Doubly Bonded Silicon Compounds Showing Intramolecular Charge-Transfer Transitions

Recent study of doubly bonded silicon compounds showing intramolecular charge-transfer transition was reviewed. Trialkylaryldisilenes having 1-naphthyl, 9-phenanthyl, or 9-anthryl substituent were synthesized. X-ray diffraction analysis shows that π(Si=Si) and π(aryl) systems in the trialkylaryldisilenes are almost perpendicular to each other suggesting no significant conjugative interactions between two π systems, but they exhibit intramolecular charge-transfer (ICT) transitions from π(Si=Si) to π*(aryl). Especially, 9-anthryltrialkyldisilene shows a distinct ICT band at 525nm, which redshifts to 535nm in more polar 1,2-dichlorobenzene. Reaction of the anthryldisilene gives the corresponding [2 + 1] cycloadduct, disilacyclopropanimine, which undergoes further isomerization to give 3-silylene-2-silaaziridine with 9-anthryl substituent as a novel exocyclic silene. The anthrylsilene shows also a distinct ICT transition from π(Si=C) to π*(aryl). The high energy levels of π(Si=Si) and π(Si=C) and the low-lying π*(aryl) would be responsible for the distinct ICT band of the disilenes and the silene.