Electronic structure, geometry, and reactivity of arylsilenes: a quantum-chemical study

The geometry and electronic structure of 1,4-di(silaethen-1-yl)benzene (2), itsmeta- andbrtho-isomers (3 and4, respectively), and its carbon analog, 1,4-divinylbenzene (5), were studied by the semiempirical MNDO-PM3 method. Unlike5, two pairs of the frontier MOs in isomers2–4 are mainly π-orbitals of Si=C bonds, while the structure of the lowest occupied π-MO indicates delocalization of π-electrons of the entire system. The main characteristic features of the double Si=C bonds (the high polarity and narrow HOMO-LUMO energy gap, which favors the 2+2]-cycloaddition reaction) remain in arylsilenes2–4. The interaction between π-electrons of benzene fragment and the double Si=C bonds results in violation of the benzene ring symmetry, which is most pronounced in structure5. Weakening of the C−H bonds in theortho-positions of the aromatic nucleus in the compounds under study is observed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 256–260, February, 1999.