5,5-Dimethyl-2,8-diphenyl-5H-dibenzo[b,f]silepine: a synchrotron study

Abstract

The molecule of the title silepine compound, C28H24Si, lies on a crystallographic general position but has almost exact mirror symmetry. The seven-membered silepine ring has a boat conformation, with a fold angle of 99.99 (9)° between the C—C=C—C stern and the C—Si—C prow. The planes of the phenyl substituents are rotated by 32.23 (6) and 31.80 (7)° out of the planes of the respective fused benzene rings. Similar folded conformations are found for other dibenzo[b,f]silepines, while analogous dibenzo[b,f]borepines, in which the B atom can participate in conjugation, have a more flattened heterocyclic ring.