Synthesis and physical properties of α,ω-bis[Co2(CO)6{μ-η2:η2-C(R)C}]oligothiophenes

alpha.omega-Bis[Co-2(CO)(6){mu-eta(2):eta(2)-C(R)=C}]oligothiophene derivatives (6-10), in which two dicobalt hexacarbonyl acetylides are pi-conjugated onto both terminals of the oligothiophene, were prepared by the reaction of the alpha,omega-bis(alkynyl)oligothiophenes (1-5) with Co-2(CO)(8). The molecular structures of new compounds were identified by spectroscopic methods and elemental analysis. In cyclic voltammetry of the clusters 6-10, two oligothiophene-based oxidation processes (one for 7) occur between - 0.2 and 1.5 V, and the one reductive process of the metal cluster moieties occurs between 0.0 and - 1.6 V, which is not present for the oligothiophenes (1-5). The silence of the expected electronic communication of the clusters 6-10 may be attributed to the reduction process followed by fast chemical reactions at ambient temperature. The clusters 6-10 commonly exhibit three characteristic bands: a moderately intense, high-energy band, strong medium-energy band and weak-low energy band. The high-energy bands are attributed to the a pi-pi* localized excitation. The medium- and low-energy bands may be ascribed to the metal-to-ligand (d(Co)-pi(ligand)(*)) charge-transfer transitions of the cluster moiety. (C) 2000 Elsevier Science S.A. All rights reserved.