Fluorinated boranes in dehydrocoupling and hydroboration
This thesis describes the chemistry of the Lewis adducts of mono- and bis-(pentafluorophenyl)borane (LB·BHn(C6F5)3−n; n = 1, 2; LB = SMe2, NH3) as it applies to the development of novel perfluoroarylboranes. Chapter 2 details the use of Me2S·BHn(C6F5)3−n in the preparation of the pentafluorophenyl substituted amine borane adducts, LB·BHn(C6F5)3−n (LB = NR3, NHR2, NH2R, py). Their solid state structures feature N—H···H—B and N—H···F—C hydrogen bonding interactions, important structural motifs for further application of these materials. The related pentafluorophenyl substituted amine boranes H3N·BHn(C6F5)3−n may be used as ligand precursors for the synthesis of group 4 metallocene amidoborane complexes. Chapter 3 desribes the divergent chemistry observed for each of the group 4 metals in the presence of the pentafluorophenyl substituted amidoborane ligands, including N—H activation with hafnium, B—H activation in the case of zirconium and single electron reduction of titanium. In all but one instance, the crystal structures of isolated group 4 metallocene amidoboranes display a β-B-agostic interaction. This structural feature is proposed to play a significant role in catalytic dehydrocoupling of amine boranes by early transition metal catalysts. Chapter 4 describes the preparation of novel pentafluorophenyl substituted organoboranes RnB(C6F5)3−n (n = 1, 2) through facile hydroboration of alkenes using Me2S·BHn(C6F5)3−n. In particular, the double hydroboration of 1,5-cyclooctadiene with Me2S·BH2(C6F5) resulted in isolation and crystallographic characterization of pentafluorophenyl-9-borobicyclo[3.3.1]nonane dimethylsulfide adduct, the –C6F5 substituted analog of the popular hydroboration reagent 9-BBN (9-borabicyclo[3.3.1]nonane).
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