Aromatic benzannulated germole dianions. The dilithio and disodio salts of a germaindenyl dianion

Article abstract of DOI:10.1021/om990991t

Conversion of the neutral 1,1-dichloro-DPGI (1) (DPGI = 2,3-diphenyl-1-germaindene) to the lithium dianion (2a) or sodium dianion (2b) leads to the highly unusual phenomenon of aromatization of the GeC₄ portion of 1-germaindene at the expense of the aromatic annulated C₆ ring. Treatment of 2a with trimethylchlorosilane gave the 1,1-bis(trimethylsilyl)-DPGI derivative (3) in high yield. The structure of 2a was determined by X-ray crystallography and found to possess two η⁵-coordinated lithium ions. The five-membered ring of the germaindenyl system undergoes significant carbon-carbon bond equalization upon formation of the dianion, while the remaining four carbon atoms become diene-like, exhibiting two short bonds separated by a long bond.

Full text of DOI:10.1021/om990991t

1806
Organometallics 2000, 19, 1806-1809
Ar om a tic Ben za n n u la ted Ger m ole Dia n ion s. Th e Dilith io
a n d Disod io Sa lts of a Ger m a in d en yl Dia n ion
Seok-Bong Choi, Philip Boudjouk,* and Kun Qin
Center for Main Group Chemistry, Department of Chemistry, North Dakota State University,
Fargo, North Dakota 58105
Received December 14, 1999
Summary: Conversion of the neutral 1,1-dichloro-DPGI
(1) (DPGI ) 2,3-diphenyl-1-germaindene) to the lithium
dianion (2a ) or sodium dianion (2b) leads to the highly
unusual phenomenon of aromatization of the GeC4
portion of 1-germaindene at the expense of the aromatic
annulated C6 ring. Treatment of 2a with trimethylchlo-
rosilane gave the 1,1-bis(trimethylsilyl)-DPGI derivative
(3) in high yield. The structure of 2a was determined by
X-ray crystallography and found to possess two η5-
coordinated lithium ions. The five-membered ring of the
germaindenyl system undergoes significant carbon-
carbon bond equalization upon formation of the dianion,
while the remaining four carbon atoms become diene-
like, exhibiting two short bonds separated by a long
bond.
version between the structures a and b in solution.3
Moreover, we were also able to directly compare the
aromaticity between the silole dianion and benzene in
silaindenyl dianion molecule d , which indicates that the
significant aromaticity in the silicon-containing ring is
responsible for changing the fused benzene ring in the
precursor to a cyclohexadiene moiety in the dianionic
silaindene.4
Herein we report the synthesis and characterization
of the first benzannulated germole dianions, dilithium
DPGI (2a ) (DPGI ) 2,3-diphenyl-1-germaindene) and
disodium DPGI (2b). To our surprise, we find that, upon
formation of the dianion, the germanium-containing
ring becomes aromatic, apparently at the expense of the
fused benzene ring, which takes on the features of a
conjugated diene (e).
In tr od u ction
Resu lt a n d Discu ssion
The structural characterization of the dianionic siloles
and germoles by West,1 Tilley,2 and our group3,4 provide
strong support for our initial postulation, based on NMR
data,5 that these species were aromatic. All the spec-
troscopic data and the typical structures a and b in
R4E2-‚2M+ (E ) Si, Ge; M ) Li, Na, and K) have also
been supported by calculations.6
Stirring of 1,1-dichloro-DPGI (1)7 with excess lithium
in THF produced a dark red solution. After removal of
unreacted lithium, treatment of this solution with an
excess of trimethylchlorosilane gave 1,1-bis(trimethyl-
silyl)-DPGI (3) in high yields (eq 1).
(1)
For comparative purposes, the molecular structure of
1,1-bis(trimethylsilyl)-DPGI (3) was determined. The
X-ray structure of 1,1-bis(trimethylsilyl)-DPGI (3) is
shown in Figure 1. The crystallographic data are in
Table 1. Selected bond lengths and bond angles are
listed in Table 2. The GeC4 ring has inequivalent C-C
distances, indicating isolated single (1.485 Å) and double
Recently we have reported the unique bonding struc-
ture c providing the strong possibility for the intercon-
(1) (a) West, R.; Sohn, H.; Bankwitz, U.; Calabrese, J .; Apeloig, Y.;
Mueller, T. J . Am. Chem. Soc. 1995, 117, 11608. (b) West, R.; Sohn,
H.; Bankwitz, U.; Powell, D. R.; Mueller, T.; Apeloig, Y. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 1002.
(2) (a) Freeman, W. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Angew. Chem., Int. Ed. Engl. 1996, 35, 882. (b) Freeman, W. P.; Tilley,
T. D.; Liable-Sands, L. M.; Rheingold, A. L. J . Am. Chem. Soc. 1996,
118, 10457.
(3) Choi, S.-B.; Boudjouk, P.; Hong, J .-H. Organometallics 1999, 18,
2919.
(5) (a) Hong, J .-H.; Boudjouk, P.; Castellino, S. Organometallics
1994, 13, 3387. (b) Hong, J .-H.; Boudjouk, P. Bull. Chem. Soc. Fr. 1995,
132, 495.
(6) (a) Goldfuss, B.; Schleyer, P. v. R.; Hampel, F. Organometallics
1996, 15, 1755. (b) Goldfuss, B.; Schleyer, P. v. R. Organometallics
1997, 16, 1543.
(4) Choi, S.-B.; Boudjouk, P.; Wei, P. J . Am. Chem. Soc. 1998, 120,
5814.
(7) Kanj, A.; Meunier, P.; Gautheron, B. J . Organomet. Chem. 1993,
454, 51.
10.1021/om990991t CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/31/2000

Notes
Organometallics, Vol. 19, No. 9, 2000 1807
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 3
Ge(1)-C(1)
Ge(1)-Si(1)
C(1)-C(2)
C(2)-C(3)
C(4)-C(5)
C(6)-C(7)
C(7)-C(15)
1.9477(18)
2.3849(7)
1.388(3)
1.391(3)
1.386(3)
1.485(2)
1.498(2)
Ge(1)-C(8)
Ge(1)-Si(2)
C(1)-C(6)
C(3)-C(4)
C(5)-C(6)
C(7)-C(8)
C(8)-C(9)
1.9615(18)
2.3838(6)
1.410(3)
1.378(3)
1.396(3)
1.356(2)
1.481(2)
C(1)-Ge(1)-C(8)
88.23(7)
C(1)-Ge(1)-Si(1) 105.12(6)
C(1)-Ge(1)-Si(2) 117.95(6)
Si(1)-Ge(1)-Si(2) 114.46(2)
C(8)-Ge(1)-Si(1) 101.73(6)
C(8)-Ge(1)-Si(2) 125.06(5)
C(2)-C(1)-C(6)
119.66(17) C(2)-C(1)-Ge(1)
131.84(15)
120.1(2)
C(6)-C(1)-Ge(1) 108.42(12) C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(4)-C(5)-C(6)
C(1)-C(6)-C(7)
C(8)-C(7)-C(6)
120.33(18) C(5)-C(4)-C(3)
120.18(19) C(1)-C(6)-C(5)
116.38(15) C(5)-C(6)-C(7)
116.63(15) C(8)-C(7)-C(15)
120.38(19)
119.32(17)
124.30(17)
123.63(16)
126.83(16)
122.10(13)
C(6)-C(7)-C(15) 119.73(15) C(7)-C(8)-C(9)
C(7)-C(8)-Ge(1) 109.79(12) C(9)-C(8)-Ge(1)
F igu r e 1. ORTEP drawing of 3 showing 30% probability
ellipsoids.
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 2a ‚LiCl‚3TMEDA a n d 3
2a ‚LiCl‚3TMEDA
3
empirical formula
fw
C
38H62ClGeLi3N6
C26H32GeSi2
473.29
731.80
temp, K
cryst syst
space group
a, Å
b, Å
c, Å
298(2)
triclinic
P1h
11.1629(10)
11.1858(10)
17.4193(16)
97.964(2)
93.703(2)
96.514(2)
2133.1(3), 2
295(2)
monoclinic
P2(1)/n
7.6855(11)
26.523(4)
12.7667(18)
90
94.531(2)
90
R, deg
â, deg
γ, deg
volume (Å3), Z
2594.3(6), 4
1.212
1.283
density(calcd), Mg/m3 1.139
abs coeff, mm-1
F(000)
0.812
780
992
F igu r e 2. Thermal ellipsoid diagram (30% probability) of
structure 2a ‚2TMEDA. LiCl‚TMEDA and all hydrogens are
omitted for clarity.
cryst size, mm
θ range, deg
index ranges
0.3 × 0.4 × 0.3
1.84-25.00
-13 e h e 13
-13 e k e 13
-15 e l e 20
0.6 × 0.6 × 0.8
1.54-28.30
-10 e h e 7
-35 e k e 35
-16 e l e 16
15 675
linkage, the analysis of the X-ray data for 2a shows two
η5-coordinated lithium ions with monomeric crystal
packing. Most notable among the structural differences
between the 2a and 3 are those in the carbon-carbon
bond lengths in both the germole ring and the six-
membered carbon ring (Figure 3).
no. of reflns collected 11 018
no. of ind reflns 7368
[R(int) ) 0.0142]
5947
[R(int) ) 0.0638]
5947/0/262
no. of data/restraints/ 7368/0/442
params
goodness-of-fit on F2
final R indices
[I > 2σ(I)]
0.946
R1 ) 0.0428
wR2 ) 0.1040
0.994
Significant shortening of the C6-C7 bond to 1.438 Å
from 1.485 Å in 3 and lengthening of the C1-C6 and
C7-C8 bonds to 1.443 and 1.483 Å, respectively, (1.410
and 1.356 Å in 3) are observed in the germole ring of
2a . In contrast, the three nearly equal (1.391, 1.378,
1.386 Å) carbon-carbon bonds linking C2, C3, C4, and
C5 in 3, consistent with a high degree of aromaticity in
the six-membered ring, undergo bond length alternation
(1.350, 1.412, 1.359 Å) in that portion of 2a (Figure 3, a
and b). The germanium carbon bonds in germoles
appear to be relatively insensitive to the nature of the
substituents on germanium (germanium-carbon bond
distances: 1.949, 1.987 Å in 2a ; 1.948, 1.962 Å in 3).
This is similar to that observed in the analogous
silaindene system. For example, the Si-C bond dis-
tances are 1.836 and 1.856 Å in 1,1-dichloro-3-n-butyl-
R1 ) 0.0339
wR2 ) 0.0817
0.416 and -0.555
largest diff peak and 0.682 and -0.623
hole, e Å-3
(1.356, 1.410 Å) bonds. Meanwhile the fused six-
membered carbon ring has the equalized C-C bond
distances of benzene.
Compound 2a , while extremely air sensitive, is ther-
mally stable under argon. X-ray quality crystals of 2a
were grown from a concentrated ether solution in the
presence of TMEDA (tetramethylethylenediamine) at
room temperature. The X-ray structure of 2a is shown
in Figure 2. The crystallographic data are in Table 1.
Selected bond lengths and bond angles are listed in
Table 3. Unlike the silaindenyl dianion, which has η1-
and η5-lithium coordination with polymeric crystal

1808 Organometallics, Vol. 19, No. 9, 2000
Notes
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d
becomes aromatic like other germole dianions and the
six-membered ring takes on the properties of a cyclo-
hexadiene. Consistent with this proposal is the planar
geometry of the GeC4 ring (∑ring ) 540.0°) in 2a . It is
noteworthy that the carbon-carbon bond distances in
2a and in 1,1-dilithio-3-n-butyl-2-phenyl-1-silaindene
are very similar despite different heteroatoms and
different substituents at the C7 position (Figure 3, b
and c).
The 1H and 13C NMR spectra for 2a and 2b have
essentially the same patterns and differ only slightly
in chemical shifts for both nuclei. It is noteworthy that
the 1H NMR chemical shifts of the hydrogens on C3 and
C4 for 2a and 2b (6.38 and 6.03 ppm; 6.34 and 6.00 ppm,
respectively) are significantly upfield from that of 1 (7.4
ppm), consistent with π-localization in the six-membered
ring.
An gles (d eg) for 2a ‚LiCl‚3TMEDAa
Ge(1)-C(1)
Ge(1)-Li(2)
N(1)-Li(1)
Li(1)-C(8)
Li(1)-C(6)
C(1)-C(2)
C(1)-Li(2)
Li(2)-N(4)
Li(2)-C(7)
C(2)-C(3)
C(4)-C(5)
C(6)-C(7)
C(7)-C(15)
1.949(3)
2.694(4)
2.227(5)
2.295(5)
2.496(5)
1.425(4)
2.566(5)
2.143(5)
2.350(5)
1.350(4)
1.359(4)
1.438(4)
1.500(3)
Ge(1)-C(8)
Ge(1)-Li(1)
Li(1)-N(2)
Li(1)-C(7)
Li(1)-C(1)
C(1)-C(6)
Li(2)-N(3)
Li(2)-C(8)
Li(2)-C(6)
C(3)-C(4)
C(5)-C(6)
C(7)-C(8)
C(8)-C(9)
1.987(2)
2.716(4)
2.115(5)
2.330(5)
2.604(5)
1.443(4)
2.120(5)
2.340(5)
2.471(5)
1.412(5)
1.420(4)
1.438(3)
1.483(4)
C(1)-Ge(1)-C(8)
C(8)-Ge(1)-Li(2)
C(8)-Ge(1)-Li(1)
C(2)-C(1)-C(6)
83.28(11) C(1)-Ge(1)-Li(2)
57.65(12) C(1)-Ge(1)-Li(1)
55.85(12) Li(2)-Ge(1)-Li(1)
64.79(13)
65.48(13)
98.13(14)
128.7(2)
104.46(17)
120.0(3)
121.3(3)
118.9(2)
113.7(2)
117.5(2)
116.8(3)
C(2)-C(1)-Ge(1)
C(6)-C(1)-Ge(1) 114.54(19) Li(2)-C(1)-Li(1)
C(3)-C(2)-C(1)
C(5)-C(4)-C(3)
C(5)-C(6)-C(7)
C(7)-C(6)-C(1)
122.7(3)
120.3(3)
126.5(2)
114.5(2)
C(2)-C(3)-C(4)
C(4)-C(5)-C(6)
C(5)-C(6)-C(1)
C(8)-C(7)-C(6)
C(6)-C(7)-C(15)
C(7)-C(8)-Ge(1)
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were performed under
an inert argon atmosphere using standard Schlenck tech-
niques. Air-sensitive reagents were transferred in an argon-
filled glovebox. THF was freshly distilled under nitrogen from
sodium/benzophenone ketyl immediately prior to use. Hexane
was stirred over sulfuric acid, distilled from calcium hydride,
and stored over 4 Å molecular sieves. MS data were obtained
on a Hewlett-Packard 5988A GC-MS system equipped with
a methyl silicone capillary column. NMR spectra were recorded
on a J EOL GSX400 spectrometer at 400 MHz (1H), 54 MHz
(29Si), and 100 MHz (13C).
C(8)-C(7)-C(15) 128.5(2)
C(7)-C(8)-C(9)
124.8(2)
113.93(18)
C(9)-C(8)-Ge(1) 121.26(18)
a
Symmetry transformations used to generate equivalent at-
oms: #1 -x, -y+1, -z+1.
Syn t h esis of 1,1-Dich lor o-2,3-d ip h en ylger m a in d en e
8
(1). Refluxing Cp2ZrPh2 (10 g, 25.3 mmol) and diphenylacety-
lene (4.8 g, 25.3 mmol) in toluene (150 mL) for 20 h gave an
orange solution. Concentration of this solution to 20 mL lead
to the precipitation of an orange solid. Filtration and washing
with hexane (50 mL × 3) gave 2,3-diphenyl-1-zirconaindene
(10 g, yield 71%). 1H NMR (CDCl3, ref; CDCl3 ) 7.24 ppm):
6.60-7.15 (m, 14H), 6.38 (s, 10H). 13C NMR (CDCl3, ref; CDCl3
) 77.23 ppm): 112.8 (Cp), 122.8, 123.6, 125. 1, 125.15, 125.4,
126.4, 127.4, 127.7, 130.4, 136.4, 141.2, 146.0, 146.8, 147.1,
184.9, 194.5.
2,3-Diphenyl-1-zirconaindene (10 g, 21 mmol) was dissolved
in THF (200 mL). Then GeCl4 (3.6 mL, 31.5 mmol) was added.
The mixture was stirred at 50 °C for 24 h. All of the solvent
was removed by vacuum. The residue was washed by 50 mL
of hexane and extracted with hexane (approximately 100 mL
of hexane can extract 1 g of 1) (7.2 g, 86% yield). Selected data
for 1: mp 127-130 °C; 1H NMR (CDCl3, ref; CDCl3 ) 7.24
ppm) 7.79 (d, 1H, J ) 8 Hz), 7.40-7.46 (m, 5H), 7.19-7.26
(m, 7H), 7.07 (d, 1H, J ) 8 Hz); 13C NMR (CDCl3, ref; CDCl3
) 77.23 ppm) 150, 144.3, 138.2, 135.8, 135.1, 134.6, 132.6,
131.2, 129.8, 129.32, 129.27, 129.13, 128.47, 128.43, 127.74,
125.92. Anal. Calcd for
C20H14GeCl2: C, 60.38; H, 3.55,
Found: C, 59.62; H, 3.60; MS (EI, M+) 398.
1,1-Dilith io-2,3-d ip h en ylger m a in d en e (2a ). 1 (1.2 g, 3.0
mmol) and lithium metal (0.13 g, 18.0 mmol) were stirred in
THF (25 mL) and TMEDA (3 mL) at room temperature for 12
h. All volatiles were removed under reduced pressure, and the
residue was extracted with ether (30 mL). Crystallization of
the this solution yields dark red X-ray quality crystals of 2a ‚
LiCl‚3TMEDA (0.86 g, yield 50%). The NMR sample was
prepared by dissolving the X-ray quality crystals of 2a ‚LiCl‚
3TMEDA in THF-d8. Selected data: 1H NMR (THF-d8, ref;
THF-d8 ) 1.72 ppm) 8.02 (d, 1H, J ) 8 Hz), 7.71 (d, 1H, J )
8 Hz), 7.25 (d, 2H, J ) 8 Hz), 7.21 (d, 2H, J ) 8 Hz), 7.07 (t,
F igu r e 3. (a) Selected bond lengths (Å) of 1,1-bis(tri-
methylsilyl-1-germaindene (3). (b) Selected bond lengths
(Å) and angles (deg) of 1,1-dilithio-1-germaindene (2a ). (c)
Selected bond lengths (Å) and angles (deg) of 1,1-dilithio-
1-silaindene.4
2-phenyl-1-silaindene and 1.839 and 1.860 Å in 1,1-
dilithio-3-n-butyl-2-phenyl-1-silaindene.4
We attribute these differences to a fundamental
alteration in the bonding of the germaindenyl system
upon formation of the dianion; that is, the GeC4 ring
(8) (a) Samuel, E.; Rausch, M. D. J . Am. Chem. Soc. 1973, 95, 6263.
(b) Erker, G. J . Organomet. Chem. 1977, 134, 189.

Notes
Organometallics, Vol. 19, No. 9, 2000 1809
2H, J ) 8 Hz), 6.82 (t, 1H, J ) 8 Hz), 6.72 (t, 2H, J ) 8 Hz),
6.48 (t, 1H, J ) 8 Hz), 6.38 (t, 1H, J ) 8 Hz), 6.03 (t, 1H, J )
8 Hz), 2.21 (s, 12H), 2.06 (s, 36H). 13C NMR (THF-d8, ref; THF-
d8 ) 24.45 ppm) 174.87, 167.94, 150.53, 144.95, 137.95, 136.34,
131.31, 128.12, 126.69, 125.77, 122.24, 120.82, 118.86, 117.00,
116.74, 109.92.
1,1-Disod io-2, 3-d ip h en ylger m a in d en e NMR Rea ction .
1 (50 mg, 0.13 mmol) and Na (18 mg, 0.78 mmol) were placed
in a 5 mm NMR tube with THF-d8 (0.75 mL). After sealing
the NMR tube under vacuum, sonication of the NMR tube for
12 h gave a dark red solution. Selected data for 2b: 1H NMR
(THF-d8, ref; THF-d8 ) 1.72 ppm) 8.21 (d, 1H, J ) 8 Hz), 7.79
(d, 1H, J ) 8 Hz), 7.31 (d, 2H, J ) 8 Hz), 7.17 (d, 2H, J ) 8
Hz), 7.01 (t, 2H, J ) 8 Hz), 6.69-6.75 (m, 3H), 6.47 (t, 1H, J
) 8 Hz), 6.34 (t, 1H, J ) 8 Hz), 6.00(t, 1H, J ) 8 Hz). 13C
NMR (THF-d8, ref; THF-d8 ) 24.45 ppm) 179.98, 171.02,
152.16, 145.31, 139.41, 137.29, 132.24, 129.35, 127.43, 126.88,
122.05, 120.53, 119.47, 117.79, 117.09, 109.84.
7.31 (t, 2H), 7.24 (t, 1H), 7.13-7.17 (m, 4H), 7.03-7.07 (m,
3H), 6.95-6.97 (m, 3H), 0.23 (s, 18H). 13C NMR (THF-d8, ref;
THF-d8 ) 24.45 ppm); 152.53, 150.66, 149.07, 144.37, 142.95,
140.69, 133.32, 131.12, 130.31, 129.16, 128.48, 127.99, 127.54,
126.23, 126.21, 126.06, 0.19. 29Si NMR (THF-d8, ref: ext. TMS
) 0.00) -4.95. MS (EI, M+), 478.25. Anal. Calcd for C26H32
-
GeSi2: C, 65.98; H, 6.81. Found: C, 65.30; H, 6.86.
X-r a y Str u ctu r e Deter m in a tion . X-ray quality crystals
of 2a were grown from a concentrated ether solution in the
presence of TMEDA at room temperature. X-ray quality
crystals of 3 were grown from a concentrated hexane solution
of 3. A single crystal of 2a or 3 was mounted in a thin-walled
glass capillary tube and sealed under nitrogen. Details on
machine parameters, crystal data, data collection, and refine-
ment are given in Tables 1, 2, and 3.
Ack n ow led gm en t. Financial support from the Na-
tional Science Foundation through No. 9874802 is
gratefully acknowledged. We also thank Dean G. Grier
for assistance with the X-ray crystal structure deter-
mination.
1,1-Bis(tr im eth ylsilyl)-2,3-d ip h en yl-1-ger m a in d en e (3).
Stirring of 1 (2.0 g, 5.0 mmol) and lithium (0.20 g, 30.0 mmol)
in THF (30 mL) for 3 h gives a dark red solution. Filtration
and addition to an excess of trimethylchlorosilane (4.0 mL, 30.0
mmol) with stirring at room temperature produces a pale
brown solution immediately. Additional stirring for 3 h gives
a colorless solution and a salt. All volatiles are removed under
reduced pressure, and the residue is extracted with hexane
(yield 92% based on 1H NMR). Crystallization of this solution
yields 3 as colorless crystals. Selected data for 1: mp 97-98
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances and angles, hydrogen atom coordinates, and aniso-
topic thermal parameters for 2a and 3. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
°C. H NMR (THF-d8, ref; THF-d8 ) 1.72 ppm) 7.60 (d, 1H),
OM990991T