An Experimental Charge Density Study of Two Isomers of Hexasilabenzene

摘要

The similarities and differences between carbon and its heavier congener silicon generate challenging synthetic targets, especially when multiply bonded systems are concerned. The first stable compound with a Si=Si bond goes back to West et al. in 1981, and conjugated systems with Si= Si double bonds were pioneered in 1997 by Weidenbruch et al. Whether silicon analogues of benzene can show aromatic character is still a point of constant debate. The aromatic nature of silabenzenes has been predicted theoretically,141 but the synthesis of a stable silabenzene was not accomplished until Tokitoh et al. reported the sterically encumbered 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl-sub-stituted monosila derivative. At the same time, Ando et al. independently reported the synthesis of 1,4-disila Dewar benzene. Only two years later, Sekiguchi et al. accomplished the synthesis of 1,2-disilabenzene by reacting RSi≡SiR (R = Si(CH(SiMe3)2/Pr) with PhG≡CH in a formal [2+2+2] cyclo-addition reaction. Recently, in a cooperative effort with the Roesky group, we reported the synthesis of a 1,4-disilaben-zene by reacting [{PhC(NtBu)2}Si]2 with diphenyl alkyne. With regards to homonuclear systems, the Scheschkewitz group recently made groundbreaking progress with the isolation of ring and cage'101 isomers of hexasilabenzene (Scheme 1), which prompted the present experimental charge-density study.