Diastereoselective Substitution of PR 3 for CO in Carbohydrato‐ and Menthyloxycarbene Complexes of Manganese – Synthesis of Chiral‐at‐metal Carbene and Carbyne Complexes

The substitution of PR 3 (R = C 6 H 4 CH 3 ‐ p , C 6 H 4 Cl‐ p , C 6 H 11 ,OCH 3 ) for a CO ligand in chiral carbohydratocarbene complexes [(η 5 ‐C 5 H 5 )(CO) 2 MnC(OR * )Ph] [OR * = α‐ ( 1α ) and β‐mannofuranosyl ( 1β ), (–)‐menthyloxy ( 9 )] proceeds diastereoselectively. The diastereoselectivity depends on PR 3 and on the OR * substituent and ranges from 12% de (R = OCH 3 ) to 80% (R = C 6 H 4 CH 3 ‐ p ). In contrast, the reaction of 1β with P(OPh) 3 is non‐selective. The diastereoselectivity generally increases with increasing nucleophilicity of PR 3 and decreases in the series 1β > 1α > 9 . The highest diastereoselectivity was observed in the reaction of 1β with P(C 6 H 4 CH 3 ‐ 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 BF 3 afforded the carbyne‐manganese complex ( S Mn )‐[(η 5 ‐C 5 H 5 ){P(C 6 H 4 CH 3 ‐ p ) 3 }(CO)MnCPh]BF 4 .