4478
reported when we have completed additional chemical and physical measurements with a variety of mono-, di-, tri-, and tetradentate ligands.
Under these conditions the metalation of tetramethylsilane requires several days, showing that the protons in MesSiCl are significantly more acidic than those in Me4%. Steric hindrance t o coupling appears to be Jack Schubert, V. S. Sharma vital for lithiation of trimethylchlorosilane, for with E. R. White, Linda S. Bergelson Radiation Health Diuision, Graduate School of Public Health n-butyllithium, either with or without TMEDA, triUnicersity of Pitrsburgh, Pittsburgh, Pennsyhania 15213 methylchlorosilane gives exclusively the coupling prodReceioed April 19, I968 uct n-b~tyltrimethylsilane.~ Other electronegative substituents on silicon lead to variable and often unexpected results upon treatment with t-butyllithium-TMEDA (Table I). TrimethylLithiation of Trimethylsilyl Compounds fluorosilane gives exclusively the coupling product t Sir: butyltrimethylsilane. The latter is also the principal Lithiation of tetramethylsilane by n-butyllithium in product with methoxytrimethylsilane, along with a the presence of N,N,N',N'-tetramethylethylenediamine minor amount of the metalation product Me3SiCH2(TMEDA)' has recently been reported by Peterson. SiMezOMe.8 However, ethoxytrimethylsilane gives uirIn work contemporaneous with Peterson's, we have obtually exclusiue lithiation to yield ultimately Me3SiCH2served lithiation of methyl groups in various organoSiMezOEt,6 only a trace of coupling being observed. silanes, with and without potentiating catalysts such as Thus the slight increase in steric requirement from the TMEDA.3 Silylmethyl protons appear to be dismethoxy to the ethoxy compound changes the nature of tinctly more acidic than methyl protons in hydrocarthe reaction completely. Acetoxytrimethylsilane yields bons. Probably silicon, like phosphorus, stabilizes 3,3-dimethyl-2-trimethylsiloxy-l-butene6 (2) in a rapid the partial negative charge on attached CR2Li groups reaction. The formation of this unsaturated product by means of dative i~ bonding from carbon into lowcan be accounted for by the following reaction seenergy unfilled orbitals of the Si atom. quence. Table I.
Reactions t-BuLi,a TMEDA,
Silane ( M )
M
M
MesSiCl (0.36)b Me3SiCl (0,2) Mersi (0.12) (Me3Si)?0(0.22) Me3SiOCH2CH,(0.07) Me3SiOMe (0.2) Me3SiF (0,2) Me3SiOC(0)CH3(0.2)
0.12 0.05 0.1 0.1 0,03 0.05 0.05 0.05
0.00 0,012 0,025 0,025 0.008 0.012 0,012 0.012
Temp, "C
Reacn time
Products
(zyield)E
- 78 2 hr M ~ ~ S ~ C H Z S(33); ~ MMesSiCMe3 ~ ~ C ~ (25); Me3SiCHzSiMez-t-Bu (10) 15-30
