2,5-Dianilinoterephthalate bridged MM quadruply bonded complexes of molybdenum and tungsten

From the reactions between 2,5-dianilinoterephthalic acid and M2(O2CBut)4 in toluene the dicarboxylate bridged complexes [(ButCO2)3M2]2{µ-1,4-(CO2)2-2,5-(NHPh)2C6H2}, 1 (M = Mo) and 2 (M = W) have been isolated. The compounds are air sensitive, sparingly soluble in aromatic hydrocarbons but appreciably soluble in tetrahydrofuran. Electronic structure calculations employing density functional theory on the model compounds [(HCO2)3M2]2{µ-1,4-(CO2)2-2,5-(NHPh)2C6H2}, indicate that the ground state structure contains a planar bridge and that for molybdenum the HOMO is a bridge based molecular orbital. However, the compounds show reversible oxidation waves (CV and DPV) that for both M = Mo and W are metal based oxidations. Furthermore, the cations 1+ and 2+ are shown to be valence trapped and fully delocalized respectively. The magnitude of the electronic coupling of the two M2 centers, Hab, can be estimated as 383 cm−1 for 1+ and 1500 cm−1 for 2+ based on the corresponding low energy IVCT or charge resonance bands