Thienyl Carboxylate Ligands Bound to and Bridging MM Quadruple Bonds, M = Mo or W:  Models for Polythiophenes Incorporating MM Quadruple Bonds

Abstract

A series of compounds of the form [M(2)L(4)] and [[((t)()BuCO(2))(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 Mo(2)(O(2)C-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.

The remarkable influence of M 2 δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

“…We have been interested for some time in incorporating MM quadruple bonds into these oligomers by use of the carboxylate tether (8)(9)(10), such that the M 2 ␦ electrons can be brought into conjugation with an extended -framework of the thiophene moiety. As shown in Scheme 1, the out-of-phase combination of the carboxylate * orbitals mix strongly with the M 2 ␦ orbital whereas the in-phase combination has no symmetry match (11).…”

Oligothiophenes Incorporating Metal–Metal Quadruple Bonds

“…The work of Manners and co-workers [1] with metallocene-derived polymers, Friend, Raithby, and co-workers [2] with metallated polyynes and poly(phenylenvinylene)s, Wolf and co-workers [3] with metallated polythiophenes, and Thompson, Forrest, and co-workers [4] with iridium and platinum complex doped conjugated polymers, represent four prime areas of recent research interest. The majority of efforts thus far have focused on the use of the Group 8 metals (the metals of the iron, cobalt, and nickel triads), in which the metal ions are d 6 or d 8 . We are interested in incorporating metal-metal quadruple bonds with a s 2 p 4 d 2 configuration into organic conjugated polymers because the dinuclear center is redox-active and its ease of oxidation can be tuned over a considerable range by the selection of the metal (M = Cr, Mo, W) and the ancillary ligands, [5] even to the point that the M 2 center is more easily oxidized than cesium.…”

“…We recently illustrated this by the preparation of some discrete model complexes of the type [M 2 (O 2 CR) 4 ], in which R = mono-, bi-, and terthienyl (a,a') groups. [8] Herein, we describe our synthesis of oligomeric/polymeric thienyl-based materials incorporating metal-metal quadruple bonds. The general reaction is shown in Equation (1),…”

Mixed valency and metal–metal quadruple bonds

“…This has been well documented for oxalate [22], terephthalate [23], and 2,5-thiophenyl bridges [24]. The (MM) value of the quadruple bond shifts to lower energy upon oxidation as the bond order is reduced to form 4 to 3.5 in a valence trapped MV ion, or 3.75 in a totally delocalized MV ion.…”