Thienyl carboxylate ligands bound to and bridging MM quadruple bonds, M = Mo or W: Models for polythiophenes incorporating MM quadruple bonds

A series of compounds of the form [M₂L₄] and [{( ^tBuCO₂)₃M₂}₂(μ- L′)] have been made where M = Mo or W, L = a thienyl, bithienyl, or terthienyl carboxylate, and L′ = a corresponding thienyl dicarboxylate. The electronic absorption spectra are reported and the electronic structures discussed. Intense metal-to-ligand charge transfer bands traverse the visible and near-IR regions of the electronic absorption spectrum. The compounds show reversible metal-based oxidations and quasireversible ligand-based reductions. The molecular structure of Mo₂(O₂C-2-Th) ₄·2THF is reported, on the basis of a single crystal X-ray diffraction study. These compounds provide insight into the expected properties of related dimetalated polythiophenes incorporating MM quadruple bonds.