Models for the Interaction of Nitrogen with Transition Metals. Part III. Preparation and Properties of some Cationic Arylazo Complexes of Iron

Abstract

Fe(CO)3(PPh3)2 reacts with p-substituted aryl diazonium tetrafluoroborates to yield the compounds [Fe(CO)2(PPh3)2(N2C6H4X)]BF4 (where X = F, Cl, Br, H, NO2, OCH3, and OH but not NEt2). The complex cation displays properties consistent with replacement of an equatorial CO ligand in Fe(CO)3(PPh3)2 by the more effective π-acceptor ligand [N2C6H4X]+ analogous to NO+. A very strong band at ca. 1720 cm−1 in the i.r. spectrum due to v(N2) has been identified by 15N isotopic substitution. This value is much higher than for most other arylazo complexes yet prepared and the azo group resists catalytic hydrogenation. A number of spectroscopic measurements are reported, including unusually small quadrupole splitting effects in the Mössbauer spectra.