Cyclic boron compounds. Part VIII. Amino- and hydrazino-boranes and their cyclic dimers

Abstract

2-Amino-1,3,2-benzodioxaboroles, (o-C₆H₄O₂ > B·NR′R″)_n(R′= H = R″; R′= H and R″= Me, Et, Prⁱ, Bu^t, or Ph; and R′= R″= Me or Prⁱ), have been prepared. Formation of dimers or oligomers, in the solid state or in solution but not in the gas phase, depends on R′ and R″. Monomers and oligomers in this and related systems are differentiated by (i) molecular weight, (ii) infrared spectral characteristics, and (iii) relative reactivities towards hydrolysis. Two related 2-amino-1,3,2-benzodiazaborolines, [o-C₆H₄(NH)₂ > B·NR′R″]_n have been obtained. Both for these and for 2-hydrazino-1,3,2-benzodioxaboroles, an unambiguous decision as to molecular aggregation is not possible. Criteria (ii) and (iii) were first established for the 2Me₂NBCl₂→(Me₂NBCl₂)₂ system, and further use was made of (iii) to establish that the kinetics of dimerisation in dilute solution in n-hexane at 25° is governed by a second-order rate expression.