PART 1: FORMATION OF SOME HETEROCYCLIC COMPOUNDS CONTAINING BORON, CARBON, NITROGEN, AND AN ELEMENT OF GROUP VI. PART 2: MECHANISM OF POLYMERIZATION OF IMIDAZOLE BORANE.

Abstract

Part I: Compounds of the type benzo(group VI)azole (I) were treated with diborane using standard vacuum line techniques. The group VI elements were oxygen. sulfur. and selenium. Initially. an insoluble borane adduct formed which spontaneously reduced and replaced carbon in the hetero-ring by boron via an unstable intermediate either (II) or (III). For example. benzoxazole reacted to produce 2-H-3-methyl-l.3.2- benzoxazaborole (IV). The 2-H-3-alkyl-l,3.2-benzo(group VI)azaboroles (V) were easily purified. produced in high yield, and upon methanolysis yielded N-alkyl-2-(group VI)anilines (VI). These boroles were characterized by IR, H-l and B-ll NMR spectra, and mass spectroscopy. Part II: Kinetics of the polymerization of imidazole-borane in the presence of diborane was followed by monitoring hydrogen production at 30°C. Pseudo first-order kinetics was observed at all ratios of diborane to irnidazole-borane, and the observed rate constant increased linearly with excess diborane. A mechanism is proposed in which the diborane acts as a catalyst. Half the hydrogen molecule comes from the diborane, while the other half comes from the nitrogen-bonded hydrogen on imidazole-borane. Hydrogen is formed when diborane reacts with imidazole-borane in a slow step. followed by fast coupling with another imidazole-borane and regeneration of diborane. The structure of the polymer is shown below (VII). and the average size of the polyme1 was 32-38 units.