Diastereoselective substitution of PR3 for Co in carbohydrato- and menthyloxycarbene complexes of manganese - Synthesis of chiral-at-metal carbene and carbyne complexes

Article abstract of DOI:10.1002/cber.19961290404

The substitution of PR₃ (R = C₆H₄CH₃-p, C₆H₄Cl-p, C₆H₁₁, OCH₃) for a CO ligand in chiral carbohydratocarbene complexes [(η⁵-C₅H₅)(CO) ₂Mn=C(OR*)Ph] [OR* = α- (1α) and β-mannofuranosyl (1β), (-)-menthyloxy (9)] proceeds diastereoselectively. The diastereoselectivity depends on PR₃ and on the OR* substituent and ranges from 12% de (R = OCH₃) to 80% (R = C₆H₄CH₃-p). In contrast, the reaction of 1β with P(OPh)₃ is non-selective. The diastereoselectivity generally increases with increasing nucleophilicity of PR₃ snd decreases in the series 1β > 1α > 9. The highest diastereoselectivity was observed in the reaction of 1β with P(C₆H₄CH₃-p)₃. Predominantly, the isomer with the (S) configuration at the metal [(S_Mn)-2β] was formed which could be separated from the diastereomeric mixture by chromatography and be obtained in a pure form. Subsequent reaction of (S_Mn)-2β with BF₃ afforded the carbyne-manganese complex (S_Mn)-[(η⁵-C₅H₅){P(C ₆H₄CH₃-p)₃}(CO)Mn≡CPh]BF ₄. VCH Verlagsgesellschaft mbH, 1996.