Reactivity of a germene toward terminal alkynes: Competition between cycloaddition, ene-addition, and CH-insertion

Article abstract of DOI:10.1021/om200048p

A variety of terminal alkynes were added to Mes₂Ge=CHCH ₂t-Bu, a naturally polarized germene. Three different modes of reactivity were observed: cycloaddition to give germacyclobutenes, ene-addition to give vinylgermanes, and addition across the acetylenic C-H bond to give germylacetylenes. Mechanisms for the formation of the products are proposed. The reactivity of the naturally polarized germene toward terminal alkynes is compared to that of the analogous silene.

Full text of DOI:10.1021/om200048p

ARTICLE
pubs.acs.org/Organometallics
Reactivity of a Germene toward Terminal Alkynes: Competition
between Cycloaddition, Ene-Addition, and CH-Insertion
Laura C. Pavelka and Kim M. Baines*
Department of Chemistry, University of Western Ontario, London, Ontario, N6A 5B7 Canada
S Supporting Information
b
ABSTRACT:
A variety of terminal alkynes were added to Mes2GedCHCH2t-Bu, a naturally polarized germene. Three different modes of
reactivity were observed: cycloaddition to give germacyclobutenes, ene-addition to give vinylgermanes, and addition across the
acetylenic CꢀH bond to give germylacetylenes. Mechanisms for the formation of the products are proposed. The reactivity of the
naturally polarized germene toward terminal alkynes is compared to that of the analogous silene.
Chart 1. Alkynyl Mechanistic Probes
’ INTRODUCTION
The cycloaddition reactions of silenes have attracted the
attention of the synthetic organic community.1 The regio- and
stereospecificity of the reactions and the presence of the main
group atom, which remains available for further functionalization
of the primary product, are the key features that make the
cycloaddition reactions of silenes appealing. Given the impor-
tance of the cycloaddition reactions of silenes, not only as a
fundamental reaction in silicon chemistry2 but also in organic
synthesis, our group has explored the cycloaddition reactions of
alkynes and silenes in detail.3,4
The reactivity of silenes toward alkynes has been well-studied,
especially for the relatively nonpolar Brook silenes, (Me3Si)2Sid
C(R)(OSiMe3); typically, alkyne addition yields silacyclobu-
tenes regioselectively and in high yield.2 Through the use of a
molecular probe, cyclopropyl alkynes 1aꢀc (Chart 1),5 the cyclo-
addition of alkynes to Brook silenes was determined to proceed
via a biradical intermediate (Scheme 1).3
More recently, we examined the reactivity of the naturally
polarized silene Mes2SidC(H)CH2t-Bu, 2,6 toward alkynes.4
When cyclopropyl alkynes 1aꢀc, as well as a variety of other
terminal alkynes, were added to neopentylsilene 2, the major
products isolated were silylacetylenes 3aꢀi, from insertion of the
terminal CꢀH bond of the alkyne across the SidC bond
(Schemes 2, 3). Of the numerous terminal alkynes investigated,
only phenylacetylene and ethoxyacetylene yielded cycloadducts
upon addition to 2, silacyclobutenes 4 and 5, respectively, in
addition to the corresponding silylacetylenes 3d and 3g
(Scheme 3). A minor amount of vinylsilane 6, from formal
ene-addition, was also observed in the reaction between silene 2
and phenylacetylene (Scheme 3). Since 2 did not react with the
CtC triple bond of cyclopropyl alkynes 1aꢀc, no information
could be discerned regarding the mechanism of alkyne addition
using this approach. Given the preference for insertion into the
CH bond of terminal alkynes, silene 2 does not appear to be a
general substrate for the synthesis of organic ring systems. The
preference for CH-insertion over cycloaddition was attributed to
the polarity of silene 2 and provided an interesting example of
how the polarity of the SidC bond can directly influence the type
of products formed in a given reaction.
Germenes are inherently less polar than silenes.7 Thus, the use
of a naturally polarized germene, such as Mes2GedC(H)CH2t-
Bu, 7,8 may lead to alkyne cycloadducts in higher yields
Received: January 19, 2011
Published: March 24, 2011
r
2011 American Chemical Society
2261
dx.doi.org/10.1021/om200048p Organometallics 2011, 30, 2261–2271
|

Organometallics
ARTICLE
Scheme 1. Mechanism of Alkyne Addition to Brook Silenes
Scheme 3. Addition of Simple Alkynes to Silene 2
Scheme 2. Addition of Alkynyl Probes to Silene 2
11aꢀe were isolated from residual fluorogermane 8 by chroma-
tography; however, germylacetylenes 11aꢀc could not be sepa-
rated from the corresponding vinylgermanes 10aꢀc. Germacy-
clobutenes 9aꢀc decomposed upon prolonged exposure to the
atmosphere or upon adsorption to silica gel and, thus, were not
isolated.
The addition of ethoxyacetylene to germene 7 yielded a
complex mixture of compounds within a few minutes. Germa-
cyclobutene 12 and vinylgermane 13 were identified as the major
1
products by H NMR spectroscopy (Scheme 4). The ratio of
germacyclobutene 12 to vinylgermane 13 was variable; 12
ranged from 5% to 38% of the product mixture. The relative
amount of 13 increased as the concentration of 7 increased.
Unlike aryl-substituted germacyclobutenes 9aꢀc, 12 did not
decompose to any significant degree upon adsorption to silica,
but did decompose after prolonged exposure to the atmosphere.
Despite many attempts, 12 and 13 could not be separated from
each other by chromatography; however, after the eventual
decomposition of 12, a sample of 13 was isolated.
The product ratios (9:10:11) observed in the reactions
between germene 7 and phenylacetylene, 1-ethynyl-4-(trifluoro-
methyl)benzene, 4-ethynylanisole, trimethylsilylacetylene, or
tert-butylacetylene varied considerably depending on the reac-
tion conditions (Table 1); the scale of the reaction, the order of
addition, and the alkyne concentration all influenced the ratio.
The concentration of germene 7 was kept constant in all reactions
(0.24ꢀ0.26 M).
compared to the analogous silene. Surprisingly, there are no
previous reports on the addition of alkynes to germenes.9,10
Herein, we report on the reactivity of neopentylgermene 7
toward terminal alkynes and compare the results with those
obtained from neopentylsilene 2.
’ RESULTS
Germene 78 was synthesized prior to each reaction and used
in situ without purification. A colorless pentane solution of
fluorovinylgermane 8 was cooled to ꢀ78 °C and then treated
with t-BuLi. Upon warming to room temperature, the solution
became pale yellow in color and a fine precipitate appeared (LiF),
indicating the formation of germene. It was necessary to add
slightly less than 1 equiv of t-BuLi to fluorovinylgermane 8 when
forming 7 to prevent polymerization of the germene,11 and thus,
germene 7 was always contaminated with residual fluorogermane
8 (∼5ꢀ15%). The pentane was removed and the residue was
dissolved in C6D6 before the alkyne was added; the presence of 7
Reaction of 7 with each of the aromatic alkynes gave a mixture
containing germacyclobutene 9, vinylgermane 10, and germyla-
cetylene 11. The relative amount of germylacetylene 11 varied
the most of the three products, in the range 4ꢀ84% (11a;
Table 1, entries 1ꢀ5), 12ꢀ97% (11b; Table 1, entries 6ꢀ9), and
27ꢀ62% (11c; Table 1, entries 10ꢀ13) depending on the
conditions. Furthermore, even when the reactions were carried
out under identical conditions, the relative amount of 11 varied,
at times, quite dramatically (Table 1, compare entry 3a to 3b).
Interestingly, regardless of the percentage of 11aꢀc, the ratio of
germacyclobutene 9 to vinylgermane 10 remained fairly constant
(9a:10a = 1:3, 9b:10b = 1:2, 9c:10c = 1:5), even as the absolute
amounts fluctuated. Qualitatively, of the three aromatic alkynes
investigated, 1-ethynyl-4-(trifluoromethyl)benzene reacted faster
than phenylacetylene, which reacted faster than 4-ethynylanisole
with germene 7 under identicalconditions. Plots of the normalized
1
was confirmed by H NMR spectroscopy. The reactions were
kept at room temperature for up to 6 days11 and monitored by 1H
NMR spectroscopy.
A mixture of germacyclobutene 9a, vinylgermane 10a, and
germylacetylene 11a was produced after 2ꢀ3 days upon reaction
of germene 7 with phenylacetylene (Scheme 4 and Table 1).
Analogous products were obtained with 1-ethynyl-4-(trifluoro-
methyl)benzene (9b, 10b, and 11b; ∼24 h) and 4-ethynylanisole
(9c, 10c, and 11c; 4ꢀ5 days) (Scheme 4 and Table 1). In
contrast, germylacetylene 11d and small quantities of vinylger-
mane 10d were formed when germene 7 was allowed to react
with trimethylsilylacetylene, and only a germylacetylene (11e)
was formed upon reaction with tert-butylacetylene (Scheme 4
and Table 1). Vinylgermanes 10aꢀc and germylacetylenes
2262
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
Scheme 4. Reactions of Terminal Alkynes with Germene 7
Table 1. Product Ratios from the Reactions of Terminal Alkynes with Germene 7
entry
RCtCH
Ph (a)
scalea (mmol 7)
alkyne concb (M)
orderc
product ratiod (9:10:11)
reaction time
adducte (%)
1
0.13
0.13
0.13
0.13
0.26
0.26
0.13
0.13
0.13
0.26
0.13
0.13
0.13
0.26
0.13
0.13
0.13
0.13
0.13
0.13
0.30
0.30
0.60
0.60
0.30
0.30
0.30
0.30
0.60
0.30
0.30
0.30
0.60
0.30
0.30
0.30
0.60
0.30
0.30
0.60
germene
alkyne
26:70:4
7:23:70
11:27:62
18:48:34
14:43:43
2:14:84
28:60:12
13:41:46
25:59:16
1:2:97
3 days
3 days
2 days
2 days
3 days
2 days
24 h
73
90
95
90
81
>99
90
94
95
>99
64
67
86
76
16f
39
85
28
49
72
2
3a
3b
4
alkyne
alkyne
germene
alkyne
5
6
CF3C6H4 (b)
MeOC6H4 (c)
germene
alkyne
7
24 h
8
alkyne
<24 h
<24 h
4 days
5 days
2 days
3 days
6 days
6 days
3 days
5 days
6 days
4 days
9
alkyne
10
11
12
13
14
15
16
17
18
19
germene
alkyne
12:61:27
10:52:37
8:44:48
4:34:62
0:44:56
0:8:92
alkyne
alkyne
SiMe3 (d)
t-Bu (e)
germene
alkyne
alkyne
0:6:94
germene
alkyne
0:0:100
0:0:100
0:0:100
alkyne
a The concentration of germene 7 was held constant: 0.24ꢀ0.26 M (C6D6). b Alkyne concentrations of 0.3 and 0.6 M correlate to 1.3 and 2.5 equiv,
respectively, relative to germene 7. c Reagent listed was added to NMR tube first. d Product ratios calculated from integration of the appropriate signals in
1
the H NMR spectra of the reaction mixture (after removal of the polymeric material). Product ratios calculated in this manner matched, within
experimental error, the same product ratio of the products before exposure to air. e Alkyne adduct % calculated from integration of the appropriate signals
in the 1H NMR spectra of the reaction mixture (after removal of the polymeric material) relative to the total amount of molecular products formed from
germene 7 including dimers 14, germane 15, and water adducts. f Dimers 14 were the major products formed.
amounts of 9, 10, or 11 versus time are given in Figures S16ꢀS20
(see Supporting Information). Curiously, 11 is formed rapidly in
each case, and the amount of this product remains fairly constant
throughout the reaction even as the amounts of 9 and 10 increase.
Doubling the scale of the reaction, from 0.13 to 0.26 mmol of
germene 7, while keeping the remaining variables constant, led to a
significant increase in the relative amount of 11aꢀc (Table 1,
compare entry 1 to 4, 2 to 5, 7 to 9, and 11 to 13) and,
consequently, a relative decrease in the amounts of 9aꢀc and
10aꢀc. The order of addition also had an influence on the relative
amount of germylacetylenes 11aꢀc; an increase in the relative
amount of 11aꢀc was consistently observed when the germene
was added to the alkyne as opposed to when the alkyne was added
to the germene, given the same scale and alkyne concentration
(Table 1, compare entry 1 to 2, 6 to 7, and 10 to 11). In contrast,
there was no consistent trend associated with an increase in the
alkyne concentration: the relative amount of 11a and 11b
decreased slightly, while that of 11c increased slightly (Table 1,
2263
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
Chart 2. Digermacyclobutanes 14 and Vinylgermane 15
and a signal assigned to the vinylic hydrogen (∼6.9 ppm (9aꢀc) or
5.81 ppm (12)) were observed in the 1H NMR spectra of 9aꢀc and
12. The alkene functional group was confirmed by the presence
of two signals in the 13C NMR spectra of germacyclobutenes 9aꢀc
and 12, consistent with the expected chemical shift of alkenyl
carbons. Unfortunately, the regiochemistry of the germacyclo-
butenes could not be determined on the basis of these NMR
spectroscopic data. Evidence for the assigned regiochemistry of
9aꢀc and 12 is presented below.
compare entry 2 to 3a,b, 7 to 8, and 11 to 12). A higher
concentration of alkyne did, however, lead to a decrease in the
reaction time and an increase in the percentage of alkyne adducts
produced with all the alkynes. These changes were most apparent
in the reaction with 4-ethynylanisole, which was the slowest of the
aromatic alkynes to react with germene 7.
There was no germacyclobutene formed in the reaction
between germene 7 and trimethylsilylacetylene and very little
of vinylgermane 10d. The ratio of vinylgermane 10d to germy-
lacetylene 11d was affected by the order of addition: when the
germene was added to trimethylsilylacetylene, a higher portion of
11d was obtained as compared to when trimethylsilylacetylene
was added to the germene (Table 1, compare entry 14 to 15).
The same trend was observed with the aromatic alkynes. In
addition, an increase in the concentration of trimethylsilylacety-
lene led to a notably shorter reaction time and higher yield of
alkyne adducts (Table 1, compare entry 15 to 16). The reaction
was not performed on a larger scale.
Due to the similarities between the spectroscopic data of
vinylgermanes 10aꢀd, only the spectral features of 10b will be
discussed. As with the analogous vinylsilane 6,4 there are two
pairs of doublets (6.15 and 6.38 ppm, J = 18 Hz; 6.87 and 7.28
ppm, J = 19 Hz) in the 1H NMR spectrum of 10b assigned to the
vinylic hydrogens on the two trans-oriented Ge-CHdCH-R
double bonds. The upfield pair of doublets was assigned to the
Ge-CHdCH-t-Bu moiety; both vinylic signals showed a correla-
tion to the signal assigned to the quaternary 13C of the t-Bu
13
substituent in the 1Hꢀ C gHMBC NMR spectrum of 10b. The
downfield pair of doublets was assigned to the hydrogens on the
Ge-CHdCH-Ar double bond. The existence of the two alkene
functional groups in 10b was confirmed by the presence of four
signals in the 13C NMR spectra of 10b that fell within the typical
chemical shift range for alkenic carbons: 123.83 (Ge-CHdCH-t-
Bu), 135.43 (Ge-CHdCH-Ph), 141.09 (Ge-CHdCH-Ph),
156.52 ppm (Ge-CHdCH-t-Bu).
As with vinylgermanes 10aꢀd, the spectral features of germy-
Germylacetylene 11e was the only product isolated from the
reaction of germene 7 with tert-butylacetylene. Although product
ratios are irrelevant, the order of addition and alkyne concentra-
tion both influenced the reaction time and the percentage yield of
the alkyne adducts. An increase in the relative amount of alkyne
adduct was observed when the germene was added to tert-
butylacetylene as compared to when the alkyne was added to
the germene (Table 1, compare entry 17 to 18). A further
increase in the yield of the alkyne adducts, as well as a decrease
in reaction time, was observed when the concentration of tert-
butylacetylene was doubled (Table 1, compare entry 18 to 19).
The yield of alkyne addition products decreased significantly
with increased reaction times. When left in solution for extended
periods, germene 7 dimerizes and rearranges to give digermacy-
clobutanes 14 and vinylgermane 15, respectively (Chart 2).11
Also, minor amounts of water adducts of germene 78 can form
from the addition of adventitious water. Not surprisingly, these
side reactions become more significant, contributing to lower
yields of alkyne adducts, the longer 7 is left in solution (Table 1).
Furthermore, polymeric material, from the polymerization of
germene 7, was produced in each reaction;11 the amount of
polymer remained relatively constant (∼30% of the mass
balance) and was not included in the adduct yield calculations.
Germacyclobutenes 9aꢀc were identified as part of the crude
lacetylenes 11aꢀe were very similar, and thus, only those of 11b
1
will be discussed in detail. Two multiplets in the H NMR
spectrum of germylacetylenes 11b at 1.71ꢀ1.74 and 1.75ꢀ1.78
ppm were assigned to an AA0BB0 spin system attributable to a
XꢀCH2CH2ꢀY moiety. One of the substituents on the
CH2CH2 moiety was determined to be a t-Bu group; there was
1
13
a correlation in the Hꢀ C gHMBC NMR spectrum of 11b
between a 13C signal assigned to one of the CH2 carbons and a
signal in the 1H dimension assigned to the t-Bu CH3. The other
substituent was determined to be Mes2RGe, as revealed by
correlations between one of the multiplets in the 1H dimension
and the 13C signal assigned to the aromatic ipso carbon of the
13
mesityl group in the 1Hꢀ C gHMBC NMR spectrum of 11b.
The alkyne functional group was confirmed by the presence of
two signals in the 13C NMR spectrum of 11b at 100.15 and
104.77 ppm, which fall in the typical chemical shift range for
alkynyl 13C’s, and by an absorption observed in the IR spectrum
of 11b at 2157 cmꢀ1
.
Vinylgermane 13 was formed from the reaction of 2 equiv of
germene 7 with 1 equiv of ethoxyacetylene. The high-resolution
ESI-TOF mass spectrum of 13 revealed a molecular ion at m/z
855.4116, which was in excellent agreement with the calculated
value of a 2:1 adduct (C52H73O70Ge72Ge (Mþ) m/z calcd
1
855.4125). In the H NMR spectrum of 13, there are signals
1
1
13
product mixtures by H, 13C, gCOSY, Hꢀ C gHSQC, and
gHMBC NMR spectroscopy due to their sensitivity to moisture,
which made isolation from the complex product mixtures extre-
melydifficult. Vinylgermanes 10aꢀc and germylacetylenes 11aꢀe
as well as germacyclobutene 12 and vinylgermane 13 were
consistent with the presence of four different mesityl groups, two
t-Bu groups, and one OCH2CH3 group. Also, four doublets were
observed in the vinylic region of the 1H NMR spectrum, two of
which were coupled to each other (5.94 and 6.27 ppm, J = 19
13
Hz). In the 1Hꢀ C gHMBC NMR spectrum of 13, one of the
13
identified by IR, 1H, 13C, gCOSY, 1Hꢀ C gHSQC, and gHMBC
two J-coupled vinylic doublets correlated to the quaternary 13C
signal of one of the t-Bu substituents. Thus, these two J-coupled
doublets were assigned to the vinylic hydrogens on the trans-
oriented Mes2Ge(R)-CHdCH-t-Bu moiety. Of the other two
signals in the vinylic region of the 1H NMR spectrum, one was
assigned to a third vinylic hydrogen (5.41 ppm, 1 H, J = 10 Hz)
NMR spectroscopy, and mass spectrometry after purification.
1
The H NMR spectra of germacyclobutenes 9aꢀc and 12
were similar to those of silacyclobutenes 44 and 54 and were
consistent with the proposed structures. A multiplet assigned to
the saturated CH in the ring (∼3.7 ppm (9aꢀc) or 2.99 ppm (12))
2264
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
and the other to a Ge-H (5.53 ppm, 1 H, J = 6 Hz). A correlation
Scheme 5. Ring-Opening of Germacyclobutenes 9aꢀc
was observed between the 1H signal at 5.41 ppm and a 13C signal
1
13
at 130.42 ppm in the Hꢀ C gHSQC NMR spectrum of 13,
which is consistent with a vinylic hydrogen. There was no
1
correlation from the H signal at 5.53 ppm to any signals in
the 13C dimension of the 1Hꢀ C gHSQC NMR spectrum of 13,
13
and thus, the 1H signal was assigned to the Mes2Ge-H.
In addition, two doublets of doublets, at 1.59 and 1.77 ppm, as
well as a dddd at 3.98 ppm, each integrating for 1 H, were
observed in the 1H NMR spectrum of 13 and were assigned to
the hydrogens of a CHCH2 fragment. The doublets of doublets
were assigned to the CHCH2 hydrogens, and the multiplet was
assigned to the CHCH2 hydrogen. Each of the CHCH2 1H
signals showed a correlation to the 13C signal assigned to the
irradiation of the signal at 5.81 ppm assigned to the vinylic 1H;
however, there was enhancement of the mesityl o-CH3 signals
after irradiation of the signal assigned to the OCH2CH3 hydro-
gens. Thus, the regiochemistry of 12 was determined to be
opposite that of 9aꢀc; the vinyl 1H is attached to the unsaturated
ring carbon two bonds from germanium.
The regiochemistry of the ring systems was also determined by
chemical degradation. Compounds 9aꢀc and 12 were treated
with aqueous NaOH (15%) in refluxing THF (Scheme 5). Only
germacyclobutenes 9aꢀc were observed to react with NaOH;
the ethoxy-substituted ring, 12, was unreactive toward NaOH
under these conditions.
1
13
CH3 of a second t-Bu group in the Hꢀ C gHMBC NMR
spectrum of 13, which is consistent with a CHCH2t-Bu moiety.
Also, the gCOSY NMR spectrum of 13 showed correlations
between the dddd at 3.98 ppm (CHCH2) and both doublets of
doublets (CHCH2) as well as one of the vinylic doublets (5.41
ppm, J = 10 Hz) and the Mes2Ge-H signal (5.53 ppm, J = 6 Hz).
The vinylic signal (5.41 ppm) that couples to the signal at 3.98
ppm has been assigned to the EtO-CdC-H hydrogen based on
the upfield chemical shift and a correlation to the 13C signal
assigned to the EtO-CdC-H carbon (156.36 ppm) in the
The ring-opened products, 17aꢀc were identified by IR and
1
13
1H, 13C, gCOSY, Hꢀ C gHSQC, and gHMBC NMR spec-
troscopy. There are several features in the NMR spectral data of
17aꢀc that provide unambiguous evidence for the structure of
the products. The spectral features of 17aꢀc are very similar, and
thus, only the spectral data of 17a will be discussed. A triplet
assigned to the vinylic 1H (5.60 ppm, 1 H), a doublet assigned to
the CH2t-Bu (1.96 ppm, 2 H), and a singlet assigned to the
GeCH2 (2.87 ppm, 2 H) were present in the 1H NMR spectrum
of 17a. The triplet at 5.60 ppm showed a correlation to the
doublet at 1.96 ppm in the gCOSY NMR spectrum of 17a, and
13
1Hꢀ C gHMBC NMR spectrum of 13 as well as the previously
mentioned correlation to the 13C signal at 130.42 ppm in the
13
1Hꢀ C gHSQC NMR spectrum of 13, assigned to the EtO-
CdC-H carbon. Thus, the CHCH2t-Bu fragment can be elabo-
rated to Mes2Ge(H)-CH[CHdC(R)OEt]CH2t-Bu. Given the
mass spectral data, it is clear that these two fragments, Mes2Ge-
(R)-CHdCH-t-Bu and Mes2Ge(H)-CH[CHdC(R)OEt]CH2t-
Bu, must be connected to make one molecule.
Determination of Regiochemistry. The germacyclobutenes
(9aꢀc and 12) were examined by 1H 1-D ROE spectroscopy to
determine the regiochemistry of the ring. Unfortunately, since
aryl-substituted germacyclobutenes 9aꢀc could not be isolated,
the spectra were recorded on the crude product mixture where
few signals could be cleanly irradiated. Irradiation of the signal
assigned to the saturated ring GeCH (3.75 ppm) in 9a led to
enhancement of the signal at 7.55 ppm, assigned to the ortho
hydrogen of the phenyl substituent. A similar response was
observed when the signal assigned to the saturated ring GeCH
of 9b or 9c was irradiated. Furthermore, irradiation of the signals
assigned to the ortho hydrogens of the aromatic substituents in
9aꢀc resulted in enhancement of the signals assigned to the
GeCH in each case. There was no enhancement of the vinylic 1H
signals observed when the GeCH signals were irradiated. Also,
enhancement of the mesityl o-CH3 signals was observed after
1
hence, the vinylic H is adjacent to the CH2t-Bu to give a
CdC(H)CH2t-Bu moiety. The singlet at 2.87 ppm assigned to
the GeCH2 showed correlations to the 13C signals at 125.29,
1
13
138.32, and 142.32 ppm in the Hꢀ C gHMBC NMR spec-
trum, which correspond to the two alkenic carbons and the ipso
carbon of the phenyl substituent, respectively. The two alkenic
carbon signals (125.29 and 138.32 ppm) also correlated to the
doublet at 1.96 ppm in the 1H dimension, assigned to the CH2t-
Bu hydrogens. Thus, the GeCH2 must be connected to a
C(Ph)dC(H)CH2t-Bu moiety. The spectral features of 17aꢀc
were very similar to those of the ring-opened product of
silacyclobutene 4 after treatment with NaOMe.4
The structure assigned to 17aꢀc, where the aryl substituent is
attached to the carbon two bonds from germanium, is entirely
consistent with the NMR spectroscopic data of 17aꢀc. Thus, the
aryl-substituted germacyclobutenes 9aꢀc are derived from the
addition of the terminal alkynyl carbon to the germanium of germene
7. The original regiochemistry, with respect to alkyne addition to
germene 7, should be retained in the ring-opened product. The
hydroxide anion selectively attacks the germanium, which leads to
cleavage of the former germenic GedC bond; similar behavior has
been observed when silacyclobutenes were treated with base.4,12
Alternative ring-opened products derived from a germacyclobutene
with the phenyl substituent on the carbon adjacent to the germanium
were considered; however, none of the structures were consistent
with the spectroscopic data obtained.
1
irradiation of the signal assigned to the vinylic H signal (6.92
ppm) of 9b (and vice versa). The vinylic 1H signals of 9a and 9c
could not be irradiated due the presence of overlapping signals.
1
These results suggest that the vinylic H is attached to the
unsaturated ring carbon adjacent to germanium in germacyclo-
butenes 9aꢀc.
Some key differences were noted in the 1H 1-D ROE spectro-
scopic data for ethoxy-substituted germacyclobutene 12 com-
pared to 9aꢀc. Most notably, enhancement of the signal assigned
to the vinylic 1H signal was observed after irradiation of the signal
at 2.99 ppm assigned to the saturated ring GeCH (and vice
versa). Irradiation of the signal at 0.97 ppm assigned to the
C(CH3)3 group also led to enhancement of the vinylic 1H signal.
There was no enhancement of the mesityl o-CH3 signals after
The reduced reactivity of 12 toward NaOH in comparison to
9aꢀc is consistent with the ethoxy substituent being located on
the carbon adjacent to germanium. Presumably, the intermediate
2265
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
Chart 3. Resonance Structures of Ring-Opened Anions
spectrum of 7, which contains the signals assigned to the t-Bu group,
is particularly diagnostic: only one major signal, assigned to the t-Bu
group of the germene (0.99 ppm), is observed.
The order of addition of the two reagents (germene to alkyne
or alkyne to germene) had a significant influence on the relative
amount of germylacetylenes 11. An increase in the amount of 11
was observed when the germene solution was added to the alkyne
compared to vice versa. The germene solution contains both the
initiator of the chain (trace anion) and the quencher (Mes2GeF-
(CHdCH2)). The germene solution was added dropwise to the
alkyne in an NMR tube; the mixing of the two solutions was not
efficient. As the germene solution is added to the alkyne, we
believe the chain initiates. As more germene solution is added,
the amount of quencher, fluorodimesitylvinylgermane, increases,
resulting in quenching of the reaction. When the alkyne is added
to germene, the quencher is present in the solution from the
beginning, resulting in fairly rapid quenching of the chain
reaction and, consequently, a relatively small amount of germy-
lacetylene formed. In the case of trimethylsilylacetylene and tert-
butylacetylene, the reaction between the germene and the alkyne
(rather than the acetylide anion) is evidently slow, and thus, the
only alkyne adduct observed, to any extent, is the germylacety-
lene. As with the other alkynes, when the germene is added to
the alkyne, the germylacetylene forms rapidly at the beginning of
the reaction. After formation of 11d/e, the germene slowly
disappears with the concomitant formation of dimers 14 and
germane 15.14
Scheme 6. Proposed Mechanism for the Formation of Ger-
mylacetylene 11
The absence of a germylacetylene during the addition of
ethoxyacetylene is notable, particularly since formation of an
analogous silylacetylene was observed in the reaction between
silene 2 and ethoxyacetylene.4 The conjugate base of ethoxya-
cetylene is the weakest base/nucleophile of the alkynes
investigated.15 If the addition of the acetylide anion to the
germene is the rate-determining step in the chain, one might
expect the rate of the chain reaction to be sensitive to the strength
of the anion. Furthermore, ethoxyacetylene was added as a 40 wt
% solution in hexanes, and thus, the concentrations of the
reagents in these reactions were lower than the other reactions.
Similar CH-insertion products, silylacetylenes 3aꢀi, were
observed when terminal alkynes were added to neopentylsilene
2.4 Analogous products have also been isolated from the addition
of phenylacetylene to a germanimine (GedN) and a germapho-
sphene (GedP).16,17 The formation of the σ-addition products
to the silene, germaphosphene, and germanimine was attributed
to the highly polar nature of the double bond. In each case, the
silene, germaphosphene, and the germanimine are formed by the
β-elimination of a functionalized silane/germane (R2M(X)-E-
(Li)R2). In light of our results, we believe a re-examination,
particularly of the kinetics of these reactions, is warranted to
determine if the product is indeed formed by direct reaction of
the alkyne, or its conjugate base, with the unsaturated compound.
Germacyclobutenes 9aꢀc and 12 are derived from cycloaddi-
tion between germene 7 and phenylacetylene, 1-ethynyl-
4-(trifluoromethyl)benzene, 4-ethynylanisole, or ethoxyacety-
lene, respectively. The aryl-substituted alkynes cycloadd to 7
with the same orientation that is typically observed in the
addition of terminal alkynes to silenes.18ꢀ20 Furthermore, the
regiochemistry of germacyclobutenes 9aꢀc is analogous to
silacyclobutene 4, formed in the reaction between phenylacety-
lene and neopentylsilene 2.4 Germacyclobutene 12, however,
has the opposite regiochemistry to 9aꢀc: ethoxy-substituted
germacyclobutene 12 is derived from the addition of the
anion would be much less stable with the ethoxy substituent in
this position; the added instability may be sufficient to make
NaOH addition unfavorable (Chart 3).
’ DISCUSSION
In an attempt to understand the variability associated with the
product ratios, normalized integrations of the three products
(9ꢀ11) were plotted against time (Figure S16ꢀS20, Supporting
Information). Even given experimental error, the trends revealed
are striking. In each experiment, germylacetylene 11 appears very
rapidly at the beginning of the reaction, and then the relative
amount remains fairly constant throughout the course of the
reaction. In contrast, germacyclobutenes 9 and ene-adducts 10
appear over the course of the reaction at approximately the same
rate (the ene-adduct is formed somewhat faster than the
cycloadduct). These results clearly indicate that 11 forms by a
different mechanism than 9 and 10. To account for this unusual
kinetic behavior, we propose that germylacetylenes 11 are
formed in a chain reaction initiated by trace amounts of a strong
base, which produces an acetylide anion as the chain carrier. The
acetylide anion adds to germene 7, producing an R-germyl
carbanion, which then propagates the chain by abstraction of a
proton from the acetylene (Scheme 6). The regioselective
addition of anions to germenes has been reported.8,11 On the basis
of the observed kinetic behavior, the chain is quenched early in the
reaction, presumably by residual Mes2GeF(CHdCH2). The most
likely candidate for the strong base is unreacted Mes2GeFCH-
(Li)CH2t-Bu or, perhaps, fluoride.13 Only traces of the organic anion
can exist in solution; spectroscopic evidence (1H NMR) clearly
indicates that germene 7 is formed cleanly prior to reaction with
1
the alkyne. The region between 0.8 and 1.2 ppm in the H NMR
2266
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
Chart 4. Proposed Complex between Germene 7 and
Ethoxyacetylene
Scheme 7. Proposed Mechanism for the Formation of Ger-
macyclobutenes 9
terminal alkynyl carbon to the germenic carbon of 7, rather than
to the germanium. Ethoxyacetylene was the most reactive
alkyne; the reactions were completed within a few minutes.
Qualitatively, 1-ethynyl-4-(trifluoromethyl)benzene was the most
reactive aromatic alkyne, followed by phenylacetylene and then
4-ethynylanisole.
cycloaddition products in the reaction between germene 7 and
trimethylsilylacetylene or tert-butylacetylene is, presumably, a
consequence of unfavorable steric and/or electronic effects.
Vinylgermanes 10aꢀd are the formal ene-addition products
from germene 7 and phenylacetylene, 1-ethynyl-4-(trifluoromethyl)-
benzene, 4-ethynylanisole, or trimethylsilylacetylene, respec-
tively. The alkyne acts exclusively as the enophile and germene
7 as the ene-component. Similar reactivity has previously been
observed between 7 and nonenolizable aldehydes and ketones.28
In contrast, germene 7 has been reported to act exclusively as the
enophile upon addition of enolizable aldehydes and ketones,28
most likely due to the increased acidity of the R-hydrogens of
aldehydes and ketones compared to germenes. Thus, the addi-
tion of terminal alkynes with a weakly acidic R-H may lead to
different behavior of the germene. Interestingly, the ene-addition
pathway predominates over cycloaddition in the reaction be-
tween germene 7 and carbonyl compounds, as it does in the
reaction between 7 and terminal alkynes, although the alkynes
are undoubtedly poorer enophiles compared to carbonyl com-
pounds, which evidently allows cycloaddition to compete to
some extent with ene-addition. Ene-addition was not observed
upon reaction of germene 7 with tert-butylacetylene; evidently,
the alkyne is too electron rich (or too sterically hindered) to
function as a viable enophile.
Mechanistically, either a concerted ene-addition or a hydride/
hydrogen shift from a 1,4-zwitterionic/biradical intermediate/
complex could lead to vinylgermanes 10aꢀd; we do not have
enough evidence to favor one mechanism over another. The
qualitative increase in the reaction rate with an increase in alkyne
concentration indicates at least a bimolecular reaction. Given that
the ratio of the cycloadduct to the ene-adduct remains relatively
constant throughout the reaction and between runs and the same
relative regiochemistry was observed in 10aꢀc as in the aryl-
substituted germacyclobutenes 9aꢀc, we believe that the cy-
cloadduct and the ene-adducts are derived from a common
intermediate, likely a biradical.
On the basis of the available evidence, it is difficult to make any
definitive statements regarding the mechanism of the cycloaddi-
tion reaction, particularly a unifying mechanism that explains the
reversal in the regiochemistry of the addition. If the germene
adds to the alkyne as an electrophile to give a zwitterionic
intermediate (with a negative charge centered on the germenic
carbon and a positive charge on the benzylidenic carbon), the
same regiochemistry would be expected for all alkynes studied
and 4-ethynylanisole would be expected to be more reactive than
1-ethynyl-4-(trifluoromethyl)benzene. If the germenic carbon
adds as a nucleophile to the alkyne, it would be expected to add to
the substituted sp-hybridized carbon in the case of ethoxyacety-
lene and the unsubstituted sp-hybridized carbon in the case of the
aromatic alkynes, leading to the wrong regioisomers. We do not
believe the germanium of the double bond will act as a
nucleophile in these reactions. It is tempting to attribute the
origins of the difference in behavior observed in the addition of
ethoxyacetylene compared to the aromatic alkynes to germene 7
to the formation of an oxonium complex where the oxygen of the
alkynyl ether is coordinated to the germanium. Complexes
between diethyl ether and triethylamine and the related germene,
dimesitylfluorenylidenegermane, Mes2GedCR2, have been
isolated,21 and complexes between alcohols and diarylgermenes
have been proposed.22 However, the oxygen of an acetylenic
ether is a very poor base23 and cannot be expected to form a
strong Lewis acidꢀbase complex with a germene. Interestingly,
the rate constant for the hydration of ethoxyacetylene24 is 10
orders of magnitude greater than that of phenylacetylene.25
Given that ethoxyacetylene is so reactive toward electrophiles,
we propose that the alkoxy-substituted alkyne adds to germene 7
by a different mechanism compared to the aromatic alkynes. In
the case of ethoxyacetylene, we believe the structure of germa-
cyclobutene 12 is governed by the regioselective collapse of a
hypercoordinated germanium complex, possibly 16 (Chart 4).
Similar complexes have been proposed in the reaction between
gallium trichloride and alkynes.26
The formation of vinylgermane 13 was unexpected. This unusual
adduct is derived from the reaction of ethoxyacetylene with 2 equiv
of germene. Vinylgermane 13 formation may involve an ene-
addition where a complex between the electron-rich ethoxyacety-
lene and the Lewis acidic germene acts as the ene-component and
an additional germene molecule as the enophile (Scheme 8). Ene-
addition does not occur between two molecules of germene 7 in the
absence of ethoxyacetylene. The only reaction observed between
two molecules of germene 7 is slow head-to-tail dimerization
(days);11 vinylgermane 13 formation was much faster (hours).
The complexation of ethoxyacetylene increases the electron density
For the aromatic alkynes, the trifluoromethyl-substituted aro-
matic alkyne reacts faster than the alkoxy-substituted aromatic
alkyne. The addition of a polymer radical to various substituted
alkynes follows the same reactivity trend (the rate constant for the
addition of a radical to 1-ethynyl-4-nitrobenzene is greater than to
4-ethynylanisole),27 and thus, we propose that the regiochemistry
of germacyclobutenes 9aꢀc is governed by the preferential
formation of a biradical intermediate (Scheme 7). The lack of
2267
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
Scheme 8. Proposed Mechanism for Vinylgermane 13
Formation
and the aromatic alkynes or trimethylsilylacetylene gave
vinylgermanes 10aꢀd, where the germene behaved as the
ene-component and the alkyne as the enophile. As with the
cycloadducts, an anomalous ene-adduct was observed from
the reaction with ethoxyacetylene. The difference may result
from the complexation of ethoxyacetylene to the germene; the
germeneꢀethoxyacetylene complex then behaves as the ene-
component and a second equivalent of germene 7 as the
enophile.
Our findings have important implications for the recent study
of the reactivity of the analogous silene, 2 (also formed by the
addition of a strong nucleophile/base to a vinylsilane), which
showed preferential formation of silylacetylenes over cyclo- or
ene-adducts in the reaction with terminal alkynes.4 The pre-
ference for CH-insertion was attributed to the polarity of the
SidC bond; however, the kinetics of the reaction was not
examined. As with germene 7, variability in the relative amount
of the silylacetylenes (3aꢀi) was observed in some cases.
Furthermore, it was difficult to reconcile the fact that other
polarized silenes generated in thermal reactions (as opposed to
additionꢀelimination reactions) did not insert into the CH bond
of terminal acetylenes18 and the variable reactivity of silene 2
toward terminal alkynes. If silylacetylenes 3aꢀi form by way of a
chain reaction and are the result of the addition of the conjugate
base of the alkyne, and not the alkyne itself, to the silene, some of
these discrepancies may be understood.
Further studies on this reaction are needed to verify our
current hypotheses. In particular, a computational study of the
addition of the different alkynes to the parent germene may
provide some additional insights into the mechanisms of these
reactions. Experimentally, addition of a mechanistic probe,
designed to provide evidence for transient vinylic radicals5
(Chart 1), may also be instructive. Such studies are underway
in our laboratories.
on the germenic carbon and, apparently, promotes the observed
ene-addition. The addition of nucleophiles to enhance reactivity is a
common strategy in organic chemistry; however, the nucleophile
usually behaves as a catalyst and is not incorporated into the
product. In fact, an example of nucleophilic catalysis has been
observed with germene 7; the addition of an N-heterocyclic carbene
promotes dimerization of the germene in 2 h.29 In the formation of
vinylgermane 13, however, the nucleophile does not act as a catalyst.
The incorporation of ethoxyacetylene into the product may be due
to the presence of an accessible reactive site on the complexed
molecule (a CtC bond). Furthermore, steric crowding may
prevent the complex and germene 7 from approaching one another
in the necessary orientation to react and subsequently release
ethoxyacetylene.
Summary and Conclusions. A mixture of products was
obtained when germene 7 was treated with a terminal alkyne.
Three modes of addition were consistently observed: cycloaddi-
tion, ene-addition, and CH-insertion. The relative amount of
each type of product depended on the nature of the alkyne as well
as the reaction conditions.
’ EXPERIMENTAL SECTION
General Experimental Details. All reactions were performed in
flame-dried Schlenk tubes, or NMR tubes sealed with a septum, under an
inert atmosphere of argon. Benzene-d6 was distilled from LiAlH4, stored
over 4 Å molecular sieves, and degassed prior to use. Pentane was purged
with N2 and passed through alumina prior to use. t-BuLi was purchased
from Aldrich Chemical Co. 1,1-Dimesitylneopentylgermene, 7,8 was
prepared according to the previously reported procedures. The NMR
standards used are as follows: residual C6D5H (7.15 ppm) for 1H NMR
spectra, C6D6 central transition (128.00 ppm) for 13C NMR spectra,
Insertion of the terminal CꢀH bond across the GedC bond
on germene 7 was observed with the aromatic alkynes, trimethyl-
silylacetylene, and tert-butylacetylene, to form germylacetylenes
11aꢀe. There was no evidence for this mode of addition with
ethoxyacetylene. A chain reaction is proposed to account for the
rapid formation of the germylacetylenes. The absence of a
germylacetylene in the reaction of 7 with ethoxyacetylene is
curious; it is not clear that the competing formation of a coordi-
nation complex would stop a chain reaction. The variability
observed in the relative amount of germylacetylenes formed may
be a consequence of the chain reaction mechanism, which is
expected to be highly dependent on the rate of addition of one
solution to the other as well as the efficiency of mixing. The
reactions were conducted in an NMR tube, and thus, the mixing
was not efficient.
1
29
Me4Si as an external standard (0 ppm) for Hꢀ Si gHMBC spectra,
and CF3Ph as an external standard (ꢀ63.9 ppm against CFCl3) for 19
F
NMR spectra. IR spectra were recorded (cmꢀ1) from thin films on a
Bruker Tensor 27 FT-IR spectrometer. Electron impact mass spectra
were obtained using a MAT model 8400 mass spectrometer using an
ionizing voltage of 70 eV. Mass spectral data are reported in mass-to-
charge units, m/z.
Cycloaddition to form germacyclobutenes 9aꢀc and 12,
respectively, was observed with aromatic alkynes and ethoxya-
cetylene; however, the regiochemistry of the products varied for
the different types of alkynes. We propose two different mechan-
isms to account for the change in regiochemistry: addition
through a biradical intermediate for the aromatic alkynes and
complex formation for the highly reactive ethoxyacetylene.
Ene-addition is a prominent reaction between terminal
alkynes and germene 7; reaction with all of the alkynes, except
tert-butylacetylene, gave an ene-adduct. Reaction between 7
General Procedure for the Reaction of Alkynes with
Germene 7. A pentane solution of fluorodimesitylvinylgermane, 8
(100 mg, 0.28 mmol), was converted to 1,1-dimesitylneopentylgermene,
7.8 The pentane was removed in vacuo, yielding a pale yellow residue.
The residue was dissolved in C6D6 (1.1 mL). An aliquot (0.1 mL) was
removed, and the ratio of germene 7 to fluorogermane 8 was determined
1
by H NMR spectroscopy. A portion of the germene solution (0.5 or
1.0 mL) was then added to an NMR tube. For reactions where the
germene was added to the alkyne, the NMR tube already contained the
alkyne (1.2 or 2.3 equiv) upon addition of the germene solution. For
2268
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
reactions where the alkyne was added to the germene, alkyne (1.2 equiv)
was then added to the germene solution. The progress of the reaction
was monitored by 1H NMR spectroscopy for up to 6 days. The solvent
was removed by rotary evaporation, yielding a yellow residue. Polymeric
material, from the polymerization of germene 7,11 was removed from the
crude product mixture by precipitation from a dichloromethane solution
with acetonitrile (∼30ꢀ35% by weight). The ratio of products in the
crude reaction mixture (∼65ꢀ70% by weight) was determined by 1H
NMR spectroscopy. The product mixture was usually contaminated
with residual alkyne and fluorogermane 8. The products were separated
from fluorogermane 8 and residual alkyne by chromatography on silica
gel (10a: initial plate: 5:5 hexanes/CH2Cl2, second plate: 9.5:0.5
hexanes/EtOAc; 10b: 5:5 hexanes/CH2Cl2; 10c/11c: 5:5 hexanes/
CH2Cl2; 11a: 5:5 hexanes/CH2Cl2; 11b: 5:5 hexanes/CH2Cl2; 11d: 8:2
hexanes/CH2Cl2; 11e: 8:2 hexanes/CH2Cl2; 12: 8:2 hexanes/CH2Cl2;
13: after decomposition of 12, 5:5 hexanes/CH2Cl2).
(m), 1604 (m), 2866 (m), 2958 (s); 1H NMR (C6D6) δ 0.97 (s, 9 H,
C(CH3)3), 2.13 (s, 6 H, Mes p-CH3), 2.41 (s, 12 H, Mes o-CH3), 6.15
(d, J = 18 Hz, 1 H, Ge-CHdCH-t-Bu), 6.38 (d, J = 18 Hz, 1 H, Ge-
CHdCH-t-Bu), 6.79 (s, 4 H, Mes-H), 6.87 (d, J = 19 Hz, 1 H, Ge-
CHdCH-Ar), 6.94ꢀ6.96 (m, 2 H, Ar o-H), 7.22ꢀ7.25 (m, 2 H, Ar m-
H), 7.28 (d, 1 H, Ge-CHdCH-Ar, J = 19 Hz); 13C NMR (C6D6) δ
20.99 (Mes p-CH3), 24.83 (Mes o-CH3), 28.99 (C(CH3)3), 35.22
(C(CH3)3, 123.83 (Ge-CHdCH-t-Bu), 124.97 (q, JCF = 270 Hz, CF3)
125.63 (q, JCF = 4.5 Hz, Ar m-C), 126.96 (Ar o-C), 129.41 (q, JCF = 9.2
Hz, Ar p-C), 129.60 (Mes m-C), 134.87 (Mes i-C), 135.43 (Ge-
CHdCH-Ar), 138.53 (Mes p-CH3), 141.09 (Ge-CHdCHꢀAr),
141.84 (Ar i-C), 143.44 (Mes o-C), 156.52 (Ge-CHdCH-t-Bu); 19F
NMR (C6D6) δ ꢀ62.5; high-resolution EI-MS for C33H3974GeF3 (Mþ)
m/z calcd 566.2224, found 566.2098.
10c: colorless, waxy solid as a mixture with 11c (57:43, respectively);
1H NMR (C6D6) δ 0.97 (s, 9 H, C(CH3)3), 2.13 (s, 6 H, Mes p-CH3),
2.46 (s, 13 H, Mes o-CH3), 3.22 (s, 3 H, OCH3), 6.18 (d, J = 18 Hz, 1 H,
Ge-CHdCH-t-Bu), 6.43 (d, J = 18 Hz, 1 H, Ge-CHdCH-t-Bu), 6.66ꢀ6.69
(m, 2 H, Ar m-H), 6.79 (s, 4 H, Mes-H), 7.03 (d, J = 19 Hz, 1 H, Ge-
CHdCH-Ar), 7.15 (d, J = 19 Hz, GeꢀCHdCH-Ar), 7.20ꢀ7.24 (m, 2 H,
Ar o-H); 13C NMR (C6D6) δ 21.01 (Mes p-CH3), 24.88 (Mes o-CH3),
29.07 (C(CH3)3), 35.16 (C(CH3)3), 54.70 (OCH3), 114.25 (Ar m-C),
124.56 (Ge-CHdCH-t-Bu), 128.29 (Ar o-C), 128.65 (Ge-CHdCH-Ar),
129.51 (Mes m-C), 131.80 (Ar i-C), 135.56 (Mes i-C), 138.18 (Mes p-C),
142.41 (Ge-CHdCH-Ar), 143.55 (Mes o-C), 156.06 (Ge-CHdCH-t-Bu),
160.08 (Ar p-C); high-resolution EI-MS for C33H4274GeO (Mþ) m/z calcd
528.2455, found 528.2458.
9a: 1H NMR (C6D6) δ 0.90 (s, 9 H, C(CH3)3), 1.85 (dd, J = 10, 14
Hz, 1 H, CHCH2t-Bu), 2.01 (dd, J = 1.5, 15 Hz, 1 H, CHCH2t-Bu), 2.11
(s, Mes p-CH3), 2.14 (s, 3 H, Mes p-CH3), 2.47 (s, Mes o-CH3), 2.55 (s,
6 H, Mes o-CH3), 3.75 (d, J = 10 Hz, 1 H, CHCH2t-Bu), 6.70 (Mes-H),
6.74 (Mes-H), 6.93 (s, 1 H, Ge-CHdCPh), 7.09ꢀ7.13 (m, 1 H, Ph p-
H), 7.20ꢀ7.23 (m, 2 H, Ph m-H), 7.54ꢀ7.56 (m, 2 H, Ph o-H); 13C
NMR (C6D6) δ 20.91ꢀ21.04 (Mes p-CH3), 23.98 (Mes o-CH3), 25.02
(Mes o-CH3), 29.78 (C(CH3)3), 31.12 (C(CH3)3), 43.07 (CHCH2t-
Bu), 44.35 (CHCH2t-Bu), 126.22 (Ph o-C), 127.89 (Ph p-C), 128.76
(Ph m-C), 128.98 (Mes m-C), 129.39 (Mes m-C), 133.85 (Mes i-C),
137.35 (Ge-CHdCPh), 137.73 (Ph i-C), 138.50 (Mes i-C), 142.16
(Mes o-C), 144.01 (Mes o-C), 158.94 (Ge-CHdCPh).
10d: Vinylgermane 10d was formed in small amounts and was only
identified by the characteristic signals assigned to the vinylic hydrogens
in the 1H NMR spectrum (C6D6) of the crude product: δ 0.05 (s, 9 H,
Si(CH3)3), 0.95 (s, 9 H, C(CH3)3), 6.13 (d, J = 18 Hz, 1 H, Ge-
CHdCH), 6.39 (d, J = 18 Hz, 1 H, Ge-CHdCH), 6.82 (d, J = 21 Hz, 1
H, Ge-CHdCH), 7.51 (d, J = 21 Hz, Ge-CHdCH).
9b: 1H NMR (C6D6) δ 0.88 (s, 9 H, C(CH3)3), 1.81 (d AB, J = 9.3, 15
Hz, 1 H, CHCH2t-Bu), 1.84 (d AB, J = 3.0, 15 Hz, 1 H, CHCH2t-Bu),
2.08 (s, Mes p-CH3), 2.13 (s, Mes p-CH3), 2.44 (s, 6 H, Mes o-CH3),
2.58 (s, 6 H, Mes o-CH3), 3.64 (dd, J = 2.4, 9.6 Hz, 1 H, CHCH2t-Bu),
6.75 (s, 2 H, Mes-H), 6.76 (s, 2 H, Mes-H), 6.92 (s, 1 H, Ge-CHdCAr),
7.32 ꢀ 7.37 (m, 2 H, Ar o-H), 7.38ꢀ7.44 (m, 2 H, Ar m-H); 13C NMR
(C6D6) δ 21.00 (Mes p-CH3), 23.95 (Mes o-CH3), 25.17 (Mes o-CH3),
29.70 (C(CH3)3), 31.08 (C(CH3)3), 42.74 (CHCH2t-Bu), 44.20
(CHCH2t-Bu), 124.3 (q, JCF ≈ 270 Hz, CF3),31 125.5ꢀ125.7 (m, Ar
m-C), 126.31 (Ar o-C), 129.08 (Mes m-C), 129.4ꢀ129.6 (m, Ar p-C),
129.58 (Mes m-C), 133.38 (Mes i-C), 137.96 (Mes i-C), 138.55 (Mes p-
C), 139.13 (Mes p-C), 140.60 (Ge-CHdCAr), 140.80 (Ar i-C), 142.08
(Mes o-C), 143.89 (Mes o-C), 157.2 (Ge-CHdCAr); 19F NMR (C6D6)
δ ꢀ62.2.
11a: colorless, waxy solid contaminated with 10a (85:15, re-
spectively); IR cmꢀ1 691 (s), 756 (s), 809 (m), 848 (s), 885 (w),
1026 (s), 1215 (m), 1243 (m), 1263 (m), 1290 (w), 1363 (m), 1410
(m), 1447 (s), 1467 (s), 1556 (m), 1603 (s), 2155 (m, CtC), 2865 (m),
1
2956 (s); H NMR (C6D6) δ 0.88 (s, 9 H, C(CH3)3), 1.76 (s, 4 H,
GeCH2CH2t-Bu), 2.09 (s, 6 H, Mes p-CH3), 2.60 (s, 12 H, Mes o-CH3),
6.74 (s, 4 H, Mes-H), 6.89ꢀ6.92 (m, 3 H, Ph m/p-H), 7.39ꢀ7.43 (m, 2
H, Ph o-H); 13C NMR (C6D6) δ 18.42 (GeCH2), 20.95 (Mes p-CH3),
24.21 (Mes o-CH3), 29.01 (C(CH3)3), 31.34 (C(CH3)3), 39.91 (CH2t-
Bu), 96.77 (Ge-CtC-Ph), 106.45 (GeꢀCtC-Ph), 124.50 (Ph i-C),
128.20 (Ph p-C), 128.44 (Ph m-C), 129.70 (Mes m-C), 131.87 (Ph o-C),
134.59 (Mes i-C), 138.48 (Mes p-C), 143.24 (Mes o-C); high-resolution
EI-MS for C32H4070Ge (Mþ) m/z calcd 494.2374, 494.2369.
11b: colorless, waxy solid contaminated with 10b (97:3, re-
spectively); IR cmꢀ1 703 (m), 740 (m), 843 (s), 885 (w), 1017 (m),
1067 (s), 1105 (m), 1130 (s), 1167 (s), 1220 (w), 1263 (w), 1322 (s),
1364 (m), 1405 (m), 1468 (m), 1556 (w), 1614 (m), 2157 (w, CtC),
2866 (m), 2957 (s); 1H NMR (C6D6) δ 0.89 (s, 9 H, C(CH3)3), 1.71 ꢀ
1.74 (BB0 portion of an AA0BB0 spin system, 2 H, CH2t-Bu), 1.75ꢀ1.78
(AA0 portion of an AA0BB0 spin system, 2 H, GeCH2), 2.10 (s, 6 H, Mes
p-CH3), 2.57 (s, 12 H, Mes o-CH3), 6.75 (s, 4 H, Mes-H), 7.06ꢀ7.08
(m, 2 H, Ar m-H), 7.15ꢀ7.17 (m, 2 H, Ar o-H); 13C NMR (C6D6) δ
18.38 (GeCH2), 20.93 (Mes p-CH3), 24.18 (Mes o-CH3), 28.98
(C(CH3)3), 31.34 (C(CH3)3), 39.94 (CH2t-Bu), 100.15 (Ge-CtC-
Ar), 104.77 (Ge-CtC-Ar), 124.57 (q, JCF = 270 Hz, Ar-CF3), 125.33 (q,
JCF = 5 Hz, Ar m-C), 127.88 (Ar i-C), 129.75 (q, JCF = 32 Hz, Ar p-C),
129.78 (Mes m-C), 131.98 (Ar o-C), 134.17 (Mes i-C), 138.75 (Mes p-
C), 143.15 (Mes o-C); high-resolution EI-MS for C33H39F370Ge (Mþ)
m/z calcd 562.2246, 562.2235.
9c:30 1H NMR (C6D6) δ 0.94 (s, C(CH3)3), 1.89 (dd, J = 11, 15 Hz,
CHCH2t-Bu), 1.97 (d, J = 15 Hz, CHCH2t-Bu), 2.49 (s, 6 H, Mes o-
CH3), 2.56 (s, 6 H, Mes o-CH3), 3.32 (s, 3 H, OCH3), 3.74 (d, J = 10 Hz,
CHCH2t-Bu), 6.84 (s, Ge-CHdCAr), 6.84ꢀ6.85 (m, Ar m-H),
7.51ꢀ7.53 (m, Ar o-H); 13C NMR (C6D6) δ 43.24 (CHCH2t-Bu),
44.41 (CHCH2t-Bu), 134.75 (Ge-CHdCAr), 158.56 (Ge-CHdCAr).
10a: colorless, waxy solid contaminated with 14 and water adducts
1
(81:13:6, respectively); H NMR (C6D6) δ 0.96 (s, 9 H, C(CH)3)3,
2.12 (s, 6 H, Mes p-CH3), 2.43 (s, 12 H, Mes o-CH3), 6.16 (d, J = 18 Hz,
1 H, Ge-CHdCH-t-Bu), 6.41 (d, J = 18 Hz, 1 H, Ge-CHdCH-t-Bu),
6.78 (s, 4 H, Mes-H), 6.98ꢀ7.05 (m, Ph m/p-H) and 7.03 (d, J = 18 Hz,
Ge-CHdCH-Ph) (total 4 H), 7.22ꢀ7.25 (m, 2 H, Ph o-H), 7.29 (d, J =
18 Hz, 1 H, Ge-CHdCH-Ph); 13C NMR (C6D6) δ 21.00 (Mes p-CH3),
24.86 (Mes o-CH3), 29.03 (C(CH3)3), 35.18 (C(CH3)3), 124.26 (Ge-
CHdCH-t-Bu), 126.92 (Ph o-C), 128.0 (Ph p-C),31 128.76 (Ph m-C),
129.51 (Mes m-C), 131.60 (Ge-CHdCH-Ph), 135.32 (Mes i-C),
138.25 (Mes p-C), 138.75 (Ge-CHdCH-Ph), 142.86 (Ph i-C),
143.50 (Mes o-C), 156.17 (Ge-CHdCH-t-Bu); high-resolution EI-
MS for C32H4070Ge (Mþ) m/z calcd 494.2372, found 494.2384.
10b: colorless, waxy solid contaminated with 14 (94:6, respectively)
and other minor impurities; IR cmꢀ1 797 (w), 849 (m), 992 (w), 1016
(w), 1068 (s), 1128 (s), 1166 (s), 1325 (s), 1363 (w), 1410 (w), 1467
11c: colorless, waxy solid as a mixture with 10c (43:57, respectively);
IR cmꢀ1 2153 (w, CtC); 1H NMR (C6D6) δ 0.89 (s, 9 H, C(CH3)3),
2269
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
1.78 (s, 4 H, GeCH2CH2t-Bu), 2.10 (s, 6 H, Mes p-CH3), 2.62 (s, 12 H,
Mes o-CH3), 3.11 (s, 3 H, Ar-OCH3), 6.51ꢀ6.54 (m, 2 H, Ar m-H), 6.75
(s, 4 H, Mes-H), 7.37ꢀ7.41 (m, 2 H, Ar o-H); 13C NMR (C6D6) δ 18.49
(GeCH2), 20.94 (Mes p-CH3), 24.23 (Mes o-CH3), 29.02 (C(CH3)3),
31.35 (C(CH3)3), 39.93 (CH2t-Bu), 54.62 (OCH3), 94.82 (Ge-
CtCꢀAr), 106.57 (Ge-CtC-Ar), 114.19 (Ar m-C), 116.72 (Ar i-C),
129.69 (Mes m-C), 133.36 (Ar o-C), 134.82 (Mes i-C), 138.40 (Mes p-
C), 143.28 (Mes o-C), 159.96 (Ar p-C); high-resolution EI-MS for
C33H4274GeO (Mþ) m/z calcd 528.2455, found 528.2458.
(C(CH3)3), 34.96 (C(CH3)3, 46.98 (CHCH2t-Bu), 67.56 (OCH2-
CH3), 126.59 (Ge-CHdCH-t-Bu), 129.08 (Mes m-C), 129.16 (Mes
m-C), 129.50 (Mes m-C), 129.55 (Mes m-C), 130.42 (CHdC(OEt)),
135.00 (Mes i-C), 135.42 (Mes i-C), 135.93 (Mes i-C), 135.98 (Mes i-
C), 137.98 (Mes p-C), 138.01 (Mes p-C), 138.10 (Mes p-C), 143.62
(Mes o-C), 143.65 (Mes o-C), 143.79 (Mes o-C), 143.81 (Mes o-C),
154.81 (Ge-CHdCH-t-Bu), 156.36 (CHdC(OEt)); high-resolution
ESI TOF-MS for C52H73O70Ge72Ge (M ꢀ Hþ) m/z calcd 855.4125,
found 855.4116.
11d: colorless oil, contaminated with 14 and water adducts (89:8:3,
respectively); IR cmꢀ1 2089 (w, CtC); 1H NMR (C6D6) δ 0.14 (s, 9
H, Si(CH3)3), 0.89 (s, 9 H, C(CH3)3), 1.66ꢀ1.69 (BB0 portion of an
AA0BB0 spin system, 2 H, GeCH2), 1.70ꢀ1.74 (AA0 portion of an
AA0BB0 spin system, 2 H, CH2t-Bu), 2.07 (s, 6 H, Mes p-CH3), 2.55 (s,
12 H, Mes o-CH3), 6.71 (s, 4 H, Mes-H); 13C NMR (C6D6) δ ꢀ0.20
(Si(CH3)3), 18.29 (GeCH2), 20.91 (Mes p-CH3), 24.20 (Mes o-CH3),
29.00 (C(CH3)3), 31.28 (C(CH3)3), 39.83 (CH2t-Bu), 114.54 (Ge-
CtC-SiMe3), 116.60 (Ge-CtC-SiMe3), 129.66 (Mes m-C), 134.45
(Mes i-C), 138.44 (Mes p-C), 1423 (Mes o-C); high-resolution EI-MS
for C29H4474GeSi (Mþ) m/z calcd 494.2428, found 494.240
11e: colorless oil, contaminated with 14 and water adducts (76:18:6,
respectively); IR cmꢀ1 2148 ꢀ2181 (w, CtC); 1H NMR (C6D6) δ 0.91
(s, 9 H, CH2-C(CH3)3), 1.16 (s, 9 H, CtC-C(CH3)3), 1.64ꢀ1.67 (BB0
portion of an AA0BB0 spin system, 2 H, GeCH2), 1.69ꢀ1.73 (AA0
portion of an AA0BB0 spin system, 2 H, CH2t-Bu), 2.08 (s, 6 H, Mes p-
CH3), 2.56 (s, 12 H, Mes o-CH3), 6.73 (s, 4 H, Mes-H); 13C NMR
(C6D6) δ 18.40 (GeCH2), 20.93 (Mes p-CH3), 24.18 (Mes o-CH3),
28.56 (CtC-C(CH3)3), 29.07 (CH2-C(CH3)3), 30.77 (CtC-C-
(CH3)3), 31.30 (CH2-C(CH3)3), 39.91 (CH2t-Bu), 84.08 (Ge-CtC-
t-Bu), 115.78 (Ge-CtC-t-Bu), 129.62 (Mes m-C), 135.07 (Mes i-C),
138.22 (Mes p-C), 142.5 (Mes o-C); high-resolution EI-MS for
C30H4474Ge (Mþ) m/z calcd 478.2661, found 478.2644.
12: colorless oil as a mixture with 13 (16:84, respectively) and an
unknown; 1H NMR (C6D6) δ 0.97 (s, 9 H, C(CH3)3), 1.09 (t, J = 7.2
Hz, 3 H, OCH2CH3), 1.48 (dd, J = 10, 14 Hz, 1 H, CHCH2t-Bu), 1.82
(dd, J = 3, 14 Hz, 1 H, CHCH2t-Bu), 2.076, 2.083 (each s, total 6 H, Mes
p-CH3), 2.57 (s, 6 H, Mes o-CH3), 2.60 (s, 6 H, Mes o-CH3), 2.99 (ddd,
J = 2.4, 3.0, 10 Hz, 1 H, CHCH2t-Bu), 3.55ꢀ3.63 (m, 2 H, OCH2CH3),
5.81 (d, J = 1.8 Hz, 1 H, CH dC(OEt)), 6.72 (s, Mes-H), 6.73 (s, Mes-
H); 13C NMR (C6D6) δ 14.54 (OCH2CH3), 20.96ꢀ20.98 (Mes p-
CH3), 23.94 (Mes o-CH3), 24.00 (Mes o-CH3), 29.98 (C(CH3)3),
32.25 (C(CH3)3), 32.57 (CHCH2t-Bu), 48.00 (CHCH2t-Bu), 64.50
(OCH2CH3), 116.33 (CHdC(OEt)), 128.92 (Mes m-C), 129.16 (Mes
m-C), 134.82 (Mes i-C), 136.71 (Mes i-C), 138.53 (Mes p-C), 142. 83
(Mes o-C), 143.28 (Mes o-C), 164.95 (CHdC(OEt)); high-resolution
EI-MS for C28H4074GeO (Mþ) m/z calcd 466.2295, found 466.2310.
13: colorless oil, contaminated with a minor amounts of 12 and other
impurities; IR cmꢀ1 693 (m), 741 (m), 800 (s), 848 (s), 1080 (m), 1260
(s), 1362 (m), 1409 (m), 1450 (s), 1556 (m), 1603 (s), 2732 (w), 2864
(m), 2957 (s), 3022 (w); 1H NMR (C6D6) δ 0.90 (s, 9 H, C(CH3)3),
0.99 (s, 9 H, C(CH3)3), 1.16 (t, J = 6.9 Hz, 3 H, OCH2CH3), 1.59 (dd,
J = 11, 14 Hz, 1 H, CHCH2t-Bu), 1.77 (dd, J = 1.2, 14 Hz, 1 H, CHCH2t-
Bu), 2.10 (s, 3 H, Mes p-CH3), 2.11 (s, 3 H, Mes p-CH3), 2.12 (s, 3 H,
Mes p-CH3), 2.14 (s, 3 H, Mes p-CH3), 2.37 (s, 6 H, Mes o-CH3), 2.43
(s, 6 H, Mes o-CH3), 2.46 (s, 6 H, Mes o-CH3), 2.49 (s, 6 H, Mes o-
CH3), 3.66 (dq, J = 6.9, 9.3 Hz, 1 H, OCH2CH3), 3.92 (dq, J = 6.9, 9.3
Hz, 1 H, OCH2CH3), 3.98 (dddd, J = 1.2, 6, 10, 11 Hz, 1 H, CHCH2t-
Bu), 5.41 (d, J = 10 Hz, 1 H, CHdC(OEt)), 5.53 (d, J = 6 Hz, 1 H,
Ge-H), 5.94 (d, J = 19 Hz, 1 H, Ge-CHdCH-t-Bu), 6.27 (d, J = 19 Hz,
1 H, Ge-CHdCH-t-Bu), 6.75 (s, 2 H, Mes-H), 6.76 (s, 2 H, Mes-H),
6.771, 6.775 (each s, 4 H total, Mes-H); 13C NMR (C6D6) δ 15.96
(OCH2CH3), 20.96 (Mes p-CH3), 20.98 (Mes p-CH3), 21.08 (Mes p-
CH3), 24.41 (Mes o-CH3), 24.53 (Mes o-CH3), 24.97 (Mes o-CH3),
26.53 (CHCH2), 28.75 (C(CH3)3), 30.24 (C(CH3)3), 32.57
General Reaction of Germacyclobutenes 9aꢀc with So-
dium Hydroxide. Excess sodium hydroxide solution (5 mL, 15%) was
added to the crude product mixture from the addition of aromatic alkyne to
germene 7 consisting of germacyclobutene 9a, b, or c, along with
vinylgermane 10a, b, or c, germylacetylene 11a, b, or c, and fluorovinyl-
germane 8 (∼40 mg), dissolved in THF (5 mL). The solution was refluxed
for 18 h. The mixture was extracted with diethyl ether. The organic layer was
dried over MgSO4 and filtered. The solvents were removed under vacuum
to yield a light yellow oil (∼35 mg), which was purified by preparative thin-
layer chromatography (silica gel; 17a: first plate: 8:2 hexanes/CH2Cl2,
second plate: 8:2 hexanes/EtOAc; 17bꢀc 9:1 hexanes/EtOAc). Com-
pounds 17aꢀc were isolated as colorless oils (2ꢀ5 mg).
17a: colorless oil; IR cmꢀ1 645 (m), 702 (m), 763 (w), 848 (m), 912
(w), 1027 (w), 1264 (w), 1364 (w), 1377 (w), 1409 (w), 1451 (m),
1557 (w), 1603 (m), 1727 (m), 2865 (m), 2927 (s), 2955 (s), 3022 (w),
3300ꢀ3600 (br w, OH); 1H NMR (C6D6) δ 0.78 (s, 9 H, C(CH3)3),
1.96 (d, J = 7.2 Hz, 2 H, CdCH-CH2), 2.09 (s, 6 H, Mes p-CH3), 2.38 (s,
12 H, Mes o-CH3), 2.87 (s, 2 H, GeCH2), 5.60 (t, J = 7.5 Hz, 1 H,
CdCH-CH2), 6.66 (s, 4 H, Mes-H), 6.96ꢀ6.98 (m, 1 H, Ph-H),
7.02ꢀ7.05 (m, 4 H, Ph-H); 13C NMR (C6D6) δ 20.94 (Mes p-CH3),
23.55 (Mes o-CH3), 29.39 (C(CH3)3), 31.21 (C(CH3)3), 36.85
(GeCH2), 43.23 (CH2t-Bu), 125.29 (CdCH-CH2t-Bu), 126.56 (Ph
p-C), 127.89 (Ph m-C), 129.05 (Ph o-C), 129.45 (Mes m-C), 136.42
(Mes i-C), 138.32 (CdCH-CH2t-Bu), 138.67 (Mes p-C), 142.32 (Ph i-
C), 143.01 (Mes o-C); low-resolution EI-MS 516 (Mþ, <0.5%), 498
(Mþ ꢀ H2O, 3%), 329 (Mes2GeOHþ, 100%).
17b: colorless oil; IR cmꢀ1 848 (m), 1018 (w), 1070 (m), 1125 (m),
1164 (m), 1325 (s), 1452 (w), 1603 (w), 1734 (w), 2868 (m), 2957 (s),
3300ꢀ3600 (br w, OH); 1H NMR (C6D6) δ 0.79 (s, 9 H, C(CH3)3),
1.88 (d, J = 7.2 Hz, 2 H, CdCH-CH2), 2.08 (s, 6 H, Mes p-CH3), 2.31 (s,
12 H, Mes o-CH3), 2.74 (s, 2 H, GeCH2), 5.65 (t, J = 7.2 Hz, 1 H,
CdCH-CH2), 6.60 (s, 4 H, Mes-H), 6.82ꢀ6.88 (m, 2 H, Ar-H),
7.15ꢀ7.19 (m, Ar-H); 13C NMR (C6D6) δ 20.85 (Mes p-CH3),
23.47 (Mes o-CH3), 29.36 (C(CH3)3), 31.29 (C(CH3)3), 36.33
(GeCH2), 43.11 (CH2t-Bu), 124.57 (q, JCF = 3.5 Hz, Ar m-C),
125.131 (q, JCF = 270 Hz, CF3), 126.31 (CdCHꢀCH2t-Bu), 128.42
(Ar p-C), 129.31 (Ar o-C), 129.47 (Mes m-C), 136.04 (Mes i-C), 137.22
(CdCHꢀCH2t-Bu), 138.95 (Mes p-C), 142.77 (Mes o-C), 145.58 (Ar
i-C); low-resolution EI-MS 580 (Mþ, <0.2%), 565 (Mþ ꢀ F, 0.5%), 329
(Mes2GeOHþ, 100%).
17c: colorless oil, contaminated with 11c and Mes2Ge(OH)CH2-
CH2t-Bu (65:23:12, respectively); IR cmꢀ1 3100ꢀ3600 (br w, OH); 1H
NMR (C6D6) δ 0.82 (s, 9 H, C(CH3)3), 2.00 (d, J = 7.8 Hz, 2 H,
CdCH-CH2), 2.09 (s, Mes p-CH3), 2.40 (s, 12 H, Mes o-CH3), 2.88 (s,
2 H, GeCH2), 3.27 (s, 3 H, OCH3), 5.58 (t, J = 7.2 Hz, 1 H, CdCH-
CH2), 6.62ꢀ6.67 (m, Ar-H) and 6.66 (s, Mes-H) (6 H total), 6.95ꢀ6.99
(m, 2 H, Ar-H); low-resolution EI-MS 546 (Mþ, <0.5%), 329
(Mes2GeOHþ, 100%).
’ ASSOCIATED CONTENT
Supporting Information. 1H NMR spectra for all new
S
b
compounds and plots of the formation of the products versus
time. This material is available free of charge via the Internet at
http://pubs.acs.org.
2270
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271

Organometallics
ARTICLE
’ AUTHOR INFORMATION
(18) Conlin, R. T.; Kwak, Y.-W.; Huffaker, H. B. Organometallics
1983, 2, 343.
Corresponding Author
*E-mail: kbaines2@uwo.ca
(19) Apeloig, Y.; Bravo-Zhivotovskii, D.; Zharov, I.; Panov, V.;
Leigh, W. J.; Sluggett, G. W. J. Am. Chem. Soc. 1998, 120, 1398.
(20) (a) Brook, A. G.; Harris, J. W.; Lennon, J.; El Sheikh, M. J. Am.
Chem. Soc. 1979, 101, 83. (b) Brook, A. G.; Baumegger, A.; Lough, A. J.
Organometallics 1992, 11, 3088. (c) Lassacher, P.; Brook, A. G.; Lough,
A. J. Organometallics 1995, 14, 4359. (d) Naka, A.; Ishikawa, M.; Matsui,
S.; Ohshita, J.; Kunai, A. Organometallics 1996, 15, 5759. (e) Naka, A.;
Ishikawa, M. Organometallics 2000, 19, 4921. (f) Naka, A.; Ishikawa, M. J.
Organomet. Chem. 2000, 611, 248. (g) Naka, A.; Ikadai, J.; Motoike, S.;
Yoshizawa, K.; Kondo, Y.; Kang, S.-Y.; Ishikawa, M. Organometallics
2002, 21, 2033. (h) Yoshizawa, K.; Kondo, Y.; Kang, S.-Y.; Naka, A.;
Ishikawa, M. Organometallics 2002, 21, 3271. (i) Naka, A.; Ishikawa, M.
Chem. Lett. 2002, 3, 364. (j) Naka, A.; Ohnishi, H.; Miyahara, I.; Hirotsu,
K.; Shiota, Y.; Yoshizawa, K.; Ishikawa, M. Organometallics 2004,
23, 4277. (k) Naka, A.; Ohnishi, H.; Ohshita, J.; Ikadai, J.; Kunai, A.;
Ishikawa, M. Organometallics 2005, 24, 5356. (l) Ohshita, J.; Ohnishi, H.;
Naka, A.; Senba, N.; Ikadai, J.; Kunai, A.; Kobayashi, H.; Ishikawa, M.
Organometallics 2006, 25, 3955. (m) Naka, A.; Motoike, S.; Senba, N.;
Ohshita, J.; Kunai, A.; Yoshizawa, K.; Ishikawa, M. Organometallics 2008,
27, 2750.
(21) (a) Couret, C.; Escudiꢀe, J.; Satgꢀe, J.; Lazraq, M. J. Am. Chem. Soc.
1987, 109, 4411. (b) Lazraq, M.; Escudiꢀe, J.; Couret, C.; Satgꢀe, J.;
Dr€ager, M.; Dammel, R. Angew. Chem., Int. Ed. Engl. 1988, 27, 828.
(22) (a) Toltl, N. P.; Leigh, W. J. J. Am. Chem. Soc. 1998, 120, 1172.
(b) Leigh, W. J.; Potter, G. D.; Huck, L. A.; Bhattacharya, A. Organo-
metallics 2008, 27, 5948.
(23) We estimate the pKa of the conjugate acid of ethoxyacetylene to
be ca. ꢀ20 based on the reported pKa of PhCtCOH (ca. ꢀ3: Chiang,
Y.; Kresge, A. J.; Paine, S. W.; Popik, V. V. J. Phys. Org. Chem. 1996, 9,
361) and a difference of 17 pKa units between alcohols and their
conjugate acids.
’ ACKNOWLEDGMENT
We thank the NSERC (Canada) and the University of
Western Ontario for financial support, Professor Emeritus J. P.
Guthrie (UWO) for useful discussions, and Teck Metals Ltd. for
a generous donation of GeCl4.
’ REFERENCES
(1) Ottosson, H.; Steel, P. G. Chem.—Eur. J. 2006, 12, 1576.
(2) For reviews on silenes see: (a) Gusel’nikov, L. E.; Nametkin,
N. S. Chem. Rev. 1979, 79, 529. (b) Raabe, G.; Michl, J. Chem. Rev. 1985,
85, 419. (c) Brook, A. G.; Baines, K. M. Adv. Organomet. Chem. 1986,
25, 1. (d) Brook, A. G.; Brook, M. A. Adv. Organomet. Chem. 1996,
39, 71. (e) M€uller, T.; Ziche, W.; Auner, N. The Chemistry of Organic
Silicon Compounds; Rappoport, Z.; Apeloig, Y., Eds.; Wiley & Sons: New
York, 1998; Vol. 2, Part 2, pp 857ꢀ1062. (f) Morkin, T. L.; Owens,
T. R.; Leigh, W. J. The Chemistry of Organic Silicon Compounds;
Rappoport, Z.; Apeloig, Y., Eds.; Wiley & Sons: New York, 2001; Vol.
3, pp 949ꢀ1026. (g) Ottosson, H.; Ekl€of, A. M. Coord. Chem. Rev. 2008,
252, 1287.
(3) (a) Milnes, K. K.; Jennings, M. C.; Baines, K. M. J. Am. Chem. Soc.
2006, 128, 2491. (b) Milnes, K. K.; Baines, K. M. Can. J. Chem. 2009,
87, 307.
(4) Milnes, K. K.; Pavelka, L. C.; Baines, K. M. Organometallics 2010,
29, 5972.
(5) (a) Milnes, K. K.; Gottschling, S. E.; Baines, K. M. Org. Biomol.
Chem. 2004, 2, 3530. (b) Gottschling, S. E.; Grant, T. N.; Milnes, K. K.;
Jennings, M. C.; Baines, K. M. J. Org. Chem. 2005, 70, 2686.
(6) (a) Delpon-Lacaze, G.; Couret, C. J. Organomet. Chem. 1994,
480, C14. (b) Delpon-Lacaze, G.; de Battisti, C.; Couret, C. J. Organo-
met. Chem. 1996, 514, 59.
(7) Trinquier, G.; Barthelat, J.-C.; Satge, J. J. Am. Chem. Soc. 1982,
104, 5931.
(8) Couret, C.; Escudiꢀe, J.; Delpon-Lacaze, G.; Satgꢀe, J. Organome-
tallics 1992, 11, 3176.
(24) Stamhuis, E. J.; Drenth, W. Rec. Trav. Chim. 1961, 80, 797.
(25) Banait, N.; Hojatti, M.; Findlay, P.; Kresge, A. J. Can. J. Chem.
1987, 65, 441.
(26) Amemiya, R.; Yamaguchi, M. In Acid Catalysis in Modern
Organic Synthesis; Yamamoto, H. Ishihara, K., Eds.; Wiley-VCH: Weinheim,
2008; Vol. 1, pp 347ꢀ375.
(27) Higashiura, K.; Oiwa, M. J. Poly. Sci. Part A-1: Polym. Chem.
1968, 6, 1857.
(28) Delpon-Lacaze, G.; Couret, C.; Escudiꢀe, J.; Satgꢀe, J. Main Group
Met. Chem. 1993, 16, 419.
(29) Rupar, P. A. Ph.D. Thesis, UWO, 2009.
(30) Data were obtained from the crude reaction mixture, and thus,
only partial data could be extracted.
(9) For reviews on multiply bonded species containing Ge, Sn, and
Pb see: (a) Power, P. P. Chem. Rev. 1999, 99, 3463. (b) Tokitoh, N.;
Okazaki, R. Adv. Organomet. Chem. 2001, 47, 121. (c) Tokitoh, N.;
Okazaki, R. The Chemistry of Organic Germanium, Tin and Lead
Compounds; Rappoport, Z., Ed.; Wiley & Sons: New York, 2002;
Vol. 2, Part 1, pp 843ꢀ901.
(31) Chemical shift estimated from gHMBC spectrum.
(10) For reviews on germenes see: (a) Wiberg, N. J. Organomet.
Chem. 1984, 273, 141. (b) Barrau, J.; Escudiꢀe, J.; Satgꢀe, J. Chem. Rev.
1990, 90, 283. (c) Escudiꢀe, J.; Couret, C.; Ranaivonjatovo, H. Coord.
Chem. Rev. 1998, 180, 565.
(11) Germene 7 slowly reacts to give dimers 14, isomeric germane
15, and polymeric material when left in solution (C6D6) for several days:
Pavelka, L. C.; Holder, S. J.; Baines, K. M. Chem. Commun. 2008, 2346.
(12) Mohseni-Ala, J.; Auner, N. Inorg. Chim. Acta 2006, 359, 4677.
(13) Fluoride is quite basic in non-hydrogen bonding solvents (i.e.,
DMSO): Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456.
(14) In some cases, the appearance of the germylacetylene is slower
(i.e., see plot for entry 19 in the Supporting Information).
(15) (a) Kresge, A. J.; Powell, M. F. J. Org. Chem. 1986, 51, 819.
(b) Tupitsyn, I. F.; Popov, A. S.; Shibaev, A. Yu. J. Gen. Chem. USSR
1992, 62, 2277. (c) Tupitsyn, I. F. Russ. J. Gen. Chem. 2004, 74, 1020.
(16) (a) Riviꢁere-Baudet, M.; Khallaayoun, A.; Satgꢀe, J. J. Organomet.
Chem. 1993, 462, 89. (b) Riviꢁere-Baudet, M.; Khallaayoun, A.; Satgꢀe, J.
Organometallics 1993, 12, 1003.
(17) Escudiꢀe, J.; Couret, C.; Andrianarison, M.; Satgꢀe, J. J. Am. Chem.
Soc. 1987, 109, 386.
2271
dx.doi.org/10.1021/om200048p |Organometallics 2011, 30, 2261–2271