CONTROLLED CONVERSION OF THE TRANSIENT 2-MESITYL-1,1-BIS(TRIMETHYLSILYL)SILENE INTO A TETRAHYDRO-2,3-DISILANAPHTHALENE, A 1,2-DISILACYCLOBUTANE, OR A 1,3-DISILACYCLOBUTANE

Mesityl[tris(trimethylsilyl)silyl]methanol (1) reacts with strong bases with elimination of trimethylsilanolate according to a Peterson-type mechanism, the outcome of the reaction being dependent on solvent, temperature, and nature of the organometallic base applied. Thus, 1 was converted by treatment with MeLi in ether at -78 degrees C to (E)-1,2,3,8a-tetrahydro-1-mesityl-5,7,8a-trimethyl-2,2,3,3-tetrakis(trimethylsilyl)-2,3-disilanaphthalene (3), formally a [2 + 4] cyclodimer of the transient silene (Me(3)Si)(2)Si=CHMes (2). The reaction of 1 with PhMgBr in THF after some days resulted in the formation of (Z)-3,4-dimesityl-1,1,2,2-tetrakis(trimethylsilyl)-1,2-disilacyclobutane (6) as the main product besides small quantities of 3, the polysilane (Me(3)Si)(3)SiSi(SiMe(3))(2)CH(2)Mes (10), and the alkoxysilane (Me(3)Si)(3)SiCH (Mes)OSi(SiMe(3))(2)CH(2)Mes (7). Compound 6, the formal [2 + 2] cycloadduct of 2, can also be obtained by thermal treatment of 3 and is considered to be the thermodynamically more stable silene dimer whereas 3 is the kinetically preferred product. At high LiBr concentrations in the reaction mixture 1 was converted by PhMgBr in THF to (E)-2,4-dimesityl-1,1,3,3-tetrakis(trimethylsilyl)-1,3-disilacyclobutane (13) besides 6 and [bis(trimethylsilyl)silyl]mesityl(trimethylsiloxy)methane (11). The unforeseen formation of 13 is discussed as proceeding via the silene-lithium bromide adduct (Me(3)Si)(2)Si(Br)CH(Li)Mes (12). In the absence of LiBr 1 was converted by MeLi in THF at -78 degrees C to 11 and the trisilane (Me(3)Si)(2)Si(Me)CH(2)Mes (4b). Probable pathways of the formation of all new compounds are discussed. For 6 and 13 the results of the X-ray structural analyses are given.