Organometallics 2009, 28, 5281–5284 DOI: 10.1021/om900532v
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Synthesis of Potassium-Magnesium Ate Complexes with a Bulky Diamido Ligand Chengfu Pi,†,§ Li Wan,† Yingying Gu,† Haoyu Wu,† Chengxi Wang,† Wenjun Zheng,*,† Linhong Weng,† Zhenxia Chen,† Xiaodian Yang,§ and Limin Wu§ †
Department of Chemistry and §Laboratory of Advanced Materials, Fudan University, Handan Road 220, Shanghai 200433, People’s Republic of China Received June 19, 2009
Summary: Two mixed potassium-magnesium complexes (magnesiates) with novel structural conformations were prepared by the reduction of a neutral magnesium ([(μ-Mg){η2:η1Me2Si(NDipp)2}]2) complex bearing bulky diamido ligands with metallic potassium.
Introduction The application of the mixed alkali-metal-magnesium ate complexes (magnesiates)1 to the deprotonation of organic or organometallic species such as benzene, toluene, bis(benzene)chromium, and metallocenes has recently attracted considerable interest, as their behaviors are neither conventional alkali-metal chemistry nor conventional magnesium chemistry but a unique new synergic chemistry. The preparation of the magnesiates was reported by adding together the alkyl magnesium and alkyl alkali-metal in the presence of H-acidic N-ligands or directly mixing magnesium amide and alkali-metal amide.1-3 On the other hand, cation-π interactions between alkali-metal ions and arenes (or substituted *To whom correspondence should be addressed. E-mail: wjzheng@ fudan.edu.cn. (1) Overviews: (a) Mulvey, R. E.; Mongin, F.; Uchiyama, M.; Kondo, Y. Angew. Chem., Int. Ed. 2007, 46, 3802–3824. (b) Mulvey, R. E. Organometallics 2006, 25, 1060–1075. (c) Krasovskiy, A.; Krasovskaya, V.; Knochel, P. Angew. Chem., Int. Ed. 2006, 45, 2958–2961. (d) Blair, V. L.; Kennedy, A. R.; Klett, J.; Mulvey, R. E. Chem. Commun. 2008, 5426–5428. (e) Kennedy, A. R.; O'Hara, C. T. Dalton. Trans. 2008, 4975–4977. (f) Garcia-Alvarez, J.; Graham, D. V.; Hevia, E.; Kennedy, A. R.; Klett, J.; Mulvey, R. E.; O'Hara, C. T.; Weatherstone, S. Angew. Chem., Int. Ed. 2008, 47, 8079–8081. (g) Mulvey, R. E. Acc. Chem. Res. 2009, 42, 743-755, and references therein. (2) Fukuhara, K.; Takayama, Y.; Sato, F. J. Am. Chem. Soc. 2003, 125, 6884–6885. (3) (a) Blair, V. L.; Carrella, L. M.; Clegg, W.; Conway, B. R.; Harrington, W.; Hogg, L. M.; Klett, J.; Mulvey, R. E.; Rentschler, E.; Russo, L. Angew. Chem., Int. Ed. 2008, 47, 6208–6211. (b) Andrikopoulos, P. C.; Armstrong, D. R.; Clegg, W.; Gilfillan, C. J.; Hevia, E.; Kennedy, A. R.; Mulvey, R. E.; O'Hara, C. T.; Parkinson, J. A.; Tooke, D. M. J. Am. Chem. Soc. 2004, 126, 11612–11620. (c) Hao, H. J.; Roesky, H. W.; Ding, Y. Q.; Cui, C. M.; Schormann, M.; Schmidt, H.-G.; Noltemeyer, M.; Zemva,, B. J. Fluor. Chem. 2002, 115, 143–147. (d) Forbers, G. C.; Kennedy, A. R.; Mulvey, R. E.; Rodger, P. J. A.; Rowlings, R. B. J. Chem. Soc., Dalton Trans. 2001, 1477–1484. (e) Andrews, P. C.; Kennedy, A. R.; Mulvey, R. E.; Raston, C. L.; Roberts, B. A.; Rowlings, R. B. Angew. Chem., Int. Ed. 2000, 39, 1960–1962. (4) (a) Ma, J. C.; Dougherty, D. A. Chem. Rev. 1997, 97, 1303–1324. (b) Suelter, C. H. Science 1970, 168, 789–795. (c) Masson, E.; Schlosser, M. Org. Lett. 2005, 7, 1923–1925. (5) (a) Biot, C.; Wintjens, R.; Rooman, M. J. Am. Chem. Soc. 2004, 126, 6220–6221. (b) DeVos, A. M.; Ultsch, M.; Kossiakoff, A. A. Science 1992, 255, 306–312. (c) Hong, B. H.; Bae, S. C.; Lee, C.-W.; Jeong, S.; Jim, K. S. Science 2001, 294, 348–351. r 2009 American Chemical Society
arenes) recently emerged as an important binding force in a diverse range of biological and chemical settings.4-6 Therefore, the investigation of the structural conformations of the alkali-metal-magnesium complexes as well as of complexes with alkali-metal cation-π interactions seemed to be required for advances in this area. Herein, we report the synthesis of two mixed potassium-magnesium complexes involving cation-π interactions between potassium and substituted arene groups by the reduction of a neutral magnesium diamido complex.7
Results and Discussion The synthetic chemistry of complexes 2-4 is shown in Scheme 1. The reaction of silanediamine H2[Me2Si(Ndipp)2]2 (1, Dipp = 2,6-iPr2C6H3)8 with (n-Bu)2Mg in n-hexane gave magnesium diamido complex [(μ-Mg){η2:η1-Me2Si(Ndipp)2}]2 (2) in 78% yield. The treatment of 2 with 2 equiv of potassium graphite (C8K) in toluene smoothly gave complex [(η6:η6-K)þ]2[Mg{η2-Me2Si(Ndipp)2}2]2- (3) as light yellow crystals in 52% isolated yield (based on 2). This compound is well soluble and readily recrystallized in THF to afford a solvated complex, [(η6:η6-K(THF)(η6:η6-K(THF)2)]2þ[Mg{η2-Me2Si(Ndipp)2}2]2- (4), in high yield. Complexes 2-4 were characterized by spectral and analytical methods as well as X-ray diffraction analysis. No N-H stretching bands are found in the IR spectrum of solid 2, suggesting that the NH groups of the ligand have been completely deprotonated. The structure elucidation of 2 revealed a dimeric species with η2:η1-bridging coordination sites, thus forming a folded ladder with Mg2N2 and SiN2Mg four-membered rings (Figure 1).9 (6) (a) Gokel, G. W.; Barbour, L. J.; DeWall, S. L.; Meadows, E. S. Coord. Chem. Rev. 2001, 222, 127–154. (b) Gokel, G. W.; Barbour, L. J.; Ferdani, R.; Hu, J.-X. Acc. Chem. Res. 2002, 35, 878–886. (7) The reduction of organometal halide or neutral organozinc compounds with metallic potassium led to ate complexes in which cation-π interactions were infrequently involved between potassium cations and arene groups of the ligands. (a) Pu, L.; Phillips, A. D.; Richards, A. F.; Stender, M.; Simons, R. S.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 11626–11636. (b) Tsai, Y.-C.; Lu, D.-Y.; Lin, Y.-M.; Hwang, J.-K.; Yu, J.-S. K. Chem. Commun. 2007, 4125–4127. (c) Alvarez, E.; Grirrane, A.; Resa, I.; del Ro, D.; Rodrguez, A.; Carmona, E. Angew. Chem., Int. Ed. 2007, 46, 1296–1299. (d) Richards, A. F.; Brynda, M.; Power, P. P. J. Am. Chem. Soc. 2004, 126, 10530–10531. (e) Twamley, B.; Power, P. P. Angew. Chem., Int. Ed. 2000, 39, 3500–3503. (f) Zhu, Z.-L.; Wang, X.-P.; Olmstead, M. M.; Power, P. P. Angew. Chem., Int. Ed. 2009, 48, 2027–2030. (8) Hill, M. S.; Hitchcock, P. B. Organometallics 2002, 21, 3258–3262. (9) Crystallographic data for 2-4 are contained in the Supporting Information. Published on Web 08/18/2009
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Figure 1. Molecular structure of 2 with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Mg(1)-N(1) 1.963(3), Mg(1)-N(2) 2.114(3), Mg(1)-N(3) 2.057(3), Mg(2)-N(4) 1.969(3), Mg(2)-N(2) 2.060(3), Mg(2)-N(3) 2.124(2); Mg(1)-N(2)-Mg(2) 85.96(10), Mg(1)-N(3)-Mg(2) 85.79(9), N(2)-Mg(1)-N(3) 93.84(10), N(2)-Mg(2)-N(3) 93.48(10), N(4)-Mg(2)-N(3) 80.62(10), N(2)-Mg(1)-N(1) 79.89(10), N(1)-Mg(1)-N(3) 152.55(11), N(4)-Mg(2)-N(2) 142.57(11).
Scheme 1. Preparation of Complexes 2-4
The average Mg-N bond length (Mg-N 2.070(3) A˚) is comparable to those found in [(tmp)12K6Mg6(C6H5)6] (Mg-N 2.019(4) A˚ (av); tmp=2,2,6,6-tetramethylpiperidide)3a and in [{CH(CMeNAr)2}Mg(μ-η1-Bu)]2 [Mg-N 2.05 A˚ (av), Ar=2,6-Me2C6H3].3c In comparison, 3 is a monomeric mixed potassium-magnesium ate complex in which the central magnesium atom is η2(N,N)-coordinated by two diamido ligands, whereas two potassium ions are π-bonded to arene groups of the
Pi et al.
ligands (Figure 2).9 The formation of 3 apparently arises from the reduction of 2 with metallic potassium. The framework of 4 is quite similar to that of 3 except for the additional coordinated THF molecules to potassium ions (Figure 3).9 The geometries of magnesium in complexes 3 and 4 are distorted tetrahedral. Interestingly, the dispositions of the metals in 3 and 4 are almost linear (the angle values of K(1)-Mg(1)-K(2) are 178.34° for 3 and 178.02° for 4). The Mg-N bond lengths of 3 and 4 are almost identical (Mg(1)-N(1) 2.131(2), Mg(1)-N(2) 2.147(2) A˚ for 3; Mg(1)-N(1) 2.133(2), Mg(1)-N(2) 2.131(2) A˚ for 4), but they are significantly longer than those found in 2. The longer bond lengths found in 3 and 4 are likely due to the larger radius of the potassium ions, the higher coordination number at the magnesium center (4 versus 3), and the repulsion of the bulky diamido groups. The K(2)-C(Ar) distances vary between 2.968(3) and 3.298(3) A˚ in 4, versus K-C bond lengths (3.156(2)-3.259(2) A˚) found in [{(thf)2K(μ-N(Ph)iPr)2}2Ca],10 indicating the slipped-η6 coordination. The distances of the K2-O bond in 4 (K(2)-O(3) 2.632(10) A˚) is slightly shorter than that of the K1-O bond (K(1)-O(1) 2.753(2), K(1)-O(2) 2.719(2) A˚) probably due to the higher coordination number of the K2 ion but close to the value (K-O 2.687(2) A˚) found in [{(thf)2K(μ-N(Ph)iPr)2}2Ca].10 To the best of our knowledge, complexes 3 and 4 are the first structurally elucidated “alkalinerich” compounds with a stoichiometry of potassium ions and magnesium ion in a ratio of 2:1 despite previously known examples with Na:Mg (2:1) and Li:Mg (2:1).11 The 1H NMR (C6D6, 23 °C) spectrum of 2 displays two sharp resonances for the -SiCH3 groups, eight sets of coupled doublets for -CH(CH3)2 groups, and four sets of septets for -CH(CH3)2 groups, clearly evidencing that the solid structure of 2 is maintained in the solution. The four sets of resonances for the nonequivalent -CH(CH3)2 groups reveal the molecular asymmetry and a hindered rotation about the C-N bond in the solution. This is in sharp contrast to previous observations in the zinc compound [Zn2(μ-η2Me2Si(NDipp)2)2].7b The 1H NMR (C6D6, 23 °C) spectra of 3 and 4 are similar except for the additional resonances assigned to the solvated THF molecules in 4. Interestingly, the resonances for the arene groups are observed at δ = 6.38-7.03 ppm for 3 (6.24-6.89 ppm for 4), slightly shifted upfield relative to the corresponding signals for 2 (δ = 6.77-7.12 ppm), which are close to those observed in potassium-zinc ate complex [(η6:η6-K)þ]2[{η2-Me2Si(Ndipp)2}Zn-Zn{η2-Me2Si(Ndipp)2}]2- (δ = 6.37-6.81 ppm).7b This is likely due to the electronic effect of the potassium ion π-bonded to the phenyl ring. In summary, we have prepared two mixed potassium-magnesium ate complexes (magnesiates) by the reduction of a neutral diamido magnesium complex with metallic potassium. They are the first examples of a mixed potassium-magnesium prepared by the reduction of a neutral magnesium complex with metallic potassium. The formation of potassium ions in 3 and 4 apparently results from the reduction of the divalent magnesium atom in 2.12,13 Further (10) Glock, C.; G€ orls, H.; Westerhausen, M. Inorg. Chem. 2009, 48, 394–397. (11) (a) Hevia, E.; Henderson, K. W.; Kennedy, A. R.; Mulvey, R. E. Organometallics 2006, 25, 1778–1785. (b) Blair, V. L.; Carrella, L. M.; Clegg, W.; Conway, B.; Harrington, R. W.; Hogg, L. M.; Klett, J.; Mulvey, R. E.; Rentschler, E.; Russo, L. Angew. Chem., Int. Ed. 2008, 47, 6208–6211. (c) Greiser, T.; Kopf, J.; Thoennes, D.; Weiss, E. Chem. Ber. 1981, 114, 209– 213.
Note
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Figure 2. Molecular structure of 3 with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Mg(1)-N(1) 2.131(2), Mg(1)-N(2) 2.147(2), Mg(1)-N(3) 2.141(2), Mg(1)-N(4) 2.131(2), K(1)-C(1) 3.089(3), K(1)-C(2) 3.340(3), K(1)-C(3) 3.383(3), K(1)-C(4) 3.282(3), K(1)-C(5) 3.078(3), K(1)-C(6) 2.957(3), K(1)-C(39) 3.064(3), K(1)-C(40) 2.986(3), K(1)-C(41) 3.027(3), K(1)-C(42) 3.129(3), K(1)-C(43) 3.189(3), K(1)-C(44) 3.203(3) ; N(1)-Mg(1)-N(2) 75.06(8), N(3)-Mg(1)-N(2) 107.27(9), N(1)-Mg(1)-N(4) 105.50(9), N(3)-Mg(1)-N(4) 75.07(9), K(1)-Mg(1)-K(2) 178.34.
work is underway in our group to explore the chemistry of these complexes.
Experimental Section General Procedures. All manipulations were carried out in a nitrogen atmosphere under anaerobic conditions using standard Schlenk vacuum line and glovebox (MBraun UniLab) techniques. All organic solvents (including deuterated solvents for the NMR measurements) were dried over sodium wire and distilled from sodium/benzophenone under nitrogen prior to use. C6D6 was distilled from potassium, degassed by three freeze-pump-thaw cycles, and stored under nitrogen. H2[Me2Si(Ndipp)2]2 (dipp = 2,6-iPr2C6H3) (1) was prepared according to the literature method.8 Potassium graphite (C8K) was freshly prepared according to the literature.14 (n-Bu)2Mg was purchased from Aldrich Chemical Co. and used as received. The 1H NMR and 13C NMR spectra were recorded with a JEOL ECA-400 spectrometer. IR measurements were carried out on a Nicolet 360 FT-IR spectrometer from Nujol mulls prepared in a drybox. Melting points were measured in sealed nitrogen-filled capillaries without temperature correction with a Reichert-Jung apparatus type 302102. Elemental analyses were carried out on an Elemental Vario EL3 (Germany) elemental analyzer. Preparation of [(μ-Mg){η2:η1-Me2Si(Ndipp)2}]2 (2). To a solution of 1 (2.05 g, 5.0 mmol)8 in n-hexane (50 mL) at 0 °C was added slowly (n-Bu)2Mg (5.0 mmol, 1.0 M in heptane) via a (12) Green, S. P.; Jones, C.; Stasch, A. Science 2007, 318, 1754–1757. (13) We noted that the reaction of magnesium chloride with a bulky bidentate N-donor R-diimine ligand in the presence of potassium metal led to a magnesiate with a novel magnesium-magnesium bond. Liu, Y.-Y.; Li, S.-G.; Yang, X.-J.; Yang, P.-J.; Wu, B. J. Am. Chem. Soc. 2009, 131, 4210–4211. (14) Bergbreiter, D. E.; Killough, J. M. J. Am. Chem. Soc. 1978, 100, 2126–2134.
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Figure 3. Molecular structure of 4 with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Mg(1)-N(1) 2.133(2), Mg(1)-N(2) 2.131(2), Mg(1)-N(3) 2.131(2), Mg(1)-N(4) 2.127(2), K(1)-O(1) 2.753(2), K(1)-O(2) 2.719(2), K(2)-O(3) 2.656(3), K(1)-C(1) 3.318(3), K(1)-C(2) 3.132(3), K(1)-C(3) 3.052(3), K(1)-C(4) 3.169(3), K(1)-C(5) 3.390(3), K(1)-C(6) 3.481(3), K(2)-C(13) 3.066(3), K(2)-C(14) 2.968(3), K(2)-C(15) 3.051(3), K(2)-C(16) 3.213(3), K(2)-C(17) 3.298(3), K(2)-C(18) 3.270(3); N(1)-Mg(1)-N(2) 75.03(8), N(4)-Mg(1)-N(1) 107.26(19) 107.88(8), N(2)-Mg(1)-N(3) 105.37(9), N(3)-Mg(1)-N(4) 75.64(8), O(1)-K(1)-O(2) 83.80(7), K(1)-Mg(1)-K(2) 178.02. syringe, and the reaction was allowed to stir for 2 h at room temperature. After the solution was refluxed for 5 h, the light yellow solution was reduced in high vacuum until a colorless solid appeared. The suspension was warmed to make the solid resolve to afford 2 as colorless crystals at room temperature (yield: 1.69 g, 78%). Mp: 119-121 °C. 1H NMR (C6D6, 23 °C): δ 7.30 (m, 2 H, Ph), 7.23 (m, 2 H, Ph), 7.12 (t, 2 H, Ph), 6.85 (m, 2 H, Ph), 6.77 (t, 4 H, Ph), 4.34 (sept, 2 H, Me2CH), 4.00 (m, 4 H, Me2CH), 3.75 (sept, 2 H, Me2CH), 1.65 (d, 6 H, (CH3)2C), 1.41 (d, 6 H, (CH3)2C), 1.37 (d, 6 H, (CH3)2C), 1.21 (t, 12 H, (CH3)2C), 1.02 (d, 6 H, (CH3)2C), 0.91 (d, 6 H, (CH3)2C), 0.12 (d, 6 H, (CH3)2C), 0.58 (s, 6 H, (CH3)2Si), -0.11 (s, 6 H, (CH3)2Si). 13C{1H} NMR (C6D6, 23 °C): δ 146.6(s), 146.0(s), 145.4(s), 144.5(s), 143.8(s), 138.8(s), 128.1(s), 127.9(s), 126.6(s), 126.0(s), 123.9(s), 123.5(s), 123.4(s), 120.7(s) (C on the phenyl rings), 28.5(s), 27.7(s), 27.3(s), 27.2(s), 27.0(s), 26.9(s), 25.6(s), 25.5(s), 24.5(s), 23.7(s), 22.7(s), 21.5(s) (C of iPr groups), 6.6(s), 0.04(s) ((CH3)2Si). IR (Nujol mull, cm-1): ν~ 3048(w), 1588(m), 1427(s), 1309(s), 1252(s), 1225(s), 1183(s), 1145(w), 1104(s), 1040(s), 935(s), 894(s), 840(s), 789(s), 723(m), 701(w), 653(w). Anal. Calcd for C52H80Mg2N4Si2 (%): C 72.12, H 9.31, N 6.47. Found: C 72.61, H 9.26, N 6.43. Preparation of [(η6:η6-K)þ]2[Mg{η2-Me2Si(Ndipp)2}2]2- (3). To a mixture of 2 (1.72 g, 2.0 mmol) and C8K (0.54 g, 4 mmol) was added toluene (50 mL) at -78 °C. The suspension was stirred for 2 h at this temperature and then allowed to warm to room temperature. The suspension was stirred for another 24 h at room temperature and then filtered through Celite. After the filtrate was concentrated under reduced pressure, n-hexane (10 mL) was added to give 3 3 0.5(n-hexane) as light yellow crystals. Yield: 1.00 g (52%). Mp: >210 °C, dec. 1H NMR (298 K, C6D6): δ 6.89 (m, 4 H, Ph), 6.58 (m, 4 H, Ph), 6.24 (t, 4 H, Ph), 4.33 (sept, 4 H, (CH3)2CH), 4.19 (sept, 4 H, (CH3)2CH), 1.80 (d, 12 H, (CH3)2C), 1.49 (d, 12 H, (CH3)2C), 1.29 (m, 4 H, CH2(n-hexane)), 1.25 (d, 12 H, (CH3)2C), 0.89 (t, 3 H, CH2(n-hexane)), 0.83 (d, 12 H, (CH3)2C), 0.38 (s, 12 H, (CH3)2Si). 13C{1H} NMR (C6D6, 23 °C): δ 157.3(s), 146.3(s), 143.4(s), 124.0(s), 123.5(s), 114.8(s) (C on the phenyl rings), 31.9(s) (n-hexane-C), 27.7(s), 27.3(s), 27.2(s), 27.1(s), 26.8(s), 26.0(s), 25.8(s), 25.7(s), 25.6(s) (C of iPr groups), 22.9(s) (n-hexane-C), 14.3(s) (n-hexane-C), 5.5(s) (CH3)2Si). IR (Nujol mull, cm-1): ν~ 3033(w), 1578(m), 1407(s), 1313(s),
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Organometallics, Vol. 28, No. 17, 2009
1247(s), 1201(m), 1144(m), 1104(s), 1037(s), 933(vs), 878(w), 822(s), 801(s), 774(s), 743(m), 682(m). Anal. Calcd for C52H80MgK2N4Si2 (%): C 67.90, H 8.77, N 6.09. Found: C 67.43, H 8.70, N 6.05 (the n-hexane molecule in the crystal lattice was pumped off when the sample was dried under high vacuum). Preparation of [(η6:η6-K(THF))þ][(η6:η6-K(THF)2)þ][(η2Mg){Me2Si(Ndipp)2}2]2- (4). 3 (3.68 g. 4.0 mmol) was dissolved in THF (20 mL). The solution was concentrated, and n-hexane (10 mL) was then added to give 4 as colorless crystals at -25 °C (4.09 g, 90%). Mp: 192-194 °C, dec. 1H NMR (C6D6, 23 °C): δ 7.03 (m, 4 H, Ph ring), 6.72 (m, 4 H, Ph ring), 6.38 (t, 4 H, Ph ring), 4.45 (sept, 4 H, Me2CH), 4.31 (sept, 4 H, Me2CH), 3.61 (m, 12 H, THF), 1.94 (d, 12 H, (CH3)2C), 1.60 (d, 12 H, (CH3)2C), 1.51 (m, 12 H, THF), 1.36 (d, 12 H, (CH3)2C), 0.95 (d, 12 H, (CH3)2C), 0.48 (s, 12 H, (CH3)2Si). 13C{1H} NMR (C6D6, 23 °C): δ 157.4(s), 146.3(s), 143.5(s), 124.0(s), 123.6(s), 114.6(s) (C on the phenyl rings), 25.6 (s, C-THF), 67.8 (s, C-THF), 27.8(s), 27.4(s), 27.1(s), 26.0(s), 25.8(s), 25.7(s) (C of iPr), 5.5 (s, CH3)2Si). IR (Nujol mull, cm-1): ν~ 3094(w), 1578(s), 1493(m), 1408(s), 1248(s), 1314(s), 1282(w), 1248(s), 1201(m), 1145(m), 1103(m), 1052(s), 1032(s), 927(s), 822(m), 800(s), 766(s), 741(m), 682(m), 620(w). Anal. Calcd for C60H96K2MgN4O2Si2 (%): C 67.76, H 9.10, N 5.27. Found: C 67.45, H 9.02, N 5.25 (one of the THF molecules could be pumped off when the sample was dried under high vacuum). X-ray Crystallography. Suitable single crystals were sealed under N2 in thin-walled glass capillaries. X-ray diffraction data were collected on a SMART APEX CCD diffractometer (graphite-monochromated Mo KR radiation, j-ω-scan technique, λ = 0.71073 A˚) at 120 K. The intensity data were integrated by means of the SAINT program.15 SADABS16 was used to perform area-detector scaling and absorption corrections. The structures were solved by direct methods and were refined against F2 using all reflections with the aid of the SHELXTL package.17 All non-hydrogen atoms were refined anisotropically. The H atoms were included in calculated (15) SAINTPlus Data Reduction and Correction Program v. 6.02 a; Bruker AXS: Madison, WI, 2000 (16) Sheldrick, G. M. SADABS, A Program for Empirical Absorption Correction; University of G€ottingen: G€ottingen, Germany, 1998. (17) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structures; University of G€ottingen: G€ottingen, Germany, 1997.
Pi et al. positions with isotropic thermal parameters related to those of the supporting carbon atoms but were not included in the refinement. All non-hydrogen atoms were found from the difference Fourier syntheses. All calculations were performed using the Bruker Smart program. Crystallographic parameters for compounds 2-4 along with details of the data collection and refinement are contained in the Supporting Information.9 Crystal data for 2: C52H80Mg2N4Si2, Mr = 866.00, orthorhombic, space group Pna21, a=21.054(3) A˚, b=18.704(2) A˚, c=13.4708(16) A˚, R=β=γ=90°, V=5304.8(11) A˚3, Z=4, Fcalcd= 1.084 Mg m-3, crystal size 0.25 0.10 0.08 mm3, F(000)=1888, μ(Mo KR)=0.126 mm-1, 10 245 independent reflections (Rint = 0.0413), restraints 10 245/1/541, Gof=1.050, final R indices were R1=0.0464 [I > 2σ(I)] and wR2=0.1294 (all data). Crystal data for 3 3 0.5(n-hexane): C52H80K2MgN4Si2 3 0.5(nhexane), Mr = 962.98, triclinic, P1, a = 13.0793(16) A˚, b = 18.673(2) A˚, c = 23.230(3) A˚, R = 93.883(2)°, β = 100.717(2)°, γ=93.795(2)°, V=5543.6(12) A˚3, Z=4, Fcalcd=1.154 Mg m-3, crystal size 0.25 0.20 0.20 mm3, F(000)=2092, μ(Mo KR)= 0.263 mm-1, Gof=1.032, 21 330 independent reflections (Rint= 0.0296), restraints 21 330/3/1202. Final R indices were R1 = 0.0540 [I > 2σ(I)] and wR2 =0.1655 (all data). Crystal data for 4: C64H104K2MgN4O3Si2, Mr = 1136.20, monoclinic, space group P21/c, a=15.295(3) A˚, b=24.825(6) A˚, c=18.799(4) A˚, R=γ=90°, β=112.095(2), V=6614(3) A˚3, Z=4, Fcalcd = 1.141 Mg m-3, crystal size 0.30 0.25 0.20 mm3, F(000) = 2472, μ(Mo KR) = 0.234 mm-1, Gof = 1.044, 11 639 independent reflections (Rint =0.0575), restraints 11 639/0/685. Final R indices were R1 =0.0550 [I > 2σ(I)] and wR2 =0.1541 (all data).
Acknowledgment. W.Z. is grateful to the National Natural Science Foundation of China (NSFC) (Grant No. 20872017). C.-F.P. is thankful to the Shanghai Science Postdoctoral Foundation for support of this research. Supporting Information Available: X-ray crystallographic files of 2-4 in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.
