Strong Electronic Effects in the cis‐Selective Asymmetric Cyclopropanation of Olefins Catalyzed by [RuCl(PNNP)]+

The cationic RuCl(PNNP)]⁺ catalysts containing tetradentate ligands with a P₂N₂ donor set (PNNP) show strong electronic effects in the cyclopropanation of para‐substituted styrenes. The reactivity trend confirms that the carbene transfer to the olefin has electrophilic character. Linear free‐energy relationships are observed for the relative reactivity, the cis/trans selectivity, and for the enantioselectivity (of the cis‐cyclopropane). The linear correlation between log (k_X/k_H) and σ shows a large value of ρ (−2.4), which is indicative of significant charge buildup in the transition state of the carbene transfer to the olefin. All the relevant parameters (reactivity, diastereoselectivity, and enantioselectivity) increase with the increasing electron density at the C=C bond. To define the scope of the RuCl(PNNP)]⁺ catalysts, 1‐ and 2‐substituted styrenes, and oct‐1‐ene were also investigated.