Diastereoselective Substitution of PR3 for CO in Carbohydrato- and Menthyloxycarbene Complexes of Manganese – Synthesis of Chiral-at-metal Carbene and Carbyne Complexes

Abstract

The substitution of PR3 (R = C6H4CH3-p, C6H4Cl-p, C6H11,OCH3) for a CO ligand in chiral carbohydratocarbene complexes [(η5-C5H5)(CO)2Mn[DOUBLE BOND]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 and 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 [(SMn)-2β] was formed which could be separated from the diastereomeric mixture by chromatography and be obtained in a pure form. Subsequent reaction of (SMn)-2β with BF3 afforded the carbyne-manganese complex (SMn)-[(η5-C5H5){P(C6H4CH3-p)3}(CO)Mn[TRIPLE BOND]CPh]BF4.