Organometallics 2009, 28, 6347–6351 DOI: 10.1021/om900694u
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Reactions of [o-(Fluorodimethylsilyl)phenyl]lithium with GeCl2 and SnCl2: Preparation of Polyfunctionalized Four-Membered and Five-Membered Cyclic Linkages of Heavier Group 14 Elements Atsushi Kawachi,* Koji Machida, and Yohsuke Yamamoto Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan Received August 5, 2009
Reactions of [o-(fluorodimethylsilyl)phenyl]lithium (1) with GeCl2 and SnCl2 produce benzosilagermacyclobutene 2 and benzosiladistannacyclopentene 3, respectively, both of which have o-(fluorodimethylsilyl)phenyl groups on the germanium and tin atoms. The molecular structures of 2 and 3 were determined by X-ray crystallographic analysis, which reveals the structural features of the functionalized four- and five-membered cyclic linkages of the heavior group 14 elements.
Introduction The fluorosilyl functionality plays an important role in main group chemistry and organic synthesis because of its unique properties. Whereas the Si-F bond is thermally stable owing to its high bond energy,1 it is chemically labile due to the strong polarization (Siδþ-Fδ-) arising from the large difference in electronegativity between silicon and fluorine.2,3 Thus, fluorosilyl groups are highly receptive toward nucleophiles, forming pentacoordinate silicon species4 or initiating nucleophilic substitution reactions at silicon,5 which enables us to perform further transformations. It is also known that fluorosilyl groups are able to coordinate to electron-deficient metals and metalloids.6 Therefore, the introduction of the fluorosilyl functionality into main group element compounds as well as organic compounds is expected to open doors to new possibilities utilizing these compounds. A conventional method that incorporates a fluorosilyl group into the framework of a main group element compound is as follows: first, a rather inert hydro, amino, or alkoxysilyl group is *Corresponding author. E-mail:
[email protected]. (1) Shaw, C. F.; Allred, A. L. Organomet. Chem. Rev., A 1970, 5, 96. (2) Pauling’s electronegativity: 3.98 for F; 1.90 for Si; and 2.01 for Ge: Emsley, J. In The Elements, 2nd ed.; Oxford University Press: Oxford, 1992. (3) C-F bonds are also labile in some cases, and fluorine-containing organometallic compounds undergo intramolecular elimination of a metal fluoride; see for example: (a) Amii, H.; Uneyama, K. Chem. Rev. 2009, 109, 2119. (b) Boche, G.; Lohrenz, C. W. Chem. Rev. 2001, 101, 697. (b) Kottke, T.; Sung, K.; Lagow, R. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 1517. (c) Bosold, F.; Zulauf, P.; Marsch, M.; Harms, K.; Lohrenz, J.; Boche, G. Angew. Chem., Int. Ed. Engl. 1991, 30, 1455, and references therein. (4) Dorsey, C. L.; Gabbaı¨ , F. P. Organometallics 2008, 27, 3065, and references therein. (5) Bassindale, A. R.; Taylor, P. G. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: Chichester, 1989; Chapter 13, pp 839-892. (6) Recent examples: (a) Sievert, N.; Fischer, A.; Klingebiel, U.; Pal, A.; Noltemeyer, M. Z. Anorg. Allg. Chem. 2007, 633, 1223. (b) Panisch, R.; Bolte, M.; M€ uller, T. J. Am. Chem. Soc. 2006, 128, 9676. (c) Molev, G.; Bravo-Zhivotovskii, D.; Kami, D.; Tumanskii, B.; Botoshansky, M.; Apeloig, Y. J. Am. Chem. Soc. 2006, 128, 2784. r 2009 American Chemical Society
initially introduced into the framework, and then, the functional group on the silicon is converted into a fluorine using a fluoride source, such as HF, KF, CuF, AgF, BF3, or HBF4.7 However, this method is not always applicable because frameworks that have small rings, multiple bonds, and/or low- and hypervalent species are labile when exposed to the fluoride source. We recently developed [o-(fluorodimethylsilyl)phenyl]lithium (1), which consists of an electrophilic fluorodimethylsilyl part and a nucleophilic phenyllithium part, as a useful tool for introducing a fluorosilyl moiety into the frameworks of main group element compounds in a nucleophilic manner.8,9 Aryllithium 1 was prepared by Br-Li exchange between o-(fluorodimethylsilyl)phenyl bromide and tert-butyllithium at -78 °C and was reacted with halosilanes to afford unsymmetrical, silicon-halogenated disilylbenzenes.8 Treatment of 1 with a haloborane produced a (fluorodimethylsilyl)borylbenzene that serves as a Si/B heteronuclear bidentate Lewis acid.9 Then, we turned our attention to the reaction of 1 with divalent species of heavier group 14 elements, the latter of which also exhibit ambiphilic character.10 Here we report that the reactions of 1 with GeCl2 and SnCl2 yield benzosilagermacyclobutene 2 and benzosiladistannacyclopentene 3, respectively, which bear two or more o-(fluorodimethylsilyl)phenyl groups on the cyclic linkages of group 14 elements.
Results and Discussion The reaction of 1 with GeCl2 3 dioxane (0.5 equiv) in Et2O was conducted at -60 °C for 19 h to yield benzosilagermacyclobutene (7) Kunai, A.; Sakurai, T.; Toyoda, E.; Ishikawa, M. Organometallics 1996, 15, 2478, and references therein. (8) Kawachi, A.; Tani, A.; Machida, K.; Yamamoto, Y. Organometallics 2007, 26, 4697. (9) Kawachi, A.; Tani, A.; Shimada, J.; Yamamoto, Y. J. Am. Chem. Soc. 2008, 130, 4222. (10) Recent examples: (a) Yao, S.; W€ ullen, C. v.; Sun, X.-Y.; Driess, M. Angew. Chem., Int. Ed. 2008, 47, 3250. (b) Rupar, P. A.; Jennings, M. C.; Ragogna, P. J.; Baines, K. M. Organometallics, 2007, 26, 4109, and references therein. Published on Web 10/08/2009
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Scheme 1. Reactions of 1 with GeCl2 and SnCl2
2 together with a small amount of dimerized product7 4 (2:4= 81:19 by 1H NMR), as shown in Scheme 1. Recrystallization of the reaction mixture from hexane afforded 2 in 55% yield as colorless crystals. The temperature control is essential to yield 2 because at the higher temperatures 1 predominantly underwent dimerization to give 4.11 The employment of 1 and GeCl2 in the mole ratio of 1:1 gave a similar result (2:4=80:20). X-ray crystallographic analysis revealed that 2 has a planar {Ge-Si-C-C} four-membered ring bearing two o-(fluorodimethylsilyl)phenyl groups on the germanium atom (Figure 1). The {Ge-Si-C-C} four-membered ring has an almost planar conformation. The Ge1-Si1 bond length of 2.371(3) A˚ is consistent with normal Ge-Si single-bond length. Acute angles of C1-Ge1-Si1 (74.2(3)°) and C2-Si1-Ge1 (76.9(3)°) are necessitated by the formation of the four-membered ring. F 3 3 3 Ge1 atomic distances (3.096(6) and 3.165(6) A˚) are within the sum of the van der Waals radii of the two elements (3.38 A˚).12 In the 29Si{1H} NMR spectra, the endocyclic silicon atom resonates at δ(29Si) = 15.3 as a triplet owing to long-range coupling to the two fluorine atoms on the exocyclic silicon atoms (5J(29Si-19F)=9 Hz). The exocyclic silicon atom resonates at δ(29Si)=21.1 as a doublet owing to 1J coupling to the one fluorine atom (1J(29Si-19F)=283 Hz). Scheme 2 shows a plausible reaction pathway to 2. The reaction of 1 with GeCl2 produces diarylgermylene 5 and subsequently (triarylgermyl)lithium 6.13,14 The low solubility of GeCl2 3 dioxane in Et2O at low temperature may create the condition where 1 is present in excess compared to GeCl2. The germyl anion center in 6 intramolecularly attacks at one of the fluorodimethylsilane moieties to furnish 2 (cyclization (a) in Scheme 2). Additional THF (Et2O-THF (8:1)) in an (11) As reported in our previous paper, 1 starts to dimerize between -40 and -50 °C; see ref 8. (12) van der Waals radii estimated by Pauling’s approximation: 1.40 A˚ for F; 1.93 A˚ for Si; 1.98 A˚ for Ge; and 2.16 A˚ for Sn: Bondi, A. J. Phys. Chem. 1964, 68, 441. (13) Examples of reactions of aryllithiums with Ge(II) or Sn(II) species to form (triarylgermyl)lithiums or (triarylstannyl)lithiums: (a) Veith, M.; Ruloff, C.; Huch, V.; T€ ollner, F. Angew. Chem., Int. Ed. Engl. 1988, 27, 1381. (b) Drost, C.; Griebel, J.; Kirmse, R.; L€onnecke, P.; Reinhold, J. Angew. Chem., Int. Ed. 2009, 48, 1962. (c) Eichler, B. E.; Phillips, A. D.; Power, P. P. Organometallics 2003, 22, 5423, and references therein. (14) For reviews of triarylgermyl-alkali metals: (a) Riviere, P.; R-Baudet, M.; Satge, J. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press, Ltd.: New York, 1982; Vol. 2, Chapter 10, pp 399-518. (b) Riviere, P.; R-Baudet, M.; Satge, J. In Comprehensive Organometallic Chemistry II; Davies, A. G., Ed.; Elsevier Science, Ltd.: Oxford, 1995; Vol. 2, Chapter 5, pp 137-216. Recent examples: (c) Kawachi, A.; Tanaka, Y.; Tamao, K. Eur. J. Inorg. Chem. 1999, 461. (d) Habereder, T.; N€oth, H. Z. Anorg. Allg. Chem. 2001, 627, 1003. (e) Berg, D. J.; Lee, C. K.; Walker, L.; Bushnell, G.; W. J. Organomet. Chem. 1995, 493, 47.
Figure 1. Molecular structure of 2 with thermal ellipsoids set at 30% probability; hydrogen atoms are omitted for clarity. Selected bond lengths [A˚] and angles [deg]: Ge1-Si1 = 2.371(3), Ge1-C1=1.986(9), Ge1-C9=1.973(9), Ge1-C17= 1.976(9), Si1-C2 = 1.890(10), C1-C2 = 1.405(12), Si2-F1 = 1.598(7), Si3-F2=1.592(6), F1 3 3 3 Ge1=3.096(6), F2 3 3 3 Ge2= 3.165(6), Ge1-C1-C2 = 102.9(6), C1-C2-Si1 = 106.0(7), C2-Si1-Ge1=76.9(3), Si1-Ge1-C1=74.2(3), C9-Ge1-C17= 111.1(4), Ge1-C1-C2-Si1=0.2(6). Scheme 2. Plausible Reaction Pathways from 1 to 2 and 3
attempt to increase the solubility of GeCl2, however, promoted dimerization of 1 (2:4=36:64). Next, 1 was allowed to react with SnCl2 under the same reaction condition as the reaction with GeCl2, as shown in Scheme 1. Recrystallization of the reaction mixture from Et2O afforded benzosiladistannacyclopentene 3 in 18% yield as colorless crystals. A trace amount of 4 was detected by 1H NMR analysis of the reaction mixture (3:4 = 88:12). The employment of 1 and SnCl2 in the mole ratio of 1:1 resulted in a complex mixture involving 4.
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Table 1. Crystallographic Data for Compounds 2 and 3
Figure 2. Molecular structure of 3 with thermal ellipsoids set at 30% probability; hydrogen atoms are omitted for clarity. Selected bond lengths [A˚] and angles [deg]: Sn1-Si1 = 2.5712(8), Sn1-Sn2 = 2.7595(2), Sn1-C9 = 2.180(3), Sn1C17 = 2.179(3), Sn2-C1 = 2.180(3), Sn2-C25 = 2.177(3), Sn2-C33 = 2.174(3), Si1-C2 = 1.904(3), C1-C2 = 1.410(4), Si2-F1 = 1.609(2), Si3-F2 = 1.611(2), Si4-F3 = 1.642(3), Si5-F4 = 1.603(3), F1 3 3 3 Sn1 = 3.0787(19), F2 3 3 3 Sn1 = 3.087(2), F3 3 3 3 Sn2 = 3.063(3), F4 3 3 3 Sn2 = 3.1380(19), Si1-Sn1-Sn2 = 88.367(18), Sn1-Sn2-C1 = 96.86(7), Sn2C1-C2 = 121.65(19), C1-C2-Si1 = 127.1(2), C2-Si1-Sn1 = 106.00(8), C9-Sn1-C17 = 102.40(10), C25-Sn2-C33 = 103.30(10), C1-Sn2-Sn1-Si1=-0.18(7), C2-Si1-Sn1-Sn2= -0.11(9).
The molecular structure of 3 was unambiguously determined by X-ray crystallographic analysis (Figure 2). 3 has a planar five-membered ring bearing two o-(fluorodimethylsilyl)phenyl groups on each tin atom. Whereas the Si1-Sn1 bond length of 2.5712(8) A˚ is consistent with normal Si-Sn single-bond lengths, the Sn1-Sn2 bond length of 2.7595(2) A˚ is slightly shorter than a normal Sn-Sn single bond. Atomic distances between each fluorine atom and the nearest tin atom (3.063(3)-3.1380(9) A˚) are within the sum of the van der Waals radii of the two elements (3.56 A˚).12 Whereas the interior angle at Si1 (106.00(8)°) is almost equal to angles in the ideal tetrahedral geometry at the silicon atom (109.5°), the interior angles at Sn1 (88.367(18)°) and Sn2 (96.86(7)°) are acute. The 29Si{1H} NMR spectra showed that the endocyclic silicon atom resonates with coupling to R- and β-tin atoms at δ(29Si)=6.0 (1J(29Si-117/119Sn)=37 Hz, 2J(29Si-117/119Sn)= 6 Hz), while the two exocyclic silicon atoms resonate with coupling to fluorine atoms at δ(29Si)=20.0 (d, 1J(29Si-19F)= 286 Hz) and 20.8 (d, 1J(29Si-19F)=286 Hz). The 119Sn{1H} NMR spectra exhibited two sets of triplets of triplets at -167.64 (4J(119Sn-19F) = 117 Hz, 5J(119Sn-19F) = 99 Hz) and -102.03 (4J(119Sn-19F)=142 Hz, 5J(119Sn-19F)=128 Hz).15 Although long-range (4J or 5J) 119Sn-19F coupling constants are usually less than 10 Hz,15a large values are also (15) Examples of long-range or through-space Sn-F coupling: (a) Barnard, M.; Smith, P. J.; White, R. F. M. J. Organomet. Chem. 1974, 77, 189. (b) Adcock, W.; Gangodawila, H.; Kok, G. B.; Iyer, V. S. Organometallics 1987, 6, 156. (c) Batsanov, A. S.; Cornet, S. M.; Dillon, K. B.; Goeta, A. E.; Thompson, A. L.; Xue, B. Y. Dalton Trans. 2003, 2496. (d) Boshra, R.; Venkatasubbaiah, K.; Doshi, A.; Lalancette, R. A.; Kakalis, L.; J€akle, F. Inorg. Chem. 2007, 46, 10174.
formula fw temp/K wavelengh/A˚ cryst color cryst size/mm cryst syst space group a/A˚ b/A˚ c/A˚ R/deg β/deg γ/deg V/A˚3 Z Fcalc/g cm-3 μ(Mo KR)/mm-1 F(000) θ range/deg data/restraints/params goodness of fit on F2 final R1, wR2 (I > 2σ(I)) final R1, wR2 (all data) large diff peak and hole/e A˚-3
2
3
C24H30F2GeSi3 513.34 200(2) 0.71069 colorless 0.30 0.20 0.20 monoclinic P21/n 29.1530(9) 9.2050(2) 9.8930(3) 90 90.4270(10) 90 2654.75(13) 4 1.284 1.312 1064 1.40-27.50 5982/0/278 1.079 0.1054, 0.3062 0.1205, 0.3095 1.335, -1.261
C43H50F5LiSi5Sn2 1046.60 200(2) 0.71069 colorless 0.30 0.30 0.30 monoclinic P21/c 11.8690(2) 16.6950(3) 26.2210(3) 90 90.8900(10) 90 5195.14(14) 4 1.338 1.121 2104 1.40-27.50 11 577/0/471 1.161 0.0410, 0.1145 0.0497, 0.1215 0.654, -2.232
observed. 4-Fluorobicyclo[2.2.2]oct-1-yltrimethylstannane, in which orbital interaction between the two bridgehead atoms is remarkable, exhibits a large 119Sn-19F coupling constant (75 Hz).15b Intramolecular coordination of a fluorine atom to a tin atom also results in large 119Sn-19F coupling constants in tin(IV) compounds bearing 2,4,6-(CF3)3C6H2 or 2,6-(CF3)2C6H3 ligands (10-19 Hz)15c and in [2-(stannyl)ferrocenyl]fluoroborate (99-372 Hz).15d Thus, the observed large values in 3 can be ascribed to through-space coupling. The atomic distances between F1/F2 and Sn1 and F3/F4 and Sn2 are within the sum of their van der Waals radii (see above); F1/F2 and F3/F4 can get close to Sn2 and Sn1, respectively, because the aryl groups are flexible in solution. Formation of 3 can be explained as shown in Scheme 2. In a similar manner to the reaction with GeCl2, diarylstannylene 7 and subsequently (triarylstannyl)lithium 8 are formed in situ.13,16 The ring-closing reaction in 8 to give benzosilastannacyclobutene 9 is, however, so slow, perhaps owing to a longer Sn-C single bond than the Ge-C single bond,17 that one more equivalent of 7 may insert into the Sn-Li bond in 8 to generate (distannyl)lithium 10 (path A in Scheme 2). Then 10 undergoes a ring-closing reaction by intramolecular nucleophilic attack of the distannyl anion at one of the fluorodimethylsilane moieties on the β-tin atom to produce 3 (cyclization (b) in Scheme 2). There may be an alternative mechanism,18 in which 9 is formed in a manner similar to 2, and 7 inserts into the reactive Sn-Si bond in 9 to provide 3 (16) For reviews of triarylstannyl-alkali metals: (a) Davies, A. G.; Smith, P. J. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press, Ltd.: New York, 1982; Vol. 2, Chapter 11, pp 519-627. (b) Davies, A. G. In Comprehensive Organometallic Chemistry II; Davies, A. G., Ed.; Elsevier Science, Ltd., Oxford, 1995; Vol. 2, Chapter 6, pp 218-303. Recent examples: (c) Tice, J. B.; Chizmeshya, A. V. G.; Groy, T. L.; Kouvetakis, J. Inorg. Chem. 2009, 48, 6314. (d) Neale, N. R.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127, 14745. (e) Habereder, T.; N€oth, H. Z. Anorg. Allg. Chem. 2001, 627, 789. (17) (a) Sum of covalent bond radii: C þ Ge=1.99 A˚; C þ Sn=2.17 A˚; see ref 2. (b) E-C(sp2) single-bond lengths in crystal structures of Ar3ELi were reported to be 2.000-2.054 A˚ for E=Ge and 2.209-2.211 A˚ for E=Sn, according to the Cambridge Structural Database (ver. 5.3). (18) We thank one of the reviewers for suggesting this mechanism.
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(path B in Scheme 2). We could not determine whether 9 was formed or not by 1H NMR analysis of the reaction mixture. Attempted preparation of 7, which should be a key intermediate in both mechanisms, by tuning the ratio of 1/SnCl2 was unsuccessful.
Conclusion We demonstrated that o-(fluorosilyl)phenyl groups were successfully introduced onto the cyclic linkages of heavier group 14 elements. The reactions of 1 with GeCl2 and SnCl2 produced benzosilagermacyclobutene 2 and benzosiladistannacyclopentene 3, bearing two or more o-(fluorodimethylsilyl)phenyl groups. To our knowledge, 2 and 3 are the first examples of benzocyclobutene and benzocyclopentene analogues incorporating two different heavier group 14 elements.19,20 The fluorosilyl functionality on 2 and 3 is expected to open the door to new reaction modes of these cyclic linkages, and further investigations are in progress at our laboratory.
Experimental Section General Procedures. 1H (400 MHz), 13C{1H} (100 MHz), 19F (376 MHz), 29Si{1H} (79.4 MHz), and 119Sn{1H} NMR (149.0 MHz) NMR spectra were recorded with a JEOL EX-400 or AL400 spectrometer. 1H chemical shifts in C6D6 were referenced to the residual proton (δ = 7.20). 13C chemical shifts were referenced to internal C6D6 (δ=128.0) or external tetramethylsilane (δ = 0). 19F chemical shifts were referenced to external CFCl3 (δ = 0). 29Si chemical shifts were referenced to external tetramethylsilane (δ = 0). 119Sn chemical shifts were referenced to external tetramethylstannane (δ=0). The mass spectra (EI) were measured at 70 eV with a JEOL SX-102A mass spectrometer at the Natural Science Center for Basic Research and Development (N-BARD), Hiroshima University: we thank Dr. Daisuke Kajiya for the measurement of the samples. Melting points were measured with a Yanaco micro melting point apparatus and are uncorrected. The elemental analyses were performed using a Perkin-Elmer 2400CHN elemental analyzer at our laboratory. tert-Butyllithium in pentane was purchased from Kanto Chemical Co., Inc. GeCl2 3 dioxane was prepared in a manner similar to the procedure in the literature.21 SnCl2 (>90.0%; Kanto Chemical Co., Inc.) was dried by an azeotropic distillation with EtOH (15 wt %) and 1,2-dichloroethane (85 wt %), and the obtained anhydrous precipitate was washed with 1,2dichloroethane and dried in vacuo at 80 °C overnight.22 Hexane was distilled under nitrogen atmosphere over calcium hydride or dehydrated solvent (
