Chirality changes in reactions of asymmetric molybdenum complexes

Optical rotatory dispersion and circular dichroism studies have allowed the determination of the changes in configuration at the molybdenum center upon displacement of carbonyl and iodide in neomenthylcyclopentadienyl—Mo(allyl)(NO)X systems. Displacement of carbonyl by iodide occurs with retention of configuration. Replacement of iodide with benzenesulfonate followed by replacement of the sulfonate with iodide occurs stereospecifically with net retention of configuration. In the case of cyclopentadienylMo(cyclooctenyl)(NO)I, the enantiomers were separated via a spontaneous resolution through crystallization of the complex in the space group P2₁2₁2₁. These studies have allowed the correlation not only of the absolute configuration at the metal center with CD studies, but also have established that a long wavelength optically active transition at approximately 400 nm can be correlated with endo-exo isomerism. Comparison of the rates of interconversion suggest that endo to exo isomerization occurs via a clockwise rotation of the allyl in the (R)-isomer. Crystallographic details: (—)-(S)-(NMCp)Mo(allyl)(NO)I crystallizes in the space group P2₁2₁2₁ with a 7.221(1), b 12.686(7), c 21.603(7) Å, Z = 4, V = 1979(2) ų; R₁ = 0.039, R₂ = 0.046; (—)-(S)-(Cp)Mo(cyclooctenyl)(NO)I crystallizes in the space group P2₁2₁2₁ with a 8.466(1), b 10.449(2), c 16.372(2) Å, Z = 4, V = 1448.3(6), R₁ = 0.038, and R₂ = 0.046.