| A wide variety of mono- and disubstituted derivatives of the 1,3,2-diazaboracyclohexane ring system were prepared as possible precursors to linear poly(iminoboranes). These "condensation monomers" were primarily synthesized by a nucleophilic substitution reaction to form products in high yield (eq 1). The 2-phenyl-1,3-diazaboracyclohexane ring system was first investigated.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)Two new diborylamines, where E = H and E{dollar}spprime{dollar} = B(NMe{dollar}sb2{dollar}), B(Ph)NMe{dollar}{lcub}sb2,{rcub}{dollar} were prepared as polymer precursors. Preliminary thermolysis studies showed that each precursor, when heated at 200{dollar}spcirc{dollar}C for 7 days, eliminated dimethylamine to form yellow oily residues. Size exclusion chromatography of these residues indicated molecular weights of ca. 6,000, corresponding to approximately 26 repeat units. However, their silylated analogues (E = SiMe{dollar}sb3{dollar}) were found to be thermally stable under the same pyrolysis conditions. Other derivatives (e.g., E, E{dollar}spprime{dollar} = SiMe{dollar}sb3{dollar}) were prepared that underwent additional derivative chemistry by Si-N bond cleavage reactions with PhBCl{dollar}sb2{dollar} to form the unstable silyl/chloro analogues. Also, a bis (bis(dimethylamino)boryl) compound (E = E{dollar}spprime{dollar} = B(NMe{dollar}sb2)sb2{dollar}), containing a long acyclic B-N skeleton, was prepared and structurally characterized. It may serve as a model for a future boron-nitrogen polymer. Its structure was corroborated by a dynamic NMR study and a B-NMe{dollar}sb2{dollar} rotational barrier of {dollar}sim{dollar}13 kcal/mol was estimated. Other derivatives were also studied by variable temperature NMR spectroscopy and their rotational barriers correspond to those reported for related compounds. Other efforts included the synthesis of a novel electrophile containing the B-OCH{dollar}sb2{dollar}CF{dollar}sb3{dollar} function, ClB(Ph)OCH{dollar}sb2{dollar}CF{dollar}sb3{dollar}. However, the reactions of this chloroborane with the R = Ph ring system led to unstable products.; It was concluded that there were many problems associated with the R = Ph ring system: (1) the inability to monosubstitute with certain electrophiles (e.g., HMe{dollar}sb2{dollar}SiCl); (2) the instability of those precursors containing trifluoroethoxy or chloro functionalities; and (3) the extremely high boiling points ({dollar}>{dollar}100{dollar}spcirc{dollar}C) of some of the B-phenyl precursors sometimes led to decomposition during distillation. Two approaches were then undertaken in order to circumvent these problems. First, the R group on the ring boron was changed both electronically and sterically to the {dollar}sp{lcub}rm i{rcub}{dollar}Pr and {dollar}sp{lcub}rm t{rcub}{dollar}Bu substituents. The second approach involved the use of a less reactive silyl substituent, namely the dimethyl(tert-butyl)silyl moiety. |
