Aromatic benzannulated silole dianions. The dilithio and disodio salts of a silaindenyl dianion [5]

Full text of DOI:10.1021/ja973170t

5814
J. Am. Chem. Soc. 1998, 120, 5814-5815
Scheme 1
Aromatic Benzannulated Silole Dianions. The
Dilithio and Disodio Salts of a Silaindenyl Dianion1
Seok-Bong Choi, Philip Boudjouk,* and Pingrong Wei
Center for Main Group Chemistry, Department of Chemistry
North Dakota State UniVersity, Fargo, North Dakota 58105
ReceiVed September 10, 1997
Interest in silole dianions has escalated sharply since the initial
report by Joo and co-workers that stable derivatives of these
species could be prepared.2 The main reason for the heightened
interest is the discovery that their spectroscopic and structural
properties are consistent with significant π-delocalization.3-5
These interpretations have been supported by calculations.4,6
In this communication we report the synthesis and characteriza-
tion of the first benzannulated silole dianions, dilithium BPSI (2)
(BPSI ) 3-n-butyl-2-phenyl-1-silaindene) and disodium BPSI (3).
To our surprise, we find that, upon formation of the dianion, the
silicon containing ring becomes aromatic, apparently at the
expense of the fused benzene ring, which takes on the features
of a conjugated diene.
Stirring 1,1-dichloro-BPSI (1)7 with excess lithium in THF im-
mediately produced a dark red solution. After removal of unre-
acted lithium, treatment of this solution with an excess of methyl
iodide or trimethylchlorosilane gave 1,1-dimethyl-BPSI (4)8 or
1,1-bis(trimethylsilyl)-BPSI (5)9 in high yields (Scheme 1). Com-
pound 2, while extremely air sensitive, is thermally stable under
argon in THF for up to 1 year.
Analysis of the X-ray data for 2 shows two differently
coordinated lithium ions (Figure 1).10 One lithium ion is η1-co-
* To whom correspondence should be addressed.
(1) Preliminary results have been presented: (a) Boudjouk, P. XIth
International Symposium on Organosilicon Chemistry, Abstract No. LC8;
September 1-6, 1996, Montpellier, France. (b) Boudjouk, P.; Choi, S.-B.
XXXth Symposium on Organosilicon Chemistry, Abstract No. A20; May 30-
31, 1997; London, Ontario, Canada.
(2) Joo, W.-C.; Hong, J.-H.; Choi, S.-B.; Son, H.-E. J. Organomet. Chem.
1990, 391, 27.
(3) Hong, J.-H.; Boudjouk, P.; Castellino, S. Organometallics 1994, 13,
3387.
(4) West, R.; Sohn, H.; Bankwitz, J.; Calabrese, J.; Apeloig, Y.; Mueller,
T. J. Am. Chem. Soc. 1995, 117, 11608.
(5) Freeman, W. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L. Angew.
Chem., Int. Ed. Engl. 1996, 35, 882.
(6) (a) Goldfuss, B.; Schleyer, P. v. R.; Hampel, F. Organomettalics 1996,
15, 1755. (b) Goldfuss, B.; Schleyer, P. v. R. Organometallics 1997, 16, 1543.
(7) 1 was prepared by a modification of the Rausch approach (Rausch, M.
D.; Klemann, L. P. J. Am. Chem. Soc. 1967, 89, 5732). n-BuLi (225 mmol)
was added to a stirred suspension of diphenylacetylene (21.5 g, 121 mmol)
in hexane (80 mL) and TMEDA (45 mL, 300 mmol) at 0 °C and stirred for
5 h at room temperature. SiCl4 (41 mL, 363 mmol) was then added at -78
°C and the mixture was stirred for 3 h while allowing the reaction mixture to
warm slowly to room temperature. Filtration, followed by the removal of vola-
tiles, afforded a viscous liquid. Crystallization of this residue in hexane at
low temperature gave white crystals of 1 (27.3 g, yield 68%). Selected data
for 1. mp 64-65 °C, 1H NMR (THF-d8, reference; THF-d8 ) 1.72 ppm),
0.85 (t, 3H), 1.34 (m, 2H), 1.57 (m, 2H), 2.64 (m, 2H), 7.27-7.71 (m, 9H);
13C NMR (THF-d8, ref; THF-d8 ) 24.45 ppm); 14.16 (CH3), 23.72 (CH2),
28.44 (CH2), 32.09 (CH2), 158.07 (C), 146.99 (C), 137.49 (C), 134.64 (C),
130.50 (C), 133.77 (CH), 132.37 (CH), 129.70 (CH), 129.49 (CH), 128.93
(CH), 127.90 (CH), 123.89 (CH), 29Si NMR (THF-d8, reference; ext. TMS )
0.00) 5.92. MS (M+, relative abundance), 336 (M+ + 4, 6), 335 (M+ + 3, 6),
334 (M+ + 2, 25), 333 (M+ + 1, 8), 332 (M+, 35), 290 (M+ - 42, 63), 253
(M+ - 79, 100), 189 (M+ - 143, 75). X-ray structure determination of C18H18-
Cl2Si (1); X-ray quality crystals of 1 were grown from a concentrated haxane
solution at room temperature. A single crystal of 1 was mounted in a thin-
walled glass capillary tube and sealed under argon. The space group is P1h,
monoclinic, with unit-cell dimensions a ) 9.4184(7) Å, b ) 10.0417(7) Å, c
) 10.5174(8) Å, R ) 66.3940(10)°, â ) 73.0090(10)°, γ ) 74.5340(10)°,
volume ) 858.88(11) Å3, Z ) 2, fw ) 333.31, dcalc ) 1.289 Mg/m3, F(000)
) 348 and abs coeff ) 0.439 mm-1. Intensity data were collected at 298(2)
K on a Siemens CCD SMART diffractometer with Mo Ka radiation and a
graphite monochromator. A total of 5117 unique reflections were measured
and 3690 [R(int) ) 0.0580] having I > 2σ(I) were independent. The structure
was solved by direct methods and refined by the full-matrix least-squares
techniques on F2 with the SHELXTL program (3679 data and 190 parameters).
Final R ) 0.0448, Rw ) 0.1242, and goodness-of-fit on F2 ) 1.064 (for all
reflections, R ) 0.0503, Rw ) 0.1232). Full details can be found in the
Supporting Information.
Figure 1. Thermal ellipsoid diagram of structure 2. Symmetry trans-
formations used to generate equivalent atoms: A, -x, -y + 1, -z; B,
1
1
1
-x, y, -z + /2; C, -x, y, -z - /2; D, -x + 1, y, -z + /2.
ordinated to the silicon atom and also coordinated to three dioxane
molecules while the other is η5-coordinated with respect to the
SiC4 ring fragment and also coordinated to two molecules of di-
oxane. These two dioxane units are linked to other η5-coordinated
(8) (a) Rausch, M. D.; Klemann, L. P.; Boon, W. H. Synth. React. Inorg.
Met.-Org. Chem. 1985, 15, 923. (b) Stirring of 1 (1.0 g, 3 mmol) in 20 mL
of THF with Li powder (130 mg, 18 mmol) for 2 h gave a dark red solution.
The solution was filtered and added to a solution of MeI (1.1 mL, 18 mmol)
in 10 mL of THF. The mixture was stirred for 5 h. After the volatiles were
removed under reduced pressure, the residue was extracted with hexane.
Evaporation of the hexane was followed by distillation of the residue under
vacuum (140-150 °C, 0.05 mmHg) to give 4 as a colorless liquid. Selected
1
data for 4: yield 95% (by GC-MS and H NMR for total reaction mixture);
1H NMR (CDCl3, reference; CDCl3 ) 7.24 ppm), 0.36 (s, 6H), 0.87 (t, 3H),
1.36 (m, 2H), 1.58 (m, 2H), 2.55 (t, 2H), 7.14-7.62 (m, 9H); 13C NMR
(CDCl3, reference; CDCl3 ) 77.23 ppm), -3.87(SiMe), 14.12 (CH3), 23.19
(CH2), 27.88 (CH2), 32.73 (CH2), 153.16 (C), 149.95 (C), 142.81 (C), 141.54
(C), 138.95 (C), 131.97 (CH), 129.95 (CH), 128.47 (CH), 127.82 (CH), 126.51
(CH), 125.70 (CH), 122.33 (CH), 29Si NMR (CDCl3, reference; ext. TMS )
0.00 ppm), 3.18 (ring Si). MS (M+, relative abundance), 294 (M+ + 2, 4.89),
293 (M+ + 1, 19.76), 292 (M+, 74.37), 277 (M+ - 15, 30.91), 250 (M+
42, 100.00).
-
(9) 1,1-Bis(trimethylsilyl)-BPSI 5: Stirring of 1 (1.0 g, 3 mmol) in 20 mL
of THF with Li powder (130 mg, 18 mmol) for 2 h gave a dark red solution.
The solution was filtered and added to a solution of (CH3)3SiCl (2.3 mL, 18
mmol) in 10 mL of THF. The mixture was stirred for 6 h. After the volatiles
were removed under reduced pressure, the residue was extracted with hexane.
Evaporation of the hexane was followed by distillation of the residue under
S0002-7863(97)03170-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 05/30/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 120, No. 23, 1998 5815
Figure 2. Thermal ellipsoid diagram of structure 1.
Figure 3. (a) Selected bond lengths (pm) of 1,1-dichloro-1-silaindene
(1). b) Selected bond lengths (pm) and angles (deg) of 1,1-dilithio-1-
silaindene (2).
lithium ions to give a polymeric crystal. Each unit molecule of
2 contains two half units of 1,4-dioxane in a unit cell.
Most notable among the structural changes when 1 is converted
plane, and the more symmetrical complex [K(18-crown-6)]2[η5,η5-
C4Me4Si]5 has a planar silole ring.
to 2 are those in the carbon-carbon bond lengths in both the
silole ring and the six-membered carbon ring (Figure 2).7
Significant shortening of the C6-C7 bond to 141.8 pm from
149.7 pm in 1 and lengthening of the C1-C6 and C7-C12 bonds
to 145.5 and 142.8 pm, respectively (141.1 and 136.5 pm in 1),
are observed in the silole ring. In contrast, the three nearly equal
(139.2, 137.5, 138.3 pm) carbon-carbon bonds linking C2, C3,
C4, and C5 in 1, consistent with a high degree of aromaticity in
the six-membered ring, undergo bond length alternation in that
portion of 2 (Figure 3). The silicon-carbon bonds are lengthened
slightly (0.35 pm) upon the conversion of 1 to 2. This change is
similar to that observed in the analogous silole system: the Si-C
bond distance in 1,1-dichloro 2,3,4,5-tetramethylsilole is 1.834
Å11 and increases to 1.840 Å5 in the aromatic dianion. The silicon
carbon bonds in siloles appear to be relatively insensitive to the
nature of the substitiuents on silicon.12-14
The 1H, 13C, and 29Si NMR spectra for 215 and 316 have
essentially the same patterns and differ only slightly in chemical
shifts for all three nuclei. It is noteworthy that the 29Si chemical
shifts for 2 and 3 are significantly downfield from that of 1 (5.92)
and very close (29.19 and 30.44 ppm, respectively), consistent
with significant π delocalization in the silicon-containing rings.
7
The Li NMR spectra of a solution of 2 show only one peak
(-0.20 ppm) over the temperature range +25 to -40 °C. These
data, as in the case for NMR data obtained for the tetraphenylsilole
dianions,3,4 do not permit unambiguous structural assignments in
solution. Processes involving η1,η5 exchanges, possibly including
7
LiCl, could explain the single peak in the Li NMR as could a
static η5,η5 structure. The latter seems less likely because of the
7
location of the Li shift. Typically η5 complexed lithium ions
are found in the -4 to -9 ppm range.6b,17,18
We attribute these changes to a fundamental alteration in the
bonding of the silaindenyl system upon formation of the dianion,
i.e., the SiC4 ring becomes aromatic like other silole dianions
and the six-membered ring takes on the properties of a cyclo-
hexadiene. Consistent with this proposal is the planar geometry
of the SiC4 ring (∑ring ) 540.0°) in 2. By comparison, the
crystal structure of [Li(THF)2][Li(THF)3][η5,η1-C4Ph4Si]4 shows
the ring to be slightly bent with the silicon atom 11 pm out of
Acknowledgment. This paper is dedicated to Professor Peter Jutzi
in celebration of his 60th birthday. Financial support from the National
Science Foundation through Grant No. OSR 9452892 is gratefully
acknowledged. We are also grateful for assistance with our NMR studies
from Dan Wanner.
Supporting Information Available: Details of the crystallographic
analyses of 1 and 2 (13 pages, print/PDF). See any current masthead
page for ordering information and Web access instructions.
JA973170T
vacuum (85-95 °C, 0.05 mmHg) to give 5 as a colorless liquid, which
solidified after a few hours at room temperature. Selected data for 5: yield
1
98% (by GC-MS and H NMR for total reaction mixture); mp 69-70 °C;
(13) Muir, K. W.; Walker, R.; Abel, E. W.; Blackmore, T.; Whitley, R. J.
J. Chem. Soc., Chem. Commun. 1975, 698.
(14) Yamaguchi, S.; Jin, R.-Z.; Tamao, K.; Shiro, M. Organometallics 1997,
16, 2230.
1H NMR (CDCl3, reference; CDCl3 ) 7.24 ppm), 0.18 (s, 18H), 0.93 (t, 3H),
1.40 (m, 2H), 1.65 (m, 2H), 2.75 (t, 2H), 7.24-7.71 (m, 9H); 13C NMR
(CDCl3, reference; CDCl3 ) 77.19 ppm), -0.50 (SiMe3), 14.12 (CH3), 23.06
(CH2), 28.33 (CH2), 32.16 (CH2), 152.61 (C), 151.43 (C), 142.93 (C), 142.60
(C), 140.48 (C), 132.49 (CH), 128.45 (CH), 128.23 (CH), 128.17 (CH), 125.50
(CH), 125.21 (CH), 122.85 (CH), 29Si NMR (CDCl3, reference; ext. TMS )
0.00 ppm) -13.86 (SiMe3), -35.01 (ring Si). MS (M+, relative abundance),
410 (M+ + 2, 0.3), 408 (M+, 2.4), 351 (M+ - 57, 1.5), 278 (M+ - 130, 2.4),
177 (M+ - 231, 2.5), 73 (M+ - 335, 100).
(15) NMR Study of 2: 1 (100 mg, 0.3 mmol) and Li (13 mg, 1.8 mmol)
powder were placed in a 5 mm NMR tube with THF-d8 (0.75 mL). After the
NMR tube was sealed under vacuum, sonication of the NMR tube for 1 h
gave a dark red solution. Selected data for 2: 1H-NMR (THF-d8, references;
THF-d8 ) 1.72 ppm) 0.99 (t, 3H), 1.45 (m, 2H), 1.73 (m, 2H), 2.99 (t, 2H),
7.85 (d, 1H), 7.45 (d, 2H), 7.37 (d, 1H), 7.03 (t, 2H), 6.77 (t, 1H), 6.42(t,
1H), 6.01 (t, 1H); 13C NMR (THF-d8, reference; THF-d8 ) 24.45 ppm) 13.99
(CH3), 23.56 (CH2), 28.99 (CH2), 34.86 (CH2), 162.28 (C), 156.39 (C), 151.86
(C), 134.50 (C), 113.95 (C), 135.15 (CH), 129.29 (CH), 125.79 (CH), 120.63
(CH), 119.86 (CH), 115.07 (CH), 109.21 (CH); 29Si NMR (THF-d8, reference;
ext. TMS ) 0.00) 29.19.
(10) X-ray structure determination of 1,1-dilithio-3-n-butyl-2-phenyl-1-
silaindene (2); X-ray quality crystals of [Li(1/2dioxane)2][Li(dioxane)3][η5,η1-
C18H18Si][(1/2dioxane)2] (2) were grown from a concentrated 1,4-dioxane
solution at room temperature. A single crystal of 2 was mounted in a thin-
walled glass capillary tube and sealed under argon. The space group is C2/c,
monoclinic, with unit-cell dimensions a ) 29.585(2) Å, b ) 16.6840(11) Å,
c ) 18.3095(12) Å, â ) 113.0690(10)°, volume ) 8314.8(10) Å3, Z ) 8, fw
(16) NMR Study of 3: 1 (60 mg, 0.18 mmol) and Na (25 mg, 1.08 mmol)
were placed in a 5 mm NMR tube followed by THF-d8 (0.75 mL). After the
NMR tube was sealed under vacuum, sonication of the NMR tube for 48 h
gave a dark red solution. Selected data for 3: 1H-NMR (THF-d8, reference;
THF-d8 ) 1.72 ppm) 0.95 (t, 3H), 1.42 (m, 2H), 1.57 (m, 2H), 2.91 (t, 2H),
8.04 (d, 1H), 7.49 (d, 2H), 7.7.29 (d, 1H), 7.01 (t, 2H), 6.71 (t, 1H), 6.37(t,
1H), 6.02 (t, 1H); 13C NMR (THF-d8, reference; THF-d8 ) 24.45 ppm) 14.80
(CH3), 24.50 (CH2), 30.12 (CH2), 35.50 (CH2), 166.80 (C), 159.61 (C), 152.85
(C), 135.61 (C), 116.63 (C), 136.54 (CH), 130.35 (CH), 126.82 (CH), 121.27
(CH), 120.56 (CH), 114.86 (CH), 109.62 (CH); 29Si NMR (THF-d8, reference;
ext. TMS ) 0.00) 30.44.
) 716.81, dcalc ) 1.145 Mg/m3, F(000) ) 3088, and abs coeff ) 0.107 mm-1
.
Intensity data were collected at 298(2) K on a Siemens CCD SMART
diffractometer with Mo Ka radiation and a graphite monochromator. A total
of 12563 unique reflections were measured and 3880 [R(int) ) 0.0770] having
I > 2σ(I) were independent. The structure was solved by direct methods and
refined by the full-matrix least-squares techniques on F2 with the SHELXTL
program (3826 data and 460 parameters). Final R ) 0.0747, Rw ) 0.2166,
and goodness-of-fit on F2 ) 0.868 (for all reflections, R ) 0.0964, Rw
0.2558). Full details can be found in the Supporting Information.
)
(11) Bankwitz, U.; Sohn, H.; Powell, D. R.; West, R. J. Organomet. Chem.
1995, 499, C7-C9.
(12) Parkanyi, L. J. Organomet. Chem. 1981, 216, 9.
(17) Sakurai, H. Pure Appl. Chem. 1994, 66, 1431.
(18) Hong, J.-H.; Boudjouk, P. Angew. Chem., Int. Ed. Engl. 1996, 35,
186.