Synthesis of chiral β-aminoalcohol-substituted carbene complexes of manganese and influence of the chiral carbene ligand on the diastereoselectivity of the CO/PR3 exchange

The acetoxy(phenyl)carbene complex [Cp(CO)2MnC(OAc)Ph] (2) reacts with chiral β-aminoalcohols HOR* [HOR*=N,N-dimethyl alaninol (3), N,N-dimethyl valinol (4), N,N-dimethyl leucinol (5), N,N-dimethylphenyl alaninol (6), and N-formylprolinol (7)] by displacement of the acetoxy substituent and formation of the β-aminoalkoxy(phenyl)carbene complexes [Cp(CO)2MnC(OR*)Ph] (8–12). Irradiation of 9–12 in the presence of PR3 (R=Ph, OMe) affords the carbene(carbonyl)cyclopentadienyl(PR3)manganese complexes [Cp(CO)(PR3)MnC(OR*)Ph]. The substitution proceeds diastereoselectively, the diastereomeric excess ranging from 28% to >90%. The highest diastereoselectivity (>90%) is observed in the reaction of 9 (R*=CH2C(NMe2)HCMe2H) with PR3. In solution, complex 9 is not stable configurationally and epimerizes within a few days. The reaction of 2 with HOC2H4SCH2Ph affords [Cp(CO)2MnC(OC2H4SCH2Ph)Ph] (22) which, on photolysis, is transformed, by loss of a CO ligand, into a chelating carbene complex (24). In the presence of PR3 compound 24 cannot be converted thermally into [Cp(CO)(PR3)MnC(OC2H4SCH2Ph)Ph].