Beiträge zur Chemie des Phosphors, 80 [1] Über die Phosphor-Bor-Dreiringverbindung (t-BuP)₂BN(i-Pr)₂ / Contributions to the Chemistry of Phosphorus, 80 [1] About the Phosphorus Boron Three-Membered Ring Compound (t-BuP)₂BN(i-Pr)₂

Abstract

<jats:p>The first three-membered P<jats:sub>2</jats:sub>B heterocycle, 1,2-di-tert-butyl-3-di-iso-propvlamino-1,2,3- diphosphaborirane (1,2-di-tert-butyl-3-di-iso-propylamino-1,2-diphospha-3-bora-cyclopro-pane) (1), was synthesized by the reaction of K(t-Bu)P-P(t-Bu)K with (i-Pr)<jats:sub>2</jats:sub>NBCl<jats:sub>2</jats:sub> in n-hexane at -40 °C. 1 is stable at room temperature under inert conditions. The hetero-cyclophosphane 1 was characterized by elemental analysis, cryoscopic molecular mass determination, mass, IR, and NMR spectroscopy. The corresponding results confirm the monomeric structure with a cyclic P<jats:sub>2</jats:sub>B skeleton. No indication for a dimerization of 1 could be observed between +50 and -140 °C. Further information about the structure of 1 was obtained by temperature dependent <jats:sup>31</jats:sup>P and <jats:sup>13</jats:sup>C NMR spectra. Accord­ingly the t-butyl groups are situated on both sides of the P<jats:sub>2</jats:sub>B ring. Furthermore the arrangement at the boron atom is pyramidal due to the small endocyclic angle in the P<jats:sub>2</jats:sub>B ring. In consequence two configurations 1a and 1b are formed which undergo rapid exchange by inversion at the boron atom above ≈−100 °C. The <jats:sup>31</jats:sup>P high field chemical shift is not consistent with a notable π back-donation from phosphorus to boron in the diphosphaborirane. </jats:p>