Additions with nucleophiles such as BH(,4)('-), BH(,3)CN('-), OH('-), etc., to a series of cationic allyl molybdenum complexes were investigated in an effort to develop practical asymmetric syntheses. A system based on Mo(NO)(CO)((eta)('3)-allyl)((eta)('5)-cyclopentadienyl) ('+) cation was found to show excellent selectivity owing to the powerful directing effect of the nitrosyl ligand on the site of attack at (pi)-allyl ligand. Nucleophiles were shown to preferentially attack the terminal carbon of the (pi)-allyl ligand that was cis to the nitrosyl ligand, regardless of which conformational isomer (endo or exo) of the cation underwent reaction.

In the synthesis of the cations, the initial isomer produced was not the thermodynamically preferred conformer; upon standing in solution a slow equilibration process yielded the more stable isomer. In order to determine the influence of this equilibrium on the product distribution of the nucleophilic addition, the mechanisms of the endo-exo interconversion and nucleophilic addition were examined.

A racemic mixture of olefins produced upon liberation of the olefins from the reaction product from the achiral cationic complexes. In order to produce optically active olefins from this system, the cyclopentadienyl ligand was replaced with neomenthylcyclopentadienyl ligand. Separation of diastereomers of the cationic complexes then became possible. ORD and CD studies of the neomenthylcyclopentadienyl complexes were undertaken, which established correlations between the sign of the absorption band at the longest wavelength in the CD spectra, endo-exo (pi)-allyl conformation and the absolute configuration.

Using this neomenthylcyclopentadienyl system, (+)-2,2,3-trimethyl-hex-4-enal, (-)-3-d-cyclooctene and (-)-cycloocten-3-ol were synthesized in high optical yield (> 95% e.e.).