Synthesis and dimerization behavior of 1,1-bis(trimethylsilyl)-2-(2,5-diisopropylphenyl)silene

Tris(trimethylsilyl)silylmagnesium bromide, (Me(3)Si)(3)SiMgBr, reacts with 2,5-diisopropylbenzaldehyde to give 2,5-diisopropylphenyl-tris(trimethylsily)silylmethanol (1). With sodium hydride in THF compound 1 undergoes a rearrangement through 1,3-Si,O-trimethylsilyl migration affording bis(trimethylsilyl)silyl-(2,5-diisopropy methane (4). The deprotonation of 1 with organolithium reagents in ether leads to the elimination of lithium trimethylsilanolate according to a modified Peterson mechanism resulting in the formation of the transient silene (Me(3)Si)(2)Si=CH(2,5-iPr(2)C(6)H(3)) (2). Treatment of 1 with an excess of phenyllithium in diethylether at low temperature gives 1,1,1,3,3,3-hexamethyl-2-phenyl-2(2,5-diisopropylbenzyl)-trisilane (3), formed in a nucleophilic addition of the excess PhLi to the silene intermediate and in the hydrolytic workup. Stochiometric quantities of MeLi in diethylether at -78 degrees C convert compound 1 into a head-to-head dimer of the silene 1,2,3,8a-tetrahydro-5,8-diisopropyl-1-(2,5-diisopropylphenyl)-2,2,3,3-tetraki silyl)-2,3-disilanaphthalene (5). Compound 5, presumably the kinetically preferred product of the cyclodimerization of 2, gradually transforms into the thermodynamically stable 3,4-bis(2,5-diisopropylphenyl)-1,1,2,2 tetrakis(trimethyl-silyl)-1,2-disilacyclobutane (6). The E/Z-isomers of 6 have been characterized by X-ray crystal structural analyses.