TRIPHENYLSILYLLITHIUM-CATALYZED DISPROPORTIONATION OF ALPHA,ALPHA,ALPHA,OMEGA,OMEGA,OMEGA-HEXAPHENYLPOLYMETHYLPOLYSILANES TO PERMETHYLATED CYCLOPOLYSILANES AND HEXAPHENYLDISILANE

Hexaphenylpolymethylpolysilanes of the formula Ph3Si(Me2Si)nSiPh3 (I) have been found to undergo disproportionation with catalytic amounts of triphenylsilyllithium in tetrahydrofuran at room temperature into two permethylated cyclopolysilanes, (Me2Si)5 (II) and (Me2Si)6 (III), and hexaphenyldisilane. The product (II) is always formed in preference to (III) in the early stages of reaction except in the case of (I) having n = 6. After many hours, however, the amount of (Ill) increases at the expense of (II), and finally an equilibrium mixture of (II) and (III) in the ratio of approximately 1 9 is formed. A possible mechanism is discussed. Chemical shifts for methyl protons of(I) are recorded. © 1969.