Crystal structures of 2-bromo-1,1,1,3,3,3-hexa­methyl-2-(tri­methyl­sil­yl)tris­ilane and 2-bromo-1,1,1,3,3,3-hexa­isopropyl-2-(triiso­propyl­sil­yl)tri­silane

摘要

The synthesis and crystal structures of two tris­(tri­alkyl­sil­yl)silyl bromide compounds, C9H27BrSi4 (I, HypSiBr) and C27H63BrSi4 (II, TipSiBr), are described. Compound I was prepared in 85% yield by free-radical bromination of 1,1,1,3,3,3-hexa­methyl-2-(tri­methyl­sil­yl)tris­ilane using bromo­butane and 2,2′-azobis(2-methyl­propio­nitrile) as a radical initiator at 333 K. The mol­ecule possesses threefold rotational symmetry, with the central Si atom and the Br atom being located on the threefold rotation axis. The Si—Br bond distance is 2.2990 (12) Å and the Si—Si bond lengths are 2.3477 (8) Å. The Br—Si—Si bond angles are 104.83 (3)° and the Si—Si—Si bond angles are 113.69 (2)°, reflecting the steric hindrance inherent in the three tri­methyl­silyl groups attached to the central Si atom. Compound II was prepared in 55% yield by free-radical bromination of 1,1,1,3,3,3-hexa­isopropyl-2-(triiso­propyl­sil­yl)tris­ilane using N-bromo­succinimide and 2,2′-azobis(2-methyl­propio­nitrile) as a radical initiator at 353 K. Here the Si—Br bond length is 2.3185 (7) Å and the Si—Si bond lengths range from 2.443 (1) to 2.4628 (9) Å. The Br—Si—Si bond angles range from 98.44 (3) to 103.77 (3)°, indicating steric hindrance between the three triiso­propyl­silyl groups.