804
Organometallics 1995, 14, 804-808
Insertion of Dihalocarbene into a Si-H Bond under Alkaline Phase-Transfer Conditions Yuri Goldberg and Howard Alper" Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario, Canada KIN 6N5 Received October 3, 1994@ Dichloro- and dibromocarbene, generated from the corresponding haloform and alkali (solid or aqueous) in the presence of a phase-transfer agent, readily insert into the Si-H bond of triisopropylsilane (1) to give (dihalomethy1)triisopropylsilane (2) in good yield. Both 1 and 2 are remarkably alkali-resistant. The same process occurs for t-BuMezSiH. Other less sterically hindered, structurally related silanes such as EtsSiH, EtzMeSiH, and PhMezSiH under identical conditions are converted mainly to the corresponding disiloxanes. In the course of the implementation of one of our projects, we needed (dihalomethy1)triisopropylsilanes2. The simplest and most convenient synthetic route to 2 is the reaction of triisopropylsilane (1) with dihalocarbenes. The insertion of dihalocarbenes into a Si-H bond, discovered by Seyferth and Burlitch,l is well documented.2 However, to our knowledge, the reaction of 1 with :CX2, and the products of structural type 2 are not described in the literature. In the present work, we have studied the reaction of silane 1 with dihalocarbenes generated from sodium trichloroacetate or haloforms (CHC13, CHBr3) using phase-transfer catalyFor comparison, similar reacsis (PTC) meth~dology.~ tions of structurally related silanes have also been studied.
Results and Discussion Among numerous methods available for the genera, ~ ~ ~ ~ procedures are certion of d i h a l o c a r b e n e ~biphasic tainly the most attractive in terms of the availability of inexpensive carbene precursors, simple reaction execution, and ~ o r k u p . ~ Dichlorocarbene, generated by the thermal decomposition of sodium trichloroacetate, suspended in an inert solvent in the presence of a phase-transfer agent,6reacts with alkyl-, aryl-, and heteroarylsilanes to give the corresponding dichloromethylsilanes in 40-70% yield.7 Abstract published in Advance ACS Abstracts, December 1,1994. (1)Seyferth, D.; Burlitch, J. M. J . Am. Chem. SOC.1963,85,2267. (2) (a)Kirmse, W. Carbene Chemistry;Academic Press: New York, 1971. (b) Fleming, I. In Comprehensive Organic Chemistry; Barton D., Ollis, W. D., Eds.; Pergamon Press: Oxford, 1982; Vol. 3, Chapter 13.3, pp 565-566. ( c ) Armitage, D. A. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A,, Eds.; Pergamon Press: Oxford, 1982; Vol. 2, Chapter 9.1, pp 111-112. (3) For recent reviews on F'TC reactions of organosilanes involving carbenes, see: (a) Goldberg, Y.; Dirnens, V.; Lukevics, E. J . Organomet. Chem. Libr. 1988,20,211. (b) Goldberg, Y. Phase Transfer Catalysis. Selected Problem and Applications; Gordon and Breach Sci. Publ.: London, 1992; Chapter 3, pp 139-144. (4) Nair, V. In comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 4, pp 10001002. ( 5 ) (a) Makosza, M.; Fedorynsky, M. Adu. Catal. 1987,35,375. (b) Dehmlow, E. V.; Dehmlow, S. S. Phase Transfer Catalysis; Verlag Chemie: Berlin, 1983; pp 220-278. (6) (a) Dehmlow, E V. Tetrahedron Lett. 1976,91. (b) Idemori, K.; Takagi, M.; Matsuda, T. Bull. Chem. SOC.Jpn. 1977,50, 1355. (7) (a)Del Valle, L.; Sandoval, S.; Larson, G. L. J . Organomet. Chem. 1981, 215, C45. (b) Lukevics, E.; Sturkovich, R.; Goldberg, Y.; Gaukhman, A. J . Organomet. Chen. 1988,345,19. @
When a mixture of silane 1, C13CCOONa (5 molar equiv), and 18-crown-6 (184-6, 0.1 molar equiv) in toluene was heated under reflux temperature for 2.5 h (method A), the dichloromethyl derivative 2a was obtained in 70%yield (Table 1, entry 1). Despite this fair yield, the method is not very convenient since it requires a 5-fold excess of sodium trichloroacetate and 0.1 molar equiv of expensive 18-C-6. The use of a i-Pr,SiH 1
:Cx,
i-Pr3SiCHX, 2a,b X = C1 (a),Br (b)
smaller excess of Cl3CCOONa (3 molar equiv) with the same amount of 18-C-6(entry 2) or 0.05 molar equiv of 18-C-6 with 5 molar equiv of C13CCOONa (entry 3) results in a considerable (20-30%)reduction of the yield of 2a. Other typical catalysts of solid-liquid FTC reactions such as TDA-1 and PEG-400 are less effective than 18-C-6and produce 2a, under identical conditions, in ca. 40%yield (entries 4 and 5). The use of ultrasonic irradiation does not affect the reaction (entry 6). PTC generation of dihalocarbenes in a biphasic halofordalkali system is a simple and efficient method for executing reactions involving these specie^.^ A limitation of the method is when the starting material and/or the product are alkali-sensitive. Indeed, an attempt to carry out the reaction of simple alkyl- and arylsilanes of type R3SiH with :CC12 in a CHCld50%aqueous NaOH system in the presence of Et3N+CHzPhCl- (TEBA) or BLuN+HSO~-(TBAH)failed to give the dichloromethylsilane. The only products of the above reactions were the corresponding disiloxanes R3SiOSiR3.8 However, the authors of ref 8 believe that the reaction occurred via an intermediate dichloromethylsilane. Bearing this in mind and also taking into account that a bulky triisopropyl group significantly retards nucleophilic substitution at silicon and reactions at adjacent center^,^ we have studied the interaction of 1 with C W O H (X = C1, Br) in the presence of a phase-transfer agent. (8)Larson, G. L.; Del Valle, L. S m t h . React. Inor.. - Met.-Org. - Chem. 1981,11, 173. (9) (a) Soderquist, J. A.; Colberg, J. C.; Del Valle, L. J . A m . Chem. SOC.1989,111, 4873. (b) Soderquist, J. A.; Rivera, I.; Negron, A. J . Or.. Chem. 1989,54,4051. ( c ) Santiago. B.: Louez. C.: Soderauist. J. A.Tetrahedron iett.'1991, 32,3457. 'idj Miraida,'E.'I.; Diai, M.'J.; Rosado, I.; Soderquist, J. A. Tetrahedron Lett. 1994,35,3221.
0276-733319512314-0804$09.00/0 0 1995 American Chemical Society
Insertion of Dihalocarbene into Si-H Bond
Organometallics, Vol. 14, No. 2, 1995 805
Table 1. PTC Reactions of Triisopropylsilane (1) with Dihalocarbenes entry
method"
precursor of :CXz
1 2 3 4 5 6 7 8
A A A A A A B C C D
C13CCOONa C13CCOONaC C13CCOONa C13CCOONa Cl3CCOONa ClsCCOONa CHC13 CHC13 CHC13 CHC13 CHC13 CHBr3g CHBr3 CHBr3 CHBr3
9 10 11 12 13 14 15
D B B C
D
base
s. NaOHh s. NaOH s. NaOH 50% NaOH 50% NaOH s. NaOH s. NaOH s. NaOH 50% NaOH
catalyst 18-C-6 18-C-6 18-C-6d TDA-1' PEG-400 18-C-6 18-C-6 18-C-6 TEBA TBAH 18-C-6 184-6 18-C-6 TEBA
ultrasoundb
reaction time, h
product
isolated yield, %
2.5 2.5 2.5 2.5 2.5 2.5 8 2.5 8 2 2 0.5 2.5 2.5 1
2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2b 2b 2b 2b
70 38 51 44 42 70 88 84 # 88 83 31 68 68
64
a Method A: 1 (5 mmol), Cl3CCOONa (25 mmol), catalyst (0.5 mmol), toluene, 110 OC. Method B: 1 (5 mmol), NaOH (25 mmol), catalyst (0.25 mmol), CHCls or CHBr3/CH&, room temperature. Method C: the same as in method B under ultrasonication. Method D: 1 (5 mmol), 50% aqueous 0.25 mmol. NaOH (25 mmol), catalyst (0.25 mmol), CHCl3 or CHBr3/CHzC12, room temperature. Branson B-12 ultrasonic cleaning bath. 15 "01. Tris(3,6-dioxaheptyl)amine.f GC data. 8 No cosolvent (CHZC12) was used. s. NaOH = solid NaOH.
We were gratified to observe that the reactions resulted in the formation of dihalomethyl derivatives 2a,b in good yields (see Table 1). In a CHClflaOH liquidsolid system containing 1842-6 (method B), silane 1 readily transforms t o silane 2a in 88% isolated yield (entry 7). When the reaction is carried out under ultrasonicationlo (method C), the yield of 2a remains almost the same, the reaction time being significantly reduced (entry 8). In the absence of a phase-transfer catalyst, the sonochemical reaction is very sluggish (entry 9). The liquid-liquid CHCl&O% aqueous NaOH system containing a quaternary ammonium salt is also useful for the preparation of 2a (method D, entries 10 and 11). Using TEBA or TBAH, one can obtain silane 2a quickly and in high yield under very mild conditions. Thus, the presence of solid or aqueous alkali does not affect either 1 or 2a. Dibromocarbene, generated by using methods B-D, also reacts with 1 to give dibromomethylsilane (2b). When CHBrJsolid NaOW18-C-6 is used, the reaction is strongly exothermic (bromoform refluxes), and perhaps due t o some decomposition at high temperature the yield of 2b is low (31%, entry 12) although even under these severe conditions no hydrolysis products (silanol or disiloxane) were detected. The dilution of bromoform with dichloromethane as cosolventll (CHBr3: CHzC12 = 1:1.5 vol) affords 2b in significantly higher (68%)yield (entry 13). Note that in the case of the more reactive dibromocarbene, the ultrasonication does not affect its PTC reaction with 1 (entry 14). Finally, method D using aqueous alkali is also effective in the case of dibromocarbene, giving rise to 2b in 64% yield. Again, the dilution of bromoform with dichloromethane is essential (entry 15). Dibromomethylsilane (2b),like 2a in a biphasic liquid-solid or liquid-liquid system, does not react with alkali. Compounds 2a and 2b are new. They were characterized by lH,13C,and 29SiN M R spectra and by elemental analysis (see Experimental Section). The structure of 2a was also confirmed by X-ray analysis (Figure 1).12 (10) (a) Xu,L.; Smith, W. B.; Brinker, U. H. J . h . Chem. Soc. 1992, 114, 783. (b) Xu, L.; Tao, F. Synth. Commun. 1988,18,2117. (c) Lukevics, E.; Gevorgyan, V.; Goldberg, Yu.;Gaukhman, A.; Gavars, M.; Popelis, J.; Shymanska, M. J. Organomet. Chem. 1984,265, 237. (11)See ref 5b, pp 260-261. (12)For the full description of the structure analysis, see the supplementary material.
@
cL2
Figure 1. ORTEP diagram of 2a.
As already mentioned (vide supra), reactions of trialkyl-, dialkylaryl-, and diarylalkylsilanes with dichlorocarbene under alkaline (50% aqueous NaOH) PTC conditions result in the formation of the corresponding disiloxanes.8 We have also examined some other structurally related silanes, which are less sterically hindered than silane 1, such as EtsSiH (3), PhzMeSiH (5), EtzMeSiH (71, and t-BuMezSiH (10). The reactions were carried out under identical conditions to those for 1.The results are summarized in Table 2. All the silanes readily reacted with CHXdOH- (X = C1, Br) in the presence of a phase-transfer agent. Their reactivity is, in general, similar t o that of 1 (100% conversion of a starting material in most cases was achieved in 2-4 h). Silane 3 in a CHClJ50% aqueous NaOWEBA system, as anticipated,8 gave hexaethyldisiloxane (4) in 86% yield. The same product was obtained in 84% yield in a C m (X= C1, Br)/solid NaOW18-C-6 system. Silane 5 behaved similarly and afforded (PhMe2Si)zO(6) both under solidfliquid and liquidfliquid PTC conditions in 93 and 90%yield, respectively. Silane 7, in the presence of solid NaOH and 18-C-6reacted with CHCl3 to give a mixture of disiloxane 8 and silanol9 in a ca. 9 5 5 ratio and 75% overall yield. When 50% aqueous NaOH was used as a base, the same two products were formed in a 1:l ratio (by lH NMR and GC). Most interesting and rather unexpected results were obtained in reactions involving t-BuMezSiH (10). Its reaction with CHC13/
806 Organometallics, Vol. 14,No. 2, 1995
Goldberg and Alper
Table 2. Reactions of Hydrosilanes with CHXJOH- under PTC Conditions silane
methoda
haloform
base
catalyst
Et3SiH (3) 3 3 MepPhSiH (5) 5 Et2MeSiH (7) 7 t-BuMepSiH(10)
B D D B D B D D
CHC13 CHC13 CHBr3 CHC13 CHC13 CHC13 CHC13 CHC13
s. NaOHh 50%NaOH s.NaOH s.NaOH 50%NaOH s.NaOH 50%NaOH 50%NaOH
18-C-6 TEBA 18-C-6 18-C-6 TEBA 18-C-6 TEBA TEBA
10 10
10 10 3
5 Ph3SiH (14)
B
CHC13
s.NaOH
18-C-6
B B B B B
CHC13 CHBr3 CHC13 CHCl3 CHC13
s. NaOH'
18-C-6 18-C-6 18-C-6 18-C-6 18-C-6
s.NaOHe s. NaOHe s. NaOHe s.NaOH
reaction time, h 4 4 2 2 2 2 2 2 4 1 3 6 24 6 2 4
4 72
product(s) (Et3Si)zO (4) 4 4
(PhMe2Si)zO (6) 6 (EtpMeSi)ZO(8) EtzMeSiOH (9) 8+9 (t-BuMe2Si)zO(11) t-BuMezSiCHClp (12)
+
+
11
+ 12 + 12 + 12 + 12 11 + 12 11 + 13 11 11 11 11 4 6
PhsSiOH (15)
yield, %,b and/or ratio' 84 86 86 93 90 75d (955) 77d (5050) 73* (80:20) 83 - (35:65) - (80:20) - (923) - (1oo:O) 55f(9:91) 6 4 8 (10:90) 88 91 78
a For reaction conditions, see footnote a for Table 1. Isolated yield. NMR and/or GC data. Overall yield. e 1 molar equiv of NaOH was used. f Isolated yield of 12. g Isolated yield of 13. s. NaOH = solid NaOH.
50% aqueous NaOWTEBA (room temperature, 2 h) resulted in a mixture consisting of disiloxane, (t-BuMe2Si120 (111, and t-BuMezSiCHCln (12) in a 4:l ratio (by lH NMR). The subsequent stirring of the reaction mixture at room temperature led to the disappearance of the dichloromethyl derivative. Similarly, GC monitoring of the reaction of 10 with CHBrdCH2Cldsolid NaOW18-C-6 revealed that the reaction occurred via t-BuMezSiCHBr2 (13): the ratio of disiloxane 11 to dibromomethylsilane 13 was 35:65, 80:20, 92:8, and 1OO:O after 1, 3, 6, and 24 h, respectively. These data are in accord with the conclusion of Larson and coworkers that PTC reactions of hydrosilanes with dichlorocarbene (CHC1$50% aqueous NaOWphase-transfer agent) occur via =SiCHClz intermediates although they were not detected in the reaction mixtures.8 These findings allowed us to assume that dihalomethylsilanes could be obtained from 10 selectively using a stoichiometric amount of alkali. Indeed, when the reaction of 10 with CHCl3 was carried out in the presence of 1 molar equiv of solid NaOH (18-C-6, 5 mol %), the correspondingdichloromethylsilane12 was formed nearly selectively (12:ll = lO:l, by lH NMR). Similarly, dibromomethylsilane 13 was obtained as the major product (selectivity: 90%) in the reaction of 10 with CHBr$CHzCld18-C-6 using 1 molar equiv of solid NaOH. Silanes 12 and 13 were isolated in pure form by vacuum distillation in 55 and 64% yield, respectively, and characterized by lH, 13C, and 29SiNMR spectroscopy as well as by elemental analysis (see Experimental Section). It should be mentioned that 12 and 13 were prepared recently by reacting t-BuMeaSiCl with CH2Clz and CH2Br2 in the presence of n-BuLi or LDA, re~pective1y.l~However, they were not adequately characterized in the prior literature: ref 13a gave spectral data for 12 with an unsatisfactory analysis and no data were given 13.13hIt should also be noted that silanes 3 and 5 afforded the corresponding disiloxanes (4 and 6) under solidfliquid PTC conditions even in the presence of a stoichiometric amount of alkali (Table 2). We have also carried out PTC reactions of some other sterically hindered silanes with halofordalkali. The ~
~~
(13)(a)Becker, P.; Brombach, H.; David, G.; Leuer, M.; Metternich, H.-J.; Niecke, E. Chem. Ber. 1992,125, 771. (bj Shinokubo, H.; Miura, K.; Oshima, K.; Utimoto, K. Tetrahedron Lett. 1993,34, 1951.
reaction of tris(triisopropy1thio)silanewith CHCl$solid NaOW18-C-6 under conditions identical to those described for l gives a complicated mixture of unidentified products which does not contain (i-PrS)3SiCHCln. Tris(trimethylsily1)- and tris(trimethylsi1oxy)silane react similarly. Triphenylsilane ( 14) behaved rather unexpectedly. When a mixture of 14, CHC13, solid NaOH, and 18-C-6 was stirred a t room temperature, neither Ph3SiCHC12 nor PhsSiOSiPh3 was formed. Instead, the evolution of hydrogen gas occurred slowly and all the silane was consumed after 72 h, and the only product isolated in 78%yield was triphenylsilanol(15). Careful GC/MS analysis of the reaction mixture also revealed the presence of trace amounts of PhaSiOEt. The evolution of Hz clearly indicates that 15 is formed via nucleophilic substitution of hydrogen with hydroxide ion solubilized in the organic phase by the crown ether.14 Similar substitution involving ethoxide ion (generated in situ from ethanol which is present in commercial chloroform, and alkali) accounts for the formation of Ph3SiOEt. Note that virtually no reaction occurs in the absence of the phase-transfer agent. In conclusion, unlike simple alkyl- and arylsilanes, triisopropylsilane reacts smoothly with dihalocarbenes (:CClz and :CBrz), generated under alkaline PTC conditions (halofordsolid or aqueous alkali/phase-transfer agent), to give the corresponding dihalomethyl derivatives in good yield. tert-Butyldimethylsilane under the same conditions gives mainly the corresponding disiloxane; however, t-BuMezSiCHXz(X= C1, Br) can also be obtained with ca. 90% selectivity and fair yield under solid/liquid PTC conditions using a stoichiometric amount of alkali. These represent the first examples of the insertion of dihalocarbene into a Si-H bond under alkaline conditions. We are currently investigating the chemistry of silanes 2, in particular, the possibility of the synthesis of stable formyltriis~propylsilane.~~ (14)For studies on the nucleophilic replacement of hydrogen from R3SiH with OH-, see: (a) Sommer, L. H.; Korte, W. D.; Frye, C . L. J . Am. Chem. SOC.1972,94,3463. (b) Ahn, N. T. Top. Curr. Chem. 1980, 88, 145. (15) (a) Soderquist, J. A.; Miranda, I. J . A m . Chem. SOC.1992,114, 10078. (b) Siverman, R. B.; Lu, X.; Banik, G. M. J . Org. Chem. 1992, 57, 6617.
Insertion of Dihalocarbene into Si-H Bond
Experimental Section lH and 13CNMR spectra were obtained on a Varian Gemini 200 spectrometer and 29Si NMR spectra on a Varian XL-300 instrument, using CDC13 as the solvent and Me& as the internal standard. GC analyses were carried out on a HewlettPackard 5890 gas chromatograph equipped with a column [1.5% OV-17 1.95% OV-210 on Chromosorb W-HP (100120 mesh)]. Melting points were measured on a Fisher-Johns melting point apparatus and are uncorrected. Sodium trichloroacetate, all hydrosilanes, 18-C-6, bromoform, TEBA, and TBAH were purchased from Aldrich and used as received. All reactions were carried out under an atmosphere of nitrogen. (Dichloromethy1)triisopropylsilane (2a). Method A. To a solution of triisopropylsilane (1, 0.79 g, 1.02 mL, 5 mmol) and 18-C-6 (132 mg, 0.5 mmol) in dry toluene (5 mL) was added finely powdered sodium trichloroacetate (4.64 g, 25 mmol). The reaction mixture was magnetically stirred at reflux temperature until the starting silane 1 was consumed (ca. 2.5 h, GC monitoring). The dark brown mixture obtained was cooled to room temperature, diluted with benzene (15mL), and filtered through silica gel. The solvents were evaporated, and the residue was distilled under vacuum to give 0.84 g (70%)of silane 2a as a colorless liquid which crystallized upon standing. 2a: bp 7OaC/0.4 mmHg; mp 27-28 "C; lH NMR (CDC13) 6 1.15 (d, J = 6.8 Hz, 18H, CH3), 1.32 (heptet, 3H, SiCHC), 5.53 (s, lH, CHC12); I3C NMR (CDCl3) 6 11.52 (SiCHC), 19.22 (CH3), 62.32 (CHC12);29Si(CDC13)6 6.69. Anal. Calcd for CloH22C12Si: C, 49.79; H, 9.13. Found: C, 49.68; H, 9.18. Method B. Solid finely powdered NaOH (1g, 25 mmol) was added in small portions, over a period of 30 min, to a mixture of triisopropylsilane (0.79 g, 1.02 mL, 5 mmol) and 1 8 4 - 6 (66 mg, 0.25 mmol) dissolved in chloroform (5 mL). The reaction mixture was magnetically stirred at room temperature for 8 h. Filtration of solids followed by evaporation of the solvent and distillation of the residue under vacuum gave 1.06 g (88%)of silane 2a. Method C. The reaction was carried out as described above for method B except the reaction flask was placed in the center of a n ultrasonic cleaning bath (Branson B-12, 80 W) at a distance of 1cm from the bottom. The reaction time was 2 h, and after standard workup, the yield of 2a was 1.01 g (84%). Method D. A solution of 50% aqueous NaOH (2 mL, 25 mmol) was added dropwise to a magnetically stirred solution of triisopropylsilane (0.79 g, 1.02 mL, 5 mmol) and TEBA (57 mg, 0.25 mmol) in chloroform (5 mL). When the addition was complete (ca. 10 min), stirring was continued for 2 h at room temperature. The mixture was diluted with water (10 mL) and chloroform (15 mL). The organic layer was separated, washed with water (3 x 10 mL), and dried over MgS04. Evaporation of the solvent and distillation of the residue under vacuum afforded silane 2a (1.06 g, 88%). (Dibromomethy1)triisopropylsilane (2b). Method B. To a solution of triisopropylsilane (3.16 g, 4.08 mL, 20 mmol) and 1 8 4 - 6 (264 mg, 1mmol) in a mixture of dichloromethane and bromoform (12 d 8 mL) was added solid, finely powdered NaOH (4 g, 100 mmol) in small portions over a period of 30 min. The reaction mixture was stirred at room temperature. A strongly exothermic reaction, causing the boiling of the mixture, begins after ca. 1.5 h. Stirring was continued for an additional 1 h, the solids were filtered, and dichloromethane as well as excess bromoform was evaporated under vacuum. The residue solidifies upon cooling to room temperature, affording 5.06 g (77%) of crude silane 2b. Recrystallization from ethanol gave 4.22 g (64% yield) of pure 2b as slightly yellowish crystals. 2b: mp 40-41 "C; 'H NMR (CDC13) 6 1.12 (d, J = 6.8 Hz, 18H, CHd, 1.37 (heptet, J = 6.8 Hz, 3H, SiCHC), 5.38 (s, l H , CHBr2); 13C NMR (CDCl3) 6 12.26 (SiCHC), 19.35 (CHJ),33.18 (CHBr2);29SiN M R (CDCl3) 6 6.24.
+
Organometallics, Vol. 14, No. 2, 1995 807 Anal. Calcd for CloHzsBrzSi: C, 36.38; H, 6.72. Found: C, 36.44; H, 6.73. Method D. A 50% aqueous NaOH (8 mL, 100 mmol) solution was added dropwise over a period of 30 min to a magnetically stirred solution of triisopropylsilane (3.16 g, 4.08 mL, 20 mmol) and TEBA (228 mg, 1 mmol) in a mixture of CHzClz and CHBr3 (12 m u 8 mL). A slightly exothermic reaction is observed at the beginning of the process. The reaction mixture was stirred overnight at room temperature. Standard workup (see preparation of 2a, method D) followed by recrystallization gave 4.41 g of 2b (67% yield). tert-Butyl(dichloromethy1)dimethylsilane(12). Finely powdered NaOH (0.1 g, 2.5 mmol) was added in small portions over a period of 10 min to a solution of tert-butyldimethylsilane (10) (0.29 g, 0.415 mL, 2.5 mmol) and 1 8 4 - 6 (33 mg, 0.125 mmol) in chloroform (2.5 mL). The reaction mixture was magnetically stirred at room temperature for 6 h. GC and 'H NMR analyses showed the formation of a mixture of siloxane 11 and silane 12 in a 9:91 ratio. The solids were filtered, and the solvent and 11 were removed at room temperature on a rotary evaporator; bulb-to-bulb distillation of the residue under vacuum (ca. 0.1 mm) at room temperature gave 0.27 g (55%) of silane 12 as colorless crystals. 12: mp 37-38 "C; 'H NMR (CDCl3) 6 0.20 [s, 6H, Si(CH&], 0.99 (s, 9H, t-Bu), 5.40 (8,lH, CHCiz); NMR (CDC13)6 -7.36 [Si(CH3)21,18.02 (SiCCHd, 27.58 (CCH3), 62.86 (CHC12);29SiNMR (CDC13) 6 14.12. Anal. Calcd for C7H&1zSi: C, 42.21; H, 8.10. Found: C, 42.53; H, 7.90. Note: lH and 13C NMR spectral data of 12 differ insignificantly from those given in ref 13a, which were obtained in benzene-de. tert-Butyl(dibromomethy1)dimethylsilane(13). Compound 13 was prepared from 10 (2.5 mmol), using the procedure described above for 12 except that a mixture of CHBr3 (1mL) and CHzCl2 (1.5 mL) was used instead of CHCl3. Reaction time: 2 h. GC and NMR analyses revealed the formation of 11 and 13 in a 10:90 ratio. Workup: the solids were filtered and dichloromethane was removed on a rotary evaporator at room temperature. Fractional distillation of the residue under vacuum afforded silane 13 (460 mg, 64% yield) as a colorless liquid. 13: bp 66 "C/2 mm; 'H NMR (CDCld 6 0.26 [s, 6H, Si(CH3)21, 1.03 (s, 9H, t-Bu), 5.28 (CHBr2); 13C NMR (CDC13) 6 -6.22 [Si(CH&], 18.55 (SiCCHd, 27.75 (CCHs), 34.72 (CHBr2); 29Si NMR (CDC13) 6 14.44. Anal. Calcd for C7Hl6Br2Si: C, 29.18; H, 5.60. Found: C, 29.11; H, 5.44. Triphenylsilanol(16).To a solution of triphenylsilane (1.3 g, 5 mmol) and 18-crown-6 (66 mg, 0.25 mmol) in chloroform (5 mL) was added solid finely powdered NaOH (1g, 25 mmol). A slightly exothermic reaction accompanied by the evolution of Hz starts almost immediately. The reaction mixture was magnetically stirred at room temperature for 72 h. The mixture was diluted with CHzCl2 (10 mL) and water (10 mL), and the organic layer was isolated, washed with water, and dried (MgS04). Evaporation of the solvents followed by the vacuum sublimation of the solid residue gave 15 (1.08 g, 78%), mp 152 "C (lit.16mp 153-154 "C). PTC reactions of all other silanes with halofodalkali were carried out as described above for 1 using the same amounts of reactants [in some cases (see text and Table 2) 1molar equiv of alkali was used]. See Table 2 for the reaction conditions and product yields andor ratios. Reaction products were identified by comparison of their physical and spectral data with those described in the 1 i t e r a t ~ r e . l ~
Acknowledgment. We are grateful to the Natural Sciences and Engineering Research Council of Canada for support of this research. Thanks are also due to Dr.
808 Organometallics, Vol. 14, No. 2, 1995
C . Bensimon for x-ray determination of 2a. We are indebted to Professor Dietmar Seyferth for constructive comments and suggestions. Supplementary Material Available: Experimental details and tables of crvstal structure determination data. atomic coordinates, anisotropic thermal parameters, and bond lengths
Goldberg and Alper and angles for compound 2a; stereoview of packing diagram; 'H, and 'Si NMR spectra of 2%2b, 12, and 13 (26 pages). This material is contained in libraries on microfiche, immediately follows this article in microfilm version of the journal, -and can be ordered from ACS; see any current masthead page for ordering information.
OM9407666
