Reactions of germenes with some para-quinones: Formation of a tricyclic compound from 1,4-benzoquinone undergoing an unexpected rearrangement

Article abstract of DOI:10.1021/om100113c

Germenes Mes₂Ge=CR₂ 1a (Mes = 2,4,6-trimethylphenyl; CR₂ = fluorenylidene) and Mes₂Ge=CR′₂ 1b (CR′₂ = 2,7-di-tert-butylfluorenylidene) react with 1,4-benzoquinone and 2,3,5,6-tetramethyl-1,

Full text of DOI:10.1021/om100113c

Organometallics 2010, 29, 4849–4857 4849
DOI: 10.1021/om100113c
Reactions of Germenes with Some para-Quinones: Formation of a
Tricyclic Compound from 1,4-Benzoquinone Undergoing an
Unexpected Rearrangement†
‡
Dumitru Ghereg, Erwan Andre, Sakina Ech-Cherif El Kettani, Nathalie Saffon,
^
4
ꢀ §
Mohamed Lazraq,^ Henri Ranaivonjatovo,‡ Heinz Gornitzka,3 Karinne Miqueu,§
§
Jean-Marc Sotiropoulos, and Jean Escudie*
,‡
ꢀ
‡
ꢀ
Universite de Toulouse, UPS, LHFA, 118 Route de Narbonne, F-31062 Toulouse, France, and CNRS,
LHFA, UMR 5069, F-31062 Toulouse Cedex 09, France, §Institut Pluridisciplinaire de Recherche sur
ꢀ ꢀ ꢀ
l’Environnement et les Materiaux, UMR-CNRS 5254, Universite de Pau et des Pays de l’Adour, Helioparc,
2 Avenue du Preꢀsident Angot, F-64053 Pau Cedex 09, France, ^Laboratoire d’Ingeꢀnierie Moleꢀculaire
ꢀ
ꢁ
ꢀ
ꢀ ꢀ
ꢀ
et Organometallique (LIMOM), BP 1796, Faculte des Sciences Dhar El Mehraz, Universite Sidi Mohamed
Abdellah, Fes-Atlas, Fes, Morocco, Structure Federative Toulousaine en Chimie Moleculaire, FR 2599,
4
ꢁ
ꢀ
3
ꢀ
Universite Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse Cedex 09, France, and Laboratoire
de Chimie de Coordination du CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex 04, France
Received February 11, 2010
Germenes Mes2GedCR2 1a (Mes = 2,4,6-trimethylphenyl; CR2 = fluorenylidene) and Mes2GedCR02
1b (CR02=2,7-di-tert-butylfluorenylidene) react with 1,4-benzoquinone and 2,3,5,6-tetramethyl-1,4-benzo-
quinone to give compounds 3a, 3b, and 5a, containing a 1,4-cyclohexadiene unit as central ring. Upon
prolonged storage in diethyl ether or THF solution, compounds 3a and 3b undergo a double 1,3-hydrogen
shift, leading to their structural isomers 4a and 4b. Theoretical calculations performed on the model
compound H2GedCH2 1H postulate that the first steps of its reaction with 1,4-benzoquinone are a double
[2þ2] cycloaddition between the GedC and CdO double bonds, leading to a transient dispiro compound
containing two oxagermetane rings, followed by its isomerization to derivative 3H. Between 1a and 9,10-
anthraquinone, a double [2þ4] cycloaddition is observed involving the oxygens and the ortho-carbon atoms
of one adjacent aromatic ring system, to generate the dioxadigermabenzopyrene derivative 2a.
Introduction
investigated in the last two decades. They display vast
differences in their properties compared to the correspond-
ing alkenes, and they constitute powerful building blocks in
organometallic and heterocyclic chemistry owing to the great
reactivity of the MdC double bond. These derivatives now
constitute an established class of compounds and have been
the topic of several review articles.1,2
Whereas the chemical behavior of metallaalkenes to-
ward many different organic functions has been reported,
their reactivity with quinones is poorly documented. The
only results published very recently are the reactions of
germene Mes2GedCR2 1a (Mes = 2,4,6-trimethylphenyl,
CR2 = fluorenylidene)3 with various naphthoquinones4,5
(Scheme 1) and stannene Tip2SndCR026 (Tip = 2,4,6-triiso-
propylphenyl, CR02 = 2,7-di-tert-butylfluorenylidene) with
para-benzoquinone, 1,4-naphthoquinone, and 9,10-anthr-
aquinone7 (Scheme 2). A different behavior was observed
Alkenes are among the most important compounds in
organic chemistry, due to the ability of the >CdC< double
bond to furnish new organic functions by undergoing vari-
ous addition or cycloaddition reactions. Some of their
heavier analogues, metallaalkenes >M14dC< (M14 = Si
(silenes),1 Ge (germenes),1f,2 and Sn (stannenes)1f,2b-d), have
been synthesized and their chemical behavior has been
†Part of the Dietmar Seyferth Festschrift. In honor of Professor Dietmar
Seyferth, in recognition of his outstanding contribution to Organometallics as
founding Editor-in-Chief.
*Corresponding author. E-mail: escudie@chimie.ups-tlse.fr.
(1) For reviews on silenes see: (a) Raabe, G.; Michl, J. Chem. Rev.
1985, 85, 419. (b) Brook, A. G.; Baines, K. M. Adv. Organomet. Chem.
1986, 25, 1. (c) Brook, A. G.; Brook, M. A. Adv. Organomet. Chem. 1996,
39, 71. (d) M€uller, T.; Ziche, W.; Auner, N. In The Chemistry of Organic
Silicon Compounds; Rappoport, Z.; Apeloig, Y., Eds.; Wiley: New York,
1998; Vol. 2, Chapter 16. (e) 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. (f) Lee, V. Ya.; Sekiguchi, A.
ꢀ
ꢀ
ꢀ
(3) (a) Couret, C.; Escudie, J.; Satge, J.; Lazraq, M. J. Am. Chem. Soc.
ꢀ
€
1987, 109, 4411. (b) Lazraq, M.; Escudie, J.; Couret, C.; Satge, J.; Drager, M.;
Dammel, R. Angew. Chem., Int. Ed. Engl. 1988, 27, 828.
(4) Ghereg, D.; Ech-Cherif El Kettani, S.; Lazraq, M.; Ranaivonja-
€
Organometallics 2004, 23, 2822. (g) Ottosson, H.; Eklof, A. M. Coord.
Chem. Rev. 2008, 252, 1287.
(2) For reviews on germenes, see: (a) Barrau, J.; Escudie, J.; Satge, J.
ꢀ
tovo, H.; Schoeller, W. W.; Escudie, J.; Gornitzka, H. Chem. Commun.
ꢀ
ꢀ
2009, 4821.
(5) Ghereg, D.; Gornitzka, H.; Ranaivonjatovo, H.; Escudie, 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.
Dalton Trans. 2010, 39, 2016.
(6) Abdoul Fatah; El Ayoubi, R.; Gornitzka, H.; Ranaivonjatovo,
ꢀ
Chem. Rev. 1998, 178, 565. (d) Escudie, J.; Ranaivonjatovo, H. Adv.
ꢀ
Organomet. Chem. 1999, 44, 114. (e) 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.
H.; Escudie, J. Eur. J. Inorg. Chem. 2008, 2007.
(7) Ghereg, D.; Ranaivonjatovo, H.; Saffon, N.; Gornitzka, H.;
ꢀ
Escudie, J. Organometallics 2009, 28, 2294.
r
2010 American Chemical Society
Published on Web 04/07/2010
pubs.acs.org/Organometallics

4850 Organometallics, Vol. 29, No. 21, 2010
Ghereg et al.
Scheme 1
Scheme 2
Figure 1. Molecular structure of 2a (thermal ellipsoids at the
50% probability level). Hydrogen atoms and noncoordinated
solvent molecules (CHCl3) are omitted; Mes and CR2 groups are
˚
simplified for clarity. Selected bond lengths (A) and angles (deg):
Ge1-C15 2.010(4); Ge1-C41 1.978(4); Ge1-C50 1.968(4);
Ge1-O1 1.816(3); C1-O1 1.362(5); C3-C15 1.587(6); C1-C2
1.371(6); C2-C3 1.516(6); C3-C4 1.493(6); C4-C5 1.306(7);
C5-C6 1.497(6); C6-C7 1.511(6); C2-C7 1.441(6); C7-C8
1.376(6); C8-C9 1.407(6); C9-C14 1.422(6); C1-C14 1.425(6);
C1-C2-C3 118.4(4); C2-C3-C15 111.8(3); C3-C15-Ge1
104.6(3); O1-Ge1-C15 99.49(15); C1-O1-Ge1 123.1(3);
O1-C1-C2 122.2(4).
calculations are also presented to understand the mechanism of
the reactions.
Results and Discussion
a. 9,10-Anthraquinone. The treatment of an ethereal solu-
tion of germene Mes2GedCR2 1a with 9,10-anthraquinone
led to product 2a in 85% yield; whatever the ratio of the
reactants, the analytical and spectral data were indicative of
a 2:1 adduct (two germenes for one quinone) (Scheme 3).
Thus, 1a behaves similarly to Tip2SndCR02, as previously
reported.7 The formation of a pentacyclic ring system has
also been observed in the addition of germylenes Ge[CH-
(SiMe3)2]2 and Ge[N(SiMe3)2]2 to 9,10-anthraquinone.8
The driving force for this reaction is presumed to be the
well-known oxophilic character of germanium and the for-
mation of two thermodynamically stable six-membered-ring
heterocycles. The formation of 2a induces aromaticity on the
central quinonic ring, thus compensating for the high thermo-
dynamic cost required to break the aromaticity of one of the
fused rings of the quinone. It is worthy to note that only one
aromatic ring was involved in the reaction, as clearly corro-
borated by the 1H and 13C NMR spectra.
Scheme 3
The 1H NMR spectrum of 2a contains two singlets for the
CR2-CH-CHd moiety at 4.41 (CR2-CH) and 4.33 (CR2-
CH-CHd) ppm. In the 13C NMR spectrum, the correspond-
ing CH signals appear at 39.54 and 123.86 ppm, in the typical
region for allylic and olefinic carbon atoms, respectively. The
hydrogen atoms in the remaining aromatic ring of the former
quinonic backbone resonate, like in the starting compound, as
two doublets of doublets at 7.48 and 8.40 ppm.
between germene and stannene in their reaction with 1,4-
naphthoquinone, since ortho-quinodimethane-type com-
pound I and derivative II (formed by a cycloaddition on the
aromatic ring) have been obtained4 from the germene
(Scheme 1), whereas it was only IV, the analogue of II, in
the case of the stannene.7 We have now addressed the question
of whether the germene would also afford cycloadducts
similar to III and V with 1,4-benzoquinone and anthraqu-
inone (Scheme 2).
The X-ray determination of 2a (Figure 1) clearly shows the
formation of two six-membered rings involving both oxygen
Herein we report our investigations in this field by studying
the behavior of germenes toward 1,4-benzoquinone, 2,3,5,
6-tetramethyl-1,4-benzoquinone, and 9,10-anthraquinone; DFT
(8) Sweeder, R. D.; Gdula, R. L.; Ludwig, B. J.; Banaszak Holl,
M. M.; Kampf, J. W. Organometallics 2003, 22, 3222.

Article
Organometallics, Vol. 29, No. 21, 2010 4851
Scheme 4
Figure 2. Molecular structure of 3a (thermal ellipsoids at the
50% probability level). Hydrogen atoms and noncoordinated
solvent molecules (pentane) are omitted; Mes and CR2 groups
˚
are simplified for clarity. Selected bond lengths (A) and angles
(deg): C2-C7 1.305(9); C7-C11A 1.527(8); C2-C11 1.484(8);
O1-C7 1.369(7); Ge1-O1 1.824(4); Ge1-C4 2.015(6);
C11A-C4 1.549(9); C7-C2-C11 123.2(6); C2-C11-C7A
112.4(5); C2-C7-C11A 124.3(6); O1-C7-C11A 111.9(5);
C7-C11A-C4 107.5(5); C11A-C4-Ge1 96.4(4); O1-Ge1-
C4 90.0(2); C7-O1-Ge1 112.3(4).
Scheme 5
and ortho-carbon atoms of one adjacent aromatic ring system.
˚
˚
The C3-C15 (1.587(6) A) and C6-C28 (1.580(6) A) bonds
are longer than standard C-C single bonds. The former
quinonic ring has been converted into an aromatic ring, as
confirmed by the shortening of the following C-C distances:
˚
˚
C1-C2 = 1.371(6) A; C7-C8 = 1.376(6) A; C8-C9 =
1.407(6) A; and C1-C14 = 1.425(6) A. The ring C2 to C7
of the former 9,10-anthraquinone is no longer aromatic,
˚
˚
from 3 to 4, which was proved by stirring the pure compound
3a overnight in Et2O at room temperature: the subsequent
analytical and spectral data revealed the presence of a
mixture of 3a and 4a in a 10/90 ratio, indicating that under
these conditions cycloadduct 3a undergoes a double 1,3-
hydrogen shift leading to 4a. When compound 3a was put in
solution in pentane, it was recovered unchanged after one
day, and thus no rearrangement occurred.
c. 2,3,5,6-Tetramethyl-1,4-benzoquinone. To determine
whether a similar cycloaddition process is also possible with
a substituted 1,4-benzoquinone, germene 1a was allowed to
react with 2,3,5,6-tetramethyl-1,4-benzoquinone (Scheme 5).
The reaction occurred nearly quantitatively (96% yield),
and no product other than 5a was observable in the crude
reaction mixture. As in the cases of 1,4-benzoquinone and
9,10-anthraquinone, whatever the ratio of the reactants, the
final product has two germene moieties for one quinone.
Physicochemical measurements (1H, 13C NMR and mass
spectrometry) of pure 5a obtained by crystallization from a
pentane solution supported the formation of a cycloadduct
analogous to 3a. Thus, the increased steric shielding in the
quinone did not prevent the attack of CR2 groups on the
carbon atoms substituted by the methyl groups. In contrast
with 3a, 5a is stable since any subsequent isomerization by a
Me shift does not occur.
˚
retaining only one double bond (C4-C5=1.306(7) A).
b. 1,4-Benzoquinone. Addition of 1,4-benzoquinone to
germene 1a in an Et2O solution furnished a mixture of two
products, 3a and 4a, which were separated by fractional
crystallization immediately after the reaction completion
and were isolated in 56% and 35% yields. Like in the case
of 9,10-anthraquinone, two equivalents of 1a were necessary
for one of quinone; when the reaction was performed with
one equivalent of each reactant, a half equivalent of quinone
was recovered. The structures of compounds 3a and 4a were
determined by NMR and X-ray analysis (Figures 2 and 4).
They are composed of a 1,4-cyclohexadiene backbone with
two additional five-membered-ring skeletons. In contrast to
the corresponding product obtained from the stannene
Tip2SndCR02 (Tip = 2,4,6-triisopropylphenyl, CR02 = 2,7-
di-tert-butylfluorenylidene),7 the two cycloadditions occur
exclusively on the opposite sides of the six-membered ring
(Scheme 4).
This surprising behavior motivated us to verify whether
germene 1b (Mes = mesityl, CR02 = 2,7-di-tert-butylfluor-
enylidene), structurally similar to the stannene Tip2SndCR02
since it displays two tert-butyl groups in 2,7 positions on the
fluorenylidene system, would furnish a different result. In
fact, 1b does not yield a compound of type III like in the case
of tin (Scheme 2) but behaves similarly to 1a, leading to the
1,4-cyclohexadiene derivatives 3b and 4b; the ratio after the
reaction was 60/40. Thus, the high steric hindrance caused by
the two tert-butyl groups has no influence on the course of
the reaction. When the reaction mixture was stirred for 5 h
before treatment, the ratio between compounds 3 and 4
changed to 20/80. This result is in favor of a rearrangement
d. 1H and 13C NMR Data for 3-5. Due to complex
spectra, the assignment of the 1H and 13C signals was based
in all cases on the homonuclear (COSY) and heteronuclear
(HSQC and HMBC) experiments.
The presence of two stereogenic centers in 3a complicates
the assignment of the 1H and 13C signals, due to the diastereo-
topic mesityl groups. For each Mes2Ge unit, one extremely

4852 Organometallics, Vol. 29, No. 21, 2010
Ghereg et al.
broad singlet at 1.98 ppm (half-width = 210 Hz) is observed
for the ortho-methyl groups of one mesityl unit and two broad
singlets at 0.79 and 2.25 ppm for the ortho-methyl groups of
the other one, suggesting that the rotation of one mesityl on
the NMR time scale is more hindered than that of the other
one: in one case the ortho methyls are broadening out, and in
the other case, the ortho methyls have already been separated
in two different signals. As expected, an NMR study per-
formed at -60 ꢀC displays that the broad signal at 1.98 ppm
splits into two signals at 1.80 and 2.26 ppm. para-Methyl
groups appear as sharp singlets (at 2.07 and 2.27 ppm), since
they are not influenced by the slow or hindered rotation
around the ipso-C-Ge bond. The four hydrogen atoms of
the former quinonic ring give two singlets at 4.01 ppm
(CHdCO) and 4.15 ppm (CHCR2), and the corresponding
carbons give signals at 93.99 ppm (CHdCO) and 50.30 ppm
(CHCR2).
Figure 3. Molecular structure of 3b (thermal ellipsoids at the
50% probability level). Hydrogen atoms, rotation disorder of
tert-butyl groups, and noncoordinated solvent molecules (THF)
are omitted; Mes and CR02 groups are simplified for clarity.
In contrast to 3a, the rearrangement product 4a exhibits
fully unrestricted free rotation on the NMR time scale; that
1
is, all H and 13C resonances appear as sharp signals. The
˚
Selected bond lengths (A) and angles (deg): C40-C41 1.494(9);
1
aliphatic zone in the H NMR spectrum displays, among
C41-C42 1.500(9); C42-C40A 1.319(9); C19-C41 1.570(9);
O1-C40 1.358(8); Ge1-O1 1.826(4); Ge1-C19 2.001(7);
Ge1-C1 1.954(7); Ge1-C10 1.962(7); C40-C41-C42 114.1(5);
C42A-C40-C41 124.3(6); C41-C42-C40A 121.5(6); O1-
C40-C41 112.5(5); C40-C41-C19 108.0(5); C41-C19-Ge1
96.3(4); O1-Ge1-C19 90.3(2); C40-O1-Ge1 112.2(4).
ortho- and para-methyl resonances of mesityl units (at 1.71
and 2.16 ppm, respectively), one signal at 2.29 ppm corre-
sponding to four methylene protons. In this case, mesityl
groups are equivalent. Together with the 13C NMR spectrum
showing one secondary carbon at 27.56 ppm (CH2) and a
quaternary one at 107.03 ppm (CdCO), these observations
are in agreement with the structure of the isomerization
product 4a (Scheme 4).
1
The H and 13C spectra of 3b are similar to those of 3a
despite the larger spatial requirement of the 2,7-di-tert-
butylfluorenylidene group than that of fluorenylidene.
Almost identical mass spectra were obtained for 3a and its
isomer 4a and 3b/4b, respectively.
As expected, mesityl moieties in 5a are not equivalent due
to the presence of two stereogenic carbon atoms. Moreover,
due to the steric crowding, the germanium mesityl bonds
rotate slowly, causing the methyl groups of mesityl frag-
ments to exhibit two singlets at 2.05 and 2.22 ppm for para-
Me protons and four sharp singlets at 0.56, 1.45, 2.42, and
2.47 ppm for ortho-Me protons. A variable-temperature
NMR was performed between 20 and 60 ꢀC in toluene-d8.
The signals, sharp at 20 ꢀC, become broad at 60 ꢀC, but the
coalescence effect has not been observed in this temperature
range. The patterns of 13C NMR spectra for 5a are similar to
those of 3a and 3b. The CCR2, CdCO, and C-O of the
former quinonic fragment display signals at 54.59, 108.05,
and 152.49 ppm, respectively.
e. X-ray Structures of 3a, 3b, 4a, and 5a. The constitution
of 3a, 3b, 4a, and 5a was confirmed by X-ray structure
analyses (3a Figure 2, 3b Figure 3, 4a Figure 4, and 5a
Figure 5). Suitable crystals for structure determination were
obtained at room temperature from pentane (3a), THF (3b),
chloroform (4a), and dichloromethane (5a).
Figure 4. Molecular structure of 4a (thermal ellipsoids at the
50% probability level). Hydrogen atoms and noncoordinated
solvent molecules (CHCl3) are omitted; Mes and CR2 groups are
˚
simplified for clarity. Selected bond lengths (A) and angles (deg):
C1-C2 1.336(9); C2-C3 1.478(9); C1-C3A 1.489(9); C1-O1
1.381(8); Ge1-O1 1.843(4); Ge1-C4 2.034(6); C2-C4 1.510(9);
Ge1-C26 1.974(7); Ge1-C17 1.970(7); C1-C2-C3 122.8(6);
C2-C3-C1A 112.8(5); C2-C1-C3A 124.5(6); C1-C2-
C4 117.1(6); Ge1-C4-C2 97.5(4); O1-Ge1-C4 89.2(2);
Ge1-O1-C1 106.8(4); O1-C1-C2 120.1(6).
˚
˚
(C2-C3 = 1.478(9) A and C1-C3A = 1.489(9) A) in 4a. In
derivatives 3b and 5a the bond lengths and angles in the
central 1,4-cyclohexadiene ring are not appreciably different
from those of compound 3a, proving that a 1,3-shift did not
occur. In all cases, the six-membered ring is nearly planar.
In derivative 4a, the five-membered rings adopt an
envelope conformation with germanium atoms being out
of the mean plane (in trans position in relation to this plane):
Ge1-C4-C2-C1 = -23.39ꢀ, Ge1-O1-C1-C2 = 16.80ꢀ.
In the nonrearranged compound 3a, the five-membered
rings are more distorted: Ge1-O1-C7-C11 = -15.23ꢀ,
The structures of 3a and 4a are easily differentiated by
X-ray structure analyses since the bond lengths in the six-
membered ring of the former quinonic ring are completely
different. The C-C distance in the two bonds joining the
central six-membered ring to oxagermanolane units changes
˚
˚
from 1.527(8) A (C7-C11A in 3a, single bond) to 1.336(9) A
(C1-C2 in 4a, double bond). The other C-C distances in
this six-membered ring change from two single bonds (C2-
˚
C11 = 1.484(8) A) and two double bonds (C2-C7 =
˚
1.305(9) A) in 3a to four remarkably short single bonds

Article
Organometallics, Vol. 29, No. 21, 2010 4853
Figure 5. Molecular structure of 5a (thermal ellipsoids at the
50% probability level). Hydrogen atoms and noncoordinated
solvent molecules (CH2Cl2) are omitted; Mes and CR2 groups
Figure 6. Energy profile (ΔE in kcal mol-1) of the reaction
3
between 1H and 1,4-benzoquinone: formation of the [2þ2]
˚
are simplified for clarity. Selected bond lengths (A) and angles
intermediates M1 and M2.
(deg): C32-C33 1.332(5); C33-C34 1.514(5); C33-C35
1.520(5); C35-C32A 1.512(5); C35-C36 1.557(5); C32-O1
1.377(4); Ge1-O1 1.817(3); Ge1-C1 2.019(4); Ge1-C14
1.978(4); Ge1-C23 1.973(4); C1-C35A 1.603(5); C32-
C33-C35 120.6(3); C33-C32-C35A 127.9(3); C32A-
C35-C33 110.8(3); C35A-C32-O1 113.2(3); C32-O1-Ge1
113.3(2); C1-Ge1-O1 89.74(14); Ge1-C1-C35A 99.8(2),
C1-C35A-C32 105.0(3).
Ge1-C4-C11-C7 = 46.32ꢀ. A similar trend is observed
in 3b.
˚
In all compounds, Ge-O distances (1.817-1.843 A) are
slightly beyond the upper limit of the standard range
9
˚
(1.73-1.79 A). The intracyclic Ge-C bonds are also elon-
˚
gated (2.001-2.034 A), whereas the acyclic Ge-C(Mes)
˚
bond lengths (1.954-1.978 A) lie in the normal range
9
˚
(1.93-1.98 A).
f. Theoretical Calculations. In order to get further in-
sight on the reaction of germene with 1,4-benzoquinone
(Scheme 4), a DFT study was carried out at the B3LYP/6-
31G** level of theory. Different hypotheses have been
investigated, and a reaction pathway, calculated in the gas
phase, has been proposed. In this study, a model of Mes2-
GedCR2 where bulky substituents are replaced by hydrogen
atoms, H2GedCH2 1H, has been chosen to reach reasonable
computation times.
In a first step, we had to determine whether the reaction
between two molecules of 1H and 1,4-benzoquinone is a one-
step concerted process or a multistep mechanism. A meti-
culous search on the potential energy surface (PES) did not
allow us to find a transition state corresponding to a direct
[2þ3] cycloaddition pathway. Only a mechanism involving
first [2þ2] cycloadditions followed by successive rearrange-
ments leading to the formal [2þ3] adduct has been found on
the PES (see Figures 6 and 7). This mechanism consists in
two successive additions of one molecule of 1H on the 1,4-
benzoquinone, which is consistent with the really low prob-
ability of a concerted reaction involving three different
molecules. The energy profile of the first steps of the reaction
and the structures of the different minima and transition
states (labeled “M” or “T”, respectively) are depicted in
Figure 6. The [2þ2] cycloaddition of the GedC double bond
on the carbonyl group of the quinone leads to M1 via the transi-
tion state T1, slightly higher in energy than the reactants
Figure 7. Energy profile (ΔE in kcal mol-1) of the reaction of
3
1H with 1,4-benzoquinone; comparison between pathways
leading to the formation of 3H and its corresponding type IIIH
compound. &Interconversion isomers. The arrows represent the
motion of the cycle leading to the corresponding isomer.
(∼2 kcal mol-1). The latter presents a Ge-O bond (1.946 A)
˚
3
˚
longer than the one in M1 (1.836 A) and a C-C1 bond not yet
formed (3.331 A), consistent with an asynchronous mecha-
˚
nism. It is noteworthy that Mosey and co-workers have
theoretically investigated the [2þ2] cycloaddition between for-
maldehyde and germene.10 In this case a synchronous mechan-
ism has been proposed with a free energy barrier around 16
kcal mol-1 (B3LYP/6-311þþG**), more important than
3
ours. The small energy barrier found for the mechanism
involving the quinone is probably due to the asynchronous
mechanism for which the geometry of the TS is close to the
reactants. The next step of the reaction corresponds to a [2þ2]
cycloaddition of a second molecule 1H to give M2. This second
step also occurs easily since an activation barrier around
7 kcal mol-1 is calculated and leads to the intermediate M2
3
(-69 kcal mol-1).
3
This result is not surprising since a [2þ2] cycloaddition
between the GedC double bond of germene 1a and one CdO
(10) Mosey, N. J.; Baines, K. M.; Woo, T. K. J. Am. Chem. Soc. 2002,
124, 13306.
(9) Baines, K. M.; Stibbs, W. G. Coord. Chem. Rev. 1995, 145, 157.

4854 Organometallics, Vol. 29, No. 21, 2010
Ghereg et al.
double bond of maleic anhydride has previously been ob-
served;11 in the case of 4-cyclopentene-1,3-dione, a double
[2þ2] cycloaddition onto both carbonyl groups occurred;11
these five-membered-ring carbonyl reagents also contain a
conjugated system OdC-CdC.
Let us consider the pathway from M2 to 3H (Figure 7).
This reaction occurs in two steps. The first one, which can
be described as a synchronous process via the transition
state T3, leads to the intermediate M3. In T3, the CR-C1 bond
˚
is elongated (2.27 A) compared to that found in M2 and
the CR-C6 distance decreases and becomes intermediate
between those of M2 and M3 (2.06 A versus 2.55 and 1.55 A,
˚
˚
respectively). Moreover the carbon atom CR, located
between C1 and C6, remains in a tetrahedral environment
P
(
∼349ꢀ), indicating the presence of a weak interaction
CR
between C6 and/or C1. The intermediate M3 exists in four
isoenergetic isomers (M3a0, M3b0, M3a00, M3b00), which corres-
pond in fact to interconversion isomers. In the second step,
which is the key step of the reaction, two different pathways
can be followed. When Cβ moves toward the carbon atom C3,
the reaction leads to the formation of 3H via the transition
state T4, while the product IIIH (observed in the case of the tin
Figure 8. Energy profile (ΔE in kcal mol-1, PCM formalism)
of the prototropy reaction from 3H to 4H taking into account
one molecule of dimethyl ether.
3
noticeably higher than the other steps of the reaction path-
way. Nevertheless, this is consistent with the slow kinetics of
the hydrogen shift observed experimentally.
0
analogue, Scheme 2) is obtained via the transition state T4
when Cβ moves toward carbon C5. The second step is
predicted, in both cases, to be exothermic (ΔE ≈ -35
We are aware that the proposed mechanisms possess
rather high activation barriers, but some factors that have
not been taken into account in this study should affect the
energy profile of the reaction. In particular, the steric
hindrance of the germene substituents could contribute to
lower all the previously discussed barriers. Nevertheless,
the proposed reaction pathway gives trends of what hap-
pens experimentally.
In conclusion germenes react with 1,4-benzoquinones and
9,10-anthraquinone in the molar ratio of 2/1 to give polycyclic
derivatives. With 1,4-benzoquinone and 2,3,5,6-tetra-
methyl-1,4-benzoquinone, formal [2þ3] cycloadducts are
obtained with the two oxagermanolane rings on opposite
sides of the central 1,4-cyclohexadiene ring; according to
DFT calculations, the first steps of these reactions are [2þ2]
cycloadditions between the GedC and CdO double bonds
followed by a rearrangement. A double 1,3-H shift is then
observed in diethyl ether in the case of 1,4-benzoquinone.
Germenes and stannenes showed a different behavior in
their reactions with 1,4-benzoquinones; by contrast, in the
case of 9,10-anthraquinone, the same type of cycloaddition
(involving one adjacent aromatic ring) occurs.
kcal mol-1). The energy gap between 3H and IIIH (2
3
3
kcal mol-1) is too small to favor one product over the other
one. The comparison of the activation barriers reveals that the
formation of 3H is kinetically favored. However, the differ-
0
ence in energy (8 kcal mol-1 between T4 and T4 ) is fairly
small and is not sufficient to explain that III is not observed
3
experimentally. This hintsthatotherfactorsshouldbe infavor
of 3a formation, such as the steric hindrance of the fluorenyli-
dene groups on CR and Cβ, which has not been taken into
account in this study.
From the experimental point of view, the last part of this
reaction (3 f 4) can be described as a 1,3 prototropy and
clearly shows that this mechanism is assisted by the solvent
since it occurs in Et2O and not in pentane. When calculations
take into account the solvent both explicitely12 and implici-
tely (PCM formalism), the pathway from 3H to 4H shows
that the intermediate MH2 and the product of this reaction,
4H, are slightly thermodynamically favored compared to 3H
by 6 and 9 kcal mol-1, respectively (Figure 8). Furthermore
two transitions states, corresponding to the two 1,3-H shifts,
have been found (TH1 and TH2, respectively). It is clear that
3
˚
the short H-O distances (respectively 1.057 and 1.054 A for
TH1 and TH2) combined with the long C3,5-H and C2,6-H
distances respectively for TH1 and TH2 (around 1.1 A) attest
Experimental Section
˚
that the reaction is explicitly assisted by the solvent, which
plays a major role in the reaction.
General Experimental Details. All experiments were per-
formed in flame-dried glassware under an argon atmosphere
using standard vacuum-line, Schlenk, and cannula techniques
with solvents being distilled over standard drying agents and
degassed before use. All reagents were purchased from Aldrich
and were used without further purification. Deuterated solvents
It is interesting to note that, without the presence of one
molecule of ether, no 1,3-H migration mechanism can be
found in the gas phase. This result can be compared to the
reaction performed in pentane, where no hydrogen shift is
observed, confirming definitely that with a lack of inter-
action with the solvent, a rearrangement is not possible.
Even considering the stabilization due to solvent effects,
the energy barriers corresponding to the two H shifts are
˚
were dried and stored over 4 A molecular sieves. NMR spectra
were recorded in CDCl3 on Bruker Avance 300 and 400 instru-
ments at the following frequencies: 300.13, 400.13 MHz (1H)
and 75.47, 100.62 MHz (13C{1H}). 1H and 13C{1H} NMR
1
assignments were confirmed by H COSY, HSQC (1H-13C),
and HMBC (1H-13C) experiments. Mass spectra were mea-
sured on a Nermag R10-10 spectrometer by CI (NH3 or CH4).
Melting points were determined on a Leitz microscope heating
stage 250 or Electrothermal apparatus (capillary). Elemental
analyses were performed by the “Service de Microanalyse de
(11) Ech-Cherif El Kettani, S.; Lazraq, M.; Ranaivonjatovo, H.;
ꢀ
Escudie, J.; Gornitzka, H.; Ouhsaine, F. Organometallics 2007, 26, 3729.
(12) The explicit assistance of the solvent was modelized by taking
into account one molecule of dimethyl ether in the reaction profile.

Article
Organometallics, Vol. 29, No. 21, 2010 4855
Table 1. Crystal Data for 2a, 3a, 3b, 4a, and 5a
2a 2CHCl3
3
3a 2C5H12
3
3b THF
3
4a 2CHCl3
3
5a CH2Cl2
3
empirical formula
fw
C78H70Cl6Ge2O2
1397.22
173(2)
triclinic
P1
11.014(2)
16.376(3)
20.416(3)
67.051(3)
89.171(3)
85.840(3)
3381.6(9)
2
C78H88Ge2O2
1202.66
193(2)
triclinic
P1
9.126(2)
13.234(2)
15.561(3)
113.855(6)
90.973(6)
107.554(7)
1617.8(5)
1
C88H104Ge2O3
1354.89
193(2)
triclinic
P1
11.142(2)
13.497(2)
14.854(2)
100.188(3)
110.955(3)
107.521(3)
1884.9(5)
1
C70H66Cl6Ge2O2
1297.11
133(2)
triclinic
P1
8.861(2)
10.974(2)
16.164(3)
91.254(4)
101.916(4)
97.471(4)
1522.9(5)
1
C73H74Cl2Ge2O2
1199.40
193(2)
triclinic
P1
11.966(1)
14.425(1)
17.809(1)
86.197(2)
85.504(1)
87.695(1)
3055.9(2)
2
temperature (K)
cryst syst
space group
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
volume (A )
Z
abs coeff (mm-1
reflns collect.
indep reflns
abs corr
)
1.173
15 047
9549 [R(int) = 0.0404] 4026 [R(int) = 0.0687] 4995 [R(int) = 0.0451] 4015 [R(int) = 0.0901] 12 326 [R(int) = 0.0720]
0.975
10 216
0.845
8081
1.296
6371
1.117
30 735
semiempirical
none
none
none
semiempirical
12326/51/756
1.025
0.0576
0.1172
0.1099
0.1391
0.742; -0.578
data/restraints/params 9549/186/878
4026/154/422
1.022
0.0596
0.1432
0.1118
0.1713
0.692; -0.732
4995/82/479
1.044
0.0639
0.1866
0.0954
0.2415
0.555; -0.569
4015/108/404
1.024
0.0699
0.1711
0.0922
0.1886
1.098; -1.659
goodness-of-fit (F2)
final R indices
(I > 2σ(I))
1.016
0.0481
0.1020
0.0854
0.1162
0.569; -0.450
R indices
(all data)
largest diff
peak, hole (e A
-3
˚
)
l0Ecole de Chimie de Toulouse”. The yields were calculated from
the starting Mes2Ge(F)-CHR2 and Mes2Ge(F)-CHR02.
All data for structures were collected at low temperature
using an oil-coated shock-cooled crystal on a Bruker-AXS Apex
˚
II diffractometer with Mo KR radiation (λ = 0.71073 A) and are
summarized in Table 1. The structures were solved by direct
methods,13 and all non-hydrogen atoms were refined anisotro-
pically using the least-squares method on F2.14
1
For the H and 13C NMR study the carbon atoms of the
fluorenyl and 2,7-di-tert-butylfluorenyl groups are numbered as
shown in Figure 9.
Figure 9
Computational Details. Calculations were performed with the
Gaussian 03 suite of programs,15 using the density functional
method.16 The hybrid exchange functional B3LYP17 set was
used. B3LYP is a three-parameter functional developed by Becke
that combines the Becke gradient-corrected exchange functional
and the Lee-Yang-Parr and Vosko-Wilk-Nusair correlation
functional with part of the exact HF exchange energy. All
Gaussian calculations were done in combination with the
6-31G(d,p) basis set for all atoms. Geometry optimizations were
carried out without any symmetry restrictions; the nature of the
extrema (minimum and transition states) was verified with ana-
lytical frequency calculations. To ensure that the transition states
are connected to the right minima, intrinsic reaction coordinate
(IRC) calculations were conducted using the Schlegel-Gonzalez
algorithm.18 All the calculated energies have been zero-point
energy (ZPE) corrected using unscaled density functional fre-
quencies. Solvent effects were taken into account through the
polarized continuum model (IEF-PCM),19 as implemented in
Gaussian03, with the UAKS standard radii set (optimized for the
PBE0/6-31G(d) level of theory).
(13) SHELXS-97: Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(14) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
€
Refinement; University of Gottingen, 1997.
(15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, T., Jr.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, R.; Fukuda, J.;
Hasegawa, M.; Ishida, T.; Nakajima, Y.; Honda, O.; Kitao, H.; Nakai,
M. X.; Klene, X.; Li, K.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
zewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, D. K.;
Malick, A. D.; Rabuck, K.; Raghavachari, J. B.; Foresman, J. V.; Ortiz,
Q.; Cui, A. G.; Baboul, S.; Clifford, O.; Cioslowski, J.; Stefanov, B. B.;
Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox,
D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision D-02; Gaussian, Inc.:
Pittsburgh, PA, 2003.
Synthesis of Germenes 1a and 1b. Germenes 1a3 and 1b5 were
prepared as previously described, by dropwise addition of 1.05
molar equiv of tert-butyllithium (1.7 M in pentane) to a solution
of 2.00 mmol of the starting fluorogermanes Mes2Ge(F)CHR2
1a (CR2 = fluorenylidene) or 1b (CR02 = 2,7-di-tert-butylfluo-
renylidene) in 20 mL of diethyl ether cooled to -78 ꢀC. Warming
to room temperature afforded an orange solution of 1a or 1b
with a precipitate of LiF. According to an 1H NMR experiment,
germenes 1 were produced in a nearly quantitative yield. Thus,
all reactions were performed on the crude reaction mixtures.
Synthesis of 2a. 9,10-Anthraquinone (1.0 mmol, 0.208 g)
dissolved in 20 mL of THF was added dropwise to a crude
solution of 1a (2.0 mmol) in 20 mL of Et2O at -78 ꢀC. The
(16) Parr, R. G.; Yang, W. Functional Theory of Atoms and Mole-
cules; Breslow, R.; Goodenough, J. B., Eds.; Oxford University Press:
NewYork, 1989.
(17) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Becke, A. D.
J. Chem. Phys. 1993, 98, 5648. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev.
B 1988, 37, 785.
(18) (a) Gonzalez, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90, 2154.
(b) Gonzalez, C.; Schlegel, H. B. J. Phys. Chem. 1990, 94, 5523.
(19) (a) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. J. Chem. Phys.
2002, 117, 43. (b) Tomasi, J.; Cammi, R.; Mennucci, B.; Cappelli, C.; Corni,
S. Phys. Chem. Chem. Phys. 2002, 4, 5697.

4856 Organometallics, Vol. 29, No. 21, 2010
Ghereg et al.
mixture was slowly warmed to ambient temperature and stirred
overnight. Volatiles were removed in vacuo, and the resulting
brownish solid was dissolved in 30 mL of pentane; LiF was
eliminated by filtration. Recrystallization from pentane at
-30 ꢀC gave pure crystals of 2a (0.98 g, 85%, mp 378 ꢀC). 1H
NMR (300.13 MHz): 0.67 and 2.73 (2s, 2 ꢀ 6H, o-Me of Mes),
1.27 and 2.61 (2 br s, 2 ꢀ 6H, o-Me of Mes), 2.10 and 2.26 (2s, 2 ꢀ
6H, p-Me of Mes), 4.33 (s, 2H, CH-CHCR2), 4.41 (s, 2H,
2 ꢀ 2H, H4 and H5 of CR02). 13C NMR (75.47 MHz): 20.83 and
20.95 (p-Me of Mes), 22.53 (2 overlapping signals) and 22.99
(o-Me of Mes), 31.05 and 31.42 (CMe3), 34.57 and 34.82 (CMe3),
50.96 (CHCR02), 57.95 (CR02), 93.85 (CHdCO), 118.47 and
119.01 (C4 and C5 of CR02), 119.11, 122.00, 122.55, and 123.51
(C1, C3, C6, and C8 of CR02), 127.65, 128.62, and 129.70 (m-CH
of Mes), 132.55 and 132.84 (ipso-C of Mes), 138.38, 138.66,
138.94, and 139.27 (p-C of Mes, C12 and C13 of CR02), 142.17,
143.60, and 143.79 (o-C of Mes), 144.69 and 146.27 (C10 and C11
of CR02), 149.25 and 149.26 (C2 and C7 of CR02), 156.00 (C-O).
MS m/z (% relative intensity): 1283 (M þ 1, 15), 1163 (M - Mes,
10), 1005 (M - CR02 - 1, 5), 587 (Mes2GedCR02 - 1, 22), 311
(Mes2Ge - 1, 25), 278 (R02CH2, 100), 263 (R02CH2 - Me, 53).
Anal. Calcd for C84H96Ge2O2 (1282.939): C, 78.64; H, 7.54.
Found: C, 78.37; H, 7.48.
3
CHCR2), 6.34 and 6.54 (2d, JHH = 7.5 Hz, 2 ꢀ 2H, H1 and
H8), 6.36 and 6.80 (2s, 2 ꢀ 2H, m-CH of Mes), 6.58 and 6.91
(2 br s, 2 ꢀ 2H, m-CH of Mes), 6.82 and 6.85 (2t, 3JHH = 7.5 Hz,
2 ꢀ 2H, H2 and H7), 7.18 and 7.21 (2t, 3JHH = 7.5 Hz, 2 ꢀ 2H,
H3 and H6), 7.48 and 8.40 (2dd, 3JHH = 7.5 Hz, 4JHH = 1.5 Hz,
CHCHCCO), 7.64 and 7.67 (2d, 3JHH = 7.5 Hz, 2 ꢀ 2H, H4 and
H5). 13C NMR (75.47 MHz): 20.78 and 21.02 (p-Me of Mes),
22.63, 22.76, and 23.30 (2 overlapping signals) (o-Me of Mes),
39.54 (CHCR2), 54.93 (CR2), 117.42 (Carom-CHCR2), 119.04
and 119.38 (C4 and C5), 123.23 and 124.97 (CHCHCCO),
123.86 (CH-CHR2), 124.87 and 125.76 (C1 and C8), 126.24,
1
4a (0.37 g, 35%, mp 373 ꢀC). H NMR (300.13 MHz): 1.71
(s, 24H, o-Me of Mes), 2.16 (s, 12H, p-Me of Mes), 2.29 (s, 4H,
CH2), 6.60 (s, 4H, m-CH of Mes), 6.92 (d, 3JHH = 7.6 Hz, 4H,
H1 and H8 of CR2), 7.09 and 7.35 (2t, 3JHH = 7.6 Hz, 2 ꢀ 4H,
H2, H3, H6, and H7 of CR2), 7.83 (d, 3JHH = 7.6 Hz, 4H, H4
and H5 of CR2). 13C NMR (75.47 MHz): 20.87 (p-Me of Mes),
22.60 (o-Me of Mes), 27.56 (CH2), 60.77 (CR2), 107.03 (CdCO),
119.65 (C4 and C5 of CR2), 124.24, 126.28, 126.82 (C1, C2, C3,
C6, C7, and C8 of CR2), 128.85 (m-CH of Mes), 132.90 (ipso-C
of Mes), 139.19 (C12 and C13 of CR2), 140.56 (p-C of Mes),
143.33 (o-C of Mes), 147.38 (C10 and C11 of CR2),153.85(C-O).MS
m/z (% relative intensity): 1058 (M, 100), 939 (M - Mes, 45), 893 (M
- CR2 - 1, 30), 585 (M - Mes2GedCR2 þ 1, 15), 476 (Mes2Ged
CR2, 15), 311 (Mes2Ge - 1, 45). Anal. Calcd for C68H64Ge2O2
(1058.515): C, 77.16; H, 6.09. Found: C, 77.52; H, 6.38.
126.33, 126.39, and 126.83 (C2, C3, C6, and C7), 127.35 (Carom
-
CO), 127.84 and 129.50 (m-CH of Mes), 128.80 and 130.80 (br
signals, m-CH of Mes), 133.77 and 136.29 (ipso-C of Mes),
138.83 and 139.38 (p-C of Mes), 141.07 and 141.93 (C12
and C13), 141.28 and 143.75 (o-C of Mes), 144.72 and 145.96
(C10 and C11), 145.59 (C-O). MS m/z (% relative intensity):
1158 (M, 20), 1039 (M - Mes, 4), 477 (Mes2GedCR2 þ 1, 40),
311 (Mes2Ge - 1, 100), 209 (M - 2Mes2GedCR2 þ 2). Anal.
Calcd for C76H68Ge2O2 (1158.632): C, 78.78; H, 5.92. Found: C,
78.90; H, 5.95.
Synthesis of 3 and 4. To a crude solution of 1 (2 mmol) in Et2O
(20 mL) cooled to -78 ꢀC was added 1 mmol of 1,4-benzoqui-
none dissolved in 5 mL of diethyl ether. The reaction mixture
was allowed to warm to room temperature, during which time its
color slowly turned from orange to brown. After 2 h of stirring
at room temperature, solvents were removed in vacuo, and the
resultant residue was dissolved in 100 mL of toluene and filtered
to eliminate lithium salts. The solvent (toluene) was removed
in vacuo and replaced by 20 mL of diethyl ether. The mixture was
filtered again; the precipitate was washed with 10 mL of diethyl
ether and then recrystallized from 10 mL of pentane to give 3.
The filtrate was concentrated to 5 mL and cooled to -20 ꢀC to
afford pure crystalline 4.
4b (0.23 g, 18%, mp 335 ꢀC). 1H NMR (300.13 MHz): 1.11 (s,
36H, CMe3), 1.73 (br s, 24H, o-Me of Mes), 2.13 (s, 12H, p-Me of
Mes), 2.34 (s, 4H, CH2), 6.58 (s, 8H, m-CH of Mes), 6.98 (d,
3
4JHH = 1.5 Hz, 4H, H1 and H8 of CR02), 7.34 (dd, JHH
=
=
8.1 Hz, 4JHH = 1.5 Hz, H3 and H6 of CR02), 7.69 (d, 3JHH
8.1 Hz, 4H, H4 and H5 of CR02). 13C NMR (75.47 MHz): 20.76
(p-Me of Mes), 22.45 (o-Me of Mes), 27.35 (CH2), 31.27 (CMe3),
34.56 (CMe3), 60.64 (CR02), 107.04 (CdCO), 118.83 (C4 and C5
of CR02), 121.01 (C1 and C8 of CR02), 123.30 (C3 and C6 of
CR02), 128.18 (m-CH of Mes), 133.49 (ipso-C of Mes), 137.95
(C12 and C13 of CR02), 138.92 (p-C of Mes), 143.22 (o-C of
Mes), 147.41 (C10 and C11 of CR02), 149.59 (C2 and C7 of
CR02), 153.47 (C-O). MS m/z (% relative intensity): 1283 (M þ 1,
15), 1163 (M - Mes, 6), 1005 (M - CR02 - 1, 10), 587 (Mes2Ged
CR02 - 1, 4), 311 (Mes2Ge - 1, 20), 278 (R02CH2, 100), 263
(R02CH2 - Me, 65). Anal. Calcd for C84H96Ge2O2 (1282.939):
C, 78.64; H, 7.54. Found: C, 78.85; H, 7.66.
3a (0.59 g, 56%, mp 338 ꢀC). 1H NMR (300.13 MHz): 0.79 and
2.25 (2 br s, 2 ꢀ 6H, o-Me of Mes), 1.98 (vbr s, Δν1/2
=
210 Hz, 12H, o-Me of Mes), 2.07 and 2.27 (2s, 2 ꢀ 6H, p-Me
of Mes), 4.01 (s, 2H, CHdCO), 4.15 (s, 2H, CHCR2), 6.42 and
=
2
6.63 (2s, 2 ꢀ 2H, m-CH of Mes), 6.58 and 7.38 (2d, JHH
Synthesis of 5a. To a solution of 1a (2.0 mmol) in 20 mL of
Et2O was added a solution of 2,3,5,6-tetramethyl-1,4-benzoqui-
none (0.164 g, 1.0 mmol) in Et2O at -78 ꢀC. The reaction mixture
was allowed to warm to room temperature and stirred for 2 h,
giving a yellow solution and a white precipitate. After filtration to
remove LiF and elimination of the solvent, the remaining solid
was washed with pentane, giving a white powder of 5a (1.07 g,
96%, mp 323 ꢀC). 1H NMR (400.13 MHz): 0.56, 1.45, 2.42, and
2.47 (4s, 4 ꢀ 6H, o-Me of Mes), 0.71 (s, 6H, MeCCR2), 1.62 (s,
6H, MeCdC), 2.05 and2.22 (2s, 2 ꢀ 6H, p-Me ofMes), 6.32, 6.55,
6.60, and 6.86 (4s, 4 ꢀ 2H, m-CH of Mes), 6.97, 7.10, 7.37 (3t,
7.5 Hz, 2 ꢀ 2H, H1 and H8 of CR2), 6.73 (s, 2H, 4H, m-CH of
Mes), 7.03, 7.15, 7.34, and 7.37 (4t, 2JHH = 7.5 Hz, 4 ꢀ 2H, H2,
H3, H6, and H7 of CR2), 7.83 and 7.86 (2d, 2JHH = 7.5 Hz, 2 ꢀ
2H, H4 and H5 of CR2). 13C NMR (75.47 MHz): 20.82 and 21.08
(p-Me of Mes), 22.15, 23.06, and 23.91 (o-Me of Mes), 50.30
(CHCR2), 58.32 (CR2), 93.99 (CHdCO), 119.38 and 119.74 (C4
and C5 of CR2), 122.64 and 124.35 (C1 and C8 of CR2), 126.11,
126.24, 126.37, and 126.77 (C2, C3, C6, and C7 of CR2), 129.45,
129.47, and 129.50 (m-CH of Mes), 132.52 and 132.56 (ipso-C of
Mes), 139.29 and 139.47 (p-C of Mes), 140.91 and 141.14 (C12
and C13 of CR2), 142.74, 143.23, and 143.74 (o-C of Mes), 144.55
and 146.33 (C10 and C11 of CR2), 155.77 (C-O). MS m/z (%
relative intensity): 1058 (M, 25), 939 (M - Mes, 10), 893 (M -
CR2 - 1, 5), 584 (M - Mes2GedCR2, 5), 477 (Mes2GedCR2þ1,
15), 311 (Mes2Ge - 1, 100), 167. Anal. Calcd for C68H64Ge2O2
(1058.515): C, 77.16; H, 6.09. Found: C, 77.74; H, 6.17.
3JHH = 7.2 Hz, 3 ꢀ 2H) and 7.30 (ddd, 3JHH = 8.0 Hz, 3JHH
=
6.0 Hz, 4JHH = 2.8 Hz, 2H) (H2, H3, H6, and H7 of CR2), 6.98
and 7.19 (2d, 3JHH = 7.2 Hz, 2 ꢀ 2H, H1 and H8 of CR2), 7.76
and 7.83 (2d, 3JHH = 7.2 Hz, 2 ꢀ 2H, H4 and H5 of CR2). 13
C
NMR (100.62 MHz): 10.51 (MeCCR2), 20.73 and 20.91 (p-Me of
Mes), 21.46, 23.08 (2 overlapping signals) and 23.86 (o-Me of
Mes), 26.97 (MeCdC), 54.59 (CCR2), 62.92 (CR2), 108.05
(CdCO), 118.84 and 119.70 (C4 and C5), 125.77, 126.08, and
126.41 (C2, C3, C6, and C7 of CR2), 126.27 and 126.60 (C1 and
C8), 127.80, 128.37, 128.99, and 131.10 (m-CH of Mes), 133.40
and 135.19 (ipso-C of Mes), 138.53 and 138.99 (p-C of Mes),
140.43, 142.18, 142.62, 143.01, 144.16, 144.60 (o-C of Mes, C12
3b (0.87 g, 68%, mp >400 ꢀC). 1H NMR (300.13 MHz): 0.78
and 2.29 (2s, 2 ꢀ 6H, o-Me of Mes), 1.06 and 1.13 (2s, 2 ꢀ 18H,
CMe3), 1.82 (br s, 12H, o-Me of Mes), 2.06 and 2.24 (2s, 2 ꢀ 6H,
p-Me of Mes), 4.01 (s, 2H, CHdCO), 4.03 (s, 2H, CHCR02), 6.38
and 6.62 (2s, 2 ꢀ 2H, m-CH of Mes), 6.56 (d, 4JHH = 1.5 Hz, 2H,
H1 of CR02), 6.71 (s, 2H, 4H, m-CH of Mes), 7.34-7.38 (m, 6H,
3
H3, H6, and H8 of CR02), 7.69 and 7.73 (2d, JHH = 7.8 Hz,

Article
Organometallics, Vol. 29, No. 21, 2010 4857
and C13), 145.65 and147.66 (C10and C11 ofCR2), 152.49(C-O).
MS m/z (% relative intensity): 1114 (M, 100), 995 (M - Mes, 40),
949 (M - CR2 - 1, 40), 476 (Mes2GedCR2, 50), 311 (Mes2Ge -
1, 50). Anal. Calcd for C72H72Ge2O2 (1114.620): C, 77.58; H,
6.51. Found: C, 77.85; H, 6.77.
pour la Recherche (contract ANR-08-BLAN-0105-01), and
the MENESR for financial support of this work and the
M3PEC mesocenter for computational facilities.
Supporting Information Available: CIF files for 2a, 3a, 3b, 4a,
and 5a. Theoretical calculation details. This material is available
free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the CNRS
(contractCNRS/JSPS no. PRC 450), the Agence Nationale