Rigid P-chiral mono and diphosphines. Configurative stability and P-inversion barrier

A group of P-chiral monophosphine oxides and one diaryl diphosphine oxide based on the dibenzophosphole skeleton have been synthesized. Preparative enantioselective chromatography of 4-trimethylsilyl-5-phenyl-5H-dibenzophosphol oxide followed by a simple transformation with exchange of substituents (and a homo-coupling reaction in one case) and a stereoselective reduction step furnished the corresponding phosphines in fair to good yield. Their relative and absolute configurations were determined by crystal structure analysis. It turned out that racemization of the phosphines through P-inversion takes place at ambient temperature and depends markedly on ortho substituents (104-114 kJ mol(-1)). In the case of the diphosphine, racemization can be suppressed when forming a chelate with Pd(II) or Ni(II) complexes. (c) 2006 Elsevier Ltd. All rights reserved.