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

Abstract

From the reactions between 2,5-dianilinoterephthalic acid and M₂(O₂CBu^t)₄ in toluene the dicarboxylate bridged complexes [(Bu^tCO₂)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, H_ab, 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.