New compounds with Ge/Ge and Ge/C multiple bonds

Article abstract of DOI:10.1016/j.jorganchem.2006.05.004

Treatment of GeCl₂ · dioxane with the Grignard reagent RMgBr (R = 2,5-tBu₂C₆H₃) furnishes the tetraaryldigermene R₂Ge{double bond, long}GeR₂ (4). The X-ray structure analysis of 4 reveals a long Ge{double bond, long}Ge double bond of 236.4 pm and the largest trans-bending angles of the substituents (42.6° and 37.2°) observed so far. The reaction of hexa-2,4-diyne with the germylene R₂Ge: (R = 2-tBu-4,5,6-Me₃C₆H) yields red crystals of the acetylene-bridged bis(germaethene) (Me)R₂Ge{double bond, long}C-C{triple bond, long}C-C{double bond, long}GeR₂(Me) 7, the red colour of which indicates conjugation between the two double bonds.

Full text of DOI:10.1016/j.jorganchem.2006.05.004

Journal of Organometallic Chemistry 691 (2006) 3540–3544
www.elsevier.com/locate/jorganchem
q
New compounds with Ge/Ge and Ge/C multiple bonds
*
Bjorn Pampuch, Wolfang Saak, Manfred Weidenbruch
¨
Institut fu¨r Reine und Angewandte Chemie, Universita¨t Oldenburg Carl-von-Ossietzky-Strasse 9-11, D-26111 Oldenburg, Germany
Received 21 March 2006; accepted 3 May 2006
Available online 11 May 2006
Abstract
Treatment of GeCl2 Æ dioxane with the Grignard reagent RMgBr (R = 2,5-tBu2C6H3) furnishes the tetraaryldigermene R2Ge@GeR2
(4). The X-ray structure analysis of 4 reveals a long Ge@Ge double bond of 236.4 pm and the largest trans-bending angles of the sub-
stituents (42.6ꢀ and 37.2ꢀ) observed so far. The reaction of hexa-2,4-diyne with the germylene R2Ge: (R = 2-tBu-4,5,6-Me3C6H) yields
red crystals of the acetylene-bridged bis(germaethene) (Me)R2Ge@C–C„C–C@GeR2(Me) 7, the red colour of which indicates conjuga-
tion between the two double bonds.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Digermene; Bis(germaethene); Conjugation; Molecular structure; Germylene; X-ray structure analysis; Acetylene linked bis(germaethene)
R
C
C
C
C
R + 2 Ar2Ge:
1. Introduction
R
GeAr2
R
The first tetraaryldigermene, a molecule with a Ge@Ge
double bond, was isolated by Masamune et al. almost 25
years ago [2] and unambiguously characterised by X-ray
crystallography two years later [3]. Meanwhile numerous
structurally investigated digermenes with widely varying
Ge@Ge bond lengths and trans-bending angles of the sub-
stituents from the GeAGe vector are known [4]. We now
report, among others, on a further tetraaryldigermene with
an unusual structure.
Similar to the digermenes, compounds with a Ge@C
double bond, the germenes, have been known for a number
of years [5]. In contrast, the synthesis – by addition of
diarylgermylenes to both triple bonds of 1,3-diynes – and
structural characterisation of the acetylene-bridged bis(ger-
maethenes) 1 and 2 were realised only recently [6–8].
C
C
C
C
Ar2Ge
Ar = 2-tBu-4,5,6-Me3C6H
1 R = nBu
2 R = C6H5
On the other hand, the structures of the simplest – with
regard to the diyne – molecules of this type with R = H or
R = CH3 have not yet been determined. Although the
structure of the compound resulting from the addition of
a germylene to tetra-1,3-diyne has not yet been elucidated
on account of its extreme sensitivity, we have now suc-
ceeded in determining the structure of the product of the
corresponding addition of a germylene to hexa-2,4-diyne.
2. Results and discussion
The tetraaryldigermenes prepared to date mostly owe
their stability in the solid state to the presence of two alkyl
groups in the ortho-positions of the aryl groups which effec-
tively shield the digermenes from subsequent reactions. We
have now addressed the question of whether digermenes
q
See [1].
*
Corresponding author. Tel.: +49 441 7983655; fax: +49 441 7983352.
E-mail address: manfred.weidenbruch@uni-oldenburg.de (M. Weiden-
bruch).
0022-328X/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.004

B. Pampuch et al. / Journal of Organometallic Chemistry 691 (2006) 3540–3544
3541
with only one alkyl group in the ortho-positions of the aryl
groups are accessible and what influence this substituent
pattern would have on the structures of the resulting
compounds.
We chose 1,4-di-tert-butylbenzene as a model com-
pound because it furnishes the Grignard compound 3 after
bromination and reaction with magnesium. Reaction of 3
with GeCl2 Æ dioxane gave orange-coloured crystals of the
digermene 4 in acceptable yield. The constitution of 4
was confirmed by X-ray crystallography (Fig. 1).
Preliminary experiments on the reactions of 4 with small
amounts of oxygen or water seemed to indicate that 4
exists, at least in part, in solution as the digermene.
Accordingly, treatment of 4 with water affords the com-
pound 5 which, to the best of our knowledge, represents
the first structurally characterised digermanol (Fig. 2).
R2
Ge
O2
H2O
R2Ge
H
GeR2
OH
4
O
O
Ge Ge
R2
2 GeCl2 · dioxane + 4 RMgBr
R2Ge
GeR2
R2
4
6
3
5
R = 2,5-tBu2C6H3
The Ge–Ge bond length in 5 of 247.6 pm is in the typical
range for Ge–Ge single bonds. Further evidence for the
proposed constitution was provided by the IR spectrum:
absorption bands at 3597 and 2086 cmꢀ1 are characteristic
for Ge–OH and Ge–H vibrations.
The trigerma-1,3-dioxolane 6 (Fig. 3), accessible by the
action of air on 4, possesses an almost planar five-mem-
bered ring (sum of angles: 539.5ꢀ) just like other rings of
this type [12]. Starting from tetramesityldigermene, Baines
et al. [12b] showed that the formation of this ring system
can be rationalised by addition of O2 to the digermene to
The Ge@Ge bond length of 236.4 pm is among the lon-
gest that has been observed in a digermene to date. Even
more unusual are the trans-bending angles of 37.2ꢀ and
42.6ꢀ from the Ge–Ge vector which are larger than the cor-
responding angles in all as yet synthesised digermenes.
This result is surprising since a similar digermene with
2-tert-butyl-4,5,6-trimethylphenyl groups possessing an addi-
tional methyl group in the ortho-positions exhibits a very
short Ge@Ge bond of 225.1 pm and almost planar envi-
ronments around the two germanium atoms in spite of
the increased steric demands [9]. The bonding parameters
determined for 4 again clearly show that a correlation with
the steric requirements of the substituents is hardly possible
[3].
Similarly unanswered is the question of the influence of
the spatial demands of the substituents on the behaviour of
tetraaryldigermenes in solution. While most digermenes
decompose to germylenes in solution, tetrakis(2,4,6-triiso-
propylphenyl)digermene [10] or the 1,2-bis(terphenyl)
digermenes [11] retain their structural integrity in solution.
O1
C15
H1
C29
Ge1
Ge2
C43
C1
Ge2
C43
H2
C1
C29
Ge1
C15
Fig. 2. Molecule of 5 in the crystal (C–H hydrogen atoms and methyl
groups omitted). Ellipsoids are drawn at 50% probability. Selected bond
lengths (pm) and bond angles (ꢀ): Ge(1)–Ge(2) 247.6(1), Ge(1)–C(1)
201.6(2), Ge(1)–C(15) 199.8(2), Ge(2)–C(29) 202.3(1), Ge(2)–C(43)
200.4(2), Ge(1)–O(1) 182.0(3) and C(15)–Ge(1)–C(1) 121.3(1), C(43)–
Ge(2)–C(29) 109.5(1).
Fig. 1. Molecule of 4 in the crystal (hydrogen atoms omitted). Ellipsoids
are drawn at 50% probability. Selected bond lengths (pm) and bond angles
(ꢀ): Ge(1)–Ge(2) 236.43(4), Ge(1)–C(1) 200.2(3), Ge(1)–C(15) 199.4(3),
Ge(2)–C(29) 200.2(2), Ge(2)–C(43) 200.1(3) and C(15)–Ge(1)–C(1)
106.2(1), C(43)–Ge(2)–C(29) 107.0(1).

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B. Pampuch et al. / Journal of Organometallic Chemistry 691 (2006) 3540–3544
C3
C4'
C17
C2
C1
C1'
C2'
C3'
Ge1'
C17'
C71
C29
Ge1
C4
C57
Ge3
Ge2
C43
O2
O1
Ge1
Fig. 4. Molecule of 7 in the crystal (hydrogen atoms omitted). Ellipsoids
are drawn at 50% probability. Selected bond lengths (pm) and bond angles
(ꢀ): C(1)–C(10) 122.8(13), C(1)–C(2) 138.9(9), C(2)–C(3) 152.9(8), Ge(1)–
C(2) 181.9(6), Ge(1)–C(4) 199.7(5), Ge(1)–C(17) 197.6(6) and Ge(1)–C(2)–
C(1) 120.7(4), Ge(1)–C(2)–C(3) 121.4(5), C(1)–C(2)–C(3) 117.9(5).
C15
C1
Fig. 3. Molecule of 6 in the crystal (hydrogen atoms and methyl group
omitted). Ellipsoids are drawn at 50% probability. Selected bond lengths
(pm) and bond angles (ꢀ): Ge(1)–O(1) 178.5(3), Ge(1)–O(2) 178.6(3),
Ge(2)–O(1) 180.3(3), Ge(2)–Ge(3) 251.3(1), Ge(3)–O(2) 178.8(3) and
O(1)–Ge(1)–O(2) 101.9(1), Ge(1)–O(1)–Ge(2) 125.3(1), O(1)–Ge(2)–
Ge(3) 93.1(1), O(2)–Ge(3)–Ge(2) 95.2(1), Ge(1)–O(2)–Ge(3) 124.0(2).
2 R2Ge:
R2Ge
GeR2
R = 2-tBu-4,5,6-Me3C6H
CH3
GeR2
CH3
C
C
C
C
(CH3
C
C
) + 2 R2Ge:
2
R2Ge
7
form a digerma-1,2-dioxetane with subsequent insertion of
a germylene into the O–O single bond.
The X-ray crystal structure analysis of 7 also exhibits
major similarities with that of 1. The bond lengths of
138.9 pm for the C1–C2 single bond and of 122.8 pm for
the formal C1–C10 triple bond can be considered as further
evidence for the conjugation in this molecule.
Although digermenes and simple germenes have been
known for many years, the synthesis and structural charac-
terisation of acetylene-bridged bis(germaethenes) were rea-
lised only recently [6,7]. The conjugation between the
multiple bonds of these molecules is reflected principally
in the electronic spectra which show bands shifted batho-
chromically by more than 100 nm in comparison to those
of the simple germenes. These compounds are prepared
by the addition of a germylene to 1,4-diphenyl- and 1,4-
di-nbutylbuta-1,3-diynes. Earlier attempts to achieve the
addition of a germylene to hexa-2,4-diyne as the as yet sim-
plest diacetylene gave rise to red solutions that could be
characterised by NMR spectroscopy but from which no
compound could be isolated [13]. On repetition of this reac-
tion, we obtained red crystals of the compound 7 which
was unambiguously characterised by, among others, an
X-ray crystal structure analysis (Fig. 4).
Apart from a somewhat increased sensitivity towards air
and moisture, compound 7 hardly differs from the 1,4-di-
nbutyl compound 1. The electronic spectrum of the dark
red solution of 7 in toluene shows the band at longest
wavelength at 500 nm (e = 8000), which barely differs from
that of 1 (k = 518 nm). In contrast, the blue-violet diphenyl
derivative 2 shows the corresponding absorption at
595 nm, indicating that the two phenyl groups participate
in the conjugation.
3. Experimental
3.1. General procedure
All reactions were carried out under an atmosphere of
1
dry argon. The H and 13C NMR spectra were obtained
on a Bruker AM 300 or a Bruker ARX 500 spectrometer
using C6D6 as solvent. The IR spectra were recorded on
a Bruker Vector 22 spectrometer. The UV/Vis spectra were
obtained on a ComSpec spectrometer with fibre optics. Ele-
mental analyses were performed by Analytische Laborat-
orien, D-51779 Lindlar, Germany.
3.2. Tetrakis(2,5-di-tert-butylphenyl)digermene (4)
To a stirred solution of ꢁ27 mmol of 2,5-di-tert-butyl-
phenylmagnesium bromide (3) {prepared from 1-bromo-
2,5-di-tert-butylbenzene [14] (7.35 g, 27.3 mmol) and a
large excess of magnesium turnings (2.5 g, 0.1 mol) in
40 ml of THF} at ꢀ 40 ꢀC, a solution of germanium(II)

B. Pampuch et al. / Journal of Organometallic Chemistry 691 (2006) 3540–3544
3543
chloride Æ dioxane (3.16 g, 13.6 mmol) in a mixture of THF
(40 ml) and 1,4-dioxane (10 ml) was added dropwise. The
mixture was then allowed to warm to room temperature
and the solvents were removed by vacuum distillation.
The residue was extracted with 200 ml of n-hexane. The
resulting dark red solution was concentrated to a volume
of 100 ml and cooled to ꢀ30 ꢀC to furnish 3.41 g (56%
(s, 3H, Ar–CH3), 3.30 (s, 3H, Ar–CH3), 7.19 (s, 2H,
ArH). 13C NMR (75 MHz): d 16.59 (Ar–CH3), 16.74
(Ar–CH3). 21.17 (Ar–CH3), 21.28 (Ar–CH3), 24.29 (Ar–
CH3), 24.70 (Ar–CH3), 32.65 [C(CH3)3], 32.86 [C(CH3)3],
33.68 (C–CH3), 36.67 [C(CH3)3], 36.85 [C(CH3)3], 111.15
(C„C), 116.92 (Ge@C), 126.48 (Ar–CH), 126.81 (Ar–
CH), 133.20, 133.52, 136.78, 137.11, 138.60, 139.19,
142.32, 143.29, 151.71, 152.17 ppm. UV/Vis: kmax (e) 500
(8000) nm. C58H82Ge2 (924.55) Anal. Calc.: C, 75.35; H,
8.94. Found: C, 74.89; H, 8.97%. Single crystals suitable
for X-ray diffraction analysis were obtained from n-pen-
tane at 4 ꢀC.
1
yield) of a red solid of 4; m.p. 135 ꢀC (dec.). H NMR
(500 MHz): d 1.31 [s, 9H, C(CH3)3], 1.38 [s, 9H,
3
4
C(CH3)3], 7.20 (dd, 1H, J = 8.32 Hz, J = 2.19 Hz), 7.34
(d, 1H, 3J = 8.34 Hz), 8.30 (d, 1H, 4J = 2.06 Hz) ppm.
13C NMR (75 MHz): d 31.57 (CH3), 33.69 (CH3), 34.32
[C(CH3)3], 36.97 [C(CH3)3], 125.24, 125.83, 126.93,
146.59, 146.79, 152.86 ppm. UV/Vis: kmax (e) 425
(4000) nm. Anal. Calc. for C56H84Ge2 (902.55): C, 74.52;
H, 9.38. Found: C, 73.94; H, 9.19%. Single crystals suitable
for X-ray diffraction analysis were obtained from n-hexane
at ꢀ4 ꢀC.
3.4. Crystallographic analyses
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 were performed with a Stoe
IPDS area detector at 153 K using graphite-monochro-
mated Mo Ka radiation (71.073 pm). The structures were
solved by direct phase determination and refined by full-
matrix least-squares techniques against F2 with the
SHELXL-97 program system [15]. Hydrogen atoms were
placed in the calculated positions, and the other atoms
were refined anisotropically. Full details of the structure
determinations (except structure factors) have been depos-
ited with the Cambridge Crystallographic Data Centre as
CCDC 602 042 (7), CCDC 602 043 (6) CCDC 602 044
(5), and CCDC 602 045 (4). Copies of this information
may be obtained free of charge from The Director, CCDC,
Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223
336 033; e-mail: deposit@ccdc.ac.uk or www: http://
www.ccdc.cam.ac.uk).
3.3. 2,5-Bis[bis(2-tert-butyl-4,5,6-
trimethylphenyl)germylene]hex-3-yne (7)
To a solution of bis(2-tert-butyl-4,5,6-trimethylphenyl)-
germylene (0.71 g, 1.68 mmol) in toluene (60 ml) was added
hexa-2,4-diyne (0.20 g, 2.56 mmol) The colour of the solu-
tion changed from orange to dark red. The mixture was
stirred for 3 days at room temperature. After this time
the solvent was removed by vacuum distillation and the
residue redissolved in n-hexane to furnish 0.56 g (72%
yield) of a red solid of 7. m.p. 80 ꢀC (dec.). 1H NMR
(300 MHz): d 1.37 [s, 9H, C(CH3)3], 1.41 [s, 9H, C(CH3)3],
1.55 (s, 3H, CH3), 2.01 (s, 3H, Ar–CH3), 2.04 (s, 3H, Ar–
CH3), 2.08 (s, 3H, Ar–CH3), 2.14 (s, 3H, Ar–CH3), 2.18
Table 1
Crystallographic data for compounds 4–7
Compound
4
5a
6b
7
Empirical formula
Formula weight
Crystal dimensions (mm)
Space group
Crystal system
a (pm)
b (pm)
c (pm)
a (ꢀ)
b (ꢀ)
C
902.41
56H84Ge2
C115H117Ge4O
1865.93
C93H147Ge3O2
1514.88
0.40 · 0.18 · 0.08
Pbcn
C63H94Ge2
996.56
0.35 · 0.25 · 0.13
P21/c
Monoclinic
2142.29(7)
1103.76(3)
2302.86(5)
0.35 · 0.24 · 0.20
0.20 · 0.09 · 0.08
ꢀ
ꢀ
P1
P1
Triclinic
1565.11(6)
1694.58(8)
2161.18(7)
99.229(5)
105.723(4)
91.150(5)
5433.8(4)
2
Orthorhombic
4430.20(12)
1959.77(4)
2041.84(4)
Triclinic
1027.55(7)
1070.47(10)
1332.37(11)
89.800(11)
89.826(9)
85.892(10)
1461.8(2)
1
103.724(3)
c (ꢀ)
Volume (·106 pm3)
Z
5289.8(3)
4
1.169
52
17727.6(7)
8
1.054
48
l (mmꢀ1
2hmax
)
1.140
52
1.063
52
Total number of reflections
Observed reflections
R (I > 2r(I))
wR2 (all data)
GOF (F2)
45495
6554
0.0354
0.0760
0.850
68128
13901
0.0442
0.1078
118033
10210
0.0521
0.1341
1.008
18001
3714
0.0756
0.2045
0.923
1.034
a
1
2
The digermanol co-crystallised with 4 and C6H14
.
b
Compound 6 crystallises with 1.5 C6H14
.

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B. Pampuch et al. / Journal of Organometallic Chemistry 691 (2006) 3540–3544
[7] F. Meiners, D. Haase, R. Koch, W. Saak, M. Weidenbruch,
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¨
Financial support of our work by the Deutsche Fors-
chungsgemeinschaft is gratefully acknowledged.
Ber./Recueil 130 (1997) 735.
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