Synthesis of chiral β-aminoalcohol-substituted carbene complexes of manganese and influence of the chiral carbene ligand on the diastereoselectivity of the CO/PR 3 exchange

Abstract

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 PR 3 (R=Ph, OMe) affords the carbene(carbonyl)cyclopentadienyl(PR 3)manganese complexes [Cp(CO)(PR 3)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*=CH 2C(NMe 2)HCMe 2H) with PR 3. In solution, complex 9 is not stable configurationally and epimerizes within a few days. The reaction of 2 with HOC 2H 4SCH 2Ph affords [Cp(CO) 2MnC(OC 2H 4SCH 2Ph)Ph] ( 22) which, on photolysis, is transformed, by loss of a CO ligand, into a chelating carbene complex ( 24). In the presence of PR 3 compound 24 cannot be converted thermally into [Cp(CO)(PR 3)MnC(OC 2H 4SCH 2Ph)Ph].