Reactivities of triethylgermylborate in methanol

Article abstract of DOI:10.1246/cl.2001.1086

The reactivity of lithium (triethylgermyl)triphenylborate, prepared from unsolvated triethylgermyllithium and triphenylborane, with organic substrates in methanol was investigated. The germylborates reacted with organic halides and acyl halides to give th

Full text of DOI:10.1246/cl.2001.1086

1086
Chemistry Letters 2001
Reactivities of Triethylgermylborate in Methanol
Masato Nanjo,* Kazuhiko Matsudo, and Kunio Mochida*
Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588
(Received August 8, 2001; CL-010762)
The reactivity of lithium (triethylgermyl)triphenylborate,
< RI for the octyl halides and phenyl halides shown in Table 1.
This order is consistent with the recognized reactivities of tri-
ethylgermyl–alkali metals in HMPA and the bond strength of
the carbon–halogen bond.7 The rest of 2 remained unreacted.
The reaction of 2 with benzyl bromide afforded mainly benzyl-
triethylgermane in low yield. Several unidentified byproducts
were also detected by GC–MS spectra.
No formation of coupling products derived by elecetron-
transfer in the reactions of 2 with organic halides were detceted
by GC.
prepared from unsolvated triethylgermyllithium and triphenyl-
borane, with organic substrates in methanol was investigated.
The germylborates reacted with organic halides and acyl
halides to give the corresponding germyl-substituted com-
pounds. From the reaction with carbonyl compounds, esters,
carboxylic acid, alkenes, and alkynes, germylborates were com-
pletely recovered.
The group 14 element–alkali metal species as nucleophiles
have been extensively studied in organic and organometallic
syntheses, e.g., the introduction of group 14 elements into
organic halides, metal halides, carbonyl compounds, etc.1–3
Very recently, our group reported the first successful isola-
tion of lithium (triethylgermyl)triphenylborate (1), prepared
from unsolvated triethylgermyllithium4 and triphenylborane 5,6
The polymeric structure of germylborate 1 in the solid state
was destroyed by addition of MeOH to give a dimeric structure
of 1 with coordination of MeOH to the lithium atoms,
{[Et3GeBPh3][Li(MeOH)]}2 (2). The molecular structures of 1
and 2 were confirmed by X-ray diffraction analysis. We report
herein some reactions of 2 with organic substrates in MeOH.
At first, the stability of the MeOH-coordinated germylbo-
rate 2 was examined in excess of degassed MeOH and H2O.
The germylborate 2 was very stable in excess degassed MeOH
and H2O at room temperature for 1–4 days, and was completely
recovered unreacted. The germylborate 2 did not change in
degassed MeOH even at 50 °C for 10 h. The stability of 2 is
may be explained by its planar four-membered ring composed
of two lithium and two oxygen atoms.5
With acyl chlorides, the germylborate 2 in MeOH at room
temperature for 2 days gave the corresponding triethylgermyl
ketones as the sole product in high yields.8
The results of the reactions of 2 with various acyl chlorides
(RCOCl) in MeOH are summarized in Table 2.
The displacement of halides and other groups from organic
substrates by metalate anions represents one of the most impor-
tant routes for the formation of metal–carbon σ bonds. The
reactions of 2 with simple alkyl halides and aromatic halides
(RX) in MeOH solvent were carried out at room temperature
for 4 days. Hydrolysis of the reaction mixture led to triethyl-
germyl-substituted products as major products together with
some unidentified byproducts. All products were identified by
comparing their NMR, GC–MS spectra, and retention times on
GC with those of authentic samples. The results are summa-
rized in Table 1.
The MeOH-coordinated germylborate 2 smoothly reacted
with trimethylacetyl chloride and aroyl chlorides in MeOH to
give the corresponding germylketones, respectively, in high
yields shown in Table 2. These germylketones are commonly
yellow, which were purified by rapid column chromatographic
separation (silica gel, hexane/ether) and were identified by
NMR and GC–MS spectra.
Representative methods of preparation of acylgermanes
hitherto reported are (a) germylation of an acyl anion equivalent
based on dithiane compounds followed by hydrolysis,9,10 (b)
The yields of the products increased in the order of RCl < RBr
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
1087
germylation of metalated enol ethers,11 (c) direct carbonylation
by germyl–lithiums,12 (d) Pd-catalyzed germylation of acyl
halides,13 (e) germylation of acyl chlorides by germyl-
cuprates,14–16 (f) hydrolysis of α-chloro ethers.17 However,
these reactions involve strongly reducing conditions, oxidation
procedures, or severe reaction conditions. The germylborate 2
is a very useful reagent of germylation of acyl halides in MeOH
solvent.
The reactions of the MeOH-coordinated germylborate as
nucleophiles with carbonyl compounds, esters, carboxylic acid
and carbon–carbon multiple bonds were also examined. The
reaction of MeOH-coordinated germylborate 2 with 3-pen-
tanone in MeOH did not occur at 50 °C for 6 h, and remained
unreacted. To the MeOH solution of 2 was added benzophe-
none under similar reaction conditions. The color of the solu-
tion turned to yellow, but the germylborate 2 was mostly recov-
ered. The observed color may arise from a charge-transfer
interaction of the σ HOMO of germylborate and the LUMO of
carbony compound.
Ryoiki, 30, 67 (1976). c) M. Fujita and T. Hiyama,
Yukigosei Kagaku Kyokaishi, 42, 293 (1984).
3
For example, see a) P. Riviere, M. R-Baudet, and J. Satge,
“Comprehensive Organometallic Chemistry,” ed. by G.
Wilkinson, F. G. A. Stone, and E. W. Abel, Pergamon,
New York (1982), Vol. 2, Chap. 10, pp 468–473. b) M.
Lesbre, P. Mazerolles, J. Satge, “Organic Compounds of
Germanium,” Interscience, New York (1971). c) K.
Mochida, Yukigosei Kagaku Kyokaishi, 49, 288 (1991).
Unsolvated triethylgermyllithium could be prepared from
triethylgermane, di-tert-butylmercury, and lithium metal in
benzene
K. Matsudo, M. Nanjo, and K. Mochida, 10th International
Confererence on the Coordination and Organometallic
Chemistry of Germanium, Tin and Lead, Bordeaux
(France), 2001 (July), Abstr., No. 2p13; M. Nanjo, K.
Matsudo, and K. Mochida, submitted for publication.
No structural information of the HMPA complex of lithium
(triethylgermyl)triphenylborate has been reported; E. J.
Bulten and J. G. Noltes, J. Organomet. Chem., 29, 409
(1971).
4
5
6
7
8
K. Mochida and N. Matsushige, J. Organomet. Chem, 229,
11 (1982).
The typical experimental procedure of the reaction of
MeOH-coordinated germylborate 2 with benzoyl chloride
in the MeOH solvent is as follows: to a stirred MeOH-
coordinated lithium (triethylgermyl)triphenylborane (100
mg, 0.245 mmol) and degassed MeOH (1.5 mL) in a 25-
mL Schlenk tube was added benzoyl chloride (140 mg, 1.0
mmol) at room temperature under Ar. The reaction mix-
ture was stirred for 2 days. After evaporation of MeOH
and unreacted benzoyl chloride, the resulting residue was
purified by column chromatography (silica gel,
hexane/ether).
The reaction of 2 with acetic acid in MeOH did not proceed at
room temperature for 4 days and recovered unreacted. With
methyl acetate the germylborate 2 in MeOH under similar reac-
tion conditions did not change.
The germylborate 2 in MeOH proved to be unreactive
toward carbon–carbon multiple bonds. With 2,3-dimethyl-2-
butene and 6-dodecyne under similar reaction conditions, the
germylborate 2 recovered unreacted from the MeOH solutions.
These results observed in MeOH are in marked contrast to
those in the reactions of triethylgermyllithium with carbonyl
compounds, esters, alkenes, and alkynes in HMPA.2 It is well
known that the germyllithium in HMPA reacts with carbonyl
compounds, esters, alkenes, and alkynes to give the correspon-
ding germyl-substituted products.1
9
A. G. Brook, J. M. Duff, P. F. Jones, and N. R. Davies, J.
Am. Chem. Soc., 89, 431 (1967).
10 E. J. Corey, D. Seebach, and R. Freeman, J. Am. Chem.
Soc., 89, 434 (1967).
11 J. A. Sonderquist and A. Hassnser, J. Am. Chem. Soc.,
102, 1577 (1980).
12 R. J. Cross and F. Glockling, J. Organomet. Chem., 3, 146
(1965).
We thank Mitsubishi Material Co. Ltd., for the gift of ger-
manium tetrachloride. This work was partially supported by
the Ministry of Education, Science, Culture and Sports.
13 K. Yamamoto, A. Hayashi, S. Suzuki, and J. Tsuji,
Organometallics, 6, 974 (1987).
Dedicated to Professor Hideki Sakurai on the occasion of
his 70th birthday.
14 E. Piers and R. Lemieux, Organometallics, 14,
5011(1995).
References and Notes
15 D. P. Curran, U. Diederichsen, and M. Palovich, J. Am.
Chem. Soc., 119, 4797 (1997).
1
D. D. Davies and C. E. Gray, Organomet. Chem. Rev. A, 6
283 (1970).
16 U. Iserloh and D. P. Curran, J. Org. Chem., 63, 471
(1998).
17 R. Johannesen and T. Benneche, J. Chem. Soc., Perkin
Trans. 1, 2000, 2677.
2
For examples see a) D. A. Armitage, “Comprehensive
Organometallic Chemistry,” ed. by G. Wilkinson, F. G. A.
Stone and E. W. Abel, Pregamon, New York (1982),
Vol.2, Chap.9, pp 99–104. b) H. Sakurai, Kagaku no