Note pubs.acs.org/Organometallics
Two-Coordinate Gallium Ion [tBu3Si-Ga-SitBu3]+ and the Halonium Ions [tBu3Si-X-SitBu3]+ (X = Br, I): Sources of the Supersilyl Cation [tBu3Si]+ Alexandra Budanow, Tanja Sinke, Jan Tillmann, Michael Bolte, Matthias Wagner, and Hans-Wolfram Lerner* Institut für Anorganische Chemie, Goethe-Universität Frankfurt am Main, Max-von-Laue-Straße 7, 60438 Frankfurt am Main, Germany S Supporting Information *
ABSTRACT: The ion pair [tBu3Si-Ga-SitBu3][Al(OC(CF3)3)4] was formed quantitatively by treatment of (tBu3Si)2GaCl with Ag[Al(OC(CF3)3)4] in methylene chloride. Single crystals of yellow [tBu3Si-GaSitBu3][Al(OC(CF3)3)4] were available from the filtered reaction solution at ambient temperature (space group P21/c). The isolated [tBu3Si-GaSitBu3]+ cation is isostructural with isoelectronic [tBu3Si-Zn-SitBu3] and [tBu3Si-Cu-SitBu3]−, respectively. Additionally, the reactions of tBu3SiX (X = Br, I) with Ag[Al(OC(CF3)3)4] are described by which the halonium ions [tBu3Si-X-SitBu3]+ were formed. We found that the two-coordinate Ga cation [tBu3Si-Ga-SitBu3]+ and the halonium ions [tBu3Si-X-SitBu3]+ (X = Br, I) are highly reactive. The salts [tBu3Si-X-SitBu3][Al(OC(CF3)3)4] (X = Ga, Br, I) decompose in CH2Cl2 at room temperature to give tBu3SiF and tBu3SiCl. It is worth mentioning that the ratio of tBu3SiF to tBu3SiCl in these decomposition reactions is the same. We concluded that the same reactive intermediate, the supersilyl cation [tBu3Si]+, was thereby formed.
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INTRODUCTION Developing highly reactive Lewis acids as borinium cations,1 e.g., for polymerization catalysis, has received great interest in recent years; however, information regarding the structure and reactivity of borinium analogues is still rather limited. It was found that two-coordinate alumenium ions [R2Al]+ (R = alkyl) are more reactive than the homologous borinium ions.2 Due to anion degradation, the preparation of such cations was difficult.3 Reed and co-workers, however, could isolate the ion-like alumenium salts [Et2Al]+[CB11H6X6]− (X = Cl, Br).4 In these compounds the [Et2Al]+ cations are stabilized by weak aluminum halogen interactions.5 Recently, Wehmschulte et al. have reported that discrete gallium cations [(2,6Mes2C6H3) 2Ga]+ are present in the mixed salt [(2,6Mes2C6H3)2Ga]Li[Al(OCH(CF3)2)4]2, which was synthesized by the metathesis reaction of (2,6-Mes2C6H3)2GaCl with 2 equiv of Li[Al(OCH(CF3)2)4] in chlorobenzene at room temperature.6 In the course of our investigations of low-coordinate gallium compounds7 we prepared (tBu3Si)2GaCl from GaCl3 and tritert-butylsilanide (supersilanide) Na[SitBu3].8,9 When GaCl3 in pentane was treated with one or two molar equivalents of Na[SitBu3],8,9 the reaction mixture underwent a color change to bright yellow.10 It is worth mentioning that in both cases treatment of GaCl3 with Na[SitBu3] exclusively yielded the disupersilylated chlorogallane (tBu3Si)2GaCl, and no mono© 2012 American Chemical Society
supersilylated dichlorogallane tBu 3 SiGaCl 2 was formed (Scheme 1).10 In this reaction the second substitution reaction of Na[SitBu3] must be much faster than the first one. Surprisingly, after multiple recrystallizations we isolated colorless crystals of (tBu3Si)2GaCl.11 Therefore we suggested that in solution an equilibrium of (tBu3Si)2GaCl and GaCl3 with the ion pair [tBu3Si-Ga-SitBu3][GaCl4] exists,12 and the yellow color proceeds from the cation [tBu3Si-Ga-SitBu3]+. However, Scheme 1. Synthesis of (tBu3Si)2GaCl and [tBu3Si-GaSitBu3]+ ([1]+)a
a (i) +GaCl3, −2NaCl, in pentane at −78 °C. (ii) +Ag[Al(OC(CF3)3)4], −AgCl, −[Al(OC(CF3)3)4]−, in CH2Cl2 or +GaCl3, −[GaCl4]−, in CH2Cl2.
Received: September 4, 2012 Published: September 27, 2012 7298
dx.doi.org/10.1021/om300854e | Organometallics 2012, 31, 7298−7301
Organometallics
Note
up to now we could not isolate [tBu3Si-Ga-SitBu3]+. If indeed the cation [tBu3Si-Ga-SitBu3]+ is present in an equilibrium concentration, it should be possible to obtain it with an appropriate anion. For this approach we have chosen [Al(OC(CF3)3)4]−. In this paper we present the synthesis and the structure of [tBu3Si-Ga-SitBu3][Al(OC(CF3)3)4] ([1][Al(OC(CF3)3)4]). The structural features of the gallium cation [1]+ were compared with those of the isoelectronic supersilyl zinc [tBu3Si-Zn-SitBu3] and copper complex [tBu3Si-Cu-SitBu3]−. In addition we report here the reactions of tBu3SiX (X = Br, I) with Ag[Al(OC(CF3)3)4], which give the corresponding halonium ions [tBu3Si-X-SitBu3]+ (X = Br, I).
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RESULTS AND DISCUSSION Treatment of (tBu3Si)2GaCl with the “Krossing salt” Ag[Al(OC(CF3)3)4]13 in 1:1 molar ratio in CH2Cl2 resulted in an immediate reaction. The mixture quickly became heterogeneous, while the NMR spectra of the solution revealed new signals. After filtering, bright yellow crystals of [1][Al(OC(CF3)3)4] were grown from the filtrate at ambient temperature. In contrast to [(2,6-Mes2C6H3)2Ga]+, the supersilylated Ga cation [1]+ has an impressive color. The UV−vis spectrum of [1][Al(OC(CF3)3)4] is characterized by absorption bands at λmax = 393 nm as well as λmax = 433 nm (Figure 2S). Moreover, we found that the supersilyl-substituted Ga cation [1]+ is highly reactive and decomposes in the presence of CH2Cl2. After storing a solution of [1][Al(OC(CF3)3)4] in CH2Cl2 for 1 week at room temperature, the signals of [1][Al(OC(CF3)3)4] were no longer recognizable in the NMR spectra. Instead resonances attributable to the fluorsilane tBu3SiF8 and the chlorsilane tBu3SiCl8 were observed. The supersilyl cation [tBu3Si]+ in the equilibrium with [1]+ apparently underwent reactions with [Al(OC(CF3)3)4]−14 and CH2Cl215 to give tBu3SiF and tBu3SiCl, respectively. In Figures 1 and 2 the molecular structure of [1][Al(OC(CF3)3)4] is shown. Similar to the isoelectronic compounds [tBu3Si-Zn-SitBu3]8,16 and [tBu3Si-Cu-SitBu3]−,8,17 the Si−M− Si unit in [1]+ is perfectly linear (Figure 1), as found for the C− Ga−C axis in [(2,6-Mes2C6H3)2Ga]+, whereas the related complex [Ga(PtBu3)2]+18 displays an angled backbone. The Ga−Si distance of 2.4276(18) Å in [1]+ is, however, longer than the related Zn−Si bond in [tBu3Si-Zn-SitBu3] and the Cu−Si distance in [tBu3Si-Cu-SitBu3]− (Table 1). To the best of our knowledge this represents the first structural characterization of a silyl-substituted borinium homologue by means of X-ray crystallography. In addition, we have investigated the reactions of tBu3SiX (X = Br, I) with Ag[Al(OC(CF3)3)4]. The halosilanes tBu3SiX (X = Br, I) react with Ag[Al(OC(CF3)3)4] at −50 °C, forming quantitatively the corresponding halonium ion [tBu3Si-XSitBu3]+ (Scheme 2). The cations [2]+ and [3]+ were identified by low-temperature NMR spectroscopy (see Supporting Information Figures 3S−8S). Unfortunately both cations [2]+ and [3]+ are rather unstable, and therefore we were unable to obtain single crystals. However, it is interesting that the ratio of tBu3SiF to tBu3SiCl in the decomposition reactions of the twocoordinate Ga cation [1]+19 as well as of the halonium ions [2]+ and [3]+ was always 15:85 (Scheme 3). Therefore we suggested that in all three reactions the same reactive intermediate, the ion-like supersilylium [tBu3Si]+,20 was formed. However the decomposition speeds of [1]+, [2]+, and [3]+ differ strongly (stability: [1]+ > [2]+ > [3]+). Additionally, we found that the
Figure 1. Solid-state structure of one of two crystallographically independent cations [1]+ in [1][Al(OC(CF3)3)4] (monoclinic, P21/c). Displacement ellipsoids are drawn at the 50% probability level. H atoms are omitted for clarity. Selected bond lengths (Å), bond angles (deg), and torsion angles (deg): Ga(1)−Si(1) = 2.4276(18), Si(1)− C(61) = 1.896(8), Si(1)−C(71) = 1.919(9), Si(1)−C(51) = 1.930(8); Si(1A)−Ga(1)−Si(1) = 180.0, C(61)−Si(1)−C(71) = 115.8(4), C(61)−Si(1)−C(51) = 115.8(3), C(71)−Si(1)−C(51) = 113.8(4), C(61)−Si(1)−Ga(1) = 103.4(2), C(71)−Si(1)−Ga(1) = 101.8(2), C(51)−Si(1)−Ga(1) = 103.6(2); Si(1A)-Ga(1)−Si(1)−C(61) = −134(3), Si(1A)-Ga(1)−Si(1)−C(71) = −14(3), Si(1A)-Ga(1)− Si(1)−C(51) = 105(3), Symmetry transformations used to generate equivalent atoms: A −x, −y+1, −z.
Figure 2. Crystal packing of [1][Al(OC(CF3)3)4].
Table 1. Selected Averaged Bond Lengths [Å] and Angles [deg] of Isoelectronic Complexes [tBu3Si-Ga-SitBu3]+, [tBu3Si-Zn-SitBu3], and [tBu3Si-Cu-SitBu3]− +
[tBu3Si-Ga-SitBu3] (M = Ga) [tBu3Si-Zn-SitBu3] (M = Zn) [tBu3Si-Cu-SitBu3]− (M = Cu)
7299
M−Si
Si−M−Si
average Si−C
2.428(2) 2.384(1) 2.307(2)
180.0 180.0 180.0
1.915(8) 1.943(4) 1.972(6)
dx.doi.org/10.1021/om300854e | Organometallics 2012, 31, 7298−7301
Organometallics
Note
Scheme 2. Reaction of tBu3SiX (X = Br, I) with Ag[Al(OC(CF3)3)4]a
and [3][Al(OC(CF3)3)4] is always the same. Therefore we suggest that in all three reactions the same reactive intermediate, the supersilyl cation [tBu3Si]+, was formed.
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EXPERIMENTAL SECTION
General Procedures. All reactions and manipulations were carried out under dry, oxygen-free nitrogen by using standard Schlenk ware or in an argon-filled M. Braun glovebox. The solvents thf, Et2O, pentane, benzene, and [D6]benzene were stirred over sodium/benzophenone and distilled prior to use. CH2Cl2 and CD2Cl2 were dried over CaH2 and freshly distilled prior to use. Na[SitBu3],9 tBu3SiBr,9 tBu3SiI,9 and (tBu3Si)2GaCl10 were prepared according to the published procedures. The NMR spectra were recorded on a Bruker AM 250, a Bruker DPX 250, a Bruker Avance 300, and a Bruker Avance 400 spectrometer. NMR chemical shifts are reported in ppm and referenced to external tetramethylsilane (1H, 13C, 29Si). Elemental analysis was performed by the Microanalytical Laboratory Pascher. Abbreviations: s = singlet; q = quartet. Synthesis of [1][Al(OC(CF3)3)4]. (tBu3Si)2GaCl (160 mg, 0.31 mmol) and Ag[Al(OC(CF3)3)4]13 (270 mg, 0.31 mmol) were dissolved in CH2Cl2 (2.5 mL). The reaction mixture was stirred at room temperature for 30 min in the dark. Single crystals of [1][Al(OC(CF3)3)4] were isolated from the filtered reaction solution. Yield: 276 mg (62%). 1H NMR (300.1 MHz, CD2Cl2): δ 1.39 (s, 18H; 6 tBu). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ 27.7 (C(CH3)3), 32.8 (CH3), 120.3 (q, 1JCF = 293 Hz; CF3). 19F NMR (282.3 MHz) δ −75.74. 29Si{1H} NMR (59.6 MHz, CD2Cl2): δ 54.1. UV−vis spectrum see Supporting Information Figure 2S. Anal. Calcd for C40H54AlF36GaO4Si2 (1435.67): C 33.46; H 3.79. Found: C 33.61; H 3.84. After storing a solution of [1][Al(OC(CF3)3)4] in CH2Cl2 for 1 week at room temperature the signals of [1][Al(OC(CF3)3)4] were no longer recognizable in the 29Si NMR spectrum. Instead of resonances attributable to the fluorsilane tBu3SiF, those of the chlorsilane tBu3SiCl were observed (1H/29Si HETCOR NMR spectrum see Supporting Information Figure 9S). The signal ratio of tBu3SiF and tBu3SiCl was 15:85. Reaction of tBu3SiBr with Ag[Al(OC(CF3)3)4]. An NMR tube was charged with tBu3SiBr (29 mg, 0.1 mmol) and Ag[Al(OC(CF3)3)4]13 (83 mg, 0.1 mmol). CD2Cl2 was condensed on tBu3SiBr and Ag[Al(OC(CF3)3)4],13 which were cooled by liquid nitrogen (−196 °C). The NMR spectra of the reaction solution at −50 °C revealed exclusively the signals of [2][Al(OC(CF3 )3) 4] (see Supporting Information Figures 3S−5S). 1H NMR (250 MHz, CD2Cl2, −50 °C): δ 1.17 (s, 3 tBu). 13C{1H} NMR (62.9 MHz, CD2Cl2, −50 °C): δ 24.3 (C(CH3)3), 29.0 (CH3), 120.8 (q, 1JCF = 292 Hz; CF3). 29Si{1H} NMR (59.6 MHz, CD2Cl2, −50 °C): δ 52.1. After storing a solution of [2][Al(OC(CF3)3)4] for 2 h at room temperature, only the signals of tBu3SiF and tBu3SiCl were observable in the NMR spectra (tBu3SiF:tBu3SiCl = 15:85; 29Si NMR spectrum see Supporting Information Figure 10S). Reaction of tBu3SiI with Ag[Al(OC(CF3)3)4]. An NMR tube was charged with tBu3SiI (32 mg, 0.1 mmol) and Ag[Al(OC(CF3)3)4] (83 mg, 0.1 mmol). CD2Cl2 was condensed on tBu3SiI and Ag[Al(OC(CF3)3)4],13 which were cooled by liquid nitrogen (−196 °C). The NMR spectra of the reaction solution at −50 °C revealed exclusively the signals of [3][Al(OC(CF3)3)4] (see Supporting Information Figures 6S−8S). 1H NMR (300.1 MHz, CD2Cl2, −50 °C): δ 1.24 (s, 3 tBu). 13C{1H} NMR (75.5 MHz, CD2Cl2, −50 °C): δ 25.5 (C(CH3)3), 29.9 (CH3), 120.5 (q, 1JCF = 293 Hz; CF3). 29Si{1H} NMR (59.6 MHz, CD2Cl2, −50 °C): δ 72.9. When the reaction solution was warmed to room temperature, only the signals of tBu3SiF and tBu3SiCl were observable in the NMR spectra (tBu3SiF:tBu3SiCl = 15:85; [3][Al(OC(CF3)3)4]). X-ray Crystallography of [1][Al(OC(CF3)3)4]. In one of the two crystallographically independent cations the tBu groups are disordered over two positions with a site occupation factor of 0.56(1) for the major occupied site. The disordered atoms have just been isotropically refined, and equivalent C−C distances and C−C−C angles have been
(i) +Ag[Al(OC(CF3)3)4], −AgX ([2]+ (X = Br), [3]+ (X = I)), in CH2Cl2 at −50 °C. a
Scheme 3. Decomposition of the Two-Coordinate Ga Cation [1]+ As Well As of the Halonium Cations [2]+ and [3]+ in CH2Cl2 at Room Temperaturea
(i) −tBu3SiX ([1]+ (X = Ga),19 [2]+ (X = Br), [3]+ (X = I)); (ii) −CF4F8O,14 −[((CF3)3CO)3Al-F-Al(OC(CF3)3)3]−,14 in CH2Cl2 at room temperature; (iii) +CH2Cl2, −CH2Cl+,15 −[Al(OC(CF3)3)4]−, in CH2Cl2 at room temperature. a
supersilylated halonium ions [tBu3Si-X-SitBu3]+ are much more reactive than the trimethylsilylated analogues [Me3Si-XSiMe3]+.21,22 In this context it should be noted that unequal dihedral angles α1 ≠ α2 ≠ 60° (Figure 3), as found in the
Figure 3. Staggered conformation (α1 = 60°) and the conformation of sterically overcrowded compounds (α1 ≠ α2 ≠ 60°).24
isoelectonic disiloxane tBu3Si-O-SitBu3,23 indicate that this supersilylated compound is sterically overcrowded.24 The lesser stability of supersilylated halonium ions compared to the trimethylsilyl analogues can be caused by steric repulsion and, as a consequence thereof, by the liberation of the highly reactive supersilyl cation [tBu3Si]+. Finally the supersilyl cation [tBu3Si]+ reacted with [Al(OC(CF3)3)4]−14 and CH2Cl215 to give tBu3SiF and tBu3SiCl, as shown in Scheme 3.25,26
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CONCLUSION In the course of this study aimed at finding crystallographic proof for the proposed structure of the two-coordinate gallium cation [1]+ we were able to obtain crystallographic data for the ion pair [1][Al(OC(CF3)3)4]. These data help to fill in some of the blank spots on the map of crystallographically characterized borinium homologues. In the reactions of the halosilanes tBu3SiX (X = Br, I) with Ag[Al(OC(CF3)3)4], the halonium cations [tBu3Si-X-SitBu3]+ were formed. The ratio of tBu3SiF to tBu3SiCl in the decomposition reactions of [1][Al(OC(CF3)3)4] as well as of the halonium salts [2][Al(OC(CF3)3)4] 7300
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Schwenk-Kircher, H.; Warchold, M. Z. Naturforsch. 2001, 56b, 634− 651. (13) Krossing, I. Chem.Eur. J. 2001, 7, 490−502. Krossing, I.; Reisinger, A. Coord. Chem. Rev. 2006, 250, 2721−2744. (14) Decomposition of [Al(OC(CF3)3)4]− induced by strong Lewis acids; see: Bihlmeier, A.; Gonsior, M.; Raabe, I.; Trapp, N.; Krossing, I. Chem.Eur. J. 2004, 10, 5041−5051. Krossing, I.; Raabe, I. Chem. Eur. J. 2004, 10, 5017−5030. (15) Stability and decomposition of CHnX3−n+ (X = F, Cl, Br, I; n = 0, 1, 2); see: Raabe, I. Ph.D. thesis, École Polytéchnique Fédérale de Lausanne, Switzerland, 2007. (16) Wiberg, N.; Amelunxen, K.; Lerner, H.-W.; Nöth, H.; Appel, A.; Knizek, J.; Polborn, K. Z. Anorg. Allg. Chem. 1997, 623, 1861−1870. (17) Lerner, H.-W.; Scholz, S.; Bolte, M. Organometallics 2001, 20, 575−577. (18) Higelin, A.; Sachs, U.; Keller, S.; Krossing, I. Chem.Eur. J. 2012, 18, 10029−10034. (19) A dark precipitate was formed in this reaction. Additionally, small signals of a minor component were observed in the 13C NMR spectrum, which could be assigned to the tetrahedrane (tBu3Si)4Ga4 (δ(13C) = 26.7, 32.7). (20) The supersilyl cation [tBu3Si]+ is unknown in the literature. References for related silylium compounds: Reed, C. A. Acc. Chem. Res. 1998, 31, 325−332. Reed, C. A. Acc. Chem. Res. 2010, 43, 121− 128. Avelar, A.; F. S. Tham, F. S.; Reed, C. A. Angew. Chem., Int. Ed. 2009, 48, 3491−3493. Hoffmann, S. P.; Kato, T.; Tham, F. S.; Reed, C. A. Chem. Commun. 2006, 767−769. (21) Schulz, A.; Villinger, A. Chem.Eur. J. 2010, 16, 7276−7281. Lehmann, M.; Schulz, A.; Villinger, A. Angew. Chem., Int. Ed. 2009, 48, 7444−7447. Ibad, M. F.; Langer, P.; Schulz, A.; Villinger, A. J. Am. Chem. Soc. 2011, 133, 21016−21027. (22) Schulz, A.; Villinger, A. Angew. Chem., Int. Ed. 2012, 51, 4526− 4528. (23) Wiberg, N.; Kühnel, E.; Schurz, K.; Borrmann, H.; Simon, A. Z. Naturforsch. 1988, 43b, 1075−1086. (24) Bolte, M.; Lerner, H.-W. J. Chem. Crystallogr. 2011, 41, 132− 136. Vitze, H.; Wietelmann, U.; Murso, A.; Bolte, M.; Wagner, M.; Lerner, H.-W. Z. Naturforsch. 2009, 64b, 223−228. (25) The literature-known compound [Et2OH][B(C6F5)4] (see ref 26) was the only compound that could be isolated from the reaction of tBu3SiI with Ag[B(C6F5)4]. Structural details: CCDC 898528. (26) Jutzi, P.; Müller, C.; Stammler, A.; Stammler, H.-G. Organometallics 2000, 19, 1442−1444. (27) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
restrained to be equal. Only the ordered cation is discussed and mentioned in Figure 1. In the anion three CF3 groups are disordered over two positions with a site occupation factor of 0.58(1) for the major occupied site. The disordered atoms have just been isotropically refined. All C−F distances were restrained to 1.31(1) Å, and all C−C distances in the anion were restrained to 1.52(2) Å. The disordered C atoms in the anion were refined with a common isotropic displacement parameter. Data collection was performed on a Stoe-IPDS-II diffractometer, with empirical absorption correction using MULABS. The structure was solved with direct methods and refined against F2 by full-matrix least-squares calculation with SHELXL-97.27 Hydrogen atoms were placed on ideal positions and refined with fixed isotropic displacement parameters using a riding model. CCDC reference number: 898527 ([1][Al(OC(CF3)3)4]).
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ASSOCIATED CONTENT
S Supporting Information *
Structure of the anion of [1][Al(OC(CF3)3)4], UV−vis spectrum of [1][Al(OC(CF3)3)4], NMR spectra of [2][Al(OC(CF3)3)4] and [3][Al(OC(CF3)3)4], NMR spectra of the decomposition reactions of [1][Al(OC(CF3)3)4] and [2][Al(OC(CF3)3)4], and table of X-ray parameters. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Fax: +49-69798-29260. E-mail:
[email protected]. de. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by Merck KGaA, Darmstadt, Germany.
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REFERENCES
(1) Piers, W. E.; Bourke, S. C.; Conroy, K. D. Angew. Chem., Int. Ed. 2005, 44, 5016−5036. (2) Khandelwal, M.; Wehmschulte, R. J. Angew. Chem., Int. Ed. 2012, 51, 7323−7326. (3) Bochmann, M.; Sarsfield, M. J. Organometallics 1998, 17, 5908− 5912. (4) Kim, K.-C.; Reed, C. A.; Long, G. S.; Sen, A. J. Am. Chem. Soc. 2002, 124, 7662−7663. (5) Related alumenium cations have been recently published: Ivanov, S. V.; Peryshkov, D. V.; Miller, S. M.; Anderson, O. P.; Rappé, A. K.; Strauss, S. H. J. Fluorine. Chem. 2012, DOI: org/ 10.1016/j.jfluchem.2012.02.001. Kessler, M.; Knapp, C.; Zogaj, A. Organometallics 2011, 30, 3786−3792. (6) Wehmschulte, R. J.; Steele, J. M.; Young, J. D.; Khan, M. A. J. Am. Chem. Soc. 2003, 125, 1470−1471. (7) Wiberg, N.; Amelunxen, K.; Lerner, H.-W.; Nöth, H.; Ponikwar, W.; Schwenk, H. J. Organomet. Chem. 1999, 574, 246−251. (8) Lerner, H.-W. Coord. Chem. Rev. 2005, 249, 781−798. (9) Wiberg, N.; Amelunxen, K.; Lerner, H.-W.; Schuster, H.; Nöth, H.; Krossing, I.; Schmidt-Ameluxen, M.; Seifert, T. J. Organomet. Chem. 1997, 542, 1−18. (10) Wiberg, N.; Amelunxen, K.; Lerner, H.-W.; Nöth, H.; Knizek, J.; Krossing, I. Z. Naturforsch. 1998, 53b, 333−348. (11) At first we obtained yellow single crystals of (tBu3Si)2GaCl. However after multiple recrystallizations we isolated colorless crystals of (tBu3Si)2GaCl. Structural details: CCDC 287117. (12) Wiberg, N.; Amelunxen, K.; Blank, T.; Lerner, H.-W.; Polborn, K.; Nöth, H.; Littger, R.; Rackl, M.; Schmidt-Amelunxen, M.; 7301
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