Dinitrogen complexes of rhenium(I) and rhenium(II)
Dinitrogen complexes of rhenium(I) are prepared by the reaction of benzoylazo-complexes, [Re(NNCOPh)Cl2(PPh3)xLy](L = monodentate ligand or ½ bidentate ligand; x= 0 or 2, x+y= 3), with certain ligands in boiling methanol. The dinitrogen complexes are of the type trans-[ReCl(N2)LxL′y](L = a variety of organophosphines; L′= L or some other organophosphine, CO or PF3; x+y= 4). For L = L′= PMe2Ph the dinitrogen complex has an exceptionally low ν(N2)(1925 cm–1). Despite its low ν(N2), it is not easily reduced and strong Brønsted acids protonate the metal rather than the bound dinitrogen. On oxidation, the dinitrogen complexes form moderately stable paramagnetic cations, e.g., trans-[ReCl(N2)(Ph2PCH2CH2PPh2)2]+.