One-pot synthesis of a tetragermabutadiene and its reactions with oxygen and sulfur

Article abstract of DOI:10.1021/om020956d

Hexakis(2,4,6-triisopropylphenyl)tetragermabuta-1,3-diene (2) is easily accessible by the reaction of the Grignard compound RMgBr, R = 2,4,6-iPr₃C₆H₂, with GeCl₂·dioxane and magnesium. Treatment of 2 with sulfur furnishes a thiatetragermacyclopentene derivative with an endocyclic Ge=Ge double bond. The reaction of 2 with dry air yields a compound with a 2,4,7,8-tetraoxa-1,3,5,6-tetragermabicyclo[4.1.1]octane skeleton.

Full text of DOI:10.1021/om020956d

1302
Organometallics 2003, 22, 1302-1304
On e-P ot Syn th esis of a Tetr a ger m a bu ta d ien e a n d Its
Rea ction s w ith Oxygen a n d Su lfu r 1
Gerhard Ramaker, Annemarie Scha¨fer, Wolfgang Saak, and
Manfred Weidenbruch*
Fachbereich Chemie, Universita¨t Oldenburg, Carl-von-Ossietzky-Strasse 9-11,
D-26111 Oldenburg, Germany
Received November 19, 2002
Hexakis(2,4,6-triisopropylphenyl)tetragermabuta-1,3-diene (2) is easily accessible by the
reaction of the Grignard compound RMgBr, R ) 2,4,6-iPr3C6H2, with GeCl2‚dioxane and
magnesium. Treatment of 2 with sulfur furnishes a thiatetragermacyclopentene derivative
with an endocyclic GedGe double bond. The reaction of 2 with dry air yields a compound
with a 2,4,7,8-tetraoxa-1,3,5,6-tetragermabicyclo[4.1.1]octane skeleton.
In tr od u ction
We recently prepared the compounds 12 and 23 as the
first and as yet only examples of molecules containing
conjugated SidSi and GedGe double bonds, respec-
tively. Starting from a tetraaryldisilene, compound 1
was constructed by a sequence of metalation, halogena-
tion, and intermolecular coupling reactions2 and has
since been characterized by a series of 1,2- and 1,4-
addition as well as cycloaddition reactions.4
Although the yield of this synthetic route still only
amounts to about 30%, the one-pot procedure does allow
the isolation of 2 on a gram scale from readily accessible
or commercially available starting materials and thus
makes first investigations of the reactions of the tet-
ragermabutadiene possible.
Compound 2 is accessible from a tetraaryldigermene
by an analogous sequence of reactions. Although com-
pound 1 is formed in yields of up to 60%, the synthesis
of 2 requires tedious separation steps and furnishes a
maximum yield of 11%, which has up to now hindered
the further characterization of this compound. We now
describe a simple, one-pot synthesis of 2 and report on
the first reactions of this tetragermabutadiene.
Reactions of 1 with sulfur or, in the presence of
triethylphosphane, with selenium and tellurium pro-
ceeded through formal [4+1] cycloadditions to afford the
corresponding chalcogenatetrasilacyclopentenes with
endocyclic SidSi double bonds in yields of 80% each.5
Compound 2 also reacts with sulfur to smoothly give
the thiatetragermacyclopentene 3 as yellow needles
isolated in 75% yield (eq 2).
An X-ray crystallographic analysis of 3 (Figure 1)
reveals the presence of an almost planar five-membered
ring (sum of the endocyclic angles: 539.5°). With an
average value of 2.45 Å the Ge(1)-Ge(2) and Ge(3)-
Ge(4) bonds are of the typical size for Ge-Ge single
bonds. The GedGe double bond length of 2.2841(5) Å is
somewhat longer than the corresponding bonds in the
as yet only other known molecules with endocyclic Ged
Ge bonds, namely, (tBu3Si)4Ge36 with 2.239 Å and (tBu3-
Si)3Ge3Br7 with 2.2743 Å. Like most other digermenes,
compound 3 shows a trans-bending of the substituents
referred to the Ge(2)-Ge(3) vector, which, in this case,
Resu lts a n d Discu ssion
Slow, dropwise addition of a solution of GeCl2‚dioxane
in THF at -50 °C to a mixture of 2,4,6-triisopropylphe-
nylmagnesium bromide and magnesium in the same
solvent leads at first to a red solution, which upon
warming to room temperature takes on a black-blue
color. Replacement of THF by n-pentane and repeated
crystallizations from this solvent afford black crystals
with analytical and spectroscopic data identical to those
of an authentic sample of 23 (eq 1).
(1) Compounds of Germanium, Tin, and Lead. Part 41. Part 40:
Scha¨fer, A.; Saak, W.; Weidenbruch, M. Organometallics 2003, 22, in
press.
(2) Weidenbruch, M.; Willms, S.; Saak, W.; Henkel, G. Angew. Chem.
1997, 109, 2612; Angew. Chem. Int. Ed. Engl. 1997, 36, 2503.
(3) Scha¨fer, H.; Saak, W.; Weidenbruch, M. Angew. Chem. 2000, 112,
3847; Angew. Chem., Int. Ed. 2000, 39, 3703.
(5) Grybat, A.; Boomgaarden, S.; Saak, W.; Marsmann, H.; Weiden-
bruch, M. Angew. Chem. 1999, 111, 2161; Angew. Chem., Int. Ed. 1999,
38, 2010.
(6) Sekiguchi, A.; Yamazaki, H.; Kabuto, C.; Sakurai, H.; Nagase,
S. J . Am. Chem. Soc. 1995, 117, 8025.
(4) For a review see: Weidenbruch, M. J . Organomet. Chem. 2002,
646, 39.
(7) Sekiguchi, A.; Ishida, Y.; Fukaya, N.; Ichinohe, M.; Takagi, N.;
Nagase, S. J . Am. Chem. Soc. 2002, 124, 1158.
10.1021/om020956d CCC: $25.00 © 2003 American Chemical Society
Publication on Web 02/14/2003

One-Pot Synthesis of a Tetragermabutadiene
Organometallics, Vol. 22, No. 6, 2003 1303
F igu r e 2. Molecule of 5 in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and bond angles (deg): Ge(1)-O(1) )
1.789(3), O(1)-Ge(2) ) 1.754.(3), Ge(2)-O(2) ) 1.806(4),
Ge(2)-O(3) ) 1.774(3), O(2)-Ge(3) ) 1.820(3), O(3)-Ge-
(3) ) 1.831(4), Ge(3)-Ge(4) ) 2.4997(8), Ge(4)-O(4) )
1.814(3), O(4)-Ge(1) ) 1.792(3), Ge(1)-O(4)-Ge(4) )
132.17(18), Ge(1)-O(1)-Ge(2) ) 124.71(18), Ge(2)-O(2)-
Ge(3) ) 90.66(15), Ge(2)-O(3)-Ge(3) ) 91.31(16), O(3)-
Ge(2)-O(2) ) 88.24(17), O(3)-Ge(3)-O(2) ) 86.14(15).
F igu r e 1. Molecule of 3 in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and bond angles (deg): Ge(1)-Ge(2) )
2.4526(4), Ge(2)-Ge(3) ) 2.2841(5), Ge(3)-Ge(4) ) 2.4482-
(4), Ge(1)-S ) 2.2669(8), Ge(4)-S ) 2.2666(8), Ge(1)-Ge-
(2)-Ge(3) ) 108.620(15), Ge(2)-Ge(3)-Ge(4) ) 107.898-
(16),Ge(3)-Ge(4)-S )102.93(2),Ge(4)-S-Ge(1))116.46(3),
S-Ge(1)-Ge(2) ) 102.54(2).
is very pronounced with values of 29.9° at Ge(2) and
35.7° at Ge(3).
Sch em e 1
Selenium and tellurium also react with 2 in the
presence of triethylphosphane as chalcogen transfer
reagent; however the yields of products that can be
isolated are so low that their unambiguous character-
ization has not yet been possible.
Oxygen reacts with simple digermenes through 1,2-
addition at the GedGe double bond to afford 3,4-
digermadioxetanes that rearrange to 2,4-digermadiox-
etanes only at higher temperatures or under irradiation.8
Disilenes also react with oxygen initially through 1,2-
addition to 3,4-disiladioxetanes; however, only cyclo-
disiloxanes can be isolated.9 Analogously, the action of
dry air on 1 leads to a product in which two cyclodisi-
loxane rings are linked by a disiloxane bridge.10 If the
two double bonds of 2 were to react like simple di-
germenes, the compound 4 or a rearrangement product
of this molecule would be formed. The reaction of 2 with
dry air gave a product isolated in 77% yield for which
the analytical data were indicative of a 1:2 adduct of
diene 2 and O2. However, the X-ray crystallographic
data of the pale yellow crystals gave an unexpected
result. Neither the compound 4 nor a possible rear-
rangement product thereof had been formed. Instead
the product proved to be compound 5, with a tetraoxa-
tetragermabicyclo[4.1.1]octane skeleton (Scheme 1). In
contrast to our expectations, the folded cyclodigermox-
ane ring (fold angle ) 14.5°) in the bicyclic system was
not formed by addition of O2 to one of the two double
bonds but rather must be the result of a [2+4] cycload-
dition of O2 to the terminal germanium atoms of 2 to
Sch em e 2
afford compound 6, followed by a 1,2-addition of a second
oxygen molecule to the newly formed double bond to give
the intermediate 7. Rearrangement reactions of the two
O-O bonds of 7 should then furnish the isolated product
5 (Scheme 2).
Although the formation of the bicyclic compound 5
cannot yet be interpreted unequivocally, it seems clear
that the conjugated double bonds in 2 can exhibit
different reaction modes from those that are possible
for digermenes with isolated double bonds.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were carried out
in oven-dried glassware under an atmosphere of dry argon.
1
(8) Masamune, S.; Batcheller, S. A.; Park, J .; Davis, W. M.; Ya-
mashita, O.; Ohita, Y.; Kabe, Y. J . Am. Chem. Soc. 1989, 111, 1888.
(9) McKillop, K. L.; Gillette, G. R.; Powell, D. R.; West, R. J . Am.
Chem. Soc. 1992, 114, 5203.
(10) Willms, S.; Grybat, A.; Saak, W.; Weidenbruch, M. Z. Anorg.
Allg. Chem. 2000, 626, 1148.
The H and 13C NMR spectra were obtained on a Bruker ARX
500 spectrometer using C6D6 as solvent. The UV/vis spectra
were recorded with a Comspec spectrometer with fiber optics.
Elemental analyses were performed by Analytische Labora-
torien, D-51779 Lindlar, Germany.

1304 Organometallics, Vol. 22, No. 6, 2003
Ramaker et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for 3 a n d 5
1,1,2,3,4,4-Hexakis(2,4,6-tr iisopr opylph en yl)tetr ager m -
a bu ta -1,3-d ien e (2). At -50 °C a solution of GeCl2‚dioxane
(5.15 g, 22.2 mmol) in THF (40 mL) was added dropwise to a
mixture of 2,4,6-triisopropylphenylmagnesium bromide, pre-
pared from 1-bromo-2,4,6-triisopropylphenylbenzene (9.79 g,
34.6 mmol) and excess magnesium (1.3 g, 53 mmol) in THF
(30 mL). The color of the mixture changed from yellow to red.
The mixture was allowed to come to room temperature. THF
was removed from the black mixture, the black residue was
extracted with n-pentane (250 mL), and all insoluble products
were filtered off. After cooling for 24 h at -30 °C all insoluble
compounds were again filtered off. The filtrate was concen-
trated to a volume of 100 mL and stored for 5 days at -30 °C.
After this time the crude product was filtered off and recrys-
tallized from n-pentane to furnish 2.6 g (31% yield) of black
crystals of 2. The analytical and spectroscopic data were
identical to those of an authentic sample of 2.3
3
5
empirical
formula
fw
C
90H138Ge4S‚2C6H12
C
90H138Ge4O4‚1.5C7H8
1710.74
14.4535(5)
17.0514(9)
22.7739(13)
110.735(6)
101.723(5)
97.573(5)
5010.8(4)
2
1712.56
16.8134(3)
21.0889(6)
27.1986(6)
90
98.253(2)
90
9544.1(4)
4
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
d(calcd) (g cm-3
cryst size (mm)
cryst syst
space group
2θmax (deg)
no. of reflns
measd
)
1.134
1.192
0.38 × 0.17 × 0.10
triclinic
P1h
52
61 022
0.20 × 0.15 × 0.06
monoclinic
P21/n
52
79 739
2,2,3,4,5,5-H exa k is(2,4,6-t r iisop r op ylp h en yl)-1-t h ia -
2,3,4,5-tetr a ger m a cyclop en t-3-en e (3). Sulfur (1.0 g, 31.2
mmol, large excess) was added to a solution of 2 (0.80 g, 0.43
mmol) in toluene (30 mL), and the mixture heated under reflux
for 3 h. During this time the color changed from blue-black to
yellow. Toluene was replaced by n-pentane (40 mL), excess
sulfur was filtered off, and the solvent was evaporated.
Crystallization from toluene provided yellow needles of 3 (0.61
g, 77%): mp 199-201 °C; 1H NMR δ 0.19 (d, 6 H, 3J ) 6.6
no. of unique
reflns
17 981
1.250
17 646
1.295
lin abs coeff
(mm-1
)
no. of params
R (I > 2σ(I))
wR2 (all data)
GOF (F2)
929
828
0.0363
0.0872
0.904
0.0515
0.1098
0.796
3
Hz), 0.48 (d, 6 H, 3J ) 6.6 Hz), 0.49 (d, 6 H, J ) 6.1 Hz), 0.52
3
3
(d, 6 H, J ) 6.6 Hz), 0.63 (d, 6 H, J ) 6.6 Hz), 0.71 (d, 6 H,
2 H), 6.73 (s, 2 H), 6.76 (s, 2 H), 6.80 (s, 2 H), 6.85 (s, 2 H),
6.92 (s, 2 H), 7.03 (s, 2 H); 13C NMR δ 21.36, 22.93, 23.40,
23.70, 23.81, 23.95, 24.02, 24.11, 24.36, 24.44, 24.56, 24.74,
24.97, 25.15, 26.70, 28.57, 34.30, 34.38, 34.58, 35.85, 38.25,
121.49, 121.88, 122.19, 122.40, 122.74, 123.16, 123.29, 123.58,
123.91, 124.01, 125.63, 127.80, 127.99, 128.18, 128.50, 129.27,
129.98, 137.77, 141.29, 149.74, 149.94, 152.16, 152.54, 154.36,
155.73. Anal. Calcd for C90H138Ge4O4: C, 68.65; H, 8.83.
Found: C, 68.63; H, 8.59. Single crystals of 5 were grown from
toluene at -30 °C.
Cr ysta llogr a p h ic An a lyses. Crystal and numerical data
of structure determinations are given in Table 1. In each case
the crystal was mounted in an inert oil. Data collection was
performed with a Stoe IPDS area detector at 193(2) K using
graphite-monochromated Mo KR radiation (0.71073 Å). The
structures were solved by direct phase determination and
refined by full-matrix least-squares techniques against F2 with
the SHELXL-97 program system.11 Hydrogen atoms were
placed in the calculated positions, and all other atoms were
refined anisotropically. The data have been deposited with the
Cambridge Crystallographic Data Centre: CCDC 195 983 (3)
and CCDC 195 984 (5).
3J ) 7.1 Hz), 0.91 (d, 6 H, J ) 6.6 Hz), 1.11 (d, 6 H, J ) 7.1
3
3
Hz), 1.15 (d, 6 H, 3J ) 7.1 Hz), 1.18 (d, 6 H, J ) 6.6 Hz), 1.21
3
3
3
(d, 6 H, J ) 6.1 Hz), 1.27 (d, 6 H, J ) 6.6 Hz), 1.28 (d, 6 H,
3J ) 7.1 Hz), 1.32 (d, 6 H, J ) 6.6 Hz), 1.40 (d, 6 H, J ) 6.6
3
3
Hz), 1.43 (d, 6 H, 3J ) 6.6 Hz), 1.64 (d, 6 H, J ) 6.6 Hz), 1.75
3
(d, 6 H, 3J ) 6.6 Hz), 2.69 (sept, 2 H), 2.82 (sept, 2 H) 3.18
(sept, 2 H), 3.63 (sept, 2 H), 3.89 (sept, 4 H), 3.94 (sept, 2 H),
4.64 (sept, 2 H), 7.15 (m, 12 H); 13C NMR δ 21.49, 24.02, 24.07,
24.10, 24.14, 24.18, 24.36, 24.61, 24.67, 24.86, 25.34, 26.15,
26.28, 26.83, 27.76, 29.24, 35.98, 37.87, 121.66, 121.78, 122.75,
122.80, 123.58, 123.82, 127.80, 127.99, 128.19, 128.29, 128.50,
129.03, 129.27, 138.95, 140.74, 146.70, 149.00, 140.54, 149.66,
150.67, 153.04, 154.20, 154.51, 155.78; UV/vis (n-hexane) λmax
(ꢀ) 400 (1750 nm). Anal. Calcd for C90H138Ge4S: C, 70.08; H,
9.02; S, 2.08. Found: C, 69.88; H, 9.05; S. 2.19. Single crystals
of 3 were grown from methylcyclopentane at +4 °C.
1,3,3,5,5,6-Hexa k is(2,4,6-tr iisop r op ylp h en yl)-2,4,8-tet-
r a oxa -1,3,5,6-tetr a ger m a bicyclo[4.1.1]octa n e (5). At 0 °C
dry air was passed over a solution of 2 (0.60 g, 0.40 mmol) in
toluene (30 mL). After 10 min the color of the solution had
changed from blue-black to yellow. Toluene was distilled off,
the residue was redissolved in n-pentane (40 mL), and the
insoluble products were filtered off. Crystallization from
toluene furnished pale yellow crystals of 5 (0.48 g, 77%): mp
Ack n ow led gm en t. Financial support of our work
by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie is gratefully acknowledged.
1
3
241-244 °C; H NMR δ 0.15 (d, 6 H, J ) 6.6 Hz), 0.18 (d, 6
3
3
3
H, J ) 6.6 Hz), 0.26 (d, 6 H, J ) 6.6 Hz), 0.33 (d, 6 H, J )
3
3
Su p p or t in g In for m a t ion Ava ila b le: Listing of atomic
coordinates, anisotropic displacement parameters, and bond
lengths and angles for 3 and 5. This material is available free
of charge via the Internet at http://pubs.acs.org.
6.6 Hz), 0.38 (d, 6 H, J ) 6.6 Hz), 0.46 (d, 6 H, J ) 6.6 Hz),
3
3
0.51 (d, 6 H, J ) 6.6 Hz), 0.52 (d, 6 H, J ) 6.6 Hz), 0.62 (d,
6 H, 3J ) 6.6 Hz), 1.45 (m, 6H), 1.48 (d, 6 H, 3J ) 6.6 Hz), 1.53
3
3
(d, 6 H, J ) 6.6 Hz), 1.58 (d, 6 H, J ) 6.0 Hz), 1.61 (d, 6 H,
3J ) 6.6 Hz), 1.69 (d, 6 H, J ) 6.6 Hz), 1.73 (d, 6 H, J ) 6.6
3
3
OM020956D
Hz), 1.78 (d, 6 H, 3J ) 6.6 Hz), 1.85 (d, 6 H, J ) 6.6 Hz), 2.65
3
(sept, 4 H), 2.75 (sept, 2 H) 2.96 (sept, 2 H), 3.26 (sept, 2 H),
3.55 (sept, 2 H), 4.23 (sept, 2 H), 4.46 (sept, 2 H), 4.57 (sept,
(11) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.