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 [{((BuCO2)-Bu-t)(3)M-2}(2)(mu-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.