Synthesis and structure of a 1-germapropadiene

Article abstract of DOI:10.1021/om980152r

The reaction of t-BuLi with a fluoroalkynyl-germane produces the title compound, 1. Single-crystal X-ray analysis shows the Ge=C bond length to be 1.783(2) ?. The Ge atom is somewhat pyramidalized, and the Ge=C=C bond angle (159.2°) reveals a bent structure at the central carbon atom.

Full text of DOI:10.1021/om980152r

Organometallics 1998, 17, 2147-2148
2147
Syn th esis a n d Str u ctu r e of a 1-Ger m a p r op a d ien e
Barrett E. Eichler, Douglas R. Powell, and Robert West
Department of Chemistry, The University of Wisconsin, Madison, Wisconsin 53706
Received March 2, 1998
Sch em e 1a
Summary: The reaction of t-BuLi with a fluoroalkynyl-
germane produces the title compound, 1. Single-crystal
X-ray analysis shows the GedC bond length to be
1.783(2) Å. The Ge atom is somewhat pyramidalized,
and the GedCdC bond angle (159.2°) reveals a bent
structure at the central carbon atom.
Compounds with cumulated double bonds to metalloid
atoms have been of considerable interest during the past
few years. The first 1-silapropadiene1 was reported in
1993, and the synthesis of three additional examples of
1-silaallenes2 has recently been published. A germa-
phosphaallene3 has been characterized, and evidence
has been presented for the existence of a 1-germapro-
padiene4 as a transient reaction intermediate. We now
report the synthesis and characterization by single-
crystal X-ray diffraction of a stable 1-germapropadiene,
1.
a
Tip ) 2,4,6-triisopropylphenyl.
Compound 1 was synthesized5 by the route shown in
Scheme 1. In the final step, fluoroalkynylgermane 26
was treated with 1 equiv of tert-butyllithium in diethyl
ether at -78 °C. The presumed intermediate 3 rapidly
(1) Miracle, G. E.; Ball, J . L.; Powell, D. R.; West, R. J . Am. Chem.
Soc. 1993, 115, 11598.
(2) Trommer, M.; Miracle, G. E.; Eichler, B. E.; Powell, D. R.; West,
R. Organometallics 1997, 16, 5737.
(3) Ramdane, H.; Ranaivonjatovo, H.; Escudie´, J .; Mathieu, S.;
Knouzi, N. Organometallics 1996, 15, 3070.
(4) Kishikawa, K.; Tokitoh, N.; Okazaki, R. Organometallics 1997,
16, 5127.
(5) 1: A 1.7 M solution of t-BuLi in pentane (1.00 mL, 1.70 mmol,
1.02 equiv) was syringed into a solution of 2 (1.0033 g, 1.6737 mmol)
in diethyl ether at -78 °C. The light yellow solution was stirred at
-78 °C for 1 h. The solution was warmed to 0 °C for 5 min, turning it
deep red. This was cooled for 3 days at -20 °C to produce crystals of
1. Mp: 125 °C. 1H NMR (500 MHz, toluene-d8, 253 K): δ 1.16-1.19
3
(m, 36H, i-Pr CH3), 1.34 (s, 9H, t-Bu), 2.71 (sept, 2H, J HH ) 6.8 Hz),
3
3.62 (sept, 4H, J HH ) 6.8 Hz), 7.01 (1H, obscured by solvent), 7.05
(2H, obscured by solvent), 7.06 (s, 4H, Tip aryl H), 7.27 (d, 2H, 3J HH
)
8.1 Hz). 13C NMR (126 MHz, toluene-d8, 253 K): δ 24.2, 24.7, 24.9,
30.2, 34.7, 37.6, 38.1, 121.8, 126.1, 127.5, 128.9, 136.5, 144.0, 149.8,
150.7, 153.4, 235.1 (GedC).
F igu r e 1. Molecular structure of 1-germapropadiene, 1.
Thermal ellipsoid (50% probability level) drawing with
hydrogen atoms omitted for clarity. Selected bond lengths
(Å) and angles (deg): Ge-C(1) 1.783(2), Ge-C(13) 1.950(2),
Ge-C(28) 1.951(2), C(1)-C(2) 1.314(2), C(2)-C(3) 1.498(3),
C(2)-C(9) 1.537(3); Ge-C(1)-C(2) 159.2(2), C(1)-Ge-
C(28) 123.15(8), C(1)-Ge-C(13) 111.24(8), C(13)-Ge-
C(28) 114.04(7), C(1)-C(2)-C(3) 119.9(2), C(1)-C(2)-C(9)
121.6(2), C(3)-C(2)-C(9) 118.4(2).
(6) 2: To 25.7 g (1.32 equiv) of ethynylbenzene in 150 mL of dry
THF at -78 °C was added 0.21 mol of n-BuLi (1.1 equiv). The resulting
solution was slowly added to a solution of bis(2,4,6-triisopropylphenyl)-
difluorogermane8 (98.64 g, 0.1907 mol) in dry THF (350 mL) at -78
°C. The solution was stirred at -78 °C for 1.5 h. Water (100 mL) was
poured into the flask, and the solution was warmed to room temper-
ature overnight. The solvents were removed by rotary evaporation, and
the residue was taken up in diethyl ether and washed with water. The
organic layer was dried with MgSO4 and gravity filtered, and the ether
was removed by rotary evaporation. Bulb-to-bulb distillation (195-
200 °C/0.02 Torr) gave 2 as a colorless oil. The oil was recrystallized
from hot 2-methoxyethanol, giving colorless crystals of 2 (96.28 g,
0.1606 mol, 84.2%). Mp: 123 °C. 1H NMR (300 MHz, CDCl3): δ 1.14
eliminated lithium fluoride to give the 1-germapropa-
diene 1 in approximately 85% conversion. The latter
is stable in ether solution only up to 0 °C, so it was
isolated by crystallization at -20 °C as colorless plates.
The synthetic protocol for 1 is analogous to that used
for preparation of the isostructural silicon compound 4.
In the silicon case, however, the intermediate lithium
compound analogous to 3 is stable up to 0 °C, and so
could be isolated and studied by crystallography. Com-
3
3
3
(d, J HH ) 6.4 Hz, 12H), 1.16 (d, J HH ) 6.4 Hz, 12H), 1.23 (d, J HH
)
6.8 Hz, 12H), 2.87 (sept, 3J HH ) 6.8 Hz, 2H), 3.58 (sept, 3J HH ) 6.6 Hz,
4H), 7.03 (s, 4H), 7.29-7.31 (m, 3H), 7.46-7.49 (m, 2H). 13C NMR (75.6
MHz, CDCl3, 1H decoupled): δ 23.9, 24.6, 24.8, 33.7, 33.8, 34.4, 93.6
(d, 2J CF ) 24.2 Hz), 106.2 (d, 3J CF ) 5.1 Hz), 122.1, 122.8, 128.4, 129.0,
2
131.8 (d, J CF ) 12.7 Hz), 132.0, 151.3, 153.9. 19F NMR (282.2 MHz,
CDCl3, 1H decoupled): δ -6.32. Anal. Calcd for C38H51GeF: C, 76.14;
H, 8.58. Found: C, 75.81; H, 8.80. MS[EI] [m/z (Irel)]: 600 [0.5, M+],
580 [1.1, -HF], 498 [10.2, - H-CC-Ph], 478 [14.5, -F, - H-CC-
Ph, -H], 202 [100, Tip-H].
S0276-7333(98)00152-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/08/1998

2148 Organometallics, Vol. 17, No. 11, 1998
Communications
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1
1). The GedC bond length is 1.783(2) Å. It is of interest
to compare the structure of 1 with that of the exactly
isostructural silicon compound 4. In both compounds
the MdCdC skeleton is nonlinear, but the bending at
the central C atom is much greater in 1 (159.2°) than
in 4 (172.0°). The germanium atom in 1 is also much
more strongly pyramidalized than the silicon atom in
4; the sum of the bond angles at Ge is 348.4° and at Si
is 357.2°. Also, the angle between the plane defined by
C(13)-Ge-C(28) and the vector made by the Ge-C(1)
bond is 147.4°, which is much more bent than the
corresponding angle in 4 (163.8°). The isopropyl group
C(37)-C(39) is disordered and modeled in two orienta-
tions with refined occupancies of 0.420(6) for one set of
atoms and 0.580(6) for the others.
formula
fw
C42H60Ge
637.49
cryst size (mm3)
a (Å)
0.52 × 0.34 × 0.26
31.6357(11)
12.0309(5)
21.9950(10)
90
b (Å)
c (Å)
R (deg)
â (deg)
114.2900(10)
90
γ (deg)
cryst syst
space group
vol. (Å3)
monoclinic
C2/c
7630.3(5)
1.110
Dcalcd (g cm-3
)
Z
8
wavelength (Å)
temp (K)
0.710 73
133(2)
0.828
semiempirical
0.753/0.928
18 608
8989
6938
404
abs coeff (mm-1
abs corr
)
The 13C NMR spectra of 1-silapropadienes and al-
lenes, in general, show characteristically deshielded
central carbon atoms. For 4, the central C atom
resonance lies at +223.6 ppm; in 1,5 the analogous
carbon resonance is found at +235.1 ppm.
An important difference between 1 and 4 is in their
thermal stability in solution. In diethyl ether or hexane
solution, 1 is stable indefinitely at 0 °C but is completely
decomposed after 15 h at 25 °C, whereas 4 is unchanged
in toluene up to 135 °C. Crystalline 1 is more stable,
decomposing only above 90 °C.
min/max trans
no. of reflns collected
no. of indep reflns
no. of obsd reflns
no. of params
restraints
65(disorder)
2.51-29.34
1.026
0.418
-0.383
0.0362
θ range (deg)
goof on F2
largst diff peak (eÅ-3
)
)
largst diff hole (eÅ-3
R1 (%)
wR2 (%)
0.0874
largst and mean D/esd
0.005/0.000
Compound 4, the silicon analogue of 1, was found to
undergo various addition reactions at the SidC bond2.
The reaction chemistry of 1 is currently under investi-
gation.
pound 3 was never detected in the reaction mixture; the
weaker Ge-F bond evidently favors rapid LiF elimina-
tion from 3. Low-temperature elimination of LiF from
R-lithiofluorogermanes has also been observed in the
preparation of the germaphosphaallene3 and in the
synthesis of a germene.7
Ack n ow led gm en t. This work was supported by a
grant from the National Science Foundation.
The structure of 1, determined by single-crystal X-ray
crystallography at -140 °C, is shown in Figure 1 (Table
Su ppor tin g In for m ation Available: Tables giving atomic
coordinates, hydrogen coordinates, anisotropic displacement
parameters, bond lengths, bond angles, and torsion angles and
a figure of the unit cell diagram of 1 (8 pages). Ordering
information is given on any current masthead page.
(7) Couret, C.; Escudie´, J .; Satge´, J .; Lazraq, M. J . Am. Chem. Soc.
1987, 109, 4411.
(8) Chaubon, M. A.; Dittrich, B.; Escudie´, J .; Ramdane, H.; Rana-
ivonjatovo, H.; Satge´, J . Synth. React. Inorg. Met.-Org. Chem. 1997,
27 (4), 519.
OM980152R