Preparation, structure, and reactions of a lattice-framework disilene

Reduction of tri-tert-butyl-3-(tribromosilyl)cyclopropene with potassium graphite yielded a unique lattice-framework disilene, a racemate of (4R,6R,4′R,6′R)- and (4S,6S,4′S,6′S)-2,3,4,6,7,8, 2′,3′,4′,6′,7′,8′-dodeca-tert-butyl-[5, 5′]bi{1,5-disilatricyclo[4.2.0.0^1,4]octylidene}-2,7,2′, 7′-tetraene (dl-2). Oxidation of dl-2 gave the corresponding 1,3,2,4-dioxadisiletane derivative stereospecifically. Trapping experiments revealed that a thermal equilibrium between dl-2 and the corresponding silylene, 2,3,4,6,7,8-hexa-tert-butyl-1,5-disilatricyclo-[4.2.0.0^1,4]octa-2,7- diene-5,5-diyl (6), existed in solution at room temperature. Thus, the intermediate 6 reacted with methanol, halides, and acetylenes to give the corresponding methoxysilane, dihalosilanes, and silacyclopropenes, respectively. The reactions were accelerated by irradiation. DFT calculations of dl-2 and the related compounds well reproduced the experimental results of the thermal equilibrium between dl-2 and 6. TD-DFT calculations of dl-2 revealed that an intramolecular through-space interaction exists between the π* _si=si and π*c=c orbitals in the LUMO of dl-2, contributing to the stabilization of the LUMO.