Ring strain in boroxine rings: computational and experimental considerations

B3LYP/6-311 + G(d) calculations indicate that (HBO)(3) (4) and (HBO)(4) (5) possess (zero-point energy corrected) strain enthalpies of 11.4 and 31.6 k J mol(-1) respectively. The absence of eight-membered (RBO)(4) rings is att ributed to a combination of ring strain and the lability of the B-O bond. T he synthesis, characterization and molecular structure of (PhBO)(3). pyridi ne (1) are described and chemical phenomena related to the addition of amin es to triorganoboroxine rings are rationalized in terms of relief of ring s train in 4. (C) 2001 Elsevier Science B.V. All rights reserved.