REACTIONS OF H(PHMESI)(X)H (X=2, 3, 4) WITH TRIFLIC ACID - COMPETITIVE CLEAVAGE AND REARRANGEMENT PROCESSES

The removal of phenyl groups in H(PhRSi)(x)H (R = Me, x = 2, 3, 4; R = Ph, x = 2) with 1 to x equiv of triflic acid, HOTf, was examined in hexane, toluene, and methylene chloride. The resulting triflate-substituted oligomers were not isolated but reacted with Grignard reagents or LiAlH4 to provide air and moisture stable products, which were purified by preparative gas chromatography and characterized by H-1, C-13, and Si-29 NMR spectroscopy. From H(PhRSi)(2)H and 1 equiv of HOTf, disilanes such as HPhMeSiSiMe(2)H, HPhMeSiSiMeH(2), and HPh(2)SiSiPhMeSiH were produced in modest yields. Treatment of H(PhMeSi)(3)H with 1 equiv of HOTf in CH2Cl2 followed by MeMgBr provided HPhMeSiSiPhMeSiMe(2)H and HPhMeSiMe(2)SiPhMeH as mixtures of diastereomers and revealed the competitive cleavage of internal vs terminal SiPh groups by HOTf. Similarly, quenching of (TfO)Ph(2)Me(3)Si(3)H(2) with LiAlH4 provided two isomers of Ph(2)Me(3)Si(3)H(3), which could be separated prior to spectroscopic characterization. The reaction of H(PhMeSi)(3)H with 2 equiv of HOTf in CH2Cl2 followed by MeMgBr resulted in the isolation of PhMe(5)Si(3)H(2) as two isomers, both with terminal SiH groups. Reactions of H(PhMeSi)(3)H with 3 equiv of HOTf followed by RMgX also revealed the formation of two isomers, which were assigned the structures H(RMeSi)(3)H and HRMeSiSiMeHSiMeR(2) based on spectroscopic data. The results of the reactions of the trisilane with 2 and 3 equiv of triflic acid are unexpected and require a rearrangement of a group from a terminal silicon to the internal silicon which can be rationalized through a cationic intermediate. The reactions of H(PhMeSi)(4)H with HOTf appear to follow the trend established in the reactions of the trisilanes.