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Isolation of RSi Dianion, a Bridged Tricyclic Isomer of Dianionic Hexasilabenzene Yang Li, Jianfeng Li, Jianying Zhang, Haibin Song, and Chunming Cui J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b12163 • Publication Date (Web): 10 Jan 2018 Downloaded from http://pubs.acs.org on January 10, 2018
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Isolation of R6Si6 Dianion, Dianion, a Bridged Tricyclic Isomer of Dianionic HexHexasilabenzene Yang Li,† Jianfeng Li,† Jianying Zhang,† Haibin Song,† and Chunming Cui*†‡ †State Key Laboratory of Elemento-Organic Chemistry and College of Chemistry, Nankai University, Tianjin 300071, People’s Republic of China ‡Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, People’s Republic of China Supporting Information Placeholder ABSTRACT: A new strategy for the highly selective synthesis
of tricyclo[2,2,0,02,5]hexasilanes R6Si6X2 (R = 2,4,6-Me3C6H2; X = H, Cl) and a bridged tricyclic R6Si6 dianion starting from the tetrachlorotrisilane RCl2SiSi(H)RSiCl2R (1) was described. Reduction of 1 with lithium naphthalene afforded tricyclohexasilane R6Si6H2 (2), which was halogenated to give the dichloride R6Si6Cl2 (3). Reduction of 3 with four equivalents of potassium graphite in the presence of 18-crown-6 afforded the first R6Si6 dianion (5) paired with [K(18-crown-6)]+2 counterions. The dianion 5 could act as a two-electron reductant towards transition metal halides and a nucleophile towards chlorosilanes. These reactions allowed the efficient and selective access to three types of silicon cages. The structures of the representative cages were confirmed by X-ray diffraction studies. Density functional theory calculations on 5 indicate that the negative charges are localized mainly on the anionic silicon atoms.
ported the synthesis of hexasilaprismanes Dip6Si6 I and Tip6Si6 II (Chart 1, Dip = 2,6-iPr2C6H3, Tip = 2,4,6iPr3C6H2).4a,d Later, Scheschkewitz et al. reported the aromatic isomer III (Chart 1) and its isomerization reactions.4b,c More recently, the hexasilabenzvalene IV (Chart 1) was reported by Kyushin et al.4e Besides these, the closely related tricyclohexasilane (R′Me2Si)8Si6 V (Chart 1) was reported by Kira et al.9 In view of the diverse structural and electronic profiles that have been observed for neutral isomers of hexasilabenzenes, exploring the structural and electronic properties of the charged species is essential. Although sily-substituted benzene dianions have been reported,10 dianionic R6E6 (E = Si, Ge, Sn) isomers have not been explored experimentally. Herein we report the synthesis, structure and reactivity of the first R6Si6 dianion with a tricyclic skeleton, which has been selectively obtained via a pathway involving reductive coupling of the tetrachlorotrisilane derivative 1 (Scheme 1). Chart 1. The Isolated Hexasilabenzene Isomers and Tricyclohexasilane
The isolation of anionic main group species, such as silyl anions, is crucially important for gaining insight into their geometric and electronic characteristics and for understanding of their reactivity.1 Silyl anions, which have fascinating properties and are distinct from those of carbanions,1c–f are useful as building blocks in silicon and coordination chemistry.1d–f In particular, it has been demonstrated that oligosilyl anions are indispensable for the construction of novel oligosilanes and metal complexes.1f,2 Among oligosilyl anions, the polycyclic anions are of great interest from fundamental and synthetic viewpoints, but research on these species is surprisingly scarce. Polycyclic silicon compounds of the type (RSi)n constitute an important class of silicon clusters because of their unique bonding, isomerization reactions and stability.3–5 Among these, hexasilabenzenes are particularly attractive species because they are related to aromatic benzene, which is the most stable of the more than 200 C6H6 isomers.6 Thus, a considerable amount of research has been devoted to the exploration of hexasilabenzenes and their isomers over the past several decades.4,7 However, hexasilabenzenes are difficult to stabilize because of the weak π-bonding between silicon atoms.8 Nevertheless, a few of their isomers have been isolated by using bulky substituents and new synthetic strategies. For examples, Sekiguchi et al. and Scheschkewitz et al. independently re-
We and others previously reported that dehydrohalogenation of hydrochlorosilanes with N-heterocyclic carbenes could afford chlorooligosilanes.2l,11 It is envisioned that the chlorooligosilanes with suitable organic substituents might be synthetically useful for the construction of unsaturated and polycyclic oligosilanes via reductive coupling reactions. Thus, reactions of easily available RSiHCl2 (R = 2,4,6-Me3C6H2) with N-heterocyclic carbenes were investigated. It was found that the reaction of RSiHCl2 with 1,3-di-tert-butyl-imidazol-2ylidene in toluene afforded the 1,1,3,3-tetrachlorotrisilane RCl2SiSi(H)RSiCl2R (1, Scheme 1) in good yields. The trisilane 1 was fully characterized by NMR spectroscopy and X-ray diffraction analysis (Figure S1). Reduction of 1 with four equivalents of potassium graphite (KC8) in THF afforded the tricyclohexasilane R6Si6H2 (2, Scheme 1) as pale yellow solid in 91% yield. Compound 2
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was fully characterized by IR and NMR spectroscopy, and Xray diffraction analysis (Figure 1, Table S1). A broad band with medium intensity located at 2094 cm-1 for 2 in the solidstate IR spectrum is consistent with the existence of a Si−H bond. Its 29Si NMR spectrum in C6D6 contained one singlet at δ –78.7 and two doublets at δ –48.0 (2JSiH = 20 Hz) and 4.4 ppm (1JSiH = 184 Hz). On the basis of the large Si−H coupling constant,4d the signal at δ 4.4 ppm can be assigned to the silicon resonance in RSiH group. The calculated 29Si NMR chemical shifts at the B97-2/pcSseg-1 level for 2 (δ -76.1, -40.4 and 7.3 ppm in Table S3) agree well with the experimental values. Compound 2 represents a rare example of this type. The first example V (Chart 1) was prepared by the photolysis of its isomer tricyclo[3,1,0,02,4]hexasilane by Kira et al.,9 and another example was obtained by the halogenation of an isomer of III (Chart 1) by Scheschkewitz et al..4c Scheme 1. Synthesis of Tricylic Silicon Clusters 2, 3 and 5
3 RSiHCl2
2 NHC
H R R Si R Si Si Cl Cl Cl Cl
4 KC8
R
Si Si Si
Si R
H R
Si Si
H
2
1
R = 2,4,6-Me3C6H2
R
R
R
CCl4 R
R R 4 KC8, THF Si Si Cl 18-crown-6 R Si Si Si Si R R (2) DME Si Si R Si Si Cl R R R R 5 [K(18-crown-6)(DME)]2 3
[K+(18-crown-6)(DME)]2
R
Si Si
(1)
Figure 1. Ortep drawing of 2 at 30% ellipsoid probability. Hydrogen atoms except those on silicon atoms are omitted. Selected bond lengths (Å) and angles (°): Si1−Si2 2.347(2), Si2−Si3 2.335(1), Si3−Si5 2.360(5), Si5−Si6 2.377(4), Si4−Si6 2.329(8), Si1−Si4 2.355(3), Si1−Si5 2.386(10), Si3−Si4 2.363(5); Si1−Si2−Si3 76.85(5), Si1−Si4−Si3 76.17(5), Si1−Si4−Si6 97.46(6), Si1−Si5−Si6 95.31(6), Si3−Si4−Si6 84.94(5), Si3−Si5−Si6 83.95(5), Si4−Si6−Si5 75.91(5). The molecular structure of 2 is shown in Figure 1. It features a tricyclic skeleton with the endocyclic Si−Si bond lengths in the narrow range from 2.329(8) to 2.386(10) Å, which are only slightly shorter than those found in the tricyclosilane V (Chart 1, 2.3888(8)-2.4745(9) Å).9 Chlorination of 2 with CCl4 readily afforded 1,4dichlorotricyclohexasilane 3 (Scheme 1) in almost quantitative yield.12 The 29Si NMR spectrum of 3 displayed three signals at δ –72.8, –69.5, and 45.2 ppm. The lowest-field signal at 45.2
ppm can be assigned to the silicon resonance in the RSiCl fragments on the basis of the calculated chemical shifts (δ 72.1, -62.5 and 57.8 ppm, Table S3). Next we carried out the reduction of 3 with either lithium/naphthalene (Li/Np) or potassium graphite (KC8) in THF. Treatment of 3 with two equivalents of Li/Np resulted in the formation of hexasilaprismane 4 as air-sensitive yellow crystals in 82% yield (Scheme 2). Synthesis of hexasilaprismanes Dip6Si6 and Tip6Si6 have been previously reported:4a,d the former was obtained in very low yields by reduction of DipSiCl3 or DipCl2SiSiCl2Dip, and the latter was prepared in ca. 30% yield by reduction of silacyclopropane Tip3Si3Cl3. The generation of 4 from 3 implies that it might be formed via the rearrangements of the diradical intermediate shown in Scheme 2. Hexasilaprismane 4 was fully characterized by NMR spectroscopy, elemental analysis, and X-ray single-crystal analysis (Table S1 and Figure S3). Reduction of 3 with two equivalents of KC8 also led to the formation of 4 but in less than 20% yield. The similar reduction has also been investigated with an excess of the reductants. Reduction of 3 with four equivalents of Li/Np yielded an air- and moisture-sensitive red species, which could not be isolated in pure form. However, reduction of 3 with four equivalents of KC8 in the presence of 18-crown-6 allowed the isolation of the potassium salt of the dianion 5 as red crystals in 27% yield (Scheme 1). The dianion 5, which is thermally unstable and slowly decomposed at elevated temperatures, has been fully characterized by NMR spectroscopy and X-ray diffraction analysis. In order to clarify whether 4 is the intermediate to 5, reduction of 4 with two equivalents of KC8 in the presence of 18-crown-6 was conducted. It was observed that the reaction led to an unidentified mixture probably because of the nonselective reductive cleavage of the Si−Si bonds in the Si6 cluster. We proposed that 5 was very likely to be formed by the reduction of the diradical intermediate shown in Scheme 2. Scheme 2. Synthesis of Hexasilaprismane 4
The 29Si NMR spectrum of hexasilaprismane 4 displayed one signal at −31.5 ppm, which is noticeably upfield shifted compared to those reported for hexasilaprismanes I and II (δ 22.3 and -23.1 ppm, Chart 1).4a,d The latter compounds were reported to be air- and moisture-stable, whereas 4 was found to be air-sensitive and thermally unstable, having a decomposition temperature around 80 °C. These differences indicate the pronounced steric effects of the substituents on the stability of such compounds. X-ray crystallographic analysis of 4 (Figure S3) disclosed that the Si−Si bond lengths in the range from 2.352 to 2,371(8) Å were very close to those reported for hexasilaprismanes4a,d and theoretical predictions.13 The dianion 5, featuring a bridged tricyclic structure (Figure 2), can be formally viewed as the deprotonation product by the deprotonation of 2. The Si−Si bond lengths (2.375(2)– 2.436(2) Å) were noticeably stretched compared to those in 2 (2.329(8)–2.386(10) Å); and the difference was especially pronounced for bonds involving the anionic silicon atoms, indicating that the negative charges were delocalized over the
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Journal of the American Chemical Society silicon skeleton to some extent. In line with this, the resonances at δ −55.7, 10.0, and 19.5 ppm in the 29Si NMR spectrum of 5 appeared at significantly lower field than those of 2 (δ −78.7, −47.4, and 4.4 ppm). The signal at δ 10.0 ppm can be assigned to the anionic silicon atoms based on the calculated 29Si NMR trends (-51.6, 31.6 and 35.6 ppm in Table S3). Remarkably, the Si−Si−Si bond angles around the anionic silicon atoms in 5 are much smaller than those in 2 (Si1−Si2−Si3 = 76.85(5)°, Si4−Si6−Si5 = 75.91(5)° in 2; Si1−Si2−Si3 = 70.28(6)°, Si4−Si6−Si5 = 70.31(6)° in 5), leading to the close nonbonding contacts between Si1 and Si3 and between Si4 and Si5 atoms (2.779(5) and 2.786(10) Å), respectively.
Figure 3. Frontier orbitals of 2 and 5 obtained by DFT calculations.
Figure 2. Ortep drawing of 5 at 30% ellipsoid probability. Hydrogen atoms and potassium cations have been omitted for clarity. Selected bond lengths (Å) and angles (°): Si1−Si2 2.423(3), Si2−Si3 2.405(4), Si3−Si5 2.386(2), Si5−Si6 2.402(4), Si4−Si6 2.436(2), Si1−Si4 2.416(2), Si1−Si5 2.375(2), Si3−Si4 2.391(7); Si1−Si2−Si3 70.28(6), Si1−Si4−Si3 70.61(6), Si1−Si4−Si6 101.16(7), Si1−Si5−Si6 103.41(8), Si3−Si4−Si6 91.21(7), Si3−Si5−Si6 92.21(7), Si4−Si6−Si5 70.31(6). To elucidate the electronic structures of these cages, we performed density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) (2) and B3LYP/6-31G+(d,p) (3 and 5) levels of theory. The optimized structural geometries and parameters (Figures S5 and S7) for 2 and 5 are very close to the experimentally determined values (Table S2 in the SI). The calculated frontier orbitals for 2 and 5 are shown in Figure 3. The HOMO of 2 corresponds mainly to the Si−Si σ bond with some contributions from the π orbitals of the aryl rings; and the HOMO of 5 involves mainly the two lone pairs on the silicon atoms and three Si−Si σ bonds. Natural Bond Orbital (NBO) analysis of 5 revealed that the two lone pairs with high s character (57.12% and 57.16%) have noticeable donor– acceptor interactions with the adjacent Si−Si σ* bonds (2.47, 3.26, 2.48, and 3.25 kcal/mol), leading to the lengthening of the Si−Si bonds. The calculated NBO charges of the six silicon atoms in 5 (0.024, 0.025, 0.302, 0.303, 0.303, and 0.303) were significantly smaller than those calculated for 2 (0.378, 0.394, 0.397, 0.401, 0.595, and 0.599), consistent with the anionic nature of 5.
Reaction of 5 with Cp*2TiCl2 (Cp* = C5Me5) in C6D6 immediately produced hexasilaprismane 4 in ca. 95% yield, as disclosed by NMR analysis (Scheme 3). However, the reduced titanium species cannot be isolated and identified. Treatment of 5 with one equivalent of (PPh3)2PdCl2 led to an immediate color change from yellow to red with the formation of 4, along with black palladium precipitates. The easy reduction of Cp*2TiCl2 indicates that the dianion 5 is an excellent twoelectron reductant with a high reduction potential. This behavior resembles that reported for silole dianions.14 Scheme 3. Reactions of 5 with Metal Halides
Dianion 5 also acts as a nucleophile toward chlorosilanes: reactions of 5 with Me3SiCl and RSiCl3 yielded the substitution products 6 and 7 in good yields (Scheme 4). Both the 29Si NMR spectra of 6 and 7 showed three signals (6: δ −69.0, −51.7, and 20.2 ppm; 7: δ −59.4, −59.3, and 24.7 ppm) for the silicon resonances. The lowest-field chemical shifts at δ 20.7 and 24.7 ppm can be assigned to the silicon atoms of RSiSiMe3 and RSiSiRCl2 fragments in 6 and 7, respectively. Comparison of these chemical shifts with the corresponding silicon resonances of 2 (δ −78.7, −47.4 and 4.4 ppm) suggests that 6 and 7 are very likely to have a similar tricyclic structure with 2. Scheme 4. Reactions of 5 with Chlorosilanes
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In summary, the first tricyclic R6Si6 dianion (5) has been synthesized and structurally characterized. The synthetic route to 5 involved the selective reduction of a tetrachlorotrisilane followed by chlorination and the subsequent reduction. This strategy also allowed the synthesis of R6Si6 and R6Si6X2 isomers and represents the most selective and efficient route so far reported for these rarely isolated organosilicon cages. The dianion 5 could act as a two-electron reductant and a nucleophile depending on substrates. Investigations of the synthetic applications of 5, especially for the construction of large silicon clusters, are currently underway in our laboratory.
ASSOCIATED CONTENT Supporting Information Synthetic procedures and characterization data for the new compounds reported in this paper, crystallographic data for 1, 2, 4, and 5, and DFT calculations for 2, 3 and 5 in PDF format. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION Corresponding Author
[email protected]. Notes The authors declare no competing financial interests.
ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (grant nos. 21632006 and 21472098).
REFERENCES (1) (a) Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis; University Science Books: Sausalito, CA, 2010. (b) Yamashita, M.; Nozaki, K. In Synthesis and Application of Organoboron Compounds; Fernández, E., Whiting, A., Eds.; Springer International Publishing: Switzerland, 2015; p1. (c) Hengge, E. Silicon Chemistry II; Topics in Current Chemistry, Vol. 51; Springer: Berlin, Heidelberg, Germany, 1974; pp 1−127.(d) Lee, VY.; Sekiguchi, A. Heavy analogs of carbanions: Si-, Ge-, Sn- and Pb-centered anions. Lee, V.Y., Sekiguchi, A., Eds.; Organometallic compounds of low-coordinate Si, Ge, Sn, and Pb. Wiley, Chichester, 2010. (e) Präsang, C.; Scheschkewitz, D. Silyl Anions. Scheschkewitz, D., Eds.; Functional Molecular Silicon Compounds II; Springer International Publishing: Germany, 2014. (f) Marschner, C.; oligosilanes. Scheschkewitz, D., Eds.; Functional Molecular Silicon Compounds I; Springer International Publishing: Germany, 2014. (2) For leading references, see: (a) Kayser, C.; Kickelbick, G.; Marschner, C. Angew. Chem. Int. Ed. 2002, 41, 989−992. (b) Fischer, R.; Frank, D.; Gaderbauer, W.; Kayser, C.; Mechtler, C.; Baumgartner, J.; Marschner, C. Organometallics 2003, 22, 3723−3731. (c) Marschner, C. Organometallics 2006, 25, 2110−2125. (d) Zirngast, M.; Baumgartner, J.; Marschner, C. Organometallics 2008, 27, 6472−6478. (e) Abersfelder, K.; Scheschkewitz, D. J. Am. Chem. Soc. 2008, 130, 4114−4121. (f) Wallner, A.; Hlina, J.; Konopa, T.; Wagner, H.; Baumgartner, J.; Marschner, C. Organometallics 2010, 29, 2660−2675. (g) Klapötke, T. M.; Vasisht, S. K.; Fischer, G.; Mayer, P. J. Organomet. Chem. 2010, 695,667−672. (h) Iwamoto, T.; Tsushima, D.; Kwon, E.; Ishida, S.; Isobe, H. Angew. Chem. Int. Ed. 2012, 51, 2340−2344. (i) Arp, H.; Zirngast, M.; Marschner, C.; Baumgartner, J.; Rasmussen, K.; Zark, P.; Müller, T. Organometallics 2012, 31,
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4309−4319. (j) Zitz, R.; Gatterer, K.; Reinhold, C. R. W.; Müller, T.; Baumgartner, J.; Marschner, C. Organometallics 2015, 34, 1419−1430. (k) Zitz, R.; Hlina, J.; Meshgi, M. A.; Krenn, H.; Marschner, C.; Szilvasi, T.; Baumgartner, J. Inorg. Chem. 2017, 56, 5328−5341. (l) Olaru, M.; Hesse, M. F.; Rychagova, E.; Ketkov, S.; Mebs, S. Beckmann, J. Angew. Chem. Int. Ed. 2017, 56, 16490−16494. (3) For Si4R4 isomers, see: (a) Wiberg, N.; Finger, C. M. M.; Polborn, K. Angew. Chem. Int. Ed. 1993, 32, 1054-1056. (b) Ichinohe, M.; Toyoshima, M.; Kinjo, R.; Sekiguchi, A. J. Am. Chem. Soc. 2003, 125, 13328-13329. (c) Meyer-Wegner, F.; Scholz, S.; Sänger, I.; Schodel, F.; Bolte, M.; Wagner, M.; Lerner, H-W. Organometallics 2009, 28, 6835-6837. (d) Suzuki, K.; Matsuo, T.; Hashizume, D.; Fueno, H.; Tanaka, K.; Tamao, K. Science, 2011. 331, 1306-1309. (4) For Si6R6 isomers, see: (a) Sekiguchi, A.; Yatabe, T.; Kabuto, C.; Sakurai, H. J. Am. Chem. Soc. 1993, 115, 5853-5854. (b) Abersfelder, K.; White, A. J. P.; Rzepa, H. S.; Scheschkewitz, D. Science 2010, 327, 564-566. (c) Abersfelder, K.; White, A. J. P.; Berger, R. J. F.; Rzepa, H. S.; Scheschkewitz, D. Angew. Chem., Int. Ed. 2011, 50, 7936-7939. (d) Abersfelder, K.; Russell, A.; Rzepa, H. S.; White, A. J. P.; Haycock, P. R.; Scheschkewitz, D. J. Am. Chem. Soc. 2012, 134, 1600816016. (e) Tsurusaki, A.; Iizuka, C.; Otsuka, K.; Kyushin, S. J. Am. Chem. Soc. 2013, 135, 16340−16343. (5) For Si8R8 isomers, see: (a) Matsumoto, H.; Higuchi, K.; Hoshino, Y.; Koike, H.; Naoi, Y.; Nagai, Y. J. Chem. Soc., Chem. Commun. 1988, 1083-1084.(b) Unno, M.; Matsumoto, T.; Mochizuki, K.; Higuchi, K.; Goto, M.; Matsumoto, H. J. Organomet. Chem. 2003, 685,156-161. (c) Sekiguchi, A.; Yatabe, T.; Kamatani, H.; Kabuto, C.; Sakurai, H. J. Am. Chem. Soc. 1992, 114, 6260-6262. (d) Matsumoto, H.; Higuchi, K.; Kyushin, S.; Goto, M. Angew. Chem. Int. Ed. 1992, 31, 1354-1356. (e) Ishida, S.; Otsuka, K.; Toma, Y.; Kyushin, S. Angew. Chem. Int. Ed. 2013, 52, 2507-2510. (f) Sekiguchi, A.; Nagase, S. Polyhedral silicon compounds. Rappoport, Z.; Apeloig, Y. Eds.; The chemistry of organosilicon compounds, Wiley, West Sussex, 1998. (6) Dinadayalane, T. C.; Priyakumar, U. D.; Sastry, G. N. J. Phy. Chem. A. 2004, 108, 11433-11448. (7) For examples, see: (a) Nagase, S.; Kudo, T.; Aoki, M. J. Chem. Soc., Chem. Commun. 1985, 1121-1122. (b) Zhao, M.; Gimarc, B. M. Inorg. Chem. 1996, 35, 5378-5386. (c) Moteki, M.; Maeda, S.; Ohno, K. Organometallics 2009, 28, 2218-2224. (d) Szilvási, T.; Veszprémi, T. Organometallics 2012, 31, 3207-3212. (e) Ivanov, A. S.; Boldyrev, A. I. J. Phys. Chem. A 2012, 116, 9591-9598. (f) Benedek, Z.; Szilvási,T.; Veszprémi, T. Dalton Trans. 2014, 43,1184-1190. (8) Nagase, S.; Teramae, H.; Kudo, T. J. Chem. Phys. 1987, 86, 4513-4517. (9) Iwamoto, T.; Uchiyama, K.; Kabuto, C.; Kira M. Chem. Lett. 2007, 36, 368-369. (10) (a) Sekiguchi, A.; Ebata, K.; Kabuto, C.; Sakurai, H. J. Am. Chem. Soc. 1991, 113, 1464-1465. (b) Sekiguchi, A.; Ebata, K.; Kabuto, C.; Sakurai, H. J. Am. Chem. Soc. 1991, 113, 7081-7782. (11) (a) Cui, H.-Y.; Shao, Y.-J.; Li, X.-F.; Kong, L.-B. Cui, C. Organometallics 2009, 28, 5191-5195. (b) Cui, H.-Y.; Cui, C. Dalton Trans. 2011, 40, 11937-11940. (c) Cui, H.; Cui, C. Chem. –Asian J. 2011, 6, 1138–1141. (12) Kawase, T.; Batcheller, S.A.; Masamune, S. Chem. Lett. 1987, 16, 227-230. (13) Nagase, S.; Nakano, M.; Kudo, T. J. Chem. Soc., Chem. Commun.1987, 60-62. (14) Han, Z.; Li, J.; Hu, H. ; Zhang, J.; Cui, C. Inorg. Chem. 2014, 53, 5890−5892.
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Journal of the American Chemical Society R
R
Si Si
R
Si
Cl R
Cl Si Si Si R R
2e r
R
R Si
Si
Si Si Si
Si Si R
R
R
2e oxidation
Si R
n
Si
R = 2,4,6-Me 3C 6H 2
tio uc
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d re
ed uc t i
on
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R
R
Si Si Si R
R
R bridged tricyclic isomer of dianionic hexasilabenzene
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