Silylenes with a Small Chalcogenide Substituent: Tuning Frontier Orbital Energies from O to Te.

The general synthesis of heteroleptic acyclic silylenes with a bulky carbazolyl substituent (Cbz) is detailed and a series of compounds with a chalcogenide substituent of the type [(Cbz)SiER] (ER=OBu, SEt, SePh, TePh) is reported. With the bulky carbazolyl substituent present, the chalcogenide moiety can be very small, as is shown by incorporating groups as small as ethyl, phenyl or tert-butyl. For the first time, the electronic properties of the silylene can be tuned along a complete series of chalcogenide substituents. The effects are clearly visible in the NMR and UV/Vis spectra, and were rationalised by DFT computations. The reactivity of the heaviest chalcogenide-substituted silylenes was probed by reactions with trimethylphosphine selenide and the terphenyl azide TerN (Ter=2,6-dimesitylphenyl).