Electronic Control of the Asymmetry in Heteroatom Monosubstituted Olefin Bonding to the Cyclopentadienyl Iron(II) Dicarbonyl Cation. A Hammett Correlation Study

Abstract

Nucleophilic substitution of CpFe(CO)2(η2-H2CC(H)OEt)+PF6- with para-substituted anilines was used to prepare a series (4−10) of η2-vinyl aniline Fp+ complexes of the general formula CpFe(CO)2[η2-CH2C(H)NH(p-C6H4X)]+PF6-, where X = OMe (4), Me (5), H, (6), Br (7), COMe (8), CN (9), and NO2 (10). Correlation of the Hammett σ para parameters with the 13C NMR shifts of the metal-coordinated vinyl carbons demonstrated the ability to control the position of the Fp+ moiety along the olefin face. As the electron-donating character of the para substituent was increased, the Fp+ moiety was displaced away from the nitrogen-bearing carbon, increasing the asymmetry of the metal−olefin bonding. These conclusions were further supported by determining the X-ray crystal structure of the p-Me (5) and the p-acetyl (8) derivatives.