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 (PPh 3 ) 2 reacts with p-substituted aryl diazonium tetrafluoroborates to yield the compounds [Fe(CO) 2 (PPh 3 ) 2 (N 2 C 6 H 4 X)]BF 4 (where X = F, Cl, Br, H, NO 2 , OCH 3 , and OH but not NEt 2 ). The complex cation displays properties consistent with replacement of an equatorial CO ligand in Fe(CO) 3 (PPh 3 ) 2 by the more effective π-acceptor ligand [N 2 C 6 H 4 X] + analogous to NO + . A very strong band at ca. 1720 cm −1 in the i.r. spectrum due to v(N 2 ) has been identified by 15 N 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.