silane precursors - American Chemical Society

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Organometallics 1993, 12,493Q-4939

Novel (Fluoromethy1)silicon Derivatives from (Fluorodibromomethy1)silane Precursors Hans Burger* and Peter Moritz Anorganische Chemie, FB 9, Universitat-GH, 42097 Wuppertal, Germany Received May 11, 1 9 9 P

Dibromofluoromethylation of Sic&and organochlorosilanes R,SiCL, has been achieved with a reagent prepared from (MezN)&=C(NMeZ)z and CFBr3, yields ranging from 27 to 54%. The reactivity of the silanes depends both on the nature of R and on n. Novel (dibromofluoromethy1)silicon derivatives (R = Me, n = 1-3; R = Et, n = 1, 2; R = n-Pr, LPr, i-Bu, and s-Bu, n = 1) as well as CFBrzSiC13were obtained and characterized. By treatment with ( ~ - B U ) ~ reduction S~H of both the CFBrz and the SiR,Cls, groups occurred, and the corresponding fluoromethylsilanes CH2FSiR,H3, were obtained with yields ranging from 81to 98 % . Functional fluoromethylsilicon chlorides and bromides CHZFSiR,Xs,, X = C1 and Br, were prepared by reaction of the hydrides with SnC14 and Bra, respectively. Substitution reactions of CHzFSiBr3 take place selectively a t the Si atom, and novel CHzFSiY3 derivatives, Y = F, C1, NCO, OMe, and Ph, have been synthesized. The first di(fluoromethyl)diorganosilane, (CHzF)zSiMez, has been isolated from the dibromofluoromethylation of CHzFSiMezCl followed by reduction with (n-Bu)3SnH. Several additional compounds emerging from partial substitution, rearrangement, and dismutation reactions have been identified, some of which were isolated. All compounds were characterized by their multinuclear NMR spectra and furthermore studied by IR, Raman, and mass spectroscopy. Introduction it was shown that CHF emerging from the decomposition of intermediate CHFzSi derivatives had inserted into an (Fluoromethy1)silanes CHgnF,SiR3 belong to the class SiH bond.6 Although this reaction pathway is not very of (a-halomethy1)silicon compounds which tend to deuseful for the synthesis of CHzFSi compounds7 due to the compose readily by elimination of carbene with concomlack of a readily available and suitable CHF source,B itant formation of a strong silicon-halogen bond. The insertion of the carbene CFBr into the Si-H bond of resulting low thermal stability, which can be increased by triethylsilane has been used for the synthesis of Etabulky and electron-releasingsubstituents, e.g. alkyl groups, SiCHFBr. Its selective reduction with tri-n-butyltin is particularly pronounced for the fluoromethyl derivatives, hydride afforded Et3SiCHzF, which is one of the first fully and the number of fully-characterized examples has grown characterized (monofluoromethy1)silicon compounds.9 only slowly. (Fluoromethy1)silanesSi(CH3)a(CH~F)b(CHF~)c(CF3)d, The reaction of a silyl chloride X3SiC1 with a reagent prepared from P(NEtd3 and CF3Br in a polar solvent (eq a + b + c + d = 4, have been obtained unselectively by 1)logives access to CF3SiX3 compounds on a large scale low temperature fluorination of SiMe4 with Fz diluted by Also, CFzBr2 and with a variety of substituents X.11J2 a noble gas.' Insertion of SiFz into the C-I bond of CF3I has yielded CF3SiF212whose reaction with SbF3 afforded CF3Br + P(NEt,), + X3SiC1 X3SiCF3 CF3SiF32 while CF3SiH3 was obtained by its reduction with LiA1H4.3 P(NEt,),BrCl (1) Since both reaction pathways are convenient for routine laboratory work much effort has been invested in the past CFBr3 are known to form different kinds of (trihalomethto find easy, selective, and versatile syntheses of (fluoy1)phosphonium salts when reacted with tertiary phosromethy1)silanes. However, attempts to convert, for p h i n e ~but , ~ ~these have not yet been used for transfer of example, CHzClSi derivatives into the corresponding a CFBrz group to silicon. (monofluoromethy1)silanesby treatment with AgF,48KF,4b The strong electron donor tetrakis(dimethylamin0)KF in toluene? and SbF54dresulted only in breakdown ethylene (3) has been shown to react with various of the (halomethy1)siliconmoiety. Furthermore organopolyhalomethanes to yield, in a first step, a trihalometallic reagents like Hg(CF&a and Cd(CF3)zDsb had methanide anion (eq 2).14 led to fluoro rather than (fluoromethy1)siliconderivatives. Formation of species containing a CHzFSi fragment was (5) (a) Morrison, J. A.; Gerchman, L. L.; Eujen, R.; Lagow, R. J. J. Fluorine Chem. 1977,10,333. (b) Lange, H.; Naumann, D. J. Fluorine observed during thermal decomposition of CF3SiH3, and


*Abstract published in Advance ACS Abstracts, November 1, 1993. (1) (a) Liu, E. K. S.; Lagow, R. J. J.Am. Chem. SOC. 1976, 98, 8270. (b) Liu, E. K. S.; Lagow, R. J. J. Organomet. Chem. 1978,145, 167. (c) Lagow, R. J.;Morrison, J. A. Adu. Inorg. Chem. Radiochem. 1980,18,177. (2) Sharp, K. G.; Coyle, T. D. J. Fluorine Chem. 1971/72, 1, 249. (3) Beckers, H.; Biirger, H.; Eujen, R. J.Fluorine Chem. 1986,27,461. (4) (a) Bellama, J. M.; MacDiarmid, A. G. J. Organomet. Chem. 1969, 18, 275. (b) Cunico, R. F.; Chou, B. B. J. Organomet. Chem. 1978,154, C45. (c) Damrauer, R.; Yost, V. E.; Danahey, S. E.; O'Connell, B. K. Organometallics 1986, 4, 1779. (d) Hairston, T. J.; OBrien, D. J. J. Organomet. Chem. 1970,23, C41.


Chem. 1986,27, 115. (6) Beckere, H.; Biuger, H. J. Organomet. Chem. 1990,385, 207. (7) Bilrger, H.; Moritz, P. J. Organomet. Chem. 1992,427, 293. (8)Schlosser, M.; Heinz, G. Chem. Ber. 1971, 104, 1934. (9) Seyferth, D.; Hopper, S.P. J. Organomet. Chem. 1973,51,77. (IO)Ruppert, I.; Schlich, K.; Volbach, W. Tetrahedron Lett. 1984,25, 2195. (11)Beckers, H.; Borger, H.; Bursch, P.; Ruppert, I. J. Organomet. Chem. 1986,316,41. (12) Beckers, H.; Bwger, H.; Eujen, R. Z. Anorg. Allg. Chem. 1988, 563, 38. (13) Burton, D. J. J. Fluorine Chem. 1983, 23, 339.

0 1993 American Chemical Society 02~6-~333/93/2312-4930~04.00/0


3 + CC1,Br


Organometallics, Vol. 12,No. 12, 1993 4931


[(MezN)zCC(NMez)212+ Br-

+ CC1; (2)

In an analogous reaction with CF31a reactive intermediate was obtained with which CF3- groups can be transferred to silicon, and accordingly MeaSiCFs and Me2Si(CF3)2 were prepared in yields of 94 and 63%, respectively.l5 Thus the reagent combination 3JCF3Iis a promising alternative to the P(NEtddCF3Br system. Making use of the observation that (Si)C-F bonds are resistant toward reducing agents like LiAlHPJ6J7 and (nBu)sSnH,S a novel route to (monofluoromethy1)silicon derivatives starting from fluorodichloromethyl precursors has been developed. Good yields of Me3SiCHFCl and MesSiCHzF were obtained by treatment of Me3SiCFC12 with stoichiometric amounts of (n-Bu)sSnH.17 Recently, (n-Bu)sSnH was also used to reduce CFC1zSiC13l8which is a suitable precursor for Si-functional (monofluoromethy1)silanes CHFzSiX3 (X = H, halogen, NRz, et^.).^ This reduction however does not proceed in a fully satisfactory fashion, at best a 1:l mixture of CHzFSiH3 (1) and CHFClSiH3 (21, with a total yield of ca. 55% being ~ b t a i n e d .In ~ addition to the laborious separation of 1 and 2, the optimized yield of CFClzSiC13 was not higher than 25% .7J8 Thus better access to 1 and its derivatives appeared desirable; therefore we have tested whether replacement of CFClz groups by CFBr2 groups would be advantageous. We report here on the fluorodibromomethylation of chlorosilanes and describe the synthesis of many novel (monofluoromethy1)silicon compounds.


(Dibromofluoromethy1)silanes. We have found that 3 combined with CFBr3will place CFBrz groups on silicon. Various organosilicon substrates were tested, and numerous novel (dibromofluoromethy1)siliconderivatives were obtained according to (eq 3) with yields of 27-54%, as reported in Table I. R,,SiCl,

+ 3 + CFBr,




[ (MezN),CC(NMe2),1 "Cl-Br-


With the exception of t-BuSiCl3, monoalkyltrichlorosilanes reacted readily with the 3lCFBr3 reagent. Dialkyland trialkylsilicon chlorides are less reactive, dibromofluoromethylation occurring only in the case of primary alkyl substituents. Thus, steric shielding of the chlorosilane has a pronounced effect on its coupling with a CFBr2 group. This behavior is in agreement with an S~Z-type substitution mechanism involving a ionic nucleophile CFBrz-, as suggested previously.18 Yields are somewhat curtailed by side reactions undergone by the 3lCFBr3reagent, which involve irreversible formation of the salt [(MezN)2CC(NMez)zlBrz and the carbene CFBr, yielding polymeric, unidentified material. The intermediacy of CFBr has been confirmed by its reaction with vinyl bromide.19 Compounds 4-7 are colorlesssolids at room temperature while 8-11, 13, and 14 are liquids. All compounds are (14) Carpenter, W. J. Org. Chem. 196S, 30, 3082. (15) (a) Pawelke, G.J.Fluorine Chem. 1989,42,429. (b)Pawelke, G. J. Fluorine Chem. 1991,54,60. (18) Fritz,G.; Bauer, H. Angew. Chem. 1983,95, 740. (17) Broicher, V.; Geffken, D. J. Organomet. Chem. 1990, 381, 315. (18) Josten, R.; Ruppert, I. J. Organomet. Chem. 1987,329,313. (19) Pawelke, G. Unpublished resulta.

Table I. Products from the Reaction of R&iCl, CFBrJ UiCl,, Sic14 MeSiC13 MezSiC12 Me3SiC1 EtSiCl3 EtzSiC12 n-PrSiCl3 i-PrSiC13 (i-Pr)3SiCl (n-Bu)3SiCI i-BuSiCl3 (i-Bu),SiCl s-BuSiCI3 (s-Bu)zSiCIz t-BuSiCl3 PhpSiCl a

mmol of &,,SiCIn:3:CFBr3 133:133:137 3433:33 22:22:20 24:21:23 26:24:26 20:19:21 40:31:41 20:20:20 23:25:21 50:51:53 31:29:32 23:23:22 34:32:34 28:31:28 4 1:42:40 16:18:15

with 3 and


% yield

CFBrzSiCla (4) CFBrzSiMeClz (5) CFBrzSiMezCl(6) CFBrzSiMe3 (7) CFBrZSiEtClz (8) CFBrzSiEtzCl(9) CFBrzSi(n-Pr)CIz(10) CFBrzSi(i-Pr)Cl (11) no reaction CFBrzSi(n-Bu)p (12) CFBr2Si(i-Bu)Clz(13) no reaction CFBrzSi(s-Bu)CIz(14) no reaction no reaction no reaction

30 44 35 54 49 51 42 36 39 27

Could not be separated from (n-Bu)3SiCl, yield unknown.

Table 11. Physical Properties of Selected Comwunds compd 4 5 6 7 8 9 10 11 13 14 21 22 23 24 25 26 21 28 29 30 33 34

mp, bp, "CIP, OC mbar 58-60 52-54 51-54 53-55