Cycloaddition reactions of an acetylene-linked bis(germaethene)

Article abstract of DOI:10.1021/om020320m

3,5-Di-tert-butyl-1,2-benzoquinone reacts with the acetylene-linked bis(germaethene) Ar₂Ge=C(R)-C≡C-C(R)=GeAr₂, R = C₆H₅, Ar = 2-tBu-4,5,6-Me₃C₆H (4), in a [4+2] fashion to furnish the sterically crowded product 5 of 2-fold cycloaddition to the Ge=C bonds. The reaction of 4 with 1,2-dicyanoethylene proceeds differently, namely, by [2+4] cycloaddition of one of the C≡N bonds to the Ge=C and C≡C bonds, followed by a [2+2] cycloaddition of the remaining Ge=C bond to the newly formed C=C bond to give the bicyclic compound 6. An unprecedented C-H activation of a tert-butyl and an aryl C-H bond leads finally to the hexacyclic compound 8 via the tetracyclic product 7. Cyanogen gas reacts similarly by [2+4] and [2+2] cycloadditions to furnish the bicyclic compound 9. In this case, no C-H addition to the endocyclic C=N bond is observed.

Full text of DOI:10.1021/om020320m

3990
Organometallics 2002, 21, 3990-3995
Cycloa d d ition Rea ction s of a n Acetylen e-Lin k ed
Bis(ger m a eth en e)1,2
Frank Meiners, Detlev Haase, Rainer Koch, Wolfgang Saak, and
Manfred Weidenbruch*
Fachbereich Chemie, Universita¨t Oldenburg, Carl-von-Ossietzky-Strasse 9-11,
D-26111 Oldenburg, Germany
Received April 22, 2002
3,5-Di-tert-butyl-1,2-benzoquinone reacts with the acetylene-linked bis(germaethene)
Ar2GedC(R)-CtC-C(R)dGeAr2, R ) C6H5, Ar ) 2-tBu-4,5,6-Me3C6H (4), in a [4+2] fashion
to furnish the sterically crowded product 5 of 2-fold cycloaddition to the GedC bonds. The
reaction of 4 with 1,2-dicyanoethylene proceeds differently, namely, by [2+4] cycloaddition
of one of the CtN bonds to the GedC and CtC bonds, followed by a [2+2] cycloaddition of
the remaining GedC bond to the newly formed CdC bond to give the bicyclic compound 6.
An unprecedented C-H activation of a tert-butyl and an aryl C-H bond leads finally to the
hexacyclic compound 8 via the tetracyclic product 7. Cyanogen gas reacts similarly by [2+4]
and [2+2] cycloadditions to furnish the bicyclic compound 9. In this case, no C-H addition
to the endocyclic CdN bond is observed.
Sch em e 1
In tr od u ction
Since the discovery of thermally stable germaethenes,
compounds with a Ge-C double bond, the structures of
five representatives have been unambiguously eluci-
dated.3-7 Common features of these compounds are the
short Ge-C double bond lengths of between 1.77 and
1.84 Å and the shielding of the two participating atoms
by bulky substituents that effectively prevents further
reactions of the multiple bond system. Recently, we
allowed the germylene 2, which is formed in solution
from the digermene 1,8,9 to react with 1,3-diynes and
obtained the acetylene-linked bis(germaethenes) 3 and
4; the structure of 3 was confirmed by an X-ray crystal
structure analysis.10 The conjugation between the mul-
tiple bonds in 3 and 4 is reflected less in the bond
lengths but more so in the electronic spectra, in which
the absorptions at longest wavelengths experience ba-
thochromic shifts of 100 and 150 nm, respectively, in
comparison to those of the yellow or orange germa-
ethenes.
We now report on the crystal structure of 4 and its
cycloaddition reactions, which, in part, follow a very
unusual course.
Resu lts a n d Discu ssion
The most important features to distinguish between
the acetylene-linked bis(germaethenes) 3 and 4 are their
colors and, accordingly, their absorptions at longest
wavelength in their electronic spectra. While the dark
red dialkyl compound 3 shows an absorption at 518 nm,
the dark blue diaryl compound 4 exhibits a marked red-
shift to furnish an absorption at 595 nm. This suggests
that the two phenyl groups are also involved in the
conjugation.
Crystals of 4 suitable for X-ray structure analysis
(Figure 1) were obtained from a THF solution and
contained five molecules of the solvent per molecule of
product. The more extensive conjugation of the multiple
bonds in 4 as compared to that of 3 has no influence on
the bond lengths and angles of the former compound:
only slight differences between the two molecules are
found. Compound 4, obtained in almost quantitative
yield, reacts differently to the simple germaethenes.
Although the latter undergo smooth cycloaddition reac-
tions with phosphaalkynes11 or with 2,3-dimethylbuta-
diene,12,13 compound 4 does not react with these part-
(1) Compounds of Germanium, Tin, and Lead. Part 38. Part 37:
Scha¨fer, H.; Saak, W.; Weidenbruch, M. Angew. Chem. 2000, 112, 3847;
Angew. Chem., Int. Ed. 2000, 39, 3703.
(2) Dedicated to Professor Gottfried Huttner on the occasion of his
65th birthday.
(3) Meyer, H.; Baum, G.; Massa, W.; Berndt, A. Angew. Chem. 1987,
99, 790; Angew. Chem., Int. Ed. Engl. 1987, 26, 798.
(4) Lazraq, M.; Escudie´, J .; Couret, C.; Satge´, J .; Dra¨ger, M.;
Dammel, R. Angew. Chem. 1988, 100, 885; Angew. Chem., Int. Ed.
Engl. 1988, 27, 828.
(5) Tokitoh, N.; Kishikawa, K.; Okazaki, R. J . Chem. Soc., Chem.
Commun. 1995, 1425.
(6) Stu¨rmann, M.; Saak, W.; Weidenbruch, M.; Berndt, A.; Schesch-
kewitz, D. Heteroat. Chem. 1999, 10, 554.
(7) Meiners, F.; Saak, W.; Weidenbruch, M. Chem. Commun. 2001,
215.
(8) Weidenbruch, M.; Stu¨rmann, M.; Kilian, H.; Pohl, S.; Saak, W.
Chem. Ber. 1997, 130, 735.
(9) Della Bona, M. A.; Cassani, M. C.; Keates, J . M.; Lawless, G.;
Lappert, M. F.; Stu¨rmann, M.; Weidenbruch, M. J . Chem. Soc., Dalton
Trans. 1998, 1187.
(10) Meiners, F.; Saak, W.; Weidenbruch, M. Organometallics 2000,
19, 2835.
10.1021/om020320m CCC: $22.00 © 2002 American Chemical Society
Publication on Web 08/16/2002

Acetylene-Linked Bis(germaethene)
Organometallics, Vol. 21, No. 19, 2002 3991
F igu r e 1. Molecule of 4 in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and bond angles (deg): Ge(1)-C(2) )
1.840(4), C(1)-C(2) ) 1.428(5), C(1)-C(1a) ) 1.205(7), Ge-
(1)-C(9) ) 1.991(3), Ge(1)-C(22) ) 1.978(4), C(2)-C(1)-
C(1a) ) 177.6(3), C(1)-C(2)-Ge(1) ) 116.4(3), C(2)-Ge(1)-
C(9) ) 119.32(16), C(2)-Ge(1)-C(22) ) 117.56(15), C(9)-
Ge(1)-C(22) ) 123.11(14).
F igu r e 2. Molecule of 5 in the crystal (hydrogen atoms
and tert-butyl groups are omitted for clarity). Ellipsoids are
drawn at 50% probability. Selected bond lengths (Å) and
angles (deg): Ge(1)-C(2) ) 2.086(3), C(1)-C(2) ) 1.472-
(4), C(1)-C(1a) ) 1.196(5), Ge(1)-C(23) ) 2.022(3), Ge-
(1)-C(36) ) 2.010(3), Ge(1)-O(1) ) 1.8360(19), C(2)-C(1)-
C(1a) ) 175.38(19), C(1)-C(2)-Ge(1) ) 116.31(19), C(23)-
Ge(1)-C(36) ) 122.34(11), C(3)-C(2)-O(2) ) 104.9(2).
Sch em e 2
ners even under harsher conditions. In contrast, 4
participates in mostly rapid reactions with electron-poor
multiple bond systems. For example, its reaction with
two molecules of 3,5-di-tert-butyl-1,2-benzoquinone pro-
ceeds through [4+2] cycloadditions at both Ge-C double
bonds to furnish the acetylene-linked product 5.
The X-ray crystal structure analysis of the cycload-
duct 5 (Figure 2) clearly reveals the steric overcrowding
of the molecule in the form of longer than usual bond
lengths14 and, in part, by widened bond angles.
While the Ge-C double bonds of 4 behave as ene
components toward the diheterodiene, the compound
reacts with one of the C-N triple bonds of 1,2-dicya-
noethene as a 4π-electron donor to form initially an
unsaturated six-membered ring. However, this is not
stable on account of the cumulated C-C double bonds
and undergoes a spontaneous [2+2] cycloaddition of the
second Ge-C double bond to one of the cumulated C-C
double bonds to afford the bicyclic compound 6.
The X-ray crystallographic analysis of 6 (Figure 3)
provided an unexpected result: the isomeric compound
7 (Figure 4) was observed in the crystal together with
compound 6. Presumably, the exocyclic acrylonitrile
increment of 6 is able to activate a nonpolar C-H bond
of a tert-butyl methyl group to such an extent that an
addition to the N-C double bond occurs to furnish the
tetracyclic compound 7.
F igu r e 3. Molecule of 6 in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and angles (deg): Ge(1)-C(8) ) 2.033(4),
C(8)-C(9) ) 1.475(6), C(9)-C(10) ) 1.355(6), C(10)-Ge-
(1) ) 2.010(4), N(1)-C(17) ) 1.238(9), C(8)-Ge(1)-C(10)
) 69.53(18), C(17)-C(18)-C(19) ) 123.5(8), C(18)-C(19)-
C(20) ) 122.1(9), Ge(2)-N(1)-C(17) ) 125.0(4).
A further X-ray crystallographic analysis performed
to substantiate the above observation again furnished
a surprising result. In addition to 7, the also isomeric
compound 8 was observed. In this case an ortho-phenyl
C-H bond of low polarity is activated to such an extent
that an addition to the C-C double bond of the exocyclic
acrylonitrile unit takes place to afford the hexacyclic
product 8. Although such cyanoethylations15 are not
uncommon, they usually require the presence of polar
bonds. Each of the three isomers crystallizes with a
(11) Lazraq, M.; Escudie´, J .; Couret, C.; Bergstra¨sser, U.; Regitz,
M. J . Chem. Soc., Chem. Commun. 1993, 569.
(12) Couret, C.; Escudie´, J .; Satge´, J .; Lazraq, M. J . Am. Chem. Soc.
1987, 109, 4411.
(13) Anselme, G.; Escudie´, J .; Couret, C.; Satge´, J . J . Organomet.
Chem. 1991, 403, 93.
(14) Baines, K. M.; Stibbs, W. G. Coord. Chem. Rev. 1995, 145, 157.
(15) For a review, see: Patai, S.; Rappoport, Z. In The Chemistry of
Alkenes; Patai S., Ed.; Wiley: London, 1964; Vol. 1, p 469.

3992 Organometallics, Vol. 21, No. 19, 2002
Meiners et al.
F igu r e 6. Molecule of 9 in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and angles (deg): Ge(1)-C(8) ) 2.049(3),
C(8)-C(9) ) 1.489(5), C(9)-C(10) ) 1.355(5), C(10)-Ge-
(1) ) 2.015(3), N(1)-C(17) ) 1.279(4), N(1)-Ge(2) ) 1.910-
(3), C(18)-N(2) ) 1.150(5), C(8)-Ge(1)-C(10) ) 69.78(13),
C(17)-N(1)-Ge(2) ) 119.4(2), N(2)-C(18)-C(17) ) 176.6-
(4).
F igu r e 4. Molecule of 7 in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and angles (deg): Ge(1)-C(8) ) 2.040(3),
C(8)-C(9) ) 1.469(4), C(9)-C(10) ) 1.359(5), C(10)-Ge-
(1) ) 2.004(3), C(19)-C(20) ) 1.4703(10), C(20)-N(2) )
1.1503(10), C(8)-Ge(1)-C(10) ) 69.43(13), C(17)-C(18)-
C(19) ) 123.2(16), C(18)-C(19)-C(20) ) 122.4(17).
Sch em e 3
tive of a 1:1 adduct of the type 6 of the starting
materials. However, the reaction proceeds more rapidly
and furnishes a pure final product compared to the
reaction of 4 with dicyanoethylene. The X-ray crystal-
lographic analysis confirmed the constitution deduced
from the NMR data and showed the product to be
compound 9. In analogy to the reaction of 4 with
dicyanoethene, this sequence should also start with the
[2+4] cycloaddition of one CN group to the C-C triple
bond and one of the Ge-C double bonds, followed by
the spontaneous [2+2] cycloaddition of the second Ge-C
double bond to the newly formed C-C double bond with
formation of compound 9. In contrast to 6, which
undergoes a C-H addition to the endocyclic CdN bond,
the bicyclic compound 9 is now the final product of the
reaction sequence.
To gain more insight into the unusual rearrangement
(Scheme 3), we employed quantum-mechanical methods.
The size of the molecules in question prohibit the use
of suitable ab initio or density functional theory methods
without significant simplifications. Therefore, we de-
cided to apply the semiempirical method PM3, which
is the only Hamiltonian with a parametrization for
germanium,16,17 and to verify its reliability.
F igu r e 5. Molecule of 8 in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and angles (deg): Ge(1)-C(8) ) 2.040(3),
C(8)-C(9) ) 1.469(4), C(9)-C(10) ) 1.359(5), C(10)-Ge-
(1) ) 2.004(3), C(10)-C(11) ) 1.482(4), C(16)-C(18) )
1.537(5), N(1)-C(57) ) 1.471(5), C(8)-Ge(1)-C(10) )
69.43(13), C(16)-C(18)-C(17) ) 113.2(4), N(2)-C(20)-
C(13) ) 179.0(9).
molecule of dicyanoethene and an additional molecule
of n-hexane that serves merely to stabilize the lattices
and does not enter into any interactions with the
germanium atoms.
We do not know what the driving force for the 2-fold
C-H activation of the predominately nonpolar bonds
that leads from the bicyclic compound 6 to the tetracy-
clic species 7 and finally to the hexacyclic compound 8
is. One possibility could be the steric overcrowding in
the molecules 6 and 7, which forces the C-H bonds to
approach the double bonds so closely that new, pre-
dominately strain-free six-membered rings form in order
to reduce these interactions.
The primary step in the reaction of 4 with cyanogen
seems to proceed similarly since the analytical data
(16) Stewart, J . J . P. J . Comput. Chem. 1989, 10, 209.
(17) Stewart, J . J . P. J . Comput. Chem. 1991, 12, 320.
1
together with the H and 13C NMR spectra are indica-

Acetylene-Linked Bis(germaethene)
Organometallics, Vol. 21, No. 19, 2002 3993
Ta ble 1. Com p a r ison of Selected P M3-Ca lcu la ted
a n d Obser ved Bon d Len gth s (Å)
Ta ble 2. Com p a r ison of Ca lcu la ted Rela tive
En er gies (k ca l m ol-1) for th e Mod el Rea ction (see
text for d eta ils)
4
6
7
8
PM3
B3LYP/6-31G(d)
X-ray PM3 X-ray PM3 X-ray PM3 X-ray PM3
4 + NCCHdCHCN
0.0
-30.8
-68.4
0.0
-35.4
-83.5
Ge1-N 1.840 1.787 1.878 1.863 1.878 1.866 1.882 1.874
Ge1-C1 1.978 1.885 1.994 1.954 1.994 1.927 1.987 1.939
Ge1-R1 1.991 1.900 2.018 1.956 2.018 1.918 2.022 1.922
Ge1-R2 1.428 1.396 1.954 1.916 2.100 1.903 1.998 1.906
C1-C2 1.205 1.208 1.352 1.317 1.352 1.314 1.353 1.317
primary product
6
investigate the complete sequence leading to the unex-
pected product 8 (Scheme 3). The same restrictions as
for the geometry comparison apply. The first step is the
[2+4] cycloaddition of a CN group to the CC triple bond
of 4 with a barrier of about 20 kcal mol-1. This primary
product then undergoes a spontaneous [2+2] cycload-
dition to the isoenergetic structure 6, for which no
transition state could be localized. From a thermody-
namical point of view, the sequence is favorable, since
structure 8 is the most stable molecule. It is 78 kcal
mol-1 lower in energy than the starting molecules (7,
-58 kcal mol-1; 6, -51 kcal mol-1). Of particular
interest in the light of the unexpected C-H activations
are the two transition states connecting 6 to 7 and 7 to
8, respectively. The activation energy required for the
step from the bicyclic compound 6 to the tetracyclic 7 is
calculated to be around 90 kcal mol-1, which is slightly
lower than the barrier for the C-H addition of ethane
to N-ethylidenemethanamine (102 kcal mol-1).18 The
second C-H reaction possesses an activation energy of
less than 50 kcal mol-1, so that it will proceed much
more readily. The model character of the calculation
however does not fully account for the enormous steric
strain in the molecules 6-8, so that the derived activa-
tion barriers may be estimated as too high.
C2-C3
C3-C4
C4-N
1.474 1.471 1.474 1.469 1.468 1.457
1.425 1.469 1.566 1.497 1.481 1.491
1.236 1.287 1.518 1.485 1.482 1.484
2.036 2.002 2.036 2.005 2.037 2.022
2.476 2.479 2.476 2.481 2.480 2.460
1.357 1.351 1.357 1.351 1.362 1.355
2.007 1.994 2.007 1.986 2.002 1.971
2.020 1.884 2.020 1.885 2.025 1.885
C2-Ge2
C3-Ge2
C3-C5
C5-Ge2
Ge2-R1
Sch em e 4
Sch em e 5
Exp er im en ta l Section
A comparison of selected bond lengths of the calcu-
lated geometries with those of 4 and 6-8 is given in
Table 1, where the only modification is the use of three
phenyl and one 2-tert-butylphenyl group in the theoreti-
cal study (Scheme 5) instead of the four 2-tert-butyl-
4,5,6-trimethylphenyl groups (Ar in Scheme 1).
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.
The H and 13C NMR spectra were obtained on a Bruker ARX
1
500 spectrometer using C6D6 as solvent. Elemental analyses
were performed by Analytische Laboratorien, D-51789 Lindlar,
Germany. Compound 4 was prepared according to the litera-
ture procedure.10 Single crystals of 4 were grown from THF
at room temperature.
It can be clearly seen that the PM3-derived bond
lengths are in good agreement with the experimental
data. The only discrepancies are the Ge-R1 distances,
which come out slightly too short. This however can be
attributed to the smaller phenyl groups used in the
calculations so that the steric repulsion is reduced and
the Ge-C(phenyl) contacts are more pronounced.
In contrast to the above structural discussion, where
experimental data are available to assess the quality
of the PM3 calculation, it is necessary to employ ab
initio or DFT calculations to get information on the
validity of PM3-derived relative energies. For compu-
tational efficiency, both R1 and R2 were replaced by
methyl groups as well as the phenyl substituents at C1
by hydrogen atoms. The reaction of 4 with NCCHd
CHCN to give a primary cycloaddition product and
subsequently 6 was investigated with the B3LYP/6-31G-
(d) method-basis set combination and PM3. The DFT
calculation confirmed all structures to have singlet
ground states, and the calculated relative energies agree
well with the semiempirical results (Table 2).
5,7-Di-ter t-bu tyl-2,2-bis(6-ter t-bu tyl-2,3,4-tr im eth ylph e-
n yl)-3-{[5,7-d i-ter t-bu tyl-2,2-bis(6-ter t-bu tyl-2,3,4-tr im eth -
ylp h en yl)-3-p h en yl-2,3-d ih yd r o-1,4,2-ben zod ioxa ger m in -
3-yl]e t h yn yl}-3-p h e n yl-2,3-d ih yd r o-1,4,2-b e n zod ioxa -
ger m in e (5). To a solution of the bisgermaethene 4 (ca. 0.35
mmol), prepared from the digermene 1 (0.302 g, 0.36 mmol)
and 1,4-diphenylbuta-1,3-diyne (0.071 g, 0.35 mmol) in toluene
(40 mL), was added 5,7-di-tert-butyl-1,2-benzoquinone (0.155
g, 0.70 mmol) with stirring. The color of the solution changed
immediately from dark blue to colorless. The solution was
concentrated to a volume of 20 mL and cooled to -20 °C for
several days to furnish 0.380 g (84% yield) of a colorless solid
of 5: mp 275-277 °C; 1H NMR δ 0.38 (s, 6 H, CH3), 0.63 (s, 9
H, tBu), 0.85 (s, 6 H, CH3), 0.88 (s, 9 H, tBu), 0.90 (s, 6 H,
CH3), 1.22 (s, 36 H, tBu), 1.56 (s, 9 H, tBu), 1.73 (s, 9 H, tBu),
1.98 (s, 3 H, CH3), 2.04 (s, 3 H, CH3), 2.08 (s, 3 H, CH3), 2.10
(s, 3 H, CH3), 2.57 (s, 3 H, CH3), 2.71 (s, 3 H, CH3), 6.93-7.45
(m, 18 H, Ar-H). Owing to the low solubility of 5, a 13C NMR
spectrum could not be obtained. Anal. Calcd for C96H126
-
Ge2O4: C, 77.43; H, 8.53. Found: C, 77.61; H, 8.48. Single
crystals suitable for X-ray diffraction analysis were obtained
from benzene at room temperature.
From the above results, we can conclude that PM3
appears to be suitable for the study of the systems
presented in this work, and it therefore is used to
(18) Koch, R. Unpublished results.

3994 Organometallics, Vol. 21, No. 19, 2002
Ta ble 3. Cr ysta llogr a p h ic Da ta for 4, 5, 6/7,a 7/8,a a n d 9
Meiners et al.
4
5
6/7
7/8
9
empirical formula
fw
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
C
68H86Ge2‚5 THF
C96H126Ge2O4‚2C6H6 C72H88Ge2N2‚C4H2N2‚C6H14 C72H88Ge2N2‚C4H2N2‚C6H14 C70H86Ge2N2‚C6H14
1409.07
19.2928(10)
9.5428(3)
23.0232(10)
90
110.350(5)
90
3974.2(3)
2
1645.36
19.4916(3)
19.4916(39
50.1999(12)
90
1290.87
20.5379(9)
17.6749(5)
21.9050(9)
90
1290.87
20.5938(8)
17.5927(5)
21.9977(8)
90
1186.76
11.5069(5)
16.0706(8)
19.6696(14)
75.763(7)
79.852(7)
75.474(5)
3387.4(3)
2
90
90
109.883(5)
90
110.377(4)
90
19072.1(16)
8
7477.6(5)
4
7471.0(5)
4
d (calcd)
1.178
1.146
1.147
1.148
1.164
(g cm-3
)
cryst size
(mm)
0.34 × 0.31 × 0.22 0.40 × 0.31 × 0.30
0.25 × 0.13 × 0.10
0.50 × 0.26 × 0.19
0.31 × 0.23 × 0.17
cryst syst
space group
2θmax (deg)
no. of rflns measd 28 840
no. of unique rflns 7562
monoclinic
P2/n
52
tetragonal
I41/a
52
71 021
9255
0.680
monoclinic
P21/n
52
60 080
14 290
0.848
monoclinic
P21/n
52
60 330
14 287
0.848
triclinic
P1h
52
40 991
12 115
0.929
lin abs
0.806
coeff (mm-1
)
no. of params
R (I >2σ(I))
wR2 (all data)
GOF (F2)
438
478
641
736
683
0.0597
0.1679
0.953
0.0487
0.1286
0.977
0.0584
0.1560
0.866
0.0483
0.1352
0.898
0.0479
0.1188
0.924
a
For explanations, see text.
(Z)-3-[4,4,7,7-Tetr a k is(6-ter t-bu tyl-2,3,4-tr im eth ylp h e-
n yl)-5,8-d ip h en yl-3-a za -4,7-d iger m a b icyclo[4.2.0]oct a -
1(8),2,5-tr ien -2-yl]-2-p r op en n itr il (6), (E)-3-[10,10,12-Tr is-
(6-ter t-bu tyl-3,4,5-tr im eth ylph en yl)-1,2,3,5,5-pen tam eth yl-
9,11-d ip h e n yl-5,8,10,12-t e t r a h yd r o-6H -ge r m e t o[2′,3′:
4,5][1,2]a za ger m in o[2,1-a ][2,1]b en za za ger m in -8-yl]-2-
pr open n itr il (7), an d [5,7,7-Tr is(6-ter t-bu tyl-2,3,4-tr im eth -
ylphenyl)-2,3,4,15,15-pentamethyl-6-phenyl-5,7,12,12a,14,15-
h exa h yd r o[1,2]a za ger m in o[1,2-a ]ben zo[g]ger m eto[2,3,4-
d e][1,2]ben za za ger m in -12-yl]a ceton itr ile (8). To a suspen-
sion of 1 (0.68 g, 0.80 mmol) in n-hexane (80 mL) was added
1,4-diphenylbuta-1,3-diyne (0.163 g, 0.8 mmol), and the mix-
ture was stirred for 4 days at room temperature. After this
time dicyanoethylene (0.126 g, 1.6 mmol) was added and the
stirring continued for 2 days. After filtration, the solution was
concentrated to a volume of 40 mL and cooled at -20 °C. After
several months, orange crystals (0.410 g, 51% yield) of the
isomers 6-8 were isolated: mp > 175 °C. Since a separation
of the isomers was not possible, reasonable spectral data could
not be obtained. Anal. Calcd for C72H88Ge2N2‚NCCHCHCN:
C, 75.77; H, 7.53; N, 4.65. Found: C, 75.77; H, 7.75; N, 4.46.
Single crystals suitable for X-ray diffraction analysis were
grown from n-hexane at room temperature.
(m, 14 H, Ar-H); 13C NMR δ 14.28, 15.36, 15.91, 20.87, 20.99,
21.08, 22.99, 26.26, 27.19, 31.90, 32.61, 32.91, 33.57, 33.95,
34.12, 37.33, 114.79, 126.79, 127.80, 128.95, 133.09, 136.52,
136.73, 141.26, 141.78, 152.67, 153.14, 161.87, 164.37, 167.78,
176.39. Anal. Calcd for C70H86Ge2N2: C, 76.39; H, 7.88; N, 2.55.
Found: C, 76.09; H, 8.08; N, 2.66.
Cr ysta llogr a p h ic An a lyses. Crystal and numerical data
of structure determinations are given in Table 3. 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.20 Hydrogen atoms were
placed in the calculated positions, and the other atoms were
refined anisotropically. The carbon atoms C11-C16 and C18-
C20 as well as the nitrogen atom N2 of 6 and 7 were refined
isotropically. The solvent molecules of 6/7 and 7,8 are disor-
dered and were refined on two positions with occupancy factors
of 0.5 each. The carbon atoms C58-C70 of 9 are disordered
and were refined on two positions with occupancy factors of
0.5 each. The data have been deposited with the Cambridge
Crystallographic Data Centre: CCDC-182 236 (4), CCDC-182
233 (5), CCDC-182 235 (6, 7), CCDC-182 234 (7, 8), and CCDC-
182 724 (9).
4,4,7,7-Tetr a k is(6-ter t-bu tyl-2,3,4-tr im eth ylp h en yl)-5,8-
d ip h en yl-3-a za -4,7-d iger m a b icyclo[4.2.0]oct a -1(8),2,5-
tr ien e-2-ca r bon itr ile (9). Cyanogen was prepared according
to the literature procedure from potassium cyanide and copper-
(II) sulfate.19 At -70 °C, an excess of anhydrous cyanogen (2.6
g, 50 mmol) was condensed onto a suspension of 4 (ca. 1.7
mmol) in n-hexane (80 mL), which had been freshly prepared
from 1 (1.44 g, 1.7 mmol) and 1,4-diphenylbuta-1,3-diyne
(0.344 g, 1.7 mmol). The mixture was allowed to come to room
temperature. During this time the color of the mixture changed
from dark blue to greenish yellow. After filtration the solution
was concentrated to a volume of 40 mL and left to crystallize
at 20 °C for 2 days to yield 1.07 g (57% yield) of yellow crystals
Com p u ta tion a l Deta ils. All geometries were optimized
with the semiempirical method PM3 employing the program
(20) Sheldrick, G. M. SHELXL-97: Program for Crystal Structures
Refinement; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.
(21) Stewart, J . J . P. MOPAC 2002; Fujitsu Limited: Tokyo, J apan,
2002.
(22) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens. Matter
1988, 37, 785.
(23) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
(24) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
1
of 9, mp 208-211 °C; H NMR δ 0.86 (s, 3 H, CH3), 0.88 (s, 9
H, CH3), 1.22 (s, 3 H, CH3), 1.23 (s, 3 H, CH3), 1.36 (s, 3 H,
CH3), 1.48 (s, 9 H, tBu), 1.50 (s, 3 H, CH3), 1.53 (s, 3 H, CH3),
1.56 (s, 3 H, CH3), 1.61 (s, 3 H, CH3), 1.65 (s, 3 H, CH3), 2.06
(s, 9 H, tBu), 2.11 (s, 9 H, tBu), 2.13 (s, 9 H, tBu), 6.94-7.40
(19) Brauer, G. Handbuch der Pra¨parativen Anorganischen Chemie;
Enke Verlag: Stuttgart, 1954; Vol. 2, p 628.

Acetylene-Linked Bis(germaethene)
Organometallics, Vol. 21, No. 19, 2002 3995
package MOPAC 2002.21 Local minima and transition states
were verified through calculation of the number of imaginary
frequencies. The additional DFT calculations at the hybrid
functional Becke3LYP22,23 level of theory (within both the
restricted and the unrestricted framework of the Hartree-
Fock theory) with the 6-31G(d) basis set were performed with
the program package Gaussian 9824 and, again, the nature of
the obtained geometries was verified.
Chemischen Industrie, and the EU (INTAS project) is
gratefully acknowledged.
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 4, 5, 6/7, 7/8, and 9. This material is
available free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. Financial support of our work
by the Deutsche Forschungsgemeinschaft, the Fonds der
OM020320M