Communications
Experimental Section
All manipulations were carried out under a protective atmosphere of
argon, using Schlenk techniques or in a glove box.
4: At À1968C, THF (20 mL) was condensed onto the lithium salt
of 3a[6a] (5.40 g, 6.33 mmol) and TipSiCl3 (2.14 g, 6.33 mmol). The
[14]
mixture was slowly brought to room temperature (30 min) and then
stirred for 15 h. All volatiles were removed under high vacuum, and
the orange residue was dissolved in hexane (50 mL). Solid LiCl was
removed by filtration, and the clear orange solution was concentrated
to dryness, affording 4 as an orange solid (6.07 g, 99%). The product
was used for the subsequent reactions without further purification.
1H NMR (500 MHz, [D6]benzene, 258C): d = 7.09, 7.07, 7.01, 6.94 (s,
8H, Ar-H), 4.37, 4.31 (hept, 4H, iPr-CH), 4.03 (br, 2H, iPr-CH), 3.59
(hept, 2H, iPr-CH), 2.72, 2.63 (hept, 4H, iPr-CH), 1.41, 1.22, 1.14,
1.13, 1.08, 1.07, 0.89 ppm (d, 72H, iPr-CH3); 13C NMR (125 MHz,
[D6]benzene, 258C): d = 156.60, 155.97, 155.23, 154.03, 152.42, 151.74,
151.23, 151.03, 135.00, 134.12, 130.50, 130.13 (Ar-C), 122.67, 122.55,
122.36 (Ar-CH), 39.15, 38.37, 37.84, 34.74, 34.65, 34.45, 34.39, 34.22
(iPr-CH), 25.49, 25.18, 24.42, 24.31, 23.99, 23.95, 23.88, 22.69 ppm (iPr-
CH3); 29Si NMR (99 MHz, [D6]benzene, 258C): d = 99.1, 54.7,
11.7 ppm.
5: At À1968C, THF (20 mL) was added by vacuum transfer to 4
(5.90 g, 6.09 mmol) and Mg* (0.65 g, 24.3 mmol), prepared by the
thermal decomposition of magnesium anthracene.[10] While the
suspension was brought to room temperature, it gradually darkened
until it appeared almost black after 1 h. All volatiles were then
removed under high vacuum, and the solid residue was extracted with
toluene (50 mL). Following filtration, the solution was concentrated
to approximately 5 mL, and pentane (50 mL) was added. The solution
was kept at À308C overnight, leading to the precipitation of 5.10 g of
an orange–red solid. After three recrystallizations, 5 was isolated as
orange blocks (2.81 g, 42%). M.p. 2098C (minimal decomposition);
1H NMR (300 MHz, [D6]benzene, 258C): d = 7.25, 7.15 (d, 2H, Ar-
H), 7.05 (s, 2H, Ar-H), 7.02, 6.99, 6.94, 6.84 (d, 4H, Ar-H), 4.88, 4.68,
4.37, 4.10, 4.09 (hept, 7H, iPr-CH), 3.67 (br, 4H, THF), 3.45 (hept,
1H, iPr-CH), 3.19 (br, 4H, THF), 2.88, 2.81, 2.76 (hept, 4H, iPr-CH),
1.77, 1.60, 1.59, 1.53, 1.51, 1.42, 1.40, 1.32, 1.31, 1.25, 1.24, 1.23, 1.21,
1.19, 1.06, 0.89, 0.87, 0.69, 0.63, 0.58 ppm (d, 72H, iPr-CH3); 13C NMR
(75 MHz, [D6]benzene, 258C): d = 156.01, 153.85, 153.83, 153.42,
152.89, 152.26, 151.78, 148.15, 147.27, 147.24, 147.11, 145.96, 144.32,
143.65, 142.52 (Ar-C), 122.47, 122.13, 121.23, 121.02, 120.55, 120.33,
120.30 (Ar-CH), 70.16 (br, THF), 69.36 (br, THF), 37.28, 36.38, 36.19,
36.01, 35.90, 35.56, 34.93, 34.82, 34.73, 34.50, 33.25 (iPr-CH), 27.30,
26.60, 26.43, 26.34, 26.06, 25.59, 25.41, 25.09, 24.78, 24.65, 24.58, 24.56,
24.49, 24.46, 24.36, 24.32, 24.24, 24.12, 23.94 ppm (iPr-CH3); 29Si NMR
(60 MHz, [D6]benzene, 258C): d = 143.9, 134.5, À44.4 ppm. UV/Vis
(pentane): lmax(e) 415 nm (3200 LmolÀ1 cmÀ1).
Figure 1. Structure of 5 in the solid state. Thermal ellipsoids set at
50% probability. Hydrogen atoms,isopropyl groups,and the minor
disorder component of one of the THF molecules (O2) are omitted for
À
clarity. Selected bond lengths [pm] and angles [8]: Si1 Si2 219.8(1),
À
À
À
À
Si2 Si3 236.2(1),Si1 C1 191.5(2),Si2 C16 191.7(2),Si3 C31
À
À
À
193.4(2),Si3 C46 194.4(2),Si1 Mg1 255.2(1),Si3 Mg1 262.5(1),
Mg1 O1 205.1(2),Mg1 O2 203.4(2); Si1-Si2-Si3 102.52(4),C1-Si1-Si2
120.98(7),Si1-Si2-C16 127.83(7),C16-Si2-Si3 129.48(7).
À
À
delocalization of the negative charges across the three silicon
atoms. The slight elongation of the bonds between Si3 and the
À
À
ipso carbon atoms (Si3 C31: 193.4(2); Si3 C46: 194.4(2) pm)
is probably also due to the bulkiness of the Tip substituents.
To test its suitability as a precursor for unsaturated
heterocyclic oligosilanes, we treated 5 with Me2SnCl2 in
[D6]benzene. The reaction proceeded smoothly to afford the
four-membered ring 6 (Scheme 3), which was unambiguously
Scheme 3. Preparation of 6.
identified by multinuclear NMR spectroscopy. As expected,
the 29Si NMR spectrum of 6 consists of three signals at d =
105.2, 92.5, and À26.2 ppm, all of which show 117/119Sn
satellites (d(119Sn) = À39.3 ppm). Although the silicon atoms
adjacent to tin formally differ in hybridization, the coupling
6: In a glove box, 5 (100 mg, 0.091 mmol) and Me2SnCl2 (21 mg,
0.095 mmol) were placed in an NMR tube and dissolved in
[D6]benzene (0.5 mL). The initially orange solution changed rapidly
to yellow. After centrifugation of the NMR tube to deposit
precipitated MgCl2, NMR spectra were recorded. 1H NMR
(300 MHz, [D6]benzene, 258C): d = 7.22, 7.20 (d, 2H, Ar-H), 7.03,
6.99 (s, 4H, Ar-H), 6.96, 6.87 (d, 2H, Ar-H), 4.69, 4.14, 4.06, 4.01, 3.64,
3.48, 2.85–2.61 (hept, 12H, iPr-CH), 1.72, 1.63, 1.53, 1.52, 1.47, 1.42
(br), 1.36, 1.30, 1.28, 1.24–1.08, 1.01, 0.88, 0.86 (d, 60H, iPr-CH3), 0.80
1
constants are quite similar (sp2: J(29Si,119Sn) = 479 Hz, sp3:
1J(29Si,119Sn) = 497 Hz). Even the coupling to the central
silicon atom is remarkably large (2J(29Si,119Sn) = 228 Hz). In
1
the H and 13C NMR spectra of 6, two different signals are
2
(s, 3H, J(1H,117/119Sn) = 45 Hz, SnCH3), 0.73, 0.64, 0.48, 0.45 ppm (d,
12H, iPr-CH3), 0.23 ppm (s, 3H, 2J(1H,117/119Sn) = 43 Hz, SnCH3);
13C NMR (75 MHz, [D6]benzene, 258C): d = 155.65, 154.73, 154.71,
154.59, 153.59, 152.23, 152.05, 151.14, 150.85, 149.69, 149.10, 136.92,
136.89, 136.67, 133.51 (Ar-C), 122.46, 122.36, 121.91, 121.48, 121.17,
120.77 (Ar-CH), 38.02, 37.64, 37.48, 36.90, 36.62, 35.99, 34.83, 34.79,
34.74, 34.46 (iPr-CH), 27.76, 26.98, 26.81, 25.90, 25.67 (br), 24.82,
24.75, 24.44, 24.34, 24.23, 24.16, 24.09, 23.96, 21.77 (iPr-CH3), À4.08
(SnCH3), À6.48 ppm (SnCH3); 29Si NMR (60 MHz, [D6]benzene,
observed for the methyl groups bonded to tin, which could be
due to a lowering of the Cs symmetry through a distortion of
the four-membered ring from planarity or a less-symmetric
arrangement of the Tip substituents.
The successful synthesis of 6 leads to the expectation that
a variety of new unsaturated homo- and heterocyclic silanes
might be accessible starting from 5. The reactivity of 5
towards other main-group and transition-metal electrophiles
is currently under investigation.
258C): d = 105.2 (1J(29Si,117/119Sn) = 458/479 Hz, Si SiTipSn), 92.5
=
(2J(29Si,117/119Sn) = 218/228 Hz, Si SiTipSi), À26.2 ppm (1J(29Si,
=
1644
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1643 –1645