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.