Journal of Organometallic Chemistry, 461(1993) 31-M JOM 23751 31 Reactions of compounds of the type (Me,Si) $( SiMe,C,H,Y)( SiMe,X) with trifluoroacetic acid Colin Eaborn, Karen L. Jones and Paul D. Lickiss ’ School zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Chemistry and Molecular Sciences, University of Sussex, Brighton BNI 9QJ (UK) (Received March 22, 1993) Abstract The iodides (Me,Si),C(SiMe,C,H.,Yl(SiMeJ), with Y = H, p-OMe, and p-Cl, react with trifluoroacetic acid at 35°C to give the bi&rifluoroacetate) (Me,Si),C(SiMe,O,CCF,)2, 8. The initial reaction involves solvolysis at the Si-I bond to give HI and (Me,Si),CtSiMe,C,H,YXSiMe,OCCF,), and the HI then cleaves the Si-aryl bond in the latter and in the starting material to give (Me,Si)C(SiMe,IXSiMe,O,CCF,) and (Me,Si),C(SiMe,I),, which then undergo further solvolysis, with anchimeric assistance by y-O$CF, or y-1 to leaving of I-. In the case of the corresponding reaction of the bromide (Me,Si),CiSiMe,PhXSiMezBr) the dibromide is clearly seen as an intermediate. In keeping with the above, when Et,N is present to neutralize the HI the reaction of (Me$i),C%iMe&H,Cl-p)(SiMe,I) gives only the expected (Me,Si),C(SiMe,C,H,Cl-pXSiMe,O,CCF3). The reactions of the compounds (Me,Si),C(SiMe,PhXSiMezOR), R = Me or H, also give 8, but the initial reaction is cleavage of the Si-Ph bond by CF$O,H, and it is suggested that this process is assisted by initial protonation of the OR group followed by transfer of the proton to the nearby ipso carbon atom of the phenyl group. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1. Introduction We recently described the results of a study of the solvolysis of the iodides (Me,Si),C(SiMe,C,H,Y)- (SiMe,I) (Y = m-CF3, p-Cl, H, p-Me, and p-OMe) in (CF,),CHOH, CF,CH,OH, MeOH, and aqueous-di- oxane [1,2]. We showed that the reactions with the fluorinated alcohols (which are relatively acidic and electrophilic) proceed by an ionization (S,l) mecha- nism, anchimeric assistance by the aryl group in the rate-determining step of leaving of I- leading to for- mation of a Id-bridged cation (I), which is then rapidly attacked by the solvent ROH at the (Y- or y-silicon atom to give (Me,Si),C(SiMe,C,H,YXSiMe,OR). In MeOH this type of process was accompanied by a direct bimolecular (S,2) attack of the solvent on the Si-I bond, and in aqueous dioxan this was the greatly dominant process. We now report on the reactions of some compounds of the type (Me,Si),C(SiMe,Ph)- (SiMe,X) and related species (compounds l-6) with Correspondence to: Professor C. Eaborn. ’ Present address: Department of Chemistry and Applied Chem- istry, University of Salford, Salford MS 4WT, UK 0022-328X/93/$6.00 trifluoracetic acid. In this much more acidic and more electrophilic medium even the iodide (Me,Si),CSiMe,I undergoes reaction by the S,l mechanism (as shown by the fact that the closely related compound (Me,Si),CSiEt,I reacts to give the rearranged product (Me,Si),C(SiEt,MeXSiMe,O,CCF,) along with the normal product (Me,Si),CSiEt,O,CCF, [3]). Me9 Me2 I 2. Results and discussion (Me,Si),C(SiMe,PhXSiMe,I) 1 (Me,Si),C(SiMe,C,H,Me-pXSiMe,I) 2 (Me,Si),C(SiMe,C,H,Cl-pXSiMe,I) 3 (Me,Si),C(SiMe,PhXSiMe,Br) 4 (Me,Si),C(SiMe,PhXSiMe,OMe) 5 (Me,Si),C(SiMe,PhXSiMe,OH) 6 0 1993 - Elsevier Sequoia S.A. All rights reserved