Synthesis, X-ray, and DFT study of the double-bond pyramidalization in 1,7,8,9-tetraphenyl-4,10,10-trimethyl-4-aza-10-silatricyclo[5.2.1.0. 2,6]deca-8-ene-3,5-dione and Its germanium analogue

Article abstract of DOI:10.1021/om050671b

Diels - Alder adducts of 1-sila-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4- cyclopentadiene and 1-germa-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-cyclopentadiene with N-methylmaleimide and maleic anhydride were prepared by high-pressure reactions. Their X-ray struct

Full text of DOI:10.1021/om050671b

Organometallics 2006, 25, 111-117
111
Synthesis, X-ray, and DFT Study of the Double-Bond
Pyramidalization in 1,7,8,9-Tetraphenyl-4,10,10-
trimethyl-4-aza-10-silatricyclo[5.2.1.0.2,6]deca-8-ene-3,5-dione and Its
Germanium Analogue
Davor Margetic´,*,† Yasujiro Murata,‡ Koichi Komatsu,*,‡ and Mirjana Eckert-Maksic´*,†
Laboratory for Physical-Organic Chemistry, DiVision of Organic Chemistry and Biochemistry,
Ru[er BosˇkoVic´ Institute, 10001 Zagreb, Croatia, and Institute for Chemical Research,
Kyoto UniVersity, Uji, Kyoto 611-0011, Japan
ReceiVed August 3, 2005
Diels-Alder adducts of 1-sila-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-cyclopentadiene and 1-germa-2,3,4,5-
tetraphenyl-1,1-dimethyl-2,4-cyclopentadiene with N-methylmaleimide and maleic anhydride were prepared
by high-pressure reactions. Their X-ray structures were determined and compared to literature data. In
addition, the B3LYP/6-31G* method was used to study their molecular and electronic structure. X-ray
analysis revealed that the extent of pyramidalization of the double bond in all studied compounds is
small (molecules 1 and 2) or negligible (3). B3LYP/6-31G* calculations were found to overestimate
pyramidalization by 5.3-9.4°, presumably due to crystal-packing forces. The effect of phenyl groups on
the geometry of the double bond is discussed.
Introduction
The effect of heteroatoms on pyramidalization of the double
bond in the norbornene moiety, either alone or fused to another
strained ring, has attracted considerable interest from experi-
mental as well as theoretical points of view.1 Particularly
interesting in this context are molecules in which the carbon
atom of the methano-bridge is replaced by a group 14 element.
Contrary to the parent hydrocarbon, all such molecules studied
Figure 1. 7-Metalonorbornenes investigated in this study
experimentally so far exhibit only small or negligible deviation
of the double bond from planarity.2,3
of the double bonds incorporated into strained polycyclic
molecules by us6-9 and by other research groups.10 Recently,
however, its reliability for calculating geometries with the
second-row elements was questioned by Schaefer and Allinger.11
Therefore, we thought it would be of interest to check whether
the latter holds also for molecule 1, as well as for the closely
related germyl adducts considered in the present work. We were
particularly interested in possible consequences of such an
inaccuracy, if any, on pyramidalization of the double bond.
In this study we report on the preparation and X-ray structures
of novel cycloadducts 1 and 2 (Figure 1). In addition, X-ray
structure analysis of the known compound 3 was undertaken
for the sake of completeness. We also intended to measure the
X-ray structure of the silicon analogue of 3, synthesis of which
has been previously reported in the literature,4 but we were not
able to grow X-ray quality crystals. In the second part of the
paper, the geometries of 1-3 will be compared with the
geometries of previously published structurally related silicon
and germanium compounds, with particular emphasis on pyra-
midalization of the double bond. Finally, the effect of phenyl
groups on the extent of the double-bond folding will be explored.
For this purpose we shall use density functional theory (DFT)
using the B3LYP/6-31G* method, which has been successfully
used in studying geometries of organosilicon compounds.5 It
was also proven to provide a reliable description of the geometry
Results and Discussion
Compounds 1-3 were prepared by high-pressure-assisted
Diels-Alder reactions12 of 1-sila-2,3,4,5-tetraphenyl-1,1-di-
(5) For a recent review article see: Karni, M.; Apeloig, Y.; Kapp, J.;
Schleyer, P. v. R. In The chemistry of organic silicon compounds, Vol. 3;
Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, 2001; pp 1-188, and
references therein.
(6) Williams, R. V.; Colvin, M. E.; Tran, N.; Warrener, R. N.; Margetic´,
D. J. Org. Chem. 2000, 65, 562-567.
(7) Antol, I.; Eckert-Maksic´, M.; Margetic´, D.; Maksic´, Z. B.; Kowski,
K.; Rademacher, P. Eur. J. Org. Chem. 1998, 1403-1408.
(8) Margetic´, D.; Warrener, R. N.; Butler, D. N. Paper 39, Sixth electronic
computational chemistry conference; 1999; Homeier, H., Ed., http://
www.chemie.uni-regensburg.de/ECCC6/.
(9) Eckert-Maksic´, M.; Margetic´, D.; Kirin, S.; Milic´, D.; Matkovic´-
Cˇ alogovic´, D. Eur. J. Org. Chem. 2005, 4612-4620.
(10) Saracoglu, N.; Talaz, O.; Azizoglu, A.; Watson, W. H.; Balci, M.
J. Org. Chem. 2005, 70, 5403-5408.
(11) Ma, B.; Lii, J.-H.; Schaefer, H. F., III; Allinger, N. L. J. Phys. Chem.
1996, 100, 8763-8769.
* Corresponding authors. E-mail: margetid@emma.irb.hr (D.M.);
mmaksic@emma.irb.hr (M.E.M.); komatsu@scl.kyoto-u.ac.jp (K.K.).
† Ru[er Bosˇkovic´ Institute.
‡ Kyoto University.
(1) For a recent review article see: Va´zquez, S.; Camps, P. Tetrahedron
2005, 61, 5147-5208, and references therein.
(2) Paddon-Row, M. N.; Wong, S. S.; Jordan, K. D. J. Am. Chem. Soc.
1990, 112, 1710-1722.
(3) Paddon-Row, M. N.; Wong, S. S.; Jordan, K. D. J. Chem. Soc., Perkin
Trans. 2 1990, 417-423.
(4) Henry, G. K.; Shinimoto, R.; Zhou, Q.; Weber, W. P. J. Organomet.
Chem. 1988, 350, 3-8.
10.1021/om050671b CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/24/2005

112 Organometallics, Vol. 25, No. 1, 2006
Margetic´ et al.
Figure 4. ORTEP plot of molecule 3. Atoms are presented as
thermal ellipsoids at 30% probability. The atom-numbering scheme
is given in Figure 1.
Figure 2. ORTEP plot of molecule 1. Atoms are presented as
thermal ellipsoids at 30% probability. The atom-numbering scheme
is given in Figure 1.
NMR chemical shifts of the studied molecules are in accord
with those observed earlier in structurally related cycloadducts.13
The same holds for the 29Si chemical shift of 1, which reflects
a typical 29Si nuclear deshielding16,17 when compared with
unstrained organosilicon compounds.18 It is also worth noting
that in the crystal structure they do not possess a plane of
symmetry (see Experimental Section), in sharp contrast to the
situation encountered in solution.
Crystal Molecular Structure of 1-3. In addition to con-
firming stereochemistry, the X-ray data reveal several interesting
features of the molecular structure of the considered adducts
1-3 (Table 1). We shall commence discussion by considering
the structure of molecule 1. Perhaps, the most prominent feature
of its molecular structure concerns orientation of the phenyl
groups with respect to the basic plane of the 7-silanorbornene
ring defined by the C(2), C(6), C(8), and C(9) atoms. The
deviation angles have values of 18.7°, 79.9°, 90.2°, and 55.2°
for the phenyl rings attached to the C(1), C(7), C(8), and C(9)
atoms, respectively. It is interesting to note that one of the phenyl
rings at the bridgehead positions (Ph(C7)) is almost perpen-
dicular to the C(2)-C(6)-C(8)-C(9) plane, while the Ph(C1)
ring deviates from coplanarity with the C(2)-C(6)-C(8)-C(9)
plane by only 18.7°. Similarly, one of the aromatic rings attached
to the olefinic carbon atoms is rotated by 90.2° (Ph(C8)) and
the other by 55.2° (Ph(C9)) relative to the same plane. It is
noteworthy that the orientation of the phenyl groups encountered
in the crystal of 1 strongly resembles those in the crystal
structure of structurally related 11,11-dimethyl-9,10-epoxy-1,4-
sila-1,2,3,4-tetraphenyl-1,4,4a,9,9a,10-hexahydroanthracene 4
(where Ph(C1), Ph(C7), Ph(C8), and Ph(C9) angles are 27.2°,
85.3°, 80.2°, and 42.5°, respectively).19 On the other hand, in
tetraphenyl silabenzonorbornadiene molecule 6 (Chart 1), all
phenyl rings are perpendicular to the C(2)-C(6)-C(8)-C(9)
plane. Another characteristic feature common to all silanor-
bornene derivatives studied so far concerns elongation of the
endocyclic C-Si interatomic distances within the 7-silanor-
bornene ring relative to their exocyclic counterparts, the latter
Figure 3. ORTEP plot of molecule 2. Atoms are presented as
thermal ellipsoids at 30% probability. The atom-numbering scheme
is given in Figure 1.
methyl-2,4-cyclopentadiene and 1-germa-2,3,4,5-tetraphenyl-
1,1-dimethyl-2,4-cyclopentadiene as reactive dienes.13,14 Under
reaction conditions employed (8 kbar, 70 °C in dichloro-
methane), these organometallic dienes readily underwent [4π+2π]
cycloadditions with electron-poor dienophiles (maleic anhydride
and N-methylmaleimide) to give the desired cycloaducts 1-3
as the single products.
The molecular structure and stereochemistry of the so-
obtained cycloadducts were determined by NMR spectroscopic
analysis and NOE experiments (see Experimental Section) and
by means of X-ray diffraction analysis. The X-ray structures
are displayed in Figures 2-5. Both approaches revealed that
all three adducts have an endo-configuration, in accordance with
expected stereochemical outcome.15 The measured 1H and 13
C
(12) Matsumoto, K., Acheson, R. M., Eds. Organic Synthesis at High
Pressures; Wiley: New York, 1990.
(13) Dubac, J.; Laporterie, A.; Manuel, G. Chem. ReV. 1990, 90, 215-
263.
(16) Sakurai, H.; Sakabo, H.; Nakadaira, Y. J. Am. Chem. Soc. 1982,
104, 6156-6158.
(17) Marinetti-Mignani, A.; West, R. Organometallics 1987, 6, 141-
144.
(14) Hota, N. K.; Willis, C. J. J. Organomet. Chem. 1968, 15, 89-96.
(15) Dubac, J.; Gue´rin, C.; Meunier, P. In The Chemistry of Organic
Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York,
1998; pp 1961-2036.
(18) Marsmann, H. In NMR-Basic Principles and Progress; Diehl, P.,
Fluck, E., Koesfeld, R., Eds.; Springer: Berlin, 1981; Vol. 17.
(19) Kirin, S. I.; Vikic´-Topic´, D.; Mesˇtrovic´, E.; Kaitner, B.; Eckert-
Maksic´, M. J. Organomet. Chem. 1998, 566, 85-91.

Double-Bond Pyramidalization
Organometallics, Vol. 25, No. 1, 2006 113
Figure 5. Crystal packing of molecules 1-3.
Table 1. Selected X-ray and B3LYP/6-31G* Geometrical Parameters of Molecules 1-3a
1 X-ray
1 calc
2 X-ray
2 calc
3 X-ray
3 calc
d (Å)
C(1)-C(2)
1.584(4)
1.568(4)
1.509(4)
1.504(4)
1.394(3)
1.378(4)
1.548(4)
1.547(4)
1.531(4)
1.356(4)
1.915(3)
1.910(3)
1.856(3)
1.864(3)
1.584
1.577
1.537
1.525
1.393
1.389
1.561
1.548
1.543
1.368
1.938
1.933
1.888
1.891
1.580(3)
1.561(3)
1.519(3)
1.517(3)
1.377(3)
1.377(3)
1.553(3)
1.533(3)
1.526(3)
1.355(3)
2.004(2)
2.000(2)
1.937(2)
1.941(2)
1.577
1.569
1.537
1.524
1.394
1.388
1.562
1.541
1.536
1.369
2.000
1.995
1.946
1.947
1.575(3)
1.564(3)
1.517(3)
1.509(3)
1.391(3)
1.386(3)
1.545(3)
1.534(3)
1.534(3)
1.354(3)
2.017(2)
2.009(2)
1.931(3)
1.948(2)
1.574
1.570
1.530
1.519
1.390
1.386
1.553
1.542
1.536
1.370
2.000
1.997
1.944
1.947
C(6)-C(7)
C(2)-C(3)
C(5)-C(6)
C(3)-X(4)
C(5)-X(4)
C(2)-C(6)
C(1)-C(9)
C(7)-C(8)
C(8)-C(9)
C(1)-M(10)
C(4)-M(10)
M(10)-C(11syn-)b
M(10)-C(11anti-)
θ (deg)
C(1)-C(9)-C(8)
C(7)-C(8)-C(9)
C(1)-M(10)-C(7)
C(2)-C(1)-C(9)
C(6)-C(7)-C(8)
112.9(3)
112.3(2)
83.1(12)
104.9(2)
107.1(2)
112.9
112.5
82.8
105.2
107.6
113.6(19)
112.9(19)
79.6(9)
105.5(18)
107.5(18)
113.5
113.1
80.7
106.0
108.5
113.8(16)
113.2(18)
79.5(9)
107.4(18)
107.7(17)
113.4
113.2
80.7
106.1
108.2
ψ/deg
C(7)-C(8)-C(9)-C(Ph9)
C(1)-C(9)-C(8)-C(Ph8)
2.2(2)
0.8(2)
9.6
0.4
3.2(2)
1.6(2)
8.6
2.6
1.0(19)
0.1(2)
10.4
1.1
Etot
-1847.126175
-3632.643784
-3613.185052
a Butterfly bendings (ψ) and bond angles (θ). b syn(anti) orientation of methyl groups is defined with respect to the double bond.
being of the same order of magnitude as in unstrained
silanes.20-22 This trend is customarily explained by electron
density delocalization from the endocyclic C-Si σ bonds into
π* system of the double bond.23

114 Organometallics, Vol. 25, No. 1, 2006
Margetic´ et al.
Chart 1. Literature Examples of 7-Silanorborn(adi)ene and 7-Germanorborn(adi)ene Derivatives Investigated by X-ray
Crystallography
The measured values of bond angles (Table 1) are also in
the range of the bond angles found in the structurally related
compounds.14,15 We shall single out only the C(1)-Si(10)-
C(7) angle, which was found to be 83.1°, indicating that
molecule 1 has a markedly strained structure. Finally, we note
that the double bond in the 7-silanorbornene ring is practically
planar, again in accordance with the situation found earlier in
structurally related molecules (Chart 1). Specifically, the py-
ramidalization angles at C(8) and C(9) of 2.1° and 0.8° were
found. This result is in accord with the expected decrease of
π-electron density of the double bond due to π-electron transfer
from the double bond into low-lying unoccupied σ-molecular
orbital of the silicon (germanium) bridge.24 On the other hand,
it is in contrast to the related norbornenes and 7-oxanorbornenes,
where experimental nonplanarity of the double bond lies within
a range of 5-16°.25,26
groups relative to the basic molecular plane defined by the C(2),
C(6), C(8), and C(9) atoms. Furthermore, in analogy with the
adduct 1, the endocyclic C(1)-Ge(10) bonds (2.000-2.017 Å)
in 2 and 3 are found to be longer than the exocyclic ones
(1.931-1.948 Å). The latter values are similar to the typical
literature value for the carbon-germanium single-bond distance
of 1.950 Å. Furthermore, the C(1)-Ge(10)-C(7) angles in 2
and 3 were found to be 79.9° and 79.5°, which are slightly
smaller than the corresponding values found in the literature
(Chart 1).
It is also noteworthy that, likewise in compound 1, the
aromatic rings attached to the olefinic bond are only slightly
displaced from the plane defined by the C(1), C(9), C(8), and
C(7) atoms. Specifically, germanium adduct 2 exhibits ψ ) 3.2°
at C(9) and 1.6° at C(8), while in adduct 3 deviation of the
double bond from planarity is even less pronounced (ψ ) 1.0°
at C(9) and 0.1° at C(8)).
Comparison with X-ray Structures of Related Molecules.
It is interesting to put the results considered so far into
perspective by comparison with available results of X-ray
analysis of related 7-silanorborn(adi)ene and 7-germanorborn-
(adi)ene derivatives. They are collected in Chart 1.
In carrying out this analysis we were particularly interested
in the geometry of the double bond. Unfortunately, it appeared
that in most of the older studies pyramidalization of the double
bond was not considered.33,34 Therefore we extracted pyrami-
The molecular structures of 2 and 3 closely resemble that of
1. This holds in particular for the orientations of the phenyl
(20) Baxter, S.; Mislow, K.; Blount, J. Tetrahedron 1980, 36, 605-616.
(21) Shafiee, F.; Damewood, J. R., Jr.; Haller, K. J.; West, R. J. Am.
Chem. Soc. 1985, 107, 6950-6956.
(22) Carrell, H.; Donohue, J. Acta Crystallogr. Sect. B 1972, 28, 1566-
1571.
(23) Sekiguchi, A.; Ziegler, S. S.; Haller, K. J.; West, R. Recl. TraV.
Chim. Pays-Bas 1988, 107, 197-202.
(24) See for example: Bock, H.; Solouki, B. In Photoelectron spectra
of silicon compounds; Patai, S., Rappaport, Z., Eds.; The Chemistry of
Organic Silicon Compounds, Vol. 1; Wiley: Chichester, 1989; pp 555-
651.
(25) Carrupt, P.-A.; Vogel, P. J. Mol. Struct. (THEOCHEM) 1985, 124,
9-23.
(26) Eckert-Maksic´, M.; Novak-Doumbouya, N.; Kiralj, R.; Kojic´-Prodic´.
B. J. Chem. Soc., Perkin Trans. 2 2000, 1483-1487.
(27) Maslennikova, O. S.; Nosov, K. S.; Faustov, V. I.; Egorov, M. P.;
Nefedov, O. M.; Aleksandrov, G. G.; Eremenko, I. L.; Nefedov, S. E. Russ.
Chem. Bull. (Translation of IzV. Akad. Nauk, Ser. Khim.) 2000, 49, 1275-
1282.

Double-Bond Pyramidalization
Organometallics, Vol. 25, No. 1, 2006 115
Chart 2. 1,7,8,9-Tetraphenylnorbornene Derivatives 16 and
17
dalization angles from the coordinates deposited with the CCDC
where possible.35 This analysis revealed that most of the
7-silanorbornene and 7-germanorbornene derivatives reported
so far exhibit a negligible to small degree of olefinic bond
pyramidalization, in accordance with the results obtained for
molecules 1-3. It is also interesting to note that examples of
the endo- as well as the exo-deviations of the substituents
attached to the olefinic carbon atoms from planarity were found.
The crystal structure of syn-benzo-1,2,3,4,11-pentaphenyl-11-
silanorbornadiene (12) reported by Mu¨ller and co-workers is
particularly interesting in this context.30 The unit cell of this
compound consists of two independent molecules having slightly
different geometries. Similarly to 1-3, both molecules exhibit
the asymmetric out-of-plane bending of the double bond. In one
of the molecules one of the olefinic carbon atoms is essentially
planar (ψ ) 0.1°), while the pyramidalization at the second
olefinic carbon is as large as 13.9°. In the second molecule of
the unit cell phenyl groups bonded to the olefinic carbon atoms
are displaced toward the endo-face of the bicyclic ring by 9.8°
and 2.5°, respectively.
spectroscopic data of the considered compounds does not allow
any conclusion about the extent of pyramidalization at the
olefinic carbon atoms. This is not surprising given that even in
syn- and anti-sesquinorbornenes, which are paradigmatic ex-
amples of the pyramidalized and planar strained olefins,
respectively, the 13C chemical shifts of the olefinic carbon atoms
differ by only ca. 2.0 ppm (151.6 vs 153.9 ppm).40
Computational Analysis. Having the experimental values
at our disposal we are now in a position to check the validity
of the B3LYP/6-31G* method for calculating geometries and,
in particular, its reliability for calculating pyramidalization
angles at the olefinic carbon atoms in sila (germa) norbornenes.
The relevant calculated structural parameters of 1-3, along with
their total energies, are summarized in Table 1. Comparison of
the calculated geometries with the X-ray data reveals that there
is a good agreement between two sets of data, particularly if
experimental errors are taken into account. The largest discrep-
ancy is observed for the C(1)-Si(10) bond (0.023 and 0.032 Å
for the endocyclic and exocyclic bond, respectively), in ac-
cordance with previously published finding.11 On the other hand,
the C(1)-Ge(10) bond distances appear to be slightly under-
estimated (Table 1).
As to the pyramidalization angles, we observe that the B3LYP
method overestimates the extent of pyramidalization of the
double bond in all three adducts (Table 1) by ψ ) 5.3-9.4°.
This result is somewhat surprising, since in most of the systems
reported so far the B3LYP method was found to underestimate
double-bond folding.6,8,41 To check whether this discrepancy is
due to inaccuracy of the calculated C-Si bond lengths, the
structure of 1 was reoptimized with the C(1)-Si(10) and C(7)-
Si(10) bond lengths constrained to the experimental value of
1.910 Å. This calculation resulted in a change of pyramidal-
ization angles of as small as 0.1°, implying that the observed
overestimation of the endocyclic carbon-silicon bonds has a
negligible effect on the calculated pyramidalization angles in
1.
We shall close this discussion by considering the effect of
the phenyl groups on the pyramidalization angles in some of
the studied molecules. For this purpose, we relay on the results
of the B3LYP/6-31G* calculations. The calculated angles for
molecules 1-3b are summarized in Table 3.
Starting with molecules 1-3, we observe that replacement
of the phenyl groups at the bridgehead position with the
hydrogen atoms leads to an increase in pyramidalization at the
C(8), while the pyramidalization angle at C(9) decreases. It is
also worth noting that replacement of the phenyl groups at the
olefinic positions has the same effect (Table 3). A similar trend
is observed for the other sets of studied molecules. For instance,
the B3LYP/6-31G*-optimized structure of the adduct 13 (Chart
On the other hand, the X-ray structures of 13 and 14 published
by Mochida and co-workers31 exhibit exo-folding of the double
bond with pyramidalization angles at the olefinic carbon atoms
of 6.1° and 4.5°, respectively. Furthermore in the crystal
structure of 15,32 one of the phenyl groups at the olefinic carbon
atoms is displaced out by 3.7° in the exo- and the other one by
2.5° in the endo-direction (relative to the 7-silanorbornadiene
ring). On the basis of these facts we conclude that the extent of
the folding of the double bond in the considered molecules is
a result of a fine balance of (a) the nature of the substituents
and their substitution pattern at the 7-metallonorbornene ring
and (b) intermolecular forces and crystal-packing effects.36,37
It should be underlined in this context that similar trends were
also found in crystal structures of several tetraphenylated
norbornene derivatives.38,39 Characteristic examples are provided
by the crystal structures of Diels-Alder adducts of 2,3,4,5-
tetraphenylcyclopenta-2,4-dien-1-one, such as 1638 and 1739
(Chart 2). These structures are asymmetric in the crystal, and
the phenyl rings attached to the olefinic C(8)-C(9) bond are
displaced from the plane defined by C(1), C(9), C(8), and C(7)
by ψ ) 11.9° (C8) and 1.1° (C9) in molecule 16 and by 14.7°
(C8) and 3.8° (C9) in adduct 17.
In contrast to the trends observed in the crystal structures of
the studied compounds, analysis of the available 13C NMR
(28) Kako, M.; Mori, M.; Hatakenaka, K.; Kakuma, S.; Nakadaira, Y.;
Yasui, M.; Iwasaki, F. Tetrahedron 1997, 53, 1265-1274.
(29) Belzner, J.; Ihmels, H.; Kniesel, B. O.; Gould, R. O.; Herbst-Irmer,
R. Organometallics 1995, 14, 305-311.
(30) Schuppan, J.; Herrschaft, B.; Mu¨ller, T. Organometallics 2001, 20,
4584-4592.
(31) Mochida, K.; Shimizu, H.; Kugita, T.; Nanjo, M. J. Organomet.
Chem. 2003, 673, 84-94.
(32) Wrackmeyer, B.; Milius, W.; Bhatti, M. H.; Ali, S. J. Organomet.
Chem. 2003, 665, 196-204.
(33) Nefedov, M.; Egorov, M. P. Structure and reactivity of 7-sila- and
7-germanorbornadienes as precursors of silylenes and germylenes. In
Frontiers of Organosilicon Chemistry; Bassindale, A. R., Gaspar, P. P. Eds.;
The Royal Society of Chemistry: Cambridge, 1991; pp 145-158.
(34) Egorov, M. P.; Ezhova, M. B.; Antipin, M. Yu.; Struchkov, Y. T.
Main Group Metal Chem. 1991, 14, 19-23.
(35) All crystallographic data presented here were retrieved from the
Cambridge Crystallographic Data Centre (CCDC), www.ccdc.cam.ac.uk.
(36) Tiekink, E. R. T.; Hall, V. J.; Buntine, M. A.; Hook, J. Z. Kristallogr.
2000, 215, 23-33.
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116 Organometallics, Vol. 25, No. 1, 2006
Table 2. Crystallographic Details Collected at 100 K
Margetic´ et al.
1
2
3
empirical formula and weight
wavelength
C35H31NO2Si, 525.21
0.71073 Å
C35H31GeNO2, 571.16
0.71073 Å
C34H28GeO3, 558.12
0.71073 Å
cryst syst
monoclinic
monoclinic
monoclinic
space group
P2(1)/c
P2(1)/c
P2(1)/c
unit cell dimens
a ) 15.7865(19) Å
R ) 90°
a ) 15.8304(17) Å
R ) 90°
a ) 11.8390(12) Å
R ) 90°
b ) 11.9788(14) Å
â ) 103.035(2)°
c ) 15.5336(19) Å
γ ) 90°
b ) 11.9315(13) Å
â ) 103.268(2)°
c ) 15.6080(17) Å
γ ) 90°
b ) 10.2678(11) Å
â ) 98.830(2)°
c ) 22.278(2) Å
γ ) 90°
volume
2861.8(6) Å3
2869.4(5) Å3
2676.0(5) Å3
Z
4
4
4
density (calcd)
absorp coeff
F(000)
cryst size
θ range for data collect
index ranges
1.220 Mg/m3
1.320 Mg/m3
1.383 Mg/m3
0.114 mm-1
1.099 mm-1
1.179 mm-1
1112
1184
1152
0.12 × 0.12 × 0.04 mm3
0.33 × 0.24 × 0.10 mm3
0.22 × 0.20 × 0.14 mm3
1.32 to 26.00°
1.32 to 26.00°
1.74 to 25.99°
-11 e h e 19, -14 e k e 14,
-19 e l e 18
15 896
5605 [R(int) ) 0.0624]
99.5%
empirical (SADABS)
0.9954 and 0.9864
full-matrix least-squares on F2
5605/0/355
-18 e h e 19, -13 e k e 14,
-19 e l e 15
15 859
5637 [R(int) ) 0.0314]
99.7%
empirical (SADABS)
0.8980 and 0.7130
full-matrix least-squares on F2
5637/0/355
-14 e h e 12, -11 e k e 12,
-25 e l e 27
14 830
5260 [R(int) ) 0.0294]
99.8%
empirical (SADABS)
0.8524 and 0.7815
full-matrix least-squares on F2
5260/0/345
no. of reflns collected
no. of indep reflns
completeness to θ ) 26.00°
absorp corr
max. and min transmn
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.005
1.003
1.003
R1 ) 0.0466, wR2 ) 0.0845
R1 ) 0.0965, wR2 ) 0.1175
0.309 and -0.296 e Å-3
R1 ) 0.0310, wR2 ) 0.0702
R1 ) 0.0458, wR2 ) 0.0848
0.618 and -0.311 e Å-3
R1 ) 0.0333, wR2 ) 0.0671
R1 ) 0.0466, wR2 ) 0.0694
0.629 and -0.390 e Å-3
largest diff peak and hole
Table 3. Comparison of Experimental and Calculated Interplanar Angles between the Phenyl Groups and the C2-C6-C8-C9
Plane (deg) in 1-3 and the Effect of Phenyl Groups on the Pyramidalization Angles
X-ray
B3LYP
X-ray
B3LYP
X-ray
B3LYP
1
1
1a
1b
2
2
2a
2b
3
3
3a
3b
Interplanar Angles
Ph(C1)
Ph(C7)
Ph(C8)
Ph(C9)
18.7
79.9
90.2
55.2
20.4
83.6
81.8
35.6
25.3
74.0
71.9
33.6
46.8
80.0
90.3
24.5
22.5
82.9
85.8
42.5
19.1
52.6
93.9
32.8
78.3
27.4
64.8
33.6
75.5
40.6
Pyramidalization Angles
Ψ(C8)
Ψ(C9)
0.8
2.1
0.4
9.7
4.7
7.0
1.4
1.4
1.6
3.2
2.6
8.6
2.7
7.2
2.5
2.5
0.1
1.0
1.1
10.5
2.9
7.4
2.5
2.5
1) exhibits asymmetric deformation of the double bond by 2.5°
at C(8) and 4.8° at C(9) in the exo-direction. This should be
compared with the experimentally determined folding of 6.1°
in the exo-direction. Replacement of the phenyl groups at the
bridgehead positions with the hydrogen atoms leading to 13a
results in a pyramidalization angle of 4.3° in the endo-direction
and 8.4° in the exo-direction at C(8) and C(9) atoms, respec-
tively. Finally, in the unsubstituted adduct 13b a pyramidaliza-
tion angle of 1.6° at both olefinic atoms toward the endo-face
of the molecule was found. As a last example we shall consider
the effect of gradual replacement of the phenyl groups on the
geometry of the double bond in the adduct 14. For this molecule
B3LYP calculations predict a symmetrical structure with 7.3°
exo-bending, which is in fair agreement with the measured angle
of 4.5° in the crystal structure (X-ray geometry was used as
the initial guess in optimization).31 When the phenyl groups of
14 at the bridgehead positions C(7) and C(8) were replaced by
the hydrogen atoms leading to 14a, the double bond was found
to be asymmetrically bent with ψ ) 8.3° in the endo-direction
and ψ ) 2.1° in the exo-direction at the C(8) and C(9) atoms,
respectively. Finally, replacement of all four phenyl groups with
hydrogen atoms resulted in a symmetrical structure, 14b,
exhibiting only minute endo-pyramidalization (1.6°).
Conclusion
The synthesis and X-ray structures of 7-silanorbornene and
7-germanorbornene derivatives 1-3 are presented. The com-
pounds were prepared by high-pressure-assisted cycloaddition
reactions of 1-sila-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-cyclo-
pentadiene and 1-germa-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-
cyclopentadiene with N-methylmaleimide in high yields. The
reactions gave endo-adducts as the single products with olefinic
bonds exhibiting negligible (3) to very small (1 and 2)
pyramidalization in the endo-direction. Pyramidalization of the
double bond in the adducts 1-3 was also compared with
available X-ray data for a number of 7-silanorborn(adi)ene and
7-germanorborn(adi)ene derivatives. On the basis of analysis
of these results it was concluded that the extent of pyramidal-
ization in the studied molecules strongly depends on the nature
and substitution pattern, as well as on the saddle effects of the
crystal-packing forces. Finally, it is shown that the B3LYP/
6-31G* method considerably overestimates the extent of the
double bond bending in 1-3.

Double-Bond Pyramidalization
Experimental Section
Organometallics, Vol. 25, No. 1, 2006 117
(C1,C7), 125.3 (CAr), 126.0 (CAr), 127.1 (CAr), 127.4 (CAr), 129.6
(CAr), 130.2 (CAr), 136.4 (CdC), 137.7 (CAr), 141.1 (CAr), 177.1
(CdO). 29Si NMR (CDCl3) δ (ppm): 46.6. HRMS calcd for C35H31-
NO2Si: m/z 525.2124, found 525.2129. Anal. Calcd for C35H31-
NO2Si: C, 79.96; H, 5.94; N, 2.66. Found: C, 80.39; H, 5.54; N,
3.02.
Computational Methods. All geometry optimizations were
carried out with the Gaussian 98 suite of programs42 employing
the density functional theory (DFT) hybrid B3LYP method using
the 6-31G* basis set.43,44 Harmonic vibration frequencies were
calculated for all localized stationary structures to verify whether
they are minima. Pyramidalizations angles at the olefinic carbon
atoms are reported in terms of the butterfly bending angle (ψ) as
defined in refs 41 and 45. Calculations were carried out on the
dual Athlon MP and Pentium III personal computers under the
Linux Redhat 8.0 operating system.
Experimental Details. Silole and germole were prepared by
known methods.46,47 The 1H, 13C, and 29Si NMR spectra were
recorded in CDCl3 solutions containing tetramethylsilane as internal
standard on Bruker AMX300 or 600 MHz instruments. Melting
points were determined using a Gallenkamp digital melting point
apparatus and are uncorrected. The high-resolution mass spectra
were recorded on a Micromass Platform II single quadrupole
AutoSpec instrument. Centrifugal radial chromatography was
carried out with a chromatotron, Model No. 79245T, using 1 mm
plates with silica gel 60F254 as the stationary phase with ethyl
acetate-petroleum ether (40-60 °C) mixture as eluent. High-
pressure reactions were performed using a high-pressure piston-
cylinder apparatus, in Teflon cells, and pentane as piezotransmitter
liquid. The single-crystal X-ray data were collected on a Bruker
SMART APEX diffractometer equipped with a CCD area detector
at 100 K. All structures were solved by direct methods and refined
using full-matrix least-squares with the SHELX-97 software pack-
age.48
1,7,8,9-Tetraphenyl-4,10,10-trimethyl-4-aza-10-germa-
1r,2r,6r,7r-tricyclo [5.2.1.0.2,6]deca-8-ene-3,5-dione (2). A solu-
tion of 1-germa-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-cyclopenta-
diene (50 mg, 0.109 mmol) and N-methylmaleimide (12 mg, 0.109
mmol) in dichloromethane (1 mL) was pressurized at 8 kbar at 70
°C for 3 days. Solvent was then removed in vacuo to afford a yellow
solid, which was subjected to radial chromatography (petroleum
ether-ethyl acetate, 20:1, then the solvent polarity was gradually
increased to pure ethyl acetate) to afford 2 as a yellow solid (50
mg, 85%, mp 249-251 °C). An X-ray sample was obtained by
crystallization from ethyl acetate. 1H NMR (CDCl3) δ (ppm): 0.47
(3H, s, GeCH3), 0.79 (3H, s, GeCH3), 3.05 (3H, s, NCH3), 4.35
(2H, s, Hexo), 6.59 (2H, d, J ) 8.1 Hz, HAr), 6.89-6.90 (6H, m,
HAr), 7.06-7.08 (2H, m, HAr), 7.12-7.16 (4H, m, HAr), 7.21-
7.23 (4H, d, J ) 7.7 Hz, HAr). 13C NMR (CDCl3) δ (ppm): -5.3
(GeCH3), -0.7 (Ge CH3), 25.1 (C2,C6), 50.6 (NCH3), 56.8 (C1,C7),
125.3 (CAr), 126.0 (CAr), 127.3 (CAr), 127.5 (CAr), 129.5 (CAr),
130.4 (CAr), 136.9 (CdC), 138.8 (CAr), 144.1 (CAr), 174.3 (Cd
O). HRMS calcd for C35H31NO2Ge: m/z 571.1567, found 571.1581.
Anal. Calcd for C35H31NO2Ge: C, 73.72; H, 5.48; N, 2.46. Found:
C, 73.42; H, 5.23; N, 2.76.
1,7,8,9-Tetraphenyl-10,10-dimethyl-4-oxa-10-germa-
1r,2r,6r,7r-tricyclo [5.2.1.0.2,6]deca-8-ene-3,5-dione (3).14
A
solution of 1-germa-2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-cyclopen-
tadiene (25 mg, 0.0545 mmol) and maleic anhydride (9 mg, 0.0545
mmol) in dichloromethane (1 mL) was pressurized at 8 kbar at 70
°C for 3 days. Solvent was then removed and residue recrystallized
from ethyl acetate to afford 3 as a colorless solid (12 mg, 40%,
mp 222-224 °C). An X-ray sample was obtained by crystallization
from dichloromethane-petroleum ether. 1H NMR (CDCl3) δ
(ppm): 0.53 (3H, s, GeCH3), 0.86 (3H, s, GeCH3), 4.62 (2H, s,
Hexo), 6.66-7.23 (20H, m, HAr). 13C NMR (CDCl3) δ (ppm): -5.1
(GeCH3), -0.3 (GeCH3), 25.4 (C2,C6), 51.7 (NCH3), 57.1 (C1,C7),
125.9 (CAr), 126.4 (CAr), 127.4 (CAr), 127.5 (CAr), 129.3 (CAr),
130.5 (CAr), 136.2 (CdC), 137.7 (CAr), 142.7 (CAr), 172.1
(CdO). HRMS calcd for C34H28O3Ge: m/z 558.1250, found
558.1259. Anal. Calcd for C34H28O3Ge: C, 73.29; H, 5.07. Found:
C, 73.56; H, 4.72.
1,7,8,9-Tetraphenyl-4,10,10-trimethyl-4-aza-10-sila-1r,2r,6r,7r-
tricyclo [5.2.1.0.2,6]deca-8-ene-3,5-dione (1). A solution of 1-sila-
2,3,4,5-tetraphenyl-1,1-dimethyl-2,4-cyclopentadiene (50 mg, 0121
mmol) and N-methylmaleimide (13 mg, 0.121 mmol) in dichlo-
romethane (1 mL) was pressurized at 8 kbar at 70 °C for 3 days.
Solvent was then removed in vacuo to afford a yellow solid, which
was recrystallized from ethyl acetate to afford 1 as a yellow solid
(48 mg, 76%, mp 252-254 °C). 1H NMR (CDCl3) δ (ppm): 0.28
(3H, s, SiCH3), 0.65 (3H, s, SiCH3), 3.07 (3H, s, NCH3), 4.30 (2H,
s, Hexo), 6.58-7.29 (20H, m, HAr). 13C NMR (CDCl3) δ (ppm):
-6.4 (SiCH3), -3.5 (SiCH3), 25.0 (C2,C6), 49.5 (NCH3), 53.7
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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.;
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Full crystallographic data for compounds 1, 2, and 3 have been
deposited with the Cambridge Crystallographic Data Centre,
deposition numbers CCDC 271104, CCDC 271105, and CCDC
271106. Copies may be obtained free of charge from the Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223
336 033; e-mail: deposit@ccdc.cam.ac.uk).
Acknowledgment. Financial support of the Ministry of
Science, Education and Sport of Croatia, project nos. 0098056
(M.E.M.) and 0098147 (D.M.), is gratefully acknowledged. Mr.
Zˇ. Marinic´ is thanked for recording NMR spectra, and Central
Analytic Service at Ru[er Bosˇkovic´ Institute is acknowledged
for microanalyses.
Supporting Information Available: Cartesian coordinates for
all calculated structures are available free of charge via the Internet
at http://pubs.acs.org.
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