Practical applications of chelating bidentate Lewis acids: A synthetic, structural and reactivity study of perfluoro-ortho-phenylenediboranes.

摘要

Borane-based Lewis acids containing fluoroaryl groups have received considerable attention as catalysts or co-catalysts in numerous applications. Originally discovered in the 1960's, this class of compounds did not attract widespread interest until the early 1990's when B(C6F5) 3 was reported to be an efficient co-catalyst for group IV metallocene catalyzed olefin polymerization. This discovery sparked a renaissance in fluoroarylborane chemistry and has led to numerous studies of B(C6F5) 3 and its derivatives in a variety of applications ranging from olefin polymerization to organic transformations.; The chemistry of bidentate, specifically chelating, Lewis acids has lagged far behind its monodentate counterparts. In fact, only a handful of bidentate fluoroaryldiboranes have been reported in literature. The reasons for this stems from the synthetic difficulties associated with their preparation, which in turn is related to the high reactivity typically observed in these species. Nonetheless, the potential utility of bidentate Lewis acids has been recognized in the enhanced activation of basic substrates, the selective binding of small anions and the generation of weakly coordination anions.; This dissertation addresses synthetic strategies and the reactivity of two perfluoro-ortho-phenylenediboranes along with some potential applications. The exploration of these Lewis acids has been separated into three distinct areas. Firstly, the novel, mercury-free syntheses of both C 6F4-1,2-[B(C6F5)2] 2 and C6F4-1,2-[B(C12F8)] 2, which previously utilized highly toxic mercury reagents in their preparation, will be reported. Fundamental investigations of their reactivity, predominantly C6F4-1,2-[B(C6F5) 2]2, towards Lewis basic substrates will be explored next. The generation of unexpected compounds in the presence of methanol and water has, in part, led to the investigations of C6F4-1,2-[B(C 6F5)2]2 as a co-initiator for aqueous suspension isobutylene polymerization, which will also be discussed. Finally, the persistence of diborate anions, derived from C6F4-1,2-[B(C 6F5)2]2, in the presence of highly electrophilic species including metallocenium, stannylium, oxonium and silylium cations are investigated. Owing to their kinetic and thermodynamic stability in the presence of metallocenium cations, these anions have also been utilized in ion pair reorganization studies; which potentially shed light on conflicting reports found in literature for the mechanism of ion pair reorganization.