Origin of enantioselectivity in asymmetric Pauson–Khand reactions catalyzed by [(BINAP)Co2(CO)6]

The quantum mechanics/molecular mechanics (QM/MM) ONIOM(B3LYP:UFF) approach is applied to the study of the asymmetric carbonylative intramolecular cycloaddition of a HCC–CH2–N(Ts)–CH2–CHCH2 enyne (Ts = tosyl) catalyzed by [(BINAP)Co2(CO)6] (BINAP = (1,1′-binaphtalene)-2,2′,diylbis(diphenylphosphine)). The experimental results, showing formation of the R product when the S-BINAP ligand is used, are reproduced. Comparison of the structures of the computed transition states leading to the R and S products provides a qualitative explanation for the origin of selectivity based on steric repulsions between specific substituents.

The selectivity in the Pauson–Khand intramolecular cyclization of prochiral enynes catalyzed by [(BINAP)Co2(CO)6] is controlled by enyne-phenyl and carbonyl-phenyl steric repulsions.Figure optionsDownload high-quality image (70 K)Download as PowerPoint slide