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.

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(+)-(R)-4-Trimethylsilyl-5-phenyl-5H-dibenzophosphol oxideC21H21OPSi[α]D20=+281 (c 1.21, CHCl3)Source of chirality: enantioselective chromatography (Chiralcel OD®)Absolute configuration: (R)P

(−)-(S)-4-Iodo-5-phenyl-5H-dibenzophosphol oxideC18H12IOP[α]D20=-77.2 (c 1.03, CHCl3)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P

(−)-(S)-4,5-Diphenyl-4H-dibenzophosphol oxideC24H17OP[α]D20=-199 (c 1.03, CHCl3)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P

(−)-(S)-4-(2-Naphthyl)-5-phenyl-4H-dibenzophosphol oxideC28H19OP[α]D20=-357 (c 1.01, CHCl3)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P

(+)-(S)-4-(9-Anthryl)-5-phenyl-4H-dibenzophosphol oxideC32H21OP[α]D20=+45 (c 0.43, CHCl3)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P

(−)-(S)-4,5-Diphenyl-4H-dibenzophospholC24H17P[α]D20=-164 (c 1.00, CHCl3)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P

(−)-(S)-4-(2-Naphthyl)-5-phenyl-4H-dibenzophospholC28H19P[α]D20=-162 (c 1.00, CHCl3)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P

(+)-(R)-4-Trimethylsilyl-5-phenyl-5H-dibenzophospholC21H21PSi[α]D20=+291 (c 0.740, CHCl3)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (R)P

(+)-(S,S)-5,5′-Diphenyl-4,4′-bis(5H-dibenzophosphol oxide)C36H24O2P2[α]D20=+213 (c 0.736, CH2Cl2)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P(S)P

(−)-(S,S)-5,5′-Diphenyl-4,4′-bis(5H-dibenzophosphol)palladium dichloride complexC36H24Cl2P2Pd[α]D20=-373 (c 0.105, CH2Cl2)Source of chirality: enantioselective chromatography of a precursor (Chiralcel OD®)Absolute configuration: (S)P(S)P