Synthese und Dimerisierungsverhalten des l,l-Bis(trimethylsilyl)-2-(2,5-diisopropylphenyl)silens Synthesis and Dimerization Behavior of 1,1 -Bis(trimethylsilyl)-2-(2,5-diisopropylphenyl)silene

Tris(trimethylsilyl)silylmagnesium bromide, (Me^SiX^SiMgBr, reacts with 2.5-diisopropylbenzaldehyde to give 2,5-diisopropylphenyl-tris(trimethylsilyl)silylmethanol (1). With sodium hydride in THF compound 1 undergoes a rearrangement through 1,3-Si,O-trimethylsilyl mi­ gration affording bis(trimethylsilyl)silyl-(2,5-diisopropylphenyl)-trimethylsiloxy-methane (4). The deprotonation of 1 with organolithium reagents in ether leads to the elimination o f li­ thium trimethylsilanolate according to a modified Peterson mechanism resulting in the for­ mation o f the transient silene (Me3Si)2Si=CH(2,5-/Pr2C6H3) (2). Treatment o f 1 with an excess o f phenyllithium in diethylether at low temperature gives 1,1,1,3,3,3-hexamethyl-2phenyl-2-(2,5-diisopropylbenzyl)-trisilane (3), formed in a nucleophilic addition o f the ex­ cess PhLi to the silene intermediate and in the hydrolytic workup. Stochiometric quantities o f MeLi in diethylether at -7 8 °C convert compound 1 into a head-to-head dimer o f the si­ lene 1,2,3,8a-tetrahydro-5,8-diisopropyl-1 -(2,5-diisopropylphenyl)-2,2,3,3-tetrakis-(trimethylsilyl)-2,3-disilanaphthalene (5). Compound 5, presumably the kinetically preferred product of the cyclodimerization o f 2, gradually transforms into the thermodynamically stable 3,4-bis(2,5diisopropylphenyl)-l, 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.