Supporting Information. Synthesis, Molecular Structure, and Facile Ring Flipping of a Bicyclo[1.1.0]tetrasilane

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1 Supporting Information Synthesis, Molecular Structure, and Facile Ring Flipping of a Bicyclo[1.1.0]tetrasilane Kiyomi Ueba-Ohshima, Takeaki Iwamoto,*,# Mitsuo Kira*, #Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aoba-ku, Sendai , Japan Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai , Japan Contents 1. Experimental Details 2. NMR spectra of hexakis(t-butyldimethylsilyl)bicyclo[1.1.0]tetrasilane (3) and 1,3-dibromohexakis(t-butyldimethylsilyl)cyclotetrasilane (6) 3. UV-vis spectrum of 3 4. X-Ray Analysis of 6 5. Eyring plot for ring flipping of 3 6. Theoretical calculations 7. References S1

2 1. Experimental Details General Procedures All reactions treating air-sensitive compounds were carried out under argon atmosphere using high-vacuum line, standard Schlenk techniques, and dry and oxygen-free solvents. 1 H (400 MHz), 13 C (100 MHz), and 29 Si (79 MHz) NMR spectra were recorded on a Bruker Avance 400P FT NMR spectrometer. Sampling of bicyclotetrasilane 3, was carried out by using a VAC NEXUS type glove box. UV-vis spectra were recorded on a Hewlett-Packard Agilent 8453 and JASCO V-660 equipped with Oxford IT502 cryostat. X-ray analyses of 3 and 6 were carried out using a Rigaku /MSC Mercury and Saturn CCD diffractometer. Materials THF, hexane, benzene-d 6, 3-methylpentane, and toluene were dried in a tube covered with potassium mirror, and then distilled prior to use by using vacuum line. 1,2-Dibromoethane was dried over calcium hydride. Hexakis(t-butyldimethylsilyl)cyclotrisilane (10) S1 and KC S2 8 were prepared according to the procedure described in the literatures. Preparation of 1,3-dibromo-1,2,2,3,4,4-hexakis(t-butyldimethysilyl)cyclotetrasilane (6) R R Si R Si Si R R R 10 1) Li/THF 2) (CH 2 Br) 2 R = t-bume 2 Si R R Br Si R Si Si R Si Br R R 6 (50.8%) In a Schlenk flask, a suspension of hexakis(t-butyldimethysilyl)cyclotrisilane 10 S1 (5.34 g, 6.88 mmol) and lithium wire (0.47 g, 68.8 mmol, 10 eq.) in dry THF (50 ml) was stirred at room temperature for 10 h. After the removal of excess lithium, 1,2-dibromoethane (1.27 g, 6.88 mmol) was added slowly to the resulting solution and stirred for 1 h. After the solvent was changed from THF to benzene, the resulting benzene suspension was heated to dissolve the product and the resulting salt was immediately filtered off. Recrystallization from benzene gave pure 6 as colorless crystals (1.68 g, 1.74 mmol) in 50.8% yield. 6: colorless crystals; mp o C; 1 H NMR (C 6 D 6, ) 0.53 (s, 12H, Si-Me), 0.54 (s, 12H, Si-Me), 0.77 (s, 12H, Si-Me), 1.17 (br, 54H, t-bu); 13 C NMR (C 6 D 6, ) 1.3, 2.5, 5.1, 20.4, 22.3, 29.7, 29.9; 29 Si NMR (C 6 D 6, ) 35.9 (Si(SiMe 2 t-bu) 2 ), 3.7 (SiBr(SiMe 2 t-bu)), 9.1 (Si(SiMe 2 t-bu) 2 ), 20.8 (SiBr(SiMe 2 t-bu)); MS (EI, 70eV) m/z (%) (24, M + ), (23, M + -SiMe 2 t-bu), (38, M + -(SiMe 2 t-bu)-br), 72.9 (100); Anal. calcd for C 36 H 90 Si 10 Br 2 : C, 44.86; H, Found: C, 44.89; H, Synthesis of hexakis(t-butyldimethysilyl)bicyclo[1.1.0]tetrasilane (3) S2

3 Br R R R Si R Si Si Si Br R R 6 KC 8 /THF -20 C R = t-bume 2 Si 3 (52%) In a Schlenk flask, a suspension of 6 (400 mg, 415 µmol) and potassium graphite (123 mg, 913 µmol) in dry and oxygen-free THF (10 ml) was stirred at 20 ºC for 15 h. Keeping the resulting dark red suspension at the temperature below 40 ºC, the solvent was changed from THF to hexane, and then the resulting salt and graphite was filtered off by using glass filter. Recrystallization from hexane at 30 ºC gave pure yellow crystals of 3 (173 mg, 216 µmol) in 52.0% yield. 3: air-sensitive yellow crystals; mp. < 0 ºC (decomp.); 1 H NMR (400 MHz, toluene-d 8, 243 K ) 0.44 (s, 12H, Si-Me), 0.47 (s, 24H, Si-Me), 1.21 (s, 54H, t-bu); 1 H NMR (400 MHz, toluene-d 8, 208 K, ) 0.44 (s, 12H, Si-Me), 0.48 (s, 12H, Si-Me), 0.50 (s, 12H, Si-Me), 1.23 (s, 54H, t-bu); 13 C NMR (100 MHz, THF-d 8, 208 K, ) 0.9, 3.4 (br), 17.9 (br), 19.8 (br) 20.5, 27.6, 28.8, 30.1; 29 Si NMR (79.5 MHz, toluene-d 8, 208 K, ) (Si(SiMe 2 t-bu)), 90.6 (Si(SiMe 2 t-bu) 2 ), 3.7 (br, Si(SiMe 2 t-bu) 2 ), 8.1 (br, Si(SiMe 2 t-bu) 2 ), 8.7 (Si(SiMe 2 t-bu)); UV vis (3-methypentane, 230 K) max /nm (/10 3 ) 299 (16.6), 390 (2.6), 459 (1.3); Anal. calcd for C 36 H 90 Si 10 : C, 53.78; H, Found: C, 53.68; H, S3

4 2. NMR spectra of hexakis(t-butyldimethylsilyl)bicyclo[1.1.0]tetrasilane (3) and 1,3-dibromohexakis(t-butyldimethylsilyl)cyclotetrasilane (6) Figure S1. 1 H NMR spectrum of bicyclo[1.1.0]tetrasilane 3 in toluene-d 8 at 243 K. Figure S2. 13 C NMR spectrum of bicyclo[1.1.0]tetrasilane 3 in THF-d 8 at 208 K. S4

5 Figure S3. 29 Si NMR spectrum of bicyclo[1.1.0]tetrasilane 3 in THF-d 8 at 208 K. Figure S4. 1 H NMR spectrum of 1,3-dibromohexakis(t-butyldimethylsilyl)cyclotetrasilane 6 in benzene-d 6 at 293 K. Signal marked is due to residual protons in benzene-d 6. S5

6 Figure S5. 13 C NMR spectrum of 1,3-dibromohexakis(t-butyldimethylsilyl)cyclotetrasilane 6 in benzene-d 6 at 293 K. Figure S6. 29 Si NMR spectrum of 1,3-dibromohexakis(t-butyldimethylsilyl)cyclotetrasilane 6 in benzene-d 6 at 293 K. S6

7 3. UV-vis spectrum of hexakis(t-butyldimethylsilyl)bicyclo[1.1.0]tetrasilane (3) UV-vis spectra of 3 were observed at various temperatures between 230 to 110 K (Figure S7). To calculate, the density of 3-methypentane at various temperatures was corrected according to the literature. S3 Figure S7. UV-vis spectrum of hexakis(t-butyldimethylsilyl)bicyclo[1.1.0]tetrasilane (3) in 3-methylpentane at 230 K (red line) to 110 K (blue line) where is the molar extinction coefficient (dm 3 mol -1 cm -1 ). Table S1. Absorption Maxima and Extinction Coefficients of 3 at 230 K and 110 K. max /nm ( 10-3 ) 230 K 110 K 299 (16.6) 298 (27.5) 390 (2.6) 374 (3.2) 459 (1.3) 457 (0.6) S7

8 4. X-Ray Analysis of 1,3-dibromohexakis(t-butyldimethylsilyl)hexasilylcyclotetrasilane (6) Recrystallization from benzene at +20 C gave single crystals of 6 suitable for data collection. Crystal data of 6 ( 100 ºC): Si 10 C 36 H 90 Br 2, FW = , triclinic, P-1, a = (1) Å, b = (4) Å, c = (2) Å, = (7) º, = (10) º, = (7) º, V = (14) Å 3, Z = 1, D calcd = g/cm 3, R1 = 2.78%, wr2 = 6.83%, GOF = Figure S8. ORTEP drawing of 1,3-dibromocyclotetrasilane 6 with the 30% probability thermal ellipsoids. All hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Si1 Si (7), Si1 Si2* (7), Si1 Br (5), Si1 Si (6), Si2 Si (6), Si2 Si (7), Br1 Si1 Si (2), Br1 Si1 Si2* (2), Si2 Si1 Si2* 93.67(2), Si1 Si2 Si1* 86.33(2). S8

9 5. Eyring plot for the ring flipping of 3 Figure S9. An Eyring plot for the ring flipping of bicyclo[1.1.0]tetrasilane 3 in toluene-d 8. S9

10 6. Theoretical calculations DFT calculations were carried out using Gaussian 03 S4 program packages at the B3LYP/6-31G(d) level. GIAO calculations were carried out at the B3LYP/6-311+G(2df,p) level//b3lyp/6-31g(d) level. Table S2. Atomic Coordinates of 7-LB at the Optimized Geometry Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z (E(+ZPE)= ) Table S3. Atomic Coordinates of 8-LB at the Optimized Geometry Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z S10

11 (E(+ZPE)= ) Table S4. Atomic Coordinates of 9-SB at the Optimized Geometry Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z S11

12 (E(+ZPE)= ) 7. References S1. Preparation of hexasilylcyclotrisilanes: Kira, M.; Iwamoto, T.; Kuzuguchi, T.; Yin, D.; Kabuto, C.; Sakurai, H. J. Chem. Soc., Dalton Trans., 2002, S2. Cleij, T. J.; Tsang, S. K. Y.; Jenneskens, L. W. Chem. Commun. 1997, 329. S3. Ruth, A. A.; Nickel, B.; and Lesche, H. Z. Phys. Chem., 1992, 175, 91. S4. Gaussian 03, Revision C.02, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; and Pople, J. A.; Gaussian, Inc., Wallingford CT, S12