The reaction of ortho-halogenated aromatic aldazine ligands with Fe2(CO)9: symmetrical cleavage of the azine and carbon–halogen activation

Azine ligands derived from hydrazine and benzaldehyde derivatives bearing halogen substituents in ortho-position with respect to the carbonyl function upon treatment with Fe2(CO)9 show two typical reaction principles. One is the symmetrical cleavage of the N–N bond of the azine to yield either di- or trinuclear iron carbonyl compounds [Fe2(CO)6(μ2-Ndouble bond; length as m-dashCHR)2] and [Fe3(CO)9(μ2-Ndouble bond; length as m-dashCHR)(μ2-η2-Ndouble bond; length as m-dashCHR)] each showing two arylidenimido moieties. In addition, a trinuclear iron carbonyl cluster compound exhibiting a tetrahedral Fe3N cluster core is isolated. The cluster shows only one half of the former azine ligand. It is a ionic compound of the general formula [Fe3(CO)9(μ3-η2-Ndouble bond; length as m-dashCHR)]Na × H2O. This trinuclear cluster compound is quantitatively converted into [Fe3(CO)9(μ2-H)(μ3-η2-Ndouble bond; length as m-dashCHR)] upon treatment with phosphorous acid. Most interestingly, we were also able to isolate two types of compounds in which an activation of one of the carbon halogen bonds in ortho-position with respect to the imine functions of the azine has occured in terms of an ortho-metallation reaction. In the N–N bond of the azine is still preserved, whereas in [Fe3(CO)9(μ3-η3-Ndouble bond; length as m-dashCHR)] again only one half of the former azine ligand is coordinated in an arylidenimido fashion. In both types of compounds one additional iron carbon bond is present due to the activation of an aromatic carbon halogen bond. The reaction of iron carbonyls with 2,6-difluorobenzonitrile produces [Fe3(CO)9(μ3-η2-Ntriple bond; length of mdashCR)] as the sole product. All new iron carbonyl compounds are characterized by means of X-ray crystallography.