Synthesis, Structures, and Isomerization of 9,10-Di-tert-butyl-9,10-dihydro-9,10-disilaanthracenes

Abstract

9,10-Di-tert-butyl-9,10-dihydro-9,10-disilaanthracenes (trans-3 and cis-3) were synthesized, and their structures were determined by X-ray crystallography. The trans and cis isomers have a different conformation of the disilacyclohexadiene rings: trans-3 has a chair-like structure, while cis-3 has a boat-like structure. On irradiation of a solution of trans-3 or cis-3 in the presence of di-tert-butyl peroxide, trans-3 and cis-3 isomerized to each other and reached an equilibrium to give a mixture of cis-3 (81%) and trans-3 (19%). The isomerization shows the inversion of the radical center of the intermediate silyl radicals, which is rare in reactions of silyl radicals. Considering the reaction mechanism, the silyl radicals derived from trans-3 and cis-3 are found to be relatively stable, probably due to bulky tert-butyl substituents.

Synthesis and structure of 9,10-bis(2,4,6-triisopropylphenyl)-9,10-dihydro-9,10-disilaanthracene

“…The phenyl groups of the Tip groups are oriented perpendicular to the C1eC6eC7eC12 plane. The tricyclic DSA framework has a folded structure with a dihedral angle (also known as a butterfly angle) of 157 , which is within the range of reported values for similar compounds (9,9,10,10-tetramethyl-9,10-dihydro-9,10-disilaanthracene [20] and 9,10-dihydro-9,10-disilaanthracene, 156 [21]; cis-9,10-di-tert-butyl-9,10-dihydro-9,10-disilaanthracene, 161 [3]). …”

“…Cis-4 is thermodynamically more stable than the trans isomer by 1.13 kcal/mol according to calculations at the B3LYP/6-31G(d,p) level of theory, as described below. The slight predominant formation of trans-4 can be attributed to the kinetically controlled ring closure reaction, as observed in the synthesis of the corresponding 9,10-di-tert-butyl derivatives reported by Kyushin and coworkers [3].…”

“…The above observation indicates the chemical equivalency of the two Tip groups as well as the two ortho isopropyl groups. It is not clear whether the reason for the chemical equivalency of the two Tip groups is rapid ring-flapping of the boat-like central ring or a rigid chair-like conformation of the central ring as observed in the trans-9,10-di-tert-butyl derivative [3].…”

“…9,10-Dihydro-9,10-disilaanthracenes (DSAs) have attracted considerable attention as precursors of organosilicon reactive intermediates such as silyl anions [1,2] and silyl radicals [3]. We [4,5] and Chatgilialoglu and coworkers [6] independently reported that DSA derivatives can be used as radical-reducing agents, and the DSA framework is essential to generate the silyl radical efficiently [7].…”

Silyl Radicals

“…Of those few, Matsumoto and coworkers investigated the isomerization of silyl radicals derived from 9,10-di-tert-butyl-9,10-dihydro-9, 10-disilaanthracenes (2) 6 . Irradiation of a di-tert-butyl peroxide (DTBP)/pentane solution of either cis-2 or trans-2 affords the same 81% cis/19% trans mixture of 2.…”