First synthesis of the three isomeric parent disilacyclohexanes. An improved preparation of methylene di-grignard

Article abstract of DOI:10.1021/ol900462z

Ring closure of 1,5-dibromo-1,5-disilapentane with methylene di-Grignard was the key step in the preparation of the parent 1,3-disilacyclohexane. For that purpose, the preparation of methylene di-Grignard has been improved and simplified. The successful s

Full text of DOI:10.1021/ol900462z

ORGANIC
LETTERS
2009
Vol. 11, No. 9
2015-2017
First Synthesis of the Three Isomeric
Parent Disilacyclohexanes. An Improved
Preparation of Methylene Di-Grignard
Palmar I. Gudnason† and Ingvar Arnason*
Science Institute, UniVersity of Iceland, Dunhaga 3, IS-107 ReykjaVik, Iceland
ingVara@raunVis.hi.is
Received March 5, 2009
ABSTRACT
Ring closure of 1,5-dibromo-1,5-disilapentane with methylene di-Grignard was the key step in the preparation of the parent 1,3-disilacyclohexane.
For that purpose, the preparation of methylene di-Grignard has been improved and simplified. The successful synthesis of the isomeric 1,2-
and 1,4-disilacyclohexanes is also reported.
Saturated six-membered ring systems in which one or more
CH2 units in cyclohexane have been replaced by SiH2 units
are of general interest because they provide good examples
to compare cyclohexane with its closest analogues. Known
examples are 1-silacyclohexane,1 1,3,5-trisilacyclohexane,2
and cyclohexasilane.3 The parent disilacyclohexanes have
not been described in the literature so far; however, a number
of substituted derivatives of 1,2-disilacyclohexane,4 1,3-
disilacyclohexane,5 and 1,4-disilacyclohexane6 have been
reported. Because the Si-H bond has a higher reactivity than
Si-alkyl or Si-aryl bonds, it is more convenient to prepare
and work with substituted disilacyclohexanes. This may be
a reason why the unsubstituted rings have remained a missing
link in the field of silacyclohexanes for decades.
In recent years, the stereochemistry of six-membered
silicon-containing ring systems has been of special interest
in our group. In particular, we have studied the conforma-
tional energy surface of silacyclohexane7 and the confor-
mational properties of some of its monosubstituted deriva-
tives.8 Furthermore, we have investigated the gas-phase
structure of 1,3,5-trisilacyclohexane,9 its conformational
surface, and the conformational behavior of its mono-, di-,
and trisubstituted alkyl derivatives as deduced from NMR
(5) (a) Anteunis, M. J. O.; Dedeyne, R. Bull. Soc. Chim. Belg. 1976,
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127–132. (c) Fritz, G. Z. Anorg. Allg. Chem. 1970, 375, 171. (d) Lyssenko,
K. A.; Astapova, T. V.; Antipin, M. Y.; Makarova, N. N. MendeleeV
Commun. 1998, 87–88. (e) Mizuno, K.; Inamasu, N.; Shimizu, M.; Hiyama,
T. Chem. Lett. 1996, 1083–1084. (f) Shimizu, M.; Mizuno, K.; Inamasu,
N.; Masai, H.; Hiyama, T. Inorg. Chim. Acta 1999, 296, 231–235. (g)
Shimizu, M.; Mizuno, K.; Inamusu, N.; Hiyama, T. Chem. Lett. 1996, 1083–
1084.
† Present address: Ossur hf, Grjothalsi 5, IS-110, Reykjavik, Iceland.
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(2) Fritz, G.; Fro¨hlich, H. Z. Anorg. Allg. Chem. 1971, 382, 9–26.
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J. E.; Kaszynski, P.; Jacobs, S. J. Organometallics 1998, 17, 2018–2026.
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Polishchuk, E. E. Polym. Sci. Ser. A 2000, 42, 1320–1325. (e) Murray,
R. W.; Kaplan, M. L. Tetrahedron 1969, 25, 1651. (f) Polishchuk, A. P.;
Makarova, N. N.; Astapova, T. V.; Petrova, I. M. Crystallogr. Rep. 2002,
47, 791–797. (g) Volkova, L. M.; Petrova, I. M.; Chizhova, N. V.; Petrovskii,
P. V.; Vinogradova, L. E.; Makarova, N. N. Russ. Chem. Bull. 1999, 48,
1712–1716.
(4) (a) Cha, S. H.; Lee, K. K.; Kwak, Y. W.; Choi, H. J.; Park, Y. S.;
Naka, A.; Ishikawa, M. Organometallics 2001, 20, 3718–3723. (b) Ishikawa,
M.; Shirai, S.; Naka, A.; Kobayashi, H.; Ohshita, J.; Kunai, A.; Yamamoto,
Y.; Cha, S. H.; Lee, K. K.; Kwak, Y. W. Organometallics 2002, 21, 4206–
4211. (c) Tamao, K.; Ishikawa, M.; Kumada, M. J. Chem. Soc., Dalton
Trans. 1969, 73. (d) Tamao, K.; Kumada, M.; Ishikawa, M. J. Organomet.
Chem. 1971, 31, 169–177. (e) Tamao, K.; Kumada, M.; Noro, A. J.
Organomet. Chem. 1971, 31, 169–177. (f) Tamao, K.; Tsuji, H.; Terada,
M.; Asahara, M.; Tamaguchi, S.; Toshimitsu, A. Angew. Chem., Int. Ed.
2000, 39, 3287–3290.
(7) (a) Arnason, I.; Kvaran, A.; Bodi, A. Int. J. Quantum Chem. 2006,
106, 1975–1978. (b) Arnason, I.; Thorarinsson, G. K.; Matern, E. Z. Anorg.
Allg. Chem. 2000, 626, 853–862.
10.1021/ol900462z CCC: $40.75
Published on Web 04/02/2009
 2009 American Chemical Society

spectra10 as well as from quantum chemical calculations.11
The 1,3-disilacyclohexane is an intermediate between the
former two ring systems, and it was of interest to explore
its chemistry.
experimental procedure for the methylene di-Grignard is
given in the Supporting Information.
The reaction of di-Grignard 2 with 1,5-disilapentane 1 in
diethyl ether resulted in ring closure and formation of
disilacyclohexane 3 in 17% yield (Scheme 1). Small amounts
of 2,6-disilaheptane (detectable in the 1H and 13C NMR and
MS spectra) are formed as a side product in this reaction,
probably by reaction of traces of CH3MgBr with 1.
One possible way to achieve its preparation is shown in
Scheme 1. Compound 1 may be prepared in a three-step
procedure from allyltrichlorosilane;12 the methylene di-
Grignard 2, however, has not been readily available. In fact,
2 has been known since as early as 1926, when it was first
prepared by Emschwiller from methylene bromide and
magnesium in diethyl ether.13 The yields of 2 were originally
low and unreliable, and its synthetic use was limited because
of CH3MgBr contamination but its preparation has been
improved in several steps.14 These include the use of
magnesium amalgam instead of magnesium metal15 and the
use of diisopropyl ether as the reaction medium in which 2
does not dissolve. After the reaction, the diisopropyl ether
can be decanted and the crude product dissolved in a 1:1
diethyl ether/benzene mixture from which the di-Grignard
can be isolated. In this way, the contamination of CH3MgBr,
which will interfere with further reactions of 2, is greatly
diminished.16 However, this last improvement as described
by Bickelhaupt et al. requires the use of twice-sublimed
magnesium, which is not commercially available, and an
evacuated whole-glass manifold with break-seals. Most
likely, these are the main reasons why Bickelhaupt’s method
has not found a common use.
Scheme 1
.
Synthetic Route for 1,3-Disilacyclohexane 3
Scheme 2
.
Synthetic Route for 1,4-Disilacyclohexane 6
We have been able to simplify this process considerably,
thereby keeping its main features unchanged. We have found
that commercial Mg powder (-50 mesh, 99+%) may be
used instead of twice-sublimed magnesium. Although our
yields are, on the average, only 40% (compared with 80%
according to Bickelhaupt), we found on the other hand that
the amount of dibromomethane may be scaled up by a factor
4 (using the same amounts of solvents) without affecting
the percentage yield of 2. Thus, the amount of product per
run can be doubled. Using a special reaction flask, the entire
process can be carried out employing standard Schlenk
techniques and commercially available starting materials.
One such run can be completed in 2 days. A detailed
Encouraged by the successful synthesis of 1,3-disilacyclo-
hexane, we looked for possible reactions by which 1,4-
disilacyclohexane might be prepared. Coupling reactions be-
tween 1,4-dibromo-1,4-disilabutane and 1,2-dibromoethane with
lithium metal resulted in a complete reaction of the metal, but
no traces of the desired product could be isolated. A second,
more promising, synthetic route is shown in Scheme 2.
Kaszynski et al. have published a preparation of 4.17
Because it involves a tedious three-step synthesis, we decided
first to prepare 1,1-diphenylsilacyclohexane as a model
compound in order to test on it successive reactions with
triflic acid and LiAlH4.
(8) (a) Arnason, I.; Kvaran, A.; Jonsdottir, S.; Gudnason, P. I.;
Apparently, diphenylsilacyclohexane has not been de-
scribed in the literature before. Its preparation went smoothly
(eq 1); the reaction with 2 equiv of freshly distilled triflic
acid turned it quantitatively into its triflic derivative, and a
further reaction with LiAlH4 resulted in the known silacy-
clohexane.
Oberhammer, H. J. Org. Chem. 2002, 67, 3827–3831. (b) Bodi, A.; Kvaran,
´
A.; Jonsdottir, S.; Antonsson, E.; Wallevik, S. O.; Arnason, I.; Belyakov,
A. V.; Baskakov, A. A.; Ho¨lbling, M.; Oberhammer, H. Organometallics
2007, 26, 6544–6550. (c) Favero, L. B.; Velino, B.; Caminati, W.; Arnason,
I.; Kvaran, A. Organometallics 2006, 25, 3813–3816. (d) Favero, L. B.;
Velino, B.; Caminati, W.; Arnason, I.; Kvaran, A. J. Phys. Chem. A 2006,
110, 9995–9999. (e) Girichev, G. V.; Giricheva, N. I.; Bodi, A.; Gudnason,
P. I.; Jonsdottir, S.; Kvaran, A.; Arnason, I.; Oberhammer, H. Chem.sEur.
J. 2007, 13, 1776–1783.
(9) Arnason, I.; Oberhammer, H. J. Mol. Struct. 2001, 598, 245–250.
(10) (a) Arnason, I. Z. Anorg. Allg. Chem. 1998, 624, 1973–1976. (b)
Arnason, I. Z. Anorg. Allg. Chem. 1999, 625, 97–101. (c) Arnason, I.;
Kvaran, A. Z. Anorg. Allg. Chem. 1998, 624, 65–73.
(11) Arnason, I.; Matern, E. THEOCHEM 2001, 544, 61–68.
(12) Mitzel, N. W.; Schmidbaur, H.; Rankin, D. W. H.; Smart, B. A.;
Hofmann, M.; Schleyer, P. V. Inorg. Chem. 1997, 36, 4360–4368.
(13) Emschwiller, G. C.R. Acad. Sci. Paris 1926, 183, 665.
(14) Bickelhaupt, F. J. Organomet. Chem. 1994, 475, 1–14.
(15) Bertini, F.; Grasselli, P.; Zubiani, G.; Cainelli, G. Tetrahedron 1970,
26, 1281–1290.
In a similar manner, 4 reacted with triflic acid to give 5,
which in turn was hydrogenated with LiAlH4 to 1,4-
disilacyclohexane 6.
(16) Heisteeg, B. J. J. V. d.; Schat, G.; Akkerman, O. S.; Bickelhaupt,
F. J. Organomet. Chem. 1986, 308, 1–10.
(17) See ref 6c.
2016
Org. Lett., Vol. 11, No. 9, 2009

methods. Compound 7 was then converted to 1,2-disilacy-
clohexane 8 as outlined in Scheme 3.
Scheme 3. Synthetic Route for 1,2-Disilacyclohexane 8
All three disilacyclohexanes are colorless liquids at
room temperature. Their syntheses should be carried out
under inert atmosphere using standard Schlenk techniques.
However, the products are not extremely air sensitive, and
they can be exposed to dry air for a short time without
decomposition.
In conclusion, we have been able to synthesize the three
isomeric unsubstituted disilacyclohexanes for the first time.
We have also improved considerably the synthesis of the
simplest di-Grignard, CH2(MgBr)2. Additional investigations
on the gas-phase molecular structures of the disilacyclohex-
1
anes, their potential energy surfaces, and H NMR spectra
analysis are currently underway.
Acknowledgment. This work was supported by the
University of Iceland Research Fund.
Supporting Information Available: Experimental pro-
cedures and spectral data for all new products. This
material is available free of charge via the Internet at
http://pubs.acs.org.
We then turned to the last one of the isomeric disilacy-
clohexanes, the 1,2-disilacyclohexane. After several unsuc-
cessful attempts, we came up with a similar strategy as in
the case of 1,4-disilacyclohexane. 1,1,2,2-Tetraphenyl-1,2-
disilacyclohexane 7 was prepared by well-known synthetic
OL900462Z
Org. Lett., Vol. 11, No. 9, 2009
2017