DIRHENIUM(III) COMPLEXES WITH N,N-DIMETHYLADENINE AND 7-AZAINDOLE

Re2X2(CH3CO2)4 (X = Cl, Br) reacts with anionic N6,N6-dimethyladenine (dmad-) in ethanol to form dark purple Re2X2(dmad)4, in which the acetate ligands are replaced by the N3/N9-bridging purine. Different relative orientations of the dissymmetric ligands about the Re-Re axis lead to four stereoisomers producing resolved signals in the H-1 NMR spectra. The compound can be reversibly protonated at N7 to yield the [ReX2(Hdmad)4]4+ ion. Hdmad and (Bu4N)2[Re2Cl8] in ethanol form a red-brown dinuclear material formulated as [Re2Cl4(Hdmad)2]-Cl.4H2O.0.5C2H5OH, where the purine is N3/N9-bridging and N7-protonated. Heating (BU4N)2[Re2Cl8] and 7-azaindole (Haza) without solvent leads to a brown Re2Cl2(aza)4 material, in which different orientations of the NI/N7-bridging ligand again produce various stereoisomers. Magnetic anisotropy of the quadruple metal-metal bond probably contributes to the very large downfield shifts observed for the C-13 signals of the carbon atoms just above the Re-Re vector.