The origin of diastereoselectivity in cyclopropanation reactions of the iron carbene complex [(η5-C5H5)(CO)2FeCH[(η6-o-CH3OC6H4)Cr(CO)3]]+

The origin of diastereoselectivity in cyclopropanation reactions of the iron carbene complex [(η5-C5H5)(CO)2FeCH[(η6-o-CH3OC6H4)Cr(CO)3]]+ has been investigated. The chromium participation has been proved by the upfield shifts of both 1H- and 13C-NMR for CαH and Cα, which stabilized the iron carbene and may result in a late transition-state for the cyclopropanation reaction via tricarbonylchromium-complexed iron carbene. Hence, trans selectivity is expected. However, when using aromatic alkenes, a π stacking effect may exist during the transition-state, resulting in the cis selectivity for cyclopropanation.