7H15CdI
C10H21CdI
0.30 Cd 0.25 BuI
0.30 Cd 0.25 C7H15I
0.30 Cd 0.25 C10H21I 0.010 CuI; 0.020 BuMgI
0.010 CuI; 0.020 BuMgI
0.010 CuI; 0.020 BuMgI
48
59
a
b
Zinc alkyls were obtained by thermal disproportionation of AlkZnHlg. Before AlkZnBr disproportionation, the liquid part of the
c
reaction mixture was separated from the solid residue. 2-Ethylhexylzinc bromide was synthesized from 2-ethylhexyl bromide.
Yield of the ketone isolated from the reaction of the synthesized AlkZnBr with acetyl chloride.
d
with zinc, and alkyl iodides and alkyl bromides, with
the transition metal subhalide with the nontransition
metal with the formation of the corresponding surface
halide of the nontransition metal and adsorbed atoms
of the transition metal, and formation of the target
mixed organometallic compound by the reaction of
the alkyl radical and the surface halide of the non-
transition metal.
cadmium. The results of the syntheses of certain full
and mixed alkyl derivatives of zinc and cadmium in
the presence of stimulating systems based on copper(I)
iodide are shown in the table. Thus, the proposed
procedure for stimulating the direct synthesis of
organometallic compounds is highly efficient in the
preparation of zinc and cadmium alkyl derivatives
and is very simple in implementation.
It should be emphasized that these stages by no
means reflect the whole set of processes that take
place under the conditions of the direct synthesis of
organometallic compounds in the presence of the
stimulating systems under consideration. The mech-
anism of operation of the stimulating systems and
the influence of the nature of the components on their
activity and selectivity will be considered in more
detail in a series of subsequent papers.
The assumed mechanism of operation of the
stimulating systems based on derivatives of transition
metals and organometallic compounds can be illu-
strated by the following most important target stages.
The heterogeneous reaction of a transition metal
derivative and an organometallic compound proceeds
on the surface of the transition metal derivative
(which does not dissolve in the reaction mixture) to
give a full alkyl compound of the transition metal.
This stage is followed by the mass transfer of the
transition metal alkyl compound onto the surface of
the nontransition metal to be alkylated, decomposition
of the transition metal alkyl compound on the surface
of the nontransition metal with the formation of
adsorbed transition metal atoms, insertion of the
transition metal atoms into the carbon halogen bonds
of the organic halide with the formation of a mixed
alkyl compound of the transition metal, decomposi-
tion of this compound with the formation of the alkyl
radical and transition metal subhalide, reduction of
EXPERIMENTAL
In the work we used PTs-10-grade zinc [TU (Tech-
nical Specifications) 48-4015-1/0-81] and pure-
grade cadmium [TU (Technical Specifications) 6-09-
02-40086]. Grignard reagents were synthesized accord-
ing to [17]. Heptyl iodide, 2-ethylhexyl bromide, and
decyl iodide were synthesized from the corresponding
alcohols and hydrogen halides [18]. A solution of
methylaluminum sesquiiodide in methyl iodide was
obtained from PA-1 grade aluminum and methyl
iodide. Ethylzinc bromide was synthesized from zinc
powder and ethyl bromide in the presence of the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 4 2003

558
EREMEEV et al.
stimulating system copper(I) iodide ethylzinc
bromide by the previously developed procedure [16].
The resulting solution of ethylzinc bromide in ethyl
bromide was separated from unchanged zinc, and
ethyl bromide was distilled off in vacuum. The result-
ing crystalline ethylzinc bromide was dissolved in the
corresponding alkyl bromide for the subsequent use in
the stimulating system. The other substances were of
the grade required for their use in reactions. Alkyl
halides were dried in a vacuum desiccator over
calcium chloride and distilled directly before intro-
ducing into the reaction. Diethyl ether was dried over
metallic sodium and distilled before use. The organo-
metallic compounds were synthesized as indicated in
the table.
Synthesis of alkylzinc- and alkylcadmium
halides was carried out similarly to the first stage of
the synthesis of zinc dialkyls. Alkylmagnesium
iodides contained in the stimulating systems were
added into the reactor as solutions in diethyl ether.
After termination of the heating and stirring of the
reaction mixture, the solution obtained was decanted
from the solid residue, which was washed with diethyl
ether (2 200 ml). The washing liquid was combined
with the liquid part of the reaction mixture. In the case
of the synthesis of alkylcadmiun iodides, the main
part of diethyl ether was distilled off, 100 ml of
heptane was added, and distillation of diethyl ether
was continued. Then the distillation flask was cooled
to 20 C, and the crystalline precipitate was separated
from the liquid phase. The yield of alkylcadmiun
iodide was calculated from the weight of the pre-
cipitate obtained, in which the cadmium content
agreed with the calculated values.
Synthesis of zinc alkyls. Copper(I) iodide and zinc
were placed in a reactor equipped with a stirrer and a
reflux condenser. The reactor was evacuated for
10 min and filled with thoroughly dried and deoxy-
genated argon. Then the organic halide and the organo-
metallic compound of the stimulating system as a
solution in the corresponding alkyl halide were added.
The free end of the reflux condenser was closed with a
calcium chloride tube. The first stage of the synthesis
[synthesis of alkylzinc halide by scheme (1)] was
carried out with vigorous stirring. After completion
of this stage, the stirrer was taken out of the reaction
mixture, the reactor was cooled to room temperature,
the reflux condenser was replaced by a descending
condenser, and the thermal disproportionation of the
alkylzinc halide by scheme (2) with simultaneous
vacuum distillation of the zinc dialkyl was carried out.
The yields of 2-ethylhexyl- and decylzinc bromides
were estimated in the same way as in the synthesis of
zinc dialkyls. Furthermore, the resulting alkylzinc
bromides without their isolation as pure compounds
were brought into the reaction with acetyl chloride to
obtain ketones [18]. The reaction was carried out at a
temperature below 8 C by adding dropwise a solution
of acetyl chloride (0.3 mol) in 50 ml of diethyl ether
to a solution alkylzinc bromide. After adding acetyl
chloride, the reaction mixture was stirred for 1 h,
40 ml of distilled water and 10 ml of sulfuric acid
(2.3 M) were added, and the mixture was stirred for
an additional 10 min. Then 100 ml of diethyl ether
was added, and the oily layer was separated and
washed with distilled water, sodium carbonate solu-
tion (0.5 M), and again water. After that, the resulting
substance was dried in a vacuum desiccator over
sodium sulfate, and the solvent was distilled off in a
vacuum. The residue was crystallized from acetone
on cooling to 17 C. The yields of ketones are given
in the table. The ketones obtained were identified by
1H NMR spectroscopy on a Tesla BS-487 instrument
(80 MHz). The melting point of methyl decyl ketone
agreed with the published data [20].
To obtain dipropyl- and dibutylzinc, the liquid part
of the reaction mass was decanted from unchanged
zinc after completion of preparation of alkylzinc
bromide, and the solid residue was washed with
several portions of the corresponding alkyl bromide.
After each washing, the liquid phase was decanted
from the solid residue. Then all portions of the wash
liquid and the liquid part of the reaction mass were
combined, the alkyl bromide was distilled off in a
vacuum, and the alkylzinc bromide was subjected to
the thermal disproportionation. The measured charac-
teristics of the zinc dialkyls obtained agreed with the
published data [1]. The yield of zinc dialkyls was
calculated from the amount of the isolated product.
The yield of alkylzinc bromides in the first stage of
the synthesis was estimated from the content of zinc
ions, which was determined by Na2EDTA titration
[19] of a sample of the reaction mixture (free from
solid fragments) after hydrolysis of alkylzinc bromide
and dissolution of the precipitated zinc hydroxide in
an aqueous solution of hydrogen chloride.
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