Electronic control of the competitive π donation in heteroatom substituted CpFe(CO)2(olefin)BF4 complexes and the resulting influence on the symmetry of the metal to olefin bond

Nucleophilic, single substitution of CpFe(CO)2(cis-η2-(EtO)CHCH(OEt))+BF4- with para substituted anilines was used to prepare a series of cis Fp olefin complexes 10–14 of the general formula, CpFe(CO)2[η2-(EtO)CHCHNH(p-C6H4X)]+BF4-, where X = OMe (10), Me (11), Cl, (12), COMe (13), and CN (14). These complexes contain both vinyl oxygen and vinyl nitrogen π donors capable of p–π donation to the olefin. This series allows a comparison of competitive π donor strengths as X is varied across the series. Correlation of the Hammett σpara parameters for X with the 13C NMR shifts of the metal coordinated vinyl carbons demonstrated that as the electron withdrawing character of the para substituent was increased, the aniline (while still the dominant π donor) competed less effectively with the cis ethoxy group, moving the Fp+ moiety toward a more central point along the olefin face. The implication of such control for the nucleophilic substitution chemistry of these complexes is discussed.

CpFe(CO)2(cis-η2-(EtO)CHCH(OEt))+BF4- was reacted with p-substituted anilines to prepare a series of complexes of the general formula, CpFe(CO)2[cis-η2-(EtO)CHCHNH(p-C6H4X)]BF4. Correlation of the Hammett σpara parameters for X with the 13C NMR shifts of the vinyl carbons demonstrated control of the competing π donation (O vs. N), directly affecting the metal–olefin bond symmetry.Figure optionsDownload as PowerPoint slide