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°C to (E)‐1,2,3,8a‐tetra ‐hydro‐1‐mesityl‐5,7,8a‐trimethyl‐2,2,3,3‐tetrakis (trimethylsi‐lyl)‐2,3‐disilanaphthalene (3), formally a [2 + 4] cyclodimer of the transient silene (Me₃Si)₂Si=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 (Me₃SiSi(SiMe₃)₂CH₂Mes (10), and the alkoxysilane (Me₃Si)₃SiCH(Mes)OSi(Si‐Me₃)₂CH₂Mes (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(tri‐ methylsilyl)‐1,3‐disilacyclobutane (13) besides 6 and [bis(tri‐methylsilyl)silyl]mesityl(trimethylsiloxy)methane (11). The unforeseen formation of 13 is discussed as proceeding via the silene‐lithium bromide adduct (Me₃Si)₂Si(Br)CH(Li)Mes (12). In the absence of LiBr 1 was converted by MeLi in THF at –78°C to 11 and the trisilane (Me₃Si)₂Si(Me)CH₂Mes (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.