Furan- and selenophene-2-carboxylato derivatives of dimolybdenum and ditungsten (MM): a comparison of their chemical and photophysical properties

Abstract

From the reactions between M₂(TⁱPB)₄, where TⁱPB = 2,4,6-triisopropylbenzoate and two equivalents each of 2-furan carboxylic acid, FuCO₂H, and 2-selenophene carboxylic acid, SpCO₂H in toluene, the new compounds trans-M₂(TⁱPB)₂(O₂CFu)₂ (1a M = Mo, 2a M = W) and trans-M₂(TⁱPB)₂(O₂CSp)₂ (1b M = Mo, 2b M = W) were formed. These new compounds have been characterized by ¹H NMR, steady-state UV-Vis-NIR absorption and emission spectroscopy, cyclic and differential pulse voltammetry, and fs and ns transient absorption spectroscopy. The compound Mo₂(TⁱPB)₂(O₂CSp)₂ (1b) has been characterized by single crystal X-ray crystallography. These data are compared with those previously reported for related 2-thiophene carboxylate derivatives: M₂(TⁱPB)₂(O₂CTh)₂. The physico–chemical data correlate well with electronic structure calculations performed on model compounds. All compounds have detectible S₁ photoexcited states with lifetimes that vary from ∼5 ps to < 1 ps. The molybdenum compounds have T₁ states with microsecond lifetimes that are assigned as MMδδ* whereas the T₁ states for tungsten are ³MLCT with lifetimes on the order of nanoseconds. In all cases, shorter lifetimes were seen in complexes containing heavier atoms.