Synthesis of stable 2-silanaphthalenes and their aromaticity

Article abstract of DOI:10.1021/ja992024f

Stable neutral silaaromatic compounds, 2-silanaphthalenes (1a; R = Tbt, 1b; R = Bbt), were synthesized by taking advantage of extremely bulky and efficient steric protection groups, 2,4,6-tris[bis-(trimethylsilyl)methyl]phenyl (Tbt) and 2,6-bis[bis(trimet

Full text of DOI:10.1021/ja992024f

11336
J. Am. Chem. Soc. 1999, 121, 11336-11344
Synthesis of Stable 2-Silanaphthalenes and Their Aromaticity
Keiji Wakita,† Norihiro Tokitoh,*,†, Renji Okazaki,*,†,# Shigeru Nagase,‡
Paul von Rague´ Schleyer,§ and Haijun Jiao|
Contribution from the Department of Chemistry, Graduate School of Science, The UniVersity of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan, Department of Chemistry, Graduate School of Science,
Tokyo Metropolitan UniVersity, Minamiosawa, Hachioji, Tokyo 192-0397, Japan, The Center for
Computational Quantum Chemistry, The UniVersity of Georgia, Athens, Georgia 30602, and
Computer-Chemie-Centrum, Institut fu¨r Organishe Chemie, UniVersita¨t Erlangen-Nu¨rnberg,
Henkestrasse 42, D-91054 Erlangen, Germany
ReceiVed June 15, 1999
Abstract: Stable neutral silaaromatic compounds, 2-silanaphthalenes (1a; R ) Tbt, 1b; R ) Bbt), were
synthesized by taking advantage of extremely bulky and efficient steric protection groups, 2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl (Tbt) and 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl
(Bbt). 2-Silanaphthalenes 1a,b were isolated as colorless crystalline compounds, and the structure of Tbt-
1
substituted 1a was determined by X-ray crystallographic analysis. All H, 13C, and 29Si NMR signals of the
silanaphthalene ring of 1 were in good agreement with those calculated; downfield-shifted 1H signals indicating
aromatization were observed. Refined NICS (nucleus-independent chemical shift) calculations which separate
the σ and π contributions revealed the presence of comparably large ring current effects in the two rings of
2-silanaphthalene. The aromatic stabilization energies (ASEs) of 1-, 2-, and 9-silanaphthalenes, computed by
a novel isomerization method, are almost the same as naphthalene. UV-vis and Raman spectra, and the
computed (B3LYP/6-311+G(d,p)) structure of 2-silanaphthalene were similar to those of naphthalene, although
characteristic changes resulting from the replacement of carbon to silicon were observed. 2-Silanaphthalene
1a is still highly reactive due to its polarized SidC moiety, but was relatively stable toward air in the solid
state and showed no complex formation with THF in solution. Considering all experimental and theoretical
results, the 2-silanaphthalenes were concluded to have considerable aromatic character, closely approaching
that of naphthalene itself.
Introduction
theoretical results, simple silaaromatic compounds such as
silabenzenes and disilabenzenes are highly reactive and have
only been characterized spectroscopically in low-temperature
matrices or in the gas phase.5 Ma¨rkl et al. reported the synthesis
of a “stable” silabenzene, 2,6-bis(trimethylsilyl)-1,4-di-tert-
butylsilabenzene, but this survives only in solution (THF/Et2O/
petroleum ether, 4:1:1) below -100 °C. The stabilization is,
however, apparently due to coordination of the solvent Lewis
base, judging from the 29Si NMR chemical shift (δSi ) 26.8)
observed at a relatively high field (vide infra).1d,e,6,7
Much attention in recent decades has been focused on
silaaromatic compounds,1 namely, Si-containing [4n + 2]π ring
systems, since these represent the heavier congeners of the
carbocyclic aromatic compounds2 which play such important
roles in organic chemistry. Although the aromatic character of
silole anions and dianions,3 as well as those of cyclic diami-
nosilylenes,4 were recently revealed from experimental and
† The University of Tokyo.
‡ Tokyo Metropolitan University.
§ The University of Georgia.
| Universita¨t Erlangen-Nu¨rnberg.
(4) (a) Arduengo, A. J., III; Bock, H.; Chen, H.; Denk, M.; Dixon, D.
A.; Green, J. C.; Hermann, W. A.; Jones, N. L.; Wagner, M.; West, R. J.
Am. Chem. Soc. 1994, 116, 6641. (b) West, R.; Denk, M. Pure. Appl. Chem.
1996, 68, 785. (c) Heinemann, C.; Mu¨ller, T.; Apeloig, Y.; Schwarz, H. J.
Am. Chem. Soc. 1996, 118, 2023. (d) Boehme, C.; Frenking, G. J. Am.
Chem. Soc. 1996, 118, 2039. (e) West, R.; Buffy, J. J.; Haaf, M.; Mu¨ller,
T.; Gehrhus, B.; Lappert. M. F.; Apeloig, Y. J. Am. Chem. Soc. 1998, 120,
1639.
(5) (a) Solouki, B.; Rosmus, P.; Bock, H.; Maier, G. Angew. Chem., Int.
Ed. Engl. 1980, 19, 51. (b) Maier, G.; Mihm, G.; Reisenauer, H. P. Angew.
Chem., Int. Ed. Engl. 1980, 19, 52. (c) Kreil, C. L.; Chapman, O. L.; Burns,
G. T.; Barton, T. J. J. Am. Chem. Soc. 1980, 102, 841. (d) Maier, G.; Mihm,
G.; Reisenauer, H. P. Chem. Ber. 1982, 115, 801. (e) Maier, G. Mihm, G.;
Baumga¨rtner, R. O. W.; Reisenauer, H. P. Chem. Ber. 1984, 117, 2337. (f)
Maier, G.; Scho¨ttler, Reisenauer, H. P. Tetrahedron Lett. 1985, 26, 4079.
(g) van den Winkel, Y.; van Barr, B. L. M.; Bickelhaupt, F.; Kulik, W.;
Sierakowski, C.; Maier, G. Chem. Ber. 1991, 124, 185. (h) Hiratsuka, H.;
Tanaka, M.; Okutsu, T.; Oba, M.; Nishiyama, K. J. Chem. Soc., Chem.
Commun. 1995, 215.
Present address: Institute for Fundamental Research of Organic
Chemistry, Kyushu University.
# Present address: Department of Chemical and Biological Sciences,
Faculty of Science, Japan Women’s University.
(1) For reviews on silaaromatic compounds, see: (a) Raabe, G.; Michl,
J. Chem. ReV. 1985, 85, 419. (b) Raabe, G.; Michl, J. In The Chemistry of
Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New
York, 1989; pp 1102-1108. (c) Apeloig, Y. ibid., pp 151-166. (d) Brook,
A. G.; Brook, M. A. AdV. Organomet. Chem. 1996, 39, 71. (e) Apeloig,
Y.; Karni, M. In The Chemistry of Organic Silicon Compounds; Rappoport,
Z., Apeloig, Y., Eds.; Wiley: New York, 1998; Vol. 2, Chapter 1.
(2) Minkin, V. J.; Glukhovtsev, M. N.; Simkin, Y. B. Aromaticity and
Antiaromaticity; Electronic and Structural Aspects; Wiley: New York, 1994.
(3) Recent reports on the delocalization of silole anions and dianions:
(a) Freeman, W. P.; Tilley, T. D.; Liable-Sands, L. M.; Rheingold, A. L. J.
Am. Chem. Soc. 1996, 118, 10457. (b) Goldfuss, B.; Schleyer, P. v. R.
Hampel, F. Organometallics 1996, 15, 1755. (c) Goldfuss, B.; Schleyer, P.
v. R. Organometallics 1997, 16, 1543. (d) Choi, S.-B.; Boudjouk, P.; Wei,
P. J. Am. Chem. Soc. 1998, 120, 5814. (e) Dysard, J. M.; Tilley, T. D. J.
Am. Chem. Soc. 1998, 120, 8245.
(6) Ma¨rkl, G.; Schlosser, W. Angew. Chem., Int. Ed. Engl. 1988, 27,
963.
10.1021/ja992024f CCC: $18.00 © 1999 American Chemical Society
Published on Web 11/25/1999

Synthesis of Stable 2-Silanaphthalenes
J. Am. Chem. Soc., Vol. 121, No. 49, 1999 11337
Many theoretical calculations have been reported for sila- and
disilabenzenes,1c,e and they indicate that silabenzenes have a
delocalized structure and considerable aromaticity (e.g., ∼80%
of benzene from energetic criteria8). This implies that silaarenes
might exist as stable molecules if their high reactivity could be
suppressed.
In view of the increasing number of stable unconjugated
doubly bonded organosilicon compounds which were synthe-
sized successfully by taking advantage of steric protection,9,10
stable silaaromatic compounds with appropriately bulky sub-
stituents are expected to be synthesizable.
Results and Discussion
Synthesis of 2-Silanaphthalenes. Although many synthetic
routes to silabenzenes have been developed,1a,b the flow
pyrolysis of 2-allyl-2-methyl-1,2-dihydro-2-silanaphthalene was
the only example reported for the preparation of a transient
2-silanaphthalene derivative.20 To synthesize 2-silanaphthalenes
in a preparative scale, we selected a method based on treatment
of the corresponding halosilanes with a base.
Bromosilanes 6a,b, the precursors of 2-silanaphthalenes 1a,b,
were synthesized from 1,2,3,4-tetrahydro-2-silanaphthalene
2,21,22 following the route shown in Scheme 1. Thus, treatment
We have already developed an extremely bulky and effective
steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl (denoted as Tbt hereafter),11 and many novel reactive
species have been prepared as stable compounds by taking
advantage of this Tbt group. For example, a stable silanethione12
and its heavier element group 14 analogues13,14 (we call these
compounds “heavy ketones”) were successfully synthesized
utilizing a single Tbt group in combination with another
considerably bulky substituent (bulky substituents can only be
introduced onto one terminal of the double bond). Moreover,
the first stable distibene15 and dibismuthene16 were also
synthesized by introducing the Tbt group on each group 15
element where only one substituent can be introduced.
In a preliminary contribution,17 we reported that the successful
application of the Tbt group to the kinetic stabilization of
silaaromatic compounds led to the first isolation of a stable
2-silanaphthalene. In this paper, we describe the details of the
synthesis, structure, and reactivity of the kinetically stabilized
2-silanaphthalenes bearing 2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl (Tbt)11 and 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(tri-
methylsilyl)methyl]phenyl (denoted as Bbt) groups.18,19 These
results, as well as those of theoretical calculations focus on the
aromaticity of these new silaaromatics in particular.
Scheme 1
(7) It is well-established in the chemistry of silicenium ions that the
coordination of a Lewis base to the silicon center induces a high-field shift
in the 29Si NMR spectrum. See: (a) Maerker, C.; Schleyer, P. v. R. In The
Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.;
Wiley: New York, 1998; Vol. 2, Chapter 10. (b) Lickiss, P. D. ibid., Chapter
11.
of 2 with TbtLi or BbtLi resulted in moderate yields of
hydrosilanes 3a,b bearing these bulky substituents. The bromi-
nation of 3 with excess NBS gave a complex mixture containing
products with a 3,4-double bond; this mixture was further
reduced with LiAlH4 to give an inseparable mixture of 4 and
5.23 Lithiation of the mixture of 4 and 5 with t-BuLi followed
by quenching with aqueous solution of NH4Cl afforded hy-
drosilanes 4 as pure compounds. Finally, bromosilanes 6a,b,
the precursors of 2-silanaphthalenes, were prepared as pure,
stable compounds by careful bromination of 4 with equimolar
amounts of NBS at 0 °C.
(8) Gordon, M. S.; Boudjouk, P.; Anwari, F. J. Am. Chem. Soc. 1983,
105, 4972.
(9) Recent reviews on low-coordinated organosilicon compounds: (a)
Okazaki, R.; West, R. AdV. Organomet. Chem. 1996, 39, 232. (b) Baines,
K. M.; Stibbs, W. G. AdV. Organomet. Chem. 1996, 39, 275. See also ref 1.
(10) A stable tetrasila-1,3-butadiene was recently synthesized also
utilizing steric protection. Weidenbruch, M.; Willms, S.; Saak, W.; Henkel,
G. Angew. Chem., Int. Ed. Engl. 1997, 36, 2503.
(11) Okazaki, R.; Tokitoh, N.; Matsumoto, T. In Synthetic Methods of
Organometalic and Inorganic Chemistry; Herrmann, W. A., Ed.; Thieme:
New York, 1996; Vol. 2 (Auner, N., Klingebiel, U., Vol. Eds.), pp 260-
269 and references therein.
Treatment of the bromosilanes 6a,b thus obtained with 1
equiv of t-BuLi in hexane resulted in the formation of the
expected 2-silanaphthalenes 1a,b ( ∼80% conversion based on
NMR), which were confirmed by their characteristic low-field
29Si NMR signals (1a, 87.3 ppm; 1b, 86.7 ppm; in C6D6)
(Scheme 2).24 2-Silanaphthalenes 1a,b were isolated as colorless
(12) (a) Suzuki, H.; Tokitoh, N.: Nagase, S.; Okazaki, R. J. Am. Chem.
Soc. 1994, 116, 11578. (b) Suzuki, H.; Tokitoh, N.; Okazaki, R.; Nagase,
S.; Goto, M. J. Am. Chem. Soc. 1998, 120, 11096.
(13) (a) Tokitoh, N.; Matsumoto, T.; Manmaru, K.; Okazaki, R. J. Am.
Chem. Soc. 1993, 115, 8855. (b) Matsumoto, T.; Tokitoh, N.; Okazaki, R.
Angew. Chem., Int. Ed. Engl. 1994, 33, 2316. (c) Tokitoh, N.; Matsumoto,
T.; Okazaki, R. J. Am. Chem. Soc. 1997, 119, 2337.
(14) (a) Tokitoh, N.; Saito, M.; Okazaki, R. J. Am. Chem. Soc. 1993,
115, 2065. (b) Saito, M.; Tokitoh, N.; Okazaki, R. J. Am. Chem. Soc. 1997,
119, 11124.
(15) Tokitoh, N.; Arai, Y.; Sasamori, T.; Okazaki, R.; Nagase, S.; Uekusa,
H,; Ohashi, Y. J. Am. Chem. Soc. 1998, 120, 433.
(16) Tokitoh, N.; Arai, Y.; Okazaki, R.; Nagase, S. Science 1997, 227,
78.
(17) Tokitoh, N.; Wakita, K.; Okazaki, R.; Nagase, S.; Schleyer, P. v.
R.; Jiao, H. J. Am. Chem. Soc. 1997, 119, 6951.
(18) Unno, M. Dissertation, The University of Tokyo, 1988.
(19) Bbt group has almost the same steric protection ability as that of
Tbt group. For recent applications of Bbt group, see: (a) Kano, N.; Tokitoh,
N.; Okazaki, R. Organometallics 1998, 17, 1241. (b) Tokitoh, N.; Sasamori,
T.; Okazaki, R. Chem. Lett. 1998, 725.
(20) (a) Kwak, Y.-W.; Lee, J.-B.; Lee, K.-K.; Kim, S.-S.; Boo, B. H.
Bull. Korean Chem. Soc. 1994, 15, 410. (b) Kwak, Y.-W.; Lee, K.-K.; Yoh,
S.-D. Bull. Korean Chem. Soc. 1997, 18, 552.
(21) 1,2,3,4-Tetrahydro-2-silanaphthalene 2 was synthesized by LiAlH4
reduction of the corresponding dichlorosilane. See Experimental Section.
(22) For the reason we use dihydrosilane 2 instead of dihalosilanes, see:
Wakita, K.; Tokitoh, N.; Okazaki, R. Chem. Lett. 1998, 687.
(23) The structure of 5 is still preliminary because the separation of 4
and 5 was not achieved.
(24) Starting from 6-phenyl-1,2,3,4-tetrahydro-2-silanaphthalene, we
succeeded in the synthesis of 6-phenyl-2-{2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl}-2-silanaphthalene (δSi ) 87.8). Their details will be reported
elsewhere.

11338 J. Am. Chem. Soc., Vol. 121, No. 49, 1999
Wakita et al.
Table 1. Observed and Calculated 13C and 29Si NMR Chemical Shifts (ppm) for 2-Silanaphthalenes
compound
C1
Si2
C3
C4
C5
C6
C7
C8
C9
C10
1a (R ) Tbt, obsd)
1b (R ) Bbt, obsd)
1c (R ) H, calcd)a
1d (R ) Me, calcd)a
1e (R ) Ph, calcd)a,b
116.0
115.0
128.5
120.4
121.6
87.3
86.8
67.8
101.0
94.3
122.6
122.0
125.1
122.7
123.6
149.0
149.0
153.4
153.3
152.5
133.3
133.3
137.3
137.2
137.1
120.6
120.6
125.4
124.0
124.5
126.7
126.8
130.5
130.4
130.4
128.8
128.7
131.8
131.7
132.3
146.5
146.5
151.7
152.0
151.6
128.3
128.6
134.5
133.7
133.7
a Calculated by GIAO-B3LYP/6-311G(d)(6-311G(3d) for Si)//B3LYP/6-31G(d) level. b The phenyl group is fixed in such a way that it is
perpendicular to the 2-silanaphthalene ring.
with low-temperature data collection, we could not obtain
refined data free from severe disorder around the 2-silanaph-
thalene ring. This prevented accurate experimental determination
of bond lengths and angles in the 2-silanaphthalene ring. We
will discuss, therefore, the structure of 2-silanaphthalene based
on the available spectroscopic data and theoretical calculations.
NMR Spectra, NICS, and Energetic Evaluation of Aro-
maticity. As mentioned above, 2-silanaphthalene 1 showed 29Si
NMR signals of the central Si atoms around 87 ppm. Uncon-
jugated silenes are also known to have low-field shifted δSi
values, but they are widely scattered depending on the difference
of substituents (41-144 ppm).1d Although no simple silene with
carbon substituents has been reported yet, the δSi values of 1
are reasonably compared with that of Couret’s Mes2SidC(H)-
CH2(t-Bu) (δSi ) 77.6)26 and clearly different from that of
Ma¨rkl’s 2,6-bis(trimethylsilyl)-1,4-di-tert-butyl-1-silabenzene
(δSi ) 26.8).6 At present, however, we cannot judge the
aromaticity from the 29Si chemical shifts because of the scarcity
of examples for both silenes and silaaromatic compounds.
1
The H and 13C signals of 1 were assigned by 2D NMR
techniques together with differential NOE and decoupling
experiments. The 13C NMR assignments are listed in Table 1
along with the calculated values for some other 2-silanaphtha-
lenes. The agreement between experimental and theoretical
values is excellent, especially for 1e (R ) Ph).
Figure 1. X-ray crystallographic analysis of 1a (ORTEP, 30%
probability). (a) Full view of the molecule. (b) Top view of the
2-silanaphthalene ring. Data collection was performed at -80 °C.
It is well-established that the coupling constant of adjacent
two atoms can be a good index for the bond order.27 Values
around 50 Hz are known for typical Si-C single bonds,27
whereas 83-85 Hz values are reported for Si-C double bonds
(although the number of examples is still limited).28 For 1a,
JSi-C1 and JSi-C3 were measured to be 92 and 76 Hz,
respectively; both values exceed those of Si-C single bonds
considerably, and suggest double bond character for these Si-C
bonds as in naphthalene (see below).
crystals by recrystallization from hexane in a glovebox filled
with argon. Interestingly, bromosilane 7a, prepared by NBS
bromination of 3a, did not react with t-BuLi under the same
conditions as those for 6a.
Scheme 2
The assignments of 1H signals of 2-silanaphthalenes 1a,b are
shown in Table 2, including calculated values for 1c-e and
those observed for the dihydro derivatives 4a,b. H3 and H4
protons in 1a,b resonate at approximately 1 ppm lower field
than those in 4a,b consistent with the predicted aromatization
effect of the Si-containing rings in 1c-e. A similar change also
occurs between naphthalene (H3, 7.46; H4 7.81 ppm) and 1,2-
dihydronaphthalene (H3, 5.82; H4, 6.33 ppm).
We have recently proposed the nucleus-independent chemical
shifts (NICSs) as convenient criteria of aromaticity,29 and NICSs
of silanaphthalenes were reported in the preliminary com-
munication.17 We have refined this method further to separate
the π and σ contributions.30 The refined NICSs are shown in
Although 2-silanaphthalene 1a was moisture-sensitive, it was
thermally very stable under an inert atmosphere in the solid
state at room temperature or in solution at 100 °C; no
dimerization product was detected. The high stability of 1a
demonstrates the excellent steric protection afforded by the Tbt
group. In contrast, the tert-butyl group in 1,4-di-tert-butyl-1-
silabenzene, which reportedly undergoes facile dimerization
even at 0 °C, is ineffective.25
The structure of 1a was finally determined by X-ray crystal-
lographic analysis, which revealed the planar geometry of the
2-silanaphthalene ring and the central silicon atom (Figure 1).
Despite a number of trials using different single crystals even
(26) Delpon-Lacaz, G.; Couret, G. J. Organomet. Chem. 1994, 480, C14.
(27) Kalinowski, H.-O.; Berger, S.; Braun, S. Carbon-13 NMR Spec-
troscopy, translated by J. K. Becconsall; Wiley: New York, 1986; p 600.
(28) Brook, A. G.; Abdesaken, F.; Gutekunst, G.; Plavac, N. Organo-
metallics 1982, 1, 994.
(29) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes,
N. J. R. v. E. J. Am. Chem. Soc. 1996, 118, 6317.
(25) Ma¨rkl, G.; Hofmeister, P. Angew. Chem., Int. Ed. Engl. 1979, 18,
789.
(30) Schleyer, P. v. R.; Jiao, H.; Hommes, N. J. R. v. E.; Malkin, V. G.;
Malkina, O. L. J. Am. Chem. Soc. 1997, 119, 12669.

Synthesis of Stable 2-Silanaphthalenes
J. Am. Chem. Soc., Vol. 121, No. 49, 1999 11339
1
Table 2. Observed and Calculated H NMR Chemical Shifts (ppm) for 2-Silanaphthalenes and Their Dihydro Derivatives
compound
H1
H2
H3
H4
H5
H6
H7
H8
1a (R ) Tbt, obsd)
1b (R ) Bbt, obsd)
1c (R ) H, calcd)a
1d (R ) Me, calcd)a
1e (R ) Ph, calcd)a,b
4a (R ) Tbt, obsd)
4b (R ) Bbt, obsd)
7.40
7.33
7.74
7.26
7.32
2.45c
2.46c
7.24
7.19
7.27
7.03
7.08
6.27
6.30
8.48
8.49
8.64
8.50
8.55
7.30
7.29
7.60
7.60
7.69
6.99
7.00
7.23
7.20
7.20
7.40
7.64
7.64
7.62
6.37
7.60
7.11
7.32
7.54
7.67
7.17
7.36
7.59
∼7.1d
∼7.1d
∼7.1d
∼7.1d
∼7.1d
∼7.1d
∼7.1d
∼7.1d
a Calculated by GIAO-B3LYP/6-311G(d)(6-311G(3d) for Si)//B3LYP/6-31G(d) level. b The phenyl group is fixed in such a way that it is
perpendicular to the 2-silanaphthalene ring. c These values are the average of the chemical shifts of two geminal protons. d These signals are observed
in the range between 7.09 and 7.15 ppm but cannot be exactly assigned due to the overlap of the signals.
Table 3. Calculated NICSs of 2-Silanaphthalene 1c (IGLO
pw91/III)a
NICS(0)total NICS(1)total NICS(0)π
NICS(1)π
Si-ring
C-ring
naphthalene
-8.0
-8.4
-8.9
-9.4
-10.3
-10.8
-17.7 [-0.3] -9.5 [-0.1]
-20.7 [-0.4] -10.5 [-0.3]
-20.3 [0.0] -10.1 [0.0]
a Distances from ring centers to the calculated points (Å) are
described in parentheses, and contribution of the opposite rings are in
square brackets (see the text for details). Data for naphthalene are
provided for comparison.
Figure 3. Calculated vibration modes with maximum intensity. (a)
2-Phenyl-2-silanaphthalene. (b) Naphthalene.
methyl-substituted aromatic isomers. The evaluations are self-
consistent, and methyl groups have little effect on arene
aromaticity. We argue that such isomerization reactions, involv-
ing highly similar structures, provide better aromaticity estimates
than more conventional equations based on small reference
molecules. These do not balance the strain and other energetic
effects as effectively.
Figure 2. Calculated isodesmic isomerization energies (kcal/mol,
B3LYP/6-311+G(d,p)//Fopt).
The data demonstrate that incorporation of silicon into the
arene frameworks not only has very little effect on the aromatic
stabilization but also shows that there is no significant position
dependence in naphthalene.
UV-Vis Spectra. 2-Silanaphthalene 1a shows three absorp-
tion maxima at 267 (ꢀ 2 × 104), 327 (7 × 103), and 387 (2 ×
103) nm in hexane. Despite the shift to longer wavelengths, they
clearly correspond to the E1, E2, and B bands of naphthalene
[221 (ꢀ 1.33 × 105), 286 (9.3 × 103), and 312 (2.9 × 102) nm].
This documents the structural resemblance between 2-silanaph-
thalene and naphthalene. Similar UV-vis spectra relationships
are also observed for the benzene-silabenzene-1,4-disilaben-
zene series in low-temperature matrix spectra.5f
Table 3. Although quite different methods and levels are
employed (here IGLO PW91/III), the NICS(0) values here are
not very different from those we obtained earlier (-8.9 for Si-
ring, -9.5 for C-ring, GIAO-SCF/6-31G(d) level).17 All the
data show the Si-ring to be only slightly less aromatic than the
C-ring. The other (C-C and C-H σ bonds etc.) contributions
are paratropic, explaining why the NICS(0)π values are larger
in magnitude than the NICS(0)total values. Fortuitously, the
other contributions decrease and largely cancel at points 1 Å
above the rings; hence, the NICS(1)total and NICS(1)π values
are nearly the same. This supports our suggestion that NICS-
(1)total values may serve as a good indicator of ring current
effects (aromaticity).
Raman Spectra. The Raman spectrum of 1a showed the most
intense Raman line at 1368 cm-1, while the most intense line
for naphthalene was observed at 1382 cm-1. The strongest
Raman shifts observed for 1a and naphthalene are in good
agreement with the theoretically calculated vibrational frequen-
cies (1377 and 1389 cm-1 for 1e and naphthalene, respectively,
computed at the B3LYP/6-31G(d) level and scaled by 0.9831).
Furthermore, the calculated vibration modes of 1e showed a
The two rings do not influence each other significantly. This
is shown by the small values in square brackets, which
summarize the π contributions from the two remote double
bonds in the opposite rings.
We have also carried out the quantitative energetic evaluation
of 1- (1c), 2-, and 9-silanaphthalene isomers along with those
for naphthalene, benzene, and silabenzene for comparison, the
results of which are summarized in Figure 2. The novel method
employed is based on the DFT-computed isodesmic isomeriza-
tion energies of nonaromatic polyenes into the corresponding
(31) For the scaling factor of 0.98, see: Bauschlicher, C. W., Jr.;
Partridge, H. J. Chem. Phys. 1995, 103, 1788.

11340 J. Am. Chem. Soc., Vol. 121, No. 49, 1999
Wakita et al.
Table 4. Observed and Calculated Bond Lengths (Å) of 2-Silanaphthalenes, Their Isomers, and Parent Naphthalene (Si-C Lengths Are
Described in Bold Type)
compound
1-2
2-3
3-4
4-10
10-5
5-6
6-7
7-8
8-9
9-1
9-10
1a (R ) Tbt, obsd)a
1.704
1.750
1.750
1.386
1.378
1.375
1.765
1.791
1.417
1.424
1.421
1.415
1.36
1.27
1.66
1.36
1.37
1.40
1.30
1.64
1.39
1c (R ) H, calcd)b
1.379
1.382
1.383
1.378
1.374
1.432
1.429
1.418
1.425
1.420
1.422
1.424
1.418
1.425
1.420
1.376
1.374
1.383
1.378
1.374
1.414
1.412
1.424
1.421
1.415
1.375
1.376
1.386
1.378
1.374
1.428
1.419
1.786
1.425
1.420
1.426
1.803
1.786
1.425
1.420
1.445
1.418
1.792
1.426
1.431
1-silanaphthalene (calcd)b
9-silanaphthalene (calcd)b
naphthalene (obsd)c
naphthalene (calcd)b
a These values are not exact as mentioned in the text. b B3LYP/6-311+G(d,p) c From ref 32.
isomers are small, 1- and 2-silanaphthalenes having almost the
same energy. These results indicate that three silanaphthalene
isomers have similar delocalized structure and stability. Thus,
1- and 9-silanaphthalenes can be synthetic targets if an effective
steric protection group is introduced and an adequate synthetic
route is developed.
Reactivity of 2-Silanaphthalene. Aromatic compounds are
generally stable and have low reactivity despite the presence
of unsaturated bonds. Silicon-containing doubly bonded com-
pounds are highly reactive, more so than their carbon counter-
parts. Hence, silaaromatic compounds can be expected to behave
not only as heteroaromatic compounds but as conjugated double-
bond organosilicon compounds. Judging from the reactions
reported for transient silabenzenes and 1,4-disilabenzenes,1a,b
silaaromatic species are still highly reactive, serving as Si-
containing ethylene or 1,3-butadiene. The considerable aromatic
stabilization predicted theoretically is not sufficient to overcome
the inherent reactivity conferred by the presence of the silicon.
Indeed, despite the high thermal stability of 2-silanaphthalene
1a, its SidC bond is quite reactive toward various reagents as
shown in Scheme 3. D2O and MeOH reacted smoothly with 1a
Figure 4. Calculated Si-C bond lengths (Å) of 2-silanaphthlaene 1c
and related compounds (B3LYP/6-311+G(d,p)).
Table 5. Relative Energies of Silanaphthalene Isomers (B3LYP/
6-311+G(d,p), kcal/mol)
compound
relative energy
1-silanaphthalene
2-silanaphthalene
9-silanaphthalene
0.2
0
2.9
close resemblance to those of naphthalene (Figure 3), suggesting
the structural similarity between 2-silanaphthalene and naph-
thalene.
Theoretically Optimized Structures. Table 4 summarizes
the observed and calculated bond lengths of silanaphthalenes
and naphthalene. Some computed Si-C bond lengths are also
shown in Figure 4. The two different types of Si-C bond lengths
(1.750 and 1.791 Å) in 2-silanaphthalene 1c are between those
of Si-C single (1.885 Å) and double bonds (1.708 Å), have
the same average length as the 1.771 Å Si-C bond of
silabenzene, and are clearly different from the Si-C lengths
computed for the nonaromatic 2-silabutadiene.
Scheme 3
In some fused aromatic systems, it is known that the
aromaticity of one ring can be influenced by that of another
ring.33 If one ring is more aromatic, the aromaticity of a second
ring may be reduced. However, the similar bond length patterns
in 2-sila- vs naphthalene, as well as the similar ASEs (Figure
2) indicated that the degree of electron delocalization of the
ring containing Si-atom is not appreciably reduced. This is
consistent with the conclusion obtained by NMR spectra and
NICS calculations.
Comparison between Silanaphthalene Isomers. To obtain
information about possibilities to synthesize other silanaphtha-
lene isomers, 1- and 9-silanaphthalenes, theoretical calculations
were performed on these isomers, the calculated bond lengths
and relative energies of which are shown in Tables 4 and 5,
respectively.
to give the corresponding adducts 8 (72%) and 9 (59%),
respectively. Reactions of 1a with benzophenone, mesitonitrile
oxide, and 2,3-dimethyl-1,3-butadiene afforded the correspond-
ing [2 + 2], [2 + 3], and [2 + 4] cycloadducts 10, 11, and 12
in good yields. All of these reactions are similar to those of
silenes whose reactivity has been much explored.1a,d Attempted
reactions of 1a with dienophiles such as phenylacetylene, maleic
anhydride, or tetracyanoethylene gave none of the expected
cycloadducts, but rather complex mixtures.
The structure of 12 was established by X-ray crystallographic
analysis, the results of which are shown in Figure 5 and Table
6. The high reactivity of 2-silanaphthalene 1a and the inspection
of the molecular structure of 12 indicate that Tbt group affords
enough reaction space around the central Si atom despite its
strong steric protection.
As shown in Table 4, all Si-C bond lengths of silanaphtha-
lenes are between those of typical Si-C single (1.89 Å) and
double bonds (1.71 Å), and the C-C bond lengths of silanaph-
thalenes have a close resemblance to those of naphthalene.
Differences in relative energies between the silanaphthalene
(32) Brock, C. P.; Dunits, J. D.; Hirshfeld, F. L. Acta Crystallogr. 1991,
B47, 789.
(33) (a) Hess, B. A., Jr.; Schaad, L. J.; Agranat, F. J. Am. Chem. Soc.
1978, 100, 5268. (b) Mitchell, R. H.; Iyer, V. S.; Khalifa, N.; Mahadevan,
R.; Venugopalan, S.; Weerawarna, S. A.; Zhou, P. J. Am. Chem. Soc. 1995,
117, 1514.
It is known that SidC and SidSi bonds react with elemental
sulfur to afford the corresponding three-membered rings.34

Synthesis of Stable 2-Silanaphthalenes
J. Am. Chem. Soc., Vol. 121, No. 49, 1999 11341
this reaction may be due to steric effects. Indeed, most cyclic
polysulfides containing Tbt-substituted group 14 elements have
five-membered rings.12-14
Stability of 2-Silanaphthalene. 2-Silanaphthalene 1a was
moisture-sensitive as mentioned above, but about one-third of
1a was recovered after exposure to air in the solid state for 30
min. This remarkable stability toward air is noticeable when
compared with that of unconjugated (Me3Si)2SidC(Ad)OSiMe3
which reportedly decomposes in air immediately even in the
solid state.36
It is known that the silicon center of silenes has a strong Lewis
acid character and is stabilized by complexation with Lewis
bases such as THF, Me3N, F-, etc.37 Such complex formation
results in an upfield shift in the 29Si NMR spectrum.1d,7 The
29Si chemical shift of 2-silanaphthalene 1a (δSi ) 87.3) in THF/
C6D6 (6:1), however, did not differ from that measured in C6D6,
indicating that 1a does not form a complex with THF. In
contrast, as mentioned earlier, the Si chemical shift of Ma¨rkl’s
silabenzene measured in THF/Et2O/petroleum ether (4:1:1)6 is
at a much higher field (δSi ) 26.8) than that of 1a, indicating
that it is coordinated with the solvent molecule, most likely THF,
and hence stabilized in such a mixed solvent. The absence of
complex formation of 1a suggests the remarkable effectiveness
of Tbt as a steric protecting group.
Figure 5. ORTEP drawing of 12 (30% probability) with nonhydrogen
atoms.
Table 6. Selected Bond Lengths of 12 (Å)
C1-Si2
Si2-C3
C3-C4
C4-C10
C10-C5
C5-C6
C6-C7
1.900(4)
1.853(4)
1.326(5)
1.467(7)
1.400(6)
1.377(7)
1.386(6)
C8-C9
1.385(5)
1.515(3)
1.395(6)
1.914(3)
1.565(2)
1.896(4)
1.326(5)
C9-C1
C9-C10
Si2-C11
C1-C12
Si2-C13
C14-C15
Conclusion and Outlook
Is the 2-silanaphthalene aromatic? Finally, we must answer
this simple, yet important question from the results obtained
experimentally and theoretically in this study. Although the
definitive structural parameters were not determined experi-
mentally by X-ray analysis, theoretical calculations revealed the
structure of 2-silanaphthalene. Furthermore, important features
theoretically predicted for the 2-silanaphthalene, namely, the
delocalization of the SidC double bond and structural similarity
between 2-silanaphthalene and naphthalene, are also supported
by the experimental NMR coupling constants and UV-vis and
Raman spectra. Large negative NICS values and theoretical
energetic evaluations (Figure 2) also indicate the ring current
effects and energetic stabilization of the 2-silanaphthalene. Thus,
all the results obtained theoretically and experimentally point
to the aromatic character of the 2-silanaphthalene.
Moreover, a variety of cyclic polysulfides containing group 14
elements were synthesized as stable compounds by utilizing the
steric protection due to the Tbt group.35 Sulfurization of 1a was
examined in the hope of obtaining some polysulfides fused with
a 2-silanaphthalene ring. The reaction mixture of 2-silanaph-
thalene 1a with 1 equiv (as S atom) of elemental sulfur showed
a
29Si NMR signal at -67.6 ppm, assignable to thiasililane 13
by comparison with the values reported for thiasililane and
thiadisililane rings 15-17. However, 13 decomposed during
attempted separation, and its exact structure was not determined.
Reaction of excess sulfur with 1a afforded a new cyclic trisulfide
14 (Scheme 4). The formation of the five-membered ring in
Scheme 4
Despite its aromatic character, 2-silanaphthalene 1a, unlike
naphthalene, is highly reactive and similar to unsaturated silicon
compounds. Molecules with an isolated SidC double bond are
inherently much more reactive than those with a CdC double
bond. For example, addition of water to a SidC double bond
is more exothermic than addition to a CdC double bond by 60
kcal/mol.38 Since the data in Figure 2 indicate that the
six-membered ring containing silicon in the 2-silanaphthalene
has essentially the same aromatic stabilization effect toward
reactions which result in a single benzene moiety as that of
naphthalene (around 11-12 kcal/mol39), the energy of addition
of water to 2-silanaphthalene is greater. Thus, the high reactivity
(36) Brook, A. G.; Abdesaken, F.; Gutekunst, B.; Gutekunst, G.; Kallury,
R. K. M. R. J. Chem. Soc., Chem. Commun. 1981, 181.
(37) Wiberg, N.; Wagner, G.; Reber, G.; Riede, J.; Mu¨ller, G. Organo-
metallics 1987, 6, 35.
(38) Nagase, S.; Kudo, T.; Ito, K. In Applied Quantum Chemistry; Smith,
V. H. Jr., Shaefer, H. F., III, Morokuma, K., Eds.; Reidel: Dordrecht, 1986;
pp 249-267. See also ref 1c.
(34) (a) Brook, A. G.; Kumarathasan, R.; Lough, A. J. Organometallics
1994, 13, 424. (b) West, R.; De Young, D. J.; Haller, J. K. J. Am. Chem.
Soc. 1985, 107, 4942.
(35) (a) Takeda, N.; Tokitoh, N.; Imakubo, T.; Goto, M.; Okazaki, R.
Bull. Chem. Soc. Jpn. 1995, 68, 2757. (b) Tokitoh, N.; Suzuki, H.;
Matsumoto, T.; Matsuhashi, Y.; Okazaki, R.; Goto, M.; J. Am. Chem. Soc.
1991, 113, 7047. (c) Tokitoh, N.; Kano, N.; Shibata, K.; Okazaki, R.
Organometallics 1995, 14, 3121. (d) Tokitoh, N.; Okazaki, R. J. Chem.
Soc., Dalton Trans. manuscript in preparation.
(39) In typical reactions of naphthalene involving one of the rings,
the total aromatic stabilization energy (ASE) of naphthalene must be re-
duced by the ASE of benzene since one benzene moiety remains after the
reaction. The ASEs depend on the method of evaluation as described in
ref 2. For a recent paper, see: Wiberg, K. B. J. Org. Chem. 1997, 62,
5720.

11342 J. Am. Chem. Soc., Vol. 121, No. 49, 1999
Wakita et al.
Preparation of 2-{2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl}-
1,2,3,4-tetrahydro-2-silanaphthalene (3a). To a solution of TbtBr
(10.96 g, 17.3 mmol) in THF (100 mL) was added t-BuLi (1.75 M in
pentane, 5.11 mmol) at -78 °C. After the mixture was stirred for 30
min, a solution of 2 (2.57 g, 17.3 mmol) in THF (20 mL) was added
dropwise at -78 °C to it. The reaction mixture was warmed to room
temperature within 10 h. After removal of the solvent the residue was
dissolved in hexane (50 mL) and filtered. Purification by WCC (SiO2/
hexane) followed by reprecipitation from CH2Cl2/EtOH afforded 3a
(4.08 g, 34%) as a white powder. 3a: mp 211-215 °C; 1H NMR
(CDCl3) δ 0.01 (s, 18H), 0.04 (s, 18H), 0.04 (s, 18H), 1.09-1.13 (m,
2H), 1.32 (s, 1H), 2.04 (s, 2H), 2.29-2.38 (m, 2H), 2.86 (dt, J ) 14,
8 Hz, 1H), 2.94 (d, J ) 8, 5 Hz, 1H), 4.49 (quint, J ) 4 Hz, 1H), 6.28
(br s, 1H), 6.40 (br s, 1H), 7.09-7.17 (m, 4H); 13C NMR (CDCl3) δ
0.72 (q), 0.75 (q), 1.04 (q), 6.77 (t), 20.52 (t), 28.64 (d), 29.06 (t),
29.92 (t), 30.42 (d), 121.78 (d), 124.95 (s), 125.38 (s), 126.64 (d),
126.84 (d), 128.13 (d), 129.64 (d), 138.25 (d), 141.10 (s), 144.65 (s),
151.48 (s), 151.82 (s); 29Si NMR (CDCl3) δ -26.59, 1.75, 1.89; HRMS
(EI, 70 eV): found m/z 698.3868, calcd for C36H70Si7 ([M]+) 698.3863.
Anal. Calcd for C36H70Si7: C, 61.81; H, 10.09. Found: C, 61.52; H,
10.36.
Preparation of 2-{2,6-Bis[bis(trimethylsilyl)methyl]-4-[tris(tri-
methylsilyl)methyl]phenyl}-1,2,3,4-tetrahydro-2-silanaphthalene (3b).
Compound 3b was synthesized by the same procedure as that for 3a.
The use of BbtBr (9.67 g, 13.7 mmol), t-BuLi (1.75 M, 26.8 mmol),
and 2 (3.15 g, 23.1 mmol) gave 3b as a white powder. 3b: mp 276-
280 °C dec; 1H NMR (CDCl3) δ 0.05 (s, 18H), 0.07 (s, 18H), 0.26 (s,
27H), 1.08-1.15 (m, 1H), 1.17-1.21 (m, 1H), 2.17 (s, 2H), 2.36 (dd,
J ) 14.3, 6.9 Hz, 1H), 2.37 (dd, J ) 14.3, 2.5 Hz, 1H), 2.86 (td, J )
13.8, 5.0 Hz, 1H), 2.97 (dt, J ) 13.8, 5.0, 1H), 4.44-4.47 (br m, 1H),
6.72 (s, 2H), 7.10-7.18 (m, 4H); 13C NMR (CDCl3) δ 1.43 (q), 1.45
(q), 5.47 (q), 9.16 (t), 21.04 (t), 22.23 (s), 29.85 (d), 29.97 (t), 125.43
(d), 126.50 (d), 126.69 (d), 127.94 (s), 128.12 (d), 129.56 (d), 138.15
(s), 140.92 (s), 146.49 (s), 151.52 (s); 29Si NMR (CDCl3) δ -25.77,
0.72, 1.51, 1.58; HRMS (EI, 70 eV): found m/z 770.4288, calcd for
C39H78Si8 ([M]+) 770.4258. Anal. Calcd for C39H78Si7: C, 60.69; H,
10.18. Found: C, 60.66; H, 9.96.
of the 2-silanaphthalene is not inconsistent with its aromaticity,
which is insufficient to suppress an addition reaction across the
SidC bond.
Considering all of the results, we can conclude with confi-
dence that the 2-silanaphthalene is highly aromatic.
Experimental Section
General Procedure. All experiments were performed under an argon
atmosphere unless otherwise noted. Solvents were dried by standard
1
methods and freshly distilled prior to use. H (500 MHz), 13C (125
MHz), and 29Si (99 or 54 MHz) NMR spectra were recorded on a JEOL
JNM-A500, Bruker AM-500, or JEOL JNM-EX270 spectrometer at
room temperature. Chemical shifts were measured with tetramethyl-
silane as an external standard. High-resolution mass spectral data were
obtained on a JEOL JMS-SX102 mass spectrometer. SCC (short column
chromatography) and WCC (wet column chromatography) were
performed on Wakogel C-200. PTLC and DCC (dry column chroma-
tography) were carried out on Merck Kieselgel 60 PF254 Art. 7743
and ICN Silica DCC 60A, respectively. Preparative HPLC was
performed on an LC-908 (Japan Analytical Industry Co., Ltd.) equipped
with JAI-gel 1H and 2H columns (eluent: chloroform). All melting
points were determined on a Yanaco micro melting point apparatus
and are uncorrected. Elemental analyses were carried out at the
Microanalytical Laboratory of the Department of Chemistry, Faculty
of Science, The University of Tokyo. 1-Bromo-2,4,6-tris[bis(trimeth-
ylsilyl)methyl]benzene (TbtBr),11 1-bromo-2,6-bis[bis(trimethylsilyl)-
methyl]-4-[tris(trimethylsilyl)methyl]benzene (BbtBr),18 and 2,2-dichloro-
1,2,3,4-tetrahydrosilanaphthalene40 were prepared according to the
reported procedures.
Computational Methods. The geometries of various silanaphtha-
lenes and related reference molecules were optimized by using the
Gaussian 98 program at B3LYP/6-311+G(d,p) levels of density
functional theory.41 We have also carried out NICS calculations at the
SOS-DFPT-IGLO42 level using the Perdew-Wang-91 exchange-
correlation functional and the IGLO III TZ2P basis set as implemented
in the deMon NMR program using the Pipek-Mezey localization
procedure for analyzing the σ and π contributions.43
Preparation of 2-{2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl}-
1,2-dihydro-2-silanaphthalene (4a). A mixture of 4a (2.90 mg, 4.15
mmol), NBS (4.43 g, 24.9 mmol), and a catalytic amount of benzoyl
peroxide was dissolved in benzene (300 mL) and refluxed for 2 h. After
removal of the solvent, addition of THF (200 mL), and cooling to 0
°C, LiAlH4 (1.5 g, 40 mmol) was added to the mixture, which was
stirred for 2 h. AcOEt (20 mL) was added, the solvent evaporated, and
the residue dissolved in chloroform (300 mL) and filtered. Purification
by WCC (SiO2/hexane) gave an inseparable mixture of 4a and 5a (∼3:2
ratio determined by NMR).
Preparation of 1,2,3,4-Tetrahydro-2-silanaphthalene (2). To the
suspension of LiAlH4 (1.5 g, 40 mmol) in ether (30 mL) was added
1,2,3,4-tetrahydro-2,2-dichloro-2-silanaphthalene (5.95 g, 27.4 mmol)
dropwise at room temperature. After the reaction mixture was stirred
for 30 min, AcOEt (5 mL) was added to it, and the solvent was
evaporated. Removal of inorganic salts by SCC (SiO2/hexane) gave
almost pure 2 (4.09 g, 100%) as a colorless liquid. 2: bp 88 °C/23
1
mmHg; H NMR (CDCl3) δ 0.99-1.03 (m, 2H), 2,17 (t, J ) 3.2 Hz,
2H), 2.78 (t, J ) 6.9 Hz, 2H), 3.83 (quint, J ) 3.5 Hz, 2H), 7.10-7.17
(m, 4H); 13C NMR (CDCl3) δ 3.51 (t), 12.94 (t), 29.07 (t), 125.38 (d),
126.73 (d), 128.22 (d), 129.52 (d), 136.97 (s), 141.40 (s); HRMS (EI,
70 eV): found m/z 148.0699, calcd for C9H12Si ([M]+) 148.0709. Anal.
Calcd for C9H12Si: C, 72.90; H, 8.15. Found: C, 73.08; H, 8.01.
This mixture was dissolved in THF (80 mL) and cooled to -78 °C;
to this mixture was added t-BuLi (0.56 M in pentane, 3.6 mmol). After
the solution was stirred for 1 min, excess amount of aqueous NH4Cl
was added. The solvent was evaporated, and inorganic salts were
removed by SCC (SiO2/hexane). Reprecipitation from CH2Cl2/CH3CN
gave pure 4a (2.22 g, 77% from 3a) as a white powder. 4a: mp 135-
(40) Zhdanov, A. A.; Andrianov, K. A.; Odinets, V. A.; Karpova, I. V.
Zh. Obshch. Khim. 1966, 36, 521. (b) Chernyshev, E. A.; Komalenkova,
N. G.; Bashkirova, S. A.; Kuz′mina, T. M.; Kisin, A. V. Zh. Obshch. Khim.
1975, 45, 2227.
1
138 °C; H NMR (CDCl3) δ -0.09 (s), -0.08 (s), -0.00 (s), -0.03
(s), -0.03 (s), 1.30 (s, 1H), 2.16 (br s, 1H), 2.22 (br s, 1H), 2.39 (dd,
J ) 17, 4 Hz, 1H), 2.50 (dd, J ) 17, 5 Hz, 1H), 5.00 (t, J ) 4 Hz,
1H), 6.24 (br s, 1H), 6.36 (br s, 1H), 6.27 (d, J ) 14 Hz, 1H), 7.09-
7.15 (m, 4H), 7.30 (d, J ) 14 Hz, 1H); 13C NMR (CDCl3) δ 0.39 (s),
0.67 (s), 0.70 (s), 1.01 (s), 17.37 (t), 28.66 (d), 28.98 (d), 30.46 (d),
121.71 (d), 124.52 (s), 125.89 (d), 126.29 (d), 126.65 (d), 127.75 (d),
130.75 (d), 132.29 (d), 135.14 (s), 135.40 (s), 144.90 (s), 147.00 (d),
151.83 (s), 152.10 (s); 29Si NMR (CDCl3) δ -43.91, 1.72, 1.81. HRMS
(EI, 70 eV): found m/z 696.3702, calcd for C36H68Si7 ([M]+) 696.3706.
Anal. Calcd for C36H68Si7: C, 61.98; H, 9.82. Found: C, 61.70; H,
9.69.
(41) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A. Jr.;
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.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.5;
Gaussian, Inc.: Pittsburgh, PA, 1998.
Preparation of 2-{2,6-Bis[bis(trimethylsilyl)methyl]-4-[tris(tri-
methylsilyl)methyl]phenyl}-1,2-dihydro-2-silanaphthalene (4b). Com-
pound 4b was synthesized by the same procedure as that for 4a. The
use of 3b (1.90 g, 2.46 mmol), NBS (2.67 mg, 1.50 mmol), and LiAlH4
(0.7 g, 18 mmol) gave an inseparable mixture of 4b and 5b ( ∼5:4
ratio determined by NMR), which was treated with t-BuLi (1.81 M in
(42) (a) Malkin, V. G.; Malkin, O. L.; Eriksson, L. A.; Salahub, D. R.
Modern Density Functional Theory; Seminario, J. M., Politzer, P., Eds.;
Elsevier: Amsterdam, 1995; p 273. (b) Malkin, V. G.; Malkin, O. L.;
Eriksson, L. A.; Salahub, D. R. J. Am. Chem. Soc. 1994, 116, 5898.
(43) Pipek, J.; Mezey, P. G. J. Chem. Phys. 1989, 90, 4916.

Synthesis of Stable 2-Silanaphthalenes
J. Am. Chem. Soc., Vol. 121, No. 49, 1999 11343
pentane, 4.9 mmol) to afford 4b as a white powder. 4b: mp 208-212
°C; 1H NMR (CDCl3) δ -0.06 (s, 18H), 0.10 (s, 18H), 0.25 (s, 27H),
2.38 (s, 2H), 2.42 (dd, J ) 16.8, 4.8 Hz, 1H), 2.50 (dd, J ) 16.8, 4.4
Hz, 1H), 5.03(br m, 1H), 6.30 (d, J ) 14.0 Hz, 1H), 6.70 (s, 2H),
7.10-7.14 (m, 4H), 7.29 (d, J ) 14.0 Hz, 1H); 13C NMR (CDCl3) δ
1.11 (q), 1.46 (q), 5.40 (q), 17.36 (t), 22.23 (s), 22.91 (d), 125.96 (d),
126.39 (d), 126.55 (d), 127.09 (s), 127.76 (d), 130.74 (d), 132.19 (d),
135.07 (s), 135.33 (s), 146.68 (s), 146.77 (d), 151.78 (s); 29Si NMR
(CDCl3) δ -42.82, 0.69, 1.44, 1.54. HRMS (EI, 70 eV): found m/z
768.4097, calcd for C39H76Si8 ([M]+) 768.4101. Anal. Calcd for C39H76-
Si8: C, 60.85; H, 9.95. Found: C, 60.69; H, 9.73.
were calculated, assuming that 1a was pure. 1a: mp 151-155 °C (dec);
1H NMR (C6D6) δ 0.14 (s, 36H), 0.16 (s, 18H), 1.53 (s, 1H), 2.61 (br
s, 1H), 2.72 (br s, 1H), 6.61 (br s, 1H), 6.73 (br s, 1H), 6.99 (ddd, J )
8.1, 6.9, 1.2 Hz, 1H), 7.20 (ddd, J ) 8.1, 6.9, 1.2 Hz, 1H), 7.24 (dd,
J ) 13.0, 2.2 Hz, 1H), 7.40 (d, J ) 2.2 Hz, 1H), 7.60 (d, J ) 8.1 Hz,
1H), 7.64 (d, J ) 8.1 Hz, 1H), 8.48 (d, J ) 13.0 Hz, 1H); 13C NMR
(C6D6, 126 MHz) δ 0.62 (q), 0.82 (q), 31.51 (d), 36.87 (d), 37.50 (d),
116.01 (d), 120.58 (d), 121.53 (d), 122.56 (d), 125.69 (s), 126.08 (d),
126.70 (d), 128.26 (s), 128.77 (d), 133.27 (d), 146.53 (s), 148.01 (s),
148.95 (d), 152.33 (s), 152.38 (s); 29Si NMR(C6D6, 54 MHz) δ 2.2,
2.5, 87.3; UV-vis (hexane) λmax 267 nm (ꢀ 2 × 104), 327 nm (ꢀ 7 ×
103), 387 nm (ꢀ 2 × 103). HRMS (EI, 70 eV): found m/z 694.3554
([M]+), calcd for C36H66Si7 694.3549. Anal. Calcd for C36H66Si7: C,
62.17; H, 9.56. Found: C, 60.97; H, 9.44.
Synthesis of 1b. Compound 1b was synthesized by the same
procedure as that for 1a. The use of 6b (216 mg, 0.254 mmol) and
t-BuLi (0.45 M in hexane, 3.0 mmol) gave 2-{2,6-bis[bis(trimethylsilyl)-
methyl]-4-[tris(trimethylsilyl)methyl]phenyl}-2-silanaphthalnene (1b)
( ∼50% yield estimated by NMR spectra). Recrystallization from
hexane gave small amount of 1b as a white powder. 1b: 1H NMR
(C6D6) δ 0.15 (s, 36H), 0.36 (s, 27H), 2.85 (s, 2H), 7.00 (ddd, J ) 8.2,
7.0, 1.2 Hz, 1H), 7.06 (s, 2H), 7.19 (dd, J ) 13.1, 2.2 Hz, 1H), 7.20
(ddd, J ) 8.2, 7.0, 1.2 Hz, 1H), 7.33 (d, J ) 2.2 Hz, 1H), 7.60 (d, J
) 8.2 Hz, 1H), 7.64 (d, J ) 8.2 Hz, 1H), 8.49 (d, J ) 13.1 Hz, 1H);
13C NMR (C6D6) δ 1.19 (q), 5.46 (q), 23.29 (s), 39.25 (s), 114.97 (d),
120.55 (d), 121.96 (d), 125.99 (d), 126.77 (d), 128.59 (s), 128.72 (s),
133.30 (d), 146.49 (s), 148.99 (d), 149.59 (s), 151.94 (s); 29Si NMR
(C6D6) δ 1.15, 2.18, 86.68.
Bromination of 4a. 4a (50 mg, 0.072 mmol) and NBS (13 mg,
0.073 mmol) were dissolved in CCl4 (10 mL) under dry air, and the
solution was stirred at 0 °C. After disappearance of 4a ( ∼5 days) the
solvent was evaporated, hexane (10 mL) was added, and the mixture
was filtered. Removal of the solvent afforded almost pure 2-{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}-2-bromo-1,2-dihydro-2-silanaph-
thalene (6a) (48.5 mg, 87%) as white powder. As 6a gradually
decomposed in air to give TbtH, further purification was not performed.
6a: mp 168-176 °C dec; 1H NMR (C6D6, 500 MHz) δ 0.12 (s, 18H),
0.15 (s, 9H), 0.19 (s, 9H), 0.20 (s, 9H), 0.26 (s, 9H), 1.44 (s, 1H), 2.67
(br s, 1H), 2.70 (br s, 1H), 3.07 (d, J ) 16.2 Hz, 1H), 3.19 (d, J )
16.2 Hz, 1H), 6.47 (br s, 1H), 6.60 (br s, 1H), 6.61 (d, J ) 13.5 Hz,
1H), 6.87-7.06 (m, 5H); 13C NMR (C6D6, 126 MHz) δ 0.91 (q), 0.94
(q), 1.01 (q), 1.14 (q), 1.54 (q), 1.65 (q), 27.91 (t), 29.18 (d), 29.56
(d), 31.11 (d), 122.86 (d), 123.55 (s), 126.62 (d), 128.29 (d), 128.42
(d), 129.40 (d), 130.68 (d), 132.00 (d), 134.79 (s), 135.04 (s), 144.85
(d), 146.82(s), 152.84 (s), 153.46 (s); 29Si NMR (C6D6, 54 MHz) δ
-7.51, 1.68, 2.16, 2.30, 2.78. HRMS (FAB): found m/z 776.2819, calcd
for C36H6781BrSi7 ([M]+) 776.2790. Anal. Calcd for C36H67BrSi7: C,
55.69; H, 8.69; Br, 10.29. Found: C, 56.43; H, 9.01; Br, 7.71.
Bromination of 4b. Bromination of 4b was performed by the same
procedure as that for 4a. The use of 4b (200 mg, 0.260 mmol), NBS
(46.7 mg, 0.262 mmol) gave almost pure 2-{2,6-bis[bis(trimethylsilyl)-
methyl]-4-[tris(trimethylsilyl)methyl]phenyl-2-bromo-1,2-dihydro-2-si-
lanaphthalene (6b) (216 mg, 98%) as a white powder. 6b was also
Crystal Data of 1a. Formula C36H66Si7, M ) 695.52, monoclinic,
space group P21/c, a ) 12.762(6) Å, b ) 9.91(1) Å, c ) 34.67(1) Å,
â ) 96.58(3) °, V ) 4356(4) Å3, Z ) 4, Dc ) 1.060 g cm-3, R )
0.071 (Rw ) 0.047). Colorless and prismatic single crystals of 1a were
grown by the slow evaporation of its hexane solution. The intensity
data were collected on a Rigaku AFC7R diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.71069 Å) at 193 K. The
structure was solved by direct method with SHELXS-86, and refined
by the full-matrix least-squares method. All the non-hydrogen atoms
were refined anisotropically, and all hydrogen atoms were located by
calculation. The final cycles of the least-squares refinements were based
on 6018 observed reflections (I > 5.00σ|I|) and 388 variable parameters.
Reaction of 1a with Deuterium Oxide. To 1a (30 mg, 0.043 mmol
if pure) was added deuterium oxide (0.5 mL) and THF (2 mL). After
the solution was stirred for 10 min, the solvent was removed.
Purification by PTLC (hexane/chloroform ) 2:1) afforded 1-deuterio-
2-hydroxy-2-{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}-1,2-dihydro-
2-silanaphthalene (8) as a white powder (25.8 mg, 84%). As the D
1
unstable in air. 6b: mp 192-198 °C dec; H NMR (C6D6) δ 0.19 (s,
18H), 0.28 (s, 18H), 0.32 (s, 27H), 2.84 (s, 2H), 3.02 (d. J ) 16.5 Hz,
1H), 3.18 (d, J ) 16.5 Hz, 1H), 6.63 (d, J ) 13.7 Hz, 1H), 6.88 (s,
2H), 6.88-6.97 (m, 4H), 7.06 (d, J ) 7.3 Hz, 1H); 13C NMR (C6D6)
δ 1.87 (q), 2.01 (q), 5.67 (q), 22.67 (s), 27.74 (d), 30.04 (d), 126.32
(s), 126.64 (d), 127.71 (d), 128.29 (d), 128.44 (d), 129.60 (d), 130.61
(d), 131.92 (d), 134.70 (s), 134.89 (s), 144.41 (d), 148.73(s), 152.81
(s); 29Si NMR (C6D6) δ -8.12, 1.06, 1.96, 2.48. HRMS (FAB): found
m/z 846.3199, calcd for C39H7579BrSi8 ([M]+) 846.3207. Anal. Calcd
for C39H75BrSi8: C, 55.19; H, 8.90; Br, 9.41. Found: C, 56.06; H,
8.83; Br, 8.74.
1
content of the white powder was 70% (from H NMR), the net yield
Bromination of 3a. Bromination of 3a was performed by the same
procedure as that for 4a. The use of 3a (50 mg, 0.071 mmol) and NBS
(14.0 mg, 0.079 mmol) gave almost pure 2-{2,4,6-tris[bis(trimethyl-
silyl)methyl]phenyl}-2-bromo-1,2,3,4-tetrahydro-2-silanaphthalene (7a)
(56.7 mg, 100%) as a white powder. 7a was also unstable in air. 7a:
1H NMR (CDCl3) δ 0.02 (s, 9H), 0.05 (s, 9H), 0.06 (s, 18H), 0.10 (s,
9H), 0.11 (s, 9H), 1.36 (s, 1H), 1.50 (ddd, J ) 15.6, 10.8, 5.5 Hz, 1H),
1.72 (dt, J ) 14.8, 5.2 Hz, 1H), 2.05 (br s, 1H), 2.11 (br s, 1H), 2.77
(ddd, J ) 14.8, 10.8, 5.0 Hz, 1H), 2.83 (d, J ) 14.5 Hz, 1H), 2.92 (d,
J ) 14.5 Hz, 1H), 2.97 (dt, J ) 14.3, 5.6 Hz, 1H), 6.31 (br s, 1H),
6.44 (br s, 1H), 7.14-7.20 (m, 4H); 13C NMR (CDCl3) δ 0.39 (q),
0.80 (q), 0.98 (q), 1.03 (q), 1.53 (q), 20.42 (t), 28.64 (d), 29.14 (d),
29.53 (t), 30.50 (t), 30.72 (d), 122.38 (d), 124.53 (s), 125.99 (d), 126.67
(d), 127.44 (d), 127.68 (d), 130.54 (d), 135.98 (s), 139.89 (s), 146.29
(s), 151.85 (s), 152.77 (s).
Synthesis of 1a. To a solution of 6a (334 mg, 0.43 mmol) in hexane
(10 mL) was added t-BuLi (0.59 M in hexane, 0.045 mmol) with
stirring. The solution was transferred into a Pyrex tube and degassed
and sealed. After opening the tube in the glovebox filled with argon,
the solvent was slowly removed. Generation of 2-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-2-silanaphthalene (1a) was confirmed
by NMR spectra ( ∼80%), although only small amount of pure 1a
was obtained by careful recrystallization from hexane. This crude
mixture was used for further reactions without purification, and yields
of 8 was 59%. The following data were obtained for the sample which
was prepared by the reaction of 1a with H2O. 8: mp 169-171 °C dec;
1H NMR (CDCl3, 500 MHz) δ -0.07 (s, 9H), -0.05 (s, 9H), 0.04 (s,
18H), 0.05 (s, 9H), 0.09 (s, 9H), 1.31 (s, 1H), 1.67 (s, 1H), 2.42 (br s,
1H), 2.46 (br s, 1H), 2.48 (d, J ) 16.8 Hz, 1H), 2.55 (d, J ) 16.8 Hz,
1H), 6.25 (br s, 1H), 6.36 (d, J ) 14.0 Hz, 1H), 6.37 (br s, 1H), 7.08-
7.14 (m, 4H), 7.27 (d, J ) 14.0 Hz, 1H); 13C NMR (CDCl3, 126 MHz)
δ 0.54 (q), 0.73 (q), 0.77 (q), 0.89 (q), 1.14 (q), 24.77 (t), 28.27 (d),
28.54 (d), 30.42 (d), 122.08 (d), 125.78 (d), 125.99 (s), 127.06 (d),
127.51 (d), 130.48 (d), 130.55 (d), 133.23 (d), 135.10 (s), 136.00 (s),
144.99 (s), 146.03 (d), 151.51 (s), 151.97 (s); 29Si NMR (CDCl3, 54
MHz) δ -11.70, 1.61, 1.78, 2.13. HRMS (FAB): found m/z 712.3628
([M]+), calcd for C36H68OSi7 712.3655. Anal. Calcd for C36H68OSi7:
C, 60.59; H, 9.60. Found C, 60.29; H, 9.65.
Reaction of 1a with Methanol. To 1a (30 mg, 0.043 mmol if pure)
was added methanol (0.5 mL) and THF (2 mL). After the solution was
stirred for 10 min, the solvent was removed. Purification by PTLC
(hexane/chloroform ) 2:1) afforded 2-methoxy-2-{2,4,6-tris[bis(tri-
methylsilyl)methyl]phenyl}-1,2-dihydro-2-silanaphthalene (9) as a white
1
powder (22.6 mg, 72%). 9: mp 162-164 °C; H NMR (CDCl3, 500
MHz) δ -0.10 (s, 9H), -0.07 (s, 9H), 0.03 (s, 18H), 0.05 (s, 9H),
0.08 (s, 9H), 1.29 (s, 1H), 2.34 (d, J ) 17.2 Hz, 1H), 2.47 (br s, 1H),
2.50 (br s, 1H), 2.55 (d, J ) 17.2 Hz, 1H), 3.32 (s, 3H), 6.22 (br s,
1H), 6.29 (d, J ) 14.0 Hz, 1H), 6.35 (br s, 1H), 7.08-7.14 (m, 4H),

11344 J. Am. Chem. Soc., Vol. 121, No. 49, 1999
Wakita et al.
7.38 (d, J ) 14.0 Hz, 1H); 13C NMR (CDCl3, 126 MHz) δ 0.50 (q),
0.72 (q), 0.73 (q), 0.77 (q), 0.86 (q), 1.17 (q), 21.63 (t), 28.09 (d),
28.33 (d), 30.34 (d), 50.21 (q), 122.02 (d), 125.64 (d), 125.65 (s), 126.97
(d), 127.45 (d), 128.20 (d), 130.72 (d), 132.17 (d), 135.12 (s), 136.48
(s), 144.73 (s), 147.30 (d), 151.66 (s), 152.14 (s); 29Si NMR (CDCl3,
54 MHz) δ -11.12, 1.44, 1.75, 2.23. HRMS (FAB): found m/z
726.3784 ([M]+), calcd for C37H70OSi7 726.3811. Anal. Calcd for
C37H70OSi7‚0.5H2O: C, 60.33; H, 9.71. Found C, 60.29; H, 9.65.
Reaction of 1a with Benzophenone. 1a (30 mg, 0.043 mmol if
pure) and benzophenone (30 mg, 0.16 mmol) were dissolved in C6D6
(0.8 mL). 1a disappeared immediately, and removal of the solvent
followed by purification by PTLC (hexane/chloroform ) 1:1) afforded
3,9b-dihydro-1,1-diphenyl-3-{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}-
1H-[2]benzosilino[2,1-b][1,2]oxasilete (10) as a white powder (23.4
(d), 41.84 (t), 122.18 (d), 125.86 (d), 126.55 (s), 126.96 (s), 127.44
(d), 127.97 (d), 128.26 (s), 128.77 (d), 130.45 (d), 132.42 (d), 135.85
(s), 141.39 (s), 144.07 (s), 144.61 (d), 151.52 (s), 151.97 (s); 29Si NMR
(CDCl3, 54 MHz) δ -24.87, 1.68, 1.78, 1.96. HRMS (EI, 70 eV):
found m/z 776.4315 ([M]+); calcd for C42H76Si7 776.4332. Anal. Calcd
for C42H76Si7: C, 64.86; H, 9.85. Found C, 64.60; H, 9.56.
Crystal Data of 12. Formula C42H76Si7, M ) 777.66, triclinic, space
group P1h, a ) 13.220(2) Å, b ) 16.128(3) Å, c ) 12.486(3) Å, R )
93.33(2)°, â ) 97.11(1)°, γ ) 106.66(1)°, V ) 2518.4(8) Å3, Z ) 2,
Dc ) 1.025 g cm-3, R ) 0.056 (Rw ) 0.038). Colorless and prismatic
single crystals of 12 were grown by the slow evaporation of its CHCl3/
CH3CN solution. The intensity data were collected on a Rigaku AFC5R
diffractometer with graphite-monochromated Mo KR radiation (λ )
0.71069 Å) at 296 K. The structure was solved by direct method with
SHELXS-86, and refined by the full-matrix least-squares method. All
the non-hydrogen atoms were refined anisotropically, and all hydrogen
atoms were located by calculation. The final cycles of the least-squares
refinements were based on 5179 observed reflections (I > 3.00σ|I|)
and 442 variable parameters.
Reaction of 1a with 1 Equiv Amount of Elemental Sulfur. 1a
(30 mg, 0.043 mmol) and elemental sulfur (1.4 mg, 0.044 mmool as S
atom) were dissolved in C6D6 (0.7 mL). After the solution was
transferred into an NMR tube, degassed, and sealed, the signal
assignable to 13 (δSi ) -67.62) was observed by 29Si NMR. However,
purification of this reaction mixture by PTLC (hexane/chloroform )
2:1) gave only a hydrolyzed product (11.3 mg, 37%), and the rest was
a complex mixture.
1
mg, 62%). 10: mp 230-235 °C dec; H NMR (CDCl3) δ -0.19 (s,
9H), -0.15 (s, 9H), 0.013 (s, 18H), 0.017 (s, 9H), 0.05 (s, 9H), 1.32
(s, 1H), 1.90 (br s, 1H), 1.93 (br s, 1H), 4.49 (s, 1H), 6.09 (d, J ) 14.7
Hz, 1H), 6.25 (br s, 1H), 6.36 (br s, 1H), 6.79 (d, J ) 7.0 Hz, 1H),
6.88-6.91 (m, 4H), 7.05-7.14 (m, 4H), 7.19-7.27 (m, 3H), 7.43 (d,
J ) 7.3 Hz, 1H), 7.62 (d, J ) 7.3 Hz, 2H); 13C NMR (CDCl3, 126
MHz) δ 0.44 (q), 0.61 (q), 0.67 (q), 0.77 (q), 1.11 (q), 28.45 (d), 29.26
(d), 30.72 (d), 48.72 (q), 92.42 (s), 121.40 (d), 125.39 (d), 125.64 (d),
126.01 (d), 126.17 (s), 126.19 (d), 126.39 (d), 126.72 (d), 126.86 (d),
126.91 (d), 127.69 (d), 127.73 (d), 131.94 (d), 132.61 (d), 135.71 (s),
136.32 (s), 143.69 (s), 146.24 (s), 150.13 (d), 150.53 (s), 150.87 (s),
151.01 (s); 29Si NMR (CDCl3, 54 MHz) δ 1.82, 2.40, 5.11. HRMS-
(FAB): observed m/z 877.4375 ([M + H]+); calcd for C49H76OSi7
877.4375. Anal. Calcd for C49H76OSi7: C, 67.05; H, 8.72. Found C,
67.32; H, 8.84.
Reaction of 1a with an Excess Amount of Elemental Sulfur. 1a
(98.8 mg, 0.142 mmol) and elemental sulfur (50 mg, 1.56 mmol as S
atom) were dissolved in benzene (4 mL). After removal of the solvent,
the crude products were submitted to separation by WCC (hexane/
chloroform ) 2:1) and HPLC to afford 4,10b-dihydro-4-{2,4,6-tris-
[bis(trimethylsilyl)methyl]phenyl}-[2]benzosilino[2,1-d]-1,2,3,4-trithia-
Reaction of 1a with Mesitonitrile Oxide. By the same procedure
as that for 9, 1a (30 mg, 0.043 mmol if pure) and mesitonitrile oxide
(30 mg, 0.19 mmol) afforded 4,10b-dihydro-1-mesityl-4-{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-[2]benzosilino-[1,2-d][1,2,5]ox-
azasilole (11) as a white powder (28.5 mg, 77%). 11: mp 224-232
1
silole (14) as a white powder (23.0 mg, 20%). H NMR (CDCl3) δ
1
°C; H NMR (CDCl3) δ -0.12 (s, 9H), -0.08 (s, 9H), 0.01 (s, 18H),
-0.10 (s, 9H), -0.05 (s, 9H), 0.02 (s, 18H), 0.07 (s, 9H), 0.11 (s, 9H),
1.32 (s, 1H), 2.46 (s, 2H), 4.40 (s, 1H), 6.14 (d, J ) 13.8 Hz, 1H),
6.29 (br s, 1H), 6.41 (s, 1H), 7.15-7.26 (m,5H); 13C NMR (CDCl3,
126 MHz) δ 0.55 (q), 0.73 (q), 0.89 (q), 0.98 (q), 1.30 (q), 29.2 (d),
29.50 (d), 30.89 (d), 44.11 (d), 118.56 (s), 122.70 (d), 126.66 (d), 127.79
(d), 127.97 (d), 128.26 (d), 131.20 (d), 134.13 (d), 134.58 (s), 136.00
(s), 144.15 (d), 147.18 (s), 153.57 (s), 153.95 (s); 29Si NMR (CDCl3,
54 MHz) δ 1.99, 2.16, 2.57, 15.37. HRMS(FAB): observed m/z
791.2773, calcd for C36H67Si7S3 791.2790. Anal. Calcd for C36H67-
Si7S3: C, 54.62; H, 8.40; S, 12.15. Found C, 53.91; H, 8.33; S, 10.32.
0.03 (s, 9H), 0.05 (s, 9H), 1.36 (s, 1H), 1.38 (s, 3H), 1.88 (br s, 1H),
1.97 (br s, 1H), 2.20 (s, 3H), 2.25 (s, 3H), 3.85 (s, 1H), 6.25 (d, J )
14.4 Hz, 1H), 6.35 (br s, 1H), 6.46 (br s, 1H), 6.48 (d, J ) 7.6 Hz,
1H), 6.55 (s, 1H), 6.83 (s, 1H), 6.90 (t, J ) 7.7 Hz, 1H), 7.12 (d, J )
7.6 Hz, 1H), 7.17 (t, J ) 7.3 Hz, 1H), 7.37 (d, J ) 14.7 Hz, 1H); 13C
NMR (CDCl3, 126 MHz) δ 0.34 (q), 0.68 (q), 0.71 (q), 0.91 (q), 1.23
(q), 18.60 (q), 19.68(q), 21.03 (q), 29.37 (d), 29.83 (d), 30.79 (d), 41.65
(d), 121.85 (d), 123.71 (s), 125.56 (d), 126.80 (d), 127.45 (d), 127.83
(d), 127.86 (d), 127.98 (d), 128.63 (s), 130.22 (s), 131.84 (d), 134.74
(d), 135.20 (s), 135.30 (s), 137.89 (s), 138.03 (s), 146.27 (s), 148.48
(d), 151.87 (s), 152.26 (s), 166.04 (s). 29Si NMR (CDCl3, 54 MHz) δ
1.61, 1.85, 2.68, 6.86. HRMS (FAB): observed m/z 856.4485 ([M +
H]+); calcd for C46H79ONSi7 856.4469. Anal. Calcd for C46H77ONSi7‚
H2O: C, 63.16; H, 9.10; N, 1.60. Found C, 63.47; H, 9.18; N, 1.35.
Reaction of 1a with 2,3-Dimethyl-1,3-butadiene. To a solution 6a
(87.8 mg, 0.113 mmol) in hexane (2 mL) was added t-BuLi (0.56 M
in hexane, 0.134 mmol) and 2,3-dimethyl-1,3-butadiene (1 mL). The
solution was transferred into a Pyrex tube and degassed and sealed.
After heating at 100 °C for 20 h, the tube was opened. Purification by
DCC (hexane) afforded 4b,5,8,8a-tetrahydro-6,7-dimethyl-8a-{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}-8a-silaphenanthrene (12) as a
white powder (62.9 mg, 72%). 12: mp 153-159 °C; 1H NMR (CDCl3)
δ -0.07 (s, 9H), -0.06 (s, 9H), -0.04 (s, 9H), 0.009 (s, 9H), 0.011 (s,
9H), 0.04 (s, 9H), 1.26 (s, 1H), 1.49 (s, 3H), 1.66 (s, 3H), 1.70 (d, J )
15.6 Hz, 1H), 1.79 (t, J ) 6.7 Hz, 1H), 2.10 (br s, 1H), 2.15 (br s,
1H), 2.36 (d, J ) 6.7 Hz, 1H), 2.53 (t, J ) 6.7 Hz, 1H), 6.06 (d, J )
Acknowledgment. This work was partially supported by
Grants-in-Aid for Scientific Research from the Ministry of
Education, Science, Sports and Culture, Japan (Nos. 08454197
and 10440184) and at Erlangen by the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemische Industrie. We are
grateful to Professor Yukio Furukawa, Waseda University, for
the measurement of FT-Raman spectra. We also thank Shin-
etsu Chemical Co., Ltd. and Tosoh Akzo Co., Ltd. for the
generous gift of chlorosilanes and alkyllithiums, respectively.
Supporting Information Available: Tables of crystal data,
structure solution and refinement, atomic coordinates, bond
lengths and angles, and anisotropic thermal parameters for 1a
and 12, and total electronic energies and atomic coordinations
for all molecules used in Figure 2 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
14.0 Hz, 1H), 6.22 (br s, 1H), 6.34 (br s, 1H), 7.01-7.17 (m, 5H); 13
C
NMR (CDCl3) δ 0.62 (q), 0.72 (q), 0.82 (q), 0.86 (q), 1.06 (q), 1.40
(q), 20.80 (q), 22.45 (q), 23.04 (t), 28.01 (d), 28.40 (d), 28.60 (d), 30.26
JA992024F