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

Abstract

Abstract Tris(trimethylsilyl)silylmagnesium bromide, (Me3Si)3SiMgBr, 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 migration affording bis(trimethylsilyl)silyl-(2,5-diisopropylphenyl)-trimethylsiloxy-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 (Me3Si)2Si=CH(2,5-iPr2C6H3) (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 °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-tetrakis-(trimethylsilyl)- 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.