Synthesis, Structures, and Unusual Photoluminescence of O- and N-Functional Cyclohexasilanes

The reaction of chloropermethylcyclohexasilanes Si6Me12-nCln (n = 1−3) with lithium
silanolates affords the siloxy derivatives Si6Me12-n(OR)n (n = 1−3; R = SiMe3, SiMe2-t-Bu).
All compounds exhibit bathochromically shifted first UV absorption maxima and room-temperature photoluminescence in solution with emission maxima near 340 nm and
remarkably enhanced luminescence intensity as compared to the data for Si6Me12. The
solution photoemission spectra of the corresponding aminocyclohexasilanes Si6Me12-n(NR2)n
(n = 1, 2; R = −SiMe3), which are accessible from Si6Me12-nCln and LiN(SiMe3)2, do not
show any luminescence above 300 nm. Crystal structure analyses of the 1,3- and 1,4-disubstituted derivatives exhibit the cyclohexasilane ring in the chair conformation with
the −OR or −NR2 groups in either axial or equatorial positions, depending on the steric
bulk of the hetero substituents.