Temperature-dependent Ring-Opening and -Closure of a Cyclic Phosphane-Borane

Marcus Sigl, Annette Schier, Hubert Schmidbaur

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9 Scopus citations


A phosphane-borane (3) with the P-B bond integrated into a seven-membered ring was prepared from 4-pentenyl-diphenylphosphane (4) by hydroboration using 9-borabicyclononane (9-BBN). The product was confirmed to have a ring structure in the solid state by single crystal X-ray diffraction. The P-B distance of 2.057(2) Å is indicative of a standard donor-acceptor bond similar to the type found in homologous five- and six-membered rings. The room-temperature 31P-NMR signal of the compound in various solvents (δ = - 15) is not compatible with the cyclic structure and suggests that ring opening occurs as the compound is dissolved. Variable-temperature NMR work corroborated this assumption, and the enthalpy of ring closure was determined to be ΔH = -30.5(4) kJmol-1. In CD2Cl2 at -90°C, δ31P is shifted to +3.5 ppm to low field, suggesting virtually complete ring closure under these conditions.

Original languageEnglish
Pages (from-to)951-954
Number of pages4
JournalChemische Berichte
Issue number7
StatePublished - 1997
Externally publishedYes


  • Medium-sized rings
  • Phosphane-boranes
  • Phosphorus/boron
  • Ring opening and closure
  • Temperature-dependent NMR studies


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