Addition of aldehydes to germenes: The influence of solvent

Article abstract of DOI:10.1021/om200114n

The addition of trans-(2-phenylcyclopropyl) carboxaldehyde to dimesitylfluorenylidenegermane produced four diastereomers of a 1,2-oxagermin, 7a-d, 2,2,4,4- tetramesityl-1,3-dioxadigermetane (8), and fluorenylidene- (trans-2-phenylcyclopropyl)methane (9). The ratio of the products showed a strong dependence on the solvent: 7a-d were formed almost exclusively when ether or benzene was used as the solvent for the reaction, whereas 1,3-dioxadigermetane 8 and alkene 9 were the major products formed in THF. A mechanism is proposed to account for the observations.

Full text of DOI:10.1021/om200114n

ARTICLE
pubs.acs.org/Organometallics
Addition of Aldehydes to Germenes: The Influence of Solvent
Christopher J. Allan, Crispin R. W. Reinhold, Laura C. Pavelka, and Kim M. Baines*
Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
S Supporting Information
b
ABSTRACT: The addition of trans-(2-phenylcyclopro-
pyl)carboxaldehyde to dimesitylfluorenylidenegermane pro-
duced four diastereomers of a 1,2-oxagermin, 7aꢀd, 2,2,4,4-
tetramesityl-1,3-dioxadigermetane (8), and fluorenylidene-
(trans-2-phenylcyclopropyl)methane (9). The ratio of the
products showed a strong dependence on the solvent: 7aꢀd
were formed almost exclusively when ether or benzene was used
as the solvent for the reaction, whereas 1,3-dioxadigermetane 8
and alkene 9 were the major products formed in THF. A
mechanism is proposed to account for the observations.
’ INTRODUCTION
Using this approach, we have found that the mechanistic
Although the discovery of silenes1ꢀ3 and germenes4,5 took
place over 40 years ago, the fundamental chemistry of these
molecules remains an active area of interest,6,7 as an under-
standing of their reactivity is critical for the development of
potential applications of the chemistry (for example in organic
synthesis8 or in material sciences9). One of the most important
reactions of the lighter group 14 metallenes (R2MdCR02; M = Si,
Ge) is the addition of carbonyl compounds. With nonenolizable,
saturated ketones and aldehydes, metallaoxetanes (1a) are most
often formed, although the four-membered ring often undergoes
cleavage.6,7 In contrast, the addition of unsaturated ketones and
aldehydes usually leads to formal [4 þ 2] adducts (1b), while ene
adducts (1c) are often formed upon addition of ketones and
aldehydes with an R-hydrogen (Scheme 1). The addition of the
carbonyl compound to the metallene generally occurs cleanly in
high yield, and thus, these reactions have been used extensively
during the development of the chemistry of silenes and germenes
to provide evidence for transient species.
pathway is highly dependent on the nature of the (di)metallene.
For silenes, the addition of aldehydes to the naturally polarized
neopentylsilene Mes2SidCHCH2t-Bu proceeds via a zwitterio-
nic intermediate.13 In contrast, the addition of aldehydes to the
relatively nonpolar Brook silene (Me3Si)2SidC(OSiMe3)R,13
the nonpolar disilene Mes2SidSiMes2,10,11 or the relatively
10,11
nonpolar germasilene Mes2GedSiMes2
proceeds by way
of a biradical intermediate. The addition of the probe to the
nonpolar digermene Mes2Ge=GeMes2, surprisingly, was found
to proceed through a zwitterionic intermediate.12 Although the
mechanism of aldehyde addition has been investigated for many
group 14 (di)metallenes, the mechanism of the addition of
carbonyl compounds to germenes (R2Ge=CR2) has not yet
been examined experimentally.
Mosey et al. have investigated the mechanism of formaldehyde
addition to the parent (di)metallenes (H2MdEH2: M = Si, Ge;
E = C, Si, Ge) using density functional theory.17 In the addition
of formaldehyde to the parent silene, disilene, germasilene, and
digermene, the lowest energy reaction pathway found was the
same as that determined through the experimental studies. In
agreement with a previous computational study,18 the addition of
formaldehyde to germene followed a concerted reaction path-
way; zwitterionic and biradical intermediates were not located as
stationary points on the potential energy surface. The computa-
tional study did not consider the effect of substituents on the
mechanism of the cycloaddition reaction. More recently, the
addition of 1,4-benzoquinone to H2GedCH219 and the addition
of R-ethylenic aldehydes and ketones to HPdCdGeH220 have
been examined using density functional computational methods.
In each case, the one-step cycloaddition reaction of the carbonyl
functionality to the germaniumꢀcarbondoublebondwasdescribed
We have utilized trans-(2-phenylcyclopropyl)carboxaldehyde
(2) as a probe to examine the nature of any reactive inter-
mediates that may form during the cycloaddition of aldehydes
to a variety of group 14 (di)metallenes.10ꢀ13 The probe is able
to distinguish between biradical and cationic intermediates.
Rapid and regioselective ring opening occurs upon the forma-
tion of an R-cyclopropyl radical (2b); in contrast, the analogous
R-cyclopropyl cation (2a) does not rearrange (Scheme 2). The
rate constant for the rearrangement of 2b has been estimated to
be greater than 2 ꢁ 1010 s
.
ꢀ1 14ꢀ16 Thus, the isolation of ring-
opened adducts of aldehyde 2 provides strong evidence for a
biradical intermediate. The cyclopropyl ring would not be
expected to open during a concerted cycloaddition, and thus,
it is necessary to use other techniques to differentiate between
a concerted reaction pathway and one involving a cationic
intermediate.
Received: February 6, 2011
Published: May 10, 2011
r
2011 American Chemical Society
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Scheme 1. Aldehyde Addition to a Metallene
Scheme 3. Synthesis of Germene 4
rather than methanol/triethylamine was used as the reagent in
step 1). The purification of fluorofluorenyldimesitylgermane (6)5
was problematic: sublimation of the crude product mixture was
required to remove excess fluorene, followed by fluorination and
subsequent chromatography of the residue to remove the hydrolysis
byproducts of difluorodimesitylgermane. After purification, fluoro-
germane 6 was isolated in reasonable purity in 64% yield from
Mes2GeF2 (41% yield from Mes2GeCl2). The yield of the
fluorogermane 6 was greatly improved by the direct alkylation
of Mes2GeCl2 with fluorenyllithium to give chlorofluorenyl-
dimesitylgermane, which was isolated without an aqueous
workup and readily purified by recrystallization. Treatment
of the chlorogermane with AgBF4 gave 6 in 75% yield (from
Mes2GeCl2) after purification by chromatography (Scheme 3,
method 2).
Scheme 2. Reactivity of trans-(2-Phenylcyclopro-
pyl)carboxaldehyde toward Radicals and Cations
The NMR data of fluorogermane 6 clearly show the presence
of the fluorine substituent: the signals assigned to the o-Me of the
mesityl substituents in both the 13C and the 1H NMR spectra of 6
appear as doublets due to coupling to the fluorine. Furthermore,
the signals assigned to the quaternary carbons of the fluorenyl
substituent and the ipso carbon of the mesityl substituents in the
13C NMR spectrum of the fluorogermane 6 are also doublets,
again, due to coupling with the fluorine. The molecular structure
of 6 was determined by X-ray crystallography; all bond lengths
and angles fall within normal ranges (see Figure S1 in the
Supporting Information).26
as being asynchronous, with GeꢀO bond formation preceding
CꢀC bond formation.
Herein, we now report on the addition of probe 2 to a stable
germene to investigate the mechanism of this important reac-
tion.19ꢀ21 Two naturally polarized germenes were considered as
substrates for this study: 1,1-dimesitylneopentylgermene22 (3)
and dimesitylfluorenylidenegermane (4).5 Both germenes are
stable in solution and can be readily synthesized. The addition of
a number of aldehydes and ketones, including diketones and
quinones, to germenes 323 and 419,21b,21d,21f,21g,24 has been
reported. Given that the addition of carbonyl compounds to
germene 3 often results in the formation of ene adducts,23
germene 4 was chosen as the substrate for this study.
Treatment of fluorogermane 6 with 1 equiv of t-BuLi in diethyl
ether gives germene 4 in quantitative yield by NMR spectros-
1
copy. Accordingly, the signals in the H and the 13C NMR
spectra of germene 4 in deuterated benzene show no evidence of
coupling to fluorine and the 19F NMR spectrum of the germene
shows only a weak signal due to residual fluorogermane 6.
The addition of trans-(2-phenylcyclopropyl)carboxaldehyde
(2) to germene 4 yielded diastereomers 7aꢀd and/or 2,2,4,4-
tetramesityl-1,3-dioxadigermetane (8) and alkene 9, depending
on the solvent of the reaction (Scheme 4). Chromatographic
separation of the crude product mixture allowed for the isolation
of a mixture of diastereomers 7a,b, diastereomer 7c, diastereo-
mer 7d, and a mixture of 1,3-dioxadigermetane 827 and alkene 9.
1
’ RESULTS AND DISCUSSION
Diastereomers 7aꢀd and 9 were identified by H, gCOSY,
13
1
13
Germene 4 was synthesized in four steps from dichlorodime-
sitylgermane, as outlined in Scheme 3 (method 1), with only minor
modifications to the published procedure5,25 (sodium methoxide
1Hꢀ C gHMBC, and Hꢀ C gHSQC NMR spectroscopy
and mass spectrometry. Given the critical role the structures of
the adducts play in the mechanistic interpretation, we include a
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Scheme 4. Addition of Aldehyde 2 to Germene 4
Scheme 5. Conversion of Oxagermetane 10 to
Dioxadigermetane 8 and Alkene 9
systems that each integrated for 4H. These signals were assigned
to a fluorenyl system. Total correlation spectroscopy (TOCSY)
was performed on the sample. Irradiation of the signal at
6.11 ppm showed enhancement of the 1H signals at 0.97, 1.29,
1.97, and 2.54 ppm. On the basis of the splitting patterns and
chemical shifts, these signals were assigned to a 1,2-disubstituted
cyclopropyl ring with a trans orientation of the substituents. All
data are in agreement with the structure assigned to alkene 9.
The solvent of the reaction greatly influences the product
distribution (see Table 2 in the Experimental Section). When the
aldehyde was added to the germene formed in situ in Et2O,
oxagermins 7aꢀd were the major products (91% of the adducts).
In contrast, when the reaction was carried out in THF under
identical conditions, 8 and 9 were formed in quantitative yield.
To determine that germene 4 is the reactive species and not
Mes2GeFCLiR2 (the immediate precursor to germene 4; CR2 =
fluorenylidene), the germene was isolated and purified by
trituration prior to the addition of the aldehyde. Addition of
aldehyde 2 to the isolated germene 4 in benzene (a weakly
coordinating solvent) gave almost exclusively oxagermins 7aꢀd,
whereas the addition of aldehyde 2 to the isolated germene 4 in
THF gave 8 and 9 as the major products (77% of the adducts).
Alkene 9 is likely formed by the decomposition of the
intermediate oxagermetane 10 (Scheme 5). Compound 9 was
observed in the crude reaction mixture before exposure to air,
moisture, or chromatography, and thus, it is probable that
cycloadduct 10 spontaneously decomposes. The isolation of
1,3-dioxadigermetane 8 provides further evidence for the forma-
tion of the intermediate oxagermetane.
The absence of products derived from ring opening of the
cyclopropyl substituent of the aldehyde demonstrates that no
radical developed at the cyclopropyl carbinyl position during the
formation of 7aꢀd or oxagermetane 10 (or the subsequent
cleavage of 10 to give 8 and 9). The absence of a cyclopropyl
carbinyl radical is further evidenced by the formation of only four
diastereomers of oxagermin 7; if the cyclopropyl ring were to
open during the reaction, scrambling of the stereochemistry of
the cyclopropyl substituents would be expected to produce up to
eight diastereomers (see Figure S2 in the Supporting In-
formation). These results, together with the results of the
computational studies which indicate the absence of any
intermediates,17ꢀ20 suggest that the addition of aldehyde 2 to
germene 4 partitions between two pathways: a concerted [4 þ 2]
cycloaddition followed by a hydrogen transfer to give 7aꢀd and a
concerted [2 þ 2] pathway to give 10. However, it is difficult to
reconcile the dramatic influence of the solvent on the product
distribution if all products are derived from (at least initially)
brief discussion of the salient features of the spectroscopic data
that lead to the unequivocal identification of the products.
The spectral features of all diastereomers of 7 are similar, and
thus, only the spectral identification of 7d is presented here. The
highest mass ion in the mass spectrum of 7d was observed at m/z
622, which corresponds to a 1:1 adduct of the aldehyde and the
germene. The 1H NMR spectrum of diastereomer 7d
contained signals in three regions: 1.03ꢀ2.54, 4.26ꢀ4.79, and
1
1
6.29ꢀ7.76 ppm. The Hꢀ H gCOSY NMR spectrum of dia-
1
stereomer 7d showed correlations between the H signals at
2.2,28 1.67 (dddd), 1.28 (ddd), and 1.03 ppm (ddd). On the basis
of the observed correlations, multiplicities, and chemical shifts of
1
the signals, these signals were assigned to the H nuclei of an
intact cyclopropyl ring. Furthermore, on the basis of the magni-
tude of the coupling constants, the stereochemistry of the two
substituents on the cyclopropyl ring was determined to be trans.
A correlation between the 1H signal at 4.79 ppm (d) and the 1H
1
signal at 1.67 ppm, assigned to a cyclopropyl H, was also
apparent. On the basis of the chemical shift of the signal at
4.79 ppm, the signal was assigned to the former aldehydic 1H of
the probe. Signals were also apparent in the 1H NMR spectrum of
7d, which were consistent with two nonequivalent mesityl
substituents and a phenyl group. In addition, two separate spin
1
systems were observed in the aromatic region of the H NMR
spectrum of 7d at 7.76 (d), 7.58 (d), 7.24 (t), and 7.2 ppm28 and
at 7.70 (d), 7.50 (d), and 7.28 ppm (t). The signal at 4.26 ppm (s)
showed correlations to the 13C signals of both aromatic spin
1
13
systems in the Hꢀ C gHMBC spectrum of 7d and, thus, is
assigned to a doubly benzylic 1H. Taken together, these data lead
to the assignment of the structure shown in Scheme 4. Notably,
the stereochemistry of the cyclopropyl rings was determined
to be trans in each stereoisomer of 7 (see Figure S2 in the
Supporting Information).
Attempted isolation of 9 by chromatography yielded a sample
contaminated with 1,3-dioxadigermetane 8.29 Purification of 9
was achieved by fluorination of the dioxadigermetane, followed
by chromatographic separation of the products. The highest
mass ion in the mass spectrum of 9 was observed at m/z 294,
corresponding to the molecular ion; notably, the isotopic pattern
1
typical of germanium was absent. The 1Hꢀ H gCOSY spectrum
of the isolated compound showed a correlation between the
1
signal at 6.11 ppm, assigned to a vinylic H, and the signal at
2.54 ppm. The gCOSY spectrum also showed two aromatic spin
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Scheme 6. Proposed Mechanism for the Formation of 7aꢀd
Scheme 7. Proposed Mechanism for the Formation of
8 and 9
concerted reaction pathways. Thus, we propose that the two
types of products (7aꢀd and 8/9) are derived from two different
species. We believe that the formation of diastereomers 7aꢀd
occurs by way of a concerted [4 þ 2] cycloaddition between
germene 4 and aldehyde 2, where the aldehyde acts as the
dienophile and the germene as the diene, followed by a hydrogen
transfer (Scheme 6). The reaction is completely regioselective,
presumably due to the formation of the energetically favorable
GeꢀO bond and the polarities of the CdO and the GedC
bonds. Alternatively, nucleophilic addition of a donor complex of
the germene (11) to aldehyde 2 gives oxagermetane 10 (perhaps
via the zwitterion 12), which spontaneously decomposes to 8
and 9 (Scheme 7).
There are two plausible candidates for donors: the solvent
molecules and/or fluoride ion. Both THF and diethyl ether have
been reported to form adducts with germene 4;5a coordination
with the solvent would increase the nucleophilicity of the
germenic carbon. In support of this hypothesis, the relative
amount of 9 increases with increasing donor abilities of
the solvents: THF > Et2O . benzene.30,31 On the other hand,
the molecular structures of the proposed THF or Et2O adducts of
germene 4 were not determined;5a the crystals isolated by Couret
et al. may have been solvates of the germene rather than discrete
complexes. Furthermore, we did not observe the formation of
solvates/donor complexes of germene 4. Despite an earlier report
which stated that Ph2GedCH2 may complex weakly with THF,32
Leigh reported that the λmax values of the UV/vis spectra of bis
(p-trifluoromethylphenyl)germene21c and a germahexatriene21e
(microsecond lifetimes) are unaffected upon varying the solvent
from hexanes to THF. Thus, the evidence for the complexation
of germene 4 by solvent is somewhat ambiguous.
relative amount of 9 correlates to the donor ability of the solvent
and the fact that we observe the formation of 8/9 in THF after
attempts to remove fluoride, we favor a solvent-donor complex of
germene 4 as the reactive species; however, we cannot rule out
that fluoride may catalyze the reaction.
Although solvent effects are common in many areas of
chemistry, our results represent a rare example of where the
solvent dramatically influences the product distribution of a
reaction of a (di)metallene. In 1996, Ishikawa noted that donor
solvents (THF, CH3CN) influenced the diastereoselectivity of
the products derived from the addition of acetone to a
silatriene.35 The authors attributed the effect to coordination
of the solvents to the silene. In 2006, Oehme reported that the
product ratios of the aldehyde adducts of an intramolecularly
stabilized silene vary on changing the solvent from heptane to
THF; however, they concluded that this was not the result of a
change in mechanism, but rather a consequence of the stabiliza-
tion of the proposed zwitterionic intermediates by solvent.36
Interestingly, in no other study of the reactivity of germene 4
toward carbonyl compounds19,21b,21d,21f,21g,24 did the germene
act as the 4π component in a cycloaddition reaction with the
carbonyl group. With our results, a direct comparison can be made
between the addition of germene 4 to two different aldehydes:
benzaldehyde and trans-(2-phenylcyclopropyl)carboxaldehyde (2).
Both reactions were carried out in diethyl ether. When PhCHO
was added to germene 4, a stable [2 þ 2] adduct was isolated,24a
and when 2 was added, a product derived from [4 þ 2]
cyclization was obtained (i.e., 7aꢀd) with the germene acting
as the diene. Furthermore, the [2 þ 2] adduct between germene
4 and aldehyde 2 (10) does not appear to be stable. Perhaps there
are favorable interactions between the aromatic aldehyde and the
fluorenyl substituent in the transition state of the addition of
PhCHO to 4, which leads to the [2 þ 2] cycloadduct. A detailed
understanding of the factors influencing the different modes of
addition between carbonyl compounds and germene 4 requires
more study.
One equivalent of LiF is formed during the synthesis of 4.33
The solubility of LiF in THF or benzene is known (0.09 mM and
0.011 mM, respectively);34 however, the solubility of LiF in
diethyl ether has not been reported to our knowledge. Et2O is
comparable in polarity to benzene but is a much better donor.30
Possibly, the different solubilities of LiF in THF and in Et2O
account for the different results observed when the germene is
generated and used in situ in either THF or Et2O. The addition of
a few milligrams of LiF and aldehyde 2 to the isolated germene 4
redissolved in THF did result in a small increase in the amount of
alkene 9 relative to oxagermins 7aꢀd; however, a significant
increase in the amount of hydrolysis products was also observed
under these conditions and it is difficult to separate the influence
of added LiF from that of adventitious water. Given that the
In summary, the addition of trans-(2-phenylcyclopropyl)-
carboxaldehyde (2) to dimesitylfluorenylidenegermane (4) yields
both six-membered and four-membered rings. In both instances,
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the probe 2 did not rearrange, and thus, a biradical intermediate
can be ruled out. We favor a two-step reaction pathway, a [4 þ 2]
cycloaddition followed by a hydrogen transfer, for the formation
of the oxagermins on the basis of the results of a computational
study of a similar reaction.37 The solvent of the reaction
dramatically influences the outcome of the reaction: in diethyl
ether or benzene, oxagermins 7aꢀd are the major products,
whereas in THF, 8 and 9 are the major products observed. The
change in product distribution can be readily understood in
terms of the different coordination abilities of the solvents. THF
strongly coordinates to the Ge of the germene; the complex then
acts as a nucleophile toward the aldehyde, which ultimately
results in the formation of dioxadigermetane 8 and alkene 9.
Ether does not coordinate as strongly, and hence, less alkene is
formed during reactions in ether. Benzene does not coordinate,
and accordingly, oxagermins 7aꢀd are formed in quantitative
yield. We acknowledge that the methods used to remove fluoride
from the reaction mixture may not have been sufficient and
fluoride may be the catalyst in the reaction. The results presented
here illustrate, for the first time, the dramatic effect that the
solvent and/or a donor can play on the outcome of the reactions
of germenes.
Table 1. Crystallographic Parameters for 6
empirical formula
formula wt
cryst syst
C31H31GeF
496.15
monoclinic
P121/n1
8.8747(12)
9.2127(11)
30.870(4)
90
space group
a (Å)
b (Å)
c (Å)
R (deg)
β (deg)
90.004(7)
90
γ (deg)
V (Å3)
2523.9(5)
4
Z
no. of data/restraints/params
goodness of fit
R (I > 2σ(I))
wR2 (all data)
6018/0/304
1.014
0.0480
0.0978
largest diff peak, hole (e Åꢀ3
)
0.445, ꢀ0.457
heterogeneous mixture. After the mixture was stirred for 1 h at room
temperature, the solids were removed by decantation and the solvent
was removed in vacuo. The residue was purified by preparative thin-layer
chromatography (SiO2, CHCl3) to give a colorless solid (128 mg,
0.26 mmol, 86%) identified as fluorogermane 6. The spectral data agreed
well with the published values5a (1H NMR chemical shifts, (0.05 ppm;
19F NMR chemical shifts, (2.5 ppm). 13C NMR (C6D6): δ 143.59
(d, fluorenyl C, JCF = 2.3 Hz), 143.30 (Mes o-C), 141.96 (d, fluorenyl C,
JCF = 0.9 Hz), 140.12 (Mes p-C), 134.21 (d, Mes i-C, JCF = 9.9 Hz), 129.60
(Mes CH), 127.19 (fluorenyl CH), 126.79 (fluorenyl CH), 124.88 (d,
fluorenyl CH, JCF = 1.8 Hz), 120.14 (fluorenyl CH), 46.71 (d, fluorenyl CH,
JCF = 12.8 Hz), 23.09 (d, Mes o-CH3, JCF = 4.1 Hz), 20.95 (Mes p-CH3).
A translucent colorless blocklike crystal of C31H31FGe, approximate
dimensions 0.07 mm ꢁ 0.08 mm ꢁ 0.11 mm, was used for X-ray
crystallographic analysis. Data were collected at low temperature
(ꢀ123 °C) on a Bruker Apex II CCD X-ray diffractometer (Mo KR
radiation, λ = 0.710 73 Å, 50 kV/30 mA). The structure was solved by
direct methods using SHELXS-97 and refined by full-matrix least
squares on F2 using SHELXL-97.40 Data were corrected for absorption
effects using the multiscan method (SADABS). The crystallographic
parameters are given in Table 1.
Typical Procedure for the Synthesis of Germene 4. Fluoro-
germane 6 (45 mg, 0.09 mmol) was dissolved in diethyl ether (10 mL);
the solution was cooled in a dry ice/acetone bath. tert-Butyllithium
(0.05 mL, 1.7 M in pentane, 0.09 mmol) was added slowly, and then the
solution was warmed to room temperature. During this time, the clear
solution changed from yellow to dark orange. After 1 h at room
temperature, the ether was removed in vacuo. The residue was triturated
with C6D6 and then centrifuged. The supernatant was analyzed by 1H
NMR spectroscopy and was found to contain germene 4 (88%),
[Mes2Ge(fluorenyl)]2O24a (9%), residual fluorogermane 6 (3%), and
traces of Mes2GeH(fluorenyl)5a (<1%). No evidence for the Et2O
adduct of the germene was observed.5a 1H NMR5a (C6D6): δ 7.88
(dt, 1H, fluorenyl, JHH = 7.4, 0.9 Hz), 7.74 (dt, 1H, fluorenyl, JHH = 7.6,
0.8 Hz), 7.19 (td, 1H, fluorenyl, JHH = 7.4, 1.0 Hz), 7.10 (td, 1H,
fluorenyl, JHH = 7.4, 1.1 Hz), 6.73 (s, 4H, Mes H), 2.39 (s, 12H, Mes o-
CH3), 2.06 (s, 6H, Mes p-CH3). 13C NMR (C6D6): δ 143.45 (fluorenyl
C), 143.12 (Mes o-C), 141.03 (Mes p-C), 136.53 (Mes i-C), 135.78
(fluorenyl C), 133.56 (GedC), 129.14 (Mes CH), 126.12 (fluorenyl
CH), 124.16 (fluorenyl CH), 121.23 (fluorenyl CH), 120.02 (fluorenyl
CH), 24.01 (Mes o-CH3), 21.19 (Mes p-CH3). 19F NMR (C6D6):
δ no significant signals observed; ꢀ173 (residual 6).
’ EXPERIMENTAL SECTION
All experiments were carried out in flame-dried glassware under an
atmosphere of argon using a Schlenk line or in a nitrogen-filled glovebox.
All solvents were dried by passing through an alumina column and
purged with nitrogen, with the exception of solvents used for chromato-
graphic separations. NMR spectra were recorded on an Inova 400 or 600
MHz spectrometer. 1H NMR spectra are referenced to C6D5H at 7.15
ppm, 13C NMR spectra are referenced to C6D6 at 128.00 ppm and
CF3Ph as an external standard (ꢀ63.9 ppm against CFCl3) for 19F NMR
spectra. trans-(2-Phenylcyclopropyl)carboxylic acid was reduced with
lithium aluminum hydride in diethyl ether to give the corresponding
alcohol,38 which was subsequently oxidized using Swern conditions to
trans-(2-phenylcyclopropyl)carboxaldehyde.39
Synthesis of Chlorofluorenyldimesitylgermane. A solution
of fluorene (1.31 g, 7.9 mmol) dissolved in THF (25 mL) was cooled to
ꢀ78 °C. t-BuLi (5.2 mL, 1.5 M in pentane, 7.9 mmol) was added slowly
to the solution, which became bright orange. After the mixture was
stirredfor1.5 h, a solutionof dichlorodimesitylgermane (3.0g, 7.9mmol)
dissolved in THF (25 mL) was added slowly to the reaction mixture.
The solution was stirred for 3 h at ꢀ78 °C and then warmed to room
temperature and stirred overnight. The solvent was removed in vacuo;
hexanes were added to the residue to give a suspension. The solids were
removed by filtration, and the solvent was removed in vacuo to give a
residue which was recrystallized from hexanes to yield a colorless solid
(3.5 g, 6.8 mmol, 87%). Mp: 202ꢀ204 °C. 1H NMR (C6D6): δ 7.75 (br
d, 1H, fluorenyl, JHH = 7.6 Hz), 7.69 (d, 1H, fluorenyl, JHH = 7.6 Hz),
7.20 (tt, 1H, fluorenyl, JHH = 7.6, 0.9 Hz), 7.02 (dt, 1H, fluorenyl, JHH
=
1.0, 7.6 Hz), 6.58 (s, 4H, Mes H), 5.00 (s, 1H, GeCH), 2.12 (s, 12H, Mes
o-CH3), 1.97 (s, 6H, Mes p-CH3). 13C NMR (C6D6): δ 143.84
(fluorenyl C), 142.99 (Mes o-C), 142.05 (fluorenyl C), 139.87 (Mes
p-C), 136.02 (Mes i-C), 130.04 (Mes CH), 127.76 (fluorenyl CH),
126.99 (fluorenyl CH), 125.20 (fluorenyl CH), 120.07 (fluorenyl CH),
48.49 (GeCH), 24.12 (Mes o-CH3), 20.86 (Mes p-CH3). High-resolu-
tion EI-MS for C31H3170Ge35Cl (Mþ): m/z calcd 508.1357, found
508.1336. Anal. Calcd for C31H31GeCl: C, 72.77; H, 6.11. Found: C,
71.38; H, 6.00.
Synthesis of Fluorofluorenyldimesitylgermane (6). AgBF4
(240 mg, 1.23 mmol) was added to a solution of chlorofluorenyldime-
sitylgermane (154 mg, 0.30 mmol) dissolved in DCM (10 mL) to give a
3014
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ARTICLE
Table 2. Relative Ratios of Productsa Obtained under Vary-
ing Conditions
1.83 (s, 3H, Mes p-CH3), 1.82 (s, 3H, Mes p-CH3), 1.74ꢀ1.78 (m, 1H,
cyclopropyl), 1.61ꢀ1.66 (m, 1H, cyclopropyl), 1.27 (ddd, 1H, cyclo-
propyl, JHH = 4.8, 5.4, 8.4 Hz), 1.06 (ddd, 1H, cyclopropyl, JHH = 4.2, 4.2,
9.6 Hz), 0.93 (ddd, 1H, cyclopropyl, JHH = 4.8, 4.8, 9.6 Hz), 0.90 (ddd,
1H, cyclopropyl, 4.8, 4.8, 9.0 Hz); 13C NMR (C6D6) δ 144.46 (fluorenyl
C), 143.45 (phenyl), 143.41 (phenyl), 143.22 (Mes o-C), 143.13 (Mes
o-C), 142.86 (Mes o-C), 142.79 (Mes o-C), 141.95 (fluorenyl C), 141.90
(fluorenyl C), 141.55 (fluorenyl C), 141.54 (fluorenyl C), 139.71
(fluorenyl C), 139.54 (fluorenyl C), 139.37 (Mes p-C), 139.32 (Mes
p-C), 139.18 (fluorenyl C), 139.09 (Mes p-C), 139.06 (Mes p-C),
135.21 (Mes i-C), 135.03 (Mes i-C), 134.43 (Mes i-C), 134.20 (Mes i-
C), 129.87 (Mes CH), 129.82 (Mes CH), 129.02 (Mes CH), 128.99
(Mes CH), 128.53 (phenyl), 128.51 (phenyl), 126.90 (fluorenyl CH),
126.86 (fluorenyl CH), 126.79 (fluorenyl CH), 126.71 (fluorenyl CH),
126.63 (phenyl), 126.44 (phenyl), 125.63 (fluorenyl CH), 125.56
(fluorenyl CH), 124.79 (fluorenyl CH), 124.73 (fluorenyl CH),
124.51 (fluorenyl CH), 124.44 (fluorenyl CH), 120.65 (fluorenyl CH),
118.55 (fluorenyl CH), 118.47 (fluorenyl CH), 79.95 (OCH), 78.11
(OCH), 44.15 (GeCH), 43.91 (GeCH), 32.27 (cyclopropyl), 31.94
(cyclopropyl), 23.95 (Mes o-CH3), 23.84 (Mes o-CH3), 22.43 (Mes o-
CH3), 22.31 (Mes o-CH3), 22.10 (cyclopropyl), 21.59 (cyclopropyl),
21.05 (Mes p-CH3), 20.74 (Mes p-CH3), 14.00 (cyclopropyl), 13.32
(cyclopropyl); high-resolution EI-MS for C41H4074GeO (Mþ) m/z
calcd 622.2300, found 622.2311.
method
solvent
7a,b
7c
7d
9
A
A
B
B
Et2O
58
0
19
0
14
0
9
THF
100
1
benzene
50
25
24
THF
10
7
6
77
a The ratios are an average of two to five runs, and values vary typically by
(3%, except for method B (THF), where greater variability was noted.
Procedures for the Addition of trans-(2-Phenylcyclopro-
pyl)carboxaldehyde (2) to Dimesitylfluorenylidenegermane
(4). Method A. Fluorogermane 6 (100 mg, 0.2 mmol) was dissolved in
diethyl ether (or THF) (3 mL); the solution was cooled in a dry ice/
acetone bath. tert-Butyllithium (0.1 mL, 1.7 M in pentane, 0.19 mmol)
was added slowly. The solution was warmed to room temperature.
During this time, the clear solution changed from yellow to dark orange.
trans-(2-Phenylcyclopropyl)carboxaldehyde (29 mg, 0.2 mmol) dis-
solved in ether (or THF) (1 mL) was added slowly. The mixture was
stirred for 1 h, during which time the solution decolorized. The solvent
was removed in vacuo and the residue analyzed by 1H NMR spectros-
copy. Product ratios, as determined by 1H NMR spectroscopy, are given
in Table 2. The products were purified by preparative thin-layer
chromatography on silica gel using hexanes/dichloromethane as the
eluent (50:50 ratio for reactions done in ether and 70:30 for reactions
done in THF). The bands were removed from the plate and suspended
in dichloromethane. The solid was removed by filtration, and the solvent
was removed under vacuum.41,42 Dioxadigermetane 829 and alkene 9
were isolated as a mixture from the reaction in THF. The mixture was
dissolved in THF (20 mL). HF (48%; 1 mL) was added to the solution,
which was then stirred for 1 h. The reaction was quenched with sodium
sulfate. The solids were removed by filtration and washed with hexanes.
After removal of the solvents, the residue was passed through a silica
plug. If necessary, the residue was purified by preparative thin-layer
chromatography (silica gel; 70:30 hexanes/dichloromethane) to give
alkene 9.
1
7c: pale yellow oil, contaminated with starting material; H NMR
(C6D6) δ 7.75 (d, 1H, fluorenyl, JHH = 7.8 Hz), 7.63 (d, 1H, fluorenyl,
JHH = 7.2 Hz), 7.59 (d, 1H, fluorenyl, JHH = 7.2 Hz), 7.46 (d, 1H,
fluorenyl, JHH = 7.2 Hz), 7.24 (t, 1H, fluorenyl, JHH = 7.5 Hz), 7.228
(fluorenyl), 7.08ꢀ7.06 (m, 1H, phenyl), 7.03ꢀ7.00 (m, 2H, phenyl),
6.84 (s, 2H, Mes H), 6.36 (s, 2H, Mes H), 4.62 (d, 1H, OCH, JHH = 7.8
Hz), 4.26 (s, 1H, GeCH), 2.56 (s, 6H, Mes o-CH3), 2.17 (s, 3H, Mes p-
CH3), 2.04 (m, 1H, cyclopropyl), 1.87 (s, 6H, Mes o-CH3), 1.82 (s, 3H,
Mes p-CH3), 1.79ꢀ1.75 (m, 1H, cyclopropyl), 1.22 (ddd, 1H, cyclo-
propyl, JHH = 4.8, 4.8, 9.6 Hz), 1.04 (ddd, 1H, cyclopropyl, JHH = 4.8, 4.8,
9.0 Hz); 13C NMR (C6D6) δ 144.40 (fluorenyl C), 143.29 (phenyl),
142.61 (fluorenyl C), 142.52 (Mes o-C), 142.27 (Mes o-C), 141.24
(fluorenyl C), 140.26 (fluorenyl C), 140.03 (fluorenyl C), 139.24 (Mes
p-C), 138.92 (Mes p-C), 137.50 (Mes i-C), 136.30 (Mes i-C), 129.88
(Mes CH), 128.86 (Mes CH), 128.73 (phenyl), 126.91 (fluorenyl CH),
126.75 (fluorenyl CH), 126.49 (fluorenyl CH), 126.12 (phenyl), 125.80
(phenyl), 124.72 (fluorenyl CH), 123.46 (fluorenyl CH), 120.87
(fluorenyl CH), 119.09 (fluorenyl CH), 76.02 (OCH), 42.93 (GeCH),
24.05 (Mes o-CH3), 23.09 (Mes o-CH3), 22.98 (cyclopropyl), 21.57
(cyclopropyl), 21.08 (Mes p-CH3), 20.72 (Mes p-CH3), 14.75 (cyclo-
propyl); high-resolution EI-MS for C41H4074GeO (Mþ) m/z calcd
622.2300, found 622.2287.
Method B. A solution of germene 4 was prepared using the typical
procedure (see above). A benzene solution of trans-(2-phenylcyclopro-
pyl)carboxaldehyde (1 equiv) was added to the germene. After the
mixture was stirred for 1 h, the solvent was removed under vacuum and
1
the residue was analyzed by H NMR spectroscopy. Alternatively, the
solvent (C6D6) was removed in vacuo from the solution of germene 4,
prepared using the typical procedure (see above). The residue was then
dissolved in THF, and trans-(2-phenylcyclopropyl)carboxaldehyde
(1 equiv), also dissolved in THF, was added to the solution. Because
of the numerous manipulations of the germene, [Mes2Ge(fluorenyl)]2O24a
and/or Mes2Ge(OH)(fluorenyl)5a were often present as byproducts
in varying amounts in the product mixtures produced. The presence
of the hydrolysis products did not significantly influence the ratios of
7aꢀd and 9.
7d: pale yellow oil, contaminated; 1H NMR (C6D6) δ 7.76 (d, 1H,
fluorenyl, JHH = 7.2 Hz), 7.70 (d, 1H, fluorenyl, JHH = 7.8 Hz), 7.58 (d,
1H, fluorenyl, JHH = 7.8 Hz), 7.50 (d, 1H, fluorenyl, JHH = 7.2 Hz), 7.28
(t, 1H, fluorenyl, JHH = 7.8 Hz), 7.24 (t, 1H, fluorenyl, JHH = 7.8 Hz),
7.228 (fluorenyl), 7.0ꢀ7.2 (m, phenyl), 6.82 (s, 2H, Mes H), 6.29 (s, 2H,
Mes H), 4.79 (d, 1H, JHH = 6.0 Hz, OCH), 4.26 (s, 1H, GeCH), 2.54 (s,
6H, Mes o-CH3), 2.228 (m, 1H, cyclopropyl), 2.16 (s, 3H, Mes p-CH3),
1.80 (s, 9H, Mes p- and o-CH3), 1.67 (dddd, 1H, cyclopropyl, JHH = 5.7,
5.7, 5.7, 9.0 Hz), 1.28 (ddd, 1H, cyclopropyl, JHH = 4.8, 4.8, 9.0 Hz), 1.03
(ddd, 1H, cyclopropyl, JHH = 4.8, 4.8, 9.0 Hz); 13C NMR (C6D6) δ
144.07 (fluorenyl C), 143.36 (phenyl), 142.22 (fluorenyl C), 142.19
(Mes o-C), 141.89 (Mes o-C), 141.07 (fluorenyl C), 140.00 (fluorenyl
C), 139.86 (fluorenyl C), 138.86 (Mes p-C), 138.49 (Mes p-C), 136.97
(Mes i-C), 135.63 (Mes i-C), 129.50 (Mes CH), 128.55 (Mes CH), 126.44
(fluorenyl CH), 126.41 (fluorenyl CH), 126.15, 126.13 (fluorenyl CH,
phenyl), 125.28 (phenyl), 124.34 (fluorenyl CH), 123.17 (fluorenyl
CH), 120.51 (fluorenyl CH), 118.71 (fluorenyl CH), 74.57 (OCH), 42.62
(GeCH), 27.51 (cyclopropyl), 23.71 (Mes o-CH3), 22.52 (Mes o-CH3),
7a,b: pale yellow oil, 50:50 mixture of two diastereomers; 1H NMR
(C6D6) δ 7.75 (d, 1H, fluorenyl, JHH = 7.2 Hz), 7.74 (d, 1H, fluorenyl,
JHH = 7.8 Hz), 7.64 (d, 1H, fluorenyl, JHH = 7.8 Hz), 7.60 (d, 1H,
fluorenyl, JHH = 7.2 Hz), 7.52 (d, 1H, fluorenyl, JHH = 7.8 Hz), 7.51 (d,
1H, fluorenyl, JHH = 7.2 Hz), 7.23 (t, 3H, fluorenyl, JHH = 7.5 Hz), 7.18
(t, 2H, fluorenyl, JHH = 7.2 Hz), 6.94ꢀ7.15 (fluorenyl, phenyl), 6.79 (s,
2H, Mes H), 6.73 (s, 2H, Mes H), 6.40 (s, 2H, Mes H), 6.39 (s, 2H, Mes
H), 4.89 (d, 1H, OCH, JHH = 6.0 Hz), 4.64 (s, 1H, GeCH), 4.63 (d, 1H,
JHH = 7.8 Hz, OCH), 4.59 (s, 1H, GeCH), 2.59 (br s, 6H, Mes o-CH3),
2.51 (br s, 6H, Mes o-CH3), 2.21 (ddd, 1H, cyclopropyl, JHH = 4.8, 4.8,
9.0 Hz), 2.13 (s, 3H, Mes p-CH3), 2.11 (s, 3H, Mes p-CH3), 2.09 (ddd,
1H, cyclopropyl, JHH = 4.8, 4.8, 9.0 Hz), 1.88 (br s, 12H, Mes o-CH3),
3015
dx.doi.org/10.1021/om200114n |Organometallics 2011, 30, 3010–3017

Organometallics
ARTICLE
20.71 (Mes p-CH3), 20.35, 20.32 (cyclopropyl, Mes p-CH3), 13.12
(cyclopropyl CH2); high-resolution EI-MS for C41H4074GeO (Mþ)
m/z calcd 622.2300, found 622.2299.
9: yellow solid; mp 107ꢀ113 °C; H NMR (C6D6) δ 7.90 (d, 1H
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,
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Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York,
1998; Vol. 2, Chapter 16. (f) Morkin, T. L.; Owens, T. R.; Leigh, W. J. In
The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y.,
Eds.; Wiley: New York, 2001; Vol. 3, Chapter 17. (g) Ottosson, H.;
Ekl€of, A. M. Coord. Chem. Rev. 2008, 252, 1287.
(7) For reviews on germenes see: (a) Barrau, J.; Escudiꢀe, J.;
Satgꢀe, J. Chem. Rev. 1990, 90, 283. (b) Baines, K. M.; Stibbs, W. G.
Adv. Organomet. Chem. 1996, 39, 275. (c) Escudie, J.; Couret, C.;
Ranaivonjatovo, H. Coord. Chem. Rev. 1998, 180, 565. (d) Tokitoh, N.;
Okazaki, R. In The Chemistry of Organic Germanium, Tin and Lead
Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 2002;
Vol. 2, Chapter 13. (e) Lee, V. Y.; Sekiguchi, A. Organometallics 2004,
23, 2822.
(8) Ottosson, H.; Steel, P. G. Chem. Eur. J. 2006, 12, 1576.
(9) (a) Pavelka, L. C.; Milnes, K. K.; Baines, K. M. Chem. Mater.
2008, 20, 5948. (b) Pavelka, L. C.; Holder, S. J.; Baines, K. M. Chem.
Commun. 2008, 2346. (c) Bravo-Zhivotovskii, D.; Melamed, S.; Molev,
V.; Sigal, N.; Tumanskii, B.; Botoshansky, M.; Molev, G.; Apeloig, Y.
Angew. Chem., Int. Ed. 2009, 48, 1834.
(10) Dixon, C. E.; Hughes, D. W.; Baines, K. M. J. Am. Chem. Soc.
1998, 120, 11049.
(11) Samuel, M. S.; Jenkins, H. A.; Hughes, D. W.; Baines, K. M.
Organometallics 2003, 22, 1603.
(12) Samuel, M. S.; Baines, K. M. J. Am. Chem. Soc. 2003, 125, 12702.
(13) Milnes, K. K.; Baines, K. M. Organometallics 2007, 26, 2392.
(14) (a) Ha, C.; Horner, J. H.; Newcomb, M.; Varick, T. R.; Arnold,
B. R.; Lusztyk, J. J. Org. Chem. 1993, 58, 1194. (b) Johnson, C. C.; Horner,
J. H.; Tronche, C.; Newcomb, M. J. Am. Chem. Soc. 1995, 117, 1684.
(15) Zelechonok, Y.; Silverman, R. B. J. Org. Chem. 1992, 57, 5785.
(16) Castellino, A. J.; Bruice, T. C. J. Am. Chem. Soc. 1988, 110, 7512.
(17) Mosey, N. J.; Baines, K. M.; Woo, T. K. J. Am. Chem. Soc. 2002,
124, 13306.
(18) Khabashesku, V. N.; Kudin, K. N.; Margrave, J. L. Russ. Chem.
Bull. 2001, 50, 20.
(19) Ghereg, D.; Andre, E.; Ech-Cherif El Kettani, S.; Saffon, N.;
Lazraq, M.; Ranaivonjatovo, H.;Gornitzka, H.;Miqueu, K.; Sotiropoulos,
J.-M.; Escudie, J. Organometallics 2010, 29, 4849.
1
fluorenyl, JHH = 8 Hz), 7.58ꢀ7.57 (m, 2H, fluorenyl), 7.53ꢀ7.52 (m,
1H, fluorenyl), 7.23ꢀ7.18 (m, 2H, fluorenyl), 7.14ꢀ7.12 (m, 3H,
fluorenyl, Ph m-CH), 7.06ꢀ7.00 (m, 2H, fluorenyl, Ph p-CH),
6.98ꢀ6.96 (m, 2H, Ph o-CH), 6.11 (d, 1H, vinyl, JHH = 9.6 Hz), 2.54
(dddd, 1H, cyclopropyl CHR, JHH = 4.2, 5.4, 9.0, 9.0 Hz), 1.97 (ddd, 1H,
cyclopropyl CHPh, JHH = 4.2, 6.0, 10 Hz), 1.29 (ddd, 1H, cyclopropyl
CH2, JHH = 4.8, 6.0, 8.4 Hz), 0.97 (ddd, 1H, cyclopropyl CH2, JHH = 4.2,
4.2, 10 Hz); 13C NMR (C6D6) δ 141.74 (i-Ph), 141.07 (fluorenyl C),
139.77 (fluorenyl C), 138.84 (fluorenyl C), 137.93 (fluorenyl C), 135.89
(CdCH), 132.81 (CdCH), 128.79 (Ph m-CH), 127.92 (fluorenyl CH),
127.66 (fluorenyl CH), 127.21 (fluorenyl CH), 127.02 (fluorenyl CH),
126.31 (Ph p-CH), 126.29 (Ph o-CH), 124.78 (fluorenyl CH), 120.13
(fluorenyl CH), 119.93 (fluorenyl CH), 119.89 (fluorenyl CH), 27.65
(cyclopropyl), 25.08 (cyclopropyl), 18.90 (cyclopropyl); IR (cmꢀ1
)
3060 (w), 3028 (w), 2922 (w), 2851 (w), 1644 (m), 1603 (m), 1495 (w),
1447 (m), 1183 (w), 1030 (w), 935 (w), 773 (m), 728 (s), 696 (m); high-
resolution EI-MS for C23H18 (Mþ) m/z calcd 294.1409, found 294.1411.
[Mes2Ge(fluorenyl)]2O:24a 1H NMR (C6D6) δ 7.91ꢀ8.44 (br s,
2H), 7.77 (br d, 2H), 7.24 (br s, 2H), 6.97 (br s, 2H), 5.48ꢀ6.43 (br s,
4H), 5.38 (s, 1H), 3.02ꢀ3.69 (br s, 3H), 1.03ꢀ2.62 (br s, 16H); low-
resolution ESI-MS m/z 991 (M þ Naþ), 661 (M ꢀ 2 fluorenyl þ Naþ).
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files giving crystallo-
b
graphic data for 6 and figures giving a thermal ellipsoid plot of
6, the stereoisomers of 7, and 1H NMR spectra of 7aꢀd and 9.
This material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: kbaines2@uwo.ca.
(20) Ouhsaine, F.; Andre, E.; Sotiropoulos, J. M.; Escudie, J.;
Ranaivonjatovo, H.; Gornitzka, H.; Saffon, N.; Miqueu, K.; Lazraq, M.
Organometallics 2010, 29, 2566.
’ ACKNOWLEDGMENT
(21) For recent publications regarding the addition of carbonyl
compounds to germenes, see: (a) Leung, W.-P.; Kan, K.-W.; So,
C.-W.; Mak, T. C. W. Organometallics 2007, 26, 3802. (b) Ech-Cherif
El Kettani, S.; Lazraq, M.; Ranaivonjatovo, H.; Escudie, J.; Gornitzka, H.;
Ouhsaine, F. Organometallics 2007, 26, 3729. (c) Leigh, W. J.; Potter,
G. D.; Huck, L. A.; Bhattacharya, A. Organometallics 2008, 27, 5948. (d)
Ech-Cherif El Kettani, S.; Lazraq, M.; Ouhsaine, F.; Gornitzka, H.;
Ranaivonjatovo, H.; Escudie, J. Org. Biomol. Chem. 2008, 6, 4064. (e)
Lollmahomed, F.; Leigh, W. J. Organometallics 2009, 28, 3239. (f)
Ghereg, D.; Ech-Cherif El Kettani, S.; Lazraq, M.; Ranaivonjatovo, H.;
Schoeller, W. W.; Escudie, J.; Gornitzka, H. Chem. Commun. 2009, 4821.
(g) Ghereg, D.; Gornitzka, H.; Ranaivonjatovo, H.; Escudie, J. Dalton
Trans. 2010, 39, 2016. (h) Naka, A.; Ueda, S.; Fujimoto, H.; Miura, T.;
Kobayashi, H.; Ishikawa, M. J. Organomet. Chem. 2010, 695, 1663.
(22) Couret, C.; Escudiꢀe, J.; Delpon-Lacaze, G.; Satgꢀe, J. Organome-
tallics 1992, 11, 3176.
We thank the Natural Sciences and Engineering Research
Council of Canada and the University of Western Ontario for
financial support, Teck Metals Ltd. for a generous gift of GeCl4,
and G. Popov for assistance with the X-ray structure
determination.
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contamination, primarily with silicone grease, despite extensive chro-
1
matography. The H NMR spectra of the samples are given in the
Supporting Information.
(42) Low isolated yields were obtained due to extensive
chromatography.
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dx.doi.org/10.1021/om200114n |Organometallics 2011, 30, 3010–3017