Crystal structures of three sterically congested disilanes

Abstract

In the three sterically congested silanes, C24H38Si2(1) (1,1,2,2-tetraisopropyl-1,2-diphenyldisilane), C24H34Br4Si2(2) [1,1,2,2-tetrakis(2-bromopropan-2-yl)-1,2-diphenyldisilane] and C32H38Si2(3) (1,2-di-tert-butyl-1,1,2,2-tetraphenyldisilane), the Si—Si bond length is shortest in (1) and longest in (2), with (3) having an intermediate value, which parallels the increasing steric congestion. A comparison of the two isopropyl derivatives, (1and2), shows a significant increase in the Si—C(ipso) distance with the introduction of bromine. Also, in the brominated compound2, attractive intermolecular Br...Br interactions exist with Br...Br separationsca0.52 Å shorter than the sum of the van der Waals radii. In compound2, one of the bromoisopropyl groups is rotationally disordered in an 0.8812 (9):0.1188 (9) ratio. Compound3exhibits `whole molecule' disorder in a 0.9645 (7):0.0355 (7) ratio with the Si—Si bonds in the two components making an angle ofca66°.