886
Chemistry Letters 2001
Selective Synthesis of Chlorohydrogermanes from Mono-, Di-, and Trihydrogermanes
Joji Ohshita, Yutaka Toyoshima, Arihiro Iwata, Heqing Tang, and Atsutaka Kunai*
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University,
Higashi-Hiroshima 739-8527
(Received April 6, 2001; CL-010310)
Treatment of hydrogermanes, R4–nGeHn (R = Hex, Et, Ph,
n = 1–3), with 2 equiv of CuCl2 in ether at room temperature or
in toluene under reflux led to selective replacement of an H–Ge
bond with a Cl–Ge bond, giving the corresponding
chlorohydrogermanes, R4–nGeHn–1Cl, selectively.
Halogermanes are useful reagents in the synthesis of a vari-
ety of organogermanium compounds.1 Of these, halohydro-
germanes are of high importance, as exemplified by dehydro-
halogenative coupling of chlorohydrogermanes forming a Ge–Ge
bond.2 A few methods for the synthesis of halohydrogermanes,
including redistribution reactions of organohydrogermanes with
tetrachlorogermane3 and selective monohalogenation of dihydro-
germanes with HgCl2, ClCH2OCH3 in the presence of AlCl3 as
the catalyst, or N-bromosuccinimide (NBS), have been published
to date.4 However, these monohalogenation involves the use of
toxic or costly reagents. Although partial hydrogenation of
dihalogermanes has been also reported, it may be applied to only
some special cases.5 Recently, we have demonstrated that treat-
ment of mono-, di-, and trihydrosilanes with 2 equiv of CuCl2 in
the presence of a catalytic amount of CuI (2CuCl2(CuI) reagent)
leads to the selective transformation of an H–Si bond to a Cl–Si
bond, providing a readily accessible route to bifunctional chloro-
hydrosilanes [eq (1)].6 In this paper, we report the selective syn-
thesis of chlorogermanes from hydrogermanes by CuCl2 in the
absence or presence of the CuI catalyst, in which one hydrogen
atom on the germanium atom was selectively replaced with a
chlorine atom with the use of 2 equiv of CuCl2.
Monochlorination reactions occured also in the absence of
CuI, although a longer reaction time was required to complete
the chlorination, in particular for that in ether at room tempera-
ture. The required reaction time in ether may be reduced by
heating the reaction mixture, although the yield dropped slight-
ly, due to the formation of unidentified by-products. This is in
marked contrast to the chlorination of hydrosilanes with the
CuCl2(CuI) reagent which occurs only in the presence of the
CuI catalyst. The starting hydrosilanes are recovered
unchanged from the reactions in the absence of CuI under the
same conditions. For the dichlorination of hydrogermanes,
however, it was necessary to use the CuI catalyst [eq (3)].
Without the CuI catalyst, only monochlorinated products were
obtained even when a large excess of CuCl2 was used.
Monohydrogermanes, Hex3GeH and Et3GeH were also readily
chlorinated by similar treatment in ether.
Chlorination with the use of the CuCl2(CuI) reagent can be
also applied to the selective chlorination of trihydrogermane
PhGeH3 as can be seen in Table 1 [eq (3), R = Ph, n = 3]. Thus,
by changing the amount of the reagent, we could obtain desired
chlorohydrogermanes with complete selectivity. Perchlorina-
tion of PhGeH3 afforded PhGeCl3 as the sole volatile product in
80% yield [eq (4)].
When Hex2GeH2 was treated with 2CuCl2(CuI) in toluene
under reflux for 5 h, Hex2GeHCl was obtained in 91% isolated
yield [eq (2) and Table 1].7 In this reaction, no other volatile
products were detected by GLC analysis of the reaction mix-
ture. The chlorination proceeded also in ether at lower temper-
ature to give Hex2GeHCl in good to high yields. In this reac-
tion, however, a trace of Hex2Ge(OEt)Cl was found to be
formed by GC–MS of the reaction mixtures. The ethoxy group
would come from the solvent, ether. Similar treatment of
Hex2GeH2 with 4 equiv of CuCl2(CuI) in toluene afforded
Hex2GeCl2 in 87% isolated yield [eq (3)]. From the reaction of
Et2GeH2 in ether and Ph2GeH2 in toluene, mono- and dichlori-
nated products were obtained again selectively, depending on
the amount of CuCl2 used. The reactions of Ph2GeH2 proceed-
ed at a slower rate as compared with those of Hex2GeH2, i.e.;
both the mono- and dichlorination of Hex2GeH2 completed in a
shorter period than those of Ph2GeH2 under essentially the same
conditions, respectively.
The present chlorination of hydrogermanes may be
explained by a mechanism shown in Scheme 1, as proposed for
previously reported chlorination of hydrosilanes.6 In the pres-
ence of the CuI catalyst, CuICl seems to be formed as the actual
active species. The Ge–H bond would be initially converted to
a Ge–I bond, which is then replaced with a Ge–Cl bond by the
interaction with CuCl2. Whereas, in the absence of CuI, the
Ge–H bond may react directly with 2 equiv of CuCl2 giving
Ge–Cl and 2CuCl·HCl.
One might consider that a radical process is included in the
chlorination. Although we have not yet obtained any direct evi-
dences to support the reaction mechanism shown in Scheme 1,
the high selectivities in the present system may exclude the pos-
sibility of a radical mechanism.
The present reaction is oxidative in nature and CuCl2 acts
as the oxidant. Presumably, replacement of the hydrogen atom
Copyright © 2001 The Chemical Society of Japan
Ohshita, Joji
