Cyclopentadienyliron complexes of nitrosobenzene: Preparation, structure and reactivity with olefins

The preparation, characterization and reactivity of (η5-cyclopentadienyl)iron complexes of nitrosobenzene are investigated as potential intermediates in the [CpFe(CO)2]2 (1)-catalyzed allylic amination of olefins by nitroarenes. The oxidation of 1 by [Cp2Fe]+ in the presence of PhNO produces a novel dinuclear complex {[CpFe-μ-(η2-(N,O)-PhNO)]2-μ-NHPh}BF4 (2) along with [CpFe(CO)3]BF4 and [CpFe(CO)2(NH2Ph)]BF4; 2 has been characterized spectroscopically and by X-ray diffraction. Reaction of CpFe(CO)2I with PhNO and AgSbF6 produces the mononuclear complex [CpFe(CO)2(η2-PhNO)]SbF6 (3) which has also been characterized spectroscopically, crystallographically and by PM3 MO calculations. The reaction of 3 with α-methyl styrene affords [CpFe(CO)2(PhNH2)SbF6] and a trace of N-phenyl-2-phenylallyl amine 4, while the reaction of 3 with 2,3-dimethyl-1,3-butadiene affords the aniline complex and a hetero-Diels-Alder adduct 5, indicative of PhNO dissociation. Together these results preclude the involvement of nitrosoarene complex 3 as an important intermediate in the allylic amination catalyzed by [CpFe(CO)2]2.

Graphical abstractTwo novel CpFe-nitrosobenzene complexes have been prepared and structurally characterized. {[CpFe-μ-(η2-(N,O)-PhNO)]2-μ-NHPh}BF4 (2) features bridging PhNO and PhNH- units, whereas [CpFe(CO)2(η1-PhNO)]SbF6 (3) exhibits η1-N(O)Ph coordination. The possible intermediacy of 3+ in [CpM(CO)2]2-catalyzed allylic amination of alkene by nitroarenes is evaluated via reactions with a representative alkene and diene.Figure optionsDownload full-size imageDownload as PowerPoint slide